Journal articles on the topic 'Galaxies : full-spectral fitting'
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Ruiz-Lara, Tomás, M. A. Beasley, C. Gallart, J. Falcón-Barroso, G. Battaglia, E. Bernard, C. Brook, et al. "Full-spectral fitting techniques to characterise the stellar content of ultra diffuse galaxies." Proceedings of the International Astronomical Union 14, S344 (August 2018): 408–12. http://dx.doi.org/10.1017/s174392131800577x.
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AbstractUnderstanding the peculiar properties of Ultra Diffuse Galaxies (UDGs) via spectroscopic analysis is a challenging task that is now becoming feasible. The advent of 10m-class telescopes and high sensitivity instruments is enabling the gathering of high quality spectra even for the faintest systems. In addition, advances in the modelling of stellar populations, stellar libraries, and full-spectral fitting codes are allowing the recovery of the stellar content shaping those spectra with unprecedented reliability. In this contribution we report on the extensive tests we have carried out using the inversion code STECKMAP. The similarities between the Star Formation Histories (SFH) recovered from STECKMAP (applied to high-quality spectra) and deep Colour-Magnitude diagrams fitting (resolved stars) in two Local Group dwarf galaxies (LMC and LeoA) are remarkable, demonstrating the impressive performance of STECKMAP. We exploit the capabilities of STECKMAP and perform one of the most complete and reliable characterisations of the stellar component of UDGs to date using deep spectroscopic data. We measure radial and rotation velocities, SFHs and mean population parameters, such as ages and metallicities, for a sample of five UDG candidates in the Coma cluster. From the radial velocities, we confirm the Coma membership of these galaxies. We find that their rotation properties, if detected at all, are compatible with dwarf-like galaxies. The SFHs of the UDG are dominated by old (∼ 7 Gyr), metal-poor ([M/H] ∼ -1.1) and alpha-enhanced ([Mg/Fe]∼ 0.4) populations followed by a smooth or episodic decline which halted ∼ 2 Gyr ago, possibly a sign of cluster-induced quenching. We find no obvious correlation between individual SFH shapes and any UDG morphological properties. The recovered stellar properties for UDGs are similar to those found for DDO 44, a local UDG analogue resolved into stars. We conclude that the UDGs in our sample are extended dwarfs whose properties are likely the outcome of both internal processes, such as bursty SFHs and/or high-spin haloes, as well as environmental effects within the Coma cluster.
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Scott, Nicholas. "Spatially resolved stellar populations with SAMI." Proceedings of the International Astronomical Union 10, S309 (July 2014): 343–44. http://dx.doi.org/10.1017/s1743921314010369.
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AbstractUsing data from the SAMI Galaxy Survey we measure azimuthally averaged stellar age and metallicity profiles for ∼ 500 galaxies, using both luminosity-weighted Lick indices and mass-weighted full spectral fitting. We find a weak trend for steeper (i.e. more negative) metallicity gradients in more massive galaxies, however, below stellar masses ∼ 1010.5 M⊙, the scatter in metallicity gradient increases dramatically.
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Katkov, Ivan Yu, and Igor V. Chilingarian. "Multi-component parametric inversion of galaxy kinematics and stellar populations using full spectral fitting." Proceedings of the International Astronomical Union 7, S284 (September 2011): 69–71. http://dx.doi.org/10.1017/s1743921312008770.
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AbstractThe stellar line-of-sight velocity distribution (LOSVD) can be strongly asymmetric in regions where the light contributions of both disc and bulge in spiral and lenticular galaxies are comparable. Existing techniques for the stellar kinematics analysis do not take into account the difference of disc and bulge stellar populations. Here we present a novel approach to the analysis of stellar kinematics and stellar populations. We use a two-component model of spectra where different stellar population components are convolved with pure Gaussian LOSVDs. For this model we present Monte-Carlo simulations demonstrating degeneracies between the parameters.
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Lonoce, I., C. Maraston, D. Thomas, M. Longhetti, T. Parikh, P. Guarnieri, and J. Comparat. "Stellar population properties of individual massive early-type galaxies at 1.4 < z < 2." Monthly Notices of the Royal Astronomical Society 492, no. 1 (December 10, 2019): 326–51. http://dx.doi.org/10.1093/mnras/stz3404.
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ABSTRACT We analyse publicly available, individual spectra of four massive ($M\gt 10^{11}\, \mathrm{M}_{\odot }$) early-type galaxies with redshifts in the range 1.4 ≤ z ≤ 2 to determine their stellar content, extending our previous work up to z ∼ 2. The wide wavelength range of the VLT/X-Shooter spectroscopic data in the UV–Optical–NIR arms along with the availability of spectro-photometry allows us to explore different techniques to obtain the stellar population properties, namely through age/metallicity-sensitive spectral indices, full spectral fitting, and broad-band photometric fitting. Moreover, together with the widely used optical Lick indices, we consider further indices in the UV rest frame, and demonstrate that UV indices significantly help the accuracy of the resulting population parameters. We find galaxy ages ranging from 0.2 to 4 Gyr, where the oldest galaxy is found at the lowest redshift, with an excellent agreement between ages determined via indices, full spectral fitting, or broad-band colours. These ages are in perfect agreement with ages of local galaxies at the same velocity dispersion when we assume pure passive evolution. Total metallicities derived from indices show some scatter (between less than half-solar to very high values, [Z/H] ∼ 0.6). We speculate on possible mechanisms explaining these values, but given the sample size and low S/N of the spectra no conclusion can be made. Indices in the UV rest frame generally lead to similar conclusions as optical indices. For the oldest galaxy (4 Gyr), we show that its UV indices can only be explained by stellar population models including a UV contribution from old stellar populations, suggesting that old, UV bright populations start to inhabit mature galaxies of a few Gyr of age. This is the highest redshift (z ∼ 1.4) detection of the UV upturn up to date.
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Martins, Lucimara P. "Recovering the star formation history of galaxies through spectral fitting: Current challenges." Proceedings of the International Astronomical Union 15, S359 (March 2020): 386–90. http://dx.doi.org/10.1017/s1743921320001647.
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AbstractWith the exception of some nearby galaxies, we cannot resolve stars individually. To recover the galaxies star formation history (SFH), the challenge is to extract information from their integrated spectrum. A widely used tool is the full spectral fitting technique. This consists of combining simple stellar populations (SSPs) of different ages and metallicities to match the integrated spectrum. This technique works well for optical spectra, for metallicities near solar and chemical histories not much different from our Galaxy. For everything else there is room for improvement. With telescopes being able to explore further and further away, and beyond the optical, the improvement of this type of tool is crucial. SSPs use as ingredients isochrones, an initial mass function, and a library of stellar spectra. My focus are the stellar libraries, key ingredient for SSPs. Here I talk about the latest developments of stellar libraries, how they influence the SSPs and how to improve them.
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da Cunha, Elisabete. "Panchromatic star formation rate indicators and their uncertainties." Proceedings of the International Astronomical Union 11, A29B (August 2015): 184–85. http://dx.doi.org/10.1017/s1743921316004816.
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AbstractThe star formation rate (SFR) is a fundamental property of galaxies and it is crucial to understand the build-up of their stellar content, their chemical evolution, and energetic feedback. The SFR of galaxies is typically obtained by observing the emission by young stellar populations directly in the ultraviolet, the optical nebular line emission from gas ionized by newly-formed massive stars, the reprocessed emission by dust in the infrared range, or by combining observations at different wavelengths and fitting the full spectral energy distributions of galaxies. In this brief review we describe the assumptions, advantages and limitations of different SFR indicators, and we discuss the most promising SFR indicators for high-redshift studies.
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Feldmeier-Krause, A., I. Lonoce, and W. L. Freedman. "Stellar Population and Elemental Abundance Gradients of Early-type Galaxies*." Astrophysical Journal 923, no. 1 (December 1, 2021): 65. http://dx.doi.org/10.3847/1538-4357/ac281e.
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Abstract The evolution of galaxies is imprinted on their stellar populations. Several stellar population properties in massive early-type galaxies have been shown to correlate with intrinsic galaxy properties such as the galaxy’s central velocity dispersion, suggesting that stars formed in an initial collapse of gas (z ∼ 2). However, stellar populations change as a function of galaxy radius, and it is not clear how local gradients of individual galaxies are influenced by global galaxy properties and galaxy environment. In this paper, we study the stellar populations of eight early-type galaxies as a function of radius. We use optical spectroscopy (∼4000–8600 Å) and full spectral fitting to measure stellar population age, metallicity, slope of the initial mass function (IMF), and nine elemental abundances (O, Mg, Si, Ca, Ti, C, N, Na, and Fe) out to 1 R e for each galaxy individually. We find a wide range of properties, with ages ranging from 3–13 Gyr. Some galaxies have a radially constant, Salpeter-like IMF, and other galaxies have a super-Salpeter IMF in the center, decreasing to a sub-Salpeter IMF at ∼0.5 R e . We find a global correlation of the central [Z/H] with the central IMF and the radial gradient of the IMF for the eight galaxies, but local correlations of the IMF slope with other stellar population parameters hold only for subsets of the galaxies in our sample. Some elemental abundances also correlate locally with each other within a galaxy, suggesting a common production channel. These local correlations appear only in subsets of our galaxies, indicating variations of the stellar content among different galaxies.
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Tsuchikawa, T., H. Kaneda, S. Oyabu, T. Kokusho, H. Kobayashi, and Y. Toba. "Spitzer/IRS Full Spectral Modeling to Characterize Mineralogical Properties of Silicate Dust in Heavily Obscured AGNs." Astrophysical Journal 941, no. 1 (December 1, 2022): 50. http://dx.doi.org/10.3847/1538-4357/ac9b23.
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Abstract Mid-infrared silicate dust bands observed in heavily obscured active galactic nuclei (AGNs) include information on the mineralogical properties of silicate dust. We aim to investigate the mineralogical picture of the circumnuclear region of heavily obscured AGNs to reveal obscured AGN activities through the picture. In our previous study, we investigated the properties of silicate dust in heavily obscured AGNs, focusing on the mineralogical composition and the crystallinity with Spitzer/IRS 5.3–12 μm spectra. In this study, we model the full-range Spitzer/IRS 5–30 μm spectra of 98 heavily obscured AGNs using a one-dimensional radiative transfer calculation with four dust species in order to evaluate wider ranges of the properties of silicate dust more reliably. Comparing fitting results between four dust models with different sizes and porosities, 95 out of the 98 galaxies prefer a porous silicate dust model without micron-sized large grains. The pyroxene mass fraction and the crystallinity are overall consistent with—but significantly different from—the previous results for the individual galaxies. The pyroxene-poor composition, small dust size, and high porosity are similar to newly formed dust around mass-loss stars as seen in our Galaxy, which presumably originates from the recent circumnuclear starburst activity. The high crystallinity on average suggests dust processing induced by AGN activities.
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Davison, Thomas A., Mark A. Norris, Ryan Leaman, Harald Kuntschner, Alina Boecker, and Glenn van de Ven. "Mapping accreted stars in early-type galaxies across the mass–size plane." Monthly Notices of the Royal Astronomical Society 507, no. 2 (August 19, 2021): 3089–112. http://dx.doi.org/10.1093/mnras/stab2362.
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ABSTRACT Galaxy mergers are instrumental in dictating the final mass, structure, stellar populations, and kinematics of galaxies. Cosmological galaxy simulations indicate that the most massive galaxies at z = 0 are dominated by high fractions of ‘ex-situ’ stars, which formed first in distinct independent galaxies, and then subsequently merged into the host galaxy. Using spatially resolved MUSE spectroscopy we quantify and map the ex-situ stars in thirteen massive early-type galaxies. We use full spectral fitting together with semi-analytic galaxy evolution models to isolate the signatures in the galaxies’ light which are indicative of ex-situ populations. Using the large MUSE field of view we find that all galaxies display an increase in ex-situ fraction with radius, with massive and more extended galaxies showing a more rapid increase in radial ex-situ fraction (reaching values between ∼30 per cent and 100 per cent at 2 effective radii) compared to less massive and more compact sources (reaching between ∼5 per cent and 40 per cent ex-situ fraction within the same radius). These results are in line with predictions from theory and simulations which suggest ex-situ fractions should increase significantly with radius at fixed mass for the most massive galaxies.
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Teimoorinia, Hossen, Finn Archinuk, Joanna Woo, Sara Shishehchi, and Asa F. L. Bluck. "Mapping the Diversity of Galaxy Spectra with Deep Unsupervised Machine Learning." Astronomical Journal 163, no. 2 (January 18, 2022): 71. http://dx.doi.org/10.3847/1538-3881/ac4039.
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Abstract Modern spectroscopic surveys of galaxies such as MaNGA consist of millions of diverse spectra covering different regions of thousands of galaxies. We propose and implement a deep unsupervised machine-learning method to summarize the entire diversity of MaNGA spectra onto a 15 × 15 map (DESOM-1), where neighboring points on the map represent similar spectra. We demonstrate our method as an alternative to conventional full spectral fitting for deriving physical quantities and full probability distributions much more efficiently than traditional resource-intensive Bayesian methods. Since spectra are grouped by similarity, the distribution of spectra onto the map for a single galaxy, i.e., its “fingerprint,” reveals the presence of distinct stellar populations within the galaxy, indicating smoother or episodic star formation histories. We further map the diversity of galaxy fingerprints onto a second map (DESOM-2). Using galaxy images and independent measures of galaxy morphology, we confirm that galaxies with similar fingerprints have similar morphologies and inclination angles. Since morphological information was not used in the mapping algorithm, relating galaxy morphology to the star formation histories encoded in the fingerprints is one example of how the DESOM maps can be used to make scientific inferences.
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Carnall, Adam C., Ross J. McLure, James S. Dunlop, Massissilia Hamadouche, Fergus Cullen, Derek J. McLeod, Ryan Begley, et al. "The Stellar Metallicities of Massive Quiescent Galaxies at 1.0 < z < 1.3 from KMOS + VANDELS." Astrophysical Journal 929, no. 2 (April 1, 2022): 131. http://dx.doi.org/10.3847/1538-4357/ac5b62.
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Abstract We present a rest-frame UV–optical (λ = 2500–6400 Å) stacked spectrum representative of massive quiescent galaxies at 1.0 < z < 1.3 with log(M */M ⊙) > 10.8. The stack is constructed using VANDELS survey data, combined with new KMOS observations. We apply two independent full-spectral-fitting approaches, measuring a total metallicity [Z/H] = −0.13 ± 0.08 with Bagpipes and [Z/H] = 0.04 ± 0.14 with Alf, a fall of ∼0.2–0.3 dex compared with the local universe. We also measure an iron abundance [Fe/H] = −0.18 ± 0.08, a fall of ∼0.15 dex compared with the local universe. We measure the alpha enhancement via the magnesium abundance, obtaining [Mg/Fe] = 0.23 ± 0.12, consistent with galaxies of similar mass in the local universe, indicating no evolution in the average alpha enhancement of log(M */M ⊙) ∼ 11 quiescent galaxies over the last ∼8 Gyr. This suggests the very high alpha enhancements recently reported for several bright z ∼ 1–2 quiescent galaxies are due to their extreme masses, log(M */M ⊙) ≳ 11.5, in accordance with the well-known downsizing trend, rather than being typical of the z ≳ 1 population. The metallicity evolution we observe with redshift (falling [Z/H], [Fe/H], constant [Mg/Fe]) is consistent with recent studies. We recover a mean stellar age of 2.5 − 0.4 + 0.6 Gyr, corresponding to a formation redshift z form = 2.4 − 0.3 + 0.6 . Recent studies have obtained varying average formation redshifts for z ≳ 1 massive quiescent galaxies, and, as these studies report consistent metallicities, we identify models with different star formation histories as the most likely cause. Larger spectroscopic samples from upcoming ground-based instruments will provide precise constraints on ages and metallicities at z ≳ 1. Combining these with precise stellar mass functions for z > 2 quiescent galaxies from the James Webb Space Telescope will provide an independent test of formation redshifts derived from spectral fitting.
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Buat, V., L. Ciesla, M. Boquien, K. Małek, and D. Burgarella. "Cold dust and stellar emissions in dust-rich galaxies observed with ALMA: a challenge for SED-fitting techniques." Astronomy & Astrophysics 632 (December 2019): A79. http://dx.doi.org/10.1051/0004-6361/201936643.
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Context. Over the past few years the Atacama Large Millimeter Array (ALMA) has detected dust-rich galaxies whose cold dust emission is spatially disconnected from the ultraviolet (UV) rest-frame emission. This represents a challenge for modeling their spectral energy distributions (SED) with codes based on an energy budget between the stellar and dust components. This could potentially weaken the solidity of the physical parameters measured with these modeling tools. Aims. We want to verify the validity of energy balance modeling on a sample of galaxies observed from the UV to the sub-millimeter rest frame with ALMA and decipher what information can be reliably retrieved from the analysis of the full SED and from subsets of wavelengths. Methods. We select 17 sources at z ≃ 2 in the Hubble Ultra-Deep Field (HUDF) and in the GOODS-South field detected with ALMA and Herschel and for which UV to near-infrared rest-frame ancillary data are available. We fit the data with CIGALE exploring different configurations for dust attenuation and star formation histories, considering either the full dataset or one that is reduced to the stellar and dust emission. We compare estimates of the dust luminosities, star formation rates, and stellar masses. Results. The fit of the stellar continuum alone with the starburst attenuation law can only reproduce up to 50% of the total dust luminosity observed by Herschel and ALMA. This deficit is found to be marginally consistent with similar quantities estimated in the COSMOS field and is found to increase with the specific star formation rate. The combined stellar and dust SEDs are well fitted when different attenuation laws are introduced. Shallow attenuation curves are needed for the galaxies whose cold dust distribution is very compact compared to starlight. The stellar mass estimates are affected by the choice of the attenuation law. The star formation rates are robustly estimated as long as dust luminosities are available. The large majority of the galaxies are above the average main sequence of star forming galaxies and one source is a strong starburst.
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Goudfrooij, Paul, and Randa S. Asa’d. "On the precision of full-spectrum fitting of simple stellar populations – II. The dependence on star cluster mass in the wavelength range 0.3–5.0 µm." Monthly Notices of the Royal Astronomical Society 501, no. 1 (December 3, 2020): 440–66. http://dx.doi.org/10.1093/mnras/staa3617.
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ABSTRACT In this second paper of a series on the accuracy and precision of the determination of age and metallicity of simple stellar populations (SSPs) by means of the full-spectrum fitting technique, we study the influence of star cluster mass through stochastic fluctuations of the number of stars near the top of the stellar mass function, which dominate the flux in certain wavelength regimes depending on the age. We consider SSP models based on the Padova isochrones, spanning the age range $7.0 \le \mbox{log(age/yr}) \le 10.1$. Simulated spectra of star clusters in the mass range 104 ≤ M/M⊙ < 106 are compared with SSP model spectra to determine best-fitting ages and metallicities using a full-spectrum fitting routine in four wavelength regimes: the blue optical (0.35–0.70 µm), the red optical (0.6–1.0 µm), the near-infrared (near-IR; 1.0–2.5 µm), and the mid-IR (2.5–5.0 µm). We compare the power of each wavelength regime in terms of both the overall precision of age and metallicity determination and its dependence on cluster mass. We also study the relevance of spectral resolution in this context by utilizing two different spectral libraries (BaSeL and BT-Settl). We highlight the power of the mid-IR regime in terms of identifying young massive clusters in dusty star-forming regions in distant galaxies. The spectra of the simulated star clusters and SSPs are made available online to enable follow-up studies by the community.
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Katkov, Ivan Yu, Alexei Yu Kniazev, Olga K. Sil’chenko, and Damir Gasymov. "Star formation in outer rings of S0 galaxies." Astronomy & Astrophysics 658 (February 2022): A154. http://dx.doi.org/10.1051/0004-6361/202141934.
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Aims. Although S0 galaxies are usually considered “red and dead”, they often demonstrate star formation organized into ring structures. We aim to clarify the nature of this phenomenon and how it differs from star formation in spiral galaxies. Methods. We investigated the nearby, moderate-luminosity S0 galaxy NGC 254 using long-slit spectroscopy taken with the South African Large Telescope and publicly available imaging data. Applying a full spectral fitting, we analyzed gaseous and stellar kinematics as well as ionized gas excitation and metallicity and stellar population properties resolved by radius. An advanced approach of simultaneously fitting spectra and photometric data allowed us to quantify the fraction of hidden counter-rotating stars in this galaxy. Results. We find that the ionized gas is counter-rotating with respect to the stars throughout NGC 254 disk, indicating an external origin of the gas. We argue the gas-rich galaxy merger from retrograde orbit as a main source of counter-rotating material. The star formation fed by this counter-rotating gas occurs within two rings: an outer ring at R = 55″ − 70″ and an inner ring at R = 18″. The star formation rate is weak, 0.02 solar mass per year in total, and the gas metallicity is slightly subsolar. We estimated that the accretion of the gas occurred about 1 Gyr ago, and about 1% of all stars have formed in situ from counter-rotating gas.
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Fahrion, K., M. Lyubenova, M. Hilker, G. van de Ven, J. Falcón-Barroso, R. Leaman, I. Martín-Navarro, et al. "The Fornax 3D project: Non-linear colour–metallicity relation of globular clusters." Astronomy & Astrophysics 637 (May 2020): A27. http://dx.doi.org/10.1051/0004-6361/202037686.
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Globular cluster (GC) systems of massive galaxies often show a bimodal colour distribution. This has been interpreted as a metallicity bimodality, created by a two-stage galaxy formation where the red, metal-rich GCs were formed in the parent halo and the blue metal-poor GCs were accreted. This interpretation, however, crucially depends on the assumption that GCs are exclusively old stellar systems with a linear colour–metallicity relation (CZR). The shape of the CZR and range of GC ages are currently under debate because their study requires high quality spectra to derive reliable stellar population properties. We determined metallicities with full spectral fitting from a sample of 187 GCs with a high spectral signal-to-noise ratio in 23 galaxies of the Fornax cluster that were observed as part of the Fornax 3D project. The derived CZR from this sample is non-linear and can be described by a piecewise linear function with a break point at (g−z) ∼ 1.1 mag. The less massive galaxies in our sample (M* < 1010 M⊙) appear to have slightly younger GCs, but the shape of the CZR is insensitive to the GC ages. Although the least massive galaxies lack red, metal-rich GCs, a non-linear CZR is found irrespective of the galaxy mass, even in the most massive galaxies (M* ≥ 1011 M⊙). Our CZR predicts narrow unimodal GC metallicity distributions for low mass and broad unimodal distributions for very massive galaxies, dominated by a metal-poor and metal-rich peak, respectively, and bimodal distributions for galaxies with intermediate masses (1010 ≤ M* < 1011 M⊙) as a consequence of the relative fraction of red and blue GCs. The diverse metallicity distributions challenge the simple differentiation of GC populations solely based on their colour.
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Ratsimbazafy, A., C. Cress, and S. Crawford. "Studying Luminous Red Galaxies to probe H(z) at high redshift." Proceedings of the International Astronomical Union 8, S295 (August 2012): 185. http://dx.doi.org/10.1017/s1743921313004729.
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AbstractLuminous Red Galaxies (LRGs) have old, red stellar populations often interpreted as evidence of a formation scenario in which these galaxies form in a single intense burst of star formation at high redshift. By measuring the average age of LRGs at two different redshifts, one can potentially measure the redshift interval corresponding to a time interval and thus measure the Hubble parameter H(z) ≈ −(1 + z)−1 Δ z/Δt (as in Jimenez & Loeb). The goal of this project is to measure directly the expansion rate of the universe at the redshift range 0.1 < z < 1.0 within 3% precision. We explore the age-dating of Sloan Digital Sky Survey LRGs using the stellar population models of Lick absorption line indices after stacking spectra in redshift bins to increase the signal-to-noise. We also use the method of full spectral fitting to measure the ages of LRGs observed with the Southern Africa Large Telescope (SALT).
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Fraser-McKelvie, Amelia, Michael Merrifield, Alfonso Aragón-Salamanca, Thomas Peterken, Katarina Kraljic, Karen Masters, David Stark, et al. "SDSS-IV MaNGA: The link between bars and the early cessation of star formation in spiral galaxies." Monthly Notices of the Royal Astronomical Society 499, no. 1 (September 21, 2020): 1116–25. http://dx.doi.org/10.1093/mnras/staa2866.
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ABSTRACT Bars are common in low-redshift disc galaxies, and hence quantifying their influence on their host is of importance to the field of galaxy evolution. We determine the stellar populations and star formation histories of 245 barred galaxies from the Mapping Nearby Galaxies at APO (MaNGA) galaxy survey, and compare them to a mass- and morphology-matched comparison sample of unbarred galaxies. At fixed stellar mass and morphology, barred galaxies are optically redder than their unbarred counterparts. From stellar population analysis using the full spectral fitting code starlight, we attribute this difference to both older and more metal-rich stellar populations. Dust attenuation however, is lower in the barred sample. The star formation histories of barred galaxies peak earlier than their non-barred counterparts, and the galaxies build up their mass at earlier times. We can detect no significant differences in the local environment of barred and unbarred galaxies in this sample, but find that the H i gas mass fraction is significantly lower in high-mass ($\rm {M}_{\star } \gt 10^{10}~\rm {M}_{\odot }$) barred galaxies than their non-barred counterparts. We speculate on the mechanisms that have allowed barred galaxies to be older, more metal-rich and more gas-poor today, including the efficient redistribution of galactic fountain byproducts, and a runaway bar formation scenario in gas-poor discs. While it is not possible to fully determine the effect of the bar on galaxy quenching, we conclude that the presence of a bar and the early cessation of star formation within a galaxy are intimately linked.
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Liang, Fu-Heng, Cheng Li, Niu Li, Shuang Zhou, Renbin Yan, Houjun Mo, and Wei Zhang. "Wolf-Rayet Galaxies in SDSS-IV MaNGA. II. Metallicity Dependence of the High-mass Slope of the Stellar Initial Mass Function." Astrophysical Journal 923, no. 1 (December 1, 2021): 120. http://dx.doi.org/10.3847/1538-4357/ac2bff.
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Abstract As hosts of living high-mass stars, Wolf-Rayet (WR) regions or WR galaxies are ideal objects for constraining the high-mass end of the stellar initial mass function (IMF). We construct a large sample of 910 WR galaxies/regions that cover a wide range of stellar metallicity (from Z ∼ 0.001 to 0.03) by combining three catalogs of WR galaxies/regions previously selected from the SDSS and SDSS-IV/MaNGA surveys. We measure the equivalent widths of the WR blue bump at ∼4650 Å for each spectrum. They are compared with predictions from stellar evolutionary models Starburst99 and BPASS, with different IMF assumptions (high-mass slope α of the IMF ranging from 1.0 to 3.3). Both singular evolution and binary evolution are considered. We also use a Bayesian inference code to perform full spectral fitting to WR spectra with stellar population spectra from BPASS as fitting templates. We then make a model selection among different α assumptions based on Bayesian evidence. These analyses have consistently led to a positive correlation of the IMF high-mass slope α with stellar metallicity Z, i.e., with a steeper IMF (more bottom-heavy) at higher metallicities. Specifically, an IMF with α = 1.00 is preferred at the lowest metallicity (Z ∼ 0.001), and an Salpeter or even steeper IMF is preferred at the highest metallicity (Z ∼ 0.03). These conclusions hold even when binary population models are adopted.
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Jolly, Jean-Baptiste, Kirsten Knudsen, Nicolas Laporte, Johan Richard, Seiji Fujimoto, Kotaro Kohno, Yiping Ao, et al. "ALMA Lensing Cluster Survey: A spectral stacking analysis of [C II] in lensed z ∼ 6 galaxies." Astronomy & Astrophysics 652 (August 2021): A128. http://dx.doi.org/10.1051/0004-6361/202140878.
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Context. The properties of galaxies at redshift z > 6 hold the key to our understanding of the early stages of galaxy evolution and can potentially identify the sources of the ultraviolet radiation that give rise to the epoch of reionisation. The far-infrared cooling line of [C II] at 158 μm is known to be bright and correlate with the star formation rate (SFR) of low-redshift galaxies, and hence is also suggested to be an important tracer of star formation and interstellar medium properties for very high-redshift galaxies. Aims. With the aim to study the interstellar medium properties of gravitationally lensed galaxies at z > 6, we search for [C II] and thermal dust emission in a sample of 52 z ∼ 6 galaxies observed by the ALMA Lensing Cluster Survey. Methods. We perform our analysis using LINESTACKER, stacking both [C II] and continuum emission. The target sample is selected from multiple catalogues, and the sample galaxies have spectroscopic redshift or low-uncertainty photometric redshifts (σz < 0.02) in nine galaxy clusters. Source properties of the target galaxies are either extracted from the literature or computed using spectral energy distribution fitting. Both weighted-average and median stacking are used, on both the full sample and three sub-samples. Results. Our analyses find no detection of either [C II] or continuum. An upper limit on L[CII] is derived, implying that [C II] remains marginally consistent for low-SFR z > 6 galaxies but likely is under-luminous compared to the local L[CII]-SFR relationship. We discuss potential biases and possible physical effects that may be the cause of the non-detection. Further, the upper limit on the dust continuum implies that less than half of the star formation is obscured.
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Lawler, Andrew J., and Viviana Acquaviva. "Detecting episodes of star formation using Bayesian model selection." Monthly Notices of the Royal Astronomical Society 502, no. 3 (January 19, 2021): 3993–4008. http://dx.doi.org/10.1093/mnras/stab138.
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ABSTRACT Bayesian model comparison frameworks can be used when fitting models to data in order to infer the appropriate model complexity in a data-driven manner. We aim to use them to detect the correct number of major episodes of star formation from the analysis of the spectral energy distributions (SEDs) of galaxies, modelled after 3D-HST galaxies at z ∼ 1. Starting from the published stellar population properties of these galaxies, we use kernel density estimates to build multivariate input parameter distributions to obtain realistic simulations. We create simulated sets of spectra of varying degrees of complexity (identified by the number of parameters), and derive SED fitting results and pieces of evidence for pairs of nested models, including the correct model as well as more simplistic ones, using the bagpipes codebase with nested sampling algorithm multinest. We then ask the question: is it true – as expected in Bayesian model comparison frameworks – that the correct model has larger evidence? Our results indicate that the ratio of pieces of evidence (the Bayes factor) is able to identify the correct underlying model in the vast majority of cases. The quality of the results improves primarily as a function of the total S/N in the SED. We also compare the Bayes factors obtained using the evidence to those obtained via the Savage–Dickey density ratio (SDDR), an analytic approximation that can be calculated using samples from regular Markov Chain Monte Carlo methods. We show that the SDDR ratio can satisfactorily replace a full evidence calculation provided that the sampling density is sufficient.
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Cullen, F., R. J. McLure, J. S. Dunlop, A. C. Carnall, D. J. McLeod, A. E. Shapley, R. Amorín, et al. "The VANDELS survey: a strong correlation between Ly α equivalent width and stellar metallicity at 3 ≤ z ≤ 5." Monthly Notices of the Royal Astronomical Society 495, no. 1 (May 9, 2020): 1501–10. http://dx.doi.org/10.1093/mnras/staa1260.
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ABSTRACT We present the results of a new study investigating the relationship between observed Ly α equivalent width (Wλ(Ly α)) and the metallicity of the ionizing stellar population ( Z⋆) for a sample of 768 star-forming galaxies at 3 ≤ z ≤ 5 drawn from the VANDELS survey. Dividing our sample into quartiles of rest-frame Wλ(Ly α) across the range $-58 \,\rm {\mathring{\rm A}} \lesssim$Wλ(Ly α) $\lesssim 110 \,\rm {\mathring{\rm A}}$, we determine Z⋆ from full spectral fitting of composite far-ultraviolet spectra and find a clear anticorrelation between Wλ(Ly α) and Z⋆. Our results indicate that Z⋆ decreases by a factor ≳ 3 between the lowest Wλ(Ly α) quartile (〈Wλ(Ly α)$\rangle =-18\,\rm {\mathring{\rm A}}$) and the highest Wλ(Ly α) quartile (〈Wλ(Ly α)$\rangle =24\,\rm {\mathring{\rm A}}$). Similarly, galaxies typically defined as Lyman alpha emitters (LAEs; Wλ(Ly α) $\gt 20\,\rm {\mathring{\rm A}}$) are, on average, metal poor with respect to the non-LAE galaxy population (Wλ(Ly α) $\le 20\,\rm {\mathring{\rm A}}$) with Z⋆non-LAE ≳ 2 × Z⋆LAE. Finally, based on the best-fitting stellar models, we estimate that the increasing strength of the stellar ionizing spectrum towards lower Z⋆ is responsible for ${\simeq}15{-}25{{\ \rm per\ cent}}$ of the observed variation in Wλ(Ly α) across our sample, with the remaining contribution (${\simeq}75{-}85{{\ \rm per\ cent}}$) being due to a decrease in the H i/dust covering fractions in low- Z⋆ galaxies.
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Davison, Thomas A., Harald Kuntschner, Bernd Husemann, Mark A. Norris, Julianne J. Dalcanton, Alessandra De Rosa, Pierre-Alain Duc, Stefano Bianchi, Pedro R. Capelo, and Cristian Vignali. "Old and new major mergers in the SOSIMPLE galaxy, NGC 7135." Monthly Notices of the Royal Astronomical Society 502, no. 2 (January 21, 2021): 2296–307. http://dx.doi.org/10.1093/mnras/stab162.
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ABSTRACT The simultaneous advancement of high resolution integral field unit spectroscopy and robust full-spectral fitting codes now make it possible to examine spatially resolved kinematic, chemical composition, and star-formation history from nearby galaxies. We take new MUSE data from the snapshot optical spectroscopic imaging of mergers and pairs for legacy Exploration (SOSIMPLE) survey to examine NGC 7135. With counter-rotation of gas, disrupted kinematics and asymmetric chemical distribution, NGC 7135 is consistent with an ongoing merger. Though well hidden by the current merger, we are able to distinguish stars originating from an older merger, occurring 6–10 Gyr ago. We further find a gradient in ex-situ material with galactocentric radius, with the accreted fraction rising from 0 per cent in the galaxy centre, to ∼7 per cent within 0.6 effective radii.
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Boquien, M., D. Burgarella, Y. Roehlly, V. Buat, L. Ciesla, D. Corre, A. K. Inoue, and H. Salas. "CIGALE: a python Code Investigating GALaxy Emission." Astronomy & Astrophysics 622 (February 2019): A103. http://dx.doi.org/10.1051/0004-6361/201834156.
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Context. Measuring how the physical properties of galaxies change across cosmic times is essential to understand galaxy formation and evolution. With the advent of numerous ground-based and space-borne instruments launched over the past few decades we now have exquisite multi-wavelength observations of galaxies from the far-ultraviolet (FUV) to the radio domain. To tap into this mine of data and obtain new insight into the formation and evolution of galaxies, it is essential that we are able to extract information from their spectral energy distribution (SED). Aims. We present a completely new implementation of Code Investigating GALaxy Emission (CIGALE). Written in python, its main aims are to easily and efficiently model the FUV to radio spectrum of galaxies and estimate their physical properties such as star formation rate, attenuation, dust luminosity, stellar mass, and many other physical quantities. Methods. To compute the spectral models, CIGALE builds composite stellar populations from simple stellar populations combined with highly flexible star formation histories, calculates the emission from gas ionised by massive stars, and attenuates both the stars and the ionised gas with a highly flexible attenuation curve. Based on an energy balance principle, the absorbed energy is then re-emitted by the dust in the mid- and far-infrared domains while thermal and non-thermal components are also included, extending the spectrum far into the radio range. A large grid of models is then fitted to the data and the physical properties are estimated through the analysis of the likelihood distribution. Results. CIGALE is a versatile and easy-to-use tool that makes full use of the architecture of multi-core computers, building grids of millions of models and analysing samples of thousands of galaxies, both at high speed. Beyond fitting the SEDs of galaxies and parameter estimations, it can also be used as a model-generation tool or serve as a library to build new applications.
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Martín, S., J. Martín-Pintado, C. Blanco-Sánchez, V. M. Rivilla, A. Rodríguez-Franco, and F. Rico-Villas. "Spectral Line Identification and Modelling (SLIM) in the MAdrid Data CUBe Analysis (MADCUBA) package." Astronomy & Astrophysics 631 (November 2019): A159. http://dx.doi.org/10.1051/0004-6361/201936144.
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Context. The increase in bandwidth and sensitivity of state-of-the-art radio observatories is providing a wealth of molecular data from nearby star-forming regions up to high-z galaxies. Analysing large data sets of spectral cubes requires efficient and user-friendly tools optimised for astronomers with a wide range of backgrounds. Aims. In this paper we present the detailed formalism at the core of Spectral Line Identification and Modelling (SLIM) within the MAdrid Data CUBe Analysis (MADCUBA) package and their main data-handling functionalities. These tools have been developed to visualise, analyse, and model large spectroscopic data cubes. Methods. We present the highly interactive on-the-fly visualisation and modelling tools of MADCUBA and SLIM, which includes a stand-alone spectroscopic database. The parameters stored therein are used to solve the full radiative transfer equation under local thermodynamic equilibrium (LTE). The SLIM package provides tools to generate synthetic LTE model spectra based on input physical parameters of column density, excitation temperature, velocity, line width, and source size. It also provides an automatic fitting algorithm to obtain the physical parameters (with their associated errors) better fitting the observations. Synthetic spectra can be overlayed in the data cubes/spectra to ease the task of multi-molecular line identification and modelling. Results. We present the Java-based MADCUBA and its internal module SLIM packages which provide all the necessary tools for manipulation and analysis of spectroscopic data cubes. We describe in detail the spectroscopic fitting equations and make use of this tool to explore the breaking conditions and implicit errors of commonly used approximations in the literature. Conclusions. Easy-to-use tools like MADCUBA allow users to derive physical information from spectroscopic data without the need for simple approximations. The SLIM tool allows the full radiative transfer equation to be used, and to interactively explore the space of physical parameters and associated uncertainties from observational data.
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Decker, Bandon, Mark Brodwin, Ripon Saha, Thomas Connor, Peter R. M. Eisenhardt, Anthony H. Gonzalez, Emily Moravec, et al. "The Massive and Distant Clusters of WISE Survey. XI. Stellar Mass Fractions and Luminosity Functions of MaDCoWS Clusters at z ∼ 1." Astrophysical Journal 936, no. 1 (August 31, 2022): 71. http://dx.doi.org/10.3847/1538-4357/ac85e5.
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Abstract We present stellar mass fractions and composite luminosity functions (LFs) for a sample of 12 clusters from the Massive and Distant Clusters of WISE Survey (MaDCoWS) in the redshift range 0.951 ≤ z ≤ 1.43. Using spectral energy distribution fitting of optical and deep mid-infrared photometry, we establish the membership of objects along the lines of sight to these clusters and calculate the stellar masses of member galaxies. This allows us to calculate the stellar mass of the clusters much more precisely than in previous works. We find stellar mass fractions for these clusters largely consistent with previous works, and an apparent negative correlation with total cluster mass. We measure a composite 3.6 μm LF down to m* + 2.5 for all 12 clusters. Fitting a Schechter function to the LF, we find a characteristic 3.6 μm magnitude of m* = 19.83 ± 0.12 and faint-end slope of α = −0.81 ± 0.10 for the full sample at a mean redshift of z ¯ = 1.18 . We also divide the clusters into high- and low-redshift bins at z ¯ = 1.29 and z ¯ = 1.06 , respectively, and measure a composite LF for each bin. We see a small, but statistically significant, evolution in m* and α—consistent with passive evolution—when we study the joint fit to the two parameters, which is probing the evolution of faint cluster galaxies at z ∼ 1. This highlights the importance of deep IR data in studying the evolution of cluster galaxy populations at high redshift.
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Stefanon, Mauro, Rychard J. Bouwens, Ivo Labbé, Garth D. Illingworth, Valentino Gonzalez, and Pascal A. Oesch. "Deep Spitzer/IRAC Data for z ∼ 10 Galaxies Reveal Blue Balmer Break Colors: Young Stellar Populations at ∼500 Myr of Cosmic Time." Astrophysical Journal 943, no. 2 (January 27, 2023): 81. http://dx.doi.org/10.3847/1538-4357/aca470.
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Abstract We present the deepest constraints yet on the median rest-UV+optical spectral energy distribution (SED) of z ∼ 10 galaxies prior to James Webb Space Telescope science operations. We constructed stacks based on four robust J 125 dropouts, previously identified across the GOODS fields. We used archival Hubble Space Telescope/Wide Field Camera 3 data and the full-depth Spitzer/IRAC mosaics from the GREATS program, the deepest coverage at ∼3–5 μm to date. The most remarkable feature of the SED is a blue IRAC [3.6]–[4.5] = −0.18 ± 0.25 mag color. We also find a nearly flat H 160 − [3.6] = 0.07 ± 0.22 mag color, corresponding to a UV slope β = −1.92 ± 0.25. This is consistent with previous studies and indicative of minimal dust absorption. The observed blue IRAC color and SED fitting suggest that z ∼ 10 galaxies have very young (few × 10 Myr) stellar populations, with 80% of stars being formed in the last ≲160 Myr (2σ). While an exciting result, the uncertainties on the SED are too large to allow us to place strong constraints on the presence of a nebular continuum in z ∼ 10 galaxies (as might be suggested by the blue [3.6]–[4.5] < 0 mag color). The resulting sSFR is consistent with the specific accretion rate of dark matter halos, indicative of a star formation efficiency showing quite limited evolution at such early epochs.
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Marchi, F., L. Pentericci, L. Guaita, M. Talia, M. Castellano, N. Hathi, D. Schaerer, et al. "The VANDELS survey: the role of ISM and galaxy physical properties in the escape of Lyα emission in z ∼ 3.5 star-forming galaxies." Astronomy & Astrophysics 631 (October 11, 2019): A19. http://dx.doi.org/10.1051/0004-6361/201935495.
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Aims. We wish to investigate the physical properties of a sample of Lyα emitting galaxies in the VANDELS survey, with particular focus on the role of kinematics and neutral hydrogen column density in the escape and spatial distribution of Lyα photons. Methods. From all the Lyα emitting galaxies in the VANDELS Data Release 2 at 3.5 ≲ z ≲ 4.5, we selected a sample of 52 galaxies that also have a precise systemic redshift determination from at least one nebular emission line (HeII or CIII]). For these galaxies, we derived different physical properties (stellar mass, age, dust extinction, and star formation rate) from spectral energy distribution (SED) fitting of the exquisite multiwavelength photometry available in the VANDELS fields, using the dedicated spectral modeling tool BEAGLE and the UV β slope from the observed photometry. We characterized the Lyα emission in terms of kinematics, equivalent width (EW), full width at half-maximum, and spatial extension and then estimated the velocity of the neutral outflowing gas. The ultra-deep VANDELS spectra (up to 80 h on-source integration) enable this for individual galaxies without the need to rely on stacks. We then investigated the correlations between the Lyα properties and the other measured properties to study how they affect the shape and intensity of Lyα emission. Results. We reproduce some of the well-known correlations between Lyα EW and stellar mass, dust extinction, and UV β slope, in the sense that the emission line appears brighter in galaxies with lower mass that are less dusty and bluer. We do not find any correlation with the SED-derived star formation rate, while we find that galaxies with brighter Lyα tend to be more compact in both UV and in Lyα. Our data reveal an interesting correlation between the Lyα velocity offset and the shift of the interstellar absorption lines with respect to the systemic redshift, observed for the first time at high redshifts: galaxies with higher interstellar medium (ISM) outflow velocities show smaller Lyα velocity shifts. We interpret this relation in the context of the shell-model scenario, where the velocity of the ISM and the HI column density contribute together in determining the Lyα kinematics. In support to our interpretation, we observe that galaxies with high HI column densities have much more extended Lyα spatial profiles; this is a sign of increased scattering. However, we do not find any evidence that the HI column density is related to any other physical properties of the galaxies, although this might be due in part to the limited range of parameters that our sample spans.
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Nicol, M.-H., K. Meisenheimer, C. Tapken, and C. Wolf. "COMBO-17+4: An Optical-NIR Survey for Galaxies out to z=2." Proceedings of the International Astronomical Union 2, S235 (August 2006): 419. http://dx.doi.org/10.1017/s1743921306010465.
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AbstractClassifying Object by Medium-Band Observations in 17 filters (COMBO-17) has already produced a very accurate picture of galaxy evolution since z~1 based on 25000 galaxies in 17 medium optical bands. We now extend the range of reliable multi-color redshifts with COMBO-17+4, a deep optical-NIR survey which will combine the existing optical data set of COMBO-17 with near infrared observation in three medium bands: Y(λ/Δλ = 1040/80nm), J1(1190/130nm) and J2(1320/130nm) and one broad band H(1650/300nm). The NIR bands extend the photometric redshift range to z~2.1. COMBO 17+4 will provide the first large sample of galaxies (>5000) at 1<z<2 with a redshifts accuracy of Δz<0.03(1+z). Three fields are observed: Abell 901, Abell 226 and the COMBO 11h-field, for a total coverage of 0.77□2 of the sky. Each COMBO 17+4 field measures 31 × 30 sqarcmin. The NIR bands are observed with the Omega2000 camera at Calar Alto Observatory in Spain.The scientific goals for this study are multiple. COMBO-17+4 will enable us to establish the luminosity function for the red sequence and blue galaxies in the redshift range 1<z<2. Also it will be possible to determine the formation history at z=2 by analyzing the width of the red sequence galaxies. Moreover this survey will provide several thousand of individual galaxy masses (with an accuracy <30%) obtained with Spectral Energy Distribution (SED) template fitting. Once the masses are obtained the mass function will provide a useful tool to test the hierarchical model of evolution of galaxies by checking whether the massive red sequence galaxies (logM>10.5) are already in place at z>1.5 (9Gyr).We present first results from the full 21 bands photometry in half of the Abell 901 field. It allows us to study not only z>1 galaxies but also the stellar content of several hundred cluster galaxies.
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Bell, Cameron P. M., Maria-Rosa L. Cioni, A. H. Wright, Stefano Rubele, David L. Nidever, Ben L. Tatton, Jacco Th van Loon, et al. "The intrinsic reddening of the Magellanic Clouds as traced by background galaxies – II. The Small Magellanic Cloud." Monthly Notices of the Royal Astronomical Society 499, no. 1 (September 21, 2020): 993–1004. http://dx.doi.org/10.1093/mnras/staa2786.
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ABSTRACT We present a map of the total intrinsic reddening across ≃34 deg2 of the Small Magellanic Cloud (SMC) derived using optical (ugriz) and near-infrared (IR; YJKs) spectral energy distributions (SEDs) of background galaxies. The reddening map is created using a subsample of 29 274 galaxies with low levels of intrinsic reddening based on the lephare χ2 minimization SED-fitting routine. We find statistically significant enhanced levels of reddening associated with the main body of the SMC compared with regions in the outskirts [ΔE(B − V) ≃ 0.3 mag]. A comparison with literature reddening maps of the SMC shows that, after correcting for differences in the volume of the SMC sampled, there is good agreement between our results and maps created using young stars. In contrast, we find significant discrepancies between our results and maps created using old stars or based on longer wavelength far-IR dust emission that could stem from biased samples in the former and uncertainties in the far-IR emissivity and the optical properties of the dust grains in the latter. This study represents one of the first large-scale categorizations of extragalactic sources behind the SMC and as such we provide the lephare outputs for our full sample of ∼500 000 sources.
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Rosado-Belza, D., J. Falcón-Barroso, J. H. Knapen, A. Bittner, D. A. Gadotti, J. Neumann, A. de Lorenzo-Cáceres, et al. "The kinematics of young and old stellar populations in nuclear rings of MUSE TIMER galaxies." Astronomy & Astrophysics 644 (December 2020): A116. http://dx.doi.org/10.1051/0004-6361/202039530.
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Context. Studying the stellar kinematics of galaxies is a key tool in the reconstruction of their evolution. However, the current measurements of the stellar kinematics are complicated by several factors, including dust extinction and the presence of multiple stellar populations. Aims. We use integral field spectroscopic data of four galaxies from the Time Inference with MUSE in Extragalactic Rings (TIMER) survey to explore and compare the kinematics measured in different spectral regions that are sensitive to distinct stellar populations. Methods. We derive the line-of-sight velocity and velocity dispersion of both a young (≲2 Gyr) and an old stellar population from the spectral regions around the Hβ line and the Ca II Triplet. In addition, we determine colour excess, mean age, and metallicity. Results. We report a correlation of the colour excess with the difference in the kinematic parameters of the Hβ line and the Ca II Triplet range, which are dominated by young and old stellar populations, respectively. Young stellar populations, located primarily in nuclear rings, have higher velocity dispersions than old ones. These differences in the rings are typically ∼10 km s−1 in velocity dispersion but can have a mean value as high as ∼24 km s−1 in the most extreme case. Trends with age exist in the nuclear rings but are less significant than those with dust extinction. We report different degrees of correlation for these trends among the galaxies in the sample, which are related to the size of the Voronoi bins in their rings. No clear trends for the line-of-sight velocity differences are observed. The absence of these trends can be explained as a consequence of the Hβ line masking process during the kinematic extraction, as confirmed by dedicated simulations. Conclusions. Our study demonstrates that kinematic differences caused by different stellar populations can be identified in the central regions of nearby galaxies, even from intermediate resolution spectroscopy. This opens the door to future detailed chemo-kinematic studies of galaxies, but also serves as a warning against deriving kinematics from full-spectrum fitting across very wide wavelength ranges when intense star formation is taking place.
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Leja, Joel, Joshua S. Speagle, Yuan-Sen Ting, Benjamin D. Johnson, Charlie Conroy, Katherine E. Whitaker, Erica J. Nelson, Pieter van Dokkum, and Marijn Franx. "A New Census of the 0.2 < z < 3.0 Universe. II. The Star-forming Sequence." Astrophysical Journal 936, no. 2 (September 1, 2022): 165. http://dx.doi.org/10.3847/1538-4357/ac887d.
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Abstract We use the panchromatic spectral energy distribution (SED)-fitting code Prospector to measure the galaxy logM*–logSFR relationship (the star-forming sequence) across 0.2 < z < 3.0 using the COSMOS-2015 and 3D-HST UV-IR photometric catalogs. We demonstrate that the chosen method of identifying star-forming galaxies introduces a systematic uncertainty in the inferred normalization and width of the star-forming sequence, peaking for massive galaxies at ∼0.5 and ∼0.2 dex, respectively. To avoid this systematic, we instead parameterize the density of the full galaxy population in the logM*–logSFR–redshift plane using a flexible neural network known as a normalizing flow. The resulting star-forming sequence has a low-mass slope near unity and a much flatter slope at higher masses, with a normalization 0.2–0.5 dex lower than typical inferences in the literature. We show this difference is due to the sophistication of the Prospector stellar populations modeling: the nonparametric star formation histories naturally produce higher masses while the combination of individualized metallicity, dust, and star formation history constraints produce lower star formation rates (SFRs) than typical UV+IR formulae. We introduce a simple formalism to understand the difference between SFRs inferred from SED fitting and standard template-based approaches such as UV+IR SFRs. Finally, we demonstrate the inferred star-forming sequence is consistent with predictions from theoretical models of galaxy formation, resolving a long-standing ∼ 0.2–0.5 dex offset with observations at 0.5 < z < 3. The fully trained normalizing flow including a nonparametric description of ρ ( log M * , logSFR , z ) is available online 20 20 https://github.com/jrleja/sfs_leja_trained_flow to facilitate straightforward comparisons with future work.
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Ruiz-Lara, T., C. Gallart, M. Beasley, M. Monelli, E. J. Bernard, G. Battaglia, P. Sánchez-Blázquez, E. Florido, I. Pérez, and I. Martín-Navarro. "Integrated-light analyses vs. colour-magnitude diagrams." Astronomy & Astrophysics 617 (September 2018): A18. http://dx.doi.org/10.1051/0004-6361/201732398.
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Context. Most of our knowledge of the stellar component of galaxies is based on the analysis of distant systems and comes from integrated light data. It is important to test whether the results of the star formation histories (SFH) obtained with standard full-spectrum fitting methods are in agreement with those obtained through colour-magnitude diagram (CMD) fitting (usually considered the most reliable approach). Aims. We compare SFHs recovered from the two techniques in Leo A, a Local Group dwarf galaxy most of whose stars formed during the last 8 Gyrs. This complements our previous findings in a field in the Large Magellanic Cloud bar, where star formation has been in progress since early epochs at varying rates. Methods. We have used GTC/OSIRIS in long-slit mode to obtain a high-quality integrated light spectrum by scanning a selected region within Leo A, for which a CMD reaching the old main sequence turn-off (oMSTO) is available from HST. We compared the SFH obtained from the two datasets, using state-of-art methods of integrated light (STECKMAP) and resolved stellar population analysis. In the case of the CMD, we computed the SFH both from a deep CMD (observed with HST/ACS) and from a shallower CMD (archival data from HST/WFPC2). Results. The agreement between the SFHs recovered from the oMSTO CMD and from full spectrum fitting is remarkable, particularly regarding the time evolution of the star formation rate. The overall extremely low metallicity of Leo A is recovered up to the last 2 Gyrs when some discrepancies appear. A relatively high metallicity found for the youngest stars from the integrated data is a recurring feature that might indicate that the current models or synthesis codes should be revised, but that can be significantly mitigated using a more restrictive metallicity range. We thoroughly inspect the robustness of both approaches separately, finding that the subtle differences between them are inherent to the methods themselves. The SFH recovered from the shallow CMD also presents differences with the other two. Conclusions. Modern full-spectral fitting codes are able to recover both average constant SFHs (LMC case) and SFHs with a dominant fraction of young stellar populations. The analysis of high S/N spectra seems to provide more reliable SFH estimates than that of CMDs not reaching the oMSTO. The comparison presented in this paper needs to be repeated for predominantly old systems, thus assessing the performance of full-spectrum fitting for a full range of SFHs.
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Oyarzún, Grecco A., Kevin Bundy, Kyle B. Westfall, Jeremy L. Tinker, Francesco Belfiore, Maria Argudo-Fernández, Zheng Zheng, et al. "SDSS-IV MaNGA: How the Stellar Populations of Passive Central Galaxies Depend on Stellar and Halo Mass." Astrophysical Journal 933, no. 1 (July 1, 2022): 88. http://dx.doi.org/10.3847/1538-4357/ac7048.
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Abstract We analyze spatially resolved and co-added SDSS-IV MaNGA spectra with signal-to-noise ratio ∼100 from 2200 passive central galaxies (z ∼ 0.05) to understand how central galaxy assembly depends on stellar mass (M *) and halo mass (M h ). We control for systematic errors in M h by employing a new group catalog from Tinker and the widely used Yang et al. catalog. At fixed M *, the strengths of several stellar absorption features vary systematically with M h . Completely model-free, this is one of the first indications that the stellar populations of centrals with identical M * are affected by the properties of their host halos. To interpret these variations, we applied full spectral fitting with the code alf. At fixed M *, centrals in more massive halos are older, show lower [Fe/H], and have higher [Mg/Fe] with 3.5σ confidence. We conclude that halos not only dictate how much M * galaxies assemble but also modulate their chemical enrichment histories. Turning to our analysis at fixed M h , high-M * centrals are older, show lower [Fe/H], and have higher [Mg/Fe] for M h > 1012 h −1 M ⊙ with confidence >4σ. While massive passive galaxies are thought to form early and rapidly, our results are among the first to distinguish these trends at fixed M h . They suggest that high-M * centrals experienced unique early formation histories, either through enhanced collapse and gas fueling or because their halos were early forming and highly concentrated, a possible signal of galaxy assembly bias.
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Kauffmann, O. B., O. Le Fèvre, O. Ilbert, J. Chevallard, C. C. Williams, E. Curtis-Lake, L. Colina, P. G. Pérez-González, J. P. Pye, and K. I. Caputi. "Simulating JWST deep extragalactic imaging surveys and physical parameter recovery." Astronomy & Astrophysics 640 (August 2020): A67. http://dx.doi.org/10.1051/0004-6361/202037450.
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We present a new prospective analysis of deep multi-band imaging with the James Webb Space Telescope (JWST). In this work, we investigate the recovery of high-redshift 5 < z < 12 galaxies through extensive image simulations of accepted JWST programs, including the Early Release Science in the EGS field and the Guaranteed Time Observations in the HUDF. We introduced complete samples of ∼300 000 galaxies with stellar masses of log(M*/M⊙) > 6 and redshifts of 0 < z < 15, as well as galactic stars, into realistic mock NIRCam, MIRI, and HST images to properly describe the impact of source blending. We extracted the photometry of the detected sources, as in real images, and estimated the physical properties of galaxies through spectral energy distribution fitting. We find that the photometric redshifts are primarily limited by the availability of blue-band and near-infrared medium-band imaging. The stellar masses and star formation rates are recovered within 0.25 and 0.3 dex, respectively, for galaxies with accurate photometric redshifts. Brown dwarfs contaminating the z > 5 galaxy samples can be reduced to < 0.01 arcmin−2 with a limited impact on galaxy completeness. We investigate multiple high-redshift galaxy selection techniques and find that the best compromise between completeness and purity at 5 < z < 10 using the full redshift posterior probability distributions. In the EGS field, the galaxy completeness remains higher than 50% at magnitudes mUV < 27.5 and at all redshifts, and the purity is maintained above 80 and 60% at z ≤ 7 and 10, respectively. The faint-end slope of the galaxy UV luminosity function is recovered with a precision of 0.1–0.25, and the cosmic star formation rate density within 0.1 dex. We argue in favor of additional observing programs covering larger areas to better constrain the bright end.
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Carnall, A. C., R. J. McLure, J. S. Dunlop, F. Cullen, D. J. McLeod, V. Wild, B. D. Johnson, et al. "The VANDELS survey: the star-formation histories of massive quiescent galaxies at 1.0 < z < 1.3." Monthly Notices of the Royal Astronomical Society 490, no. 1 (September 12, 2019): 417–39. http://dx.doi.org/10.1093/mnras/stz2544.
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ABSTRACT We present a Bayesian full-spectral-fitting analysis of 75 massive ($M_* \gt 10^{10.3} \, \mathrm{M_\odot }$) UVJ-selected galaxies at redshifts of 1.0 < z < 1.3, combining extremely deep rest-frame ultraviolet spectroscopy from VANDELS with multiwavelength photometry. By the use of a sophisticated physical plus systematic uncertainties model, constructed within the bagpipes code, we place strong constraints on the star-formation histories (SFHs) of individual objects. We first constrain the stellar mass versus stellar age relationship, finding a steep trend towards earlier average formation time with increasing stellar mass (downsizing) of $1.48^{+0.34}_{-0.39}$ Gyr per decade in mass, although this shows signs of flattening at $M_* \gt 10^{11} \, \mathrm{M_\odot }$. We show that this is consistent with other spectroscopic studies from 0 < z < 2. This relationship places strong constraints on the AGN-feedback models used in cosmological simulations. We demonstrate that, although the relationships predicted by simba and illustristng agree well with observations at z = 0.1, they are too shallow at z = 1, predicting an evolution of ≲0.5 Gyr per decade in mass. Secondly, we consider the connections between green-valley, post-starburst, and quiescent galaxies, using our inferred SFH shapes and the distributions of galaxy physical properties on the UVJ diagram. The majority of our lowest-mass galaxies ($M_* \sim 10^{10.5} \, \mathrm{M_\odot }$) are consistent with formation in recent (z < 2), intense starburst events, with time-scales of ≲500 Myr. A second class of objects experience extended star-formation epochs before rapidly quenching, passing through both green-valley and post-starburst phases. The most massive galaxies in our sample are extreme systems: already old by z = 1, they formed at z ∼ 5 and quenched by z = 3. However, we find evidence for their continued evolution through both AGN and rejuvenated star-formation activity.
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Maltby, David T., Omar Almaini, Ross J. McLure, Vivienne Wild, James Dunlop, Kate Rowlands, William G. Hartley, et al. "High-velocity outflows in massive post-starburst galaxies at z > 1." Monthly Notices of the Royal Astronomical Society 489, no. 1 (August 12, 2019): 1139–51. http://dx.doi.org/10.1093/mnras/stz2211.
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ABSTRACT We investigate the prevalence of galactic-scale outflows in post-starburst (PSB) galaxies at high redshift (1 < z < 1.4), using the deep optical spectra available in the UKIDSS Ultra Deep Survey (UDS). We use a sample of ∼40 spectroscopically confirmed PSBs, recently identified in the UDS field, and perform a stacking analysis in order to analyse the structure of strong interstellar absorption features such as Mg ii (λ2800 Å). We find that for massive ($M_* \gt 10^{10}\rm \, M_{\odot }$) PSBs at z > 1, there is clear evidence for a strong blue-shifted component to the Mg ii absorption feature, indicative of high-velocity outflows ($v_{\rm out}\sim 1150\pm 160\rm \, km\, s^{-1}$) in the interstellar medium. We conclude that such outflows are typical in massive PSBs at this epoch, and potentially represent the residual signature of a feedback process that quenched these galaxies. Using full spectral fitting, we also obtain a typical stellar velocity dispersion σ* for these PSBs of $\sim 200\rm \, km\, s^{-1}$, which confirms they are intrinsically massive in nature (dynamical mass $M_{\rm d}\sim 10^{11}\rm \, M_{\odot }$). Given that these high-z PSBs are also exceptionally compact (re ∼ 1–$2\rm \, kpc$) and spheroidal (Sérsic index n ∼ 3), we propose that the outflowing winds may have been launched during a recent compaction event (e.g. major merger or disc collapse) that triggered either a centralized starburst or active galactic nuclei (AGN) activity. Finally, we find no evidence for AGN signatures in the optical spectra of these PSBs, suggesting they were either quenched by stellar feedback from the starburst itself, or that if AGN feedback is responsible, the AGN episode that triggered quenching does not linger into the post-starburst phase.
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Lumbreras-Calle, A., C. Muñoz-Tuñón, J. Méndez-Abreu, J. M. Mas-Hesse, P. G. Pérez-González, B. Alcalde Pampliega, P. Arrabal Haro, et al. "Star-forming galaxies at low-redshift in the SHARDS survey." Astronomy & Astrophysics 621 (January 2019): A52. http://dx.doi.org/10.1051/0004-6361/201731670.
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Context. The physical processes driving the evolution of star formation (SF) in galaxies over cosmic time still present many open questions. Recent galaxy surveys allow now to study these processes in great detail at intermediate redshift (0 ≤ z ≤ 0.5). Aims. We build a complete sample of star-forming galaxies and analyze their properties, reaching systems with low stellar masses and low star formation rates (SFRs) at intermediate-to-low redshift. Methods. We use data from the SHARDS multiband survey in the GOODS-North field. Its depth (up to magnitude ⟨m3σ⟩~ 26.5) and its spectro-photometric resolution (R ~ 50) provides us with an ideal dataset to search for emission line galaxies (ELGs). We develop a new algorithm to identify low-redshift (z < 0.36) ELGs by detecting the [OIII]5007 and Hα emission lines simultaneously. We fit the spectral energy distribution (SED) of the selected sample, using a model with two single stellar populations. Results. We find 160 star-forming galaxies for which we derive equivalent widths (EWs) and absolute fluxes of both emission lines. We detect EWs as low as 12 Å, with median values for the sample of ~35 Å in [OIII]5007 and ~56 Å in Hα, respectively. Results from the SED fitting show a young stellar population with low median metallicity (36% of the solar value) and extinction (AV ~ 0.37), with median galaxy stellar mass ~108.5 M⊙. Gas-phase metallicities measured from available spectra are also low. ELGs in our sample present bluer colours in the UVJ plane than the median colour-selected star-forming galaxy in SHARDS. We suggest a new V-J colour criterion to separate ELGs from non-ELGs in blue galaxy samples. In addition, several galaxies present high densities of O-type stars, possibly producing galactic superwinds, which makes them interesting targets for follow-up spectroscopy. Conclusions. We have demonstrated the efficiency of SHARDS in detecting low-mass ELGs (~2 magnitudes deeper than previous spectroscopic surveys in the same field). The selected sample accounts for 20% of the global galaxy population at this redshift and luminosity, and is characterized by young SF bursts with sub-solar metallicities and low extinction. However, robust fits to the full SEDs can only be obtained including an old stellar population, suggesting the young component is built up by a recent burst of SF in an otherwise old galaxy.
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García-Benito, R., R. M. González Delgado, E. Pérez, R. Cid Fernandes, S. F. Sánchez, and A. L. de Amorim. "Spatially resolved mass-to-light from the CALIFA survey." Astronomy & Astrophysics 621 (January 2019): A120. http://dx.doi.org/10.1051/0004-6361/201833993.
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We investigated the mass-to-light vs. color relations (MLCRs) derived from the spatially resolved star formation history of a sample of 452 galaxies observed with integral field spectroscopy in the CALIFA survey. We derived the stellar mass (M⋆) and the stellar mass surface density (Σ⋆) from the combination of full spectral fitting (using different sets of stellar population models) with observed and synthetic colors in optical broad bands. This method allows obtaining the radial structure of the mass-to-light ratio (M/L) at several wavelengths and studying the spatially resolved MLCRs. Our sample covers a wide range of Hubble types from Sc to E, with stellar masses ranging from M⋆ ∼ 108.4 to 1012 M⊙. The scatter in the MLCRs was studied as a function of morphology, stellar extinction, and emission line contribution to the colors. The effects of the initial mass function (IMF) and stellar population models in the MLCRs were also explored. Our main results are that (a) the M/L ratio has a negative radial gradient that is steeper within the central 1 half-light-radius (HLR). It is steeper in Sb-Sbc than in early-type galaxies. (b) The MLCRs between M/L and optical colors were derived with a scatter of ∼0.1 dex. The smallest dispersion was found for the combinations (i, g − r) and (R, B − R). Extinction and emission line contributions do not affect the scatter of these relations. Morphology does not produce a significant effect, except if the general relation is used for galaxies redder than (u − i) > 4 or bluer than (u − i)< 0. (c) The IMF has a large effect on MLCRs, as expected. The change from a Chabrier to a Salpeter IMF produces a median shift of ∼0.29 dex when mass loss from stellar evolution is also taken into account. (d) These MLCRs are in agreement with previous results, in particular for relations with g and r bands and the B and V Johnson systems.
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Fensch, Jérémy, Remco F. J. van der Burg, Tereza Jeřábková, Eric Emsellem, Anita Zanella, Adriano Agnello, Michael Hilker, et al. "The ultra-diffuse galaxy NGC 1052-DF2 with MUSE." Astronomy & Astrophysics 625 (May 2019): A77. http://dx.doi.org/10.1051/0004-6361/201834911.
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NGC 1052-DF2, an ultra-diffuse galaxy (UDG), has been the subject of intense debate. Its alleged absence of dark matter, and the brightness and number excess of its globular clusters (GCs) at an initially assumed distance of 20 Mpc suggest a new formation channel for UDGs. We present the first systematic spectroscopic analysis of the stellar body and the GCs in this galaxy (six previously known and one newly confirmed member) using MUSE at the VLT. Even though NGC 1052-DF2 does not show any spatially extended emission lines, we report the discovery of three planetary nebulae (PNe). We conduct full spectral fitting on the UDG and the stacked spectra of all the GCs. The UDG’s stellar population is old, 8.9 ± 1.5 Gyr; metal poor, [M/H] = −1.07 ± 0.12; and with little or no α-enrichment. The stacked spectrum of all GCs indicates a similar age of 8.9 ± 1.8 Gyr, but a lower metallicity of [M/H] = −1.63 ± 0.09 and a similarly low α-enrichment. There is no evidence for a variation in age and metallicity in the GC population with the available spectra. The significantly more metal-rich stellar body with respect to its associated GCs, the age of the population, its metallicity, and its α-enrichment are all in line with other dwarf galaxies. NGC 1052-DF2 thus falls on the same empirical mass–metallicity relation as other dwarfs for the full distance range assumed in the literature. We find that both debated distance estimates (13 and 20 Mpc) are similarly likely, given the three discovered PNe.
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Llerena, M., R. Amorín, F. Cullen, L. Pentericci, A. Calabrò, R. McLure, A. Carnall, et al. "The VANDELS survey: Global properties of CIII]λ1908 Å emitting star-forming galaxies at z ∼ 3." Astronomy & Astrophysics 659 (February 25, 2022): A16. http://dx.doi.org/10.1051/0004-6361/202141651.
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Context. Strong nebular emission is ubiquitous in galaxies that contribute to cosmic reionization at redshift z ≳ 6. High-ionization UV metal lines, such as CIII]λ1908 Å, show high equivalent widths (EW) in these early galaxies, suggesting harder radiation fields at low metallicity than low-z galaxies of similar stellar mass. Understanding the physical properties driving the observed UV nebular line emission at high-z requires large and very deep spectroscopic surveys, which are now only accessible out to z ∼ 4. Aims. We study the mean properties of a large representative sample of 217 galaxies showing CIII] emission at 2 < z < 4, selected from a parent sample of ∼750 main-sequence star-forming galaxies in the VANDELS survey. These CIII] emitters have a broad range of UV luminosities, allowing for a detailed stacking analysis to characterize their stellar mass, star formation rate (SFR), and metallicity as a function of the UV emission line ratios, EWs, and the carbon-to-oxygen (C/O) abundance ratio. Methods. Stacking provides unprecedented high signal-to-noise (S/N) spectra for CIII] emitters over more than three decades in luminosity, stellar mass, and SFR. This enables a full spectral fitting to derive stellar metallicities for each stack. Moreover, we use diagnostics based on photoionization models and UV line ratios to constrain the ionization sources of the galaxies and derive the C/O abundance. Results. Reliable CIII] detections (S/N ≥ 3) represent ∼30% of the parent sample. However, stacked spectra of non-detections (S/N < 3) show weak (EW ≲ 2 Å) CIII] emission, suggesting that this line is common in normal star-forming galaxies at z ∼ 3. On the other hand, extreme CIII] emitters (EW(CIII]) ≳ 8 Å) are exceedingly rare (∼3%) in VANDELS. The UV line ratios of the sample suggest no ionization source other than massive stars. Stacks with larger EW(CIII]) show larger EW(Lyα) and lower metallicity, but not all CIII] emitters are Lyα emitters. The stellar metallicities of CIII] emitters are not significantly different from that of the parent sample, increasing from ∼10% to ∼40% solar for stellar masses log(M⋆/M⊙) ∼ 9−10.5. The stellar mass-metallicity relation of the CIII] emitters is consistent with previous works, exhibiting a strong evolution from z = 0 to z ∼ 3. The C/O abundances of the sample range between 35%−150% solar, with a noticeable increase with FUV luminosity and a smooth decrease with the CIII] EW. Here, we discuss the CIII] emitters in the C/O–Fe/H and the C/O–O/H planes and we find that they follow stellar and nebular abundance trends consistent with those of Milky Way halo and thick-disk stars and local HII galaxies, respectively. A qualitative agreement is also found with chemical evolution models, which suggests that CIII] emitters at z ∼ 3 are experiencing an active phase of chemical enrichment. Conclusions. Our results provide new insights into the nature of UV line emitters at z ∼ 2 − 4, paving the way for future studies at higher z using the James Webb Space Telescope.
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Fahrion, Katja, Iskren Georgiev, Michael Hilker, Mariya Lyubenova, Glenn van de Ven, Mayte Alfaro-Cuello, Enrico M. Corsini, Marc Sarzi, Richard M. McDermid, and Tim de Zeeuw. "Single metal-poor ultra compact dwarf galaxy at one kiloparsec distance from the low-mass elliptical galaxy FCC 47." Astronomy & Astrophysics 625 (May 2019): A50. http://dx.doi.org/10.1051/0004-6361/201834941.
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Context. Photometric surveys of galaxy clusters have revealed a large number of ultra compact dwarfs (UCDs) around predominantly massive elliptical galaxies. Their origin is still debated as some UCDs are considered to be the remnant nuclei of stripped dwarf galaxies while others seem to mark the high-mass end of the star cluster population. Aims. We aim to characterize the properties of a UCD found at very close projected distance (rwproj = 1.1 kpc) from the centre of the low-mass (M ∼ 1010 M⊙) early-type galaxy FCC 47. This is a serendipitous discovery from MUSE adaptive optics science verification data. We explore the potential origin of this UCD as either a massive cluster or the remnant nucleus of a dissolved galaxy. Methods. We used archival Hubble Space Telescope data to study the photometric and structural properties of FCC 47-UCD1. In the MUSE data, the UCD is unresolved, but we used its spectrum to determine the radial velocity and metallicity. Results. The surface brightness of FCC 47-UCD1 is best described by a single King profile with low concentration C = Rt/Rc ∼ 10 and large effective radius (reff = 24 pc). Its integrated magnitude and blue colour (Mg = −10.55 mag, (g − z) = 1.46 mag) combined with a metallicity of [M/H] = −1.12 ± 0.10 dex and an age > 8 Gyr obtained from the full fitting of the MUSE spectrum suggests a stellar population mass of M* = 4.87 × 106 M⊙. The low S/N of the MUSE spectrum prevents detailed stellar population analysis. Due to the limited spectral resolution of MUSE, we can only give an upper limit on the velocity dispersion (σ < 17 km s−1), and consequently on its dynamical mass (Mdyn < 1.3 × 107 M⊙). Conclusions. The origin of the UCD cannot be constrained with certainty. The low metallicity, old age, and magnitude are consistent with a star cluster origin, whereas the extended size is consistent with an origin as the stripped nucleus of a dwarf galaxy with a initial stellar mass of a few 108 M⊙.
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Cortijo-Ferrero, C., R. M. González Delgado, E. Pérez, R. Cid Fernandes, R. García-Benito, P. Di Matteo, S. F. Sánchez, et al. "The spatially resolved star formation history of mergers." Astronomy & Astrophysics 607 (November 2017): A70. http://dx.doi.org/10.1051/0004-6361/201731217.
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This paper presents the spatially resolved star formation history (2D-SFH) of a small sample of four local mergers: the early-stage mergers IC 1623, NGC 6090, and the Mice, and the more advanced merger NGC 2623, by analyzing IFS data from the CALIFA survey and PMAS in LArr mode. Full spectral fitting techniques are applied to the datacubes to obtain the spatially resolved mass growth histories, the time evolution of the star formation rate intensity (ΣSFR), and the local specific star formation rate (sSFR), over three different time scales (30 Myr, 300 Myr, and 1 Gyr). The results are compared with non-interacting Sbc–Sc galaxies, to quantify if there is an enhancement of the star formation and to trace its time scale and spatial extent. Our results for the three LIRGs (IC 1623 W, NGC 6090, and NGC 2623) show that a major phase of star formation is occurring in time scales of 107 yr to few 108 yr, with global SFR enhancements of between approximately two and six with respect to main-sequence star forming (MSSF) galaxies. In the two early-stage mergers IC 1623 W and NGC 6090, which are between first pericentre passage and coalescence, the most remarkable increase of the SFR with respect to non-interacting spirals occurred in the last 30 Myr, and it is spatially extended, with enhancements of factors between two and seven both in the centres (r < 0.5 half light radius, HLR), and in the disks (r > 1 HLR). In the more advanced merger NGC 2623 an extended phase of star formation occurred on a longer time scale of ~1 Gyr, with a SFR enhancement of a factor of approximately two-to-three larger than the one in Sbc–Sc MSSF galaxies over the same period, probably relic of the first pericentre passage epoch. A SFR enhancement in the last 30 Myr is also present, but only in NGC 2623 centre, by a factor of three. In general, the spatially resolved SFHs of the LIRG-mergers are consistent with the predictions from high spatial resolution simulations. In contrast, the star formation in the Mice, specially in Mice B, is not enhanced but inhibited with respect to Sbc–Sc MSSF galaxies. The fact that the gas fraction of Mice B is smaller than in most non-interacting spirals, and that the Mice are close to a prograde orbit, represents a new challenge for the models, which must cover a larger space of parameters in terms of the availability of gas and the orbital characteristics.
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Hill, Lewis, Daniel Thomas, Claudia Maraston, Renbin Yan, Justus Neumann, Andrew Lundgren, Daniel Lazarz, et al. "SDSS-IV MaStar: theoretical atmospheric parameters for the MaNGA stellar library." Monthly Notices of the Royal Astronomical Society 509, no. 3 (November 12, 2021): 4308–29. http://dx.doi.org/10.1093/mnras/stab3263.
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ABSTRACT We calculate the fundamental stellar parameters effective temperature, surface gravity, and iron abundance – Teff, log g, [Fe/H] – for the final release of the Mapping Nearby Galaxies at APO (MaNGA) Stellar Library (MaStar), containing 59 266 per-visit-spectra for 24 290 unique stars at intermediate resolution (R ∼ 1800) and high S/N (median = 96). We fit theoretical spectra from model atmospheres by both MARCS and BOSZ-ATLAS9 to the observed MaStar spectra, using the full spectral fitting code pPXF. We further employ a Bayesian approach, using a Markov Chain Monte Carlo (MCMC) technique to map the parameter space and obtain uncertainties. Originally in this paper, we cross match MaStar observations with Gaia photometry, which enable us to set reliable priors and identify outliers according to stellar evolution. In parallel to the parameter determination, we calculate corresponding stellar population models to test the reliability of the parameters for each stellar evolutionary phase. We further assess our procedure by determining parameters for standard stars such as the Sun and Vega and by comparing our parameters with those determined in the literature from high-resolution spectroscopy (APOGEE and SEGUE) and from lower resolution matching template (LAMOST). The comparisons, considering the different methodologies and S/N of the literature surveys, are favourable in all cases. Our final parameter catalogue for MaStar cover the following ranges: 2592 ≤ Teff ≤ 32 983 K; −0.7 ≤ log g ≤ 5.4 dex; −2.9 ≤ [Fe/H] ≤ 1.0 dex and will be available with the last SDSS-IV Data Release, in 2021 December.
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Fensch, Jérémy, Pierre-Alain Duc, Sungsoon Lim, Éric Emsellem, Michal Bílek, Patrick Durrell, Chengze Liu, Éric Peng, and Rory Smith. "Shedding light on the formation mechanism of shell galaxy NGC 474 with MUSE." Astronomy & Astrophysics 644 (December 2020): A164. http://dx.doi.org/10.1051/0004-6361/202038550.
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Stellar shells around galaxies could provide precious insights into their assembly history. However, their formation mechanism remains poorly empirically constrained, regarding in particular the type of galaxy collisions at their origin. We present MUSE at VLT data of the most prominent outer shell of NGC 474, to constrain its formation history. The stellar shell spectrum is clearly detected, with a signal-to-noise ratio of ∼65 pix−1. We used a full spectral fitting method to determine the line-of-sight velocity and the age and metallicity of the shell and associated point-like sources within the MUSE field of view. We detect six globular cluster (GC) candidates and eight planetary nebula (PN) candidates that are all kinematically associated with the stellar shell. We show that the shell has an intermediate metallicity, [M/H] = −0.83−0.12+0.12, and a possible α-enrichment, [α/Fe] ∼ 0.3. Assuming the material of the shell comes from a lower mass companion, and that the latter had no initial metallicity gradient, such a stellar metallicity would constrain the mass of the progenitor at around 7.4 × 108 M⊙, implying a merger mass ratio of about 1:100. However, our census of PNe and earlier photometry of the shell would suggest a much higher ratio, around 1:20. Given the uncertainties, this difference is only significant at the ≃1σ level. We discuss the characteristics of the progenitor, and in particular whether the progenitor could also be composed of stars from the low-metallicity outskirts of a more massive galaxy. Ultimately, the presented data do not allow us to put a firm constraint on the progenitor mass. We show that at least two GC candidates possibly associated with the shell are quite young, with ages below 1.5 Gyr. We also note the presence of a young (∼1 Gyr) stellar population in the center of NGC 474. The two may have resulted from the same event.
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Prugniel, Philippe, and Mina Koleva. "Spectral models of stellar populations resolved in chemical abundances." Proceedings of the International Astronomical Union 7, S284 (September 2011): 16–19. http://dx.doi.org/10.1017/s1743921312008629.
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AbstractWe present model spectra of stellar populations with variable chemical composition. We derived the [α/Fe] abundance ratio of the stars of the most important libraries (ELODIE, CFLIB and MILES) using full spectrum fitting and we generated PEGASE.HR models resolved in [α/Fe]. We used a semi-empirical approach that combines the observed spectra with synthetic stellar spectra. We tested the models using them to derive [α/Fe] in galaxies and star clusters using full spectrum fitting. The present models are available from http://ulyss.univ-lyon1.fr
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Prichard, Laura J., Sam P. Vaughan, and Roger L. Davies. "Unravelling the origin of the counter-rotating core in IC 1459 with KMOS and MUSE." Monthly Notices of the Royal Astronomical Society 488, no. 2 (May 17, 2019): 1679–94. http://dx.doi.org/10.1093/mnras/stz1191.
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ABSTRACT The massive early-type galaxy IC 1459 is a slowly rotating galaxy that exhibits a rapidly counter-rotating kinematically decoupled core (KDC, RKDC ≈ 5 arcsec ≈ 0.1Re). To investigate the origin of its KDC, we coupled large data mosaics from the near-infrared and optical integral field unit instruments K-band Multi-Object Spectrograph (KMOS) and Multi-Unit Spectroscopic Explorer (MUSE), respectively. We studied IC 1459’s stellar populations and, for the first time for a KDC, the spatially resolved initial mass function (IMF). We used full-spectral-fitting to fit the stellar populations and IMF simultaneously, and an alternative spectral-fitting method that does not assume a star formation history (SFH; although does not constrain the IMF) for comparison. When no SFH is assumed, we derived a negative metallicity gradient for IC 1459 that could be driven by a distinct metal-poor population in the outer regions of the galaxy, and a radially constant old stellar age. We found a radially constant bottom-heavy IMF out to ${\sim }\frac {1}{3}R_{\rm e}$. The radially flat IMF and age extend beyond the counter-rotating core. We detected high-velocity dispersion along the galaxy’s major axis. Our results potentially add weight to findings from orbital modelling of other KDCs that the core is not a distinct population of stars but in fact two smooth co-spatial counter-rotating populations. No clear picture of formation explains the observational results of IC 1459, but we propose it could have included a gas-rich intense period of star formation at early times, perhaps with counter-rotating accreting cold streams, followed by dry and gas-rich mergers through to the present day.
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Mulcahey, C. R., L. J. Prichard, D. Krajnović, and R. A. Jorgenson. "Deciphering the origin of ionized gas in IC 1459 with VLT/MUSE." Monthly Notices of the Royal Astronomical Society 504, no. 4 (April 22, 2021): 5087–97. http://dx.doi.org/10.1093/mnras/stab1137.
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ABSTRACT IC 1459 is an early-type galaxy (ETG) with a rapidly counter-rotating stellar core, and is the central galaxy in a gas-rich group of spirals. In this work, we investigate the abundant ionized gas in IC 1459 and present new stellar orbital models to connect its complex array of observed properties and build a more complete picture of its evolution. Using the Multi-Unit Spectroscopic Explorer (MUSE), the optical integral field unit (IFU) on the Very Large Telescope (VLT), we examine the gas and stellar properties of IC 1459 to decipher the origin and powering mechanism of the galaxy’s ionized gas. We detect ionized gas in a non-disc-like structure rotating in the opposite sense to the central stars. Using emission-line flux ratios and velocity dispersion from full-spectral fitting, we find two kinematically distinct regions of shocked emission-line gas in IC 1459, which we distinguished using narrow (σ ≤ 155 km s−1) and broad (σ > 155 km s−1) profiles. Our results imply that the emission-line gas in IC 1459 has a different origin than that of its counter-rotating stellar component. We propose that the ionized gas is from late-stage accretion of gas from the group environment, which occurred long after the formation of the central stellar component. We find that shock heating and AGN activity are both ionizing mechanisms in IC 1459 but that the dominant excitation mechanism is by post-asymptotic giant branch stars from its old stellar population.
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Zhou, Shuang, Michael Merrifield, Alfonso Aragón-Salamanca, Joel R. Brownstein, Niv Drory, Renbin Yan, and Richard R. Lane. "The impact of environment on the lives of disk galaxies as revealed by SDSS-IV MaNGA." Monthly Notices of the Royal Astronomical Society, October 12, 2022. http://dx.doi.org/10.1093/mnras/stac2913.
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Abstract Environment has long been known to have significant impact on the evolution of galaxies, but here we seek to quantify the subtler differences that might be found in disk galaxies, depending on whether they are isolated, the most massive galaxy in a group (centrals), or a lesser member (satellites). The MaNGA survey allows us to define a large mass-matched sample of 574 galaxies with high-quality integrated spectra in each category. Initial examination of their spectral indices indicates significant differences, particularly in low-mass galaxies. Semi-analytic spectral fitting of a full chemical evolution model to these spectra confirms these differences, with low-mass satellites having a shorter period of star formation and chemical enrichment typical of a closed box, while central galaxies have more extended histories, with evidence of on-going gas accretion over their lifetimes. The derived parameters for gas infall timescale and wind strength suggest that low-mass satellite galaxies have their hot haloes of gas effectively removed, while central galaxies retain a larger fraction of gas than isolated galaxies due to the deeper group potential well in which they sit. S0 galaxies form a distinct subset within the sample, particularly at higher masses, but do not bias the inferred lower-mass environmental impact significantly. The consistent picture that emerges underlines the wealth of archaeological information that can be extracted from high-quality spectral data using techniques like semi-analytic spectral fitting.
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Croom, Scott M., Matt S. Owers, Nicholas Scott, Henry Poetrodjojo, Brent Groves, Jesse van de Sande, Tania M. Barone, et al. "The SAMI Galaxy Survey: the third and final data release." Monthly Notices of the Royal Astronomical Society, February 1, 2021. http://dx.doi.org/10.1093/mnras/stab229.
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Abstract We have entered a new era where integral-field spectroscopic surveys of galaxies are sufficiently large to adequately sample large-scale structure over a cosmologically significant volume. This was the primary design goal of the SAMI Galaxy Survey. Here, in Data Release 3 (DR3), we release data for the full sample of 3068 unique galaxies observed. This includes the SAMI cluster sample of 888 unique galaxies for the first time. For each galaxy, there are two primary spectral cubes covering the blue (370–570 nm) and red (630–740 nm) optical wavelength ranges at spectral resolving power of R = 1808 and 4304 respectively. For each primary cube, we also provide three spatially binned spectral cubes and a set of standardized aperture spectra. For each galaxy, we include complete 2D maps from parameterized fitting to the emission-line and absorption-line spectral data. These maps provide information on the gas ionization and kinematics, stellar kinematics and populations, and more. All data are available online through Australian Astronomical Optics (AAO) Data Central.
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Boecker, Alina, Ryan Leaman, Glenn van de Ven, Mark A. Norris, J. Ted Mackereth, and Robert A. Crain. "A galaxy’s accretion history unveiled from its integrated spectrum." Monthly Notices of the Royal Astronomical Society, November 4, 2019. http://dx.doi.org/10.1093/mnras/stz3077.
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Abstract We present a new method of quantifying a galaxy’s accretion history from its integrated spectrum alone. Using full spectral fitting and calibrated regularization techniques we show how we can accurately derive a galaxy’s mass distribution in age-metallicity space and further separate this into stellar populations from different chemical enrichment histories. By exploiting the fact that accreted lower mass galaxies will exhibit an offset to lower metallicities at fixed age compared to the in-situ stellar population, we quantify the fraction of light that comes from past merger events, that are long since mixed in phase-space and otherwise indistinguishable. Empirical age-metallicity relations (AMRs) parameterized for different galaxy masses are used to identify the accreted stellar populations and link them back to the progenitor galaxy’s stellar mass. This allows us to not only measure the host galaxy’s total ex-situ mass fraction (facc), but also quantify the relative amount of accreted material deposited by satellite galaxies of different masses, i.e. the accreted satellite mass function in analogy to the subhalo mass function. Using mock spectra of present-day, early-type galaxies with total stellar mass ∼109 − 1012 M⊙ from the EAGLE simulation suite we demonstrate that our method can recover the total accreted fraction to within $\approx 38 \%$, the stellar mass of the most massive accreted subhalo to within $\approx 56 \%$ and the slope of the accreted satellite mass function to within $\approx 17 \%$ of the true values from the EAGLE merger trees. Future application of this method to observations could potentially provide us accretion histories of hundreds of individual galaxies, for which deep integrated light spectroscopy is available.