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1
Carlsten, Scott G., Jenny E. Greene, Johnny P. Greco, Rachael L. Beaton, and Erin Kado-Fong. "Structures of Dwarf Satellites of Milky Way-like Galaxies: Morphology, Scaling Relations, and Intrinsic Shapes." Astrophysical Journal 922, no. 2 (December 1, 2021): 267. http://dx.doi.org/10.3847/1538-4357/ac2581.
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Abstract The structure of a dwarf galaxy is an important probe of the effects of stellar feedback and environment. Using an unprecedented sample of 223 low-mass satellites from the ongoing Exploration of Local Volume Satellites survey, we explore the structures of dwarf satellites in the mass range 105.5 < M ⋆ < 108.5 M ⊙. We survey satellites around 80% of the massive, M K < − 22.4 mag, hosts in the Local Volume (LV). Our sample of dwarf satellites is complete to luminosities of M V <−9 mag and surface brightness μ 0,V < 26.5 mag arcsec−2 within at least ∼200 projected kpc of the hosts. For this sample, we find a median satellite luminosity of M V = −12.4 mag, median size of r e = 560 pc, median ellipticity of ϵ = 0.30, and median Sérsic index of n = 0.72. We separate the satellites into late- and early-type (29.6% and 70.4%, respectively). The mass–size relations are very similar between them within ∼5%, which indicates that the quenching and transformation of a late-type dwarf into an early-type one involves only very mild size evolution. Considering the distribution of apparent ellipticities, we infer the intrinsic shapes of the early- and late-type samples. Combining with literature samples, we find that both types of dwarfs are described roughly as oblate spheroids that get more spherical at fainter luminosities, but early-types are always rounder at fixed luminosity. Finally, we compare the LV satellites with dwarf samples from the cores of the Virgo and Fornax clusters. We find that the cluster satellites show similar scaling relations to the LV early-type dwarfs but are roughly 10% larger at fixed mass, which we interpret as being due to tidal heating in the cluster environments. The dwarf structure results presented here are a useful reference for simulations of dwarf galaxy formation and the transformation of dwarf irregulars into spheroidals.
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Garrison-Kimmel, Shea, Andrew Wetzel, Philip F. Hopkins, Robyn Sanderson, Kareem El-Badry, Andrew Graus, T. K. Chan, et al. "Star formation histories of dwarf galaxies in the FIRE simulations: dependence on mass and Local Group environment." Monthly Notices of the Royal Astronomical Society 489, no. 4 (September 10, 2019): 4574–88. http://dx.doi.org/10.1093/mnras/stz2507.
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ABSTRACT We study star formation histories (SFHs) of 500 dwarf galaxies (stellar mass $M_\ast =10^5\!-\!10^9\, \rm {M}_\odot$) from FIRE-2 cosmological zoom-in simulations. We compare dwarfs around individual Milky Way (MW)-mass galaxies, dwarfs in Local Group (LG)-like environments, and true field (i.e. isolated) dwarf galaxies. We reproduce observed trends wherein higher mass dwarfs quench later (if at all), regardless of environment. We also identify differences between the environments, both in terms of ‘satellite versus central’ and ‘LG versus individual MW versus isolated dwarf central.’ Around the individual MW-mass hosts, we recover the result expected from environmental quenching: central galaxies in the ‘near field’ have more extended SFHs than their satellite counterparts, with the former more closely resemble isolated (true field) dwarfs (though near-field centrals are still somewhat earlier forming). However, this difference is muted in the LG-like environments, where both near-field centrals and satellites have similar SFHs, which resemble satellites of single MW-mass hosts. This distinction is strongest for M* = 106–$10^7\, \rm {M}_\odot$ but exists at other masses. Our results suggest that the paired halo nature of the LG may regulate star formation in dwarf galaxies even beyond the virial radii of the MW and Andromeda. Caution is needed when comparing zoom-in simulations targeting isolated dwarf galaxies against observed dwarf galaxies in the LG.
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Garling, Christopher T., Annika H. G. Peter, Christopher S. Kochanek, David J. Sand, and Denija Crnojević. "A search for satellite galaxies of nearby star-forming galaxies with resolved stars in LBT-SONG." Monthly Notices of the Royal Astronomical Society 507, no. 4 (August 31, 2021): 4764–78. http://dx.doi.org/10.1093/mnras/stab2447.
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ABSTRACT We present results from a resolved stellar population search for dwarf satellite galaxies of six nearby (D < 5 Mpc), sub-Milky Way mass hosts using deep (m ∼ 27 mag) optical imaging from the Large Binocular Telescope. We perform image simulations to quantify our detection efficiency for dwarfs over a large range in luminosity and size, and develop a fast catalogue-based emulator that includes a treatment of unresolved photometric blending. We discover no new dwarf satellites, but we recover two previously known dwarfs (DDO 113 and LV J1228+4358) with MV < −12 that lie in our survey volume. We preview a new theoretical framework to predict satellite luminosity functions using analytical probability distribution functions and apply it to our sample, finding that we predict one fewer classical dwarf and one more faint dwarf (MV ∼ −7.5) than we find in our observational sample (i.e. the observational sample is slightly top-heavy). However, the overall number of dwarfs in the observational sample (2) is in good agreement with the theoretical expectations. Interestingly, DDO 113 shows signs of environmental quenching and LV J1228+4358 is tidally disrupting, suggesting that low-mass hosts may affect their satellites more severely than previously believed.
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Korol, V., S. Toonen, A. Klein, V. Belokurov, F. Vincenzo, R. Buscicchio, D. Gerosa, et al. "Populations of double white dwarfs in Milky Way satellites and their detectability with LISA." Astronomy & Astrophysics 638 (June 2020): A153. http://dx.doi.org/10.1051/0004-6361/202037764.
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Context. Milky Way dwarf satellites are unique objects that encode the early structure formation and therefore represent a window into the high redshift Universe. So far, their study has been conducted using electromagnetic waves only. The future Laser Interferometer Space Antenna (LISA) has the potential to reveal Milky Way satellites through gravitational waves emitted by double white dwarf (DWD) binaries. Aims. We investigate gravitational wave signals that will be detectable by LISA as a possible tool for the identification and characterisation of the Milky Way satellites. Methods. We used the binary population synthesis technique to model the population of DWDs in dwarf satellites and we assessed the impact on the number of LISA detections when making changes to the total stellar mass, distance, star formation history, and metallicity of satellites. We calibrated predictions for the known Milky Way satellites on their observed properties. Results. We find that DWDs emitting at frequencies ≳3 mHz can be detected in Milky Way satellites at large galactocentric distances. The number of these high frequency DWDs per satellite primarily depends on its mass, distance, age, and star formation history, and only mildly depends on the other assumptions regarding their evolution such as metallicity. We find that dwarf galaxies with M⋆ > 106 M⊙ can host detectable LISA sources; the number of detections scales linearly with the satellite’s mass. We forecast that out of the known satellites, Sagittarius, Fornax, Sculptor, and the Magellanic Clouds can be detected with LISA. Conclusions. As an all-sky survey that does not suffer from contamination and dust extinction, LISA will provide observations of the Milky Way and dwarf satellites galaxies, which will be valuable for Galactic archaeology and near-field cosmology.
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Bell, Eric F., Adam Smercina, Paul A. Price, Richard D’Souza, Jeremy Bailin, Roelof S. de Jong, Katya Gozman, et al. "Ultrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion." Astrophysical Journal Letters 937, no. 1 (September 1, 2022): L3. http://dx.doi.org/10.3847/2041-8213/ac8e5e.
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Abstract The faint and ultrafaint dwarf galaxies in the Local Group form the observational bedrock upon which our understanding of small-scale cosmology rests. In order to understand whether this insight generalizes, it is imperative to use resolved-star techniques to discover similarly faint satellites in nearby galaxy groups. We describe our search for ultrafaint galaxies in the M81 group using deep ground-based resolved-star data sets from Subaru’s Hyper Suprime-Cam. We present one new ultrafaint dwarf galaxy in the M81 group and identify five additional extremely low surface brightness candidate ultrafaint dwarfs that reach deep into the ultrafaint regime to M V ∼ − 6 (similar to current limits for Andromeda satellites). These candidates’ luminosities and sizes are similar to known Local Group dwarf galaxies Tucana B, Canes Venatici I, Hercules, and Boötes I. Most of these candidates are likely to be real, based on tests of our techniques on blank fields. Intriguingly, all of these candidates are spatially clustered around NGC 3077, which is itself an M81 group satellite in an advanced state of tidal disruption. This is somewhat surprising, as M81 itself and its largest satellite M82 are both substantially more massive than NGC 3077 and, by virtue of their greater masses, would have been expected to host as many or more ultrafaint candidates. These results lend considerable support to the idea that satellites of satellites are an important contribution to the growth of satellite populations around Milky Way–mass galaxies.
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Forbes, Duncan A. "A Tale of Giants Stealing from Dwarfs." Highlights of Astronomy 13 (2005): 177–78. http://dx.doi.org/10.1017/s1539299600015525.
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Cold Dark Matter simulations predict 10-100 x more dwarf satellite galaxies than are observed. Some of these ‘missing satellites’ may have been accreted, along with their globular clusters (GCs), by giant galaxies (Cote et al. 1998). But examples of dwarfs in the early stages of disruption have remained elusive.
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Sales, Laura V. "The Future of Dwarf Galaxy Research: What Simulations will Predict?" Proceedings of the International Astronomical Union 14, S344 (August 2018): 17–26. http://dx.doi.org/10.1017/s1743921318007391.
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AbstractWe present a summary of the predictions from numerical simulations to our understanding of dwarf galaxies. It centers the discussion around the Λ Cold Dark Matter scenario (ΛCDM) but discusses also implications for alternative dark matter models. Four key predictions are identified: the abundance of dwarf galaxies, their dark matter content, their relation with environment and the existence of dwarf satellites orbiting dwarf field galaxies. We discuss tensions with observations and identify the most exciting predictions expected from simulations in the future, including i) the existence of “dark galaxies” (dark matter halos without stars), ii) the ability to resolve the structure (size, morphology, dark matter distribution) in dwarfs and iii) the number of ultra-faint satellites around dwarf galaxies. All of these predictions shall inform future observations, not only the faintest galaxies to be discovered within the Local Volume but also distant dwarfs driving galaxy formation in the early universe.
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Fattahi, Azadeh, Julio F. Navarro, and Carlos S. Frenk. "The missing dwarf galaxies of the Local Group." Monthly Notices of the Royal Astronomical Society 493, no. 2 (February 10, 2020): 2596–605. http://dx.doi.org/10.1093/mnras/staa375.
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ABSTRACT We study the Local Group (LG) dwarf galaxy population predicted by the APOSTLE ΛCDM cosmological hydrodynamics simulations. These indicate that: (i) the total mass within 3 Mpc of the Milky Way–Andromeda mid-point (M3Mpc) typically exceeds ∼3 times the sum of the virial masses (M200crit) of the two primaries and (ii) the dwarf galaxy formation efficiency per unit mass is uniform throughout the volume. This suggests that the satellite population within the virial radii of the Milky Way and Andromeda should make up fewer than one third of all LG dwarfs within 3 Mpc. This is consistent with the fraction of observed LG galaxies with stellar mass $M_*\gt 10^7\, {\rm M}_\odot$ that are satellites (12 out of 42; i.e. 28 per cent). For the APOSTLE galaxy mass–halo mass relation, the total number of such galaxies further suggests an LG mass of $M_{\rm 3 Mpc}\sim 10^{13}\, {\rm M}_\odot$. At lower galaxy masses, however, the observed satellite fraction is substantially higher (42 per cent for $M_*\gt 10^5\, { \mathrm{ M}}_\odot$). If this is due to incompleteness in the field sample, then ∼50 dwarf galaxies at least as massive as the Draco dwarf spheroidal must be missing from the current LG field dwarf inventory. The incompleteness interpretation is supported by the pronounced flattening of the LG luminosity function below $M_*\sim 10^7\, {\rm M}_\odot$, and by the scarcity of low surface brightness LG field galaxies compared to satellites. The simulations indicate that most missing dwarfs should lie near the virial boundaries of the two LG primaries, and predict a trove of nearby dwarfs that await discovery by upcoming wide-field imaging surveys.
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Müller, Oliver, Marina Rejkuba, Marcel S. Pawlowski, Rodrigo Ibata, Federico Lelli, Michael Hilker, and Helmut Jerjen. "The dwarf galaxy satellite system of Centaurus A." Astronomy & Astrophysics 629 (August 26, 2019): A18. http://dx.doi.org/10.1051/0004-6361/201935807.
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Dwarf galaxy satellite systems are essential probes to test models of structure formation, making it necessary to establish a census of dwarf galaxies outside of our own Local Group. We present deep FORS2 VI band images from the ESO Very Large Telescope (VLT) for 15 dwarf galaxy candidates in the Centaurus group of galaxies. We confirm nine dwarfs to be members of Cen A by measuring their distances using a Bayesian approach to determine the tip of the red giant branch luminosity. We have also fit theoretical isochrones to measure their mean metallicities. The properties of the new dwarfs are similar to those in the Local Group in terms of their sizes, luminosities, and mean metallicities. Within our photometric precision, there is no evidence of a metallicity spread, but we do observe possible extended star formation in several galaxies, as evidenced by a population of asymptotic giant branch stars brighter than the red giant branch tip. The new dwarfs do not show any signs of tidal disruption. Together with the recently reported dwarf galaxies by the complementary PISCeS survey, we study the luminosity function and 3D structure of the group. By comparing the observed luminosity function to the high-resolution cosmological simulation IllustrisTNG, we find agreement within a 90% confidence interval. However, Cen A seems to be missing its brightest satellites and has an overabundance of the faintest dwarfs in comparison to its simulated analogs. In terms of the overall 3D distribution of the observed satellites, we find that the whole structure is flattened along the line-of-sight, with a root-mean-square (rms) height of 130 kpc and an rms semi-major axis length of 330 kpc. Future distance measurements of the remaining dwarf galaxy candidates are needed to complete the census of dwarf galaxies in the Centaurus group.
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Yniguez, Basilio, Shea Garrison-Kimmel, Michael Boylan-Kolchin, and James S. Bullock. "On the stark difference in satellite distributions around the Milky Way and Andromeda." Monthly Notices of the Royal Astronomical Society 439, no. 1 (February 4, 2014): 73–82. http://dx.doi.org/10.1093/mnras/stt2058.
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Abstract We compare spherically averaged radial number counts of bright (≳105 L⊙) dwarf satellite galaxies within 400 kpc of the Milky Way (MW) and M31 and find that the MW satellites are much more centrally concentrated. Remarkably, the two satellite systems are almost identical within the central 100 kpc, while M31 satellites outnumber MW satellites by about a factor of 4 at deprojected distances spanning 100–400 kpc. We compare the observed distributions to those predicted for Λ cold dark matter (ΛCDM) subhaloes using a suite of 44 high-resolution ∼1012 M⊙ halo zoom simulations, 22 of which are in pairs like the MW and M31. We find that the radial distribution of satellites around M31 is fairly typical of those predicted for subhaloes, while the MW's distribution is more centrally concentrated than any of our simulated ΛCDM haloes. One possible explanation is that our census of bright (≳105 L⊙) MW dwarf galaxies is significantly incomplete beyond ∼100 kpc of the Sun. If there were ∼8–20 more bright dwarfs orbiting undetected at 100–400 kpc distance, then the MW's radial distribution would fall within the range expected from subhalo distributions and also look very much like the known M31 system. We use our simulations to demonstrate that there is enough area left unexplored by the Sloan Digital Sky Survey and its extensions that the discovery of ∼10 new bright dwarfs is not implausible given the expected range of angular anisotropy of subhaloes in the sky.
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Korol, Valeriya, Vasily Belokurov, Christopher J. Moore, and Silvia Toonen. "Weighing Milky Way satellites with LISA." Monthly Notices of the Royal Astronomical Society: Letters 502, no. 1 (January 14, 2021): L55—L60. http://dx.doi.org/10.1093/mnrasl/slab003.
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ABSTRACT White dwarf stars are a well-established tool for studying Galactic stellar populations. Two white dwarfs in a tight binary system offer us an additional messenger – gravitational waves – for exploring the Milky Way and its immediate surroundings. Gravitational waves produced by double white dwarf (DWD) binaries can be detected by the future Laser Interferometer Space Antenna (LISA). Numerous and widespread DWDs have the potential to probe shapes, masses, and formation histories of the stellar populations in the Galactic neighbourhood. In this work we outline a method for estimating the total stellar mass of Milky Way satellite galaxies based on the number of DWDs detected by LISA. To constrain the mass we perform a Bayesian inference using binary population synthesis models and considering the number of detected DWDs associated with the satellite and the measured distance to the satellite as the only inputs. Based on a fiducial binary population synthesis model we find that for large satellites the stellar masses can be recovered to within (1) a factor 2 if the star formation history (SFH) is known and (2) an order of magnitude when marginalizing over different SFH models. For smaller satellites we can place upper limits on their stellar mass. Gravitational wave observations can provide mass measurements for large satellites that are comparable, and in some cases more precise, than standard electromagnetic observations.
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Erkal, Denis, and Vasily A. Belokurov. "Limit on the LMC mass from a census of its satellites." Monthly Notices of the Royal Astronomical Society 495, no. 3 (May 6, 2020): 2554–63. http://dx.doi.org/10.1093/mnras/staa1238.
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ABSTRACT We study the orbits of dwarf galaxies in the combined presence of the Milky Way and Large Magellanic Cloud (LMC) and find six dwarfs that were likely accreted with the LMC (Car 2, Car 3, Hor 1, Hyi 1, Phe 2, and Ret 2), in addition to the Small Magellanic Cloud (SMC), representing strong evidence of dwarf galaxy group infall. This procedure depends on the gravitational pull of the LMC, allowing us to place a lower bound on the Cloud’s mass of $M_{\rm LMC} \gt 1.24\times 10^{11} \, \mathrm{M}_\odot$ if we assume that these are LMC satellites. This mass estimate is validated by applying the technique to a cosmological zoom-in simulation of a Milky Way-like galaxy with an LMC analogue where we find that while this lower bound may be overestimated, it will improve in the future with smaller observational errors. We apply this technique to dwarf galaxies lacking radial velocities and find that Eri 3 has a broad range of radial velocities for which it has a significant chance (>0.4) of having been bound to the Cloud. We study the non-Magellanic classical satellites and find that Fornax has an appreciable probability of being an LMC satellite if the LMC is sufficiently massive ($\text{$\sim$} 2.5\times 10^{11} \, \mathrm{M}_\odot$). In addition, we explore how the orbits of Milky Way satellites change in the presence of the LMC and find a significant change for several objects. Finally, we find that the dwarf galaxies likely to be LMC satellites are slightly smaller than Milky Way satellites at a fixed luminosity, possibly due to the different tidal environments they have experienced.
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Davis, A. Bianca, Anna M. Nierenberg, Annika H. G. Peter, Christopher T. Garling, Johnny P. Greco, Christopher S. Kochanek, Dyas Utomo, et al. "The LBT satellites of Nearby Galaxies Survey (LBT-SONG): the satellite population of NGC 628." Monthly Notices of the Royal Astronomical Society 500, no. 3 (November 5, 2020): 3854–69. http://dx.doi.org/10.1093/mnras/staa3246.
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ABSTRACT We present the first satellite system of the Large Binocular Telescope Satellites Of Nearby Galaxies Survey (LBT-SONG), a survey to characterize the close satellite populations of Large Magellanic Cloud to Milky-Way-mass, star-forming galaxies in the Local Volume. In this paper, we describe our unresolved diffuse satellite finding and completeness measurement methodology and apply this framework to NGC 628, an isolated galaxy with ∼1/4 the stellar mass of the Milky Way. We present two new dwarf satellite galaxy candidates: NGC 628 dwA, and dwB with MV = −12.2 and −7.7, respectively. NGC 628 dwA is a classical dwarf while NGC 628 dwB is a low-luminosity galaxy that appears to have been quenched after reionization. Completeness corrections indicate that the presence of these two satellites is consistent with CDM predictions. The satellite colours indicate that the galaxies are neither actively star forming nor do they have the purely ancient stellar populations characteristic of ultrafaint dwarfs. Instead, and consistent with our previous work on the NGC 4214 system, they show signs of recent quenching, further indicating that environmental quenching can play a role in modifying satellite populations even for hosts smaller than the Milky Way.
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Weerasooriya, Sachi, Mia Sauda Bovill, Andrew Benson, Alexi M. Musick, and Massimo Ricotti. "Devouring the Milky Way Satellites: Modeling Dwarf Galaxies with Galacticus." Astrophysical Journal 948, no. 2 (May 1, 2023): 87. http://dx.doi.org/10.3847/1538-4357/acc32b.
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Abstract Dwarf galaxies are ubiquitous throughout the universe and are extremely sensitive to various forms of internal and external feedback. Over the last two decades, the census of dwarf galaxies in the Local Group and beyond has increased markedly. While hydrodynamic simulations (e.g., FIRE II, Mint Justice League) have reproduced the observed dwarf properties down to the ultrafaints, such simulations require extensive computational resources to run. In this work, we constrain the standard physical implementations in the semianalytic model Galacticus to reproduce the observed properties of the Milky Way satellites down to the ultrafaint dwarfs found in the Sloan Digital Sky Survey. We run Galacticus on merger trees from our high-resolution N–body simulation of a Milky Way analog. We determine the best-fit parameters by matching the cumulative luminosity function and luminosity–metallicity relation from both observations and hydrodynamic simulations. With the correct parameters, the standard physics in Galacticus can reproduce the observed luminosity function and luminosity–metallicity relation of the Milky Way dwarfs. In addition, we find a multidimensional match with half-light radii, velocity dispersions, and mass to light ratios at z = 0 down to M V ≤ −6 (L ≥ 104 L ⊙). In addition to successfully reproducing the properties of the z = 0 Milky Way satellite population, our modeled dwarfs have star formation histories that are consistent with those of the Local Group dwarfs.
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Carlsten, Scott G., Jenny E. Greene, Rachael L. Beaton, Shany Danieli, and Johnny P. Greco. "The Exploration of Local VolumE Satellites (ELVES) Survey: A Nearly Volume-limited Sample of Nearby Dwarf Satellite Systems." Astrophysical Journal 933, no. 1 (July 1, 2022): 47. http://dx.doi.org/10.3847/1538-4357/ac6fd7.
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Abstract We present the final sample of the Exploration of Local VolumE Satellites (ELVES) survey, a survey of the dwarf satellites of a nearly volume-limited sample of Milky Way (MW)−like hosts in the Local Volume. Hosts are selected simply via a cut in luminosity ( M K s < − 22.1 mag) and distance (D < 12 Mpc). We cataloged the satellites of 25 of the 31 such hosts, with another five taken from the literature. All hosts are surveyed out to at least 150 projected kpc ( ∼ R vir/2), with the majority surveyed to 300 kpc ( ∼ R vir). Satellites are detected using a consistent semiautomated algorithm specialized for low surface brightness dwarfs. As shown through extensive tests with injected galaxies, the catalogs are complete to M V ∼ −9 mag and μ 0,V ∼ 26.5 mag arcsec−2. Candidates are confirmed to be real satellites through distance measurements including redshift, tip of the red giant branch, and surface brightness fluctuations. Across all 30 surveyed hosts, there are 338 confirmed satellites with M V < −9 mag, with a further 106 candidates awaiting distance measurement. For the vast majority of these, we provide consistent multiband Sérsic photometry. We show that satellite abundance correlates with host mass, with the MW being quite typical among comparable systems, and that satellite quenched fraction rises steeply with decreasing satellite mass, mirroring the quenched fraction for the MW and M31. The ELVES survey represents a massive increase in the statistics of surveyed systems with known completeness, and the provided catalogs are a unique data set to explore various aspects of small-scale structure and dwarf galaxy evolution.
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Mutlu-Pakdil, Burçin, David J. Sand, Denija Crnojević, Michael G. Jones, Nelson Caldwell, Puragra Guhathakurta, Anil C. Seth, et al. "Hubble Space Telescope Observations of NGC 253 Dwarf Satellites: Three Ultra-faint Dwarf Galaxies*." Astrophysical Journal 926, no. 1 (February 1, 2022): 77. http://dx.doi.org/10.3847/1538-4357/ac4418.
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Abstract We present deep Hubble Space Telescope (HST) imaging of five faint dwarf galaxies associated with the nearby spiral NGC 253 (D ≈ 3.5 Mpc). Three of these are newly discovered dwarf galaxies, while all five were found in the Panoramic Imaging Survey of Centaurus and Sculptor, a Magellan+Megacam survey to identify faint dwarfs and other substructures in resolved stellar light around massive galaxies outside of the Local Group. Our HST data reach ≳3 magnitudes below the tip of the red giant branch for each dwarf, allowing us to derive their distances, structural parameters, and luminosities. All five systems contain mostly old, metal-poor stellar populations (age ∼12 Gyr, [M/H] ≲ −1.5) and have sizes (r h ∼ 110–3000 pc) and luminosities (M V ∼ −7 to −12 mag) largely consistent with Local Group dwarfs. The three new NGC 253 satellites are among the faintest systems discovered beyond the Local Group. We also use archival H i data to place limits on the gas content of our discoveries. Deep imaging surveys such as our program around NGC 253 promise to elucidate the faint end of the satellite luminosity function and its scatter across a range of galaxy masses, morphologies, and environments in the decade to come.
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Müller, Oliver, Rodrigo Ibata, Marina Rejkuba, and Lorenzo Posti. "Distance to the nearby dwarf galaxy [TT2009] 25 in the NGC 891 group using the tip of the red giant branch." Astronomy & Astrophysics 629 (August 22, 2019): L2. http://dx.doi.org/10.1051/0004-6361/201936392.
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Dwarf galaxies are key objects for small-scale cosmological tests like the abundance problems or the planes-of-satellites problem. A crucial task is therefore to get accurate information for as many nearby dwarf galaxies as possible. Using extremely deep, ground-based V and i-band Subaru Suprime Cam photometry with a completeness of i = 27 mag, we measure the distance of the dwarf galaxy [TT2009] 25 using the tip of the red giant branch as a standard candle. This dwarf resides in the field around the Milky Way-analog NGC 891. Using a Bayesian approach, we measure a distance of 10.28−1.73+1.17 Mpc, which is consistent with the distance of NGC 891, and thus confirm it as a member of NGC 891. The dwarf galaxy follows the scaling relations defined by the Local Group dwarfs. We do not find an extended stellar halo around [TT2009] 25. In the small field of view of 100 kpc covered by the survey, only one bright dwarf galaxy and the giant stream are apparent. This is comparable to the Milky Way, where one bright dwarf resides in the same volume, as well as the Sagittarius stream – excluding satellites which are farther away but would be projected in the line-of-sight. It is thus imperative to survey for additional dwarf galaxies in a larger area around NGC 891 to test the abundance of dwarf galaxies and compare this to the number of satellites around the Milky Way.
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Lee, Duane M., Kathryn V. Johnston, Bodhisattva Sen, and Will Jessop. "Reconstructing the Accretion History of the Galactic Halo Using Stellar Chemical Abundance Ratio Distributions." Proceedings of the International Astronomical Union 11, S317 (August 2015): 328–29. http://dx.doi.org/10.1017/s1743921315009801.
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AbstractIn this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from eleven “MW-like” halos to generate satellite template sets of 2D CARDs of accreted dwarf satellites which are comprised of accreted dwarfs from various mass regimes and epochs of accretion. Next, we randomly drew samples of ~ 103–4 mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those eleven halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the satellite template set (STS) used and the sample size. For certain STS used we typically can identify the relative mass contributions of all accreted satellites to within a factor of 2. We also find that this method is particularly sensitive to older accretion events involving low-luminous dwarfs e.g. ultra-faint dwarfs — precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early Universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ~ 6–9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us (given the development of new CARD–generating dwarf models) to recover the luminosity function of infalling dwarf galaxies — and the detailed accretion history of the halo — across cosmic time.
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Fritz, T. K., G. Battaglia, M. S. Pawlowski, N. Kallivayalil, R. van der Marel, S. T. Sohn, C. Brook, and G. Besla. "Gaia DR2 proper motions of dwarf galaxies within 420 kpc." Astronomy & Astrophysics 619 (November 2018): A103. http://dx.doi.org/10.1051/0004-6361/201833343.
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A proper understanding of the Milky Way (MW) dwarf galaxies in a cosmological context requires knowledge of their 3D velocities and orbits. However, proper motion (PM) measurements have generally been of limited accuracy and are available only for more massive dwarfs. We therefore present a new study of the kinematics of the MW dwarf galaxies. We use the Gaia DR2 for those dwarfs that have been spectroscopically observed in the literature. We derive systemic PMs for 39 galaxies and galaxy candidates out to 420 kpc, and generally find good consistency for the subset with measurements available from other studies. We derive the implied Galactocentric velocities, and calculate orbits in canonical MW halo potentials of low (0.8 × 1012 M⊙) and high mass (1.6 × 1012 M⊙). Comparison of the distributions of orbital apocenters and 3D velocities to the halo virial radius and escape velocity, respectively, suggests that the satellite kinematics are best explained in the high-mass halo. Tuc III, Crater II, and additional candidates have orbital pericenters small enough to imply significant tidal influences. Relevant to the missing satellite problem, the fact that fewer galaxies are observed to be near apocenter than near pericenter implies that there must be a population of distant dwarf galaxies yet to be discovered. Of the 39 dwarfs: 12 have orbital poles that do not align with the MW plane of satellites (given reasonable assumptions about its intrinsic thickness); 10 have insufficient PM accuracy to establish whether they align; and 17 satellites align, of which 11 are co-orbiting and (somewhat surprisingly, in view of prior knowledge) 6 are counter-orbiting. Group infall might have contributed to this, but no definitive association is found for the members of the Crater-Leo group.
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Higgs, C. R., A. W. McConnachie, N. Annau, M. Irwin, G. Battaglia, P. Côté, G. F. Lewis, and K. Venn. "Solo dwarfs II: the stellar structure of isolated Local Group dwarf galaxies." Monthly Notices of the Royal Astronomical Society 503, no. 1 (January 9, 2021): 176–99. http://dx.doi.org/10.1093/mnras/stab002.
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ABSTRACT The Solo (Solitary Local) Dwarf Galaxy survey is a volume-limited, wide-field g- and i-band survey of all known nearby (<3 Mpc) and isolated (>300 kpc from the Milky Way or M31) dwarf galaxies. This set of 44 dwarfs is homogeneously analysed for quantitative comparisons to the satellite dwarf populations of the Milky Way and M31. In this paper, an analysis of the 12 closest Solo dwarf galaxies accessible from the Northern hemisphere is presented, including derivation of their distances, spatial distributions, morphology, and extended structures, including their inner integrated light properties and their outer resolved star distributions. All 12 galaxies are found to be reasonably well described by two-dimensional Sérsic functions, although UGC 4879 in particular shows tentative evidence of two distinct components. No prominent extended stellar substructures, which could be signs of either faint satellites or recent mergers, are identified in the outer regions of any of the systems examined.
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D'Onghia, Elena, and George Lake. "The Magellanic Group and the Seven Dwarfs." Proceedings of the International Astronomical Union 4, S256 (July 2008): 473–78. http://dx.doi.org/10.1017/s1743921308028883.
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AbstractThe Magellanic Clouds were the largest members of a group of dwarf galaxies that entered the Milky Way (MW) halo at late times. This group, dominated by the LMC, contained ~4% of the mass of the Milky Way prior to its accretion and tidal disruption, but ≈70% of the known dwarfs orbiting the MW. Our theory addresses many outstanding problems in galaxy formation associated with dwarf galaxies. First, it can explain the planar orbital configuration populated by some dSphs in the MW. Second, it provides a mechanism for lighting up a subset of dwarf galaxies to reproduce the cumulative circular velocity distribution of the satellites in the MW. Finally, our model predicts that most dwarfs will be found in association with other dwarfs. The recent discovery of Leo V (Belokurov et al. 2008), a dwarf spheroidal companion of Leo IV, and the nearby dwarf associations supports our hypothesis.
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Martínez-Delgado, David, Dmitry Makarov, Behnam Javanmardi, Marcel S. Pawlowski, Lidia Makarova, Giuseppe Donatiello, Dustin Lang, Javier Román, Kathy Vivas, and Julio A. Carballo-Bello. "Tracing satellite planes in the Sculptor group." Astronomy & Astrophysics 652 (August 2021): A48. http://dx.doi.org/10.1051/0004-6361/202141242.
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Context. In recent years, a new generation of large-scale imaging surveys have probed wide field regions for the first time around some nearby galaxies in an unprecedentedly low surface-brightness regime (∼28.0−29.0 mag arcsec−2). This provides the chance to discover very faint dwarf satellites by means of systematic visual inspection of these public deep images. Aims. In this paper, we report the first results of a systematic survey of faint dwarf spheroidal galaxies in the vicinity of the bright late-type spiral galaxy NGC 253 by means of a visual inspection of the images taken by the Dark Energy Survey. Methods. We performed a new NGC 253 satellite search using co-added image cutouts reprocessed in the DESI Legacy image surveys. We used GALFIT software to investigate the photometric and structural properties of three dwarf galaxies. Results. We report the discovery of three new dwarf galaxies in the vicinity of the brightest member of the Sculptor filament, the late-type spiral NGC 253, located at a distance of 3.7 Mpc towards Anti-Virgo. We name them Do II, Do III, and Do IV. Assuming they are companions of NGC 253, their total absolute V-magnitudes fall in the −7 to −9 mag range, which is typical for dwarf satellites in the local Universe. The central surface brightness tends to be extremely low for all three discovered dwarfs and falls roughly in the range of 25−26 mag arcsec−2 in g-band. Using known data on distances and velocities of galaxies, we estimate the total virial mass of the NGC 253 group to be 8 × 1011 M⊙, which gives a virial radius of R200 = 186 kpc and a turn-around radius of 706 kpc. We also discuss the possible existence of a spatially flattened and velocity-correlated satellite system around NGC 253. This large-scale structure is orientated almost edge-on to the line of sight. The possible plane of satellites is only 31 kpc thick with a minor-to-major axis ratio of 0.14. Four out of five galaxies with measured velocities follow a common velocity trend similar to those observed in the planes of satellites around the Andromeda and Centaurus A galaxies. However, the small number of galaxies with known velocities prevents us from reaching a definitive conclusion about the formation scenario of the structure and its possible relation to the surrounding cosmic web.
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Shao, Shi, Marius Cautun, and Carlos S. Frenk. "Evolution of galactic planes of satellites in the eagle simulation." Monthly Notices of the Royal Astronomical Society 488, no. 1 (June 26, 2019): 1166–79. http://dx.doi.org/10.1093/mnras/stz1741.
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ABSTRACT We study the formation of planes of dwarf galaxies around Milky Way (MW)-mass haloes in the eagle galaxy formation simulation. We focus on satellite systems similar to the one in the MW: spatially thin or with a large fraction of members orbiting in the same plane. To characterize the latter, we introduce a robust method to identify the subsets of satellites that have the most coplanar orbits. Out of the 11 MW classical dwarf satellites, 8 have highly clustered orbital planes whose poles are contained within a 22° opening angle centred around (l, b) = (182°, −2°). This configuration stands out when compared to both isotropic and typical ΛCDM satellite distributions. Purely flattened satellite systems are short-lived chance associations and persist for less than $1\, \rm {Gyr}$. In contrast, satellite subsets that share roughly the same orbital plane are longer lived, with half of the MW-like systems being at least $4\, \rm {Gyr}$ old. On average, satellite systems were flatter in the past, with a minimum in their minor-to-major axes ratio about $9\, \rm {Gyr}$ ago, which is the typical infall time of the classical satellites. MW-like satellite distributions have on average always been flatter than the overall population of satellites in MW-mass haloes and, in particular, they correspond to systems with a high degree of anisotropic accretion of satellites. We also show that torques induced by the aspherical mass distribution of the host halo channel some satellite orbits into the host’s equatorial plane, enhancing the fraction of satellites with coplanar orbits. In fact, the orbital poles of coplanar satellites are tightly aligned with the minor axis of the host halo.
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Łokas, Ewa L. "Tidal evolution of dwarf galaxies with shallow dark matter density profiles." Proceedings of the International Astronomical Union 10, H16 (August 2012): 346. http://dx.doi.org/10.1017/s1743921314011181.
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AbstractOne of the scenarios for the formation of dwarf spheroidal galaxies in the Local Group proposes that the objects formed from late type dwarfs via tidal interaction with bigger galaxies such as the Milky Way and Andromeda. The scenario naturally explains the morphology-density relation observed for dwarf galaxies in the Local Group. Using N-body simulations we study the long-term tidal evolution of dwarf galaxies in the vicinity of the Milky Way. The dwarf galaxies were initially composed of stellar disks embedded in dark matter haloes of different inner density slopes including shallow ones recently obtained in N-body+hydro simulations of dwarf galaxy formation in isolation. Such progenitors were placed on five different orbits around the Milky Way and their evolution was followed for 10 Gyr. The outcome of the evolution, in terms of the mass loss, morphological transformation and randomization of stellar orbits depends very sensitively on the inner density slope of dark matter. The effects of tides are stronger for dwarfs with shallower slopes; they are more heavily stripped, in some cases down to the scale of ultra-faint satellites of the Milky Way or even dissolved completely with obvious implications for the missing satellites problem. The morphological evolution of the stellar component, from rotationally supported disks to spheroids dominated by random motions, also proceeds faster. In addition, bars which usually form at the first pericenter passage are created more easily and live longer in dwarfs with shallow dark matter density profiles on extended orbits.
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Nelson, A. H., and P. R. Williams. "Numerical Simulation of the Dwarf Companions of Giant Galaxies." Proceedings of the International Astronomical Union 3, S244 (June 2007): 226–30. http://dx.doi.org/10.1017/s1743921307014020.
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AbstractWe report simulations of the formation of a giant disc galaxy from cosmological initial conditions. Two sets of initial conditions are used, initially smooth density for both gas and stars, representing the Warm dark Matter scenario, and an initially fluctuating density representing the standard spectrum for the Cold dark Matter scenario. For the WDM initial conditions, the galaxy has a population of long lived dwarf satellites at z = 0, with orbits close to a plane coincident with that of the giant galaxy disc. The detailed properties of these dwarfs mimic closely the observed properties of Local Group dwarfs with respect to mass, and kinematics. However they do not have individual dark matter halos, but orbit in the nearly spherical dark matter halo of the giant galaxy. The reason for this is that the initial population of dwarf dark matter haloes, which form during the initial collapse phase, all merge into the halo of the giant galaxy within a few to several Gyears, while the long lived dwarfs form as a secondary population by gravitational collapse of high angular momentum gas in the outer reaches of the giants proto-galactic disc. Due to their late formation and their more distant orbits, they survive until the present epoch as individual dwarf galaxies at radii 20-50kpc from the giants centre. For CDM initial conditions there are many more dwarf satellites at z = 0, some of which form early on as gas condensations in DM sub-halos, and survive with these individual DM halos till z = 0 due to their being sufficiently well bound to avoid merging with the main galaxy. However even in this case some second generation satellites form as initially gas only objects, just as for the smooth initial conditions of WDM.
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Hammer, Francois, Jianling Wang, Marcel S. Pawlowski, Yanbin Yang, Piercarlo Bonifacio, Hefan Li, Carine Babusiaux, and Frederic Arenou. "Gaia EDR3 Proper Motions of Milky Way Dwarfs. II Velocities, Total Energy, and Angular Momentum." Astrophysical Journal 922, no. 2 (November 24, 2021): 93. http://dx.doi.org/10.3847/1538-4357/ac27a8.
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Abstract Here we show that precise Gaia EDR3 proper motions have provided robust estimates of 3D velocities, angular momentum, and total energy for 40 Milky Way dwarfs. The results are statistically robust and are independent of the Milky Way mass profile. Dwarfs do not behave like long-lived satellites of the Milky Way because of their excessively large velocities, angular momenta, and total energies. Comparing them to other MW halo populations, we find that many are at first passage, ≤2 Gyr ago, i.e., more recent than the passage of Sagittarius, ∼4–5 Gyr ago. We suggest that this is in agreement with the stellar populations of all dwarfs, for which we find that a small fraction of young stars cannot be excluded. We also find that dwarf radial velocities contribute too little to their kinetic energy when compared to satellite systems with motions only regulated by gravity, and some other mechanism must be at work such as ram pressure. The latter may have preferentially reduced radial velocities when dwarf progenitors entered the halo until they lost their gas. It could also explain why most dwarfs lie near their pericenter. We also discover a novel large-scale structure perpendicular to the Milky Way disk, which is made by 20% of dwarfs orbiting or counter-orbiting with the Sagittarius dwarf.
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Garrison-Kimmel, Shea, Philip F. Hopkins, Andrew Wetzel, James S. Bullock, Michael Boylan-Kolchin, Dušan Kereš, Claude-André Faucher-Giguère, et al. "The Local Group on FIRE: dwarf galaxy populations across a suite of hydrodynamic simulations." Monthly Notices of the Royal Astronomical Society 487, no. 1 (May 16, 2019): 1380–99. http://dx.doi.org/10.1093/mnras/stz1317.
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Abstract We present a new set of high-resolution hydrodynamic cosmological zoom-in simulations that apply the Feedback In Realistic Environments physics to both Local Group (LG)-like and isolated Milky Way (MW)-like volumes (10 host systems in total with a baryonic particle mass ${\simeq } 3500\!-\!7000\,{\rm M}_\odot$). We study the stellar mass functions, circular velocity or mass profiles, and velocity dispersions of the dwarf galaxy populations. The simulations reproduce the stellar mass function and central densities of MW satellite dwarfs for $M_\ast \ge 10^{5.5}\,{\rm M}_\odot$ and predict the existence of ∼3 unidentified galaxies with $M_\ast \sim 10^5\,{\rm M}_\odot$ within 300 kpc of the MW. Overall, we find no evidence for the classical missing satellites or too-big-to-fail (TBTF) problems for satellite galaxies in our sample. Among the satellites, TBTF is resolved primarily by subhalo disruption and overall mass-loss; central density profiles of subhaloes are of secondary importance. For non-satellite galaxies, our LG-like simulations predict as many as ∼10 as-of-yet unseen galaxies at distances $0.3\!-\!1\, \mathrm{Mpc}$ from both hosts, with $M_\ast \simeq 10^{5-6}\,{\rm M}_\odot$ (in haloes with Vmax ∼ 20 km s−1), albeit with large halo-to-halo variance. None of our simulations produces a compact, baryon-dominated, high-density dwarf elliptical-type galaxy (with Vcirc ≳ 35 km s−1 at $r\lt 1\,$ kpc), of which six may appear in the LG (but none in the MW). It may therefore remain a challenge to reproduce the full diversity of the dwarf population, including both the highest and lowest density systems.
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Jerjen, Helmut. "Dwarf Cosmology with the Stromlo Missing Satellites Survey." Advances in Astronomy 2010 (2010): 1–9. http://dx.doi.org/10.1155/2010/434390.
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The standard Lambda Cold Dark Matter model is considered to be a triumph of theoretical astrophysics but observations of the Milky Way and its system of satellite galaxies irresistibly signal that theory is incomplete on galactic and subgalactic scales. The Stromlo Missing Satellites (SMS) Survey is a critical endeavor to investigate at what level predictions of CDM cosmology are consistent with the observed matter distribution in the Milky Way halo. It will be the deepest, most extended search for optically elusive satellite galaxies to date, covering 20 000 square degrees of sky. The international SMS Survey collaboration will exploit 150 TB of CCD images in six filters acquired by the new SkyMapper telescope of the Australian National University over the next five years, expecting on completion photometric limits 0.5–1.0 mag fainter than the Sloan Digital Sky Survey. The primary objective of the program is to characterise the baryonic and dark matter components of a complete sample of MW satellites in the Southern hemisphere to provide stringent observational constraints for improving our understanding of how the Milky Way formed and what physical processes governed galaxy formation and evolution in general.
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Criswell, Alexander, and Curtis Struck. "Effects of coplanar satellite bands on galactic disc evolution." Monthly Notices of the Royal Astronomical Society 487, no. 2 (June 3, 2019): 2969–75. http://dx.doi.org/10.1093/mnras/stz1520.
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ABSTRACT Small dwarf companions have been long thought to have minimal influence on their host galaxy’s evolution without undergoing direct impacts to the host’s disc. However, in light of recent discoveries of coplanar, corotating satellite structures around the Milky Way, Andromeda, and Centaurus A, we use an N-body/test particle simulation to show that low-mass dwarf satellites within such structures are able to exert significant influence on their host’s disc, driving spiral waves and inducing stellar scattering. This is accomplished through quasi-periodic alignments of multiple small satellites within the structure that emulate the gravitational influence of a single, larger satellite such as Sagittarius Dwarf or the Large Magellanic Cloud. We find that the coplanar, corotational nature of such structures allows for repeated alignments on short enough time-scales to overcome damping within the disc, and in a consistent enough fashion to continually drive spiral waves over the course of 2 Gyr of simulation time. The spirals driven by this phenomenon tend to be flocculent and many armed due to the irregular intervals over which alignments occur. We additionally find that while the aligned satellites are able to induce noticeable thickening of the disc, their ability to drive surface density profile evolution is secondary to other effects.
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Müller, Oliver. "A whirling plane of satellite galaxies around Centaurus A challenges CDM cosmology." Proceedings of the International Astronomical Union 14, S344 (August 2018): 473–76. http://dx.doi.org/10.1017/s1743921318005781.
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AbstractThe phase-space correlation of dwarf galaxies around the Milky Way and the Andromeda galaxy pose a serious challenge to our understanding of structure formation. Recently, another planar structure was discovered around Cen A, the major galaxy of the Centaurus group. We have surveyed this galaxy group for new dwarf galaxies and presented the discovery of 57 new dwarf member candidates. Furthermore, we have studied the kinematics of previously known dwarfs and again found a kinematic coherence in their movement, similar to the Local Group satellites. In CDM simulations, such an alignment appears in less than 0.5 percent.
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Genina, Anna, Carlos S. Frenk, Alejandro Benítez-Llambay, Shaun Cole, Julio F. Navarro, Kyle A. Oman, and Azadeh Fattahi. "The distinct stellar metallicity populations of simulated Local Group dwarfs." Monthly Notices of the Royal Astronomical Society 488, no. 2 (July 8, 2019): 2312–31. http://dx.doi.org/10.1093/mnras/stz1852.
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ABSTRACT A number of Local Group dwarf galaxies are known to have two spatially segregated stellar metallicity populations, a centrally concentrated metal-rich population, and a more extended metal-poor population. In this work we discuss mechanisms that lead to the formation of two spatially segregated metallicity populations. Using a set of high-resolution hydrodynamical simulations of Local Group-like environments, we select a sample of satellite and field galaxies, spanning the stellar mass range 106–109 M⊙, that exhibit bimodality in their metallicity distributions. Among those, we identify a subsample with a strong spatial segregation in the two populations. We find three distinct mechanisms for their formation. In field dwarfs and in a small fraction of satellites, a merger causes the metal-poor stars to migrate to larger radii and encourages the available gas to sink to the centre of the dwarf. Most of the gas is subsequently blown out of the halo through star formation feedback, but the remaining gas is consumed in the formation of a metal-rich population. In the exclusive case of satellites that have retained some of their gas at infall, it is the compression of this gas by ram pressure near pericentre that triggers the formation of metal-rich stars, whilst simultaneously preventing star formation at larger radii through stripping. Additionally, in a small number of field and satellite dwarfs, interactions with gaseous filaments and other galaxies can result in the formation of a metal-rich population. Regardless of the formation mechanism, a history of mergers typically enhances the spatial segregation.
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Deason, Alis J., Sownak Bose, Azadeh Fattahi, Nicola C. Amorisco, Wojciech Hellwing, and Carlos S. Frenk. "Dwarf stellar haloes: a powerful probe of small-scale galaxy formation and the nature of dark matter." Monthly Notices of the Royal Astronomical Society 511, no. 3 (December 3, 2021): 4044–59. http://dx.doi.org/10.1093/mnras/stab3524.
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ABSTRACT We use N-body cosmological simulations and empirical galaxy models to study the merger history of dwarf-mass galaxies (with $M_{\rm halo}\sim 10^{10}\, \mathrm{M}_\odot$). Our input galaxy models describe the stellar mass–halo mass relation, and the galaxy occupation fraction. The number of major and minor mergers depends on the type of dark matter; in particular, minor mergers are greatly suppressed in warm dark matter models. In addition, the number of mergers that bring in stars is strongly dependent on the galaxy occupation model. For example, minor mergers are negligible for stellar halo growth in models with a high mass threshold for galaxy formation (i.e. $10^{9.3}\, \mathrm{M}_\odot$ at z = 0). Moreover, this threshold for galaxy formation can also determine the relative difference (if any) between the stellar haloes of satellite and field dwarfs. Using isolated simulations of dwarf–dwarf mergers, we show that the relative frequency of major and minor mergers predict very different stellar haloes: Typically, ‘intermediate’ dark matter merger ratios (∼1:5) maximize the growth of distant stellar haloes. We discuss the observability of dwarf stellar haloes and find that the surface brightness of these features are incredibly faint. However, when several dwarfs are stacked together, models that form particularly rich stellar haloes could be detectable. Finally, we show that stellar streams in the Galactic halo overlapping in phase space with known dwarf satellites are likely remnants of their stripped stellar haloes. The mere existence of dwarf stellar haloes can already put constraints on some small-scale models, and thus observational probes should be a high priority.
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Carlberg, R. G., M. Sullivan, and D. Le Borgne. "DWARF GALAXY CLUSTERING AND MISSING SATELLITES." Astrophysical Journal 694, no. 2 (March 23, 2009): 1131–38. http://dx.doi.org/10.1088/0004-637x/694/2/1131.
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Sales, Laura V., Wenting Wang, Simon D. M. White, and Julio F. Navarro. "Satellites and haloes of dwarf galaxies." Monthly Notices of the Royal Astronomical Society 428, no. 1 (October 23, 2012): 573–78. http://dx.doi.org/10.1093/mnras/sts054.
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Hausammann, Loic, Yves Revaz, and Pascale Jablonka. "Satellite dwarf galaxies: stripped but not quenched." Astronomy & Astrophysics 624 (April 2019): A11. http://dx.doi.org/10.1051/0004-6361/201834871.
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In the Local Group, quenched gas-poor dwarfs galaxies are most often found close to the Milky Way and Andromeda, while star forming gas-rich ones are located at greater distances. This so-called morphology-density relation is often interpreted as the consequence of the ram pressure stripping of the satellites during their interaction with the Milky Way hot halo gas. While this process has been often investigated, self-consistent high resolution simulations were still missing. In this study, we have analysed the impact of both the ram pressure and tidal forces induced by a host galaxy on dwarf models as realistic as possible emerging from cosmological simulations. These models were re-simulated using both a wind tunnel and a moving box technique. The secular mass growth of the central host galaxy, as well as the gas density and temperature profiles of its hot halo have been taken into account. We show that while ram pressure is very efficient at stripping the hot and diffuse gas of the dwarf galaxies, it can remove their cold gas (T < 103 K) only in very specific conditions. Depending on the infall time of the satellites relatively to the build-up stage of the massive host, star formation can thus be prolonged instead of being quenched. This is the direct consequence of the clumpy nature of the cold gas and the thermal pressure the hot gas exerts onto it. We discuss the possibility that the variety in satellite populations among Milky Way-like galaxies reflects their accretion histories.
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Greene, Jenny E., Shany Danieli, Scott Carlsten, Rachael Beaton, Fangzhou Jiang, and Jiaxuan Li. "ELVES. III. Environmental Quenching by Milky Way–mass Hosts." Astrophysical Journal 949, no. 2 (June 1, 2023): 94. http://dx.doi.org/10.3847/1538-4357/acc58c.
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Abstract Isolated dwarf galaxies usually exhibit robust star formation but satellite dwarf galaxies are often devoid of young stars, even in Milky Way–mass groups. Dwarf galaxies thus offer an important laboratory of the environmental processes that cease star formation. We explore the balance of quiescent and star-forming galaxies (quenched fractions) for a sample of ∼400 satellite galaxies around 30 Local Volume hosts from the Exploration of Local VolumE Satellites (ELVES) Survey. We present quenched fractions as a function of satellite stellar mass, projected radius, and host halo mass, to conclude that overall, the quenched fractions are similar to the Milky Way, dropping below 50% at satellite M * ≈ 108 M ⊙. We may see hints that quenching is less efficient at larger radii. Through comparison with the semianalytic modeling code SatGen, we are also able to infer average quenching times as a function of satellite mass in host halo-mass bins. There is a gradual increase in quenching time with satellite stellar mass rather than the abrupt change from rapid to slow quenching that has been inferred for the Milky Way. We also generally infer longer average quenching times than recent hydrodynamical simulations. Our results are consistent with models that suggest a wide range of quenching times are possible via ram pressure stripping, depending on the clumpiness of the circumgalactic medium, the orbits of the satellites, and the degree of earlier preprocessing.
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Karachentsev, I. D., L. N. Makarova, G. S. Anand, and R. B. Tully. "Around the Spindle Galaxy: The Dark Halo Mass of NGC 3115." Astronomical Journal 163, no. 5 (April 26, 2022): 234. http://dx.doi.org/10.3847/1538-3881/ac5ab5.
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Abstract We report observations of five dwarf galaxies in the vicinity of the luminous S0 galaxy NGC 3115 performed with the Advanced Camera for Surveys on the Hubble Space Telescope. Their distances determined via the Tip of the Red Giant Branch are: 10.05 Mpc (UGCA 193), 9.95 Mpc (KKSG 17), 10.13 Mpc (2MASX-J0957-0915), 10.42 Mpc (2dFGRS-TGN218Z179), and 11.01 Mpc (KKSG 19). With their typical distance error of about 0.75 Mpc all the five dwarfs are consistent to be true satellites of the host galaxy NGC 3115 (10.2 ± 0.2 Mpc). Using the DESI Legacy Imaging Surveys we also found five new probable dwarf satellites of NGC 3115, as well as four new probable members of the neighboring group around NGC 3521 situated 3 Mpc away from the NGC 3115 group. Based on the radial velocities and projected separations of 10 dwarf companions, we derived the total (orbital) mass of NGC 3115 to be (4.89 ± 1.48) 1012 M ⊙. The ratio of the total mass-to-K luminosity of NGC 3115 is (50 ± 15) M ⊙/L ⊙, which is typical for the early-type luminous galaxies.
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Karachentsev, I. D., L. N. Makarova, G. S. Anand, and R. B. Tully. "Around the Spindle Galaxy: The Dark Halo Mass of NGC 3115." Astronomical Journal 163, no. 5 (April 26, 2022): 234. http://dx.doi.org/10.3847/1538-3881/ac5ab5.
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Abstract We report observations of five dwarf galaxies in the vicinity of the luminous S0 galaxy NGC 3115 performed with the Advanced Camera for Surveys on the Hubble Space Telescope. Their distances determined via the Tip of the Red Giant Branch are: 10.05 Mpc (UGCA 193), 9.95 Mpc (KKSG 17), 10.13 Mpc (2MASX-J0957-0915), 10.42 Mpc (2dFGRS-TGN218Z179), and 11.01 Mpc (KKSG 19). With their typical distance error of about 0.75 Mpc all the five dwarfs are consistent to be true satellites of the host galaxy NGC 3115 (10.2 ± 0.2 Mpc). Using the DESI Legacy Imaging Surveys we also found five new probable dwarf satellites of NGC 3115, as well as four new probable members of the neighboring group around NGC 3521 situated 3 Mpc away from the NGC 3115 group. Based on the radial velocities and projected separations of 10 dwarf companions, we derived the total (orbital) mass of NGC 3115 to be (4.89 ± 1.48) 1012 M ⊙. The ratio of the total mass-to-K luminosity of NGC 3115 is (50 ± 15) M ⊙/L ⊙, which is typical for the early-type luminous galaxies.
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Bílek, Michal, Ingo Thies, Pavel Kroupa, and Benoit Famaey. "Are Disks of Satellites Comprised of Tidal Dwarf Galaxies?" Galaxies 9, no. 4 (November 10, 2021): 100. http://dx.doi.org/10.3390/galaxies9040100.
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It was found that satellites of nearby galaxies can form flattened co-rotating structures called disks of satellites or planes of satellites. Their existence is not expected by the current galaxy formation simulations in the standard dark matter-based cosmology. On the contrary, modified gravity offers a promising alternative: the objects in the disks of satellites are tidal dwarf galaxies, that is, small galaxies that form from tidal tails of interacting galaxies. After introducing the topic, we review here our work on simulating the formation of the disks of satellites of the Milky Way and Andromeda galaxies. The initial conditions of the simulation were tuned to reproduce the observed positions, velocities and disk orientations of the galaxies. The simulation showed that the galaxies had a close flyby 6.8 Gyr ago. One of the tidal tails produced by the Milky Way was captured by Andromeda. It formed a cloud of particles resembling the disk of satellites at Andromeda by its size, orientation, rotation and mass. A hint of a disk of satellites was formed at the Milky Way too. In addition, the encounter induced a warp in the disk of the simulated Milky Way that resembles the real warp by its magnitude and orientation. We present here, for the first time, the proper motions of the members of the disk of satellites of Andromeda predicted by our simulation. Finally, we point out some of the remaining open questions which this hypothesis, for the formation of disks of satellites, brings up.
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Jahn, Ethan D., Laura V. Sales, Andrew Wetzel, Michael Boylan-Kolchin, T. K. Chan, Kareem El-Badry, Alexandres Lazar, and James S. Bullock. "Dark and luminous satellites of LMC-mass galaxies in the FIRE simulations." Monthly Notices of the Royal Astronomical Society 489, no. 4 (September 5, 2019): 5348–64. http://dx.doi.org/10.1093/mnras/stz2457.
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ABSTRACT Within lambda cold dark matter ($\Lambda$CDM), dwarf galaxies like the Large Magellanic Cloud (LMC) are expected to host numerous dark matter subhaloes, several of which should host faint dwarf companions. Recent Gaia proper motions confirm new members of the LMC system in addition to the previously known SMC, including two classical dwarf galaxies ($M_\ast$$\gt 10^5$ M$_{\odot }$; Carina and Fornax) as well as several ultrafaint dwarfs (Car2, Car3, Hor1, and Hyd1). We use the Feedback In Realistic Environments (FIRE) simulations to study the dark and luminous (down to ultrafaint masses, $M_\ast$$\sim$6$\times 10^ {3}$ M$_{\odot }$) substructure population of isolated LMC-mass hosts ($M_{\text{200m}}$ = 1–3$\times 10^ {11}$ M$_{\odot }$) and place the Gaia + DES results in a cosmological context. By comparing number counts of subhaloes in simulations with and without baryons, we find that, within 0.2 $r_{\text{200m}}$, LMC-mass hosts deplete $\sim$30 per cent of their substructure, significantly lower than the $\sim$70 per cent of substructure depleted by Milky Way (MW) mass hosts. For our highest resolution runs ($m_\text{bary}$ = 880 M$_{\odot }$), $\sim 5\!-\!10$ subhaloes form galaxies with $M_\ast$$\ge 10^{4}$ M$_{\odot }$ , in agreement with the seven observationally inferred pre-infall LMC companions. However, we find steeper simulated luminosity functions than observed, hinting at observation incompleteness at the faint end. The predicted DM content for classical satellites in FIRE agrees with observed estimates for Carina and Fornax, supporting the case for an LMC association. We predict that tidal stripping within the LMC potential lowers the inner dark matter density of ultrafaint companions of the LMC. Thus, in addition to their orbital consistency, the low densities of dwarfs Car2, Hyd1, and Hyd2 reinforce their likelihood of Magellanic association.
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Nashimoto, Masashi, Masayuki Tanaka, Masashi Chiba, Kohei Hayashi, Yutaka Komiyama, and Takashi Okamoto. "The Missing Satellite Problem outside of the Local Group. II. Statistical Properties of Satellites of Milky Way–like Galaxies." Astrophysical Journal 936, no. 1 (August 29, 2022): 38. http://dx.doi.org/10.3847/1538-4357/ac83a4.
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Abstract We present a new observation of satellite galaxies around seven Milky Way (MW)–like galaxies located outside of the Local Group (LG) using Subaru/Hyper Suprime-Cam imaging data to statistically address the missing satellite problem. We select satellite galaxy candidates using magnitude, surface brightness, Sérsic index, axial ratio, FWHM, and surface brightness fluctuation cuts, followed by visual screening of false positives such as optical ghosts of bright stars. We identify 51 secure dwarf satellite galaxies within the virial radius of nine host galaxies, two of which are drawn from the pilot observation presented in Paper I. We find that the average luminosity function of the satellite galaxies is consistent with that of the MW satellites, although the luminosity function of each host galaxy varies significantly. We observe an indication that more massive hosts tend to have a larger number of satellites. Physical properties of the satellites such as the size–luminosity relation are also consistent with the MW satellites. However, the spatial distribution is different; we find that the satellite galaxies outside of the LG show no sign of concentration or alignment, while that of the MW satellites is more concentrated around the host and exhibits a significant alignment. As we focus on relatively massive satellites with M V < −10, we do not expect that the observational incompleteness can be responsible here. This trend might represent a peculiarity of the MW satellites, and further work is needed to understand its origin.
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Metz, Manuel, Pavel Kroupa, and Helmut Jerjen. "Discs of satellites: the new dwarf spheroidals." Monthly Notices of the Royal Astronomical Society 394, no. 4 (April 21, 2009): 2223–28. http://dx.doi.org/10.1111/j.1365-2966.2009.14489.x.
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Kravtsov, Andrey. "Dark Matter Substructure and Dwarf Galactic Satellites." Advances in Astronomy 2010 (2010): 1–21. http://dx.doi.org/10.1155/2010/281913.
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A decade ago cosmological simulations of increasingly higher resolution were used to demonstrate that virialized regions of Cold Dark Matter (CDM) halos are filled with a multitude of dense, gravitationally bound clumps. These dark mattersubhalosare central regions of halos that survived strong gravitational tidal forces and dynamical friction during the hierarchical sequence of merging and accretion via which the CDM halos form. Comparisons with observations revealed that there is a glaring discrepancy between abundance of subhalos and luminous satellites of the Milky Way and Andromeda as a function of their circular velocity or bound mass within a fixed aperture. This large discrepancy, which became known as the “substructure” or the “missing satellites” problem, begs for an explanation. In this paper, the author reviews the progress made during the last several years both in quantifying the problem and in exploring possible scenarios in which it could be accommodated and explained in the context of galaxy formation in the framework of the CDM paradigm of structure formation. In particular, he shows that the observed luminosity function, radial distribution, and the remarkable similarity of the inner density profiles of luminous satellites can be understood within hierarchical CDM framework using a simple model in which efficiency of star formation monotonically decreases with decreasing virial mass satellites had before their accretionwithout any actual sharp galaxy formation threshold.
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Richter, G., J. Vennik, P. Böhm, and M. Capaccioli. "The fate of dwarf satellite galaxies (or: Can we observe soft merging?)." International Astronomical Union Colloquium 174 (2000): 121–25. http://dx.doi.org/10.1017/s0252921100054865.
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AbstractDwarf satellite galaxies and globular clusters bound to luminous (in particular early type) galaxies, can be steered by interactions to orbits penetrating deep into the potential of their parent galaxy, where the outer stars are eroded and the dwarf satellite is completely destroyed in a relatively short time, resulting in very faint disturbances (soft merging) in the form of faint rings in the parent galaxy.With special image processing methods we have found faint structures in E and SO galaxies, which for many reasons (mass, statistics, etc.) can be interpreted as observational evidence of this type of soft merging. This debris of dwarf satellites can provide a considerable part of the mass of the parent galaxy.
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Fattahi, Azadeh, Alis J. Deason, Carlos S. Frenk, Christine M. Simpson, Facundo A. Gómez, Robert J. J. Grand, Antonela Monachesi, Federico Marinacci, and Rüdiger Pakmor. "A tale of two populations: surviving and destroyed dwarf galaxies and the build-up of the Milky Way’s stellar halo." Monthly Notices of the Royal Astronomical Society 497, no. 4 (August 6, 2020): 4459–71. http://dx.doi.org/10.1093/mnras/staa2221.
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ABSTRACT We use magnetohydrodynamical simulations of Milky Way-mass haloes from the Auriga project to investigate the properties of surviving and destroyed dwarf galaxies that are accreted by these haloes over cosmic time. We show that the combined luminosity function of surviving and destroyed dwarfs at infall is similar in the various Auriga haloes, and is dominated by the destroyed dwarfs. There is, however, a strong dependence on infall time: destroyed dwarfs typically have early infall times of less than 6 Gyr (since the big bang), whereas the majority of dwarfs accreted after 10 Gyr have survived to the present day. Because of their late infall, the surviving satellites have higher metallicities at infall than their destroyed counterparts of similar mass at infall; the difference is even more pronounced for the present-day metallicities of satellites, many of which continue to form stars after infall, in particular for $M_{\rm star}\gt 10^7 \, {\rm M}_\odot$. In agreement with previous work, we find that a small number of relatively massive destroyed dwarf galaxies dominate the mass of stellar haloes. However, there is a significant radial dependence: while 90 per cent of the mass in the inner regions (${\lt}20\,$ kpc) is contributed, on average, by only three massive progenitors, the outer regions (${\gt}100\,$ kpc) typically have ∼8 main progenitors of relatively lower mass. Finally, we show that a few massive progenitors dominate the metallicity distribution of accreted stars, even at the metal-poor end. Contrary to common assumptions in the literature, stars from dwarf galaxies of mass $M_{\rm star}\lt 10^7 \, {\rm M}_\odot$ make up less than 10 per cent of the accreted, metal poor stars ([Fe/H] ${\lt}-3$) in the inner $50\,$ kpc.
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Salvadori, Stefania, Andrea Ferrara, and Raffaella Schneider. "Dwarf spheroidal evolution: global view." Proceedings of the International Astronomical Union 4, S255 (June 2008): 341–45. http://dx.doi.org/10.1017/s1743921308025040.
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AbstractWe propose a cosmological approach to investigate the formation and evolution of dwarf spheroidal galaxies, satellites of the Milky Way, which allows us to follow self-consistently the dSphs and MW formation, matching simultaneously most of their observed properties.
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Doliva-Dolinsky, Amandine, Nicolas F. Martin, Zhen Yuan, Alessandro Savino, Daniel R. Weisz, Annette M. N. Ferguson, Rodrigo A. Ibata, et al. "The PAndAS View of the Andromeda Satellite System. IV. Global Properties." Astrophysical Journal 952, no. 1 (July 1, 2023): 72. http://dx.doi.org/10.3847/1538-4357/acdcf6.
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Abstract We build a statistical framework to infer the global properties of the satellite system of the Andromeda galaxy (M31) from the properties of individual dwarf galaxies located in the Pan-Andromeda Archaelogical Survey (PAndAS) and the previously determined completeness of the survey. Using forward modeling, we infer the slope of the luminosity function of the satellite system, the slope of its spatial density distribution, and the size–luminosity relation followed by the dwarf galaxies. We find that the slope of the luminosity function is β = −1.5 ± 0.1. Combined with the spatial density profile, it implies that, when accounting for survey incompleteness, M31 hosts 92 − 26 + 19 dwarf galaxies with M V < −5.5 and a sky-projected distance from M31 between 30 and 300 kpc. We conclude that many faint or distant dwarf galaxies remain to be discovered around Andromeda, especially outside the PAndAS footprint. Finally, we use our model to test if the higher number of satellites situated in the hemisphere facing the Milky Way could be explained simply by the detection limits of dwarf galaxy searches. We rule this out at >99.9% confidence and conclude that this anisotropy is an intrinsic feature of the M31 satellite system. The statistical framework we present here is a powerful tool to robustly constrain the properties of a satellite system and compare those across hosts, especially considering the upcoming start of the Euclid or Rubin large photometric surveys that are expected to uncover a large number of dwarf galaxies in the Local Volume.
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Fiorentino, Giuliana. "RR Lyrae to understand the Galactic halo." Proceedings of the International Astronomical Union 11, S317 (August 2015): 77–82. http://dx.doi.org/10.1017/s1743921315009710.
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AbstractWe present recent results obtained using old variable RR Lyrae stars on the Galactic halo structure and its connection with nearby dwarf galaxies. We compare the period and period-amplitude distributions for a sizeable sample of fundamental mode RR Lyrae stars (RRab) in dwarf spheroidals (~1300 stars) with those in the Galactic halo (~16'000 stars) and globular clusters (~1000 stars). RRab in dwarfs –as observed today– do not appear to follow the pulsation properties shown by those in the Galactic halo, nor they have the same properties as RRab in globulars. Thanks to the OGLE experiment we extended our comparison to massive metal–rich satellites like the dwarf irregular Large Magellanic Cloud (LMC) and the Sagittarius (Sgr) dwarf spheroidal. These massive and more metal–rich stellar systems likely have contributed to the Galactic halo formation more than classical dwarf spheroidals.Finally, exploiting the intrinsic nature of RR Lyrae as distance indicators we were able to study the period and period amplitude distributions of RRab within the Halo. It turned out that the inner and the outer Halo do show a difference that may suggest a different formation scenario (in situ vs accreted).
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Sand, David J., Burçin Mutlu-Pakdil, Michael G. Jones, Ananthan Karunakaran, Feige Wang, Jinyi Yang, Anirudh Chiti, Paul Bennet, Denija Crnojević, and Kristine Spekkens. "Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D ≈ 1.4 Mpc*." Astrophysical Journal Letters 935, no. 1 (August 1, 2022): L17. http://dx.doi.org/10.3847/2041-8213/ac85ee.
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Abstract We report the discovery of Tucana B, an isolated ultra-faint dwarf galaxy at a distance of D = 1.4 Mpc. Tucana B was found during a search for ultra-faint satellite companions to the known dwarfs in the outskirts of the Local Group, although its sky position and distance indicate the nearest galaxy to be ∼500 kpc distant. Deep ground-based imaging resolves Tucana B into stars, and it displays a sparse red giant branch consistent with an old, metal-poor stellar population analogous to that seen in the ultra-faint dwarf galaxies of the Milky Way, albeit at fainter apparent magnitudes. Tucana B has a half-light radius of 80 ± 40 pc and an absolute magnitude of M V = − 6.9 − 0.6 + 0.5 mag ( L V = ( 5 − 2 + 4 ) × 10 4 L ⊙), which is again comparable to the Milky Way’s ultra-faint satellites. There is no evidence for a population of young stars, either in the optical color–magnitude diagram or in GALEX archival ultraviolet imaging, with the GALEX data indicating log ( SFR NUV / M ⊙ yr − 1 ) < − 5.4 for star formation on ≲100 Myr timescales. Given its isolation and physical properties, Tucana B may be a definitive example of an ultra-faint dwarf that has been quenched by reionization, providing strong confirmation of a key driver of galaxy formation and evolution at the lowest mass scales. It also signals a new era of ultra-faint dwarf galaxy discovery at the extreme edges of the Local Group.
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Grebel, Eva K., Tsafrir Kolatt, and Wolfgang Brandner. "Orbits versus Star Formation Histories: A Progress Report." Symposium - International Astronomical Union 192 (1999): 447–50. http://dx.doi.org/10.1017/s0074180900204488.
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Milky Way dwarf companions and satellites of distant spirals seem to show a preference for polar orbits. We suggest that five out of six M31 dwarf spheroidal companions as well as two dwarf irregulars may also be located near a polar plane.We briefly discuss preliminary results from a statistical approach to study correlations between star formation histories and orbits of Local Group dwarf galaxies, such as a possible correlation between star formation episodes and galaxy separations.