Articles de revues : « Fraction massique »

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Ousmane, Moctar, Dianda Boureima, Thierry Sikoudouin Maurice K.Y, Boureima Kabore, B. Magloire Pakouzou, Salifou Ouedraogo, Amadou Konfe et al. « ETUDE DES PERFORMANCES THERMIQUES DUN SECHOIR SOLAIRE ». International Journal of Advanced Research 12, n^o 01 (31 janvier 2024) : 1062–72. http://dx.doi.org/10.21474/ijar01/18224.

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Les populations ouest africaines produisent de grandes quantites de recoltes. Malheureusement faute de moyens de conservation, ces produits pourrissent. Cest pour cette raison que nous nous sommes interesses au sechage solaire des produits agro-alimentaires avec comme produit la banana douce. Lobjectif de cette publication est letude des performances thermiques dun sechoir solaire Ã absorbeur Ã ailettes. Les materiels utilises sont : un sechoir complet constitue de cinq claies, des tranches de banane douce, dune balance de precision et dun enregistreur automatique de temperatures. Levolution de la teneur en eau nous a montre que 65% de leau des rondelles est eliminee le 1er jour et 20% le 2eme jour. Les courbes simulees de sechage traduisent que la fraction massique de la vapeur deau dans lair augmente et celle du fruit diminue car lair shumidifie par absorption deau du produit. Enfin les performances thermiques du sechoir solaire sont estimees par la masse de banane sechee et lintroduction des ailettes a developpe un ecoulement turbulent.

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Davison, Thomas A., Mark A. Norris, Ryan Leaman, Harald Kuntschner, Alina Boecker et Glenn van de Ven. « Mapping accreted stars in early-type galaxies across the mass–size plane ». Monthly Notices of the Royal Astronomical Society 507, n^o 2 (19 août 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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Sharma, Ray S., Alyson M. Brooks, Michael Tremmel, Jillian Bellovary, Angelo Ricarte et Thomas R. Quinn. « A Hidden Population of Massive Black Holes in Simulated Dwarf Galaxies ». Astrophysical Journal 936, n^o 1 (1 septembre 2022) : 82. http://dx.doi.org/10.3847/1538-4357/ac8664.

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Abstract We explore the characteristics of actively accreting massive black holes (MBHs) within dwarf galaxies in the Romulus25 cosmological hydrodynamic simulation. We examine the MBH occupation fraction, X-ray active fractions, and active galactic nucleus (AGN) scaling relations within dwarf galaxies of stellar mass 108 M ⊙ < M star < 1010 M ⊙ out to redshift z = 2. In the local universe, the MBH occupation fraction is consistent with observed constraints, dropping below unity at M star < 3 × 1010 M ⊙, M 200 < 3 × 1011 M ⊙. Local dwarf AGN in Romulus25 follow observed scaling relations between AGN X-ray luminosity, stellar mass, and star formation rate, though they exhibit slightly higher active fractions and number densities than comparable X-ray observations. Since z = 2, the MBH occupation fraction has decreased, the population of dwarf AGN has become overall less luminous, and as a result the overall number density of dwarf AGN has diminished. We predict the existence of a large population of MBHs in the local universe with low X-ray luminosities and high contamination from X-ray binaries and the hot interstellar medium that are undetectable by current X-ray surveys. These hidden MBHs make up 76% of all MBHs in local dwarf galaxies and include many MBHs that are undermassive relative to their host galaxy’s stellar mass. Their detection relies on not only greater instrument sensitivity but also better modeling of X-ray contaminants or multiwavelength surveys. Our results indicate that dwarf AGN were substantially more active in the past, despite having low luminosity today, and that future deep X-ray surveys may uncover many hidden MBHs in dwarf galaxies out to at least z = 2.

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Schootemeijer, Abel, Danny J. Lennon, Miriam Garcia, Norbert Langer, Ben Hastings et Christoph Schürmann. « Massive stars in metal-poor dwarf galaxies are often extreme rotators ». Proceedings of the International Astronomical Union 18, S361 (mai 2022) : 63–69. http://dx.doi.org/10.1017/s1743921322002538.

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AbstractWe probe how common extremely rapid rotation is among massive stars in the early universe by measuring the OBe star fraction in nearby metal-poor dwarf galaxies. We apply a new method that uses broad-band photometry to measure the galaxy-wide OBe star fractions in the Magellanic Clouds and three more distant, more metal-poor dwarf galaxies. We find OBe star fractions of ∼20% in the Large Magallanic Cloud (0.5Zȯ), and ∼30% in the Small Magellanic Cloud (0.2Zȯ) as well as in the so-far unexplored metallicity range 0.1 Z/Zȯ < 0.2 occupied by the other three dwarf galaxies. Our results imply that extremely rapid rotation is common among massive stars in metal-poor environments such as the early universe.

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Contini, Emanuele, Seyoung Jeon, Jinsu Rhee, San Han et Sukyoung K. Yi. « The Intracluster Light and Its Link with the Dynamical State of the Host Group/Cluster : The Role of the Halo Concentration ». Astrophysical Journal 958, n^o 1 (1 novembre 2023) : 72. http://dx.doi.org/10.3847/1538-4357/acfd25.

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Abstract We investigate the role of halo concentration in the formation of intracluster light (ICL) in galaxy groups and clusters, as predicted by a state-of-the-art semianalytic model of galaxy formation, coupled with a set of high-resolution dark-matter-only simulations. The analysis focuses on how the fraction of ICL correlates with halo mass, concentration, and fraction of early-type galaxies (ETGs) in a large sample of groups and clusters with 13.0 ≤ log M halo ≤ 15.0 . The fraction of ICL follows a normal distribution, a consequence of the stochastic nature of the physical processes responsible for the formation of the diffuse light. The fractional budget of ICL depends on both halo mass (very weakly) until group scales, and concentration (remarkably). More interestingly, the ICL fraction is higher in more concentrated objects, a result of the stronger tidal forces acting in the innermost regions of the halos where the concentration is the quantity playing the most relevant role. Our model predictions do not show any dependence between the ICL and ETGs fractions, and so we instead suggest the concentration rather than the mass, as recently claimed, to be the main driver of the ICL formation. The diffuse light starts to form in groups via stellar stripping and mergers and later assembled in more-massive objects. However, the formation and assembly keep going on group/cluster scales at lower redshift through the same processes, mainly via stellar stripping in the vicinity of the central regions where tidal forces are stronger.

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Shenton, Robert G., René D. Oudmaijer et Stuart L. Lumsden. « Binarity in Massive Young Stellar Objects ». Proceedings of the International Astronomical Union 18, S361 (mai 2022) : 556–58. http://dx.doi.org/10.1017/s1743921322001909.

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AbstractMost massive stars (up to 100%) are thought to be in binary systems. The multiplicity of massive stars seems to be intrinsically linked to their formation and evolution, and so Massive Young Stellar Objects are key in observing this early stage of star formation. We have surveyed hundreds of MYSOs across the Galaxy from the RMS catalogue, using UKIDSS and VVV point source data. Preliminary results show binary fractions of 44±3% for the UKIDSS sample and 32±3% for the VVV sample. In addition we use the K-band magnitudes as a proxy for the companion mass, and find a significant fraction of the detected companions have estimated mass ratios greater than 0.5, which suggests a deviation from the capture formation scenario.

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Mukherjee, Sampath, Léon V. E. Koopmans, Crescenzo Tortora, Matthieu Schaller, R. Benton Metcalf, Joop Schaye et Georgios Vernardos. « SEAGLE – III : Towards resolving the mismatch in the dark-matter fraction in early-type galaxies between simulations and observations ». Monthly Notices of the Royal Astronomical Society 509, n^o 1 (20 octobre 2021) : 1245–51. http://dx.doi.org/10.1093/mnras/stab3014.

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ABSTRACT The central dark-matter fraction of galaxies is sensitive to feedback processes during galaxy formation. Strong gravitational lensing has been effective in the precise measurement of the dark-matter fraction inside massive early-type galaxies. Here, we compare the projected dark-matter fraction of early-type galaxies inferred from the SLACS (Sloan Lens ACS Survey) strong-lens survey with those obtained from the Evolution and Assembly of GaLaxies and their Environment (EAGLE), Illustris, and IllustrisTNG hydrodynamical simulations. Previous comparisons with some simulations revealed a large discrepancy, with considerably higher inferred dark-matter fractions – by factors of ≈2–3 – inside half of the effective radius in observed strong-lens galaxies as compared to simulated galaxies. Here, we report good agreement between EAGLE and SLACS for the dark-matter fractions inside both half of the effective radius and the effective radius as a function of the galaxy’s stellar mass, effective radius, and total mass-density slope. However, for IllustrisTNG and Illustris, the dark-matter fractions are lower than observed. This work consistently assumes a Chabrier initial mass function (IMF), which suggests that a different IMF (although not excluded) is not necessary to resolve this mismatch. The differences in the stellar feedback model between EAGLE and Illustris and IllustrisTNG are likely the dominant cause of the difference in their dark-matter fraction and density slope.

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Grylls, Philip J., F. Shankar et C. J. Conselice. « The significant effects of stellar mass estimation on galaxy pair fractions. » Monthly Notices of the Royal Astronomical Society 499, n^o 2 (30 septembre 2020) : 2265–75. http://dx.doi.org/10.1093/mnras/staa2966.

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ABSTRACT Theoretical models suggest that galaxy mergers may have profoundly shaped galaxy morphologies through cosmic time. However, observational estimates of galaxy pair fractions, and implied galaxy mergers, still do not converge, suggesting different numbers and redshift evolution. This paper explores the connection between stellar mass estimation and the pair fraction of galaxies using $\rm {\small STEEL}$, the Statistical sEmi-Emprical modeL, in which galaxies are mapped on to host dark matter haloes via a stellar mass–halo mass (SMHM) relation. As haloes of different mass are predicted to undergo, on average, different degrees of mergers, we expect that galaxy merger rates at fixed stellar mass will also vary depending on the shape of the input SMHM relation. Using a variety of input SMHM relations, also including one that matches the outputs of the Illustris TNG simulation, we thoroughly explore how systematic variations in the stellar mass functions propagate on to the normalization and redshift dependence of the galaxy pair fraction. We find that (i) stellar mass functions characterized by larger number densities of massive galaxies and thus a steeper SMHM relation, result in a substantial reduction of the pair fractions of massive galaxies; (ii) a time-varying SMHM relation produces galaxy pair fractions that can have varied redshift evolutions. We argue that in a hierarchical, dark matter dominated Universe, stellar mass estimates are a considerable cause of bias that must be accounted for when comparing pair fractions from different data sets or from theoretical models developed independently of the fitted survey data.

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Yoo, Taehwa, Taysun Kimm et Joakim Rosdahl. « On the origin of low escape fractions of ionizing radiation from massive star-forming galaxies at high redshift ». Monthly Notices of the Royal Astronomical Society 499, n^o 4 (16 octobre 2020) : 5175–93. http://dx.doi.org/10.1093/mnras/staa3187.

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ABSTRACT The physical origin of low escape fractions of ionizing radiation derived from massive star-forming galaxies at z ∼ 3–4 is not well understood. We perform idealized disc galaxy simulations to understand how galactic properties such as metallicity and gas mass affect the escape of Lyman continuum (LyC) photons using radiation-hydrodynamic simulations with strong stellar feedback. We find that the luminosity-weighted escape fraction from a metal-poor (Z = 0.002) galaxy embedded in a halo of mass $M_{\rm h}\simeq 10^{11}\, \mathrm{M}_\odot$ is $\left\langle {f_{\rm esc}^{\rm 3D}}\right\rangle \simeq 10\, {{\ \rm per\ cent}}$. Roughly half of the LyC photons are absorbed within scales of 100 pc, and the other half is absorbed in the ISM ($\lesssim 2\, {\rm kpc}$). When the metallicity of the gas is increased to Z = 0.02, the escape fraction is significantly reduced to $\left\langle {f_{\rm esc}^{\rm 3D}}\right\rangle \simeq 1{{\ \rm per\ cent}}$ because young stars are enshrouded by their birth clouds for a longer time. In contrast, increasing the gas mass by a factor of 5 leads to $\left\langle {f_{\rm esc}^{\rm 3D}}\right\rangle \simeq 5\, {{\ \rm per\ cent}}$ because LyC photons are only moderately absorbed by the thicker disc. Our experiments suggest that high metallicity is likely more responsible for the low escape fractions observed in massive star-forming galaxies, supporting the scenario in which the escape fraction is decreasing with increasing halo mass. Finally, negligible correlation is observed between the escape fraction and surface density of star formation or galactic outflow rates.

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Liu, Shuang, Yizhou Gu, Qirong Yuan, Shiying Lu, Min Bao, Guanwen Fang et Lulu Fan. « Morphological Transformation and Star Formation Quenching of Massive Galaxies at 0.5 ≤ z ≤ 2.5 in 3D-HST/CANDELS ». Astrophysical Journal 923, n^o 1 (1 décembre 2021) : 46. http://dx.doi.org/10.3847/1538-4357/ac2817.

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Abstract To figure out the effect of stellar mass and local environment on morphological transformation and star formation quenching in galaxies, we use the massive (M * ≥ 1010 M ⊙) galaxies at 0.5 ≤ z ≤ 2.5 in five fields of 3D-HST/CANDELS. Based on the UVJ diagnosis and the possibility of possessing a spheroid, our sample of massive galaxies is classified into four populations: quiescent early-type galaxies (qEs), quiescent late-type galaxies (qLs), star-forming early-type galaxies (sEs), and star-forming late-type galaxies (sLs). It is found that the quiescent fraction is significantly elevated at the high ends of mass and local environmental overdensity, which suggests a clear dependence of quenching on both mass and local environment. Over cosmic time, the mass dependence of galaxy quiescence decreases while the local environment dependence increases. The early-type fraction is found to be larger only at the high-mass end, indicating an evident mass dependence of morphological transformation. This mass dependence becomes more significant at lower redshifts. Among the four populations, the fraction of active galactic nuclei (AGNs) in the qLs peaks at 2 < z ≤ 2.5, and rapidly declines with cosmic time. The sEs are found to have higher AGN fractions of 20%–30% at 0.5 ≤ z < 2 . The redshift evolution of AGN fractions in the qLs and sEs suggests that AGN feedback could have played important roles in the formation of the qLs and sEs.

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Hashimoto, Tetsuya, Tomotsugu Goto, Rieko Momose, Chien-Chang Ho, Ryu Makiya, Chia-Ying Chiang et Seong Jin Kim. « A young galaxy cluster in the old Universe ». Monthly Notices of the Royal Astronomical Society 489, n^o 2 (12 août 2019) : 2014–29. http://dx.doi.org/10.1093/mnras/stz2182.

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ABSTRACT Galaxies evolve from a blue star-forming phase into a red quiescent one by quenching their star formation activity. In high-density environments, this galaxy evolution proceeds earlier and more efficiently. Therefore, local galaxy clusters are dominated by well-evolved red elliptical galaxies. The fraction of blue galaxies in clusters monotonically declines with decreasing redshift, i.e. the Butcher–Oemler effect. In the local Universe, observed blue fractions of massive clusters are as small as ≲0.2. Here we report a discovery of a ‘blue cluster’ that is a local galaxy cluster with an unprecedentedly high fraction of blue star-forming galaxies yet hosted by a massive dark matter halo. The blue fraction is 0.57, which is 4.0σ higher than those of the other comparison clusters under the same selection and identification criteria. The velocity dispersion of the member galaxies is 510 km s−1, which corresponds to a dark matter halo mass of 2.0$^{+1.9}_{-1.0}\times 10^{14}$ M⊙. The blue fraction of the cluster is more than 4.7σ beyond the standard theoretical predictions including semi-analytic models of galaxy formation. The probability to find such a high blue fraction in an individual cluster is only 0.003 per cent, which challenges the current standard frameworks of the galaxy formation and evolution in the ΛCDM universe. The spatial distribution of galaxies around the blue cluster suggests that filamentary cold gas streams can exist in massive haloes even in the local Universe. However these cold streams have already disappeared in the theoretically simulated local universes.

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Kaviraj, Sugata, Garreth Martin et Joseph Silk. « AGN in dwarf galaxies : frequency, triggering processes and the plausibility of AGN feedback ». Monthly Notices of the Royal Astronomical Society : Letters 489, n^o 1 (26 juin 2019) : L12—L16. http://dx.doi.org/10.1093/mnrasl/slz102.

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Abstract While active galactic nuclei (AGN) are considered to be key drivers of the evolution of massive galaxies, their potentially significant role in the dwarf-galaxy regime (M* < 109 M⊙) remains largely unexplored. We combine optical and infrared data, from the Hyper Suprime-Cam (HSC) and the Wide-field Infrared Explorer, respectively, to explore the properties of ∼800 AGN in dwarfs at low redshift (z < 0.3). Infrared-selected AGN fractions are ∼10–30 per cent in dwarfs, which, for reasonable duty cycles, indicates a high black hole (BH)-occupation fraction. Visual inspection of the deep HSC images indicates that the merger fraction in dwarf AGN (∼6 per cent) shows no excess compared to a control sample of non-AGN, suggesting that the AGN-triggering processes are secular in nature. Energetic arguments indicate that, in both dwarfs and massive galaxies, bolometric AGN luminosities (LAGN) are significantly greater than supernova luminosities (LSN). LAGN/LSN is, in fact, higher in dwarfs, with predictions from simulations suggesting that this ratio only increases with redshift. Together with the potentially high BH-occupation fraction, this suggests that if AGN feedback is an important driver of massive-galaxy evolution, the same is likely to be true in the dwarf regime, contrary to our classical thinking.

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Xie, Lizhi, Gabriella De Lucia, Michaela Hirschmann et Fabio Fontanot. « The influence of environment on satellite galaxies in the GAEA semi-analytic model ». Monthly Notices of the Royal Astronomical Society 498, n^o 3 (24 août 2020) : 4327–44. http://dx.doi.org/10.1093/mnras/staa2370.

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ABSTRACT Reproducing the observed quenched fraction of satellite galaxies has been a long-standing issue for galaxy formation models. We modify the treatment of environmental effects in our state-of-the-art GAlaxy Evolution and Assembly (GAEA) semi-analytic model to improve our modelling of satellite galaxies. Specifically, we implement gradual stripping of hot gas, ram-pressure stripping of cold gas, and an updated algorithm to account for angular momentum exchanges between the gaseous and stellar disc components of model galaxies. Our updated model predicts quenched fractions that are in good agreement with local observational measurements for central and satellite galaxies, and their dependencies on stellar mass and halo mass. We also find consistency between model predictions and observational estimates of quenching times for satellite galaxies, H i, H2 fractions of central galaxies, and deficiencies of H i, H2, SFR of galaxies in cluster haloes. In the framework of our updated model, the dominant quenching mechanisms are hot gas stripping for low-mass satellite galaxies, and AGN feedback for massive satellite galaxies. The ram-pressure stripping of cold gas only affects the quenched fraction in massive haloes with Mh > 1013.5 M⊙, but is needed to reproduce the observed H i deficiencies.

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Martínez-Marín, M., K. Glazebrook, T. Nanayakkara, C. Jacobs, I. Labbé, G. G. Kacprzak, C. Papovich et C. Schreiber. « The origin of large emission line widths in massive galaxies at redshifts z ∼ 3–4 ». Monthly Notices of the Royal Astronomical Society 531, n^o 3 (31 mai 2024) : 3187–202. http://dx.doi.org/10.1093/mnras/stae1335.

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ABSTRACT We present a sample of 22 massive galaxies with stellar masses >1010 M⊙ at 3 < z < 4 with deep H and K-band high resolution spectra (R = 3500–3000) from Keck/MOSFIRE and VLT/KMOS near-infrared spectrographs. We find a large fraction have strong [O iii] 5007 and Hβ emission lines with large line widths (σ 100–450 km s−1). We measure the sizes of our galaxies from Hubble Space Telescope images and consider the potential kinematic scaling relations of our sample, and rule out an explanation for these broad lines in terms of galaxy-wide kinematics. Based on consideration of the [O iii] 5007/Hβ flux ratios, their location in the mass–excitation diagram, and the derived bolometric luminosities, we conclude that active galactic nuclei (AGN) and their narrow-line regions most likely give rise to this emission. At redshifts 3 < z < 4, we find significantly high AGN fractions in massive galaxies, ranging from 60–70 per cent for the mass range 10 < log (M⋆/M⊙) < 11, with a lower limit 30 per cent for all galaxies within that redshift range when we apply our most stringent AGN criteria. We also find a considerably lower AGN fraction in massive quiescent galaxies, ranging from 20–30 per cent. These fractions of AGN point to the period between 3 < z < 4 being a time of heightened activity for the development of supermassive black holes in the massive end of the galaxy population and provide evidence for their role in the emergence of the first massive quenched galaxies at this epoch.

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Loverde, Marilena, et Zachary J. Weiner. « Massive neutrinos and cosmic composition ». Journal of Cosmology and Astroparticle Physics 2024, n^o 12 (1 décembre 2024) : 048. https://doi.org/10.1088/1475-7516/2024/12/048.

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Abstract Cosmological data probe massive neutrinos via their effects on the geometry of the Universe and the growth of structure, both of which are degenerate with the late-time expansion history. We clarify the nature of these degeneracies and the individual roles of both probes in neutrino mass inference. Geometry is strongly sensitive to neutrino masses: within ΛCDM, the primary cosmic microwave background anisotropies alone impose that the matter fraction Ω m must increase fivefold with increasing neutrino mass. Moreover, large-scale structure observables, like weak lensing of the CMB, are dimensionless and thus depend not on the matter density (as often quoted) but in fact the matter fraction. We explore the consequential impact of this distinction on the interplay between probes of structure, low-redshift distances, and CMB anisotropies. We derive constraints on the neutrino's masses independently from their suppression of structure and impact on geometry, showing that the latter is at least as important as the former. While the Dark Energy Spectroscopic Instrument's recent baryon acoustic oscillation data place stringent bounds largely deriving from their geometric incompatibility with massive neutrinos, all recent type Ia supernova datasets drive marginal preferences for nonzero neutrino masses because they prefer substantially larger matter fractions. Recent CMB lensing data, however, neither exclude neutrinos' suppression of structure nor constrain it strongly enough to discriminate between mass hierarchies. Current data thus evince not a need for modified dynamics of neutrino perturbations or structure growth but rather an inconsistent compatibility with massive neutrinos' impact on the expansion history. We identify two of DESI's measurements that strongly influence its constraints, and we also discuss neutrino mass measurements in models that alter the sound horizon.

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Zahorecz, S., I. Jimenez-Serra, L. Testi, K. Immer, F. Fontani, P. Caselli, K. Wang et T. Onishi. « Singly and doubly deuterated formaldehyde in massive star-forming regions ». Astronomy & ; Astrophysics 653 (septembre 2021) : A45. http://dx.doi.org/10.1051/0004-6361/201937012.

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Context. Deuterated molecules are good tracers of the evolutionary stage of star-forming cores. During the star formation process, deuterated molecules are expected to be enhanced in cold, dense pre-stellar cores and to deplete after protostellar birth. Aims. In this paper, we study the deuteration fraction of formaldehyde in high-mass star-forming cores at different evolutionary stages to investigate whether the deuteration fraction of formaldehyde can be used as an evolutionary tracer. Methods. Using the APEX SEPIA Band 5 receiver, we extended our pilot study of the J = 3 →2 rotational lines of HDCO and D2CO to eleven high-mass star-forming regions that host objects at different evolutionary stages. High-resolution follow-up observations of eight objects in ALMA Band 6 were performed to reveal the size of the H2CO emission and to give an estimate of the deuteration fractions HDCO/H2CO and D2CO/HDCO at scales of ~6″ (0.04–0.15 pc at the distance of our targets). Results. Our observations show that singly and doubly deuterated H2CO are detected towards high-mass protostellar objects (HMPOs) and ultracompact H II regions (UC H II regions), and the deuteration fraction of H2CO is also found to decrease by an order of magnitude from the earlier HMPO phases to the latest evolutionary stage (UC H II), from ~0.13 to ~0.01. We have not detected HDCO and D2CO emission from the youngest sources (i.e. high-mass starless cores or HMSCs). Conclusions. Our extended study supports the results of the previous pilot study: the deuteration fraction of formaldehyde decreases with the evolutionary stage, but higher sensitivity observations are needed to provide more stringent constraints on the D/H ratio during the HMSC phase. The calculated upper limits for the HMSC sources are high, so the trend between HMSC and HMPO phases cannot be constrained.

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Gilhuly, Colleen, Allison Merritt, Roberto Abraham, Shany Danieli, Deborah Lokhorst, Qing Liu, Pieter van Dokkum, Charlie Conroy et Johnny Greco. « Stellar Halos from the The Dragonfly Edge-on Galaxies Survey ». Astrophysical Journal 932, n^o 1 (1 juin 2022) : 44. http://dx.doi.org/10.3847/1538-4357/ac6750.

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Abstract We present the primary results from the Dragonfly Edge-on Galaxies Survey, an exploration of the stellar halos of twelve nearby (d < 25 Mpc) edge-on disk galaxies with the Dragonfly Telephoto Array. The edge-on orientation of these galaxies allows their stellar halos to be explored with minimal obscuration by or confusion with the much brighter disk light. Galaxies in the sample span a range of stellar masses from 109.68 to 1010.88 M ⊙. We confirm that the wide range of stellar halo mass fractions previously seen for Milky Way–mass galaxies is also found among less massive spiral galaxies. The scatter in stellar halo mass fraction is large, but we do find a significant positive correlation between stellar halo mass fraction and total stellar mass when the former is measured beyond five half-mass radii. Reasonably good agreement is found with predictions from cosmological hydrodynamical simulations, although observed stellar halo fractions appear to be somewhat lower than expected from these simulations.

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Chamberlain, Katie, Gurtina Besla, Ekta Patel, Vicente Rodriguez-Gomez, Paul Torrey, Garreth Martin, Kelsey Johnson et al. « A Physically Motivated Framework to Compare Pair Fractions of Isolated Low- and High-mass Galaxies across Cosmic Time ». Astrophysical Journal 962, n^o 2 (1 février 2024) : 162. http://dx.doi.org/10.3847/1538-4357/ad19d0.

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Abstract Low-mass galaxy pair fractions are understudied, and it is unclear whether low-mass pair fractions evolve in the same way as more massive systems over cosmic time. In the era of JWST, Roman, and Rubin, selecting galaxy pairs in a self-consistent way will be critical to connect observed pair fractions to cosmological merger rates across all mass scales and redshifts. Utilizing the Illustris TNG100 simulation, we create a sample of physically associated low-mass (108 < M * < 5 × 109 M ⊙) and high-mass (5 × 109 < M * < 1011 M ⊙) pairs between z = 0 and 4.2. The low-mass pair fraction increases from z = 0 to 2.5, while the high-mass pair fraction peaks at z = 0 and is constant or slightly decreasing at z > 1. At z = 0 the low-mass major (1:4 mass ratio) pair fraction is 4× lower than high-mass pairs, consistent with findings for cosmological merger rates. We show that separation limits that vary with the mass and redshift of the system, such as scaling by the virial radius of the host halo (r sep < 1R vir), are critical for recovering pair fraction differences between low-mass and high-mass systems. Alternatively, static physical separation limits applied equivalently to all galaxy pairs do not recover the differences between low- and high-mass pair fractions, even up to separations of 300 kpc. Finally, we place isolated mass analogs of Local Group galaxy pairs, i.e., Milky Way (MW)–M31, MW–LMC, LMC–SMC, in a cosmological context, showing that isolated analogs of LMC–SMC-mass pairs and low-separation (<50 kpc) MW–LMC-mass pairs are 2–3× more common at z ≳ 2–3.

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Beasley, Michael A., Ryan Leaman, Ignacio Trujillo, Mireia Montes, Alejandro Vazdekis, Núria Salvador Rusiñol, Elham Eftekhari, Anna Ferré-Mateu et Ignacio Martn-Navarro. « Reconstructing the mass accretion histories of nearby red nuggets with their globular cluster systems ». Proceedings of the International Astronomical Union 15, S359 (mars 2020) : 381–85. http://dx.doi.org/10.1017/s1743921320004020.

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AbstractIt is generally recognized that massive galaxies form through a combination of in-situ collapse and ex-situ accretion. The in-situ component forms early, where gas collapse and compaction leads to the formation of massive compact systems (blue and red “nuggets”) seen at z > 1. The subsequent accretion of satellites brings in ex-situ material, growing these nuggets in size and mass to appear as the massive early-type galaxies (ETGs) we see locally. Due to stochasticity in the accretion process, in a few rare cases a red nugget will evolve to the present day having undergone little ex-situ mass accretion. The resulting massive, compact and ancient objects have been termed “relic galaxies”. Detailed stellar population and kinematic analyses are required to characterise these systems. However, an additional crucial aspect lies in determining the fraction of ex-situ mass they have accreted since their formation. Globular cluster systems can be used to constrain this fraction, since the oldest and most metal-poor globular clusters in massive galaxies are primarily an accreted, ex-situ population. Models for the formation of relic galaxies and their globular cluster systems suggest that, due to their early compaction and limited accretion of dark-matter dominated satellites, relic galaxies should have characteristically low dark-matter mass fractions compared to ETGs of the same stellar mass.

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Eckert, D., V. Ghirardini, S. Ettori, E. Rasia, V. Biffi, E. Pointecouteau, M. Rossetti et al. « Non-thermal pressure support in X-COP galaxy clusters ». Astronomy & ; Astrophysics 621 (janvier 2019) : A40. http://dx.doi.org/10.1051/0004-6361/201833324.

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Galaxy clusters are the endpoints of structure formation and are continuously growing through the merging and accretion of smaller structures. Numerical simulations predict that a fraction of their energy content is not yet thermalized, mainly in the form of kinetic motions (turbulence, bulk motions). Measuring the level of non-thermal pressure support is necessary to understand the processes leading to the virialization of the gas within the potential well of the main halo and to calibrate the biases in hydrostatic mass estimates. We present high-quality measurements of hydrostatic masses and intracluster gas fraction out to the virial radius for a sample of 13 nearby clusters with available XMM-Newton and Planck data. We compare our hydrostatic gas fractions with the expected universal gas fraction to constrain the level of non-thermal pressure support. We find that hydrostatic masses require little correction and infer a median non-thermal pressure fraction of ∼6% and ∼10% at R500 and R200, respectively. Our values are lower than the expectations of hydrodynamical simulations, possibly implying a faster thermalization of the gas. If instead we use the mass calibration adopted by the Planck team, we find that the gas fraction of massive local systems implies a mass bias 1 − b = 0.85 ± 0.05 for Sunyaev–Zeldovich-derived masses, with some evidence for a mass-dependent bias. Conversely, the high bias required to match Planck cosmic microwave background and cluster count cosmology is excluded by the data at high significance, unless the most massive halos are missing a substantial fraction of their baryons.

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Bodensteiner, J., H. Sana, C. Wang, N. Langer, L. Mahy, G. Banyard, A. de Koter et al. « The young massive SMC cluster NGC 330 seen by MUSE ». Astronomy & ; Astrophysics 652 (août 2021) : A70. http://dx.doi.org/10.1051/0004-6361/202140507.

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Context. Observations of massive stars in open clusters younger than ∼8 Myr have shown that a majority of them are in binary systems, most of which will interact during their life. While these can be used as a proxy of the initial multiplicity properties, studying populations of massive stars older than ∼20 Myr allows us to probe the outcome of these interactions after a significant number of systems have experienced mass and angular momentum transfer and may even have merged. Aims. Using multi-epoch integral-field spectroscopy, we aim to investigate the multiplicity properties of the massive-star population in the dense core of the ∼40 Myr old cluster NGC 330 in the Small Magellanic Cloud in order to search for possible imprints of stellar evolution on the multiplicity properties. Methods. We obtained six epochs of VLT/MUSE observations operated in wide-field mode with the extended wavelength setup and supported by adaptive optics. We extracted spectra and measured radial velocities for stars brighter than mF814W = 19. We identified single-lined spectroscopic binaries through significant RV variability with a peak-to-peak amplitude larger than 20 km s−1. We also identified double-lined spectroscopic binaries, and quantified the observational biases for binary detection. In particular, we took into account that binary systems with similar line strengths are difficult to detect in our data set. Results. The observed spectroscopic binary fraction among stars brighter than mF814W = 19 (approximately 5.5 M⊙ on the main sequence) is fSBobs = 13.2 ± 2.0%. Considering period and mass ratio ranges from log(P) = 0.15−3.5 (about 1.4 to 3160 d), q = 0.1−1.0, and a representative set of orbital parameter distributions, we find a bias-corrected close binary fraction of fcl = 34−7+8%. This fraction seems to decline for the fainter stars, which indicates either that the close binary fraction drops in the B-type domain, or that the period distribution becomes more heavily weighted toward longer orbital periods. We further find that both fractions vary strongly in different regions of the color-magnitude diagram, which corresponds to different evolutionary stages. This probably reveals the imprint of the binary history of different groups of stars. In particular, we find that the observed spectroscopic binary fraction of Be stars (fSBobs = 2 ± 2%) is significantly lower than that of B-type stars (fSBobs = 9 ± 2%). Conclusions. We provide the first homogeneous radial velocity study of a large sample of B-type stars at a low metallicity ([Fe/H] ≲ −1.0). The overall bias-corrected close binary fraction (log(P) < 3.5 d) of the B-star population in NGC 330 is lower than the fraction reported for younger Galactic and Large Magellanic Cloud clusters in previous works. More data are needed, however, to establish whether the observed differences are caused by an age or a metallicity effect.

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Courteau, Stéphane, et Aaron A. Dutton. « The Mass Distribution in Disk Galaxies ». Proceedings of the International Astronomical Union 11, A29B (août 2015) : 195–96. http://dx.doi.org/10.1017/s1743921316004865.

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AbstractWe present the relative fraction of baryons and dark matter at various radii in galaxies. For spiral galaxies, this fraction measured in a galaxy's inner parts is typically baryon-dominated (maximal) and dark-matter dominated (sub-maximal) in the outskirts. The transition from maximal to sub-maximal baryons occurs within the inner parts of low-mass disk galaxies (with Vtot ≤ 200 km s−1) and in the outer disk for more massive systems. The mean mass fractions for late- and early-type galaxies vary significantly at the same fiducial radius and circular velocity, suggesting a range of galaxy formation mechanisms. A more detailed discussion, and resolution of the so-called “maximal disk problem”, is presented in Courteau & Dutton, ApJL, 801, 20.

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Tanaka, Toshiyuki, et Kenji Hasegawa. « Modelling population III stars for seminumerical simulations ». Monthly Notices of the Royal Astronomical Society 502, n^o 1 (12 janvier 2021) : 463–71. http://dx.doi.org/10.1093/mnras/stab072.

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ABSTRACT Theoretically modelling the 21-cm signals caused by Population III stars (Pop III stars) is the key to extracting fruitful information on Pop III stars from current and forthcoming 21-cm observations. In this work, we develop a new module of Pop III stars in which the escape fractions of ionizing photons and Lyman–Werner (LW) photons, photoheating by UV radiation, and LW feedback are consistently incorporated. By implementing the module into a public 21-cm seminumerical simulation code, 21cmfast, we demonstrate 21-cm signal calculations, neglecting X-ray heating and focusing on the high redshifts when we assume that the formation of Pop III stars dominates that of other populations. What we find is that the contribution from Pop III stars to cosmic reionization significantly depends on the treatment of the escape fraction. With our escape fraction model, Pop III stars hardly contribute to reionization because less massive haloes, whose escape fraction are high, cannot host Pop III stars due to LW feedback. On the other hand, massive minihaloes contribute to reionization with the conventional constant escape fraction. We also find that UV photoheating has non-negligible impact on the 21-cm global signal and the 21-cm power spectrum if the ionization fraction of the Universe is higher than roughly 1 per cent. In this case, the strength of the 21-cm global signal depends on the photoheating efficiency and thus on the Pop III star mass. We conclude that detailed modelling of Pop III stars is imperative to predict 21-cm observables accurately for future observations.

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McConachie, Ian, Gillian Wilson, Ben Forrest, Z. Cemile Marsan, Adam Muzzin, M. C. Cooper, Marianna Annunziatella et al. « MAGAZ3NE : Evidence for Galactic Conformity in z ≳ 3 Protoclusters* ». Astrophysical Journal 978, n^o 1 (20 décembre 2024) : 17. https://doi.org/10.3847/1538-4357/ad8f36.

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Abstract We examine the quiescent fractions of massive galaxies in six z ≳ 3 spectroscopically confirmed protoclusters in the COSMOS field, one of which is newly confirmed and presented here. We report the spectroscopic confirmation of MAGAZ3NE J100143+023021 at z = 3.122 − 0.004 + 0.007 by the Massive Ancient Galaxies At z > 3 NEar-infrared (MAGAZ3NE) survey. MAGAZ3NE J100143+023021 contains a total of 79 protocluster members (28 spectroscopic and 51 photometric). Three spectroscopically confirmed members are star-forming ultramassive galaxies (UMGs; log ( M ⋆ / M ⊙ ) > 11), the most massive of which has log ( M ⋆ / M ⊙ ) = 11.15 − 0.06 + 0.05 . Combining Keck/MOSFIRE spectroscopy and the COSMOS2020 photometric catalog, we use a weighted Gaussian kernel density estimator to map the protocluster and measure its total mass 2.25 − 0.65 + 1.55 × 10 14 M ⊙ in the dense “core” region. For each of the six COSMOS protoclusters, we compare the quiescent fraction to the status of the central UMG as star-forming or quiescent. We observe that galaxies in these protoclusters appear to obey galactic conformity: Elevated quiescent fractions are found in protoclusters with UVJ-quiescent UMGs and low quiescent fractions are found in protoclusters containing UVJ star-frming UMGs. This correlation of star formation/quiescence in UMGs and the massive galaxies nearby in these protoclusters is the first evidence for the existence of galactic conformity at z > 3. Despite disagreements over mechanisms behind conformity at low redshifts, its presence at these early cosmic times would provide strong constraints on the physics proposed to drive galactic conformity.

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Rivero, H. D., José A. García, E. Cándido Atlatenco, Alejandro D. Basso et J. Sicora. « Effect of the ratio Mo/Cr in the precipitation and distribution of carbides in alloyed nodular iron ». MRS Proceedings 1485 (2012) : 113–18. http://dx.doi.org/10.1557/opl.2013.278.

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ABSTRACTThis investigation deals with the effect of 2/0, 1/1 and 1/0.5 Cr/Mo ratios on the local fraction, distribution and the comparative size of carbides precipitated in cast nodular iron. “Y” block castings with a thickness of 1.5 cm are cast in green sand molds. Two samples are cut from each casting, one located on the center and another on the wall. The carbide volume fraction is evaluated by a digital analysis system. Each sample is analyzed in three zones: bottom, middle and top. Carbide mappings are generated according to the average local carbide fraction in order to get the distribution of carbides on the casting. Results show that higher volume fractions of carbides precipitate for the ratio 2/0 of Cr/Mo with values between 28.5 and 19.5%. The lowest fraction of carbides is presented in nodular iron alloyed with a Cr/Mo ratio of 1/1 between 6.5 and 4.6%. Also a very heterogeneous distribution of the carbides is observed in the three alloys and massive carbides are observed in the last freezing zone of the castings.

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Reddish, J., K. Kraljic, M. S. Petersen, K. Tep, Y. Dubois, C. Pichon, S. Peirani et al. « The NewHorizon simulation – to bar or not to bar ». Monthly Notices of the Royal Astronomical Society 512, n^o 1 (26 février 2022) : 160–85. http://dx.doi.org/10.1093/mnras/stac494.

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ABSTRACT We use the NewHorizon simulation to study the redshift evolution of bar properties and fractions within galaxies in the stellar masses range M⋆ = 107.25–1011.4$\, \rm {M}_\odot$ over the redshift range of z = 0.25–1.3. We select disc galaxies using stellar kinematics as a proxy for galaxy morphology. We employ two different automated bar detection methods, coupled with visual inspection, resulting in observable bar fractions of fbar = 0.070$_{{-0.012}}^{{+0.018}}$ at z ∼ 1.3, decreasing to fbar = 0.011$_{{-0.003}}^{{+0.014}}$ at z ∼ 0.25. Only one galaxy is visually confirmed as strongly barred in our sample. This bar is hosted by the most massive disc and only survives from z = 1.3 down to z = 0.7. Such a low bar fraction, in particular amongst Milky Way-like progenitors, highlights a missing bars problem, shared by literally all cosmological simulations with spatial resolution <100 pc to date. The analysis of linear growth rates, rotation curves, and derived summary statistics of the stellar, gas and dark matter components suggest that galaxies with stellar masses below 109.5−1010$\, \rm {M}_\odot$ in NewHorizon appear to be too dominated by dark matter relative to stellar content to form a bar, while more massive galaxies typically have formed large bulges that prevent bar persistence at low redshift. This investigation confirms that the evolution of the bar fraction puts stringent constraints on the assembly history of baryons and dark matter on to galaxies.

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Patrick, L. R., D. J. Lennon, C. J. Evans, H. Sana, J. Bodensteiner, N. Britavskiy, R. Dorda, A. Herrero, I. Negueruela et A. de Koter. « Multiplicity of the red supergiant population in the young massive cluster NGC 330 ». Astronomy & ; Astrophysics 635 (mars 2020) : A29. http://dx.doi.org/10.1051/0004-6361/201936741.

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Context. The multiplicity properties of massive stars are one of the important outstanding issues in stellar evolution. Quantifying the binary statistics of all evolutionary phases is essential to paint a complete picture of how and when massive stars interact with their companions, and to determine the consequences of these interactions. Aims. We investigate the multiplicity of an almost complete census of red supergiant stars (RSGs) in NGC 330, a young massive cluster in the Small Magellanic Cloud. Methods. Using a combination of multi-epoch HARPS and MUSE spectroscopy, we estimate radial velocities and assess the kinematic and multiplicity properties of 15 RSGs in NGC 330. Results. Radial velocities are estimated to better than ±100 m s−1 for the HARPS data. The line-of-sight velocity dispersion for the cluster is estimated as σ1D = 3.20 +0.69−0.52 km s−1. When virial equilibrium is assumed, the dynamical mass of the cluster is log (Mdyn/M⊙) = 5.20 ± 0.17, in good agreement with previous upper limits. We detect significant radial velocity variability in our multi-epoch observations and distinguish between variations caused by atmospheric activity and those caused by binarity. The binary fraction of NGC 330 RSGs is estimated by comparisons with simulated observations of systems with a range of input binary fractions. In this way, we account for observational biases and estimate the intrinsic binary fraction for RSGs in NGC 330 as fRSG = 0.3 ± 0.1 for orbital periods in the range 2.3 < log P [days] < 4.3, with q > 0.1. Using the distribution of the luminosities of the RSG population, we estimate the age of NGC 330 to be 45 ± 5 Myr and estimate a red straggler fraction of 50%. Conclusions. We estimate the binary fraction of RSGs in NGC 330 and conclude that it appears to be lower than that of main-sequence massive stars, which is expected because interactions between an RSG and a companion are assumed to effectively strip the RSG envelope.

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Bladt, S., et H. Wagner. « Inhibition of MAO by Fractions and Constituents of Hypericum Extract ». Journal of Geriatric Psychiatry and Neurology 7, n^o 1 (janvier 1994) : 57–59. http://dx.doi.org/10.1177/089198879400700115.

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The inhibition of monoamine oxidase (MAO) by six fractions from hypericum extract and three characteristic constituents (as pure substances) were analyzed in vitro and ex vivo to study the antidepressive mechanism of action. Rat brain homogenates were used as the in vitro model, while the ex vivo analysis was performed after intraperitoneal application of the test substances to albino rats. Massive inhibition of MAO-A could be shown with the total extract and all fractions only at the concentration of 10-3 mol/L. At 10-4 mol/L, one fraction rich in flavonoides showed an inhibition of 39%, and all other fractions demonstrated less than 25% inhibition. Using pure hypericin as well as in all ex vivo experiments, no relevant inhibiting effects could be shown. From the results it can be concluded that the clinically proven antidepressive effect of hypericum extract cannot be explained in terms of MAO inhibition.

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Bladt, S., et H. Wagner. « Inhibition of MAO by Fractions and Constituents of Hypericum Extract ». Journal of Geriatric Psychiatry and Neurology 7, n^o 1_suppl (janvier 1994) : 57–59. http://dx.doi.org/10.1177/089198879400701s15.

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The inhibition of monoamine oxidase (MAO) by six fractions from hypericum extract and three characteristic constituents (as pure substances) were analyzed in vitro and ex vivo to study the antidepressive mechanism of action. Rat brain homogenates were used as the in vitro model, while the ex vivo analysis was performed after intraperitoneal application of the test substances to albino rats. Massive inhibition of MAO-A could be shown with the total extract and all fractions only at the concentration of 10-3 mol/L. At 10-4 mol/L, one fraction rich in flavonoides showed an inhibition of 39%, and all other fractions demonstrated less than 25% inhibition. Using pure hypericin as well as in ex vivo experiments, no relevant inhibiting effects could be shown. From the results it can be concluded that the clinically proven antidepressive effect of hypericum extract cannot be explained in terms of MAO inhibition.

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Nestor Shachar, A., S. H. Price, N. M. Förster Schreiber, R. Genzel, T. T. Shimizu, L. J. Tacconi, H. Übler et al. « RC100 : Rotation Curves of 100 Massive Star-forming Galaxies at z = 0.6–2.5 Reveal Little Dark Matter on Galactic Scales ». Astrophysical Journal 944, n^o 1 (1 février 2023) : 78. http://dx.doi.org/10.3847/1538-4357/aca9cf.

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Abstract We analyze Hα or CO rotation curves extending out to several galaxy effective radii for 100 massive, large, star-forming disk galaxies (SFGs) across the peak of cosmic galaxy star formation (z ∼ 0.6–2.5), more than doubling the previous sample presented by Genzel et al. and Price et al. The observations were taken with SINFONI and KMOS integral-field spectrographs at the ESO-Very Large Telescope, LUCI-LBT, NOEMA-IRAM, and Atacama Large Millimeter/submillimeter Array. We fit the major-axis kinematics with beam-convolved, forward models of turbulent rotating disks with bulges embedded in dark matter (DM) halos, including the effects of pressure support. The fraction of dark to total matter within the disk effective radius (R e ∼ 5 kpc), f DM(R e) = V 2 DM(R e)/V 2 circ(R e) decreases with redshift: at z ∼ 1 (z ∼ 2) the median DM fraction is 0.38 ± 0.23 (0.27 ± 0.18), and a third (half) of all galaxies are maximal disks with f DM(R e) < 0.28. DM fractions correlate inversely with the baryonic surface density, and the low DM fractions can be explained with a flattened, or cored, inner DM density distribution. At z ∼ 2, there is ≈40% less DM mass on average within R e compared to expected values based on cosmological stellar-mass–halo-mass relations. The DM deficit is more evident at high star formation rate surface densities (≳2.5 M ⊙ yr−1 kpc2) and galaxies with massive bulges (≥1010 M ⊙). A combination of stellar or active galactic nucleus feedback, and/or heating due to dynamical friction, may drive the DM from cuspy into cored mass distributions, pointing to an efficient buildup of massive bulges and central black holes at z ∼ 2 SFGs.

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Donnari, Martina, Annalisa Pillepich, Gandhali D. Joshi, Dylan Nelson, Shy Genel, Federico Marinacci, Vicente Rodriguez-Gomez et al. « Quenched fractions in the IllustrisTNG simulations : the roles of AGN feedback, environment, and pre-processing ». Monthly Notices of the Royal Astronomical Society 500, n^o 3 (10 octobre 2020) : 4004–24. http://dx.doi.org/10.1093/mnras/staa3006.

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ABSTRACT We use the IllustrisTNG hydrodynamical simulations to show how the fractions of quenched galaxies vary across different environments and cosmic time, and to quantify the role AGN feedback and pre-processing play in quenching group and cluster satellites. At z = 0, we select galaxies with Mstars = 109−12 M⊙ residing within (≤R200c) massive groups and clusters of total host mass M200c = 1013−15.2 M⊙ in TNG100 and TNG300. The model predicts a quenched fraction of ∼70–90 per cent (on average) for centrals and satellites of mass ≳ 1010.5 M⊙, regardless of host mass, cosmic time (0 ≤ z ≤ 0.5), cluster-centric distance, and time since infall in the z = 0 host. Low-mass central galaxies (≲ 1010 M⊙), on the other hand, are rarely quenched unless they become members of groups (1013–14 M⊙) or clusters (≥1014 M⊙), where the quenched fraction rises to ∼ 80 per cent. Typically, the fraction of low-mass passive galaxies is higher closer to the host centre and for progressively more massive hosts. The population of low-mass satellites accreted more than ∼ 4–6 Gyr ago in massive hosts is almost entirely passive, thus suggesting an upper limit for the time needed for environmental quenching to occur. In fact, about 30 per cent of group and cluster satellites that are quenched at z = 0 were already quenched before falling into their current host, and the bulk of them quenched as early as 4–10 billion years ago. For low-mass galaxies (Mstars ≲ 1010–10.5 M⊙), this is due to pre-processing, whereby current satellites may have been members of other hosts, and hence have undergone environmental processes, before falling into their final host, this mechanism being more common and more effective for the purposes of quenching for satellites found today in more massive hosts. On the other hand, massive galaxies quench on their own and because of AGN feedback, regardless of whether they are centrals or satellites.

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Xu, Dandan, Ling Zhu, Robert Grand, Volker Springel, Shude Mao, Glenn van de Ven, Shengdong Lu et al. « A study of stellar orbit fractions : simulated IllustrisTNG galaxies compared to CALIFA observations ». Monthly Notices of the Royal Astronomical Society 489, n^o 1 (19 août 2019) : 842–54. http://dx.doi.org/10.1093/mnras/stz2164.

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ABSTRACT Motivated by the recently discovered kinematic ‘Hubble sequence’ shown by the stellar orbit-circularity distribution of 260 CALIFA galaxies, we make use of a comparable galaxy sample at z = 0 with a stellar mass range of $M_{*}/\mathrm{M}_{\odot }\in [10^{9.7},\, 10^{11.4}]$ selected from the IllustrisTNG simulation and study their stellar orbit compositions in relation to a number of other fundamental galaxy properties. We find that the TNG100 simulation broadly reproduces the observed fractions of different orbital components and their stellar mass dependences. In particular, the mean mass dependences of the luminosity fractions for the kinematically warm and hot orbits are well reproduced within model uncertainties of the observed galaxies. The simulation also largely reproduces the observed peak and trough features at $M_{*}\approx 1\rm {-}2\times 10^{10}\, \mathrm{M}_{\odot }$ in the mean distributions of the cold- and hot-orbit fractions, respectively, indicating fewer cooler orbits and more hotter orbits in both more- and less-massive galaxies beyond such a mass range. Several marginal disagreements are seen between the simulation and observations: the average cold-orbit (counter-rotating) fractions of the simulated galaxies below (above) $M_{*}\approx 6\times 10^{10}\, \mathrm{M}_{\odot }$ are systematically higher than the observational data by $\lesssim 10{{\ \rm per\ cent}}$ (absolute orbital fraction); the simulation also seems to produce more scatter for the cold-orbit fraction and less so for the non-cold orbits at any given galaxy mass. Possible causes that stem from the adopted heating mechanisms are discussed.

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Gonzalez, Anthony H., Dennis Zaritsky et Ann I. Zabludoff. « A Census of Baryons in Galaxy Clusters and Groups ». Proceedings of the International Astronomical Union 3, S244 (juin 2007) : 167–75. http://dx.doi.org/10.1017/s1743921307013968.

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AbstractWhile the baryon fraction in galaxy groups and clusters may be expected to reflect the universal value, observations of cluster baryon fractions have generally fallen short of this expectation and indicated a possible correlation with cluster mass. We present a new determination of the total baryon budget in nearby galaxy groups and clusters that includes the contributions from stars in galaxies, intracluster stars, and the intracluster medium. We find that the baryon mass fraction within r500 is independent of system mass and lower than the WMAP value. We conclude however that the present shortfall provides no compelling evidence for additional missing baryons, since it may arise due to a theoretically predicted deficit of baryons within r500 and systematic uncertainties associated with the mass determinations. With the addition of the ICL to the stellar mass in galaxies, the increase in X-ray gas mass fraction with increasing total mass is entirely accounted for by a decrease in the total stellar mass fraction, supporting the argument that the behavior of both the stellar and X-ray gas components is dominated by a decrease in star formation efficiency in more massive environments. Within just the stellar component, the fraction of the total stellar luminosity in the central, giant brightest cluster galaxy (BCG) and ICL (hereafter the BCG+ICL component) decreases as velocity dispersion (σ) increases, suggesting that ICL may grow less efficiently in higher mass environments. The identification of low mass groups with large BCG+ICL components also demonstrates that the massive cluster environment is not required to form intracluster stars. These proceedings are a condensed version of the work presented in Gonzalez, Zaritsky & Zabludoff (2007), and we refer the reader to that paper for a more complete discussion.

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Juvela, Mika, Vincent Guillet, Tie Liu, Isabelle Ristorcelli, Veli-Matti Pelkonen, Dana Alina, Leonardo Bronfman et al. « Dust spectrum and polarisation at 850 μm in the massive IRDC G035.39-00.33 ». Astronomy & ; Astrophysics 620 (23 novembre 2018) : A26. http://dx.doi.org/10.1051/0004-6361/201833245.

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Context. The sub-millimetre polarisation of dust emission from star-forming clouds carries information on grain properties and on the effects that magnetic fields have on cloud evolution. Aims. Using observations of a dense filamentary cloud G035.39-00.33, we aim to characterise the dust emission properties and the variations of the polarisation fraction. Methods. JCMT SCUBA-2/POL-2 observations at 850 μm were combined with Planck 850 μm(353 GHz) data to map polarisation fraction at small and large scales. With previous total intensity SCUBA-2 observations (450 and 850 μm) and Herschel data, the column densities were determined via modified black-body fits and via radiative transfer modelling. Models were constructed to examine how the observed polarisation angles and fractions depend on potential magnetic field geometries and grain alignment processes. Results. POL-2 data show clear changes in the magnetic field orientation. These are not in contradiction with the uniform orientation and almost constant polarisation fraction seen by Planck, because of the difference in the beam sizes and the POL-2 data being affected by spatial filtering. The filament has a peak column density of N(H2) ~ 7 × 1022 cm−2, a minimum dust temperature of T ~ 12 K, and a mass of ~4300 M⊙ for the area N(H2) > 5 × 1021 cm−2. The estimated average value of the dust opacity spectral index is β ~ 1.9. The ratio of sub-millimetre and J-band optical depths is τ (250 μm)∕τ (J) ~ 2.5 × 10−3, more than four times the typical values for diffuse medium. The polarisation fraction decreases as a function of column density to p ~ 1% in the central filament. Because of noise, the observed decrease of p(N) is significant only at N(H2) > 2 × 1022 cm−2. The observations suggest that the grain alignment is not constant. Although the data can be explained with a complete loss of alignment at densities above ~104 cm−3 or using the predictions of radiative torques alignment, the uncertainty of the field geometry and the spatial filtering of the SCUBA-2 data prevent strong conclusions. Conclusions. The G035.39-00.33 filament shows strong signs of dust evolution and the low polarisation fraction is suggestive of a loss of polarised emission from its densest parts.

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Chang, Wenjun, Guanwen Fang, Yizhou Gu, Zesen Lin, Shiying Lu et Xu Kong. « The Physical Properties of Massive Green Valley Galaxies as a Function of Environments at 0.5 < ; z < ; 2.5 in 3D-HST/Candels Fields ». Astrophysical Journal 936, n^o 1 (30 août 2022) : 47. http://dx.doi.org/10.3847/1538-4357/ac8748.

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Abstract To investigate the effects of environment in the quenching phase, we study the empirical relations for green valley (GV) galaxies between overdensity and other physical properties (i.e., effective radius r e , Sérsic indices n, and specific star formation rate (sSFR)). Based on five 3D-HST/CANDELS fields, we construct a large sample of 2126 massive (M ⋆ > 1010 M ☉) GV galaxies at 0.5 < z < 2.5 and split it into the higher overdensity quarter and the lower overdensity quarter. The results shows that GV galaxies in denser environments have higher n values and lower sSFR at 0.5 < z < 1, while there is no discernible distinction at 1 < z < 2.5. No significant enlarging or shrinking is found for GV galaxies in different environments within the same redshift bin. This suggests that a dense environment would promote the growth of bulges and suppress star formation activity of GV galaxies at 0.5 < z < 1.5 but would not affect the galaxy size. We also study the dependence of the fraction of three populations (blue cloud, GV, and red sequence) on both environments and M ⋆. At a given M ⋆, blue cloud fraction goes down with increasing environment density, while red sequence fraction is opposite. For the most massive GV galaxies, a sharp drop appears in the denser environment. Coupled with the mass dependence of three fractions in different redshift bins, our result implies that stellar mass and environments jointly promote the quenching process. Such a dual effect is also confirmed by recalculating the new effective GV fraction as the number of GV galaxies over the number of nonquiescent galaxies.

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Sorooshian, A., S. M. Murphy, S. Hersey, H. Gates, L. T. Padro, A. Nenes, F. J. Brechtel, H. Jonsson, R. C. Flagan et J. H. Seinfeld. « Comprehensive airborne characterization of aerosol from a major bovine source ». Atmospheric Chemistry and Physics Discussions 8, n^o 3 (3 juin 2008) : 10415–79. http://dx.doi.org/10.5194/acpd-8-10415-2008.

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Abstract. We report an extensive airborne characterization of aerosol downwind of a massive bovine source in the San Joaquin Valley (California) on two flights during July 2007. The Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter probed chemical composition, particle size distribution, mixing state, sub- and supersaturated water uptake behavior, light scattering properties, and the interrelationship between these parameters and meteorology. Total PM1.0 levels and concentrations of organics, nitrate, and ammonium were enhanced in the plume from the source as compared to the background aerosol. Organics dominated the plume aerosol mass (~56–64%), followed either by sulfate or nitrate, and then ammonium. Particulate amines were detected in the plume aerosol by a particle-into-liquid sampler (PILS) and via mass spectral markers in the Aerodyne cToF-AMS. Amines were found to be a significant atmospheric base even in the presence of ammonia; particulate amine concentrations are estimated as at least 14–23% of that of ammonium in the plume. Enhanced sub- and supersaturated water uptake and reduced refractive indices were coincident with lower organic mass fractions, higher nitrate mass fractions, and the detection of amines. Kinetic limitations due to hydrophobic organic material are shown to have likely suppressed droplet growth. After removing effects associated with size distribution and mixing state, the normalized activated fraction of cloud condensation nuclei (CCN) increased as a function of the subsaturated hygroscopic growth factor, with the highest activated fractions being consistent with relatively lower organic mass fractions and higher nitrate mass fractions. Subsaturated hygroscopic growth factors for the organic fraction of the aerosol are estimated based on employing the Zdanovskii-Stokes Robinson (ZSR) mixing rule. Representative values for a parameterization treating particle water uptake in both the sub- and supersaturated regimes are reported for incorporation into atmospheric models.

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Sorooshian, A., S. M. Murphy, S. Hersey, H. Gates, L. T. Padro, A. Nenes, F. J. Brechtel, H. Jonsson, R. C. Flagan et J. H. Seinfeld. « Comprehensive airborne characterization of aerosol from a major bovine source ». Atmospheric Chemistry and Physics 8, n^o 17 (12 septembre 2008) : 5489–520. http://dx.doi.org/10.5194/acp-8-5489-2008.

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Abstract. We report an extensive airborne characterization of aerosol downwind of a massive bovine source in the San Joaquin Valley (California) on two flights during July 2007. The Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter probed chemical composition, particle size distribution, mixing state, sub- and supersaturated water uptake behavior, light scattering properties, and the interrelationship between these parameters and meteorology. Total PM1.0 levels and concentrations of organics, nitrate, and ammonium were enhanced in the plume from the source as compared to the background aerosol. Organics dominated the plume aerosol mass (~56–64%), followed either by sulfate or nitrate, and then ammonium. Particulate amines were detected in the plume aerosol by a particle-into-liquid sampler (PILS) and via mass spectral markers in the Aerodyne C-ToF-AMS. Amines were found to be a significant atmospheric base even in the presence of ammonia; particulate amine concentrations are estimated as at least 14–23% of that of ammonium in the plume. Enhanced sub- and supersaturated water uptake and reduced refractive indices were coincident with lower organic mass fractions, higher nitrate mass fractions, and the detection of amines. The likelihood of suppressed droplet growth owing to kinetic limitations from hydrophobic organic material is explored. After removing effects associated with size distribution and mixing state, the normalized activated fraction of cloud condensation nuclei (CCN) increased as a function of the subsaturated hygroscopic growth factor, with the highest activated fractions being consistent with relatively lower organic mass fractions and higher nitrate mass fractions. Subsaturated hygroscopic growth factors for the organic fraction of the aerosol are estimated based on employing the Zdanovskii-Stokes Robinson (ZSR) mixing rule. Representative values for a parameterization treating particle water uptake in both the sub- and supersaturated regimes are reported for incorporation into atmospheric models.

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Bower, Dan J., Kaustubh Hakim, Paolo A. Sossi et Patrick Sanan. « Retention of Water in Terrestrial Magma Oceans and Carbon-rich Early Atmospheres ». Planetary Science Journal 3, n^o 4 (1 avril 2022) : 93. http://dx.doi.org/10.3847/psj/ac5fb1.

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Abstract Massive steam and CO2 atmospheres have been proposed for magma ocean outgassing of Earth and terrestrial planets. Yet formation of such atmospheres depends on volatile exchange with the molten interior, governed by volatile solubilities and redox reactions. We determine the evolution of magma ocean–atmosphere systems for a range of oxygen fugacities, C/H ratios, and hydrogen budgets that include redox reactions for hydrogen (H2–H2O), carbon (CO–CO2), methane (CH4), and solubility laws for H2O and CO2. We find that small initial budgets of hydrogen, high C/H ratios, and oxidizing conditions suppress outgassing of hydrogen until the late stage of magma ocean crystallization. Hence, early atmospheres in equilibrium with magma oceans are dominantly carbon-rich, and specifically CO-rich except at the most oxidizing conditions. The high solubility of H2O limits its outgassing to melt fractions below ∼30%, the fraction at which the mantle transitions from vigorous to sluggish convection with melt percolation. Sluggish melt percolation could enable a surface lid to form, trapping water in the interior and thereby maintaining a carbon-rich atmosphere (equilibrium crystallization). Alternatively, efficient crystal settling could maintain a molten surface, promoting a transition to a water-rich atmosphere (fractional crystallization). However, additional processes, including melt trapping and H dissolution in crystallizing minerals, further conspire to limit the extent of H outgassing, even for fractional crystallization. Hence, much of the water delivered to planets during their accretion can be safely harbored in their interiors during the magma ocean stage, particularly at oxidizing conditions.

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Bower, Dan J., Kaustubh Hakim, Paolo A. Sossi et Patrick Sanan. « Retention of Water in Terrestrial Magma Oceans and Carbon-rich Early Atmospheres ». Planetary Science Journal 3, n^o 4 (1 avril 2022) : 93. http://dx.doi.org/10.3847/psj/ac5fb1.

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Abstract Massive steam and CO2 atmospheres have been proposed for magma ocean outgassing of Earth and terrestrial planets. Yet formation of such atmospheres depends on volatile exchange with the molten interior, governed by volatile solubilities and redox reactions. We determine the evolution of magma ocean–atmosphere systems for a range of oxygen fugacities, C/H ratios, and hydrogen budgets that include redox reactions for hydrogen (H2–H2O), carbon (CO–CO2), methane (CH4), and solubility laws for H2O and CO2. We find that small initial budgets of hydrogen, high C/H ratios, and oxidizing conditions suppress outgassing of hydrogen until the late stage of magma ocean crystallization. Hence, early atmospheres in equilibrium with magma oceans are dominantly carbon-rich, and specifically CO-rich except at the most oxidizing conditions. The high solubility of H2O limits its outgassing to melt fractions below ∼30%, the fraction at which the mantle transitions from vigorous to sluggish convection with melt percolation. Sluggish melt percolation could enable a surface lid to form, trapping water in the interior and thereby maintaining a carbon-rich atmosphere (equilibrium crystallization). Alternatively, efficient crystal settling could maintain a molten surface, promoting a transition to a water-rich atmosphere (fractional crystallization). However, additional processes, including melt trapping and H dissolution in crystallizing minerals, further conspire to limit the extent of H outgassing, even for fractional crystallization. Hence, much of the water delivered to planets during their accretion can be safely harbored in their interiors during the magma ocean stage, particularly at oxidizing conditions.

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Rosas-Guevara, Yetli, Silvia Bonoli, Massimo Dotti, David Izquierdo-Villalba, Alessandro Lupi, Tommaso Zana, Matteo Bonetti et al. « The evolution of the barred galaxy population in the TNG50 simulation ». Monthly Notices of the Royal Astronomical Society 512, n^o 4 (24 mars 2022) : 5339–57. http://dx.doi.org/10.1093/mnras/stac816.

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ABSTRACT We use the magnetic-hydrodynamical simulation TNG50 to study the evolution of barred massive disc galaxies. Massive spiral galaxies are already present as early as z = 4, and bar formation takes place already at those early times. The bars grow longer and stronger as the host galaxies evolve, with the bar sizes increasing at a pace similar to that of the disc scalelengths. The bar fraction mildly evolves with redshift for galaxies with $M_{*}\ge 10^{10}\rm M_{\odot }$, being greater than $\sim 40{{\ \rm per\ cent}}$ at 0.5 < z < 3 and $\sim 30{{\ \rm per\ cent}}$ at z = 0. When bars larger than a given physical size ($\ge 2\, \rm kpc$) or the angular resolution limit of twice the I-band angular PSF FWHM of the HST are considered, the bar fraction dramatically decreases with increasing redshift, reconciling the theoretical predictions with observational data. We find that barred galaxies have an older stellar population, lower gas fractions, and star formation rates than unbarred galaxies. In most cases, the discs of barred galaxies assembled earlier and faster than the discs of unbarred galaxies. We also find that barred galaxies are typical in haloes with larger concentrations and smaller spin parameters than unbarred galaxies. Furthermore, the inner regions of barred galaxies are more baryon-dominated than those of unbarred galaxies but have comparable global stellar mass fractions. Our findings suggest that the bar population could be used as a potential tracer of the buildup of disc galaxies and their host haloes. With this paper, we release a catalogue of barred galaxies in TNG50 at six redshifts between z = 4 and 0.

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Kimmig, Lucas C., Rhea-Silvia Remus, Klaus Dolag et Veronica Biffi. « The Hateful Eight : Connecting Massive Substructures in Galaxy Clusters like A2744 to Their Dynamical Assembly State Using the Magneticum Simulations ». Astrophysical Journal 949, n^o 2 (1 juin 2023) : 92. http://dx.doi.org/10.3847/1538-4357/acc740.

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Abstract Substructures are known to be good tracers for the dynamical states and recent accretion histories of the most massive collapsed structures in the universe, galaxy clusters. Observations find extremely massive substructures in some clusters, especially Abell 2744 (A2744), which are potentially in tension with the ΛCDM paradigm because they are not found in simulations directly. However, the methods to measure substructure masses strongly differ between observations and simulations. Using the fully hydrodynamical cosmological simulation suite Magneticum Pathfinder, we develop a method to measure substructure masses in projection from simulations, similarly to the observational approach. We identify a simulated A2744 counterpart that not only has eight substructures of similar mass fractions but also exhibits similar features in the hot gas component. This cluster formed only recently through a major merger together with at least six massive minor merger events since z = 1, where previously the most massive component had a mass of less than 1 × 1014 M ⊙. We show that the mass fraction of all substructures and of the eighth substructure separately are excellent tracers for the dynamical state and assembly history for all galaxy cluster mass ranges, with high fractions indicating merger events within the last 2 Gyr. Finally, we demonstrate that the differences between subhalo masses measured directly from simulations as bound and those measured in projection are due to methodology, with the latter generally 2–3 times larger than the former. We provide a predictor function to estimate projected substructure masses from SubFind masses for future comparison studies between simulations and observations.

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Reina-Campos, Marta, Meghan E. Hughes, J. M. Diederik Kruijssen, Joel L. Pfeffer, Nate Bastian, Robert A. Crain, Andreas Koch et Eva K. Grebel. « The mass fraction of halo stars contributed by the disruption of globular clusters in the E-MOSAICS simulations ». Monthly Notices of the Royal Astronomical Society 493, n^o 3 (18 février 2020) : 3422–28. http://dx.doi.org/10.1093/mnras/staa483.

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ABSTRACT Globular clusters (GCs) have been posited, alongside dwarf galaxies, as significant contributors to the field stellar population of the Galactic halo. In order to quantify their contribution, we examine the fraction of halo stars formed in stellar clusters in the suite of 25 present-day Milky Way-mass cosmological zoom simulations from the E-MOSAICS project. We find that a median of 2.3 and 0.3 per cent of the mass in halo field stars formed in clusters and GCs, defined as clusters more massive than 5 × 103 and 105 M⊙, respectively, with the 25–75th percentiles spanning 1.9–3.0 and 0.2–0.5 per cent being caused by differences in the assembly histories of the host galaxies. Under the extreme assumption that no stellar cluster survives to the present day, the mass fractions increase to a median of 5.9 and 1.8 per cent. These small fractions indicate that the disruption of GCs plays a subdominant role in the build-up of the stellar halo. We also determine the contributed halo mass fraction that would present signatures of light-element abundance variations considered to be unique to GCs, and find that clusters and GCs would contribute a median of 1.1 and 0.2 per cent, respectively. We estimate the contributed fraction of GC stars to the Milky Way halo, based on recent surveys, and find upper limits of 2–5 per cent (significantly lower than previous estimates), suggesting that models other than those invoking strong mass loss are required to describe the formation of chemically enriched stellar populations in GCs.

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Radice, David, et Sebastiano Bernuzzi. « Secular Outflows from Long-Lived Neutron Star Merger Remnants ». Journal of Physics : Conference Series 2742, n^o 1 (1 avril 2024) : 012009. http://dx.doi.org/10.1088/1742-6596/2742/1/012009.

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Abstract We study mass ejection from a binary neutron star merger producing a long-lived massive neutron star remnant with general-relativistic neutrino-radiation hydrodynamics simulations. In addition to outflows generated by shocks and tidal torques during and shortly after the merger, we observe the appearance of a wind driven by spiral density waves in the disk. This spiral-wave-driven outflow is predominantly located close to the disk orbital plane and have a broad distribution of electron fractions. At higher latitudes, a high electron-fraction wind is driven by neutrino radiation. The combined nucleosynthesis yields from all the ejecta components is in good agreement with Solar abundance measurements.

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Chen, Guoyin, Meixia Zhang, Xianyu Yao, Yiren Zhu, Yuanliu Hu, Dafeng Hui, Jianling Li, Jingwen Chen et Qi Deng. « Soil Organic Carbon Sequestration after 20-Year Afforestation of Mangrove Plantations on Qi’ao Island, Southern China ». Agronomy 13, n^o 9 (15 septembre 2023) : 2389. http://dx.doi.org/10.3390/agronomy13092389.

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Mangrove afforestation is considered an important measure in the “natural-based solution” for mitigating climate warming through sequestering massive carbon (C) into vegetation biomass, yet how the planted mangrove species facilitate soil C sequestration remains unclear. Here, we investigated the stock, source, and fraction of soil organic carbon (SOC) over 1 m depth after 20-year afforestation of five mangrove pure plantations (Acrostichum aureum, Acanthus ilicifolius, Aegiceras corniculatum, Kandelia obovate, and Excoecaria agallocha) on Qi’ao Island, South China. The results showed that SOC stocks did not significantly differ among the five plantations, with an average value of 16.7 kg C m−2. Based on the two-end-member mixing model with plant–soil C stable isotope signatures, the autochthonous (mangrove-derived) C source accounted for 20.2–34.1% of SOC but varied significantly among the plantations. The SOC stock in particulate fraction (1.2–2.0 g C kg−1) and mineral-associated fraction (14.3–16.0 g C kg−1) also significantly differed among the plantations. The similar SOC stock but different source contributions and C fractions among the plantations observed here may have important implications for mangrove afforestation to optimize stand structure and maximize C sequestration.

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Chen, Zhiwei, Youjun Lu et Yuetong Zhao. « Constraining the Origin of Stellar Binary Black Hole Mergers by Detections of Their Lensed Host Galaxies and Gravitational Wave Signals ». Astrophysical Journal 940, n^o 1 (1 novembre 2022) : 17. http://dx.doi.org/10.3847/1538-4357/ac98b7.

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Abstract A significant number of stellar binary black hole (sBBH) mergers may be lensed and detected by the third generation of gravitational wave (GW) detectors. Their lensed host galaxies may be detectable, which would thus help to accurately localize these sources and provide a new approach to study the origin of sBBHs. In this paper, we investigate the detectability of lensed host galaxies for lensed sBBH mergers. We find that the detection fraction of galaxies hosting lensed GW events can be significantly different for a survey with a given limiting magnitude if sBBHs are produced by different mechanisms, such as the evolution of massive binary stars, dynamical interactions in dense star clusters, and production assisted by active galactic nuclei or massive black holes. Furthermore, we illustrate that the statistical spatial distributions of those lensed sBBHs in their hosts resulting from different sBBH formation channels can differ. Therefore, with the third generation of GW detectors and future large-scale galaxy surveys, it is possible to independently constrain the origin of sBBHs via the detection fraction of those lensed events with identifiable lensing host signatures and/or even to constrain the fractional contributions from different sBBH formation mechanisms.

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Ogihara, Masahiro, Yasunori Hori, Masanobu Kunitomo et Kenji Kurosaki. « Formation of giant planets with large metal masses and metal fractions via giant impacts in a rapidly dissipating disk ». Astronomy & ; Astrophysics 648 (avril 2021) : L1. http://dx.doi.org/10.1051/0004-6361/202140464.

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Context. According to planetary interior models, some giant planets contain large metal masses with large metal-mass fractions. HD 149026b and TOI-849b are characteristic examples of these giant planets. It has been suggested that the envelope mass loss during giant impacts plays a key role in the formation of such giant planets. Aims. The aim of the present Letter is to propose a mechanism that can explain the origin of such giant planets. Methods. We investigate the formation of giant planets in a rapidly dissipating disk using N-body simulations that consider pebble accretion. Results. The results show that although the pebble isolation mass is smaller than the metal mass (≳30 Earth masses) in some giant planets, the interior metal mass can be increased by giant impacts between planets with the isolation mass. Regarding the metal fraction, the cores accrete massive envelopes by runaway gas accretion during the disk-dissipation phase of 1−10 Myr in a disk that evolves without photoevaporation. Although a large fraction of the envelope can be lost during giant impacts, the planets can reaccrete the envelope after impacts in a slowly dissipating disk. Here, we demonstrate that, by photoevaporation in a rapidly dissipating disk, the runaway gas accretion is quenched in the middle, resulting in the formation of giant planets with large metal-mass fractions. Conclusions. The origins of HD 149026b and TOI-849b, which are characterized by their large metal-mass fractions, can be naturally explained by a model that considers a disk evolving with photoevaporation.

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Kimbrell, Seth J., Amy E. Reines, Jenny E. Greene et Marla Geha. « A Comparison between the Morphologies and Structures of Dwarf Galaxies with and without Active Massive Black Holes ». Astrophysical Journal 958, n^o 2 (16 novembre 2023) : 115. http://dx.doi.org/10.3847/1538-4357/acf762.

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Abstract We study the morphologies and structures of 57 dwarf galaxies that are representative of the general population of dwarf galaxies and compare their demographics to a sample of dwarf galaxies hosting optically selected active galactic nuclei (AGNs). The two samples span the same galaxy stellar mass (109 ≲ M ⋆/M ⊙ ≲ 109.5) and color range, and the observations are well-matched in physical resolution. The fractions of irregular galaxies (14%) and early types/ellipticals (∼18%) are nearly identical among the two samples. However, among galaxies with disks (the majority of each sample), the AGN hosts almost always have a detectable (pseudo)bulge, while a large fraction of the non-AGN hosts are pure disk galaxies with no detectable (pseudo)bulge. Central point sources of light consistent with nuclear star clusters are detected in many of the non-AGN hosts. In contrast, central point sources detected in the AGN hosts are, on average, more than 2 orders of magnitude more luminous, suggesting the point sources in these objects are dominated by AGN light. The preference for (pseudo)bulges in dwarf AGN hosts may inform searches for massive black holes in dwarf galaxies and attempts to constrain the black hole occupation fraction, which, in turn, has implications for our understanding of black hole seeding mechanisms.

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Newnham, L., Kelley M. Hess, Karen L. Masters, Sandor Kruk, Samantha J. Penny, Tim Lingard et R. J. Smethurst. « The H i morphology and stellar properties of strongly barred galaxies : support for bar quenching in massive spirals ». Monthly Notices of the Royal Astronomical Society 492, n^o 4 (14 janvier 2020) : 4697–715. http://dx.doi.org/10.1093/mnras/staa064.

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ABSTRACT Galactic bars are able to affect the evolution of galaxies by redistributing their gas, possibly contributing to the cessation of star formation. Several recent works point to ‘bar quenching’ playing an important role in massive disc galaxies. We construct a sample of six gas-rich and strongly barred disc galaxies with resolved H i observations. This sample of galaxies, which we call H i-rich barred galaxies, was identified with the help of Galaxy Zoo to find galaxies hosting a strong bar, and the Arecibo Legacy Fast Arecibo L-band Feed Array blind H i survey to identify galaxies with a high H i content. The combination of strong bar and high gas fraction is rare, so this set of six galaxies is the largest sample of its type with resolved H i observations. We measure the gas fractions, H i morphology and kinematics, and use archival optical data from the Sloan Digital Sky Survey to reveal star formation histories and bar properties. The galaxies with the lowest gas fractions (still very high for their mass) show clear H i holes, dynamically advanced bars, and low star formation rates, while those with the highest gas fractions show little impact from their bar on the H i morphology, and are still actively star-forming. These galaxies support a picture in which the movement of gas by bars can lead to star formation quenching. How these unusual galaxies came to be is an open question.

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Dorn-Wallenstein, Trevor Z., et Emily M. Levesque. « Stellar Population Diagnostics of the Massive Star Binary Fraction ». Astrophysical Journal 867, n^o 2 (7 novembre 2018) : 125. http://dx.doi.org/10.3847/1538-4357/aae5d6.

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Sana, Hugues, et Christopher J. Evans. « The multiplicity of massive stars ». Proceedings of the International Astronomical Union 6, S272 (juillet 2010) : 474–85. http://dx.doi.org/10.1017/s1743921311011124.

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AbstractBinaries are excellent astrophysical laboratories that provide us with direct measurements of fundamental stellar parameters. Compared to single isolated stars, multiplicity induces new processes, offering the opportunity to confront our understanding of a broad range of physics under the extreme conditions found in, and close to, astrophysical objects.In this contribution, we will discuss the parameter space occupied by massive binaries, and the observational means to investigate it. We will review the multiplicity fraction of OB stars within each regime, and in different astrophysical environments. In particular we will compare the O star spectroscopic binary fraction in nearby open clusters and we will show that the current data are adequately described by an homogeneous fraction of f ≈ 0.44.We will also summarize our current understanding of the observed parameter distributions of O + OB spectroscopic binaries. We will show that the period distribution is overabundant in short period binaries and that it can be described by a bi-modal Öpik law with a break point around P ≈ 10 d. The distribution of the mass-ratios shows no indication for a twin population of equal mass binaries and seems rather uniform in the range 0.2 ≤ q = M2/M1 ≤ 1.0.

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