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Title: Probing baryonic processes and gastrophysics in the formation of the Milky Way dwarf satellites. I. Metallicity distribution properties

Abstract

The Milky Way (MW) dwarf satellites, as the smallest galaxies discovered in the present-day universe, are potentially powerful probes to various baryonic processes in galaxy formation occurring in the early universe. In this paper, we study the chemical properties of the stars in the dwarf satellites around the MW-like host galaxies, and explore the possible effects of several baryonic processes, including supernova (SN) feedback, the reionization of the universe, and H{sub 2} cooling, and how current and future observations may put some constraints on these processes. We use a semianalytical model to generate MW-like galaxies, for which a fiducial model can reproduce the luminosity function and the stellar metallicity-stellar mass correlation of the MW dwarfs. Using the simulated MW-like galaxies, we focus on investigating three metallicity properties of their dwarfs: the stellar metallicity-stellar mass correlation of the dwarf population, and the metal-poor and metal-rich tails of the stellar metallicity distribution in individual dwarfs. We find that (1) the slope of the stellar metallicity-stellar mass correlation is sensitive to the SN feedback strength and the reionization epoch; (2) the extension of the metal-rich tails is mainly sensitive to the SN feedback strength; (3) the extension of the metal-poor tails is mainlymore » sensitive to the reionization epoch; (4) none of the three chemical properties are sensitive to the H{sub 2} cooling process; and (5) a comparison of our model results with the current observational slope of the stellar metallicity-stellar mass relation suggests that the local universe is reionized earlier than the cosmic average, local sources may have a significant contribution to the reionization in the local region, and an intermediate to strong SN feedback strength is preferred. Future observations of metal-rich and metal-poor tails of stellar metallicity distributions will put further constraints on the SN feedback and the reionization processes.« less

Authors:
;  [1];  [2]
  1. Kavli Institute for Astronomy and Astrophysics, and School of Physics, Peking University, Beijing 100871 (China)
  2. National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)
Publication Date:
OSTI Identifier:
22365430
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 791; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; COMPARATIVE EVALUATIONS; COOLING; CORRELATIONS; DISTRIBUTION; DWARF STARS; EVOLUTION; FEEDBACK; GALAXIES; HYDROGEN; LUMINOSITY; MASS; METALLICITY; MILKY WAY; PROBES; SATELLITES; SIMULATION; STARS; SUPERNOVAE; UNIVERSE

Citation Formats

Hou, Jun, Yu, Qingjuan, and Lu, Youjun, E-mail: yuqj@pku.edu.cn. Probing baryonic processes and gastrophysics in the formation of the Milky Way dwarf satellites. I. Metallicity distribution properties. United States: N. p., 2014. Web. doi:10.1088/0004-637X/791/1/8.
Hou, Jun, Yu, Qingjuan, & Lu, Youjun, E-mail: yuqj@pku.edu.cn. Probing baryonic processes and gastrophysics in the formation of the Milky Way dwarf satellites. I. Metallicity distribution properties. United States. doi:10.1088/0004-637X/791/1/8.
Hou, Jun, Yu, Qingjuan, and Lu, Youjun, E-mail: yuqj@pku.edu.cn. Sun . "Probing baryonic processes and gastrophysics in the formation of the Milky Way dwarf satellites. I. Metallicity distribution properties". United States. doi:10.1088/0004-637X/791/1/8.
@article{osti_22365430,
title = {Probing baryonic processes and gastrophysics in the formation of the Milky Way dwarf satellites. I. Metallicity distribution properties},
author = {Hou, Jun and Yu, Qingjuan and Lu, Youjun, E-mail: yuqj@pku.edu.cn},
abstractNote = {The Milky Way (MW) dwarf satellites, as the smallest galaxies discovered in the present-day universe, are potentially powerful probes to various baryonic processes in galaxy formation occurring in the early universe. In this paper, we study the chemical properties of the stars in the dwarf satellites around the MW-like host galaxies, and explore the possible effects of several baryonic processes, including supernova (SN) feedback, the reionization of the universe, and H{sub 2} cooling, and how current and future observations may put some constraints on these processes. We use a semianalytical model to generate MW-like galaxies, for which a fiducial model can reproduce the luminosity function and the stellar metallicity-stellar mass correlation of the MW dwarfs. Using the simulated MW-like galaxies, we focus on investigating three metallicity properties of their dwarfs: the stellar metallicity-stellar mass correlation of the dwarf population, and the metal-poor and metal-rich tails of the stellar metallicity distribution in individual dwarfs. We find that (1) the slope of the stellar metallicity-stellar mass correlation is sensitive to the SN feedback strength and the reionization epoch; (2) the extension of the metal-rich tails is mainly sensitive to the SN feedback strength; (3) the extension of the metal-poor tails is mainly sensitive to the reionization epoch; (4) none of the three chemical properties are sensitive to the H{sub 2} cooling process; and (5) a comparison of our model results with the current observational slope of the stellar metallicity-stellar mass relation suggests that the local universe is reionized earlier than the cosmic average, local sources may have a significant contribution to the reionization in the local region, and an intermediate to strong SN feedback strength is preferred. Future observations of metal-rich and metal-poor tails of stellar metallicity distributions will put further constraints on the SN feedback and the reionization processes.},
doi = {10.1088/0004-637X/791/1/8},
journal = {Astrophysical Journal},
number = 1,
volume = 791,
place = {United States},
year = {Sun Aug 10 00:00:00 EDT 2014},
month = {Sun Aug 10 00:00:00 EDT 2014}
}
  • We study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of Milky Way (MW)-mass (M{sub vir} ∼ 10{sup 12.1} M{sub ⊙}) halos using a suite of 45 zoom-in dissipationless simulations. Empirical models are employed to relate (peak) subhalo mass to dwarf stellar mass, and we use constraints from z = 0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material. The dominant contributors to the accreted stellar mass are relatively massive dwarfs with M{sub star} ∼ 10{sup 8}–10{sup 10}M{sub ⊙}. Halos with more quiescent accretion histories tend to have lower mass progenitors (10{sup 8}–10{sup 9} M{sub ⊙}), andmore » lower overall accreted stellar masses. Ultra-faint mass (M{sub star} < 10{sup 5} M{sub ⊙}) dwarfs contribute a negligible amount (≪1%) to the accreted stellar mass and, despite having low average metallicities, supply a small fraction (∼2%–5%) of the very metal-poor stars with [Fe/H] < −2. Dwarfs with masses 10{sup 5} < M{sub star}/M{sub ⊙} < 10{sup 8} provide a substantial amount of the very metal-poor stellar material (∼40%–80%), and even relatively metal-rich dwarfs with M{sub star} > 10{sup 8} M{sub ⊙} can contribute a considerable fraction (∼20%–60%) of metal-poor stars if their metallicity distributions have significant metal-poor tails. Finally, we find that the generic assumption of a quiescent assembly history for the MW halo seems to be in tension with the mass spectrum of its surviving dwarfs. We suggest that the MW could be a “transient fossil”; a quiescent halo with a recent accretion event(s) that disguises the preceding formation history of the halo.« less
  • In this paper, we study the mass spectrum of destroyed dwarfs that contribute to the accreted stellar mass of Milky Way (MW)-mass (M vir ~ 10 12.1 M ) halos using a suite of 45 zoom-in dissipationless simulations. Empirical models are employed to relate (peak) subhalo mass to dwarf stellar mass, and we use constraints from z = 0 observations and hydrodynamical simulations to estimate the metallicity distribution of the accreted stellar material. The dominant contributors to the accreted stellar mass are relatively massive dwarfs with M star ~ 10 8–10 10M . Halos with more quiescent accretion histories tendmore » to have lower mass progenitors (10 8–10 9 M ), and lower overall accreted stellar masses. Ultra-faint mass (M star < 10 5 M ) dwarfs contribute a negligible amount (<<1%) to the accreted stellar mass and, despite having low average metallicities, supply a small fraction (~2%–5%) of the very metal-poor stars with [Fe/H] < -2. Dwarfs with masses 10 5 < M star/M < 10 8 provide a substantial amount of the very metal-poor stellar material (~40%–80%), and even relatively metal-rich dwarfs with M star > 10 8 M can contribute a considerable fraction (~20%–60%) of metal-poor stars if their metallicity distributions have significant metal-poor tails. Finally, we find that the generic assumption of a quiescent assembly history for the MW halo seems to be in tension with the mass spectrum of its surviving dwarfs. In conclusion, we suggest that the MW could be a "transient fossil"; a quiescent halo with a recent accretion event(s) that disguises the preceding formation history of the halo.« less
  • We present metallicity distribution functions (MDFs) for the central regions of eight dwarf satellite galaxies of the Milky Way: Fornax, Leo I and II, Sculptor, Sextans, Draco, Canes Venatici I, and Ursa Minor. We use the published catalog of abundance measurements from the previous paper in this series. The measurements are based on spectral synthesis of iron absorption lines. For each MDF, we determine maximum likelihood fits for Leaky Box, Pre-Enriched, and Extra Gas (wherein the gas supply available for star formation increases before it decreases to zero) analytic models of chemical evolution. Although the models are too simplistic tomore » describe any MDF in detail, a Leaky Box starting from zero metallicity gas fits none of the galaxies except Canes Venatici I well. The MDFs of some galaxies, particularly the more luminous ones, strongly prefer the Extra Gas Model to the other models. Only for Canes Venatici I does the Pre-Enriched Model fit significantly better than the Extra Gas Model. The best-fit effective yields of the less luminous half of our galaxy sample do not exceed 0.02 Z{sub sun}, indicating that gas outflow is important in the chemical evolution of the less luminous galaxies. We surmise that the ratio of the importance of gas infall to gas outflow increases with galaxy luminosity. Strong correlations of average [Fe/H] and metallicity spread with luminosity support this hypothesis.« less
  • As part of the Dwarf galaxies Abundances and Radial-velocities Team (DART) Programme, we have measured the metallicities of a large sample of stars in four nearby dwarf spheroidal galaxies (dSph): Sculptor, Sextans, Fornax and Carina. The low mean metal abundances and the presence of very old stellar populations in these galaxies have supported the view that they are fossils from the early Universe. However, contrary to naive expectations, we find a significant lack of stars with metallicities below [Fe/H] {approx} -3 dex in all four systems. This suggests that the gas that made up the stars in these systems hadmore » been uniformly enriched prior to their formation. Furthermore, the metal-poor tail of the dSph metallicity distribution is significantly different from that of the Galactic halo. These findings show that the progenitors of nearby dSph appear to have been fundamentally different from the building blocks of the Milky Way, even at the earliest epochs.« less
  • The dwarf satellite galaxies in the Local Group are generally considered to be hosted in dark matter subhalos that survived the disruptive processes during infall onto their host halos. It has recently been argued that if the majority of satellites entered the Milky Way (MW) halo in a group rather than individually, this could explain the spatial and dynamical peculiarities of its satellite distribution. Such groups were identified as dwarf galaxy associations that are found in the nearby universe. In this paper, we address the question whether galaxies in such associations can be the progenitors of the MW satellite galaxies.more » We find that the dwarf associations are much more extended than would be required to explain the disklike distribution of the MW and Andromeda satellite galaxies. We further identify a possible minor filamentary structure, perpendicular to the supergalactic plane, in which the dwarf associations are located, that might be related to the direction of infall of a progenitor galaxy of the MW satellites, if they are of tidal origin.« less