The First Generation of Stars: First Steps toward Chemical Evolution of Galaxies

Audouze, J.; Silk, Joseph

doi:10.1086/309687

Cited by 150 publications

(156 citation statements)

References 17 publications

(11 reference statements)

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“…Despite repeated efforts to find galaxies more metal poor (e.g., Terlevich et al 1991;Izotov et al 1999; Kunth and Östlin 2000) the 1 % lower limit metallicity remains today Kunth and Lebouteiller 2011). Several explanations have been put forward to account for this minimum metallicity: the self-enrichment of the HII region used for measuring (Kunth and Sargent 1986), the metal abundance of the proto-galactic cloud (Kunth and Lebouteiller 2011), the metallicity threshold set by the ejecta from population III stars (Audouze and Silk 1995;Thuan and Izotov 2005), technical difficulties for metallicity determinations below a threshold (Papaderos et al 2008), and others. None of them seem to be fully compelling.…”

Section: Metallicity Inhomogeneities and Inverted Gradientsmentioning

confidence: 99%

Star formation sustained by gas accretion

Alméida

Elmegreen

Muñoz–Tuñón

et al. 2014

Astron Astrophys Rev

178

130

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Numerical simulations predict that metal-poor gas accretion from the cosmic web fuels the formation of disk galaxies. This paper discusses how cosmic gas accretion controls star formation, and summarizes the physical properties expected for the cosmic gas accreted by galaxies. The paper also collects observational evidence for gas accretion sustaining star formation. It reviews evidence inferred from neutral and ionized hydrogen, as well as from stars. A number of properties characterizing large samples of star-forming galaxies can be explained by metal-poor gas accretion, in particular, the relationship among stellar mass, metallicity, and star-formation rate (the so-called fundamental metallicity relationship). They are put forward and analyzed. Theory predicts gas accretion to be particularly important at high redshift, so indications based on distant objects are reviewed, including the global star-formation history of the universe, and the gas around galaxies as inferred from absorption features in the spectra of background sources.

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Section: Metallicity Inhomogeneities and Inverted Gradientsmentioning

confidence: 99%

Star formation sustained by gas accretion

Alméida

Elmegreen

Muñoz–Tuñón

et al. 2014

Astron Astrophys Rev

178

130

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“…According to the claim based on the analysis of elemental abundance patterns of EMP stars (McWilliam et al 1996;Ryan et al 1996;Audouze & Silk 1995;Shigeyama & Tsujimoto 1998; …”

Section: Comparison With the Observed C/omentioning

confidence: 99%

“…Their metallicity ranges are approximately −4 < [Fe/H] < −2.5 and −3 < [Fe/H] < −2, respectively. Several theoretical works claim that the abundances of EMP stars retain the nucleosynthesis yields of individual type II supernovae (SNe II) (Audouze & Silk 1995;Shigeyama & Tsujimoto 1998;Nakamura et al 1999;Umeda & Nomoto 2002). In contrast, DLAs represent the abundances of the interstellar medium (ISM) integrated along the line of sight, which is equivalent to an average of all the mass of SNe II weighted with an initial mass function (IMF).…”

Section: Introductionmentioning

confidence: 99%

Implications of a non-universal IMF from C, N, and O abundances in very metal-poor Galactic stars and damped Lyαabsorbers

Tsujimoto

Bekki

2011

A&A

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Recently revealed C, N, and O abundances in the most metal-poor damped Lyα (DLA) absorbers are compared with those of extremely metal-poor stars in the Galactic halo, as well as extragalactic H II regions, to decipher nucleosynthesis and chemical enrichment in the early Universe. These comparisons surprisingly identify a relatively high C/O ratio and a low N/O ratio in DLA systems, which is hard to explain theoretically. We propose that if these features are confirmed by future studies, this effect occurs because the initial mass function in metal-poor DLA systems has a cut-off at the upper mass end at around 20-25 M , thus lacks the massive stars that provide the nucleosynthesis products leading to the low C/O and high N/O ratios. This finding is a reasonable explanation of the nature of DLA systems in which a sufficient amount of cold H I gas remains intact because of the suppression of ionization by massive stars. In addition, our claim strongly supports a high production rate of N in very massive stars, which might be acceptable in light of the recent nucleosynthesis calculations with fast rotation models. The updates of both abundance data and nucleosynthesis results will strengthen our novel proposition that the C/O and N/O abundances are a powerful tool for inferring the form of the initial mass function.

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“…Abundance analyses of the most metal-poor stars in the halo (½Fe=H < À2:5) reveal that the early chemical enrichment of the Galaxy was largely stochastic (McWilliam 1998;McWilliam et al 1995aMcWilliam et al , 1995bRyan et al 1996). These stars probably form from clouds polluted by a single or a few SNe (Audouze & Silk 1995;Tsujimoto, Shigeyama, & Yoshii 1999). Thus, the early chemical evolution of starforming regions within the proto-Galaxy was dominated by stochastic processes.…”

Section: Abundances and Metallicitymentioning

confidence: 99%

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Stephens

Boesgaard

2002

The Astronomical Journal

145

182

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There are stars in the halo of the Galaxy whose orbital properties are distinctly different from the majority of the halo population. One suggestion to account for these kinematically peculiar stars is that they have been gravitationally subsumed by the Milky Way through the breakup of nearby dwarf galaxies. One test of this hypothesis lies in determining the chemical composition of the deviant halo stars relative to that of normal ('' native '') halo field stars. The possibly accreted stars are predicted to have different chemical enrichments due to a slower rate of star formation in nearby low-mass spheroidal or irregular galaxies. We have obtained echelle spectra of metal-poor halo dwarfs with unusual orbital properties: from the outer halo, from the '' high '' halo, and on retrograde orbits. Our spectra are at high spectral resolution (35,000-48,000) and high signal-to-noise ratios (median value 140), primarily from the Keck I 10 m telescope with HIRES (53 stars), but also from the echelle spectrometer of the KPNO Mayall 4 m Telescope (three stars). The spectra cover a large spectral range: $4000-6800 Å . The strengths of approximately 9000 lines have been measured to determine the stellar parameters (T eff , log g, [Fe/H], and ) and the abundances of 10 elements, including Na, -fusion products (Mg, Si, Ca, Ti), iron peak elements (Cr, Fe, Ni), and neutron capture elements (Y, Ba). A model atmosphere was computed for each star, which was used to determine the composition under the assumption of LTE. The comparison of the abundances with the kinematic properties revealed no special trends, except that the ratio of the mean of the -fusion elements to Fe is weakly correlated with stellar apogalactica in the sense that the outermost stars have lower ratios of [ /Fe] than those with smaller apogalactica. The hallmark of an accreted halo star is presumed to be a deficiency (compared with normal stars) of the -elements (e.g., O, Mg, Si, Ca, Ti) with respect to Fe, a consequence of sporadic bursts of star formation within the dwarf galaxies. However [Fe/H]. The kinematically peculiar stars in our sample must have had their origins in localized star-forming regions far removed from the Galactic center. They do not carry the chemical signature of an accreted population. It seems clear that the chemical enrichment in our sample comes primarily from Type II supernovae with only a small component from Type Ia supernovae. Our stars would have formed at most $1 Gyr after the beginning of a star formation episode in the remote halo. The general conclusion extracted from these data is that the formation of the nascent Milky Way was not dominated by the late accretion of dwarf galaxies like the ones that currently orbit the Galaxy. However, the assimilation of fragments early in the evolution of the Galaxy is a natural by-product of hierarchical models of structure formation and can explain many properties of the halo population.

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The First Generation of Stars: First Steps toward Chemical Evolution of Galaxies

Cited by 150 publications

References 17 publications

Star formation sustained by gas accretion

Star formation sustained by gas accretion

Implications of a non-universal IMF from C, N, and O abundances in very metal-poor Galactic stars and damped Lyαabsorbers

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

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