Where Are the Fossils of the First Galaxies? I. Local Volume Maps and Properties of the Undetected Dwarfs

Bovill, Mia Sauda; Ricotti, Massimo

doi:10.1088/0004-637x/741/1/17

Cited by 84 publications

(65 citation statements)

References 97 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Considering a plausible chemical composition of a first galaxy that may have survived to the present day, Frebel & Bromm (2012) thus argued that Segue 1 (together with Ursa Major II, Coma Berenices, Boötes I, and Leo IV) are candidate systems for such surviving first galaxies. Bovill & Ricotti (2011) agree that most of the ultra-faint dwarfs are consistent with expectations for reionization fossils, although they do not place Segue 1 in this category as a result of earlier estimates of its metallicity lying above the luminosity-metallicity relation established by brighter dwarfs. The metallicities derived in this paper and improved measurements of the L-Z relation by Kirby et al (2013) demonstrate that Segue 1 is in fact consistent with the extrapolated metallicity-luminosity relationship of more luminous systems.…”

Section: The Chemical Evolution Of Dwarf Galaxies and The Milky Waysupporting

confidence: 48%

Segue 1: An Unevolved Fossil Galaxy From the Early Universe

Frebel

Simon

Kirby

2014

ApJ

215

264

View full text Add to dashboard Cite

We present Magellan/MIKE and Keck/HIRES high-resolution spectra of six red giant stars in the dwarf galaxy Segue 1. Including one additional Segue 1 star observed by Norris et al., high-resolution spectra have now been obtained for every red giant in Segue 1. Remarkably, three of these seven stars have metallicities below [Fe/H] = −3.5, suggesting that Segue 1 is the least chemically evolved galaxy known. We confirm previous medium-resolution analyses demonstrating that Segue 1 stars span a metallicity range of more than 2 dex, from [Fe/H] = −1.4 to [Fe/H] = −3.8. All of the Segue 1 stars are α-enhanced, with [α/Fe] ∼ 0.5. High α-element abundances are typical for metal-poor stars, but in every previously studied galaxy [α/Fe] declines for more metalrich stars, which is typically interpreted as iron enrichment from supernova Ia. The absence of this signature in Segue 1 indicates that it was enriched exclusively by massive stars. Other light element abundance ratios in Segue 1, including carbon enhancement in the three most metal-poor stars, closely resemble those of metal-poor halo stars. Finally, we classify the most metal-rich star as a CH star given its large overabundances of carbon and s-process elements. The other six stars show remarkably low neutron-capture element abundances of [Sr/H] < −4.9 and [Ba/H] < −4.2, which are comparable to the lowest levels ever detected in halo stars. This suggests minimal neutron-capture enrichment, perhaps limited to a single r-process or weak s-process synthesizing event. Altogether, the chemical abundances of Segue 1 indicate no substantial chemical evolution, supporting the idea that it may be a surviving first galaxy that experienced only one burst of star formation.

show abstract

Section: The Chemical Evolution Of Dwarf Galaxies and The Milky Waysupporting

confidence: 48%

Segue 1: An Unevolved Fossil Galaxy From the Early Universe

Frebel

Simon

Kirby

2014

ApJ

215

264

View full text Add to dashboard Cite

show abstract

“…However, as noted in Bland-Hawthorn et al (2014, referred to as Paper I), the timescale for the evaporation of gas is long enough that the star-forming gas in the inner region is protected and can form stars while the gas in the outer regions evaporates. Recent simulations support this view, finding that at least some halos with masses ∼10 7 M can survive the epoch of reionization and continue forming stars (Bovill & Ricotti 2009;Ricotti 2009;Bovill & Ricotti 2011).…”

Section: Introductionmentioning

confidence: 94%

Ultrafaint Dwarfs—star Formation and Chemical Evolution in the Smallest Galaxies

Webster

Sutherland

Bland-Hawthorn

2014

ApJ

View full text Add to dashboard Cite

In earlier work, we showed that a dark matter halo with a virial mass of 10 7 M can retain a major part of its baryons in the face of the pre-ionization phase and supernova (SN) explosion from a 25 M star. Here, we expand on the results of that work, investigating the star formation and chemical evolution of the system beyond the first SN. In a galaxy with a mass M vir = 10 7 M , sufficient gas is retained by the potential for a second period of star formation to occur. The impact of a central explosion is found to be much stronger than that of an off-center explosion both in blowing out the gas and in enriching it, as in the off-center case most of the SN energy and metals escape into the intergalactic medium. We model the star formation and metallicity, given the assumption that stars form for 100, 200, 400, and 600 Myr, and discuss the results in the context of recent observations of very low-mass galaxies. We show that we can account for most features of the observed relationship between [α/Fe] and [Fe/H] in ultra-faint dwarf galaxies with the assumption that the systems formed at a low mass, rather than being remnants of much larger systems.

show abstract

“…These differences are likely due to variations in infall times and environmental processing effects on MW satellite galaxies (e.g., Łokas et al 2012;Rocha et al 2012;Kazantzidis et al 2013). However, others have suggested that reionization can play an increasingly important role in the quenching of star formation in the lowest mass galaxies (e.g., Bullock et al 2000;Ricotti & Gnedin 2005;Bovill & Ricotti 2011aBrown et al 2012;Okamoto et al 2012). We will discuss the topics of reionization (Weisz et al 2014a) and quenching in LG dwarfs in future papers in this series.…”

Section: Trends In Star Formation History As a Function Of Galaxy Stementioning

confidence: 99%

THE STAR FORMATION HISTORIES OF LOCAL GROUP DWARF GALAXIES. I.HUBBLE SPACE TELESCOPE/WIDE FIELD PLANETARY CAMERA 2 OBSERVATIONS

Weisz¹,

Dolphin²,

Skillman³

et al. 2014

ApJ

471

561

View full text Add to dashboard Cite

We present uniformly measured star formation histories (SFHs) of 40 Local Group (LG) dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with τ ∼ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs, and dwarf ellipticals can be approximated by the combination of an exponentially declining SFH (τ ∼ 3-4 Gyr) for lookback ages >10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z = 2 ranges considerably (80% for galaxies with M < 10 5 M to 30% for galaxies with M > 10 7 M ) and is largely explained by environment; (5) the distinction between "ultra-faint" and "classical" dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z = 2 than the Sloan Digital Sky Survey galaxies from Leitner and the SFHs from the abundance matching models of Behroozi et al. This may indicate higher than expected star formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community.

show abstract

Where Are the Fossils of the First Galaxies? I. Local Volume Maps and Properties of the Undetected Dwarfs

Cited by 84 publications

References 97 publications

Segue 1: An Unevolved Fossil Galaxy From the Early Universe

Segue 1: An Unevolved Fossil Galaxy From the Early Universe

Ultrafaint Dwarfs—star Formation and Chemical Evolution in the Smallest Galaxies

THE STAR FORMATION HISTORIES OF LOCAL GROUP DWARF GALAXIES. I.HUBBLE SPACE TELESCOPE/WIDE FIELD PLANETARY CAMERA 2 OBSERVATIONS

Contact Info

Product

Resources

About