The Local High-Redshift Dwarf Galaxies Evan Kirby UC Irvine Southern California Center for Galaxy Evolution credit: John Wise Dwarf galaxies come in two main types: dwarf spheroidals and dwarf irregulars dSphs ) ⊙ M / I H M ( dIrrs g o l log D (kpc) Grcevich & Putman 2009, ApJ, 696, 385 2/15 A catalog of multi-element abundances in dwarf galaxies MW dSph N Fornax 675 Leo I 827 Keck + DEIMOSdIrr N Sculptor 376 NGC 6822 282 Leo II 258 IC 1613 125 Sextans 141 VV 124 52 Draco 298 Pegasus 94 Canes Venatici I 174 Leo A 39 Ursa Minor 212 Leo T 18 Hercules 21 Total 610 Ursa Major I 28 Leo IV 12 Canes Venatici II 15 Plus, over 1000 stars Ursa Major II 9 in satellites of M31. Coma Berenices 18 Segue 2 25 Total 3089 EK et al. 2010-2013 Simon & Geha 2007, ApJ, 670, 313 3/15 Detailed abundances may be measured from R ≈ 7000 spectra. EK et al. 2009, ApJ, 705, 328 4/15 Galaxies obey a one-parameter mass-metallicity relationship. ñ ] H / e F [ á spectroscopic metallicities: Fe lines log (Ltot/L⊙) EK et al. 2008,2013b, ApJL, ApJ, 779,685, 102L43 EK et al. 2011a, ApJ, 727, 78 5/15 … Zahid et al. 2012, ApJL, 771, L19 771, ApJL, 2012, al. et Zahid 12 + log but the gas-phase mass-metallicity (O/H) Belli et al. 2013, ApJ, 722, 141 ApJ, 2013,al. et Belli 12 + log (O/H) Peeples & Somerville 2013, MNRAS, 428, 1766 428, 2013,MNRAS, Somerville & Peeples stellar [O/H] relation does log ( log ( M M M * ( * * M / / evolve! M M ⊙ ⊙ ⊙ ) ) ) 6 /15 The [α/Fe] ratio indicates the star formation timescale. ] e Type II F / Type Ia α [ Types II+Ia [Fe/H] Draco was terrible its job. at 〈[α/Fe]〉 [Ti/Fe] [Ca/Fe] [Si/Fe] [Mg/Fe] M Draco * = 3 × 10 5 [Fe/H] M ⊙ 8 /15 Sculptor was slightly better at its job. 〈[α/Fe]〉 [Ti/Fe] [Ca/Fe] [Si/Fe] [Mg/Fe] M Sculptor * = 2 × 10 6 [Fe/H] M ⊙ 9 /15 A numerical model describes the evolution of the elements. α SFR = A* (Mgas) -t/τ Mgas(t) = Mgas(0) + Ain t e – Aout (RIa + RII) – SFR Maoz et al. 2010, ApJ, 722, 1879 Nucleosynthetic yields: Type II SNe: Nomoto et al. 2006, NuPhA, 777, 424 Type Ia SNe: Iwamoto et al., 1996, ApJS, 125, 439 AGB stars: Karakas 2010, MNRAS, 403, 1413 10/15 EK et al. 2011b, ApJ, 727, 79 727,ApJ, 2011b, al. et EK [Ti/Fe] [Ca/Fe] [Si/Fe] [Mg/Fe] dN / d[Fe/H] Low- L [Fe/H] galaxies lost a lot of gas. [Mg/Fe] [X/H] SFR mass fin t (Gyr) 11 /15 Mid- EK et al. 2011b, ApJ, 727, 79 727,ApJ, 2011b, al. et EK [Ti/Fe] [Ca/Fe] [Si/Fe] [Mg/Fe] dN / d[Fe/H] L galaxies didn't lose quite so gas. much losequite didn't galaxies [Fe/H] [Mg/Fe] [X/H] SFR mass fin t (Gyr) 12 /15 EK et al. 2011b, ApJ, 727, 79 ApJ, 2011b, al. et EK The mass-metallicity relation is really a sequence of gas loss. [X/H]stellar log Mretained (M⊙) log Mejected (M⊙) log M * ( M ⊙ ) EK, Martin, & Finlator 2011d, ApJL, 742, L25 13 /15 –3 cumulative SF SFR (10 M⊙/yr) Weisz et al. 2011, ApJ, 739, 5 ApJ, 2011, al. et Weisz We haven't found dSphs at We –3 EK et al. 2011b, ApJ, 727,ApJ, 79 2011b, al. et EK SFR (10 M /yr) lookbacktime ⊙ (Gyr) t (Gyr) Belli et al. 2013, ApJ, 722, 141ApJ, 722, 2013, al. et Belli SFR (M⊙/yr) M * = 5 × 10 z ~ 2 … yet. Leo I 6 M ⊙ log M * ( M ⊙ ) 14 /15 Conclusions ● Nearly all galaxies in the local universe obey a universal stellar mass–stellar metallicity relation. ● Smaller dwarf galaxies are less efficient at turning gas into stars than larger galaxies. ● Gas and metal loss plague all dwarf 8 galaxies with M* < 10 M⊙. 15/15.