Multi-Element Abundance Measurements From Medium-Resolution Spectra. Iii. Metallicity Distributions of Milky Way Dwarf Satellite Galaxies

Abstract

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 to 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 ⊙ , 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.

Gravitational tides and dwarf spheroidal galaxies

“…16. The observed luminosities of the four classical dSphs considered are from ) and metallicity distributions from Helmi et al (2006), Battaglia et al (2011), Tolstoy et al (2004, and Battaglia et al (2006) for Carina, Sextans, Sculptor, and Fornax, respectively; luminosities and (mean) metallicity for the remaining, mostly, ultra-faint dSphs are from Kirby et al (2011b). The use of mean metallicity does not greatly affect the observed values, which are often well represented by only slightly skewed Gaussian curves.…”

New Spectroscopic Technique Based on Coaddition of Surface Brightness Fluctuations: NGC 4449 and Its Stellar Tidal Stream

“…More massive galaxies are more metal-rich than less massive ones. This sequence extends to the dwarf galaxy regime (Kirby et al 2008b(Kirby et al , 2011) and seems to be universal for quenched and star-forming galaxies (Gallazzi et al 2005;Kirby et al 2013). In the case of streams, this metallicity-luminosity relation can be used to constrain the total luminosity of the progenitor galaxy.…”

“…The two black squares indicate the Large and Small Magellanic Clouds (LMC, SMC; Carrera et al 2008aCarrera et al , 2008b. The black triangles indicate the Milky Way dSphs (Kirby et al 2011). The black dots indicate the M31 dSphs, dEs, and M32 (Collins et al 2013;Ho et al 2015).…”

“…Figure 8 shows the metallicity-luminosity relation for dwarf galaxies. We use as reference the average metallicity based on individual RGB stars for MW dSphs, M31 faint dSphs, and M31 bright dSphs, dEs, and M32 (Kirby et al 2011;Collins et al 2013;Ho et al 2015, respectively). We also include the average stellar metallicity values for the Large and Small Magellanic Clouds (LMC, SMC; Carrera et al 2008aCarrera et al , 2008b and the Sagittarius stream (Mateo 1998).…”

“…The choice between these techniques is based on the distance of the target galaxy and its surface brightness. Galaxies of low surface brightness within the Local Group, such as the satellites of the Milky Way (MW) and M31, are studied using resolved stars because their proximity and the brightness of their individual stars allow them to be targeted spectroscopically with the current telescopes and reasonable integration times (e.g., Geha et al 2006Geha et al , 2010Simon & Geha 2007;Kirby et al 2008aKirby et al , 2008bKirby et al , 2011Tollerud et al 2012;Collins et al 2013;Ho et al 2015;Simon et al 2015). Individual stars in galaxies outside the Local Group are too faint (  I 24 mag) to be targeted spectroscopically with current telescopes.…”