Metallicity Distribution Functions of Four Local Group dwarf galaxies

Abstract

We present stellar metallicities in Leo I, Leo II, IC 1613, and Phoenix dwarf galaxies derived from medium (F390M) and broad (F555W, F814W) band photometry using the Wide Field Camera 3 (WFC3) instrument aboard the Hubble Space Telescope. We measured metallicity distribution functions (MDFs) in two ways, 1) matching stars to isochrones in color-color diagrams, and 2) solving for the best linear combination of synthetic populations to match the observed color-color diagram. The synthetic technique reduces the effect of photometric scatter, and produces MDFs 30-50 % narrower than the MDFs produced from individually matched stars. We fit the synthetic and individual MDFs to analytical chemical evolution models (CEM) to quantify the enrichment and the effect of gas flows within the galaxies. Additionally, we measure stellar metallicity gradients in Leo I and II. For IC 1613 and Phoenix our data do not have the radial extent to confirm a metallicity gradient for either galaxy. We find the MDF of Leo I (dwarf spheroidal) to be very peaked with a steep metal rich cutoff and an extended metal poor tail, while Leo II (dwarf spheroidal), Phoenix (dwarf transition) and IC 1613 (dwarf irregular) have wider, less peaked MDFs than Leo I. A simple CEM is not the best fit for any of our galaxies, therefore we also fit the `Best Accretion Model' of Lynden-Bell 1975. For Leo II, IC 1613 and Phoenix we find similar accretion parameters for the CEM, even though they all have different effective yields, masses, star formation histories and morphologies. We suggest that the dynamical history of a galaxy is reflected in the MDF, where broad MDFs are seen in galaxies that have chemically evolved in relative isolation and narrowly peaked MDFs are seen in galaxies that have experienced more complicated dynamical interactions concurrent with their chemical evolution.

15 pages, 8 figures, accepted in AJ

References in corpus (22)

• The Dartmouth Stellar Evolution Database
• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• The Tidal Evolution of Local Group Dwarf Spheroidals
• The DART imaging and CaT survey of the Fornax Dwarf Spheroidal Galaxy
• The Velocity Dispersion Profile of the Remote Dwarf Spheroidal Galaxy Leo I: A Tidal Hit and Run?
• Multi-Element Abundance Measurements from Medium-Resolution Spectra. IV. Alpha Element Distributions in Milky Way Dwarf Satellite Galaxies
• The Dearth of Neutral Hydrogen in Galactic Dwarf Spheroidal Galaxies
• The Space Motion of Leo I: Hubble Space Telescope Proper Motion and Implied Orbit
• Stellar kinematics in the remote Leo II dwarf spheroidal galaxy -- Another brick in the wall
• VLT/FLAMES spectroscopy of red giant branch stars in the Fornax dwarf spheroidal galaxy
• Star formation feedback and metal enrichment by SN Ia and SN II in dwarf spheroidal galaxies: the case of Draco
• The ACS LCID project. X. The Star Formation History of IC 1613: Revisiting the Over-Cooling Problem
• Complexity on Small Scales II: Metallicities and Ages in the Leo II Dwarf Spheroidal Galaxy
• The Chemical Evolution of Dwarf Spheroidal Galaxies: Dissecting the Inner Regions and their Stellar Populations
• The metallicity distribution of the halo and the satellites of the Milky way in the hierarchical merging paradigm
• Chemical Abundances of the Leo II Dwarf Galaxy
• The Chemical Abundances of the Stellar Populations in the Leo I and Leo II dSph Galaxies
• Stellar Content and Recent Star Formation History of the Local Group Dwarf Irregular Galaxy IC1613
• The evolved stars of Leo II dSph galaxy from near-infrared UKIRT/WFCAM observations
• A Wide-Field View of Leo II -- A Structural Analysis Using the SDSS
• Wide-field Survey around Local Group Dwarf Spheroidal Galaxy Leo II: Spatial Distribution of Stellar Content
• The RR Lyrae Variable Population in the Phoenix Dwarf Galaxy

Cited by in corpus (6)

• Observational properties of massive black hole binary progenitors
• Spectroscopic evolution of massive stars near the main sequence at low metallicity
• From K giants to G dwarfs: stellar lifetime effects on metallicity distributions derived from red giants
• Metallicity distribution of the progenitor of the Giant Stellar Stream in the Andromeda Galaxy
• The Local Ultraviolet to Infrared Treasury I. Survey Overview of the Broadband Imaging
• A machine-learning photometric classifier for massive stars in nearby galaxies II. The catalog