LEO P: HOW MANY METALS CAN A VERY LOW MASS, ISOLATED GALAXY RETAIN?

Leo P is a gas-rich dwarf galaxy with an extremely low gas-phase oxygen abundance (3% solar). The isolated nature of Leo P enables a quantitative measurement of metals lost solely due to star formation feedback. We present an inventory of the oxygen atoms in Leo P based on the gas-phase oxygen abundance measurement, the star formation history (SFH), and the chemical enrichment evolution derived from resolved stellar populations. The SFH also provides the total amount of oxygen produced. Overall, Leo P has retained 5% of its oxygen; 25% of the retained oxygen is in the stars while 75% is in the gas phase. This is considerably lower than the 20%–25% calculated for massive galaxies, supporting the trend for less efficient metal retention for lower-mass galaxies. The retention fraction is higher than that calculated for other alpha elements (Mg, Si, Ca) in dSph Milky Way satellites of similar stellar mass and metallicity. Accounting only for the oxygen retained in stars, our results are consistent with those derived for the alpha elements in dSph galaxies. Thus, under the assumption that the dSph galaxies lost the bulk of their gas mass through an environmental process such as tidal stripping, the estimates of retained metal fractions represent underestimates by roughly a factor of four. Because of its isolation, Leo P provides an important datum for the fraction of metals lost as a function of galaxy mass due to star formation.

[1]  S. Warren,et al.  CARMA CO OBSERVATIONS OF THREE EXTREMELY METAL-POOR, STAR-FORMING GALAXIES , 2015, 1510.03518.

[2]  L. Girardi,et al.  LEO P: AN UNQUENCHED VERY LOW-MASS GALAXY , 2015, 1506.05495.

[3]  L. Girardi,et al.  New PARSEC evolutionary tracks of massive stars at low metallicity: testing canonical stellar evolution in nearby star-forming dwarf galaxies , 2014, 1410.1745.

[4]  Mauro Barbieri,et al.  Improving PARSEC models for very low mass stars , 2014, 1409.0322.

[5]  S. Warren,et al.  ALFALFA DISCOVERY OF THE NEARBY GAS-RICH DWARF GALAXY LEO P. V. NEUTRAL GAS DYNAMICS AND KINEMATICS , 2014, 1404.5298.

[6]  D. Weinberg,et al.  A BUDGET AND ACCOUNTING OF METALS AT z ∼ 0: RESULTS FROM THE COS-HALOS SURVEY , 2013, 1310.2253.

[7]  Judith G. Cohen,et al.  THE UNIVERSAL STELLAR MASS–STELLAR METALLICITY RELATION FOR DWARF GALAXIES , 2013, 1310.0814.

[8]  R. Giovanelli,et al.  ALFALFA DISCOVERY OF THE NEARBY GAS-RICH DWARF GALAXY LEO P. IV. DISTANCE MEASUREMENT FROM LBT OPTICAL IMAGING , 2013, 1310.0044.

[9]  A. Dolphin.  ON THE ESTIMATION OF RANDOM UNCERTAINTIES OF STAR FORMATION HISTORIES , 2013, 1308.1740.

[10]  R. Giovanelli,et al.  ALFALFA DISCOVERY OF THE NEARBY GAS-RICH DWARF GALAXY LEO P. I. H i OBSERVATIONS , 2013, 1305.0272.

[11]  R. Giovanelli,et al.  ALFALFA DISCOVERY OF THE NEARBY GAS-RICH DWARF GALAXY LEO P. II. OPTICAL IMAGING OBSERVATIONS , 2013, 1305.0270.

[12]  R. Giovanelli,et al.  ALFALFA DISCOVERY OF THE NEARBY GAS-RICH DWARF GALAXY LEO P. III. AN EXTREMELY METAL DEFICIENT GALAXY , 2013, 1305.0277.

[13]  A. Bolatto,et al.  The CO-to-H2 Conversion Factor , 2013, 1301.3498.

[14]  L. Kewley,et al.  A CENSUS OF OXYGEN IN STAR-FORMING GALAXIES: AN EMPIRICAL MODEL LINKING METALLICITIES, STAR FORMATION RATES, AND OUTFLOWS , 2012, 1207.5509.

[15]  Benjamin D. Johnson,et al.  DIRECT OXYGEN ABUNDANCES FOR LOW-LUMINOSITY LVL GALAXIES , 2012, 1205.6782.

[16]  J. Holtzman,et al.  OBSERVATIONAL CONSTRAINTS ON THE MOLECULAR GAS CONTENT IN NEARBY STARBURST DWARF GALAXIES , 2012, 1205.2732.

[17]  Alan W. McConnachie,et al.  THE OBSERVED PROPERTIES OF DWARF GALAXIES IN AND AROUND THE LOCAL GROUP , 2012, 1204.1562.

[18]  A. Dolphin.  ON THE ESTIMATION OF SYSTEMATIC UNCERTAINTIES OF STAR FORMATION HISTORIES , 2012, 1203.4634.

[19]  K. Finlator,et al.  METALS REMOVED BY OUTFLOWS FROM MILKY WAY DWARF SPHEROIDAL GALAXIES , 2011, 1110.5624.

[20]  R. Giovanelli,et al.  THE ARECIBO LEGACY FAST ALFA SURVEY: THE α.40 H i SOURCE CATALOG, ITS CHARACTERISTICS AND THEIR IMPACT ON THE DERIVATION OF THE H i MASS FUNCTION , 2011, 1109.0027.

[21]  Benjamin F. Williams,et al.  THE ACS NEARBY GALAXY SURVEY TREASURY. IX. CONSTRAINING ASYMPTOTIC GIANT BRANCH EVOLUTION WITH OLD METAL-POOR GALAXIES , 2010, 1009.4618.

[22]  B. Miller,et al.  CHEMICAL ABUNDANCES OF SEVEN IRREGULAR AND THREE TIDAL DWARF GALAXIES IN THE M81 GROUP , 2009, 0910.3162.

[23]  M. Asplund,et al.  The chemical composition of the Sun , 2009, 0909.0948.

[24]  E. Tolstoy,et al.  Star-Formation Histories, Abundances, and Kinematics of Dwarf Galaxies in the Local Group , 2009, 0904.4505.

[25]  B. Madore,et al.  THE STAR FORMATION EFFICIENCY IN NEARBY GALAXIES: MEASURING WHERE GAS FORMS STARS EFFECTIVELY , 2008, 0810.2556.

[26]  Belgium,et al.  Evolution of asymptotic giant branch stars. II. Optical to far-infrared isochrones with improved TP- , 2007, 0711.4922.

[27]  K. Nomoto,et al.  Nucleosynthesis yields of core-collapse supernovae and hypernovae, and galactic chemical evolution , 2006, astro-ph/0605725.

[28]  K. Venn,et al.  The Spatial Homogeneity of Nebular and Stellar Oxygen Abundances in the Local Group Dwarf Irregular Galaxy NGC 6822 , 2005, astro-ph/0512428.

[29]  E. al.,et al.  The Arecibo Legacy Fast ALFA Survey. I. Science Goals, Survey Design, and Strategy , 2005, astro-ph/0508301.

[30]  J. Brinkmann,et al.  The Origin of the Mass-Metallicity Relation: Insights from 53,000 Star-forming Galaxies in the Sloan Digital Sky Survey , 2004, astro-ph/0405537.

[31]  S. Cassisi,et al.  A Large Stellar Evolution Database for Population Synthesis Studies. I. Scaled Solar Models and Isochrones , 2004, astro-ph/0405193.

[32]  A. Dolphin.  Numerical methods of star formation history measurement and applications to seven dwarf spheroidals , 2001, astro-ph/0112331.

[33]  D. Garnett,et al.  Dust in I Zw 18 from Hubble Space Telescope Narrowband Imaging , 2001, astro-ph/0109558.

[34]  P. Kroupa.  On the variation of the initial mass function , 2000, astro-ph/0009005.

[35]  E. Tolstoy,et al.  The role of stellar feedback and dark matter in the evolution of dwarf galaxies , 1999, astro-ph/9905280.

[36]  D. Strickland,et al.  Multiple superbubbles in the starburst nucleus of NGC 5253? Implications for mass loss from dwarf galaxies , 1999, astro-ph/9902188.

[37]  A. Ferrara,et al.  Starburst-driven Mass Loss from Dwarf Galaxies: Efficiency and Metal Ejection , 1998, astro-ph/9801237.

[38]  E. Skillman,et al.  Elemental Abundance Variations and Chemical Enrichment from Massive Stars in Starbursts. II. NGC 1569 , 1996, astro-ph/9706235.

[39]  G. Tenorio-Tagle.  Interstellar Matter Hydrodynamics and the Dispersal and Mixing of Heavy Elements , 1996 .

[40]  R. Kennicutt,et al.  Past and Future Star Formation in Disk Galaxies , 1994 .

[41]  R. Kennicutt,et al.  Oxygen Abundances in Nearby Dwarf Irregular Galaxies , 1989 .

[42]  J. Silk,et al.  Dwarf galaxies, cold dark matter, and biased galaxy formation , 1986 .

[43]  R. Larson.  Effects of Supernovae on the Early Evolution of Galaxies , 1974 .

[44]  Submitted to ApJ Preprint typeset using L ATEX style emulateapj v. 10/09/06 THE KINEMATICS OF THE ULTRA-FAINT MILKY WAY SATELLITES: SOLVING THE MISSING SATELLITE PROBLEM , 2022 .