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Published byBaldwin Gaines Modified over 8 years ago
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Dwarf Irregular Galaxies Models Marta Gavilán Mercedes Mollá Ángeles Díaz NGC 6822 DDO 187
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Dwarf Irregular Galaxies ● Low surface brightness m B > -23mag arcsec -2 ● Small radius: R < 5kpc ● Low mass: M < 10 10 Mo ● Large amount of gas ● Low Abundances: 12+log(O/H) ● Young population - Blue color SMC
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Looking for answers Evolution Models Chemical Abundances Gas Fraction Spectrophotometric Colors Mass-Luminosity Relation
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The Scenario: INFALL T col hh The gas fall rate is inversely to the time scale is the efficiency in forming molecular clouds h is the efficiency in forming stars Continuous Star Formation. There are not bursts. infall model
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The Model Photometry Spectroscopy G.C.E.M. INPUT OUTPUT Yields Efficiencies Time Scale SN Rates SFH Gas Abundances Synthesis PopulationModel Chemical Evolution Model: Ferrini et al. 1992 – Mollá & Díaz 2005 Synthesis Population Model Gª Vargas et al. (1998) Mollá et al. (2009) (submitted)
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Grid of Models Different masses Different infall rates (collapse time) Different efficiencies
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Data DWARF GALAXIES IN THE FIELD DDO 155 DDO 187 IC 1613 IC 4662 NGC 1559 NGC 2366 NGC 3109 NGC 4214 NGC 6822 LMC SMC AUTHORS Ferrara & Tolstoy (2000) Garnett (2002) Hunter & Elmegreen (2004) Karachentsev et al. (2004) Lee et al. (2003) Mallery et al. (2007) Sánchez-Almeida et al. (2008) Skillman et al. (1989) van Zee et al. (2000, 2006) DATA M B, (B-V), M HI, M*, M tot, 12+log(O/H), log(N/O)
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Medium-high Very low Low Medium High Very high Efficiencies color criterium Galaxy mass increases Scale factor? M6/M1 = 375 SFR 6 /SFR 1 =500 Star Formation History
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Gas fraction Lowest mass galaxy Highest mass galaxy M1 M2 M3 M4 M5 M6 Mass increases Models colors criterium
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Gas fraction gas+stars gas m=m= High infall - Max efficiency Medium infall - Low efficiency Intermediate case Problem: Mass-Luminosity relation
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Gas fraction IC 1613NGC 1569
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Nitrogen evolution
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Mallery et al. 2007 - GALEX UV – Star forming galaxies enriched gas outflow High (N/O) with low (O/H) values are not reached by our models...enriched gas outflow?
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Nitrogen evolution Data from van Zee et al. (2006)
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Nitrogen evolution
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Luminosity-Metallicity relation different evolutionary states? Data seem to follow the evolution lines, more than the final values...different evolutionary states? Correlation with mass
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Luminosity-Metallicity relation different evolutionary states? Data seem to follow the evolution lines, more than the final values...different evolutionary states? Correlation with mass
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Luminosity-Metallicity relation different evolutionary states? Data seem to follow the evolution lines, more than the final values...different evolutionary states? Correlation with mass
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Luminosity-Metallicity relation different evolutionary states? Data seem to follow the evolution lines, more than the final values...different evolutionary states? Correlation with mass
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SFR dIrr - Q-BCD Brown dots: Sánchez-Almeida et al. (2008) Quiescent BCD In low brightness range: models do not match data trend: Data: lower SFR for the same color than models. post-star burst situation?
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LMC Collase Time = 8 Gyr Efficiency: Low-Medium Age: 10 Gyr Collase Time = 20 Gyr Efficiency: Medium Age: 4 - 5 Gyr M=5 x 10 9 Mo
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NGC 1569 Collase Time = 8 Gyr Efficiency: Low-Medium Age: 7 - 9 Gyr Collase Time = 20 Gyr Efficiency: Medium Age: 2 - 4 Gyr M=5 x 10 9 Mo
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NGC 3109 Collase Time = 8 Gyr Efficiency: Low Age: 10 - 13 Gyr Collase Time = 8 Gyr Efficiency: Low - Medium Age: 4 - 6 Gyr M=5 x 10 9 Mo
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NGC 2366 Collase Time = 8 Gyr Efficiency: Low-Medium Age: 4 - 6 Gyr Collase Time = 8 Gyr Efficiency: Low - Medium Age: 4 - 6 Gyr M=10 9 MoM=5 x 10 9 Mo
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SUMMARY What can be explained with these models? Gas Fraction - Relation gas mass-stars mass-metallicity (N/O) abundances: Dispersion can be due to different SFH - efficiencies Luminosity-Metallicity relation: Data match with different evolutionary stages SFH and age: young objects
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