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The Star Formation and Extinction Coevolution of UV-Selected Galaxies over 0.05 <  z  < 1.2

The Star Formation and Extinction Coevolution of UV-Selected Galaxies over 0.05 <  z  < 1.2. Martin et al. Goal-determine the evolution of the IRX and extinction and relate to evolution of star formation rate as a function of stellar mass. Terminology.

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The Star Formation and Extinction Coevolution of UV-Selected Galaxies over 0.05 <  z  < 1.2

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  1. The Star Formation and Extinction Coevolution of UV-Selected Galaxies over 0.05 < z < 1.2 Martin et al. Goal-determine the evolution of the IRX and extinction and relate to evolution of star formation rate as a function of stellar mass.

  2. Terminology • IRX- infrared excess, log of the FUV to FIR luminosity ratio • SSFR- specific star formation rate • CMD- color-magnitude diagram • SEDs- Spectral energy distributions

  3. Background • Coevolution of extinction and star formation rate - as gas is processed in stars one expects to see an increase in extinction - galaxies exhaust gas supply expect to see correlating drop in extinction • Stellar mass related to timescale of evolution -relate to extinction and star formation rate and IRX • Relationship between metallicity and IRX • Mass-metallicity relation-low metallicity=low extinction=low stellar mass=low star formation rate

  4. Data Sets • Observations of Chandra Deep Field-South- looking at UV-selected galaxies trying to get large mass and redshift range • GALEX- NUV and FUV/ Largest FOV/ SFR • Spitzer- MIPS24 for dust luminosity and four IRAC channels – measure stellar mass • COMBO-17- used for object classification to mR-24 and determining photometric redshifts

  5. Data Sets-Problems • Galex images have source confusion • Solution- use positions from Combo-17 catalog to deblend images • Small overlap in detected sources in all 3 catalogs and mostly only for high luminosity and high mass galaxies • Solution-stacking technique • Results- range of stellar mass over 2 magnitudes and redshift range 0.05<z<1.2

  6. Color-Magnitude Diagrams Volume-corrected (MH, NUV-H) Extinction-corrected

  7. CMD Trends • Shift to blues NUV-H color and brighter MH • IRX increases with H-band luminosity • Redder galaxies have higher IRX for fixed MH • Blue sequence tilt in CMD produced from extinction-luminosity relation • Tighter distribution when apply extinction correction • Strong increase in IRX with stellar mass • Evolution-density of H-band luminous galaxies increases with redshift

  8. Mass-SSFR Distribution Weighted by SFR

  9. Average IRX vs Stellar Mass • Avg IRX increases sharply with mass till it hits a critical mass • Critical mass lower at low redshift but moves to higher mass at higher redshift

  10. Average IRX vs Z • Star formation rate density moves to higher masses at higher redshift • Left figure- IRX weighted by star formation rate

  11. Average SSFR vs Stellar Mass • For lower masses the average SSFR evolves slowly • For higher masses the average SSFR falls rapidly with time

  12. Testing Results • Using NUV or FUV to derive IRX and SFR • Stacking technique and MIPS24 detection limit • Missing objects in census i.e FIR-luminous objects • Inclination Bias • Used Monte Carlo to test IRX-mass relationship- found not to be artifact of sample selection • None of the test above significantly effected results

  13. Modeling • Evolution of IRX and SSFR modeled using simple exponential star formation histories and closed-box chemical evolution to z-1

  14. Modeling Cont. • Fit average IRX and SSFR versus mass and redshift with 5 parameters • Mass range 9.5-11.5 • Mass-metallicity relation shifts toward higher masses • Show coevolution of average SSFR and IRX • Define Turnoff mass

  15. Coevolution of average SSFR and IRX

  16. Summary • IRX grows with stellar mass until saturates at characteristic mass and falls • Characteristic mass (CM) grows with redshift • SSFR is roughly constant up to CM then falls steeply • For certain mass below CM the IRX grows with redshift • CM is “turnoff” mass indicating galaxies moving off the blue sequence • Mass-IRX relationship is influenced by gas exhaustion above the turnoff mass

  17. Summary Cont. • Use simple gas-exhaustion model for mass and evolutionary trend of the IRX and SSFR - IRX found from gas surface density and metallicity - metallicity grows with time - SFR determined by exponentially falling gas density • The rise in the SFR density to z=1 is due to Galaxies in the mass range of the turnoff mass (10.5-11.5) • Use IRX as a tool to select/distinguish galaxies, i.e. low IRX = galaxies in early stage evolution

  18. Any Questions?

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