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

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

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 m R -24 and determining photometric redshifts

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

Color-Magnitude Diagrams Volume-corrected (M H, NUV-H)Extinction-corrected

CMD Trends Shift to blues NUV-H color and brighter M H IRX increases with H-band luminosity Redder galaxies have higher IRX for fixed M H 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

Mass-SSFR Distribution Weighted by SFR

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

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

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

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

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

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

Coevolution of average SSFR and IRX

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

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 ( ) Use IRX as a tool to select/distinguish galaxies, i.e. low IRX = galaxies in early stage evolution

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