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.

TerminologyIRX- infrared excess, log of the FUV to FIR

luminosity ratioSSFR- specific star formation rateCMD- color-magnitude diagramSEDs- Spectral energy distributions

BackgroundCoevolution 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 IRXMass-metallicity relation-low metallicity=low

extinction=low stellar mass=low star formation rate

Data SetsObservations 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

Data Sets-ProblemsGalex images have source confusionSolution- use positions from Combo-17 catalog

to deblend imagesSmall overlap in detected sources in all 3

catalogs and mostly only for high luminosity and high mass galaxies

Solution-stacking techniqueResults- range of stellar mass over 2 magnitudes and redshift range 0.05<z<1.2

Color-Magnitude Diagrams

Volume-corrected (MH, NUV-H)

Extinction-corrected

CMD TrendsShift to blues NUV-H color and brighter MH

IRX increases with H-band luminosityRedder 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 massEvolution-density of H-band luminous

galaxies increases with redshift

Mass-SSFR DistributionWeighted by SFR

Average IRX vs Stellar MassAvg IRX increases sharply with mass

till it hits a critical massCritical mass lower at low redshift

but moves to higher mass at higher redshift

Average IRX vs ZStar formation rate density moves to higher

masses at higher redshiftLeft figure- IRX weighted by star formation

rate

Average SSFR vs Stellar MassFor lower masses the average SSFR evolves

slowlyFor higher masses the average SSFR falls

rapidly with time

Testing ResultsUsing NUV or FUV to derive IRX and SFRStacking technique and MIPS24 detection

limitMissing objects in census i.e FIR-luminous

objectsInclination BiasUsed Monte Carlo to test IRX-mass

relationship- found not to be artifact of sample selection

None of the test above significantly effected results

ModelingEvolution 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 parametersMass range 9.5-11.5Mass-metallicity relation shifts toward higher

massesShow coevolution of average SSFR and IRXDefine Turnoff mass

Coevolution of average SSFR and IRX

SummaryIRX grows with stellar mass until saturates at

characteristic mass and fallsCharacteristic mass (CM) grows with redshiftSSFR is roughly constant up to CM then falls

steeplyFor certain mass below CM the IRX grows

with redshiftCM is “turnoff” mass indicating galaxies

moving off the blue sequenceMass-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 (10.5-11.5)

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

Any Questions?