The Star Formation and Extinction Coevolution of UV-Selected Galaxies over 0.05
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Transcript of The Star Formation and Extinction Coevolution of UV-Selected Galaxies over 0.05
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?