Transcript Teresa Ashcraft

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 mR -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 (MH, NUV-H)
Extinction-corrected
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
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
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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
Coevolution of average SSFR
and IRX
Summary
 IRX grows with stellar mass until saturates at
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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 (10.5-11.5)
 Use IRX as a tool to select/distinguish galaxies, i.e. low
IRX = galaxies in early stage evolution
Any Questions?