SFR and COSMOS

Bahram Mobasher

+ the COSMOS Team

COSMOS offers:

• Extensive multi-waveband surveys from radio to X-ray

• Large area coverage ( 2 sq. deg.) • HST/ACS morphologies (B/D, Sersic,

concentration, asymmetry, clumpiness)• Accurate photometric/spectroscopic redshifts and

spectral types (from early-type to starburst)• Galaxy masses

How COSMOS can help to understand:

Physics of star fromation activity

Nature of star forming galaxies

Main parameters affecting the SFR

Star Formation Rate

• How different star formation diagnostics are compared ?

• What is the role of galaxy mergers on SF activity ?• How the SFR changes with redshift for different

morphologies of galaxies ?• Are dusty galaxies more actively star forming ?• How SFR depends on galaxy environment ?

Low-zQ1: How are Different SF Diagnostics Compared ?

UV (GALEX); U (CFHT); H(VLT); IRAC (Spitzer); MIPS(Spitzer); radio (VLA)

UV Luminosity (GALEX)

• Produced by young massive stars

• Is directly proportional to SFR

• Highly affected by dust extinction

• Old population also contribute to the UV flux

H Line (VLT/VIMOS)

• Emission line produced by star-forming regions

• Less affected by dust extinction

• Can be used at high redshifts

• Is directly correlated to SF activity

Mid/Far-IR Luminosity (IRAC/MIPS)

• FIR radiation is produced by absorption and re-emission of the UV light by dust

• Mid-IR emission is produced by PAH features

• Far-IR surveys provide an easy way to select unbiased samples of SF galaxies

• Need to calibrate PAH features as a measure of SFR

Radio Luminosity (VLA)

• Produced by synchrotron radiation generated by electrons from Type II SNe

• Indirectly is proportional to SFR

• Not affected by dust extinction

Q2: How the SFR is Affected by Galaxy Interaction/mergers ?

Q3: How does this change in different environments and with

redshift?

Concentration

• Most z<=1 optically selected starbursts have concentration indices which are significantly smaller than most early types

• C>0.3 : 12 % SB, 18% Late, 73% E/Sa

• Komogorov-Smirnov ( K-S) test

- SB vs Early type : 7e-7 (> 99.9%)- SB vs Late-type : 0.53

• Large C & galfit Sersic n=3-4 correlate

AGN fraction : CDF-S X-ray catalog : 2% of SB host AGN vs >25% of Early types

Asymmetry in rest frame B

• 55 % of z<=1 optically selected starbursts have high AB (>0.3) compared to lower fractions in late (20% ) and early (12%).

• K-S test on AB

- SB vs Early type : 1e-10 - SB vs Late-type : 3e-4

AB

Large AB : highly asymmetric distribution of massive SF (no m=2 symmetry)

- Externally triggered : tidal interactions, mergers

Q4: How Disk-Size Relation changes with environment and

redshift ?

Ravindranath et al. 2003

–Sersic indices n<2–Rest-frame MB <-19.5–Photometric redshifts

Disk galaxy evolution from GOODSRavindranath et al. 2003

Tendency for smaller sizes at z~1 (30% smaller) after correcting for measurement bias

Number-densities are

relatively constant to z~1

Intermediate Redshift:

Q5: How the Total SFRs Change with Redshift ?

Q6: How the SFR for Different Types of Galaxies change with

Redshift ?

Rest-frame 2800 A:

U: 0.30 < z < 0.42B: 0.52 < z < 0.68V: 0.88 < z < 1.04R: 1.13 < z < 1.37 I: 1.62 < z < 1.87z: 2.11 < z < 2.33

COSMOS-GOODS-GALEX

Q7: What is the Effect of Environment on the SFR ?

Q8: How the Environmental Effect Change with Redshift ?

Median SFRs: 0.71 (F) 0.76 (C)0.30 < z < 0.42

Median SFRs: 0.84 (F) 0.95 (C) 0.52 < z < 0.68

Median SFRs: 2.45 (F) 2.75 (C)0.88 < z < 1.04

SFR in Different Environments

Field LSS

Msun/yr

0.3 < z < 0.42 0.71 0.75

0.52 < z < 0.68 0.84 0.94

0.88 < z < 1.04 2.49 2.78

Q9: What is the LF of Star-forming Galaxies ?

Q10: How the LF for Star-forming Galaxies Change with

Redshift ?

Q11: What is the Type-dependence of the LF ?

LF Parameters for =-1.2 M*2800

0.30 < z < 0.42 -18.290.52 < z < 0.68 -18.96 0.88 < z < 1.04 –19.18 1.13 < z < 1.37 –19.31 1.62 < z < 1.87 –20.062.11 < z < 2.33 –20.38

Type-dependent 2800 A LF parameters

M* (2800A)

Total -18.96 -1.20

Early-type -19.19 -1.12

Late-Type -18.78 -0.95

Starburst -18.71 -1.55

High-z

Q12: What is the SFR and Stellar Mass Associated with LBGs and

LAEs at 4.5 < z < 6.5 ?

rest-optical & -IR at z=5.8

• SST IRAC detections of z~6 galaxies=> stellar population & dust fitting possible

Dickinson et al in prep

ch1, 3.6mrest=5300A

ch2, 4.5mrest=6600A

LBG at z=5.83Bviz (ACS) JHK (ISAAC) IRAC

LAE at z=5.7Bviz (ACS) JHK (ISAAC) IRAC

LAE LBG

z 5.7 (6.2) 5.8

E(B-V) 0.2 0.1

Age (Gyr) 0.005 1.0 (Gyr) 0.2 0.8

Metallicity 0.05 0.008

Mass (Msun/yr) 1 x 1010 2.4 x 1010

Log (Lbol) 11.9 11.3

SF Working Group

• What can we do with the available data now?

• What data we need ?

• What we plan to do with the up-coming data (ie Ha, Spitzer) ?

The available data:

UV, U-band, BVRiz, radio, phot-z’s, spectral types, mass, LSS

identification, rest-frame 2800A

Future useful data:

Near-IR spectroscopy, sub-mm data

Up-coming data:

H, Spitzer

SFR- Outstanding Questions:

• How different star formation diagnostics are compared ?

• What is the role of galaxy mergers on SF activity ?• How the SFR changes with redshift for different

morphologies of galaxies ?• Are dusty galaxies more actively star forming ?• How SFR depends on galaxy environment ?• What is the relation between the mass of galaxies

and their SFRs ? How does this depend on the environment/redshift/morphology ?

Continued…

• How the LF and correlation function of SF galaxies change with redshift/morphology ?

• What regulates the SFR for LBGs and LAEs ? ( mass ? Size? Morphology?). How different are these in terms of their SF activity ?

• Extension of SFR vs. redshift relation to z~7, using narrow-band and LBG surveys.

• Type-dependence of the SFR vs. z relation• How different is the SFR in filamentary structures

compared to clusters or isolated fields ? How does this change with morphology ?

Continued…

• Could the MIPS data be used to measure SFR (from PAH) at z~2 ? 82% of the SF galaxies in GOODS-N have MIPS detection.

• How effectively we could use Paschen lines to measure dust-free SFR ? Would IRS be useful ?

• Evolution of SFR-mass relation • Cross correlation between SFR and mass maps