The cosmic star formation history

沈世银

outline

• Cosmic Star formation history – UV luminosity function – Initial mass function – Dust extinction • Cosmic stellar mass density – Stars forming VS stars formed

Cosmic star formation history(SFH): Madau plot Madau 1998 Steidel 1999

Cosmic SFH to z=10

Bouwens et al. 2010 GALEX data z<2 Schiminovich 2005 Lyman break gals z~2~3 Reddy & Steidel 2009 B,V,i dropouts z~4,5,6 Bouwens 2009 WFC3/IR HST z,Y,J dropouts z~7,8,10 Bouwens 2010

z<2 z~5, i dropout z~2.5

z~8

Star formation rate(SFR) indicator

(Kennicutt 1998) • UV luminosity: SFR=1.4x10

-28

L v

(erg s -1 Hz) – Nearly flat in

L v

(1500-2800 Å) – Contributed by stars M> 5M ¯ – Dust: UV slope  , time scales of 10 8 year • Recombination lines: SFR=7.9x10

-42

L H

 (erg s -1 ) –

M

>10M ¯

t

<20Myr stars contribute to ionizing flux – Instantaneous measure of SFR – Dust: line ratio • forbidden lines: SFR=1.4x10

-41

L[OII]

(erg s -1 ) – to redshift z~1.6, calibrated by H  – Sensitive to abundance and the ionization state • Far-infrared Continuum: SFR=4.5x10

– Starburst: high dust opacity; within times cale for the dispersal of dust(10 8 yr) – Red gals: dust heating from the old stars -44

L v

(erg s -1 )

Other SFR indicators

• X-ray luminosity – High mass X-ray binaries • Radio luminosity – Supernova remnants – Correlated with far-infrared luminosity • UV + FIR

Key ingredients of SFR: IMF

Initial mass function(IMF) – Salpeter’s IMF •

dN/dM

/ M -2.35

– Kroupa(2001) IMF – Chabrier(2005) IMF

The choice of IMFs

• From Salpeter IMF to Kroupa IMF – decrease the SFR with a factor of 1.7

– also decrease the stellar mass of a similar factor, weekly depends on stellar age and SFH • From Kroup IMF to Chabrier IMF – Gives similar stellar mass, decrease the SFR of a factor of 1.8 • From Salpter IMF (0.1-100 M ¯ ) to Salpter IMF(0.1-125M ¯ ) – Also decrease the SFR with a factor of 1.7

– Does not change the K-band M/L

Key ingredients of SFR: dust extinction • SED fitting: model SED fold with reddening curve See Calzetti(1997) for the reddening curve of star-busts.

Dust extinction: IRX VS UV slope

 IRX=

L IR /L UV

f(  )=   Meurer, 1999 Bouwens 2009

: luminosity depends and redshift evolution Bouwens 2009 More dust in brighter galaxies Less dust at higher redshift

Dust: ULIRG

• Ultra luminous infrared galaxies(ULIRG) – Invisible in UV bands – Increase the SFR density ~20% at z~2.5 and ~10% at z~4 • Estimated from IR luminosity function

Key ingredients of Cosmic SFH:

UV luminosity function(LF) Reddy & Steidel 2009

UV LF: luminosity limit

L lim

• star formation density: LF integrated to

L Lim

–

L Lim

=0.3/0.04

L * z=3

M(1700)=-19.7/-17.5 mag • Halo evolution, luminosity evolution –

L Lim

=0, all, is it safe? dependent on  • Half the luminosity density below the detection limit (  =-1.7) • Integrated to constant number density (Papovich et al. 2010) – In the absence of mergers, the comoving number density is invariant with time • Accretion dominate over major merges in the growth of galaxies (Keres et al. 2009, Wang 2010)

SFH at high z(>2)

• Integrated to number density n=2 £ 10 -4 Mpc -3 – Rising SFH – If exponential increasing for indvidual gals • Ms=s SFR(t) dt • Constant specific SFR sSFR ~ const Papovich et al. 2010

Specific SFR of high z galaxies

Weak dependence of sSFR on redshift and stellar mass at z>4 Gonzalez et al. 2010

SFR



Gas mass



gas accretion

•From measured SFR to gas mass •Kenicutt law •size evolution, high z gals is smaller •High z gals are gas richer • gas accretion rate z>4: gas accretion phase

From halo mass



?

• SAM – Halo   SFR gas  stellar mass

SFR



stellar mass

rising SFH VS decaying SFH

Part II: Stars forming



stars formed

• Local stellar mass function – SDSS, 2df • Stellar mass sample at high redshifts – Color selected, e.g. DRG, ERO, Bzk, LBG – Infrared selection: Spitzer 3.6-4.5

 m • Photometric redshift – 35, UV selection sample, same as SFR sample

Stellar mass function

Perez-Gonzalez et al. 2008  ~1.2 at different z Caputi et al. 2010 Increased slope at higher redshifts Sample variance Photometric error

Cosmic stellar mass density

Infrared selected sample Caputi et al. 2010 UV selected sample Labbe et al. 2010

Self-consistence: SMD VS SFR integration Papovich et al. 2010 Gonzalez et al. 2010

Mismatch between SFR and SMD at high z • Some galaxies are properly missed in UV selected sample – Burst mode of SFH • Duty cycle of the high UV galaxies ~1 – Rising SFH of galaxies predict bluer H 160 -[3.6] color than observed (Labbe et al. 2010) – Halo Occupancy 0.2-0.4, star formation duty cycle=1 (Finlator et al. 2010) • Momentum driven outflow • Other systematic uncertainties, e.g. dust, IMF – From Salpter IMF to Kroupa IMF, the derived stellar mass decrease about a factor of 2

Self-consistence: SFR VS SMD differential Perez-Gonzalez et al. 2010 Bouwens et al. 2010

Mismatch between SFR and SMD at low z • SMD differential SFR is systematical lower – Chabrier IMF(z<2), top heavy at z>2 – Contradictory to high z results?

• SFR over-estimated at high z, e.g. AGN contain nation • 0

My idea

• Comprehensive self-consistence check of the SFR and SMD – IMF, sample selection, dust etc.

• Enhanced self-consistence check – SMD only constrains the number of stars formed in past, but not the way they formed – During the estimation of stellar mass, the information of the SFH is neglected.

– Can we use the cosmic stellar population at redshift z0 to constrain/compare the measured SFH at z>z0

Example: SDSS cosmic spectrum