The Star Formation History of the Universe · 2010. 5. 7. · Chary: NOAO/NSO 50th Anniversary 1/40...

Chary: NOAO/NSO 50th Anniversary 1/40

The Star Formation History of the Universe

Star-formation History:<1960 : 7 (*) papers1960-2010 : 3300 papers

General Relativity: <1960: 4001960-2010: 19000

Ranga

Ram CharySpitzer/Planck/IPAC

California Institute of Technology

x400

x40


How do galaxies evolve from the 1 kpc

irregularblobs to the structure we see today ?

Candidate z~10 galaxies (Bouwens

et al. 2010)


Extragalactic Background Light ConstraintsUV estimates of SFRIR estimates of SFRSpitzer Measured Stellar Mass DensitiesGamma-ray Bursts

•We’d like to know what the ongoing star-formation rate in galaxies is;

dust unobscured and obscured•We’d like to measure the integral of the past history of star-

formation;cross consistency depends on the stellar IMF

•We’d like to know how metallicity

evolves in galaxiescross consistency with stellar mass estimates


Extragalactic Background Light =Total Line of Sight Brightness –

Stars –

Zodiacal Light –

Interstellar Medium

Integrated Galaxy Light =Sum over light from all individually detected galaxies

IGL =< EBL


CGRB

Blazars

300μm 3μm 300nm 0.4keV 40keV 4MeV 400MeV

Hasinger

‘00


2.2 micron contributions

74%

14%

12% 0%

Zodiacal LightStarsCIRBISM

140 micron contributions

37%

27% 36%

Zodiacal LightCIRBISM

Unfortunately Sky Background at Infrared Wavelengths is Dominated By Zodiacal Light

CIRB (nW

m-2

sr-1)λ νIν

2.2: 22.4±6.03.5: 11.0±3.3140: 25±7240: 14±3


2.6’

5.8μm25 hrs

24μm10.9 hrs

3.6μm25 hrs


EBL Constraints

RC&Pope2010


Results from the EBL

•

EBL is hard to measure and is known to poor precision

•

Equal components of optical+NIR

and FIR EBL → Dust reprocessing is important

•

IGL is lower than EBL at 1.2, 2.2, 3.6 and 60 microns → Diffuse source of radiation like cometary

dust or reionization

epoch galaxies ?


Lyman break technique to identify star-forming galaxies

Vanzella

et al. 2007


Hard to do spectroscopy of dusty sources


But there is dust in different phases

Jason Marshall andIRS GTO Team


Caputi

et al. 2007,Perez-Gonzalez et al. 2004Le Floch

et al., CE01, Franceschini

et al. 02Magnelli

et al. 2009

But phot-z

errors at z>1.4 are notoriousbecause σ(Δz/1+z)~0.03⇒σ(LIR)~3

Strong Evolution of LIRG and ULIRG population between z~0 and 1


RC&Pope2010


Cosmic Evolution of Extinction


If UV slope were correct, EBL limits would be violated


Option 1: Dust extinction in many z~4 galaxies is more consistent with SMC extinction law

H. Shim et al 2010


Stars only

Nebular only

Stars+Nebular

Black line is for 1 Myr

old populationRed line is for 10 Myr

old populationCourtesy of Starburst99Leitherer

et al. 1999

Option 2: Nebular emission makes UV slopes redder

Top heavy IMF increases nebular emission


Can we reliably understand the nature of galaxies dominating the SF ?


?

Needs more data for confirmationDefinitely resolved by Herschel.LIRGs

are lower mass, ULIRGs

are higher mass


Even for objects with spec-z, some violate upper limits or FIR photometry

Evidence for AGN ?

E. Murphy et al. 2009

Intriguingly, this happens at LIR>3E12 Lwhich is the most extreme source in the local Universe


JD2: A z~2 LIRG. NOT a 6E11 M z~6.5 galaxy.

Are We Missing the z~2-3 LIRGs

?


Sensitivity of Different Wavelengths to Dust Obscured Star- Formation

Mid-Infrared wavelengths are the most sensitive and least affected by confusion.However, requires large bolometric corrections.


There are some nightmare sources!

SBS 0335−0521/40 ZHouck et al. 2004


Wilkins et al. 2008Hopkins & Beacom

2006

An Evolving IMF at z<3 ?


Reddy & Steidel

2009

Not so fast…..

Systematics

from: 1. Proper treatment of stellar

Remnants2. Integrating down the LF3. Dust corrections at z>2


Results on SF History

•

Dust reprocessing well understood at z<1•

Some constraints on z>1 from 24 microns

•

Dusty SFR >> Unobscured

SF @ z<2•

At z>2 UV slope is x2 overestimate of obscuration–

Probably because dust is grey

•

No significant discrepancy with stellar mass density → no evolving IMF at z<3


Everything Consistent ? GRB 090423 at z=8.2607.008.0

+−

•

Gamma-ray burst on 23 April 2009; highest spectroscopically

confirmed astrophysical object known; 600 Myr

after the Big Bang.

•First clue it was at high redshift

was the absence of an optical afterglow. Subsequently detected in the NIR (UKIRT/Gemini), ~0.5-1 hr after the burst.

•

Luminous (but not unusual) explosion, probably associated with the death of a massive star. 1053

ergs released within ~10s (observers frame).

•GRBs

are vital probes of metals, gas, star-formation and reionization

at early epochs since galaxies are too faint for spectroscopy (See e.g. Chary et al. 2007).

Tanvir et al. 2009, NatureSalvaterra et al. 2009


Chary, Berger & Cowie 2007

WFC3 UDF(Bouwens)


Could be due to GRB efficiency increasing as metallicity

decreases ?

Butler, Bloom et al. 2010


Metallicity

increases as (stellar mass density)^0.69+/-0.17Exactly the same as dust content

Gamma-Ray Bursts Also Trace Metallicity

Evolution


Results from GRBs

•

Star-formation rate density is higher than from field galaxy surveys

•

Not due to dust obscuration

•

Can be explained by GRB production efficiency increases with decreasing metallicity

•

GRBs

are our ONLY tracer of metallicity

evolution especially at the faint end of the galaxy LF.


Physical Triggering Mechanism ?


Understanding Modes of Star-formation: Cold Flows or Minor/Major Mergers ?

Dekel

et al. 2009>10:1 mergers


Are these starbursts or quiescent star-formation ?

Tightness of the SFR-Stellar Mass at 0.8<z<1.2seems to indicate it is quiescent star-formation

Morphological evidence is not clear –

some of theLIRGs

are spirals while some are irregular/S0s

Is this due to increasing dust content in massive galaxies ?

A starburst spans a relatively short time scale ~10% of the cosmic time within that redshiftrange. Expect a large scatter –

there is a good number of “evolved” red galaxies at z~1.

Unclear what fraction of the dust is heated by therelatively evolved stellar population rather thanyoung stars. Is this evidence that a significantfraction of MIR emission is dust heated by A stars? (Salim

et al., Bendo

et al.)Elbaz

et al. 2007Noeske

et al, Papovich

et al., Reddy et al., Daddi

et al.


Some evidence for continuous accretion at z~4

H. Shim et al.


But, some of those are morphological trainwrecks


Summary

•

We have an excellent understanding of what dominates SF over half of cosmic time (z<1)

•

At z>1, uncertainties increase due to observational selection effects. But SFRD appears to be declining. Dusty galaxies still might dominate SFRD –

Herschel will be

insightful.•

At z<1, evolution appears to be due to mergers. At z>1, still up for discussion –

accretion from IGM might

contribute a fraction but 0.0 observational evidence.•

Massive galaxies appear to turn off their star-formation first (due to gas depletion or AGN feedback ?)

•

Metals and dust increase with increasing stellar mass density but at a slower rate, probably due to outflows in low mass halos.


The Future

•

We have made immense progress in identifying star-forming galaxies to the earliest cosmic times

•

Measure EBL with precision; need to go beyond the inner solar system.

•

Measure FIR SEDs

of galaxies at z~2-4 using Herschel

•

Better spec-z in 1.4<z<2.5 range•

Get spectra of GRBs

efficiently –

best tracer of

z>6 star-formation and the first massive stars•

Get spectroscopic evidence for a cold flow before jumping on the bandwagon

The Star Formation History of the Universe · 2010. 5. 7. · Chary: NOAO/NSO 50th Anniversary 1/40...

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Transcript of The Star Formation History of the Universe · 2010. 5. 7. · Chary: NOAO/NSO 50th Anniversary 1/40...