Herschel observations: contraints on dust attenuation and star formation histories at

high redshift

Véronique BuatLaboratoire d’Astrophysique de Marseille

Elbaz’s lectures (david.elbaz3.free.fr/coursJ1.html), adapted from Devriendt+99

Visible

Infrared mm

UV

wavelength

inte

nsit

y

dust

Both UV and IR are related to recent star formationThey are anti-correlated because of dust attenuation

IR selected objects are usually obscured with a low residual emission in UV

Conversely: we expect a UV selection to be dominated by IR faint sources

A few words about the physical link between UV and IR emissions

SFR density traced by combining UV and IR surveys

Takeuchi, Buat & Burgarella, 2005

Two parts in this talk….

• Analysis of the full UV-to-IR Spectral Energy Distributions of galaxies, dust attenuation & star formation at z> 1 Véronique

• UV and IR luminosity functions, evolution of global dust attenuation and star formation rate density with redshift up to z~4 Denis

Outline of the first part

1. Fitting the full SED in a physical way2. The GOODS-Herschel project: observed SEDs of distant galaxies3. Dust attenuation curve4. Star formation rates and stellar mass determinations5. The Herschel insight on IR spectral energy distributions of distant galaxies

With Sébastien Heinis, Médéric Boquien, Denis Burgarella & the GOODS-Herschel team

1. Modeling the UV-to-IR SEDs: with or without energy budgets

Muzzin+10Stellar and dust emission fitted separately

Stellaremission

Dust emission

Da Cunha+08, Magphys code

Radiation transfer & multi-components: valid for local resolved galaxies

Popescu+12

Simple recipes: dust attenuation curves, IR librariesValid for large samples of unresolved galaxies

CIGALE code, Noll+09

Focusing on SED fitting with conservation of the energy bewteen UV-optical and IR

Metallicity fixed or variable

Stellar spectra and isochrones depend on Z

Usually Starburst law but not always

A set of templates

Various SFH, one or several populationsMinimum age free or fixed

CIGALE : Code Investigating GALaxy Emission

P.I. D. Burgarella (Noll+09) http://cigale.oamp.fr/

OUTPUT PARAMETERS :All based on a Bayesian analysis• input parameters• Stellar Mass•Dust luminosity•Amount of obscuration•D4000 break, slope of the UV continuum….

2. The GOODS-Herschel, PI D.Elbaz

GOODS-N: 10’x15’ PACS+SPIRE, 100, 160, 250, 250, 500 µm 1 mJy @ 100 µmGOODS-S/CDFS: 10’x10’ PACS 100,160 µm down to the confusion limit at 100 µm ~0.7 mJy

GO

OD

S-N

orth

fiel

d

SPITZER data

HERSCHEL data

PACS SPIRE

A public website for Herschel extragalactic and cosmological surveys: GOODS-Herschel, HerMES, HRS,

VNGShttp://hedam.lam.fr/

Building the multi-wavelength sample for objects in the CDFS

Z> 1 : to redshift the UV range in the visible optical (UV rest-frame) + IR thermal data

1<Z<3Combining GOODS-Herschel/PACS data and

Subaru/MUSYC broad and intermediate band filters (Cardamone+10)+IRAC & MIPS data (Dickinson+03)

28 photometric bands: SNR > 5 in optical and NIR + SNR> 3 at 24 µm 236 galaxies 80 sources detected with PACS, upper limits for the other ones

GOODS-H-CDFS field at 24-100-160 µm Subaru Intermediate band filters

Some examples of SEDs, with their best fit obtained with CIGALE Buat+11An absorption feature at 2175 A rest frame clearly seen and modeled.The full UV-to-IR SED fitted.Physical parameters derived from the analysis of their PDF (not from the best SED)

Calzetti et al. 94, 00: from spectroscopic datano bump in attenuation curve of local starburt galaxies, moderate rise in UV

3. Dust attenuation curve in external galaxies at 1<z<2

Buat et al. 2011, 2012Calzetti 01__ MW

---- LMC___SMC

starburst

Extinction law ≠Attenuation law

Ilbert et al. 2009- Cosmos field-30 photometric bands from UV to NIR:« A broad absorption excess at 2175 A seems necessary to explain the UV flux of some starburst galaxies »

Composite spectrum 1.5<z<2.5: evidence for a bump for 30% of the

sourcesNoll+09

But no evidence for a bump in Lyman Break Galaxies at z≈2 (Vijh+03, Reddy+08)

Some previous evidence for the presence of bumps at high z

CIGALE: optimized to study dust attenuation curves

different amount of dust attenuation (and same attenuation curve) for the young and the old stellar population

5500 Å slope

Calzetti et al. (2000) UV bump power law

AmplitudeCentral wavelength Width

Eb= 1.6 +/- 0.4 δ = -0.27 +/- 0.17

20% of the galaxies (47% of those detected in IR) have a confirmed bump (2 σlevel)20% of the galaxies (43% of those detected in IR) have a dust attenuation steeper than the Calzetti law (2 σ level)

General shape of the average attenuation curve consistent with an increase in UV similar to that of the LMC supershell extinction curve (steeper than the Calzetti curve on top of which there is a bump at 2175 A) whose amplitude is similar to that found in the LMC supershell, (45% that of the MW one) .

Large dispersions among galaxies

Derivation of a mean dust attenuation curve with a UV bump in the CDFS galaxies with 1<z<2

C00

LMC

SMC

SMC

MW

LMCC00

C00: Starburst law, Calzetti.00

3. Stellar mass and Star Formation Rate derivation for 1<z<3 galaxies

Buat+13, (A&A, under revision)

Impact of Different Star Formation Histories: • exp(-t/τ), age free, decl. τ model 1 stellar pop.•exp(t/τ), age fixed (zf ≈ 8), rising. τ model 1 stellar pop.•An old (age free or fixed) decl. τ pop. + a young, age free pop with a constant SFR 2 st. pop.

When IR data are included SFRs are well determined and are non dependent on the SFHsUncertainties remain larger for Mstar estimates

0.12 dex

0.17 dex

Base line model: 2 pop, both age free

Fits without IR data (MIPS and PACS data omitted): the SFR are poorly measured, stellar masses remain unchanged due to uncertainties on dust attenuation

Stellar mass and Star formation rate derivation (cont’d)

Buat+13 Impact of including or not IR data

w/o IR

with IR

W/o

IR-w

ith IR

Consequences on the measure of the Specific Star Formation Rate:SSFR = SFR/Mstar

Adopted Limit for Starburst galaxiesElbaz+11

Dispersion of the Main Sequence of Galaxies defined with IR data or accurate measures of dust attenuation(Noeske+07, Rodighiero+11, Salmi+12)

log(

SSFR

-with

out I

R)-lo

g(SS

FR-w

ith IR

))

Sargent+12

Dale & Helou (2002)64 semi-empirical templates

Chary & Elbaz (2001) 105 empirical templates

-Draine & Li (2007) models (Draine+07): very useful with Herschel data

4. IR SEDs: new insights from Herschel

Dale+12

Templates for the distant universe dependent on the SFR activity , Elbaz+11

« normal galaxies » Starbursting galaxies

•Main Sequence: on average SFR-M* relation, even if very luminous, PAH are prominent•Starburst galaxies: SFR/M* higher than for Main Sequence, less PAH, warmer dust

DIFFERENT FROM LOCAL TEMPLATES OF SIMILAR LUMINOSITY:The contribution of PAHs for high-z luminous galaxies is larger than in nearby galaxies of same IR luminosity

When using local templates of CE01, Lir calculated with 24 µm is overestimated at z=2, (Nordon+12)

@ z=2 8 μm rest frame, PAH dominated

« ex

act »

log(

LIR)

Original CE01 templates With the New Main Sequence templateL IR

from

mon

ochr

omati

c flu

x/L IR

(tot

al-a

ll M

IPS-

Her

sche

l dat

a)

With Herschel, the situation remains complex….

Ciesla+13, in prep.

To be optimistic: Lir estimates do not strongly depend on the adopted template when several bands are available

Casey 12Ciesla, 12, PhD thesisHerschel Reference Sample, SPITZER+ SPIRE data

Conclusions

•Fitting the full SED from the UV to the IR with a conservation of the enery balance is very powerful to constrain dust attenuation and consequently SFRs•The attenuation curve of galaxies with 1<z<2 is steeper than the law for local starbursts and is found to exhibit a bump at 2175 A with an amplitude similar to that of the LMC2 extinction curve, •Without IR data, SFRs can be over or underestimated by factors larger than 2 inducing a similar uncertainty for the SSFRs. •Stellar masses derivations are more sensitive to the adopted star formation history than SFRs. •IR SEDs at all z are constrained with Herschel data, modifying the local templates, but more work is needed to build reliable, detailed SEDs

All these analyses are based on data from the CDFS obtained in the framework of the GOODS, GOODS-Herschel and MUSYC projects

Thank You!