Herschel observations: contraints on dust attenuation and star formation histories at high redshift Véronique Buat Laboratoire dAstrophysique de Marseille

Elbazs lectures (david.elbaz3.free.fr/coursJ1.html), adapted from Devriendt+99 Visible InfraredmmUV wavelength intensity dust Both UV and IR are related to recent star formation They 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 way 2.The GOODS-Herschel project: observed SEDs of distant galaxies 3.Dust attenuation curve 4.Star formation rates and stellar mass determinations 5.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+10 Stellar and dust emission fitted separately Da Cunha+08, Magphys code

Radiation transfer & multi- components: valid for local resolved galaxies Popescu+12 Simple recipes: dust attenuation curves, IR libraries Valid 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 populations Minimum age free or fixed

CIGALE : Code Investigating GALaxy Emission P.I. D. Burgarella (Noll+09)

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: 10x15 PACS+SPIRE, 100, 160, 250, 250, 500 µm µm GOODS-S/CDFS: 10x10 PACS 100,160 µm down to the confusion limit at 100 µm ~0.7 mJy GOODS-North field SPITZER data HERSCHEL data PACS SPIRE

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

GOODS-H-CDFS field at µm Subaru Intermediate band filters

Some examples of SEDs, with their best fit obtained with CIGALE Buat+11 An 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 data no 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, 2012 Calzetti 01__ MW ---- LMC ___SMC starburst

Ilbert et al 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 sources Noll+09 But no evidence for a bump in Lyman Break Galaxies at z2 (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 Amplitude Central wavelength Width

E b = 1.6 +/- 0.4 δ = / % 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 MW LMC C00 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 (z f 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 SFHs Uncertainties remain larger for M star estimates 0.12 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 (contd) Buat+13 Impact of including or not IR data w/o IR with IR W/o IR-with IR

Consequences on the measure of the Specific Star Formation Rate: SSFR = SFR/M star Adopted Limit for Starburst galaxies Elbaz+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-without IR)-log(SSFR-with 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, z=2 8 μm rest frame, PAH dominated « exact » log(LIR)

Original CE01 templates With the New Main Sequence template L IR from monochromatic flux/L IR (total-all MIPS-Herschel data)

With Herschel, the situation remains complex…. Ciesla+13, in prep.

To be optimistic: L ir estimates do not strongly depend on the adopted template when several bands are available Casey 12 Ciesla, 12, PhD thesis Herschel Reference Sample, SPITZER+ SPIRE data