Most star and BH formation is happening insecular evolving disks

E. Daddi (CEA Saclay)

Mark Sargent(CEA), Mathieu Bethermin(CEA), Giulia Rodighiero(INAF), Georgios Magdis(Oxford), James Mullaney(Durham)

GOODS-Herschel team

Definition (operational): starburst are the ‘excess SFR’ high-gas-density phase that *can* happen during mergers (or other events)

- But does not happen in all mergers- Even in mergers excess phase is short - And in principle might be triggered by other instabilities ?

Di Matteo et al 2008Martig & Bournaud 2008

(Mihos & Hernquist 90’s)

Framework: there are 2 ‘major’ SF modes for galaxy buildup: a ‘secular’/’normal’ and a ‘starburst’

A ruler:The correlation SFR-M* at

different redshifts

Z=0, Elbaz et al, 2007

Z=1, Elbaz et al, 2007

Z=2, Daddi et al, 2007

Z=3, Magdis et al, 2010a

Z=4, Daddi et al, 2008

No main sequence seen if using Herschel data alone (SFR-selection)

What is the statistical importance of SB galaxies ? Typical answer: ~50%

COSMOS PACS dataFrom PEP(and also GOODS-S)

Near-IR galaxiesFrom BzK samples,UV-corrected SFRs

Rodighiero et al. 2011

Clumpy galaxies are not necessarily mergers,might be extremely rich

gas galaxies

Bournaud et al 2008z=1.57 BzK galaxy

UDF skywalker

See also works of Elmegreen et al., Genzel et al SINS spectroscopy

MS outliers: are they mergers ?

HGOODS objects with sSFR x4 excess and measured zspec

For all cases the UV SFR fails(optically thick)

UV underestimate similar to excess sSFR

Most likely they are indeed‘Dense’ mergers

Optically thick sources

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PAH distruction in SBs Compactness of SBs

Elbaz et al 2011; z=2 Herschel GOODS sample

We had lots of IRAM observations to look at multiple CO transitions, and continuum as a byproduct(hard and expensive to get)

This will change dramatically with ALMA

Magdis et al 2011

A way to constrain a_CO in thelocal Universe is through Mdust,As Mdust ~ Z*Mgas

Modeling approach:- Full suite of Draine and Lee 2007Models- MBB with free T and beta

Trusting the G/D trend get estimates for alpha_CO

Notice that it is very hard To overestimate much MgasHence alpha_COBecause G/D > 1/Z

And the local relation hasG/D~2/Z

Nicely confirming/supporting the bimodality in Mgas/LIR between MS/SB

Correlation of LIR/SFR with CO and Mgas(Sargent et al 2012, in preparation)

X3 offset from *observables only* X10 offset, dense gas fraction

Threshold between MS and SB is objectively defined: 0.6 dex (2.5 sigma of the distribution)Notice that SBs will be present also below the threshold, but becoming overwhelmed byNormal galaxies. Also, they would be objects with minor modification of their SFRs

SB: objects with SFR enhanced on average by x4 over what they should heve, given M*

Notice very good agreement between UV and Herschel at the high mass bin

FIR selection (dust) SMGs/Herschel galaxies are mixed bags(might explain similarities sometimes foundwith BzKs e.g. in excitation, SFE) Need different approach tu build appropriate sample of starbursts

SFRD contribution of SBs only ~10%(mergers not so important for star form.)

Near-IR selection (stars) You must be very (un)lucky topick up a SBs there (2% chance)

SB duty cycle ~20Myr Much shorter than ~200Myr typicalmerger duration (refer only to SFRnnhancement >4)

Dec. 5, 2011 13

(Main sequence + starburst) decomposition

1) Black, white… and grey: bimodality2) Merger as a Transfer function

MS/SB paradigm using mass functions to (separated)

• IR luminosity functions (Sargent+2012)• Galaxy counts (Bethermin et al in prep) (SEDs needed – Herschel)• H2/CO mass/luminosity functions (Sargent et al) (LCO/H2 to LIR – IRAM)

Sargent et al 2012

Dec. 5, 2011 14

IR luminosity function: prediction vs. observationsSargent et al 2012

A parameter-less prediction of IR galaxy counts(Bethermin et al 2012, ApJL submitted)

Fit is quite good, for fiducialmodel (no tuning)

Not perfect, but much betterthan earlier attempts already

Cosmic evolution of H2-reservoirs(Sargent et al 2012 in preparation)

Equipartition between molecular gas and stars at z~2

How do AGNs fit in all of this ?BH-galaxy correlation (local) BH assembly must know about galaxy assembly

But their BH accretion rate (Lx)doesn’t seem to care about thegalaxy (e.g., stellar mass)

Mullaney et al 2012

Doing ensemble averages ( time averages)All the picture clears up

Mullaney et al 2012 astroph

Strongly suggest that BH and galaxy do growTogether, and MBH/Mgalaxy is ~constant at theSame ratio of today through formation epoch

There is a Main Sequence also for AGNs!(when eliminating short-time fluctuations)

Level is ~ Magorrian

Summary and conclusions

We have a simple and elegant way to empirically describe the evolution of star forminggalaxies through cosmic time, and distinguish the contribution of MS (disk-like, stream-fed?) and SBs (merging driven likely) (2 SF mode framework)

We are starting to understand how to distinguish the two modes, at least Globally/statistically, as it is often harder on individual cases.

We have testable predictions from this framework, some success (IR LFs, counts, etc)

Most of today’s stars were formed in a quiescent mode

BHs apparently form in parallel with their hosts, apparently mainly on the MS as well