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Most star and BH formation is happening in secular evolving disks. E. Daddi (CEA Saclay ) Mark Sargent(CEA), Mathieu Bethermin (CEA), Giulia Rodighiero (INAF), Georgios Magdis (Oxford), James Mullaney (Durham) GOODS-Herschel team .

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Most star and BH formation is happening in

secular evolving disks

E. Daddi (CEA Saclay)

Mark Sargent(CEA), Mathieu Bethermin(CEA),

Giulia Rodighiero(INAF), GeorgiosMagdis(Oxford),

James Mullaney(Durham)

GOODS-Herschel team


Framework: there are 2 ‘major’ SF modes for galaxy buildup:

a ‘secular’/’normal’ and a ‘starburst’

Definition (operational): starburst are the ‘excess SFR’

high-gas-density phase that *can* happen during mergers

(or other events)

Di Matteo et al 2008

Martig & Bournaud 2008

(Mihos & Hernquist 90’s)

- But does not happen in all mergers

- Even in mergers excess phase is short

- And in principle might be triggered by other instabilities ?

a ruler the correlation sfr m at different redshifts
A ruler:Thecorrelation SFR-M* atdifferentredshifts

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


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


From PEP

(and also GOODS-S)

Near-IR galaxies

From BzK samples,

UV-corrected SFRs

Rodighiero et al. 2011

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


Clumpy galaxies are not necessarily mergers,might be extremely rich gas galaxiesBournaud et al 2008z=1.57 BzK galaxyUDF 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

 Distance from MS

 Optically thick sources


PAH distruction in SBs

Compactness of SBs

Elbaz et al 2011; z=2 Herschel GOODS sample


A way to constrain a_CO in the

local Universe is through Mdust,

As Mdust~ Z*Mgas

  • 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

Modeling approach:

- Full suite of Draine and Lee 2007


- MBB with free T and beta

Magdis et al 2011


Trusting the G/D trend  get estimates for alpha_CO

Notice that it is very hard

To overestimate much Mgas

Hence alpha_CO

Because G/D > 1/Z

And the local relation has


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


Notice very good agreement

between UV and Herschel

at the high mass bin

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 by

Normal 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*


FIR selection (dust)

  • SMGs/Herschel galaxies are mixed bags
  • (might explain similarities sometimes found
  • with 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 to
  • pick up a SBs there (2% chance)
  • SB duty cycle ~20Myr
  • Much shorter than ~200Myr typical
  • merger duration (refer only to SFR
  • nnhancement >4)

(Main sequence + starburst) decomposition

Sargent et al 2012

  • Black, white… and grey: bimodality
  • 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

IR luminosity function: prediction vs. observations

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

Fit is quite good, for fiducial

model (no tuning)

Not perfect, but much better

than 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 the

galaxy (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 grow

Together, and MBH/Mgalaxy is ~constant at the

Same 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
Summary and conclusions

We have a simple and elegant way to empirically describe the evolution of star forming

galaxies 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