Quiescent and Starbursting star-forming galaxies at z=2

Giulia Rodighiero (University of Padova)

On behalf of the PEP Team

Trieste - The Physics of Star Formation – 18 October 2012

COSMOS 24/100/160 μm

The Main Sequence of Star-forming galaxies at 1.4 < z < 2.5

Two regimes of star formation: quasi-steady on the main

sequence, starbursts off of it

(Daddi et al 2010)

Two regimes of star formation: quasi-steady on the main

sequence, starbursts off of it

Answering with HERSCHEL/PACS observations over the GOODS & COSMOS fields

The PEP- GOODS South

(Lutz et al. 2011)

~21’x14’

The PEP-COSMOS

~2 square degrees

HERSCHEL/PACS observations over the GOODS & COSMOS FIELDS

Rodighiero et al. (2011))

Data-set required to fully sample the stellar mass – SFR plane:

1.PACS 100μm and 160μm shallow source catalogs with extraction based on 24μm prior positions + IRAC-selected source catalog from Ilbert et al. (2010)

2.PACS 70, 100 and 160μm deep catalog in GOODS-S + multiwavelength photometry, spec & photo-z

3.BzK COSMOS catalog (Daddi/McCracken)

4.BzK GOODS-S catalog (Daddi et al. 2007)

SFR: derived from SED fitting to the complete UV-to-PACS observed photometry and converting the bolometric emission ([8-1000]μm) with the Kennicutt et al. (1998) relation (inclusion of unobscured SF does not affect the results).

STELLAR MASSES: classical SED fitting to the UV-to-IRAC (5.8μm) with Bruzual & Charlot models

Populating the mass-SFR planePopulating the mass-SFR plane

BzKPACS-deepPACS-shallow

X4-MS

Number densities as a function of mass and SSFR bins: defining the ON & OFF main sequence loci

SFR density: % OFF sequence

~10%

Number density: % OFF sequence

~2%

SFR density

Number density

ON and OFF sequence

Kaviraj et al. 2012 (arXiv 1210.2160)

Morphological WFC3/HST analysis in GOODS-S:The actual major-merger contribution to the star formation budget may be as low as~15%

DUTY CYCLE ON/OFF the MAIN SEQUENCE at 1.5<z<2.5

With only 2% of the massive galaxies being OFF the main ∼sequence, on average each galaxy spends 20 Myr in the starburst mode.

This is actually much shorter than both the gas depletion timescale (~0.5 Gyr) and the dynamical time in starburst galaxies (~50-200 Myr, Daddi et al. 2010; Genzel et al. 2010).

Not all galaxies may experience a (merger-driven) starburst during these ~2 Gyr of cosmic time interval.

ON- and OFF-main sequence IR Luminosity functionsPEP/HERMES-COSMOS-GOODS-ECDFS sources

Predictions from

Sargent et al. 2012

Gruppioni et al. (2012)

ON-MSOFF-MS

The integrated bolometric LFs confirm the dominant role of the main sequence population at 1<z<2 for the mass assembly, both in number and luminosity/SFR densities.

Gruppioni et al. (2012)

MAIN CONCLUSION

The merger-enhanced SFR phases are relatively unimportant for the stellar mass growth of z 2 ∼galaxies, and probably so at all redshifts.

Still, going through a merging-driven starburst phase may turn star-forming galaxies into passive ellipticals.

TESTING THE STARBURST-MERGER

PARADIGM

ASI Review Padova Science Activities 20

Follow-up campaign of extreme off-sequence Herschel sources at z=2 (1)

P.I. G. Rodighiero

IRAM PdB CO(2-1) line: PACS-164 5-σ detection at z=1.646

Data analysis by Chiara Feruglio

Daddi et al. (2010)

L(IR)/L(CO) larger than BzK sources

Daddi et al. (2010)

Assuming a “starburst” α(CO) value

The S-K relation(preliminary!!)

ASI Review Padova Science Activities 24

Follow-up campaign of extreme off-sequence Herschel sources at z=1.5 (2)

P.I. J. Silverman

The AGN population in the mass-SFR plane:a key test to constrain the AGN feedback and the

joint black-hole/star-formation accretion rate

The “Hidden AGN Main Sequence” at z~1 and z~2: the same secular processes that drive the bulk of star formation are also responsible for the majority of SMBH growth (Mullaney et al. 2012)

AGNs reside mostly in main-sequence hosts, reflecting the AGN - sSFR connection (Rovilos et al. 2012)

Herschel COSMOS Obscured AGN: F(24μm)/F(R)>1000 & (R-K)>4.5 (Fiore et al. 2008)

Herschel GOODS X-ray selected AGN(with thanks to P. Popesso & M. Brusa)

Singularly detected AGN seem to live preferentially on the Main Sequence

The most SB sources:x10>MS

Dominated by SFR

Obscured AGN present

but does never dominate

the bolometric far-IR emission

SED fitting of Herschel sources with local empirical templates

Type 1 AGN Type 2 AGNLow Luminosity AGNStarburstSpirals/quiescent SFR

(from C. Gruppioni SED fitting)

Hard to derive trends….

SED fitting with energy balance (Da Cunha et al. 2008/2010) + dusty torus component (Berta et al. in prep.):

Hidden AGN fraction in the mid-IR and far-IR

observed observed

Test case at 1.4<z<1.7 (preliminary…)

ON OFF

Increasing AGN fraction(from 10% to 70%)

Obscured AGN homogeneously distributed on the mass-SFR plane (at

least in bright LIR limited samples)

P.I. John Silverman

Broad emission lines consistent with nuclear activity

Courtesy of J. Silverman

X4-MSOverall test with X-ray stacking in different mass-SFR bins (in progress…):

SUMMARY

- Majority of star formation at high-z takes place on the MS

- Outliers to the MS are starbursts also in the Schmidt-Kennicutt plane (tentative… well ok … one source … but more to come!)

- AGN activity and SFR are well correlated along the MS, what’s above?

- Ideas, suggestions…?

FOR DiSCUSSION: underestimation of stellar mass in heavily extinguished galaxies

Poster & paper (submitted) by Barbara Lo Faro

Dead off-MS? sSFR of starbursts would drop down (by a factor ~6-10!)…

Thank you!