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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!