Relationship between Star Formation Rate and Black Hole Accretion At Z = 2: the Different Contributions in Quiescent, Normal, and Starburst Galaxies

Journal
Date Issued
2015
Author(s)
Rodighiero, G.
•
Brusa, M.
•
Daddi, E.
•
Negrello, M.
•
Mullaney, J. R.
•
•
Lutz, D.
•
Renzini, A.
•
Franceschini, A.
•
Baronchelli, I.
•
Pozzi, F.
•
•
•
Cimatti, A.
•
Silverman, J.
DOI
Description
G.R. acknowledges support from ASI (Herschel Science Contract 2011—I/005/011/0). M.B. acknowledges support from the FP7 Career Integration grant “eEASy” (CIG 321913). E.D. acknowledges funding support from ERC-StG grants UPGAL 240039 and ANR-08-JCJC-0008. We thank the anonymous referee for a constructive report and T. Miyaji, M. Volonteri, and L. Ferrarese for useful discussions.
Abstract
We investigate the co-evolution of the black hole accretion rate (BHAR) and the star formation rate (SFR) in 1.5\lt z\lt 2.5 galaxies displaying a greater diversity of star-forming properties compared to previous studies. We combine X-ray stacking and far-IR photometry of stellar mass-limited samples of normal star-forming, starburst, and quiescent/quenched galaxies in the COSMOS field. We corroborate the existence of a strong correlation between BHAR (i.e., the X-ray luminosity, LX) and stellar mass (M*) for normal star-forming galaxies, though we find a steeper relation than previously reported. We find that starbursts show a factor of three enhancement in BHAR compared to normal SF galaxies (against a factor of six excess in SFR), while quiescents show a deficit of a factor times 5.5 at a given mass. One possible interpretation of this is that the starburst phase does not coincide with cosmologically relevant BH growth, or that starburst-inducing mergers are more efficient at boosting SFR than BHAR. Contrary to studies based on smaller samples, we find that the BHAR/SFR ratio of main-sequence (MS) galaxies is not mass invariant, but scales weakly as M*0.43+/- 0.09, implying faster BH growth in more massive galaxies at z̃ 2. Furthermore, BHAR/SFR during the starburst is a factor of two lower than in MS galaxies, at odds with the predictions of hydrodynamical simulations of merger galaxies that foresee a sudden enhancement of LX/SFR during the merger. Finally, we estimate that the bulk of the accretion density of the universe at z̃ 2 is associated with normal star-forming systems, with only ̃ 6(+/- 1)% and ̃ 11(+/- 1)% associated with starburst and quiescent galaxies, respectively.
Volume
800
Issue
1
Start page
L10
Uri
Url
Issn Identifier
2041-8205
Ads BibCode
2015ApJ...800L..10R
Rights
open.access
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