Relationship between Star Formation Rate and Black Hole Accretion At Z = 2: the Different Contributions in Quiescent, Normal, and Starburst Galaxies
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 z∼ 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 z∼ 2 is associated with normal star-forming systems, with only ∼ 6(+/- 1)% and ∼ 11(+/- 1)% associated with starburst and quiescent galaxies, respectively.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2015
- DOI:
- 10.1088/2041-8205/800/1/L10
- arXiv:
- arXiv:1501.04634
- Bibcode:
- 2015ApJ...800L..10R
- Keywords:
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- galaxies: evolution;
- galaxies: interactions;
- galaxies: nuclei;
- galaxies: starburst;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication as ApJ Letter