X-rays across the galaxy population - II. The distribution of AGN accretion rates as a function of stellar mass and redshift

James Aird; Alison L. Coil; Antonis Georgakakis

doi:10.1093/mnras/stx2700

paper

X-rays across the galaxy population - II. The distribution of AGN accretion rates as a function of stellar mass and redshift

arXiv:1705.01132 · doi:10.1093/mnras/stx2700

Abstract

We use deep Chandra X-ray imaging to measure the distribution of specific black hole accretion rates ( $L_{X}$ relative to the stellar mass of the galaxy) and thus trace AGN activity within star-forming and quiescent galaxies, as a function of stellar mass (from $1 0^{8.5} - 1 0^{11.5} M_{⊙}$ ) and redshift (to $z \sim 4$ ). We adopt near-infrared selected samples of galaxies from the CANDELS and UltraVISTA surveys, extract X-ray data for every galaxy, and use a flexible Bayesian method to combine these data and to measure the probability distribution function of specific black hole accretion rates, $λ_{s B H A R}$ . We identify a broad distribution of $λ_{s B H A R}$ in both star-forming and quiescent galaxies---likely reflecting the stochastic nature of AGN fuelling---with a roughly power-law shape that rises toward lower $λ_{s B H A R}$ , a steep cutoff at $λ_{s B H A R} ≳ 0.1 - 1$ (in Eddington equivalent units), and a turnover or flattening at $λ_{s B H A R} ≲ 1 0^{- 3} - 1 0^{- 2}$ . We find that the probability of a star-forming galaxy hosting a moderate $λ_{s B H A R}$ AGN depends on stellar mass and evolves with redshift, shifting toward higher $λ_{s B H A R}$ at higher redshifts. This evolution is truncated at a point corresponding to the Eddington limit, indicating black holes may self-regulate their growth at high redshifts when copious gas is available. The probability of a quiescent galaxy hosting an AGN is generally lower than that of a star-forming galaxy, shows signs of suppression at the highest stellar masses, and evolves strongly with redshift. The AGN duty cycle in high-redshift ( $z ≳ 2$ ) quiescent galaxies thus reaches $\sim$ 20 per cent, comparable to the duty cycle in star-forming galaxies of equivalent stellar mass and redshift.

20 pages + 3 appendices (27 pages total) with 15 figures. The sketch shown in Figure 9 summarizes our findings. Data tables available at http://doi.org/10.5281/zenodo.1009605 . Updated FAST SED fitting code available at https://github.com/jamesaird/FAST . This is a pre-copyedited, author-produced version of an article accepted for publication in MNRAS following peer review

X-rays across the galaxy population - II. The distribution of AGN accretion rates as a function of stellar mass and redshift

Abstract

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