BLACK HOLE VARIABILITY AND THE STAR FORMATION–ACTIVE GALACTIC NUCLEUS CONNECTION: DO ALL STAR-FORMING GALAXIES HOST AN ACTIVE GALACTIC NUCLEUS?

By R. Hickox, James Mullaney, D. M. Alexander, Chien-Ting J. Chen, F. Civano, A. Goulding, K. Hainline. 2013

252 citations recorded by the source corpus.

We investigate the effect of active galactic nucleus (AGN) variability on the observed connection between star formation and black hole accretion in extragalactic surveys. Recent studies have reported relatively weak correlations between observed AGN luminosities and the properties of AGN hosts, which has been interpreted to imply that there is no direct connection between AGN activity and star formation. However, AGNs may be expected to vary significantly on a wide range of timescales (from hours to Myr) that are far shorter than the typical timescale for star formation (≳100 Myr). This variability can have important consequences for observed correlations. We present a simple model in which all star-forming galaxies host an AGN when averaged over ∼100 Myr timescales, with long-term average AGN accretion rates that are perfectly correlated with the star formation rate (SFR). We show that reasonable prescriptions for AGN variability reproduce the observed weak correlations between SFR and LAGN in typical AGN host galaxies, as well as the general trends in the observed AGN luminosity functions, merger fractions, and measurements of the average AGN luminosity as a function of SFR. These results imply that there may be a tight connection between AGN activity and SFR over galaxy evolution timescales, and that the apparent similarities in rest-frame colors, merger rates, and clustering of AGNs compared to “inactive” galaxies may be due primarily to AGN variability. The results provide motivation for future deep, wide extragalactic surveys that can measure the distribution of AGN accretion rates as a function of SFR.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Instrumentation

View Paper: https://www.semanticscholar.org/paper/7cce4935c353c4688b1f5c71da0f3a4a3cf1f793

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Citations in the corpus

Galaxy pairs in the Sloan Digital Sky Survey – IX. Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer (2014, background): “…is variable over a wide dynamic range on timescales shorter than the lifetime of merger signatures,any observed trends of merger fraction as a function of AGN luminosity will be weak, while the incidence of AGNs in merging galaxies will be still higher than in isolated systems (Hickox et al. 2014).”
Cosmic X-ray surveys of distant active galaxies (2015, methodology): “As shown by several models (e.g., Gabor and Bournaud 2013; Hickox et al 2014; Neistein and Netzer 2014; Thacker et al 2014), these apparently uncorrelated data can be explained by differences in the timescales of stability between star formation and AGN activity: star formation is assumed to be…”