Black hole variability and the star formation-AGN connection: Do all star-forming galaxies host an AGN?
Ryan C. Hickox (Dartmouth), James R. Mullaney, David M. Alexander,, Chien-Ting J. Chen, Francesca M. Civano, Andy D. Goulding, Kevin N. Hainline

TL;DR
This paper models how AGN variability affects observed correlations between star formation and black hole activity, suggesting a hidden underlying connection over galaxy evolution timescales.
Contribution
It introduces a simple variability model showing that weak observed correlations can mask a true, tight link between star formation and AGN activity.
Findings
Reasonable AGN variability models reproduce observed weak correlations.
The model explains trends in AGN luminosity functions and merger fractions.
Results imply a fundamental connection between AGN activity and star formation.
Abstract
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…
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Taxonomy
TopicsGalaxies: Formation, Evolution, Phenomena · Astronomical Observations and Instrumentation · Astronomy and Astrophysical Research
