Observing Star Formation in local Active Galactic Nuclei from Swift-BAT survey

Abstract

A hallmark of the co-evolution between a super-massive black hole (SMBH) and its host galaxy is the connection between the growth of a SMBH (AGN activity) and of the galaxy (star formation). I investigate this connection by measuring the mean star formation rates (SFRs) of a sample of 313 galaxies of AGN selected from the Swift-BAT ultra-hard (14 – 195 keV) X-ray survey of the local Universe. This is achieved by separating the contribution of the AGN and star formation from the spectral energy distributions (SEDs) of the Swift-BAT AGN using infrared photometry from Herschel and WISE. I present the mean star formation rates (SFRs) as a function of bolometric AGN luminosity (LBOL) which show a rise towards higher luminosities (LBOL ≥ 1044 erg s-1). I set out a range of methods (e.g. stellar mass offsets from star-forming galaxy relations) to show that the rise in SFR is most likely a consequence of the high fraction of the higher luminosity subset being starbursts (i.e. an intense period of star formation in a galaxy) and of mass effects (i.e. more massive galaxies hosting more luminous AGN). In support of this main project, I investigate the value of modern Herschel photometry compared to legacy IRAS photometry in the estimation of SFRs. In addition I propose a new colour diagnostic for identifying AGN using Herschel photometry and assess how reliable our SED fitting procedure is by constraining the AGN template to subarcsecond resolution mid-infrared photometry.