The Incidence of X-ray selected AGN in Nearby Galaxies
  We present the identification and analysis of an unbiased sample of AGN that
lie within the local galaxy population. Using the MPA-JHU catalogue (based on
SDSS DR8) and 3XMM DR7 we define a parent sample of 25,949 local galaxies ($z
\leq 0.33$). After confirming that there was strictly no AGN light
contaminating stellar mass and star-formation rate calculations, we identified
917 galaxies with central, excess X-ray emission likely originating from an
AGN. We analysed their optical emission lines using the BPT diagnostic and
confirmed that such techniques are more effective at reliably identifying
sources as AGN in higher mass galaxies: rising from 30% agreement in the lowest
mass bin to 93% in the highest. We then calculated the growth rates of the
black holes powering these AGN in terms of their specific accretion rates
($\propto L_X/M_*$). Our sample exhibits a wide range of accretion rates, with
the majority accreting at rates $\leq 0.5\%$ of their Eddington luminosity.
Finally, we used our sample to calculate the incidence of AGN as a function of
stellar mass and redshift. After correcting for the varying sensitivity of
3XMM, we split the galaxy sample by stellar mass and redshift and investigated
the AGN fraction as a function of X-ray luminosity and specific black hole
accretion rate. From this we found the fraction of galaxies hosting AGN above a
fixed specific accretion rate limit of $10^{-3.5}$ is constant (at $\approx
1\%$) over stellar masses of $8 < \log \mathrm{M_*/M_\odot} < 12$ and increases
(from $\approx 1\%$ to $10\%$) with redshift.
