Galaxy mergers are predicted to trigger accretion onto the central supermassive black holes , with the highest rates occurring during final coalescence .
Previously , we have shown elevated rates of both optical and mid-IR selected active galactic nuclei ( AGN ) in post-mergers , but to date the prevalence of X-ray AGN has not been examined in the same systematic way .
We present XMM-Newton data of 43 post-merger galaxies selected from the Sloan Digital Sky Survey along with 430 non-interacting control galaxies matched in stellar mass , redshift , and environment in order to test for an excess of hard X-ray ( 2–10 keV ) emission in post-mergers attributable to triggered AGN .
We find 2 X-ray detections in the post-mergers ( 4.7 ^ { +9.3 } _ { -3.8 } \% ) and 9 in the controls ( 2.1 ^ { +1.5 } _ { -1.0 } \% ) , an excess of 2.22 ^ { +4.44 } _ { -2.22 } , where the confidence intervals are 90 % .
While we therefore do not find statistically significant evidence for an X-ray AGN excess in post-mergers ( p = 0.26 ) , we find a factor of \sim 17 excess of mid-IR AGN in our sample , consistent with past work and inconsistent with the observed X-ray excess ( p = 2.7 \times 10 ^ { -4 } ) .
Dominant , luminous AGN are therefore more frequent in post-mergers , and the lack of a comparable excess of 2–10 keV X-ray AGN suggests that AGN in post-mergers are more likely to be heavily obscured .
Our results are consistent with the post-merger stage being characterised by enhanced AGN fueling , heavy AGN obscuration , and more intrinsically luminous AGN , in line with theoretical predictions .