A Luminous X-ray AGN in the Dwarf-Dwarf Galaxy Merger RGG 66

Abstract

We present the discovery of a luminous X-ray AGN in the dwarf galaxy merger RGG 66. The black hole is predicted to have a mass of $M_{\rm BH} \sim 10^{5.4} M_\odot$ and to be radiating close to its Eddington limit ($L_{\rm bol}/L_{\rm Edd} \sim 0.75$). The AGN in RGG 66 is notable both for its presence in a late-stage dwarf-dwarf merger and for its luminosity of $L_{\rm 2-10~keV} = 10^{42.2}$ erg s$^{-1}$, which is among the most powerful AGNs known in nearby dwarf galaxies. The X-ray spectrum has a best-fit photon index of $\Gamma = 2.4$ and an intrinsic absorption of $N_H \sim 10^{21}$ cm$^{-2}$. These results come from a follow-up {\it Chandra X-ray Observatory} study of four irregular/disturbed dwarf galaxies with evidence for hosting AGNs based on optical spectroscopy. The remaining three dwarf galaxies do not have detectable X-ray sources with upper limits of $L_{\rm 2-10~ keV} \lesssim 10^{40}$ erg s$^{-1}$. Taken at face value, our results on RGG 66 suggest that mergers may trigger the most luminous of AGNs in the dwarf galaxy regime, just as they are suspected to do in more massive galaxy mergers.