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Description
We report the discovery of a buried, active supermassive black hole (SMBH) in SDSS J085153.64+392611.76, a bulgeless Seyfert 2 (Sy2) galaxy. Keck near-infrared observations reveal a hidden broad-line region, allowing for the rare case where strong constraints can be placed on both the BH mass and bulge component. Using virial mass estimators, we obtain a BH mass of log(M_BH_/M_{sun}_)=6.78+/-0.50. This is one of the only Sy2 active galactic nuclei (AGNs) hosted in a bulgeless galaxy with a virial BH mass estimate and could provide important constraints on the formation scenarios of the BH seed population. The lack of a bulge component suggests that the SMBH has grown quiescently, likely caused by secular processes independent of major mergers. In the absence of a detectable bulge component, we find the M_BH_-M_stellar_ relation to be more reliable than the M_BH_-M_bulge_ relation. In addition, we detect extended narrow Pa{alpha} emission that allows us to create a rotation curve where we see counterrotating gas within the central kiloparsec. Possible causes of this counterrotation include a galactic bar or disruption of the inner gas by a recent fly-by of a companion galaxy. This in turn could have triggered accretion onto the central SMBH in the current AGN phase.
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