The Discovery of a Hidden Broad Line AGN in a Bulgeless Galaxy: Keck NIR Spectroscopic Observations of SDSS J085153.64+392611.76

Abstract

We report the discovery of a buried, active supermassive black hole 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 black hole mass and bulge component. Using virial mass estimators, we obtain a black hole mass of log($M_{\mathrm{BH}}/M_{\odot }$) = $6.78\pm 0.50$. This is one of the only Sy2 AGN hosted in a bulgeless galaxy with a virial black hole mass estimate and could provide important constraints on the formation scenarios of the black hole 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 $M_{\mathrm{BH}}$ - $M_{\mathrm{stellar}}$ relation to be more reliable than the $M_{\mathrm{BH}}$ - $M_{\mathrm{bulge}}$ relation. In addition, we detect extended narrow Pa$\alpha$ emission that allows us to create a rotation curve where we see counter-rotating gas within the central kiloparsec (kpc). Possible causes of this counter-rotation 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.

27 pages, 9 figures. Accepted by ApJ

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• NuSTAR Observes Two Bulgeless Galaxies: No Hard X-ray AGN Detected in NGC 4178 or J0851+3926
• A Near-Infrared look at AGN Feedback in Bulgeless Galaxies