Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21732604d&link_type=abstract
American Astronomical Society, AAS Meeting #217, #326.04; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Prior imaging of the lenticular galaxy, NGC 3998, with the Hubble Space Telescope (HST) revealed a small, highly inclined, nuclear ionized gas disk, the kinematics of which indicate the presence of a 270 million solar mass black hole. Plausible kinematic models are used to constrain the size of the broad line region (BLR) in NGC 3998 by modeling the shape of the broad Hα, Hβ and Hγ emission line profiles. The analysis indicates that the emitting region is large with an outer radius 7 pc, regardless of whether the kinematic model is represented by an accretion disk or a spherically symmetric inflow. The large size determined for the BLR in NGC 3998 is inconsistent with an extrapolation of the reverberation based BLR size - luminosity relationship defined by the broad emission lines of quasars and high luminosity AGNs. The AGN in NGC 3998 is able to sustain the ionization of the BLR, albeit with a high covering factor ranging between 20% and 100% depending on the spectral energy distribution adopted for the AGN. Furthermore, the electron temperature in the BLR is ≤ 28,800 K consistent with photoionization by the AGN. If the gas density in the BLR is ≥ 7 x 103cm-3 as indicated by the broad forbidden [S II] emission line ratio, then interpreting the broad Hα emission line in terms of a steady state spherically symmetric inflow leads to a rate ≤ 6.5 x 10-2 M &sun;/yr which exceeds the requirement to explain the X-ray luminosity in terms of a radiatively inefficient inflow by a factor of ≤ 18.
Support for Program number HST AR-11752.01-A was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, incorporated, under NASA contract NAS5-26555.
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