The Size, Structure and Ionization of the Broad Line Region in NGC 3227

Abstract

Hubble Space Telescope (HST) spectroscopy of the Seyfert 1.5 galaxy, NGC 3227, confirms previous reports that the broad H-alpha emission line flux is time variable, decreasing by a modest ~ 11% between 1999 and 2000 in response to a corresponding ~ 37% decrease in the underlying continuum. Modeling the gas distribution responsible for the broad H-alpha, H-beta and H-gamma emission lines favors a spherically symmetric inflow as opposed to a thin disk. Adopting a central black hole mass of 7.6 x 10^{6} Msun, determined from prior reverberation mapping, leads to the following dimensions for the size of the region emitting the broad H-alpha line; an outer radius ~ 90 l.d and an inner radius ~ 3 l.d. Thus, the previously determined reverberation size for the broad line region (BLR) consistently coincides with the inner radius of a much larger volume of ionized gas. However, the perceived size of the BLR is an illusion, a consequence of the fact that the emitting region is ionization bounded at the outer radius and diminished by Doppler broadening at the inner radius. The actual dimensions of the inflow remain to be determined. Nevertheless, the steady state mass inflow rate is estimated to be ~ 10^{-2} Msun/yr which is sufficient to explain the X-ray luminosity of the AGN in terms of radiatively inefficient accretion. Collectively, the results challenge many preconceived notions concerning the nature of BLRs in active galactic nuclei.

Accepted for publication in the Astrophysical Journal, 17 October, 2012. v2 revised to include a photoionization model and referee comments

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Cited by in corpus (8)

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• Quasars and their emission lines as cosmological probes
• A new method to obtain the Broad Line Region size of high redshift quasars
• The Broad Line Region in NGC 4051: An Inflow Illuminated by a 10^5 K Accretion Disk
• Photoionization Modeling of the Low Luminosity Seyfert 1 Nucleus in NGC 3516
• The dynamics of the broad-line region in NGC 3227
• Giant Broad Line Regions in Dwarf Seyferts