Evolution of the Nuclear Accretion Disk Emission in NGC 1097: Getting Closer to the Black Hole

Abstract

We study the evolution of the broad, double-peaked H emission-line profile of the LINER/Seyfert 1 nucleus of NGC 1097, using 24 spectra obtained over a time span of 11 years-from 1991 November through 2002 October. While in the first 5 years the main variation was in the relative intensity of the blue and red peaks, in the last years we have also observed an increasing separation between the two peaks, at the same time as the integrated flux in the broad line has decreased. We propose a scenario in which the emission originates in an asymmetric accretion disk around a supermassive black hole, whose source of ionization is getting dimmer, causing the region of maximum emission to come closer to the center (and thus to regions of higher projected velocity). We use the observations to constrain the evolution of the accretion disk emission and to evaluate two models: the elliptical-disk model previously found to reproduce the observations from 1991 to 1996 and a model of a circular disk with a single spiral arm. In both models the peak emissivity of the disk drifts inward with time, while the azimuthal orientation of the elliptical-disk or the spiral pattern varies with time. In the case of the spiral-arm model, the whole set of data is consistent with a monotonic precession of the spiral pattern, which has completed almost two revolutions since 1991. Thus, we favor the spiral-arm model, which, through the precession period, implies a black hole mass that is consistent with the observed stellar velocity dispersion. In contrast, the elliptical-disk model requires a mass that is an order of magnitude lower. Finally, we have found tentative evidence of the emergence of an accretion disk wind, which we hope to explore further with future observations.

Evolution of the accretion disc around the supermassive black hole of NGC 7213

“…We modeled the double-peaked Hα profiles using the accretion disk model described by Gilbert et al (1999), Storchi-Bergmann et al (2003), and Schimoia et al (2012Schimoia et al ( , 2015. In this formulation, the broad doublepeaked emission line originates in a relativistic Keplerian disk of gas surrounding the SMBH.…”

“…Very broad double-peaked lines -with velocity separation of ∼10,000 km s −1 between the blue and red peaks are thought to originate in the outer parts of an accretion disk (Schimoia et al 2012;Lewis et al 2010). Models of ionized gas rotating in a relativistic Keplerian accretion disk around a SMBH have been successful in accounting for such double-peaked profiles Storchi-Bergmann et al 2003;Strateva et al 2003;Lewis et al 2010). These models explain most of the observed features of the profiles (Eracleous & Halpern 2003) and can help to constrain the physical properties of the line emititing part of the disk, as, for instance, the inner and outer limits for the emitting region as well as its inclination relative to the plane of the sky.…”

Disk Corona Interaction: Mechanism for the Disk Truncation and Spectrum Change in Low-Luminosity Active Galactic Nuclei

“…Furthermore, the iron line features in which the FWHM is connected to the Keplerian motion of gas in the inner radius of the disk suggest a larger radius than the innermost stable circular orbit (ISCO; e.g., NGC 4593 in Markowitz & Reeves 2009). Finally, the double-peaked Balmer emission lines, in particular, the rarity and shapes of their profiles, have been speculated as arising from a flat, rotating, outer/truncated disk observed at a large inclination (see, e.g., Storchi-Bergmann et al 2003;Wang et al 2005;Eracleous et al 2009). Although support for such a picture has been provided by a number of phenomenological studies, an understanding of disk truncation and the spectral transition to an ADAF at low mass accretion rates remains a challenge.…”

The Time-domain Spectroscopic Survey: Target Selection for Repeat Spectroscopy

“…Thus, we refer to these objects as disk-like emitters hereafter. Previous long-term monitoring of disk-like emitters has sampled about two dozen objects over 20 years (e.g., Sergeev et al 2000Sergeev et al , 2017Storchi-Bergmann et al 2003;Gezari et al 2007;Flohic 2008;Lewis et al 2010;Popović et al 2011Popović et al , 2014, and references therein) at < z 0.4, most of which are radio loud.…”