“Comets” orbiting a black hole

Abstract

We use a long (300 ks), continuous Suzaku X-ray observation of the active nucleus in NGC 1365 to investigate the structure of the circumnuclear broad line region (BLR) clouds through their occultation of the X-ray source. The variations of the absorbing column density and of the covering factor indicate that the clouds surrounding the black hole are far from having a spherical geometry (as sometimes assumed), instead they have a strongly elongated and cometary shape, with a dense head (n ∼ 10 11 cm −3 ) and an expanding, dissolving tail. We infer that the cometary tails must be longer than a few times 10 13 cm and their opening angle must be smaller than a few degrees. We suggest that the cometary shape may be a common feature of BLR clouds in general, but which has been difficult to recognize observationally so far. The cometary shape may originate from shocks and hydrodynamical instabilities generated by the supersonic motion of the BLR clouds into the intracloud medium. As a consequence of the mass loss into their tail, we infer that the BLR clouds probably have a lifetime of only a few months, implying that they must be continuously replenished. We also find a large, puzzling discrepancy (two orders of magnitude) between the mass of the BLR inferred from the properties of the absorbing clouds and the mass of the BLR inferred from photoionization models; we discuss the possible solutions to this discrepancy.

NGC 1365: A Low Column Density State Unveiling a Low Ionization Disk Wind

“…We note that the Si and S absorption features appear to be less prominent in the first two intervals; this is similar to what has been reported for previous observations for highly ionized iron (Risaliti et al 2005a;Brenneman et al 2013;Gofford et al 2013;Maiolino et al 2010): when the primary X-ray source is more absorbed by the partial covering absorber the absorption lines are less prominent, possibly due to a lower continuum level. We found the Mg xii Lyα and Lyβ emission lines to be weaker at the beginning of the observation when the column density of the partial covering absorber is higher.…”

“…Prior to this monitoring program, the column density of the cold X-ray absorber was observed to vary from N H ∼ 10 23 -10 24 cm −2 (Risaliti et al 2009a). The likely location of this variable cold absorber, as inferred from the timescale of the fast variability, was consistent with the BLR or the outer part of the BLR (at R < 10 16 cm Brenneman et al 2013;Maiolino et al 2010;Risaliti et al 2005a). Furthermore, all the X-ray observations of NGC 1365 except for when the source is highly obscured, showed the presence of absorption lines due to a highly ionized wind (Brenneman et al 2013;Risaliti et al 2005a;Gofford et al 2013).…”

“…Furthermore, NGC 1365 is also well known for the extremely rapid variability of its X-ray absorber; the monitoring campaigns and the deep X-ray observations performed with Chandra, XMM-Newton, and Suzaku measured a variability of the column density (ranging from few ×10 23 cm −2 to 10 24 cm −2 ) and covering factor of the X-ray absorber (from 10% to 90%) on a timescale of less than a day to weeks (Risaliti et al 2005b(Risaliti et al , 2007(Risaliti et al , 2009bMaiolino et al 2010;Brenneman et al 2013). The emerging scenario for NGC 1365 is that we are viewing the central X-ray source through an absorber made of clouds (with a column density of a few ×10 23 cm −2 up to 10 24 cm −2 ) located closer in than the parsec-scale torus and most likely at a distance from the central black hole of the order of 10 16 cm (Risaliti et al 2007), which is consistent with the distance of the broad-line region (BLR) clouds.…”

Polarized radiative transfer modeling of warped and clumpy dusty tori

“…It spans from 0.03 to 0.05 pc and is filled with electrons, such that the V-band optical depth along the equator is 1 (Marin et al 2012). This equatorial inflow should not be confused with the BLR, where most of the material is neutral (as evidenced by fast variations in the neutral absorbing column seen in X-ray observations, e.g., Maiolino et al (2010) or Netzer (2013) for models). The second structure is an electron-filled hourglass-shaped wind that is outflowing from 0.1 to 30 pc from the center of the model.…”

Type 2 AGN Host Galaxies in the Chandra-COSMOS Legacy Survey: No Evidence of AGN-driven Quenching

“…Since the SMBH-powered emission contributes significantly to the ultraviolet-to-optical parts of the spectra of Type 1 AGNs (e.g., Elvis et al 2012;Hao et al 2013), it is extremely difficult to determine reliable stellar mass for Type 1 AGNs (e.g., Maiolino et al 2010). A detailed analysis of the Type 1 AGN host galaxies in the Chandra COSMOS Legacy Survey, including spectroscopic analysis in the optical and near-infrared wavelength ranges, will be presented in a second paper, Suh et al (2017, in preparation).…”