Detection of the Intermediate-Width Emission Line Region in Quasar Oi 287 With the Broad Emission Line Region Obscured by the Dusty Torus

Abstract

The existence of intermediate-width emission line regions (IELRs) in active galactic nuclei has been discussed for over two decades. A consensus, however, is yet to be arrived at due to the lack of convincing evidence for their detection. We present a detailed analysis of the broadband spectrophotometry of the partially obscured quasar OI 287. The ultraviolet intermediate-width emission lines (IELs) are very prominent, in high contrast to the corresponding broad emission lines (BELs) which are heavily suppressed by dust reddening. Assuming that the IELR is virialized, we estimated its distance to the central black hole to be ∼2.9 pc, similar to the dust sublimation radius of ∼1.3 pc. Photo-ionization calculations suggest that the IELR has a hydrogen density of ∼10 8.8 -10 9.4 cm −3 , within the range of values quoted for the dusty torus near the sublimation radius. Both its inferred location and physical conditions suggest that the IELR originates from the inner surface of the dusty torus. In the spectrum of this quasar, we identified only one narrow absorption-line system associated with the dusty material. With the aid of photo-ionization model calculations, we found that the obscuring material might originate from an outer region of the dusty torus. We speculate that the dusty torus, which is exposed to the central ionizing source, may produce IELs through photo-ionization processes, as well as obscure BELs as a natural "coronagraph." Such a "coronagraph" could be found in a large number of partially obscured quasars and may be a useful tool to study IELRs.

Reddening and He i∗ λ10830 Absorption Lines in Three Narrow-line Seyfert 1 Galaxies

“…We picked them up again during the series study of the reddening AGNs (e.g., Li et al 2015;Liu et al 2016;Pan et al 2017;Zhang et al 2017). We study the He I* λ10830 absorption lines (the first detection reported by Leighly et al 2011) as well as the continuum, and hydrogen Balmer/Paschen broad emission lines of these objects.…”

The Intermediate-Line Region in Active Galactic Nuclei

“…Additionally, Crenshaw et al (2009) detected ILR emission with width of 680 km s −1 in the historically low state spectrum of NGC 5548 obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. Using the HST/ FOS spectra of quasar OI 287, Li et al (2015) reported the detection of intermediate width emission lines originating at a distance of ∼ 2.9 pc from the central black hole. The question remains unanswered, is there any separation between gas responsible for broad and narrow line emission in different types of AGN?…”

A unifying evolutionary framework for infrared-selected obscured and unobscured quasar host haloes

“…DiPompeo et al 2014a;Runnoe et al 2014;Brotherton, Singh & Runnoe 2015;Stalevski et al 2016) and in the presence of an axis-symmetric dust distribution (the so-called "dusty-torus"), orientation alone has the potential to unify obscured and unobscured quasars, as it largely has for Seyfert galaxies (e.g. Antonucci 1993;Stalevski et al 2012;Ichikawa et al 2015;Gratadour et al 2015;Mason 2015;Netzer 2015;Siebenmorgen, Heymann & Efstathiou 2015;Li et al 2015;Wylezalek et al 2016;Obied et al 2016). On the other, attempts to explain the driving of gas into nuclear regions in order to fuel the supermassive black hole (SMBH) have resulted in models that link quasar activity to major galaxy mergers and a general evolutionary sequence (e.g.…”