The forbidden high-ionization-line region of the type 2 quasar SDSS J11311.05+162739.5: a clear view of the inner face of the torus?

Abstract

We present spectroscopic observations of the type 2 quasar SDSS J11311.05+162739.5 (z = 0.1732), which has the richest spectrum of forbidden high-ionization lines (FHILs, e.g. [Fe VII], [Fe X], [Fe XI] and [Ne V]) yet reported for an active galactic nucleus (AGN), as well as unusually strong [O III] λ4363 emission. The study of this object provides a rare opportunity to investigate the physical conditions and kinematics of the region(s) emitting the FHILs. By comparison with photoionization model results, we find that the FHIL region has high densities (10 5.5 < n H < 10 8.0 cm −3 ) and ionization parameters (−1.5 < log [U] < 0), yet its kinematics are similar to those of the low-ionization emission-line region detected in the same object (full width at half-maximum ∼360 ± 30 km s −1 ), with no evidence for a significant shift between the velocity centroid of the FHILs and the rest frame of the host galaxy. The deduced physical conditions lie between those of the broad-line (n H > 10 9 cm −3 ) and narrow-line regions (n H < 10 6 cm −3 ) of AGNs, and we demonstrate that the FHIL regions must be situated relatively close to the illuminating AGN (0.32 < r FHIL < 50 pc). We suggest that the inner torus wall is the most likely location for the FHIL region, and that the unusual strength of the FHILs in this object is due to a specific viewing angle of the far wall of the torus, coupled with a lack of dust on larger scales that might otherwise obscure our view of the torus.

THE SPITZER MID-INFRARED ACTIVE GALACTIC NUCLEUS SURVEY. I. OPTICAL AND NEAR-INFRARED SPECTROSCOPY OF OBSCURED CANDIDATES AND NORMAL ACTIVE GALACTIC NUCLEI SELECTED IN THE MID-INFRARED

“…The type-2 quasar spectrum (Figure 13) looks very similar to Seyfert-2 spectra, with strong high-ionization narrow lines, but also including low-ionization species such as [OI], consistent with the broad range of ionization expected from an AGN (though lacking the coronal lines seen in the Rose et al (2011) spectrum of SDSS J113111.05+162739.5). The composite host galaxy shows multiple Balmer absorption features, consistent with a dominant stellar population < ∼ 10 8 yr old, as has been seen in the hosts of IR-luminous type-1 quasar hosts (Canalizo & Stockton 2000).…”

On the nature of the red, 2MASS-selected AGN in the local Universe I: an optical spectroscopic study

“…16 out of 27 objects in our sample (59%) show the presence of definite BLR emission. In addition, tentative evidence for weak Hα broad line emission in J1131+16 was presented in Rose et al (2011). The broad line component in J1131+16 is consistent with the presence of a scattered (Antonucci & Miller 1985), or a directly observed, but weak, broad line region (BLR) component.…”

“…For example, we could not produce an adequate fit to the type 2 object J1131+16 because there are relatively few genuine continuum bins suitable to model the spectrum of this object. It should be noted that this object has an unusual spectrum, which contains a large number of forbidden high ionisation lines (FHILs; see Rose et al 2011). Figure 4 shows an example of a successful confit fit to a 2MASS object.…”

Intermediate inclinations of type 2 Coronal-Line Forest AGN

“…they are type 2 AGN, and so are likely observed with our line of sight at a relatively large inclination angle to the torus axis. The far wall of the torus is a plausible source for the FHILs which will be strongest if we have a maximal view of the inner wall (Nagao et al 2001;Rose et al 2011). The Coronal Line Region (CLR) lies at a distance comparable to the hot dust sublimation radius (RET15).…”