The study of Seyfert 2 galaxies with and without infrared broad lines

Abstract

From the literature, we construct from literature a sample of 25 Seyfert 2 galaxies (S2s) with a broad line region detected in near infrared spectroscopy and 29 with NIR BLR which was detected. We find no significant difference between the nuclei luminosity (extinction-corrected [OIII] 5007) and infrared color f 60 /f 25 between the two populations, suggesting that the non-detections of NIR BLR could not be due to low AGN luminosity or contamination from the host galaxy. As expected, we find significantly lower X-ray obscurations in Seyfert 2s with NIR BLR detection, supporting the unification scheme. However, such a scheme was challenged by the detection of NIR BLR in heavily X-ray obscured sources, especially in six of them with Compton-thick X-ray obscuration. The discrepancy could be solved by the clumpy torus model and we propose a toy model demonstrating that IR-thin X-ray-thick S2s could be viewed at intermediate inclinations, and compared with those IR-thick X-ray-thick S2s. We note that two of the IR-thin X-raythick S2s (NGC 1386 and NGC 7674) experienced X-ray transitions, i.e. from Comptonthin to Compton-thick appearance or vice versa based on previous X-ray observations, suggesting that X-ray transitions could be common in this special class of objects.

Detection of Faint BLR Components in the Starburst/Seyfert Galaxy NGC 6221 and Measure of the Central BH Mass

“…The detection of faint broad emission line components in AGN2 (or reddened AGN, in general), although difficult, is not uncommon (see e.g. Veilleux et al, 1997;Riffel et al, 2006;Cai et al, 2010). As discussed in the introduction, when detected, the width (e.g.…”

Detection of faint broad emission lines in type 2 AGN – II. On the measurement of the black hole mass of type 2 AGN and the unified model

“…Heckman et al 2004, from SDSS), the authors used the M BH -host scaling relations that have not yet been proven to hold for such a population (see Graham 2008;Kormendy et al 2011). Several studies have shown that many AGN2 exhibit faint broad line components if observed with high ( 20) S/N in the near-infrared (NIR; 0.8-2.5 µm), where the dust absorption is less severe than in the optical (Veilleux et al 1997;Riffel et al 2006;Cai et al 2010). Moreover observation in the NIR of AGN1, whose M BH were measured using reverberation mapping techniques (RM; Blandford & McKee 1982;Peterson 1993), have demonstrated that the virial method to measure M BH can be efficiently used with the NIR Paα λ1.875 µm and Paβ λ1.282 µm lines (Kim et al 2010;Landt et al 2011).…”

Detection of faint broad emission lines in type 2 AGN – I. Near-infrared observations and spectral fitting

“…polarimetric and/or high S/N spectroscopy, both in the optical and near infrared bands) to find evidence of the presence of the BLR also in AGN2. Several studies have shown that some AGN2 exhibit faint components of broad lines if observed with high S/N in the near infrared (NIR), where the dust absorption is less severe than in the optical (Veilleux et al 1997;Riffel et al 2006;Cai et al 2010). These studies have found evidence of faint BLR components only in few cases.…”