Orientation effects in quasar spectra: the broad- and narrow-line regions

Abstract

The definitive version can be found at : http://onlinelibrary.wiley.com/ Copyright Wiley-BlackwellWe use the Sloan Digital Sky Survey, along with the NRAO VLA Sky Survey and the Westerbork Northern Sky Survey to define a sample of 746 radio-loud quasars and measure their 330 MHz-1.4 GHz spectral indexes. Following previous authors we take the radio spectral index as an indicator of the orientation towards the quasars such that more pole-on sources tend to have flatter spectral indexes. We use this proxy for the orientation of quasars to investigate the effect orientation may have on optical spectra. Quasars with flatter spectral indexes tend to be brighter. However, we find no indication of reddening in steep-spectrum quasi-stellar objects (QSOs) to indicate obscuration of the accretion disc by a torus as a possible explanation. Nor do we find increased reddening in the flat-spectrum sources which could imply a contribution from jet-related synchrotron emission. We reproduce a previously described anticorrelation between the width of the Mg ii line and radio spectral index that indicates a disc-like geometry for the Mg ii broad-line region (BLR). However, in contrast to previous authors we find no such correlation for the C iv line suggesting a more isotropic high-ionization BLR. Both the [O ii] and [O iii] narrow lines have more flux in steep spectrum sources, while the [O iii]/[O ii] flux ratio is lower in these sources. To describe both of these effects we propose a simple geometric model in which the narrow-line region (NLR) exists primarily on the surface of optically thick clouds facing the active nucleus and the NLR is stratified such that higher ionization lines are found preferentially closer to the nucleus. Quantitatively we find that orientation may effect the observed strength of narrow lines, as well as ratios between lines, by a factor of similar to 2. These findings have implications for the use of [O iii] and [O ii] emission lines to estimate bolometric luminosities, as well as comparisons between narrow-line luminosity functions for type 1 and 2 objects and the potential of emission-line diagnostic diagrams as an accurate tool with which to distinguish types of active galactic nuclei. Finally we find no evidence that broad-absorption line (BAL) QSOs have a different spectral index distribution to non-BALs although we only have 25 obvious BALs in our sample

Evidence of powerful relativistic jets in narrow-line Seyfert 1 galaxies

“…[45]). The FWHMs of the lines were always > 2000 km/s [36,102]. The masses of the central black hole are in the range of 10 8−10 M ⊙ (e.g.…”

A Very Large Array Survey of Radio-Selected SDSS Broad Absorption Line Quasars

“…Studies so far have shown that BAL quasars have a wide range of radio spectral indices (α, defined as f ∝ ν α , where f is the radio flux and ν is the frequency), suggesting a full range of orientations (Becker et al 2000). A significant difference between the distribution of α for BAL and non-BAL quasars has not been previously identified, but the sample sizes have typically been small (Fine et al 2011). Montenegro-Montes et al (2008) did identify a difference in the α distributions of their samples-however when they restricted their analysis to include only compact sources the difference disappeared.…”

“…This was made possible mostly due to large radio surveys such as FIRST (Becker et al 1995) and NVSS (Condon et al 1998), and allowed the first true studies of the orientation of BAL quasars. Although BAL quasars often do not have extended radio structure which would allow a direct estimate of their orientation, the steepness of radio spectrum can indicate orientation (Fine et al 2011). In general, more edge-on radio sources are dominated by optically thin lobe emission, which has a steep spectrum, and more face-on sources are dominated by relativistically boosted core radio emission, which is optically thick and thus flatter due to synchrotron self absorption.…”

Microlensing of the broad line region in 17 lensed quasars

“…(1) but for the C iv line. Black-hole mass estimates derived from that line are more controversial because of uncertainties on the geometry of the C iv emitting region, because of the contamination from a putative narrow C iv emission and because virial equilibrium is not expected to hold perfectly for such high ionization lines (Richards et al 2002;Bachev et al 2004;Marziani et al 2006;Fine et al 2011;Assef et al 2011;Wang et al 2011;Richards et al 2011;Marziani & Sulentic 2012). For two systems (H1413+117 and J1131-1231), we also used H β to calculate M BH .…”