Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new user[OII] Emission, Eigenvector 1 and Orientation in Radio-quiet Quasars
115
0
0.0
(
0
)
Added by
Joanna Kuraszkiewicz
Publication date
2000
fields
Physics
and research's language is
English
Authors
J. Kuraszkiewicz
Ask ChatGPT about the research
No Arabic abstract
We present supportive evidence that the Boroson and Green eigenvector 1 is not driven by source orientation. Until recently it was generally accepted that eigenvector 1 does not depend on orientation as it strongly correlates with [OIII]5007 emission, thought to be an isotropic property. However, recent studies of radio-loud AGN have questioned the isotropy of [OIII] emission and concluded that [OII]3727 emission is isotropic. In this paper we investigate the relation between eigenvector 1 and [OII] emission in radio-quiet BQS (Bright Quasar Survey) quasars, and readdress the issue of orientation as the driver of eigenvector 1. We find significant correlations between eigenvector 1 and orientation independent [OII] emission, which implies that orientation does not drive eigenvector 1. The luminosities and equivalent widths of [OIII] and [OII] correlate with one another, and the range in luminosities and equivalent widths is similar. This suggests that the radio-quiet BQS quasars are largely free of orientation dependent dust effects and ionization dependent effects in the narrow-line region. We also conclude that neither the [OIII] emission nor the [OII]/[OIII] ratio are dependent on orientation in our radio-quiet BQS quasar sample, contrary to recent results found for radio-loud quasars.
rate research
Read More
In order to understand the role of radio-quiet quasars (RQQs) in galaxy evolution, we must determine the relative levels of accretion and star-formation activity within these objects. Previous work at low radio flux-densities has shown that accretion makes a significant contribution to the total radio emission, in contrast with other quasar studies that suggest star formation dominates. To investigate, we use 70 RQQs from the Spitzer-Herschel Active Galaxy Survey. These quasars are all at $z$ ~ 1, thereby minimising evolutionary effects, and have been selected to span a factor of ~100 in optical luminosity, so that the luminosity dependence of their properties can be studied. We have imaged the sample using the Karl G. Jansky Very Large Array (JVLA), whose high sensitivity results in 35 RQQs being detected above 2 $sigma$. This radio dataset is combined with far-infrared luminosities derived from grey-body fitting to Herschel photometry. By exploiting the far-infrared--radio correlation observed for star-forming galaxies, and comparing two independent estimates of the star-formation rate, we show that star formation alone is not sufficient to explain the total radio emission. Considering RQQs above a 2-$sigma$ detection level in both the radio and the far-infrared, 92 per cent are accretion-dominated, and the accretion process accounts for 80 per cent of the radio luminosity when summed across the objects. The radio emission connected with accretion appears to be correlated with the optical luminosity of the RQQ, whilst a weaker luminosity-dependence is evident for the radio emission connected with star formation.
We discuss 6 GHz JVLA observations covering a volume-limited sample of 178 low redshift ($0.2 < z < 0.3$) optically selected QSOs. Our 176 radio detections fall into two clear categories: (1) About $20$% are radio-loud QSOs (RLQs) having spectral luminosities $L_6 gtrsim 10^{,23.2} mathrm{~W~Hz}^{-1}$ primarily generated in the active galactic nucleus (AGN) responsible for the excess optical luminosity that defines a emph{bona fide} QSO. (2) The radio-quiet QSOs (RQQs) have $10^{,21} lesssim L_6 lesssim 10^{,23.2} mathrm{~W~Hz}^{-1}$ and radio sizes $lesssim 10 mathrm{~kpc}$, and we suggest that the bulk of their radio emission is powered by star formation in their host galaxies. Radio silent QSOs ($L_6 lesssim 10^{,21} mathrm{~W~Hz}^{-1}$) are rare, so most RQQ host galaxies form stars faster than the Milky Way; they are not red and dead ellipticals. Earlier radio observations did not have the luminosity sensitivity $L_6 lesssim 10^{,21} mathrm{~W~Hz}^{-1}$ needed to distinguish between such RLQs and RQQs. Strong, generally double-sided, radio emission spanning $gg 10 mathrm{~kpc}$ was found associated with 13 of the 18 RLQ cores having peak flux densities $S_mathrm{p} > 5 mathrm{~mJy~beam}^{-1}$ ($log(L) gtrsim 24$). The radio luminosity function of optically selected QSOs and the extended radio emission associated with RLQs are both inconsistent with simple unified models that invoke relativistic beaming from randomly oriented QSOs to explain the difference between RLQs and RQQs. Some intrinsic property of the AGNs or their host galaxies must also determine whether or not a QSO appears radio loud.
Understanding the interplay between black-hole accretion and star formation, and how to disentangle the two, is crucial to our understanding of galaxy formation and evolution. To investigate, we use a combination of optical and near-infrared photometry to select a sample of 74 quasars from the VISTA Deep Extragalactic Observations (VIDEO) Survey, over 1 deg$^2$. The depth of VIDEO allows us to study very low accretion rates and/or lower-mass black holes, and 26 per cent of the candidate quasar sample has been spectroscopically confirmed. We use a radio-stacking technique to sample below the nominal flux-density threshold using data from the Very Large Array at 1.4 GHz and find, in agreement with other work, that a power-law fit to the quasar-related radio source counts is inadequate at low flux density. By comparing with a control sample of galaxies (where we match in terms of stellar mass), and by estimating the star formation rate, we suggest that this radio emission is predominantly caused by accretion activity rather than star-formation activity.
A small subset of optically selected radio-quiet quasars showing weak or no emission lines may turn out to be the elusive radio-quiet BL Lac objects, or simply be radio-quiet QSOs with a still-forming/shielded broad line region (BLR). High polarisation ($p$ $>$ 3$-$4$%$), a hallmark of BL Lacs, can be used to test whether some optically selected `radio-quiet weak emission line quasars (RQWLQs) show a fractional polarisation high enough to qualify as radio-quiet analogs of BL Lac objects. Out of the observed six RQWLQs candidates showing an insignificant proper motion, only two are found to have $p$ $>$ 1$%$. For these two RQWLQs, namely J142505.59$+$035336.2, J154515.77+003235.2, we found polarisation of 1.03$pm$0.36$%$, 1.59$pm$0.53$%$ respectively, which again is too modest to justify a (radio-quiet) BL Lac classification. We also present here a statistical comparison of the optical spectral index, for a set of 40 RQWLQs with redshift-luminosity matched control sample of 800 QSOs and an equivalent sample of 120 blazars. The spectral index distribution of RQWLQs is found to differ, at a high significance level, from that of blazars and is consistent with that of the ordinary QSOs. Likewise, a structure-function analysis of photometric light curves presented here suggests that the mechanism driving optical variability in RQWLQs is similar to that operating in QSOs and different from that of blazars. These findings are consistent with the common view that the central engine in RQWLQs, as a population, is akin to that operating in normal QSOs and the primary differences between them might be related to differences in the BLR.
We present radio and X-ray observations, as well as optical light curves, for a subset of 26 BL Lac candidates from the Sloan Digital Sky Survey (SDSS) lacking strong radio emission and with z<2.2. Half of these 26 objects are shown to be stars, galaxies, or absorbed quasars. We conclude that the other 13 objects are Active Galactic Nuclei (AGN) with abnormally weak emission features; ten of those 13 are definitively radio-quiet, and, for those with available optical light curves, their level of optical flux variability is consistent with radio-quiet quasars. We cannot exclude the possibility that some of these 13 AGN lie on the extremely radio-faint tail of the BL Lac distribution, but our study generally supports the notion that all BL Lac objects are radio-loud. These radio-quiet AGN appear to have intrinsically weak or absent broad emission line regions, and, based on their X-ray properties, we argue that some are low-redshift analogs to weak line quasars (WLQs). SDSS BL Lac searches are so far the only systematic surveys of the SDSS database capable of recovering such exotic low-redshift WLQs. There are 71 more z<2.2 radio-quiet BL Lac candidates already identified in the SDSS not considered here, and many of those might be best unified with WLQs as well. Future studies combining low- and high-redshift WLQ samples will yield new insight on our understanding of the structure and formation of AGN broad emission line regions.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
