No Arabic abstract
Quasars accreting matter at very high rates (known as extreme Population A [xA]) may provide a new class of distance indicators covering cosmic epochs from present day up to less than 1 Gyr from the Big Bang. We report on the developments of a method that is based on virial luminosity estimates from measurements of emission line widths of xA quasars. The approach is conceptually equivalent to the virial estimates based on early and late type galaxies. The main issues related to the cosmological application of luminosity estimates from xA quasar line widths are the identification of proper emission lines whose broadening is predominantly virial over a wide range of luminosity, and the assessment of the effect of the emitting region orientation with respect to the line of sight. We report on recent developments concerning the use of the AlIII 1860 intermediate ionisation line and of the Hydrogen Balmer line H$beta$ as virial broadening estimators.
Accurately weigh the masses of SMBH in AGN is currently possible for only a small group of local and bright broad-line AGN through reverberation mapping (RM). Statistical demographic studies can be carried out considering the empirical scaling relation between the size of the BLR and the AGN optical continuum luminosity. However, there are still biases against low-luminosity or reddened AGN, in which the rest-frame optical radiation can be severely absorbed/diluted by the host and the BLR emission lines could be hard to detect. Our purpose is to widen the applicability of virial-based SE relations to reliably measure the BH masses also for low-luminosity or intermediate/type 2 AGN that are missed by current methodology. We achieve this goal by calibrating virial relations based on unbiased quantities: the hard X-ray luminosities, in the 2-10 keV and 14-195 keV bands, that are less sensitive to galaxy contamination, and the FWHM of the most important rest-frame NIR and optical BLR emission lines. We built a sample of RM AGN having both X-ray luminosity and broad optical/NIR FWHM measurements available in order to calibrate new virial BH mass estimators. We found that the FWHM of the H$alpha$, H$beta$ and NIR lines (i.e. Pa$alpha$, Pa$beta$ and HeI$lambda$10830) all correlate each other having negligible or small offsets. This result allowed us to derive virial BH mass estimators based on either the 2-10 keV or 14-195 keV luminosity. We took also into account the recent determination of the different virial coefficients $f$ for pseudo and classical bulges. By splitting the sample according to the bulge type and adopting separate $f$ factors we found that our virial relations predict BH masses of AGN hosted in pseudobulges $sim$0.5 dex smaller than in classical bulges. Assuming the same average $f$ factor for both populations, a difference of $sim$0.2 dex is still found.
The incidence of broad absorption lines (BALs) in quasar samples is often interpreted in the context of a geometric unification model consisting of an accretion disc and an associated outflow. We use the the Sloan Digital Sky Survey (SDSS) quasar sample to test this model by examining the equivalent widths (EWs) of CIV 1550AA, Mg II 2800AA, [OIII] 5007AA and C III] 1909AA. We find that the emission line EW distributions in BAL and non-BAL quasars are remarkably similar -- a property that is inconsistent with scenarios in which a BAL outflow rises equatorially from a geometrically thin, optically thick accretion disc. We construct simple models to predict the distributions from various geometries; these models confirm the above finding and disfavour equatorial geometries. We show that obscuration, line anisotropy and general relativistic effects on the disc continuum are unlikely to hide an EW inclination dependence. We carefully examine the radio and polarisation properties of BAL quasars. Both suggest that they are most likely viewed (on average) from intermediate inclinations, between type 1 and type 2 AGN. We also find that the low-ionization BAL quasars in our sample are not confined to one region of `Eigenvector I parameter space. Overall, our work leads to one of the following conclusions, or some combination thereof: (i) the continuum does not emit like a geometrically thin, optically thick disc; (ii) BAL quasars are viewed from similar angles to non-BAL quasars, i.e. low inclinations; (iii) geometric unification does not explain the fraction of BALs in quasar samples.
We wish to study the extent and subparsec scale spatial structure of intervening quasar absorbers, mainly those involving neutral and molecular gas. We have selected quasar absorption systems with high spectral resolution and good S/N data, with some of their lines falling on quasar emission features. By investigating the consistency of absorption profiles seen for lines formed either against the quasar continuum source or on the much more extended emission line region (ELR), we can probe the extent and structure of the foreground absorber over the extent of the ELR (0.3-1 pc). The spatial covering analysis provides constraints on the transverse size of the absorber and thus is complementary to variability or photoionisation modelling studies. The methods we used to identify spatial covering or structure effects involve line profile fitting and curve of growth analysis.We have detected three absorbers with unambiguous non uniformity effects in neutral gas. For one extreme case, the FeI absorber at z_abs=0.45206 towards HE 0001-2340, we derive a coverage factor of the ELR of at most 0.10 and possibly very close to zero; this implies an absorber overall size no larger than 0.06 pc. For the z_abs=2.41837 CI absorber towards QSO J1439+1117, absorption is significantly stronger towards the ELR than towards the continuum source in several CI and CI* velocity components pointing to factors of about two spatial variations of their column densities and the presence of structures at the 100 au - 0.1 pc scale. The other systems with firm or possible effects can be described in terms of partial covering of the ELR, with coverage factors in the range 0.7 - 1. The overall results for cold, neutral absorbers imply a transverse extent of about five times or less the ELR size, which is consistent with other known constraints.
Unified schemes of radio sources, which account for different types of radio AGN in terms of anisotropic radio and optical emission, together with different orientations of the ejection axis to the line of sight, have been invoked for many years. Recently, large samples of optical quasars, mainly from the Sloan Digital Sky Survey, together with large radio samples, such as FIRST, have become available. These hold the promise of providing more stringent tests of unified schemes but, compared to previous samples, lack high resolution radio maps. Nevertheless they have been used to investigate unified schemes, in some cases yielding results which appear inconsistent with such theories. Here we investigate using simulations how the selection effects to which such investigations are subject can influence the conclusions drawn. In particular, we find that the effects of limited resolution do not allow core-dominated radio sources to be fully represented in the samples, that the effects of limited sensitivity systematically exclude some classes of sources and the lack of deep radio data make it difficult to decide to what extent closely separated radio sources are associated. Nevertheless, we conclude that relativistic unified schemes are entirely compatible with the current observational data. For a sample selected from SDSS and FIRST which includes weak-cored triples we find that the equivalent width of the [OIII] emission line decreases as core-dominance increases, as expected, and also that core-dominated quasars are optically brighter than weak-cored quasars.
Quasar emission lines are often shifted from the systemic velocity due to various dynamical and radiative processes in the line-emitting region. The level of these velocity shifts depends both on the line species and on quasar properties. We study velocity shifts for the line peaks of various narrow and broad quasar emission lines relative to systemic using a sample of 849 quasars from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project. The coadded (from 32 epochs) spectra of individual quasars have sufficient signal-to-noise ratio (SNR) to measure stellar absorption lines to provide reliable systemic velocity estimates, as well as weak narrow emission lines. The sample also covers a large dynamic range in quasar luminosity (~2 dex), allowing us to explore potential luminosity dependence of the velocity shifts. We derive average line peak velocity shifts as a function of quasar luminosity for different lines, and quantify their intrinsic scatter. We further quantify how well the peak velocity can be measured for various lines as a function of continuum SNR, and demonstrate there is no systematic bias in the line peak measurements when the spectral quality is degraded to as low as SNR~3 per SDSS pixel. Based on the observed line shifts, we provide empirical guidelines on redshift estimation from [OII]3728, [OIII]5008, [NeV]3426, MgII, CIII], HeII1640, broad Hbeta, CIV, and SiIV, which are calibrated to provide unbiased systemic redshifts in the mean, but with increasing intrinsic uncertainties of 46, 56, 119, 205, 233, 242, 400, 415, and 477 km/s, in addition to the measurement uncertainties. These more realistic redshift uncertainties are generally much larger than the formal uncertainties reported by the redshift pipelines for spectroscopic quasar surveys, and demonstrate the infeasibility of measuring quasar redshifts to better than ~200 km/s with only broad lines.