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Register a new userTime delay measurement of Mg II line in CTS C30.10 with SALT
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We report 6 yr monitoring of a distant bright quasar CTS C30.10 (z = 0.90052) with the Southern African Large Telescope (SALT). We measured the rest-frame time-lag of $562pm 2$ days between the continuum variations and the response of the Mg II emission line, using the Javelin approach. More conservative approach, based on five different methods, imply the time delay of $564^{+109}_{-71}$ days. This time delay, combined with other available measurements of Mg II line delay, mostly for lower redshift sources, shows that the Mg II line reverberation implies a radius-luminosity relation very similar to the one based on a more frequently studied H$beta$ line.
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The Mg II emission line is visible in the optical band for intermediate redshift quasars (0.4 < z < 1.6) and it is thus an extremely important tool to measure the black hole mass and to understand the structure of the Broad Line Region. We aim to determine the substructure and the variability of the Mg II line with the aim to identify which part of the line comes from a medium in Keplerian motion. Using the Southern African Large Telescope (SALT) with the Robert Stobie Spectrograph (RSS) we performed ten spectroscopic observations of quasar HE 0435-4312 (z = 1.2231) over a period of three years (Dec 23/24, 2012 to Dec 7/8, 2015). Both the Mg II line and the Fe II pseudo-continuum increase with time. We clearly detect the systematic shift of the Mg II line with respect to the Fe II over the years, corresponding to the acceleration of 104 pm 14 km/s/year in the quasar rest frame. The Mg II line shape is clearly non-Gaussian but single-component, and the increase in line equivalent width and line shift is not accompanied with significant evolution of the line shape. We analyse the conditions in the Mg II and Fe II formation region and we note that the very large difference in the covering factor and the turbulent velocity also support the conclusion that the two regions are spatially separated. The measured acceleration of the line systematic shift is too large to connect it with the orbital motion at a distance of the Broad Line Region (BLR) in this source. It may imply a precessing inner disk illuminating the BLR. Further monitoring is still needed to better constrain the variability mechanism.
We investigate the relationships between Mg ii {lambda}2798 emission line properties, as well as between these properties and inclination angle and Fe ii strength, in a lobe-dominated quasar sample. We find no correlation between Mg ii line width and inclination, unlike previous studies of the general quasar population. This suggests that the Mg ii emission region in these objects is not of a thin disk geometry, however the average equivalent width of the line negates a spherical alternative. A positive correlation between Mg ii equivalent width and inclination cannot be ruled out, meaning there is no strong evidence that Mg ii emission is anisotropic. Since thin disk emission would be highly directional, the geometric implications of these two findings are compatible. The lack of line width correlation with inclination may also indicate that Mg ii is useful for estimating black hole masses in lobe-dominated quasar samples, since it is unbiased by orientation. Some quasars in our sample have almost edge-on viewing angles and therefore cannot have a smooth toroidal obscurer co-planar with the accretion disk. Alternatives may be a distorted dusty disk or a clumpy obscurer. This could result from the sample selection bias towards high inclination objects, rather than intrinsic differences between lobe-dominated and typical quasars. Five objects have visible [O iii] allowing equivalent width calculation, revealing it to be higher than in typical quasars. Since these objects are of high inclination, this finding supports the positive correlation between [O iii] equivalent width and inclination found in a previous study.
We present the single-epoch black hole mass (M$_{rm BH}$) calibrations based on the rest-frame UV and optical measurements of Mg II 2798AA and H$beta$ 4861AA lines and AGN continuum, using a sample of 52 moderate-luminosity AGNs at z$sim$0.4 and z$sim$0.6 with high-quality Keck spectra. We combine this sample with a large number of luminous AGNs from the Sloan Digital Sky Survey to increase the dynamic range for a better comparison of UV and optical velocity and luminosity measurements. With respect to the reference M$_{rm BH}$ based on the line dispersion of H$beta$ and continuum luminosity at 5100AA, we calibrate the UV and optical mass estimators, by determining the best-fit values of the coefficients in the mass equation. By investigating whether the UV estimators show systematic trend with Eddington ratio, FWHM of H$beta$, the Fe II strength, and the UV/optical slope, we find no significant bias except for the slope. By fitting the systematic difference of Mg II-based and H$beta$-based masses with the L$_{3000}$/L$_{5100}$ ratio, we provide a correction term as a function of the spectral index as $Delta$C = 0.24 (1+$alpha_{lambda}$) + 0.17, which can be added to the Mg II-based mass estimators if the spectral slope can be well determined. The derived UV mass estimators typically show $>$$sim$0.2 dex intrinsic scatter with respect to H$beta$-based M$_{rm BH}$, suggesting that the UV-based mass has an additional uncertainty of $sim$0.2 dex, even if high quality rest-frame UV spectra are available.
We generalize the semi-analytical line transfer (SALT) model recently introduced by Scarlata & Panagia (2015) for modeling galactic outflows, to account for bi-conical geometries of various opening angles and orientations with respect to the line-of-sight to the observer, as well as generalized velocity fields. We model the absorption and emission component of the line profile resulting from resonant absorption in the bi-conical outflow. We show how the outflow geometry impacts the resulting line profile. We use simulated spectra with different geometries and velocity fields to study how well the outflow parameters can be recovered. We find that geometrical parameters (including the opening angle and the orientation) are always well recovered. The density and velocity field parameters are reliably recovered when both an absorption and an emission component are visible in the spectra. This condition implies that the velocity and density fields for narrow cones oriented perpendicular to the line of sight will remain unconstrained.
We investigate the effect of Fe II equivalent width ($W_{2600}$) and fibre size on the average luminosity of [O II]$lambdalambda$3727,3729 nebular emission associated with Mg II absorbers (at $0.55 le z le 1.3$) in the composite spectra of quasars obtained with 3 and 2 arcsec fibres in the Sloan Digital Sky Survey. We confirm the presence of strong correlations between [O II] luminosity (L$_{[rm O~II]}$) and equivalent width ($W_{2796}$) and redshift of Mg II absorbers. However, we show L$_{[rm O~II]}$ and average luminosity surface density suffers from fibre size effects. More importantly, for a given fibre size the average L$_{[rm O~II]}$ strongly depends on the equivalent width of Fe II absorption lines and found to be higher for Mg II absorbers with $R equiv$ $W_{rm 2600}/W_{rm 2796}$ $ge 0.5$. In fact, we show the observed strong correlations of L$_{[rm O~II]}$ with $W_{2796}$ and $z$ of Mg II absorbers are mainly driven by such systems. Direct [O II] detections also confirm the link between L$_{[rm O~II]}$ and $R$. Therefore, one has to pay attention to the fibre losses and dependence of redshift evolution of Mg II absorbers on $W_{2600}$ before using them as a luminosity unbiased probe of global star formation rate density. We show that the [O II] nebular emission detected in the stacked spectrum is not dominated by few direct detections (i.e., detections $ge 3 sigma$ significant level). On an average the systems with $R$ $ge 0.5$ and $W_{2796}$ $ge 2$ AA are more reddened, showing colour excess E($B-V$) $sim$ 0.02, with respect to the systems with $R$ $< 0.5$ and most likely traces the high H I column density systems.
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