Related papers: Relation between the variations in the MgII $\lamb…

We present ALMA detections of the [CII] 158 micron emission line and the underlying far-infrared continuum of three quasars at 6.6<z<6.9 selected from the VIKING survey. The [CII] line fluxes range between 1.6-3.4 Jy km/s ([CII]…

The Fe II/Mg II emission line flux ratio in quasar spectra serves as a proxy for the relative Fe to alpha-element abundances in the broad line regions of quasars. Due to the expected different enrichment timescales of the two elements, they…

Based on 5344 quasar spectra taken from the SDSS Data Release 2, the dependences of various emission-line flux ratios on redshift and quasar luminosity are investigated in the ranges 2.0 < z < 4.5 and -24.5 > M_B > -29.5$. We show that the…

We present the results of a survey of the analogs of weak MgII absorbers (rest frame equivalent width W(2796) < 0.3 A) at 0 < z < 0.3. Our sample consisted of 25 HST/STIS echelle quasar spectra (R = 45,000) which covered SiII 1260 and CII…

Quasar redshifts require the best possible precision and accuracy for a number of applications, such as setting the velocity scale for outflows as well as measuring small-scale quasar-quasar clustering. The most reliable redshift standard…

We test the recently proposed (Mediavilla et al. 2018) black hole mass scaling relationship based on the redshift {with respect to the quasar's rest frame} of the Fe III$\lambda\lambda$2039-2113 line blend. To this end, we fit this feature…

High redshift quasars can be used to deduce the distribution of dark energy in the Universe, as a complementary tool to SN Ia. The method is based on determination of the size of the Broad Line Region from the emission line delay,…

The relation between quasar variability and parameters such as luminosity and redshift has been a matter of hot debate over the last few years with many papers on the subject. Any correlations which can be established will have a profound…

We obtained SDSS spectra for a set of 37 radio-quiet quasars (RQQSOs) that had been previously examined for rapid small scale optical variations, or microvariability. Their H-beta and Mg II emission lines were carefully fit to determine…

Near-infrared spectra of four QSOs located at $z>6$ are obtained with the OH-airglow suppressor mounted on the Subaru telescope. The FeII/MgII emission-line ratios of these QSOs are examined by the same fitting algorithm as in our previous…

Using the SDSS spectra of quasars included in the DR7Q or DR12Q catalogs, we search for Mg II narrow absorption doublets in the spectra data around Mg II emission lines. We obtain 17,316 Mg II doublets, within the redshift range of 0.3299<=…

We present a total of 4784 unique broad absorption line quasars from the Sloan Digital Sky Survey Third Data Release. An automated algorithm was used to match a continuum to each quasar and to identify regions of flux at least 10% below the…

Fe II emission is a well-known contributor to the UV spectra of active galactic nuclei and the modeling of this part may affect the results obtained for the MgII$\lambda2800$ emission, which is one of the lines used for black hole mass…

In this work, we revisit the relationship between [O III] line width $w_{\rm 90}$ (as the indicator of AGN outflow velocity) and the radio emission in RQQs by employing a large sample of Type I quasars ($\sim 37,000$) selected from the…

Interpretation of the \ion{Fe}{2}(UV)/\ion{Mg}{2} emission ratios from quasars has a major cosmological motivation. Both Fe and Mg are produced by short-lived massive stars. In addition, Fe is produced by accreting white dwarf supernovae…

The goal of the Complete Optical and Radio Absorption Line System (CORALS) survey is to quantify the potential impact on QSO absorber statistics from dust in intervening galaxies. Dust may introduce a selection bias in surveys which are…

We present the first systematic search for "changing-look" ("CL") behavior in the broad He ii $\lambda$4686 emission line in quasars, utilizing repeated spectroscopy from the Sloan Digital Sky Survey (SDSS). The He ii line, originating from…

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…

Intervening metal absorbers in quasar spectra at $z > 6$ can be used as probes to study the chemical enrichment of the Universe during the Epoch of Reionization (EoR). This work presents the comoving line densities ($dn/dX$) of low…

Using a sample of 166 projected quasar pairs we investigate the influence of active galactic nuclei on the circumgalactic medium (CGM) of the quasar host galaxies probed using strong Mg II absorption (i.e., $W_{2796}\ge 1\dot{A}$) at impact…