Related papers: Extreme quasars at high redshift
We present X-ray imaging and spectroscopy of the redshift z=7.084 radio-quiet quasar ULAS J112001.48+064124.3 obtained with Chandra and XMM-Newton. The quasar is detected as a point source with both observatories. The Chandra observation…
We present near-infrared spectroscopy of ten weak emission-line quasars (WLQs) at redshifts of $z\sim2$, obtained with the Palomar 200-inch Hale Telescope. WLQs are an exceptional population of type 1 quasars that exhibit weak or no broad…
Identifications of quasars at intermediate redshifts (2.2<z<3.5) are inefficient in most previous quasar surveys as their optical colors are similar to those of stars. The near-IR K-band excess technique has been suggested to overcome this…
We assemble a catalogue of 488 spectroscopically confirmed very high ($z\geq5.00$) redshift quasars and report their near- ($ZYJHK_{s}/K$) and mid- (WISE W1234) infrared properties. 97\% of the VH$z$Q sample is detected in one or more NIR…
We present JHK near-infrared (NIR) spectroscopy of 25 candidate Type II quasars selected from the Sloan Digital Sky Survey, using Triplespec on the Apache Point Observatory 3.5m telescope, FIRE at the Magellan/Baade 6.5m telescope, and…
We have compiled a catalog of 903 candidates for type 1 quasars at redshifts 3<z<5.5 selected among the X-ray sources of the serendipitous XMM-Newton survey presented in the 3XMM-DR4 catalog (the median X-ray flux is 5x10^{-15} erg/s/cm^2…
We present an analysis of UV spectra of quasars at intermediate redshifts believed to belong to the extreme Population A (xA), aimed to estimate the chemical abundances of the broad line emitting gas. We follow the approach described in a…
There are some strange quasars with multiple Gaia detections or observed with abnormal astrometric characteristics, such as with large proper motions or significant astrometric noises. Those strange quasars could be potential candidates of…
We report on observations of a TypeII quasar at redshift z=3.288, identified as a hard X-ray source in a 185 ks observation with the Chandra X-ray Observatory and as a high-redshift photometric candidate from deep, multiband optical…
Correlations of hot dust emission with outflow properties are investigated, based on a large z~2 non-broad absorption lines quasar sample built from the Wide-field Infrared Survey and the Sloan Digital Sky Survey data releases. We use the…
Using quasar spectra from the SDSS survey, we constrain the possibility of photon-axion oscillations as a source of dimming of high redshift objects. Such a process has been suggested as an explanation of the apparent faintness of distant…
We present the results of a systematic search for quasars in the Catalina Real-time Transient Survey exhibiting both strong photometric and spectroscopic variability over a decadal baseline. We identify 73 sources with specific patterns of…
We present measurements and statistical properties of the optical and ultraviolet emission lines present in the spectra of 85 bright quasars which have detailed spectral energy distributions. This heterogeneous sample has redshifts up to…
We studied the spectra of six $z \sim 2.2$ quasars obtained with the X-shooter spectrograph at the Very Large Telescope. The redshift of these sources and X-shooter's spectral coverage allow us to cover the rest spectral range $\sim1200 -…
The X-ray luminosity function of distant (3<z<5.1) unabsorbed quasars has been measured. A sample of distant high-luminosity quasars ($10^{45} \leq L_{{\rm X},2-10} < 7.5 \times 10^{45}$ erg/s in the 2--10 keV energy band) from the catalog…
We test the usefulness of the intermediate ionisation lines AlIII 1860 and CIII] 1909 as reliable virial mass estimators for quasars. We identify a sample of 309 quasars from the SDSS DR16 in the redshift range 1.2 < z < 1.4 to have [OII]…
The identifications of quasars in the redshift range 2.2<z<3 are known to be very inefficient as their optical colors are indistinguishable from those of stars. Recent studies have proposed to use optical variability or near-IR colors to…
We present radio and X-ray observations of the recently discovered $z=6.13$ radio-powerful quasar RACS J032021.44$-$352104.1 using uGMRT, ATCA, LBA, and Chandra. The observed radio properties are in line with what is typically observed in…
Extremely red quasars (ERQs) are an interesting sample of quasars in the Baryon Oscillation Spectroscopic Sample (BOSS) in the redshift range of $2.0 - 3.4$ and have extreme red colours of $i-W3\ge4.6$. Core ERQs have strong CIV emission…
We use 62185 quasars from the Sloan Digital Sky Survey (SDSS) DR5 sample to explore the quasar mass-luminosity plane view of virial mass estimation. Previous work shows deviations of ~0.4 dex between virial and reverberation masses. The…