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921. The CLASS blazar survey. I.
ID:
ivo://CDS.VizieR/J/MNRAS/326/1455
Title:
The CLASS blazar survey. I.
Short Name:
J/MNRAS/326/1455
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents a new complete and well-defined sample of flat-spectrum radio sources (FSRS) selected from the Cosmic Lens All-Sky Survey (CLASS), with the further constraint of a bright (mag<=17.5) optical counterpart. The sample has been designed to produce a large number of low-luminosity blazars in order to test the current unifying models in the low-luminosity regime. In this first paper the new sample is presented and the radio properties of the 325 sources contained therein are discussed.
922. The CLASS blazar survey. II.
ID:
ivo://CDS.VizieR/J/MNRAS/329/877
Title:
The CLASS blazar survey. II.
Short Name:
J/MNRAS/329/877
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents the optical properties of the objects selected in the CLASS blazar survey. Because an optical spectrum is now available for 70 per cent of the 325 sources present in the sample, a spectral classification, based on the appearance of the emission/absorption lines, is possible. A wide variety of optical spectral types is found. Besides `classical' BL Lacs (42), BL Lac candidates (5) and high-power (P_5GHz_>10^26^W/Hz) flat spectrum radio quasars (67), a significant number of `passive' elliptical galaxies (41) is also found. Moreover, 33 broad emission line objects with a low radio power (P(5GHz)>10^26^W/Hz) are discovered, suggesting that at least a fraction (~24-30 per cent) of low-power blazars have a broad line region. Finally, 34 objects showing only narrow emission lines, either as a result of some starburst activity in the host galaxy or as a result of the presence of an active galactic nucleus, appear in the sample.
923. The CLASS blazar survey. III.
ID:
ivo://CDS.VizieR/J/MNRAS/348/937
Title:
The CLASS blazar survey. III.
Short Name:
J/MNRAS/348/937
Date:
21 Oct 2021
Publisher:
CDS
Description:
We discuss the properties of the sources in the CLASS blazar survey, which aims at the selection of low radio power (P_5GHz_<10^25^W/Hz) blazars. We use Very Large Array (VLA) data from available catalogues and from our own observations to constrain the radio core-dominance of the sample which, together with the flat radio spectral index, is a signature of the blazar activity. X-ray data from the ROSAT All Sky Survey were also collected in order to constrain the radio-to-X-ray luminosity ratio of the sources.
924. The COS CGM compendium. I. Initial results
ID:
ivo://CDS.VizieR/J/ApJ/866/33
Title:
The COS CGM compendium. I. Initial results
Short Name:
J/ApJ/866/33
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a neutral hydrogen-selected absorption-line survey of gas with HI column densities 15<logN_HI_<19 at z<~1 using the Cosmic Origins Spectrograph on the Hubble Space Telescope. Our main aim is to determine the metallicity distribution of these absorbers. Our sample consists of 224 absorbers selected on the basis of their HI absorption strength. Here we discuss the properties of our survey and the immediate empirical results. We find singly and doubly ionized metal species, and HI typically have similar velocity profiles, implying they probe gas in the same or similar environments. The ionic ratios (e.g., N_CII_/N_CIII_, N_OI_/N_CII_) indicate that the gas in these absorbers is largely ionized, and the ionization conditions are quite comparable across the sampled N_HI_ range. The Doppler parameters of the HI imply T<~5x10^4^K on average, consistent with the gas being photoionized. The MgII column densities span >2 orders of magnitude at any given N_HI_, indicating a wide range of metallicities (from solar to <1/100 solar). In the range of 16.2<~logN_HI_<~17, there is a gap in the N_MgII_ distribution corresponding to gas with ~10% solar metallicity, consistent with the gap seen in the previously identified bimodal metallicity distribution in this column density regime. Less than 3% of the absorbers in our sample show no detectable metal absorption, implying that truly pristine gas at z<~1 is uncommon. We find <[FeII/MgII]>=-0.4+/-0.3, and since {alpha}-enhancement can affect this ratio, dust depletion is extremely mild.
925. The 2dF QSO Redshift Survey
ID:
ivo://CDS.VizieR/VII/241
Title:
The 2dF QSO Redshift Survey
Short Name:
VII/241
Date:
21 Oct 2021
Publisher:
CDS
Description:
The final catalogue of the 2dF QSO Redshift Survey (2QZ) is based on Anglo-Australian Telescope 2dF spectroscopic observations of 44576 colour-selected (ub_J_r) objects with 18.25<b_J_< 20.85 selected from automated plate measurement scans of UK Schmidt Telescope (UKST) photographic plates. The 2QZ comprises 23338 quasi-stellar objects (QSOs), 12292 galactic stars (including 2071 white dwarfs) and 4558 compact narrow emission-line galaxies. We obtained a reliable spectroscopic identification for 86 per cent of objects observed with 2dF. We also report on the 6dF QSO Redshift Survey (6QZ), based on UKST 6dF observations of 1564 brighter (16<b_J_<18.25) sources selected from the same photographic input catalogue. In total, we identified 322 QSOs spectroscopically in the 6QZ. The completed 2QZ is, by more than a factor of 50, the largest homogeneous QSO catalogue ever constructed at these faint limits (b_J_<20.85) and high QSO surface densities (35 QSOs/deg^2^). As such, it represents an important resource in the study of the Universe at moderate-to-high redshifts.
926. The 2dF QSO Redshift Survey. VIII
ID:
ivo://CDS.VizieR/J/MNRAS/328/805
Title:
The 2dF QSO Redshift Survey. VIII
Short Name:
J/MNRAS/328/805
Date:
21 Oct 2021
Publisher:
CDS
Description:
We examine the highest signal-to-noise ratio spectra from the 2dF QSO Redshift Survey (2QZ) 10k release (Cat. <VII/223>) and identify over 100 new low-ionization heavy-element absorbers: damped Lyman-{alpha} (DLA) candidates suitable for higher-resolution follow-up observations. These absorption systems map the spatial distribution of high-z metals in exactly the same volumes as the foreground 2QZ QSOs themselves sample and hence the 2QZ gives us the unique opportunity to compare directly the two tracers of large-scale structure. We examine the cross-correlation of the two populations to see how they are relatively clustered, and, by considering the colour of the QSOs, detect a small amount of dust in these metal systems.
927. The 2dF QSO Redshift Survey. V. The 10k catalogue
ID:
ivo://CDS.VizieR/VII/223
Title:
The 2dF QSO Redshift Survey. V. The 10k catalogue
Short Name:
VII/223
Date:
21 Oct 2021
Publisher:
CDS
Description:
The 2dF QSO Redshift Survey (2QZ) 10k catalogue is the first release of the 2QZ, containing over 10000 QSOs. There are a total of 20590 sources listed, for which spectra have been obtained using the 2-degree field facility at the Anglo-Australian Observatory. Current data covers an effective area of 289.6deg^2^ for QSO candidates with magnitudes 18.25<b_J_<20.85. The file 2qz_10k.dat contains the names, positions, magnitudes, spectroscopic identifications and redshifts for each of the sources.
928. The 2dF-SDSS QSO survey
ID:
ivo://CDS.VizieR/J/MNRAS/392/19
Title:
The 2dF-SDSS QSO survey
Short Name:
J/MNRAS/392/19
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the final spectroscopic QSO catalogue from the 2dF-SDSS LRG (luminous red galaxy) and QSO (2SLAQ) survey. This is a deep, 18<g<21.85 (extinction corrected), sample aimed at probing in detail the faint end of the broad line active galactic nuclei luminosity distribution at z<=2.6. The candidate QSOs were selected from SDSS photometry and observed spectroscopically with the 2dF spectrograph on the Anglo-Australian Telescope. This sample covers an area of 191.9 deg2 and contains new spectra of 16326 objects, of which 8764 are QSOs and 7623 are newly discovered [the remainder were previously identified by the 2dF QSO Redshift Survey (2QZ) and SDSS]. The full QSO sample (including objects previously observed in the SDSS and 2QZ surveys) contains 12702 QSOs. The new 2SLAQ spectroscopic data set also contains 2343 Galactic stars, including 362 white dwarfs, and 2924 narrow emission-line galaxies with a median redshift of z=0.22.
929. The doubly lensed quasar SDSS J1001+5027
ID:
ivo://CDS.VizieR/J/A+A/557/A44
Title:
The doubly lensed quasar SDSS J1001+5027
Short Name:
J/A+A/557/A44
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents optical R-band light curves and the time delay of the doubly imaged gravitationally lensed quasar SDSS J1001+5027 at a redshift of 1.838. We have observed this target for more than six years, between March 2005 and July 2011, using the 1.2-m Mercator Telescope, the 1.5-m telescope of the Maidanak Observatory and the 2-m Himalayan Chandra Telescope. Our resulting light curves are composed of 443 independent epochs, and show strong intrinsic quasar variability, with an amplitude of the order of 0.2 magnitudes. From this data, we measure the time delay using five different methods, all relying on distinct approaches. One of these techniques is a new development presented in this paper. All our time-delay measurements are perfectly compatible. By combining them, we conclude that image A is leading B by 119.3+/-3.3 days (1{sigma}, 2.8%), including systematic errors. It has been shown recently that such accurate time-delay measurements offer a highly complementary probe of dark energy and spatial curvature, as they independently constrain the Hubble constant. The next mandatory step towards using SDSS J1001+5027 in this context will be the measurement of the redshift of the lensing galaxy, in combination with deep HST imaging.
930. The ELQS in SDSS footprint. II. North Gal. Cap
ID:
ivo://CDS.VizieR/J/ApJ/863/144
Title:
The ELQS in SDSS footprint. II. North Gal. Cap
Short Name:
J/ApJ/863/144
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the North Galactic Cap sample of the Extremely Luminous Quasar Survey (ELQS-N), which targets quasars with M_1450_{<}-27 at 2.8<=z<5 in an area of ~7600deg^2^ of the Sloan Digital Sky Survey (SDSS) footprint with 90{deg}<RA<270{deg}. Based on a near-infrared/infrared JKW2 color cut, the ELQS selection efficiently uses random forest methods to classify quasars and to estimate photometric redshifts; this scheme overcomes some of the difficulties of pure optical quasar selection at z~3. As a result, we retain a completeness of >70% over z~3.0-5.0 at m_i_<~17.5, limited toward fainter magnitudes by the depth of the Two Micron All Sky Survey. The presented quasar catalog consists of a total of 270 objects, of which 39 are newly identified in this work with spectroscopy obtained at the Vatican Advanced Technology Telescope and the MMT 6.5m telescope. In addition to the high completeness, which allowed us to discover new quasars in the already well-surveyed SDSS North Galactic Cap, the efficiency of our selection is relatively high at ~79%. Using 120 objects of this quasar sample we are able to extend the previously measured optical quasar luminosity function (QLF) by one magnitude toward the bright end at 2.8<=z<=4.5. A first analysis of the QLF suggests a relatively steep bright-end slope of {beta}~-4 for this sample. This result contrasts with previous results in the same redshift range, which find a much flatter slope around {beta}~-2.5, but agrees with recent measurements of the bright-end slope at lower and higher redshifts. Our results constrain the bright-end slope at z=2.8-4.5 to {beta}{<}-2.94 with a 99% confidence.