- ID:
- ivo://CDS.VizieR/J/ApJ/776/136
- Title:
- QPQ VI. HI absorption of z~2 quasars
- Short Name:
- J/ApJ/776/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasar's environment in absorption. We use a sample of 650 projected quasar pairs to study the HI Ly{alpha} absorption transverse to luminous, z~2 quasars at proper separations of 30kpc<R_{perp}_<1Mpc. In contrast to measurements along the line-of-sight, regions transverse to quasars exhibit enhanced HI Ly{alpha} absorption and a larger variance than the ambient intergalactic medium, with increasing absorption and variance toward smaller scales. Analysis of composite spectra reveals excess absorption characterized by a Ly{alpha} equivalent width profile W=2.3{AA} (R_{perp}_/100kpc)^-0.46^. We also observe a high (=~60%) covering factor of strong, optically thick HI absorbers (HI column N_HI_>10^17.3^/cm2) at separations R_{perp}_<200kpc, which decreases to ~20% at R_{perp}_=~1Mpc, but still represents a significant excess over the cosmic average. This excess of optically thick absorption can be described by a quasar-absorber cross-correlation function {xi}_QA_(r)=(r/r_0_)^{gamma}^ with a large correlation length r_0_=12.5_-1.4_^+2.7^h^-1^Mpc (comoving) and {gamma}=1.68_-0.30_^+0.14^. The HI absorption measured around quasars exceeds that of any previously studied population, consistent with quasars being hosted by massive dark matter halos M_halo_{approx}10^12.5^M_{sun}_ at z~2.5. The environments of these massive halos are highly biased toward producing optically thick gas, and may even dominate the cosmic abundance of Lyman limit systems and hence the intergalactic opacity to ionizing photons at z~2.5. The anisotropic absorption around quasars implies the transverse direction is much less likely to be illuminated by ionizing radiation than the line-of-sight.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/602/A29
- Title:
- QSO 1308+326 at 15GHz modelfit results
- Short Name:
- J/A+A/602/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Despite numerous and detailed studies of the jets of Active Galactic Nuclei (AGN) on pc-scales, many questions are still debated. The physical nature of the jet components is one of the most prominent unsolved problems as is the launching mechanism of jets in AGN. The Quasar 1308+326 (z=0.997) allows detailed studies of the overall properties of the jet and to derive a more physical understanding of the nature and origin of jets in general. The long-term data provided by the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) survey permit tracing out the structural changes in 1308+326 presented here. The long-lived jet features in this source can be followed for about two decades. We investigate the VLBI morphology and kinematics of the jet of 1308+326 to understand the physical nature of this jet and jets in general, the role of magnetic fields, and the causal connection between jet features and the launching process. 50 VLBA observations performed at 15GHz from the MOJAVE survey have been re-modeled with Gaussian components and re-analyzed (the time covered: 1995.05-2014.07). The analysis is supplemented by multi-wavelength radio-data (UMRAO, at 4.8, 8.0, and 14.5GHz) in polarization and total intensity. We fit the apparent motion of the jet features with the help of a model of a precessing nozzle. The jet features seem to be emitted with varying viewing angles and launched into an ejection cone. Tracing the component paths yields evidence for rotational motion. Radio flux-density variability can be explained as a consequence of enhanced Doppler boosting corresponding to the motion of the jet relative to the line of sight. Based on the presented kinematics and other indicators, such as electric-vector polarization position angle (EVPA)-rotation we conclude that the jet of 1308+326 has a helical structure, i.e. the components are moving along helical trajectories, while the trajectories themselves are experiencing a precessing motion as well. A model of a precessing nozzle (Qian et al., 2014RAA....14..249Q) was applied to the data and a subset of the observed jet feature paths can be modeled successfully within this model. The data through 2012 are consistent with a swing period of 16.9 years. We discuss several scenarios to explain the observed motion phenomena, including a binary black hole model. It seems unlikely that the accretion disk around the primary black hole, that is disturbed by tidal forces of the secondary black hole, is able to launch a persistent axisymmetric jet. We conclude that we are observing a rotating helix. In particular, the observed EVPA swings can be explained by a shock moving through a straight jet pervaded by a helical magnetic field. We compare our results for 1308+326 with other astrophysical scenarios where similar, wound up filamentary structures are found. They all are related to accretion-driven processes. A helically moving or wound up object is often explained by filamentary features moving along magnetic field lines of magnetic flux tubes. It seems that a "component" is plasma tracing the magnetic field which guides the motion of the radiating radio-band plasma. Further investigations and modeling are in preparation.
- ID:
- ivo://CDS.VizieR/J/A+A/595/A96
- Title:
- QSO B0218+357 molecular absorption lines
- Short Name:
- J/A+A/595/A96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Isotopic ratios of heavy elements are a key signature of the nucleosynthesis processes in stellar interiors. The contribution of successive generations of stars to the metal enrichment of the Universe is imprinted on the evolution of isotopic ratios over time. We investigate the isotopic ratios of carbon, nitrogen, oxygen, and sulfur through millimeter molecular absorption lines arising in the z=0.68 absorber toward the blazar B 0218+357. We find that these ratios differ from those observed in the Galactic interstellar medium, but are remarkably close to those in the only other source at intermediate redshift for which isotopic ratios have been measured to date, the z=0.89 absorber in front of PKS 1830-211. The isotopic ratios in these two absorbers should reflect enrichment mostly from massive stars, and they are indeed close to the values observed toward local starburst galaxies. Our measurements set constraints on nucleosynthesis and chemical evolution models.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A144
- Title:
- QSO candidates catalog with APOP & ALLWISE (QCC)
- Short Name:
- J/A+A/618/A144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Quasars are spatially stationary, and they are essential objects in astrometry when defining reference frames. However, the census of quasars is far from complete. Mid-infared colors can be used to find quasar candidates because AGNs show a peculiar appearance in mid-infrared color, but these methods are incapable of separating quasars from AGNs.The aim of our study is to use astrometric and mid-infrared methods to select quasars and get a reliable quasar candidates catalog. We used a near-zero proper motion criterion in conjuction with WISE (all-sky Wide-field Infrared Survey Explorer) [W1-W2] color to select quasar candidates. The [W1-W2] color criterion is defined by the linear boundary of two samples: LAMOST DR5 quasars, which serve as the quasar sample, and LAMOST DR5 stars/galaxies, which serve as the non-quasar sample. The contamination and completeness are evaluated. We present a catalog of 662753 quasar candidates, with a completeness of about 75% and a reliability of 77.2%.
- ID:
- ivo://CDS.VizieR/J/MNRAS/356/331
- Title:
- QSO-candidates in OGLE-II Galactic bulge fields
- Short Name:
- J/MNRAS/356/331
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 97 QSO candidates in 48 Galactic bulge fields of the Optical Gravitational Lensing Experiment II (OGLE-II) covering ~11deg^2^, which are selected via their variability. We extend light curves of variable objects which were detected in a 3-yr baseline in the OGLE-II variable star catalogue to fourth year. We search for objects that are faint (16<I_0_<18.5) and slowly variable over 4-yr in this catalogue by using the variogram/structure function. Finding the QSOs in such stellar-crowded and high extinction fields is challenging, but should be useful for the astrometric reference frame. Spectroscopic follow-up observations are required to confirm these QSO candidates. Follow-up observations are being prepared for four of these fields (BUL_SC1, 2, 32 and 45). Follow-up observations for other fields are strongly encouraged. The complete list and light curves of all 97 candidates are available in electronic format at http://www.astro.princeton.edu/sumi/QSO-OGLEII/ .
- ID:
- ivo://CDS.VizieR/J/ApJ/747/107
- Title:
- QSO Candidates in the MACHO LMC database
- Short Name:
- J/ApJ/747/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog the 2566 QSO candidates in the MACHO LMC database. In these catalogs, we complied number of properties of the objects including RA, Dec, crossmatched IDs with several catalogs, magnitudes, photometric redshifts, etc. See Kim et al. (2011ApJ...735...68K) for the SVM (a.k.a. Support Vector Machine, a supervised machine learning algorithm) QSO classification model based on the time variability of lightcurves. We used the model to select the 2566 QSO candidates. In this work, we employed multiple diagnostics such as X-ray flux, mid-IR color and AGN SED fitting in order to select 663 promising QSO candidates among the 2,566 candidates. These candidates are flagged in the catalog. We calibrated the MACHO RA and Dec of the candidates using the UCAC3 catalog and improved the average astrometric accuracy from ~3" to ~0.5".
- ID:
- ivo://CDS.VizieR/J/MNRAS/396/223
- Title:
- QSO candidates selection in VO era
- Short Name:
- J/MNRAS/396/223
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a method for the photometric selection of candidate quasars in multiband surveys. The method makes use of a priori knowledge derived from a subsample of spectroscopic confirmed quasi-stellar objects (QSOs) to map the parameter space. The disentanglement of QSOs candidates and stars is performed in the colour space through the combined use of two algorithms, the probabilistic principal surfaces and the negative entropy clustering, which are for the first time used in an astronomical context. Both methods have been implemented in the voneural package on the Astrogrid Virtual Observatory platform. Even though they belong to the class of the unsupervised clustering tools, the performances of the method are optimized by using the available sample of confirmed quasars and it is therefore possible to learn from any improvement in the available 'base of knowledge'. The method has been applied and tested on both optical and optical plus near-infrared data extracted from the visible Sloan Digital Sky Survey (SDSS) and infrared United Kingdom Infrared Deep Sky Survey-Large Area Survey public data bases. In all cases, the experiments lead to high values of both efficiency and completeness, comparable if not better than the methods already known in the literature. A catalogue of optical candidate QSOs extracted from the SDSS Data Release 7 Legacy photometric data set has been produced.
- ID:
- ivo://CDS.VizieR/J/A+A/606/A13
- Title:
- QSO eHAQ0111+0641 spectra
- Short Name:
- J/A+A/606/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is important to understand the selection effects behind the quasar samples to fully exploit the potential of quasars as probes of cosmic chemical evolution and the internal gas dynamics of galaxies; in particular, it is vital to understand whether the selection criteria exclude foreground galaxies with certain properties, most importantly a high dust content. Here we present spectroscopic follow-up from the 10.4m GTC telescope of a dust-reddened quasar, eHAQ0111+0641, from the extended High AV Quasar (HAQ) survey. We find that the z=3.21 quasar has a foreground damped Lyman-{alpha} absorber (DLA) at z=2.027 along the line of sight. The DLA has very strong metal lines due to a moderately high metallicity with an inferred lower limit of 25% of the solar metallicity, but a very large gas column density along the line of sight in its host galaxy. This discovery is further evidence that there is a dust bias affecting the census of metals, caused by the combined effect of dust obscuration and reddening, in existing samples of z>2 DLAs. The case of eHAQ0111+0641 illustrates that dust bias is not only caused by dust obscuration, but also dust reddening.
- ID:
- ivo://CDS.VizieR/J/MNRAS/447/3856
- Title:
- QSO-galaxy pairs from SDSS
- Short Name:
- J/MNRAS/447/3856
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present photometric and spectroscopic measurements of 53 QSO-galaxy pairs from the Sloan Digital Sky Survey (SDSS), where nebular emission lines from a 0<z<0.84 foreground galaxy are detected in the fibre spectra of a background QSO, bringing the overall sample to 103 QSO-galaxy pairs detected in the SDSS. We here study the nature of these systems. Detected foreground galaxies appear at impact parameters between 0.37 and 12.68 kpc. The presence of oxygen and Balmer emission lines allows us to determine the emission line metallicities for our sample, which are on average supersolar in value. Star formation rates for our sample are in the range 0.01-12M_{sun}_/yr. We utilize photometric redshift fitting techniques to estimate the M* values of our galaxies (logM*=7.34-11.54), and extrapolate this relationship to those galaxies with no imaging detections. Where available, we measure the absorption features present in the QSO spectrum due to the foreground galaxy and the relationships between their rest equivalent widths. We report an anticorrelation between impact parameter and E(B-V)(g-i), as well as a correlation between galaxy colour (u- r) and E(B-V)(g-i). We find that our sample is one of late-type, star-forming galaxies comparable to field galaxies in a similar redshift range, providing important clues to better understand absorption systems. These galaxies represent a sample of typical galaxies in the local Universe for which abundances, extinction, morphology, and absorption properties may be measured using background QSOs with great potential for follow-up observations.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A157
- Title:
- QSO J1538+0855 MUSE datacube
- Short Name:
- J/A+A/635/A157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In recent years, Ly{alpha} nebulae have been routinely detected around high redshift, radio-quiet quasars thanks to the advent of the highly sensitive integral field spectrographs. Constraining the physical properties of the Ly{alpha} nebulae is crucial for a full understanding of the circum-galactic medium (CGM). The CGM acts both as a repository for intergalactic and galactic baryons as well as a venue of feeding and feedback processes. The most luminous quasars are privileged test-beds to study these processes, given their large ionising fluxes and dense CGM environments in which they are expected to be embedded.We aim to characterise the rest-frame ultraviolet (UV) emission lines in the CGM around a hyper-luminous, broad emission line, radio-quiet quasar at z~3.6, which exhibits powerful outflows at both nuclear and host galaxy scales.We analyse VLT/MUSE observations of the quasar J1538+08 (Lbol=6*10^47^erg/s), and we performed a search for extended UV emission lines to characterise its morphology, emissivity, kinematics, and metal content.We report the discovery of a very luminous (2*10^44^erg/s), giant (150kpc) Ly{alpha} nebula and a likely associated extended (75kpc) CIV nebula. The Ly{alpha} nebula emission exhibits moderate blueshift (440km/s) compared to the quasar systemic redshift and a large average velocity dispersion (700km/s) across the nebula, while the CIV nebula shows average velocity dispersion of 350km/s. The Ly{alpha} line profile exhibits a significant asymmetry towards negative velocity values at 20-30kpc south of the quasar and is well parametrised by the following two Gaussian components: a narrow (470km/s) systemic one plus a broad (1200km/s), blueshifted (1500km/s) one. Our analysis of the MUSE observation of J1538+08 reveals metal-enriched CGM around this hyper-luminous quasar. Furthermore, our detection of blueshifted emission in the emission profile of the Ly{alpha} nebula suggests that powerful nuclear outflows can propagate through the CGM over tens of kiloparsecs.
