- ID:
- ivo://CDS.VizieR/J/ApJS/239/23
- Title:
- CIV NAL systems from SDSS-DR14 quasar spectra
- Short Name:
- J/ApJS/239/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the quasar spectra from the Sloan Digital Sky Survey, all with two-epoch to six-epoch observations, we search for CIV{lambda}{lambda}1548,1551 narrow absorption doublets in spectral data from the blue wing {upsilon}r=30000km/s until the red wing of CIV{lambda}1549 emission lines. We have obtained 21239 CIV narrow absorption line (NAL) systems, of which 647 systems were significantly changed on timescales from {Delta}MJD=0.24 to 1842.38 days at rest-frame. Both samples of the C IV NAL systems with multi-epoch observations and the variable C IV NAL systems are the largest ones to date. The offset velocity distribution of the variable C IV NALs from quasars has a peak at {upsilon}r~2000km/s and gently extends to a larger offset velocity. There are 110 variable C IV NALs with {upsilon}r>12000km/s. In addition, about 10% intrinsic C IV NALs show time variability on a timescale of <2000 days. We find that the variations of C IV NALs are positively or negatively correlated with the alternations of quasar continua. The two kinds of correlations suggest that the variable C IV NALs included in our absorber catalog can be classified into at least two populations: (1) highly ionized systems that are dominated by highly ionized absorbing gas and negatively respond to the fluctuations of quasar emissions; and (2) lowly ionized systems that are dominated by lowly ionized absorbing gas and positively respond to fluctuations of quasar emissions. We also find that the absolute fractional changes in the absorption strengths of C IV NALs are inversely correlated with absorption strengths.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/236/39
- Title:
- CIV narrow absorption line systems in SDSS-DR14
- Short Name:
- J/ApJS/236/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We assemble 207 variable quasars from the Sloan Digital Sky Survey, all with at least 3 observations, to analyze CIV narrow absorption doublets, and obtain 328 CIV narrow absorption line systems. We find that 19 out of 328 CIV narrow absorption line systems were changed by |{Delta}W_r_^{lambda}1548^|>=3{sigma}_{Delta}Wr_^{lambda}1548^ on timescales from 15.9 to 1477 days at rest-frame. Among the 19 obviously variable CIV systems, we find that (1) 14 systems have relative velocities {upsilon}_r_>0.01c and 4 systems have {upsilon}_r_>0.1c, where c is the speed of light; (2) 13 systems are accompanied by other variable CIV systems; (3) 9 systems were changed continuously during multiple observations; and (4) 1 system with {upsilon}_r_=16862km/s was enhanced by {Delta}W_r_^{lambda}1548^=2.7{sigma}_{Delta}Wr_^{lambda}1548^ in 0.67 day at rest-frame. The variations of absorption lines are inversely correlated with the changes in the ionizing continuum. We also find that large variations of CIV narrow absorption lines are form differently over a short timescale.
- ID:
- ivo://CDS.VizieR/J/A+A/283/759
- Title:
- CIV QSO absorption systems
- Short Name:
- J/A+A/283/759
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High spectral resolution (FWHM = 0.6 or 0.35 {AA}) were obtained for six high redshift QSOs, z_em_ > 2.2, containing lines from 31 metal-rich absorption line systems amongst which 20 Civ doublets split in subcomponents with velocity differences within a system smaller than 400 km.s^-1^. Our survey has been combined with published data at similar resolution and the resulting sample comprises 35 systems, 23 of which are splitted in a total of 87 subcomponents. The mean redshift of the sample is <z> = 2.65. The observations were carried out at the F/8 Cassegrain focus of the 3.6m telescope at la Silla, between 1984 and 1989.
- ID:
- ivo://CDS.VizieR/J/ApJ/641/78
- Title:
- CIV variability in 105 SDSS quasars
- Short Name:
- J/ApJ/641/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the variability of the high-ionization CIV {lambda}1549 line in a sample of 105 quasars observed at multiple epochs by the Sloan Digital Sky Survey. We find a strong correlation between the change in the CIV line flux and the change in the line width, but no correlations between the change in flux and changes in line center and skewness. The relation between line flux change and line width change is consistent with a model in which a broad line base varies with greater amplitude than the line core. The objects studied here are more luminous and at higher redshift than those normally studied for variability, ranging in redshift from 1.65 to 4.00 and in absolute r-band magnitude from roughly -24 to -28.
- ID:
- ivo://CDS.VizieR/J/ApJS/237/31
- Title:
- CLAMATO DR1: 3D Ly{alpha} forest tomography
- Short Name:
- J/ApJS/237/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Faint star-forming galaxies at z~2-3 can be used as alternative background sources to probe the Ly{alpha} forest in addition to quasars, yielding high sightline densities that enable 3D tomographic reconstruction of the foreground absorption field. Here, we present the first data release from the COSMOS Ly{alpha} Mapping And Tomography Observations (CLAMATO) Survey, which was conducted with the LRIS spectrograph on the Keck I telescope. Over an observational footprint of 0.157deg^2^ within the COSMOS field, we used 240 galaxies and quasars at 2.17<z<3.00, with a mean comoving transverse separation of 2.37h^-1^Mpc, as background sources probing the foreground Ly{alpha} forest absorption at 2.05<z<2.55. The Ly{alpha} forest data was then used to create a Wiener-filtered tomographic reconstruction over a comoving volume of 3.15x10^5^h^-3^Mpc^3^ with an effective smoothing scale of 2.5h^-1^Mpc. In addition to traditional figures, this map is also presented as a virtual-reality visualization and manipulable interactive figure. We see large overdensities and underdensities that visually agree with the distribution of coeval galaxies from spectroscopic redshift surveys in the same field, including overdensities associated with several recently discovered galaxy protoclusters in the volume. Quantitatively, the map signal-to-noise is S/N^wiener^~3.4 over a 3h^-1^Mpc top-hat kernel based on the variances estimated from the Wiener filter. This data release includes the redshift catalog, reduced spectra, extracted Ly{alpha} forest pixel data, and reconstructed tomographic map of the absorption.
- ID:
- ivo://CDS.VizieR/J/ApJ/887/134
- Title:
- Classification of Fermi blazar cand. from the 4FGL
- Short Name:
- J/ApJ/887/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The recently published fourth Fermi Large Area Telescope source catalog (4FGL) reports 5065 gamma-ray sources in terms of direct observational gamma-ray properties. Among the sources, the largest population is the active galactic nuclei (AGNs), which consists of 3137 blazars, 42 radio galaxies, and 28 other AGNs. The blazar sample comprises 694 flat-spectrum radio quasars (FSRQs), 1131 BL Lac-type objects (BL Lacs), and 1312 blazar candidates of an unknown type (BCUs). The classification of blazars is difficult using optical spectroscopy given the limited knowledge with respect to their intrinsic properties, and the limited availability of astronomical observations. To overcome these challenges, machine-learning algorithms are being investigated as alternative approaches. Using the 4FGL catalog, a sample of 3137 Fermi blazars with 23 parameters is systematically selected. Three established supervised machine-learning algorithms (random forests (RFs), support vector machines (SVMs), artificial neural networks (ANNs)) are employed to general predictive models to classify the BCUs. We analyze the results for all of the different combinations of parameters. Interestingly, a previously reported trend the use of more parameters leading to higher accuracy is not found. Considering the least number of parameters used, combinations of eight, 12 or 10 parameters in the SVM, ANN, or RF generated models achieve the highest accuracy (Accuracy ~91.8%, or ~92.9%). Using the combined classification results from the optimal combinations of parameters, 724 BL Lac type candidates and 332 FSRQ type candidates are predicted; however, 256 remain without a clear prediction.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A10
- Title:
- 3C295 LOFAR, MERLIN and VLA images
- Short Name:
- J/A+A/658/A10
- Date:
- 02 Feb 2022 13:43:44
- Publisher:
- CDS
- Description:
- 3C295 is a bright, compact steep spectrum source with a well-studied integrated radio spectral energy distribution (SED) from 132MHz to 15GHz. However, spatially resolved spectral studies have been limited due to a lack of high resolution images at low radio frequencies. These frequencies are crucial for measuring absorption processes, and anchoring the overall spectral modelling of the radio SED. In this paper, we use International LOw-Frequency ARray (LOFAR) Telescope (ILT) observations of 3C295 to study its spatially resolved spectral properties with sub-arcsecond resolution at 132MHz. Combining our new 132MHz observation with archival data at 1.6GHz, 4.8GHz, and 15GHz, we are able to carryout a resolved radio spectral analysis. The spectral properties of the hotspots provides evidence for low frequency flattening. In contrast, the spectral shape across the lobes is consistent with a Jaffe-Perola spectral ageing model. Usingthe integrated spectral information for each component, we then fitted low-frequency absorption models to the hotspots,finding that both free-free absorption and synchrotron self-absorption models provide a better fit to the data than a standard power law. Although we can say there is low-frequency absorption present in the hot spots of 3C295, future observations with the Low Band Antenna of the ILT at 55MHz may allow us to distinguish the type of absorption.
- ID:
- ivo://CDS.VizieR/J/AJ/133/2222
- Title:
- Clustering of high-redshift QSOs from SDSS
- Short Name:
- J/AJ/133/2222
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the two-point correlation function of a uniformly selected sample of 4426 luminous optical quasars with redshift 2.9<=z<=5.4 selected over 4041deg^2^ from the Fifth Data Release of the Sloan Digital Sky Survey. We fit a power-law to the projected correlation function w_p_(r_p_) to marginalize over redshift-space distortions and redshift errors.
- ID:
- ivo://CDS.VizieR/J/A+A/478/701
- Title:
- Color excess of SDSS quasars with DLA systems
- Short Name:
- J/A+A/478/701
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyzed the spectroscopic and photometric database of the 5th data release of the Sloan Digital Sky Survey (SDSS) to search for evidence of the quasar reddening produced by dust embedded in intervening damped Ly{alpha} (DLA) systems. From a list of 5164 quasars in the interval of emission redshift 2.25<=z_e_<=3.5 and SDSS spectra with signal-to-noise ratio SNR>~4, we built up an "absorption sample" of 248 QSOs with a single DLA system in the interval of absorption redshift 2.2<z_a_<=3.5 and a "pool" of 1959 control QSOs without DLA systems or strong metal systems. For each QSO of the absorption sample we extracted from the pool a subset of control QSOs that are closest in redshift and magnitude.
- ID:
- ivo://CDS.VizieR/J/ApJ/883/78
- Title:
- Column densities of CGM absorption lines
- Short Name:
- J/ApJ/883/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the geometric distribution of gas metallicities in the circumgalactic medium (CGM) around 47, z<0.7 galaxies from the "Multiphase Galaxy Halos" Survey. Using a combination of quasar spectra from Hubble Space Telescope (HST)/COS and from Keck/HIRES or Very Large Telescope/UVES, we measure column densities of, or determine limits on, CGM absorption lines. We then use a Markov Chain Monte Carlo approach with Cloudy to estimate the metallicity of cool (T~10^4^K) CGM gas. We also use HST images to determine host-galaxy inclination and quasar-galaxy azimuthal angles. Our sample spans a HI column density range of 13.8cm^-2^<logN_HI_<19.9cm^-2^. We find (1) while the metallicity distribution appears bimodal, a Hartigan dip test cannot rule out a unimodal distribution (0.4{sigma}). (2) CGM metallicities are independent of halo mass, spanning three orders of magnitude at a fixed halo mass. (3) The CGM metallicity does not depend on the galaxy azimuthal and inclination angles regardless of HI column density, impact parameter, and galaxy color. (4) The ionization parameter does not depend on azimuthal angle. We suggest that the partial Lyman limit metallicity bimodality is not driven by a spatial azimuthal bimodality. Our results are consistent with simulations where the CGM is complex and outflowing, accreting, and recycled gas are well-homogenized at z<0.7. The presence of low-metallicity gas at all orientations suggests that cold streams of accreting filaments are not necessarily aligned with the galaxy plane at low redshifts or intergalactic transfer may dominate. Finally, our results support simulations showing that strong metal absorption can mask the presence of low-metallicity gas in integrated line-of-sight CGM metallicities.