- ID:
- ivo://CDS.VizieR/J/ApJ/721/1
- Title:
- Keck ESI observations of Ly{alpha} systems
- Short Name:
- J/ApJ/721/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results from a survey of SDSS quasars selected for strong HI damped Ly{alpha} (DLA) absorption with corresponding low equivalent width absorption from strong low-ion transitions (e.g., CII{lambda}1334 and SiII{lambda}1260). These metal-poor DLA candidates were selected from the SDSS fifth release quasar spectroscopic database, and comprise a large new sample for probing low-metallicity galaxies. Medium-resolution echellette spectra from the Keck Echellette Spectrograph and Imager spectrograph for an initial sample of 35 systems were obtained to explore the metal-poor tail of the DLA distribution and to investigate the nucleosynthetic patterns at these metallicities. We have estimated saturation corrections for the moderately underresolved spectra, and systems with very narrow Doppler parameters (b<=5km/s) will likely have underestimated abundances. For those systems with Doppler parameters b>5km/s, we have measured low-metallicity DLA gas with [X/H]<-2.4 for at least one of C, O, Si, or Fe. Assuming non-saturated components, we estimate that several DLA systems have [X/H]<-2.8, including five DLA systems with both low equivalent widths and low metallicity in transitions of both CII and OI. All of the measured DLA metallicities, however, exceed or are consistent with a metallicity of at least 1/1000 of solar, regardless of the effects of saturation in our spectra.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/221/2
- Title:
- Keck+Magellan survey for LLSs. III.
- Short Name:
- J/ApJS/221/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an absorption-line survey of optically thick gas clouds --Lyman Limit Systems (LLSs)-- observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen N_H1_ and associated metal-line transitions for 157 LLSs at z_LLS_=1.76-4.39 restricted to 10^17.3^cm^-2^<=N_HI_<10^20.3^cm^-2^. An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing N_H1_ and that the majority of LLSs are highly ionized, confirming previous expectations. The Si^+^/H^0^ ratio spans nearly four orders of magnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive detection of a metal transition; by z~3 nearly all gas that is dense enough to exhibit a very high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements to the small subset of LLS (~5%-10%) that may have super-solar abundances. High Si^+^/Fe^+^ ratios suggest an {alpha}-enhanced medium, whereas the Si^+^/C^+^ ratios do not exhibit the super-solar enhancement inferred previously for the Ly{alpha} forest.
383. KiDS-BEXGO catalog
- ID:
- ivo://CDS.VizieR/J/A+A/632/A56
- Title:
- KiDS-BEXGO catalog
- Short Name:
- J/A+A/632/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Within a Kilo-Degree Survey (KiDS) Strongly lensed QUAsar Detection project (KiDS-SQuaD), we built a catalogue of bright extragalactic objects from the KiDS DR4, with the main objective to select the reliable gravitationally lensed quasar candidates. We used machine learning algorithm, trained on Sloan Digital Sky Survey DR14 data, to classify sources from subsample (r<22mag) of KiDS DR4 on three classes: stars, quasars and galaxies. Resulting KiDS Bright EXtraGalactic Objects catalogue (KiDS-BEXGO) contains ~6M galaxies and ~0.2M quasars. KiDS-BEXGO represents the first comprehensive identification of bright extragalactic objects in the KiDS DR4 data.
384. KiDS DR3 QSO catalog
- ID:
- ivo://CDS.VizieR/J/A+A/624/A13
- Title:
- KiDS DR3 QSO catalog
- Short Name:
- J/A+A/624/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of quasars selected from broad-band photometric ugri data of the Kilo-Degree Survey Data Release 3 (KiDS DR3). The QSOs are identified by the random forest (RF) supervised machine learning model, trained on Sloan Digital Sky Survey (SDSS) DR14 spectroscopic data. We first cleaned the input KiDS data of entries with excessively noisy, missing or otherwise problematic measurements. Applying a feature importance analysis, we then tune the algorithm and identify in the KiDS multiband catalog the 17 most useful features for the classification, namely magnitudes, colors, magnitude ratios, and the stellarity index. We used the t-SNE algorithm to map the multidimensional photometric data onto 2D planes and compare the coverage of the training and inference sets. We limited the inference set to r<22 to avoid extrapolation beyond the feature space covered by training, as the SDSS spectroscopic sample is considerably shallower than KiDS. This gives 3.4 million objects in the final inference sample, from which the random forest identified 190,000 quasar candidates. Accuracy of 97% (percentage of correctly classified objects), purity of 91% (percentage of true quasars within the objects classified as such), and completeness of 87% (detection ratio of all true quasars), as derived from a test set extracted from SDSS and not used in the training, are confirmed by comparison with external spectroscopic and photometric QSO catalogs overlapping with the KiDS footprint. The robustness of our results is strengthened by number counts of the quasar candidates in the r band, as well as by their mid-infrared colors available from the Wide-field Infrared Survey Explorer (WISE). An analysis of parallaxes and proper motions of our QSO candidates found also in Gaia DR2 suggests that a probability cut of pQSO>0.8 is optimal for purity, whereas pQSO>0.7 is preferable for better completeness. Our study presents the first comprehensive quasar selection from deep high-quality KiDS data and will serve as the basis for versatile studies of the QSO population detected by this survey. We publicly release the resulting catalog at http://kids.strw.leidenuniv.nl/DR3/quasarcatalog.php, and the code at https://github.com/snakoneczny/kids-quasars
- ID:
- ivo://CDS.VizieR/J/ApJ/609/539
- Title:
- Kinematics of parsec-scale radio jets
- Short Name:
- J/ApJ/609/539
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a 15GHz (2cm) multi-epoch Very Long Baseline Array (VLBA) program, begun in 1994 to study the outflow in radio jets ejected from quasars and active galaxies.
- ID:
- ivo://CDS.VizieR/VII/11
- Title:
- Kitt Peak Quasar List
- Short Name:
- VII/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog includes the complete source list with positions of the Kitt Peak Quasar Catalog (de Veny et al., 1971PASP...83..611D). Other fields in the de Veny catalog (4C ID, B1950 equatorial positions, V, B-V, U-B, z, references to ID UBV z, and Notes and other references) are not included. The Kitt Peak Quasar Catalog sources were selected based on optical data for all confirmed quasars published prior to May or June 1971. This includes objects with only one spectral line. The published catalog includes a bibliography for all quasars with redshifts The source list also includes some additional sources included by the author.
- ID:
- ivo://CDS.VizieR/J/AJ/131/1923
- Title:
- Known quasars in the QUEST Variability Survey
- Short Name:
- J/AJ/131/1923
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present variability and multiwavelength photometric information for the 933 known quasars in the QUEST Variability Survey (Cat. <II/266>). These quasars are grouped into variable and nonvariable populations based on measured variability confidence levels.
388. KODIAQ DR2
- ID:
- ivo://CDS.VizieR/J/AJ/154/114
- Title:
- KODIAQ DR2
- Short Name:
- J/AJ/154/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and make publicly available the second data release (DR2) of the Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ) survey. KODIAQ DR2 consists of a fully reduced sample of 300 quasars at 0.07<z_em_<5.29 observed with HIRES at high resolution (36000{<=}R{<=}103000). DR2 contains 831 spectra available in continuum normalized form, representing a sum total exposure time of ~4.9 megaseconds on source. These co-added spectra arise from a total of 1577 individual exposures of quasars taken from the Keck Observatory Archive (KOA) in raw form and uniformly processed. DR2 extends DR1 by adding 130 new quasars to the sample, including additional observations of QSOs in DR1. All new data in DR2 were obtained with the single-chip Tektronix TK2048 CCD configuration of HIRES in operation between 1995 and 2004. DR2 is publicly available to the community, housed as a higher level science product at the KOA and in the igmspec database (v03).
389. KODIAQ DR1
- ID:
- ivo://CDS.VizieR/J/AJ/150/111
- Title:
- KODIAQ DR1
- Short Name:
- J/AJ/150/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and make publicly available the first data release (DR1) of the Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ) survey. The KODIAQ survey is aimed at studying galactic and circumgalactic gas in absorption at high redshift, with a focus on highly ionized gas traced by O vi, using the HIRES spectrograph on the KeckI telescope. KODIAQ DR1 consists of a fully reduced sample of 170 quasars at 0.29<z_em_<5.29 observed with HIRES at high resolution (36000{<=}R{<=}103000) between 2004 and 2012. DR1 contains 247 spectra available in continuum normalized form, representing a sum total exposure time of ~1.6 megaseconds. These coadded spectra arise from a total of 567 individual exposures of quasars taken from the Keck Observatory Archive (KOA) in raw form and uniformly processed using a publicly available HIRES data reduction package. DR1 is publicly available to the community, housed as a higher level science product at the KOA. We will provide future data releases that make available additional quasars, including those with pre-2004 observations taken with the previous-generation HIRES detectors.
- ID:
- ivo://CDS.VizieR/J/AJ/161/45
- Title:
- KODIAQ DR3: 727 quasars (01.<zem<6.4) with ESI
- Short Name:
- J/AJ/161/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and make publicly available the third data release (DR3) of the Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ) survey. KODIAQ DR3 consists of a fully reduced sample of 727 quasars at 0.1<zem<6.4 observed with the Echellette Sepctrograph and Imager at moderate resolution (4000<~R<~10000). DR3 contains 872 spectra available in flux calibrated form, representing a sum total exposure time of ~2.8 megaseconds. These coadded spectra arise from a total of 2753 individual exposures of quasars taken from the Keck Observatory Archive (KOA) in raw form and uniformly processed using a data reduction package made available through the XIDL distribution. DR3 is publicly available to the community, housed as a higher level science product at the KOA and in the igmspec database.
