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381. JHK' imaging photometry of Seyfert 1. I.
ID:
ivo://CDS.VizieR/J/ApJS/141/23
Title:
JHK' imaging photometry of Seyfert 1. I.
Short Name:
J/ApJS/141/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
Near-infrared JHK' imaging photometry was obtained of 331 AGNs consisting mainly of Seyfert 1 active galactic nuclei (AGNs) and quasars (QSOs). This sample was selected to cover a range of radio emission strength, redshift from z=0 to 1, and absolute B magnitude from M_B_=-29mag to -18mag. Among low-z AGNs with z<0.3, Seyfert 1-1.5 AGNs are distributed over a region from a location typical of "galaxies" to a location typical of "QSOs" in the two-color J-H to H-K' diagram, but Seyfert 1.8-2 AGNs are distributed around the location of "galaxies". Moreover, bright AGNs with respect to absolute B magnitude are distributed near the location of "QSOs," while faint AGNs are near the location of "galaxies". The distribution of such low-z AGNs in this diagram was found to have little dependence on their 6 cm radio flux. The near-infrared colors of the AGNs observed with an aperture of 7 pixels (7.49") are more QSO-like than those observed with larger apertures up to 15 pixels (16.1"). This aperture effect may be explained by contamination from the light of host galaxies within larger apertures. This effect is more prominent for less luminous AGNs.
382. JHK' imaging photometry of Seyfert 1. II.
ID:
ivo://CDS.VizieR/J/ApJS/141/31
Title:
JHK' imaging photometry of Seyfert 1. II.
Short Name:
J/ApJS/141/31
Date:
21 Oct 2021
Publisher:
CDS
Description:
Observations of 226 AGNs in the near-infrared J, H, and K' bands are presented along with the analysis of the observations for variability. Our sample consists mainly of Seyfert 1 AGNs and QSOs. About a quarter of the objects in each category are radio loud. The AGNs in the entire sample have the redshifts spanning the range from z=0 to 1, and the absolute magnitudes from M_B_=-29 to -18. All the objects were observed twice, and their variability was measured by differential photometry. A reduction method of differential photometry, optimized to the analysis of extended images, has been developed. The systematic error in variability arising from AGNs of highly extended images is estimated to be less than 0.01mag in each of the J, H, and K' bands. The systematic error arising from the flat-fielding is negligible for most AGNs, although it is more than 0.1mag for some particular cases. The overall average flat-fielding error is 0.03mag for the image pairs. We find that these systematic errors are superseded by statistical errors, and the overall average total systematic and statistical errors amounts to 0.05mag in the measured variability in each band.
383. JK'R magnitude of QSOs and around them
ID:
ivo://CDS.VizieR/J/A+AS/135/83
Title:
JK'R magnitude of QSOs and around them
Short Name:
J/A+AS/135/83
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have observed a sample of 15 and 8 quasars with redshifts between 0.11 and 0.87 (mean value 0.38) in the J and K' bands respectively. Eleven of the quasars were previously known to be associated with extended emission line regions. After deconvolution of the image, substraction of the PSF when possible, and identification of companions with the help of HST archive images when available, extensions are seen for at least eleven quasars. However, average profiles are different from that of the PSF in only four objects, for which a good fit is obtained with an r^1/4^ law, suggesting that the underlying galaxies are ellipticals. Redshifts were available in the literature for surrounding objects in five quasar fields. For these objects, one to five companion galaxies were found. One quasar even belongs to a richness class 1 cluster. Most other quasars in our sample have nearby galaxies in projection which may also be companions. Environmental effects are therefore probably important to account for the properties of these objects.
384. 1Jy northern AGN sample
ID:
ivo://CDS.VizieR/J/A+A/596/A106
Title:
1Jy northern AGN sample
Short Name:
J/A+A/596/A106
Date:
21 Oct 2021
Publisher:
CDS
Description:
Continuum spectra covering centimetre to submillimetre wavelengths are presented for a northern sample of 104 extragalactic radio sources, mainly active galactic nuclei, based on four-epoch Planck data. The nine Planck frequencies, from 30 to 857GHz, are complemented by a set of simultaneous ground-based radio observations between 1.1 and 37GHz. The single-survey Planck data confirm that the flattest high-frequency radio spectral indices are close to zero, indicating that the original accelerated electron energy spectrum is much harder than commonly thought, with power-law index around 1.5 instead of the canonical 2.5. The radio spectra peak at high frequencies and exhibit a variety of shapes. For a small set of low-z sources, we find a spectral upturn at high frequencies, indicating the presence of intrinsic cold dust. Variability can generally be approximated by achromatic variations, while sources with clear signatures of evolving shocks appear to be limited to the strongest outbursts.
385. Karhunen-Loeve transform of SDSS QSOs
ID:
ivo://CDS.VizieR/J/AJ/140/390
Title:
Karhunen-Loeve transform of SDSS QSOs
Short Name:
J/AJ/140/390
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Karhunen-Loeve (KL) transform can compactly represent the information contained in large, complex datasets, cleanly eliminating noise from the data and identifying elements of the dataset with extreme or inconsistent characteristics. We develop techniques to apply the KL transform to the 4000-5700{AA} region of 9800 QSO spectra with z<0.619 from the SDSS archive. Up to 200 eigenspectra are needed to fully reconstruct the spectra in this sample to the limit of their signal-to-noise (S/N). We propose a simple formula for selecting the optimum number of eigenspectra to use to reconstruct any given spectrum, based on the S/N of the spectrum, but validated by formal cross-validation tests.
386. K-band light curve of GRS 1915+105
ID:
ivo://CDS.VizieR/J/ApJ/657/409
Title:
K-band light curve of GRS 1915+105
Short Name:
J/ApJ/657/409
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of 7 years of K-band monitoring of the low-mass X-ray binary GRS 1915+105. Positive correlations between the infrared flux and the X-ray flux and X-ray hardness are demonstrated. Analysis of the frequency spectrum shows that the orbital period of the system is P_orb_=30.8+/-0.2days. The phase and amplitude of the orbital modulation suggests that the modulation is due to the heating of the face of the secondary star. We also report another periodic signature between 31.2 and 31.6days, most likely due to a superhump resonance. From the superhump period we then obtain a range for the mass ratio of the system, 0.05<q<0.12.
387. Keck ESI observations of Ly{alpha} systems
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.
388. Keck+Magellan survey for LLSs. III.
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.
389. 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.
390. 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