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891. Spitzer/IRAC variability survey of Bootes field
ID:
ivo://CDS.VizieR/J/ApJ/817/119
Title:
Spitzer/IRAC variability survey of Bootes field
Short Name:
J/ApJ/817/119
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Decadal IRAC Bootes Survey is a mid-IR variability survey of the ~9deg^2^ of the NDWFS Bootes Field and extends the time baseline of its predecessor, the Spitzer Deep, Wide-Field Survey (SDWFS), from 4 to 10 years. The Spitzer Space Telescope visited the field five times between 2004 and 2014 at 3.6 and 4.5{mu}m. We provide the difference image analysis photometry for a half a million mostly extragalactic sources. In mid-IR color-color plane, sources with quasar colors constitute the largest variability class (75%), 16% of the variable objects have stellar colors and the remaining 9% have the colors of galaxies. Adding the fifth epoch doubles the number of variable active galactic nuclei (AGNs) for the same false positive rates as in SDWFS, or increases the number of sources by 20% while decreasing the false positive rates by factors of 2-3 for the same variability amplitude. We quantify the ensemble mid-IR variability of ~1500 spectroscopically confirmed AGNs using single power-law structure functions (SFs), which we find to be steeper (index {gamma}~0.45) than in the optical ({gamma}~0.3), leading to much lower amplitudes at short time-lags. This provides evidence for large emission regions, smoothing out any fast UV/optical variations, as the origin of infrared quasar variability. The mid-IR AGN SF slope {gamma} seems to be uncorrelated with both the luminosity and rest-frame wavelength, while the amplitude shows an anti-correlation with the luminosity and a correlation with the rest-frame wavelength.
892. Spitzer/IRS ATLAS project source
ID:
ivo://CDS.VizieR/J/MNRAS/414/500
Title:
Spitzer/IRS ATLAS project source
Short Name:
J/MNRAS/414/500
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a panoramic atlas of Spitzer/Infrared Spectrograph (IRS) spectra of extragalactic sources collected from the recent literature, with value-added measurements of their spectral features obtained in a homogeneous and concise manner. The atlas covers the full spectrum of the extragalactic Universe and includes star-forming galaxies, obscured and unobscured active galaxies, luminous and ultra-luminous infrared galaxies, and hybrid objects. Measured features such as the polycyclic aromatic hydrocarbons, the strength of the silicates in emission or absorption around 9.7um, rest-frame monochromatic luminosities or colours, combined with measurements derived from spectral decomposition are used to establish diagnostics that allow for classification of sources, based on their infrared properties alone. Average templates of the various classes are also derived. The full atlas with the value-added measurements and ancillary archival data are publicly available at http://www.denebola.org/atlas, with full references to the original data.
893. Spitzer observations of radio-loud AGNs (CARLA)
ID:
ivo://CDS.VizieR/J/ApJ/769/79
Title:
Spitzer observations of radio-loud AGNs (CARLA)
Short Name:
J/ApJ/769/79
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the first results from the Clusters Around Radio-Loud AGN program, a Cycle 7 and 8 Spitzer Space Telescope snapshot program to investigate the environments of a large sample of obscured and unobscured luminous radio-loud active galactic nuclei (AGNs) at 1.2<z<3.2. These data, obtained for 387 fields, reach 3.6 and 4.5{mu}m depths of [3.6]_AB_=22.6 and [4.5]_AB_=22.9 at the 95% completeness level, which is two to three times fainter than L* in this redshift range. By using the color cut [3.6]-[4.5]>-0.1 (AB), which efficiently selects high-redshift (z>1.3) galaxies of all types, we identify galaxy cluster member candidates in the fields of the radio-loud AGN. The local density of these Infrared Array Camera (IRAC)-selected sources is compared to the density of similarly selected sources in blank fields. We find that 92% of the radio-loud AGN reside in environments richer than average. The majority (55%) of the radio-loud AGN fields are found to be overdense at a>=2{sigma} level; 10% are overdense at a>=5{sigma} level. A clear rise in surface density of IRAC-selected sources toward the position of the radio-loud AGN strongly supports an association of the majority of the IRAC-selected sources with the radio-loud AGN. Our results provide solid statistical evidence that radio-loud AGN are likely beacons for finding high-redshift galaxy (proto-)clusters. We investigate how environment depends on AGN type (unobscured radio-loud quasars versus obscured radio galaxies), radio luminosity and redshift, finding no correlation with either AGN type or radio luminosity. We find a decrease in density with redshift, consistent with galaxy evolution for this uniform, flux-limited survey. These results are consistent with expectations from the orientation-driven AGN unification model, at least for the high radio luminosity regimes considered in this sample.
894. Spitzer quasar and ULIRG evolution study
ID:
ivo://CDS.VizieR/J/ApJS/182/628
Title:
Spitzer quasar and ULIRG evolution study
Short Name:
J/ApJS/182/628
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results from a comprehensive study of 74 ultraluminous infrared galaxies (ULIRGs) and 34 Palomar-Green (PG) quasars within z~0.3 observed with the Spitzer Infrared Spectrograph (IRS). The contribution of nuclear activity to the bolometric luminosity in these systems is quantified using six independent methods that span a range in wavelength and give consistent results within ~+/-10%-15% on average. This agreement suggests that deeply buried active galactic nuclei (AGNs) invisible to Spitzer IRS but bright in the far-infrared are not common in this sample. The average derived AGN contribution in ULIRGs is ~35%-40%, ranging from ~15%-35% among "cool" (f_25_/f_60_<=0.2) optically classified HII-like and LINER ULIRGs to ~50 and ~75% among warm Seyfert 2 and Seyfert 1 ULIRGs, respectively. This number exceeds ~80% in PG QSOs.
895. Stability of VLBI reference frame
ID:
ivo://CDS.VizieR/J/A+A/375/661
Title:
Stability of VLBI reference frame
Short Name:
J/A+A/375/661
Date:
21 Oct 2021
Publisher:
CDS
Description:
The file table 2 gives the results of various tests and noise measurements performed on time serie of extragalactic radio source coordinates. Systematic and random behaviours in time serie of individual determinations of cooordinates for 283 sources over 1987-1999 are investigated. The random variability of the source coordinates is characterized by the {chi}^2^ test (Bevington, 1969, p.187) and the "goodness of fit (gof)" (Bevington, 1969, p.188). The Allan variance method (Allan, 1966, Proc. IEEE, vol. 54, 221) is used to investigate spectral characteristics of the time series. The source structure index (Fey & Charlot, 1997ApJS..111...95F, 2000, Cat. <J/ApJS/128/17>) qualifies the level of position disturbance expected at the date of the map (1 for the less disturbed, 4 for the most disturbed). The estimation of "linear rates" in the coordinates is a qualifier of the systematic parts of the source instability. This table contains the 283 best observed sources and is divided in three parts, with the left hand side giving general information and counts, the middle part giving statistics in the source local frame, and the right hand side giving statistics in the equatorial frame.
896. Steep and ultra-steep spectra RC sources
ID:
ivo://CDS.VizieR/J/AZh/87/739
Title:
Steep and ultra-steep spectra RC sources
Short Name:
J/AZh/87/739
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of spectroscopy of 71 objects with steep and ultra-steep spectra (alpha<-0.9, S{prop.to}nu^alpha^) from the "Big Trio" (RATAN-600-VLA-BTA) project, performed with the "Scorpio" spectrograph on the 6-m telescope of the Special Astrophysical Observatory (Russian Academy of Sciences). Redshifts were determined for these objects. We also present several other parameters of the sources, such as their R magnitudes, maximum radio sizes in seconds of arc, flux densities at 500, 1425, and 3940MHz, radio luminosities at 500 and 3940MHz, and morphology. Of the total number of radio galaxies studied, four have redshifts 1<=z<2, three have 2<=z<3, one has 3<=z<4, and one has z=4.51. Thirteen sources have redshifts 0.7<z<1 and 15 have 0.2<z<0.7. Of all the quasars studied, five have redshifts 0.7<z<1, seven have 1<=z<2, four have 2<=z<3, and one has z=3.57. We did not detect any spectral lines for 17 objects.
897. Stellar Catalogue in the Chandra DFS
ID:
ivo://CDS.VizieR/J/A+A/392/741
Title:
Stellar Catalogue in the Chandra DFS
Short Name:
J/A+A/392/741
Date:
21 Oct 2021
Publisher:
CDS
Description:
Stellar catalogues in five passbands (UBVRI) over an area of approximately 0.3{deg}^2^, comprising about 1200 objects, and in seven passbands (UBVRIJK) over approximately 0.1{deg}^2^, comprising about 400 objects, in the direction of the Chandra Deep Field South are presented. The 90% completeness level of the number counts is reached at approximately U=23.8, B=24.0, V=23.5, R=23.0, I=21.0, J=20.5, K=19.0. These multi-band catalogues have been produced from publicly available, single passband catalogues. A scheme is presented to select point sources from these catalogues, by combining the SExtractor parameter CLASS_STAR from all available passbands. Probable QSOs and unresolved galaxies are identified by using the previously developed {chi}^2^-technique (Hatziminaoglou et al., 2002, Cat. <J/A+A/384/81>), that fits the overall spectral energy distributions to template spectra and determines the best fitting template. Approximately 15% of true galaxies are misclassified as stars by the {chi}^2^ method. The number of unresolved galaxies and QSOs identified by the {chi}^2^-technique, allows us to estimate that the remaining level of contamination by such objects is at the level of 2.4% of the number of stars. The fraction of missing stars being incorrectly removed as QSOs or unresolved galaxies is estimated to be similar. The resulting stellar catalogues and the objects identified as likely QSOs and unresolved galaxies with coordinates, observed magnitudes with errors and assigned spectral types by the {chi}^2^-technique are presented and are publicly available.
898. Stellar masses of optical & IR QSO hosts
ID:
ivo://CDS.VizieR/J/ApJ/819/L27
Title:
Stellar masses of optical & IR QSO hosts
Short Name:
J/ApJ/819/L27
Date:
21 Oct 2021
Publisher:
CDS
Description:
The relation between star formation rates (SFRs) and stellar masses, i.e., the galaxy main sequence, is a useful diagnostic of galaxy evolution. We present the distributions relative to the main sequence of 55 optically selected PG and 12 near-IR-selected Two Micron All Sky Survey (2MASS) quasars at z<=0.5. We estimate the quasar host stellar masses from Hubble Space Telescope or ground-based AO photometry, and the SFRs through the mid-infrared aromatic features and far-IR photometry. We find that PG quasar hosts more or less follow the main sequence defined by normal star-forming galaxies while 2MASS quasar hosts lie systematically above the main sequence. PG and 2MASS quasars with higher nuclear luminosities seem to have higher specific SFRs (sSFRs), although there is a large scatter. No trends are seen between sSFRs and SMBH masses, Eddington ratios, or even morphology types (ellipticals, spirals, and mergers). Our results could be placed in an evolutionary scenario with quasars emerging during the transition from ULIRGs/mergers to ellipticals. However, combined with results at higher redshift, they suggest that quasars can be widely triggered in normal galaxies as long as they contain abundant gas and have ongoing star formation.
899. Strong MgII absorber blazars
ID:
ivo://CDS.VizieR/J/MNRAS/473/5154
Title:
Strong MgII absorber blazars
Short Name:
J/MNRAS/473/5154
Date:
21 Oct 2021
Publisher:
CDS
Description:
It is widely believed that the cool gas clouds traced by MgII absorption, within a velocity offset of 5000km/s relative to the background quasar are mostly associated with the quasar itself, whereas the absorbers seen at larger velocity offsets towards us are intervening absorber systems and hence their existence is completely independent of the background quasar. Recent evidence by Bergeron et al. (2011A&A...525A..61P, hereinafter BBM) has seriously questioned this paradigm, by showing that the number density of intervening MgII absorbers towards the 45 blazars in their sample is nearly two times the expectation based on the MgII absorption systems seen towards normal quasars (QSOs). Given its serious implications, it becomes important to revisit this finding, by enlarging the blazar sample and subjecting it to an independent analysis. Here, we first report the outcome of our re-analysis of the available spectroscopic data for the BBM sample itself. Our analysis of the BBM sample reproduces their claimed factor of 2 excess of dN/dz along blazar sightlines, vis-a-vis normal QSOs. We have also assembled an approximately three times larger sample of blazars, albeit with moderately sensitive optical spectra. Using this sample together with the BBM sample, our analysis shows that the dN/dz of the MgII absorbers statistically matches that known for normal QSO sightlines. Further, the analysis indicates that associated absorbers might be contributing significantly to the estimated dN/dz up to offset speeds {DELTA}v~0.2c relative to the blazar.
900. Study of fine-structure constants
ID:
ivo://CDS.VizieR/J/A+AS/104/89
Title:
Study of fine-structure constants
Short Name:
J/A+AS/104/89
Date:
21 Oct 2021
Publisher:
CDS
Description:
A statistical analysis of fine splitting of C IV, N V, O VI, Mg II, Al III and Si IV doublet absorption lines in quasar spectra is carried out in order to estimate a possible time variation of the fine-structure constant {alpha}= e^2^(h/2{pi})c (~1/137) over cosmological time scales t~10^10^yr. The observational basis of the analysis is a catalogue of 1414 pairs of wavelengths with redshifts z = 0.2 - 3.7, compiled from data published in 1980-1992. Robust statistical estimates like the ``trimmed mean'' are used as well as the least squares. No statistically significant time variation of {alpha} is found. The estimate {alpha}^-1^d{alpha}/dz = (-0.6+/-2.8)10^-4^ is obtained. For the 95% significance level, an upper bound on the rate of a relative variation of the fine-structure constant is |{alpha}^-1^d{alpha}/dz| < 5.6x10^-4^, which corresponds approximately to |{alpha}^-1^d{alpha}/dt| < 4x10^-14^ yr^-1^. This limit represents the strongest up-to-date restriction on the possible time variation of {alpha} for the epoch 0.2 <= z <~ 4.