- ID:
- ivo://CDS.VizieR/J/AJ/133/1236
- Title:
- Fifth VLBA calibrator survey: VCS5
- Short Name:
- J/AJ/133/1236
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the fifth part of the Very Long Baseline Array (VLBA) Calibrator Survey (VCS), containing 569 sources not observed previously with very long baseline interferometry in geodetic or absolute astrometry programs. This campaign has two goals: (1) to observe additional sources that, together with previous survey results, form a complete sample, and (2) to find new strong sources suitable as phase calibrators. This VCS extension was based on three 24-hr VLBA observing sessions in 2005. It detected almost all extragalactic flat-spectrum sources with correlated flux density greater than 200mJy at 8.6GHz above declination -30{deg} that were not observed previously. Source positions with milliarcsecond accuracy were derived from astrometric analysis of ionosphere-free combinations of group delays determined from the 2.3 and 8.6GHz frequency bands. The VCS5 catalog of source positions, plots of correlated flux density versus projected baseline length, contour plots, and FITS files of naturally weighted CLEAN images, as well as calibrated visibility function files, are available on the World Wide Web at http://vlbi.gsfc.nasa.gov/vcs5
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- ID:
- ivo://CDS.VizieR/J/AJ/138/1032
- Title:
- Filling in the gaps in the 4.85GHz sky
- Short Name:
- J/AJ/138/1032
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a 4.85GHz survey of bright, flat-spectrum radio sources conducted with the Effelsberg 100m telescope in an attempt to improve the completeness of existing surveys, such as CRATES. We report the results of these observations and of follow-up 8.4GHz observations with the VLA of a subset of the sample. We comment on the connection to the Wilkinson Microwave Anisotropy Probe point source catalog and on the survey's effectiveness at supplementing the CRATES sky coverage.
- ID:
- ivo://CDS.VizieR/J/MNRAS/462/2904
- Title:
- Final GMRT-TAU catalogue
- Short Name:
- J/MNRAS/462/2904
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observations of three active sites of star formation in the Taurus molecular cloud complex taken at 323 and 608MHz (90 and 50cm, respectively) with the Giant Metrewave Radio Telescope (GMRT). Three pointings were observed as part of a pathfinder project, targeted at the young stellar objects (YSOs) L1551 IRS 5, T Tau and DG Tau (the results for these target sources were presented in a previous paper). In this paper, we search for other YSOs and present a survey comprising of all three fields; a by-product of the large instantaneous field of view of the GMRT. The resolution of the survey is of order 10 arcsec and the best rms noise at the centre of each pointing is of order 100{mu}Jy/beam at 323MHz and 50{mu}Jy/beam at 608MHz. We present a catalogue of 1815 and 687 field sources detected above 5{sigma}_rms_ at 323 and 608MHz, respectively. A total of 440 sources were detected at both frequencies, corresponding to a total unique source count of 2062 sources. We compare the results with previous surveys and showcase a sample of extended extragalactic objects. Although no further YSOs were detected in addition to the target YSOs based on our source-finding criteria, these data can be useful for targeted manual searches, studies of radio galaxies or to assist in the calibration of future observations with the Low-Frequency Array towards these regions.
- ID:
- ivo://CDS.VizieR/J/MNRAS/370/1034
- Title:
- FIRST-APM-SDSS survey for high-z radio QSOs
- Short Name:
- J/MNRAS/370/1034
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We selected from the VLA FIRST survey a sample of 94 objects with star-like counterparts in the Sloan Digital Sky Survey (SDSS), and with APM POSS-I colour O-E>=2, i.e. consistent with their being high-redshift quasars. 78 of the 94 candidates can be classified spectroscopically on the basis of either published data (mainly SDSS) or the observations presented here. The fractions of QSOs (51 out of 78) and redshift z>3 QSOs (23 out of 78, 29 per cent) are comparable to those found in other photometric searches for high-redshift QSOs. We confirm that selecting colour O-E>=2 ensures inclusion of all QSOs with 3.7<=z<=4.4. The fraction of 2<=z<=4.4 QSOs with broad absorption lines (BALs) is 27+/-10 per cent (7/26) and the estimated BAL fraction for radio-loud QSOs is at least as high as for optically selected QSOs (~13 per cent). Both the high BAL fraction and the high fraction of low-ionization BALs among BALs (four to five out of seven) in our sample, compared to previous work, are likely due to the red colour selection O-E>=2.
- ID:
- ivo://CDS.VizieR/J/ApJS/143/1
- Title:
- FIRST-APM Source Catalog
- Short Name:
- J/ApJS/143/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a program to identify optical counterparts to radio sources from the VLA FIRST survey using the Cambridge APM scans of the POSS-I plates. We use radio observations covering 4150deg^2^ of the north Galactic cap to a 20cm flux density threshold of 1.0mJy; the 382,892 sources detected all have positional uncertainties of <1" (radius of 90% confidence). Our description of the APM catalog, derived from the 148 POSS-I O and E plates covering this region, includes an assessment of its astrometric and photometric accuracy, a photometric recalibration using the Minnesota APS catalog, a discussion of the classification algorithm, and quantitative tests of the catalog's reliability and completeness. We go on to show how the use of FIRST sources as astrometric standards allows us to improve the absolute astrometry of the POSS plates by nearly an order of magnitude to ~0.15" rms. Matching the radio and optical catalogs yields counterparts for over 70,000 radio sources; we include detailed discussions of the reliability and completeness of these identifications as a function of optical and radio morphology, optical magnitude and color, and radio flux density. An analysis of the problem of radio sources with complex morphologies (e.g., double-lobed radio galaxies) is included. We conclude with a brief discussion of the source classes represented among the radio sources with identified counterparts.
- ID:
- ivo://CDS.VizieR/J/ApJS/98/1
- Title:
- First Caltech-Jodrell Bank VLBI Survey. I.
- Short Name:
- J/ApJS/98/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results from the first Caltech-Jodrell Bank VLBI survey (the CJ1 survey). The CJ1 sample includes 135 radio sources with total flux density 1.3Jy>S_6cm>=0.7Jy, declination delta_1950>=35deg, and Galactic latitude |b^II|>10deg. It extends the flux density limit of the complete "PR" sample studied by Pearson & Readhead from 1.3 to 0.7Jy and increases the total number of sources from 65 to 200. The complete survey includes VLBI images at both lambda-18 and 6cm of all objects in the extended sample that have cores strong enough to be mapped with the Mark II VLBI system. These images provide a large enough sample to study, for example, the variety of morphologies exhibited by compact radio sources, cosmological evolution, superluminal motion, and misalignment between parsec-scale and kiloparsec-scale radio structures. In this paper we present lambda-18cm VLBI observations of 56 CJ1 and 31 PR sources made in 1990-1991, including images of 82 sources. The observations were made with a "snapshot" technique in which each source was observed in three 20-30-minute scans using an array of 12-16 antennas. The images have resolution 3-10mas and dynamic range greater than 100:1. Later papers in the series will present the remaining lambda-18cm observations, the lambda-6cm observations, and the analysis and interpretation of the results.
- ID:
- ivo://CDS.VizieR/J/ApJS/98/33
- Title:
- First Caltech-Jodrell Bank VLBI Survey. II.
- Short Name:
- J/ApJS/98/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report lambda-18 cm VLBI observations made in 1991 September of a further 25 objects from the first Caltech-Jodrell Bank VLBI Survey (the CJ1 survey). The CJ1 sample is a complete, flux-density limited sample of 135 radio sources with total flux density at lambda-6cm between 0.7 and 1.3Jy. These observations complete the lambda-18cm part of the survey. Together with the results of Paper I (Polatidis et al., <J/ApJS/98/1>), we have now observed 81 CJ1 sources at lambda-18cm. Later papers in the series will present lambda-6cm observations and the analysis and interpretation of the results.
- ID:
- ivo://CDS.VizieR/J/ApJ/757/51
- Title:
- FIRST-2MASS dust-reddened QSO spectra
- Short Name:
- J/ApJ/757/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 120 dust-reddened quasars identified by matching radio sources detected at 1.4GHz in the Faint Images of the Radio Sky at Twenty Centimeters survey (FIRST) with the near-infrared Two Micron All Sky Survey catalog (2MASS) and color-selecting red sources. Optical and/or near-infrared spectroscopy provide broad wavelength sampling of their spectral energy distributions that we use to determine their reddening, characterized by E(B-V). We demonstrate that the reddening in these quasars is best described by Small-Magellanic-Cloud-like dust. This sample spans a wide range in redshift and reddening (0.1<~z<~3, 0.1<~E(B-V)<~1.5), which we use to investigate the possible correlation of luminosity with reddening. At every redshift, dust-reddened quasars are intrinsically the most luminous quasars. We interpret this result in the context of merger-driven quasar/galaxy co-evolution where these reddened quasars are revealing an emergent phase during which the heavily obscured quasar is shedding its cocoon of dust prior to becoming a "normal" blue quasar. When correcting for extinction, we find that, depending on how the parent population is defined, these red quasars make up <~15%-20% of the luminous quasar population. We estimate, based on the fraction of objects in this phase, that its duration is 15%-20% as long as the unobscured, blue quasar phase.
- ID:
- ivo://CDS.VizieR/J/ApJ/607/60
- Title:
- FIRST-2MASS faint sources
- Short Name:
- J/ApJ/607/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have constructed a sample of bright near-infrared sources that are detected at radio wavelengths but undetected on the first-generation Palomar Observatory Sky Survey (POSSI) plates in order to search for a population of dust-obscured quasars. Optical and infrared spectroscopic follow-up of the sample has led to the discovery of 17 heavily reddened quasars (B-K>6.5), 14 of which are reported here for the first time. This has allowed us to define a region in the R-K, J-K color plane in which 50% of the radio-selected objects are highly reddened quasars. We compare the surface density of this previously overlooked population to that of ultraviolet-excess radio-selected quasars, finding that they make up ~20% of the total quasar population for K<~15.5.
- ID:
- ivo://CDS.VizieR/J/ApJ/667/673
- Title:
- FIRST-2MASS red quasar survey
- Short Name:
- J/ApJ/667/673
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Combining radio observations with optical and infrared color selection, demonstrated in our pilot study to be an efficient selection algorithm for finding red quasars, we have obtained optical and infrared spectroscopy for 120 objects in a complete sample of 156 candidates from a sky area of 2716deg^2^.
