- ID:
- ivo://CDS.VizieR/J/MNRAS/341/993
- Title:
- u_j_br photometry and redshifts of QSOs
- Short Name:
- J/MNRAS/341/993
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed analysis of a sample of radio-detected quasars, obtained by matching together objects from the FIRST (<VIII/71>) survey and the 2dF Quasar Redshift Survey (2dF, <VII/223>). The data set consists of 113 sources, spanning a redshift range 0.35<~z<~2.2, with optical magnitudes 18.25<=bj<=20.85 and radio fluxes S_1.4GHz_>=1mJy. These objects exhibit properties such as redshift and colour distribution in full agreement with those derived for the whole quasar population, suggesting that the mechanism(s) controlling the birth and lifetime of quasars are independent of their level of radio emission. The long-debated question of the radio-loud/radio quiet (RL/RQ) dichotomy is then investigated for the combined FIRST-2dF and FIRST-LBQS (Large Bright Quasar Survey) samples, as they present similar selection criteria.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/778/127
- Title:
- UKIDSS+FIRST+SDSS red QSOs candidates
- Short Name:
- J/ApJ/778/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a pilot survey to find dust-reddened quasars by matching the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) radio catalog to the UKIDSS near-infrared survey and using optical data from Sloan Digital Sky Survey to select objects with very red colors. The deep K-band limit provided by UKIDSS allows for finding more heavily reddened quasars at higher redshifts as compared with previous work using FIRST and Two Micron All Sky Survey (2MASS). We selected 87 candidates with K<=17.0 from the UKIDSS Large Area Survey (LAS) First Data Release (DR1), which covers 190deg^2^. These candidates reach up to ~1.5mag below the 2MASS limit and obey the color criteria developed to identify dust-reddened quasars. We have obtained 61 spectroscopic observations in the optical and/or near-infrared, as well as classifications in the literature, and have identified 14 reddened quasars with E(B-V)>0.1, including 3 at z>2. We study the infrared properties of the sample using photometry from the Wide-Field Infrared Survey Explorer and find that infrared colors improve the efficiency of red quasar selection, removing many contaminants in an infrared-to-optical color-selected sample alone. The highest-redshift quasars (z>~2) are only moderately reddened, with E(B-V)~0.2-0.3. We find that the surface density of red quasars rises sharply with faintness, comprising up to 17% of blue quasars at the same apparent K-band flux limit. We estimate that to reach more heavily reddened quasars (i.e., E(B-V)>~0.5) at z>2 and a depth of K=17, we would need to survey at least ~2.5 times more area.
- ID:
- ivo://CDS.VizieR/J/ApJS/91/659
- Title:
- Ultracompact HII regions radio images
- Short Name:
- J/ApJS/91/659
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radio continuum observations were made of 59 IRAS sources that have 100{mu}m flux densities >=1000Jy and far-infrared colors identified with ultracompact (UC) HII regions. Eighty percent were found to have associated compact radio sources. Seventy-five sources were detected at <~1" resolution at 3.6 and 2cm wavelengths, for which we provide contour plots and flux density distributions ranging from the radio to the near-infrared. Over half are unresolved and their morphologies undetermined. The remaining sources can be described by only five morphological classes, whose frequency of occurrence is consistent with that of the Wood and Churchwell survey (1989ApJS...69..831W). We calculate physical properties of the nebulae and show that they are consistent with UC photoionized regions. Alternative explanations are explored and found to be unlikely. The correlation of UC HII region positions with proposed spiral arms is examined and found to be well correlated only for the local spiral arm or "spur". No obvious enhancement of UC HII regions is apparent along the proposed Sagittarius and Scutum arms, probably because of inaccuracies in the kinematic distances. We find the latitude distribution of UC HII regions to lie in the range 0.5deg<[b_FWHM_]<=0.8deg. No correlation between size and density of cometary and core-halo UC HII regions is found, consistent with the bow shock interpretation of these morphologies. Spherical and unresolved UC HII regions, however, appear to show a trend toward lower densities with increasing size, as expected for expanding HII regions. The observed ratios of far-infrared to radio flux densities of UC HII regions lie in the range 10^3^ to >=10^5^. By applying the results of model atmospheres, it is shown that this ratio depends on spectral type, ranging from ~10^3^ for an O4 star to >=10^5^ for a B3 star. We find that many of the UC HII regions in our sample must be excited by a cluster of stars, and most probably contain significant amounts of dust.
- ID:
- ivo://CDS.VizieR/J/AJ/123/637
- Title:
- Ultra-steep-spectrum radio sources
- Short Name:
- J/AJ/123/637
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical and/or near-IR images of 128 ultra-steep-spectrum radio sources. Roughly half of the objects are identified in the optical images (R<~24), while in the near-IR images, more than 94% are detected at K<~22. The mean K magnitude is 19.26 within a 2" diameter aperture. The distribution of R-K colors indicates that at least one-third of the objects observed have very red colors (R-K>5). The major axes of the identifications in the K band are preferentially oriented along the radio axes, with half of them having compact morphologies. The 22 sources with spectroscopic redshifts and K-band magnitudes follow the K-z relation found from previous radio samples, but with a larger scatter.
- ID:
- ivo://CDS.VizieR/J/A+AS/108/79
- Title:
- Ultra-steep spectrum radiosources
- Short Name:
- J/A+AS/108/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radio sources with ultra-steep spectra (USS; spectral index <~ -1.0) have been found to be excellent tracers of galaxies at redshifts z>~2. The samples are selected from the set of catalogues referenced below, in a range of frequencies from 38 to 408MHz; they are are fainter by a factor of three than the previously well-studied samples of USS sources from 4C. Snapshot observations of sources from these samples have been made with the VLA at 1.5arcsec resolution and are presented in the printed paper. The list of the sources (Appendix A of the paper) includes positions, flux densities and radio structures for a total number of 605 sources derived from these observations.
- ID:
- ivo://CDS.VizieR/J/A+AS/143/303
- Title:
- Ultra steep spectrum radio sources catalog
- Short Name:
- J/A+AS/143/303
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The three tables contain the 669 Ultra Steep Spectrum sources from the 3 samples WN (WENSS-NVSS), TN (TEXAS-NVSS) and MP (MRC-PMN) (tables A.1, A.2 and A.3). For each source, the radio fluxes from the surveys and from VLA or ATCA observations are given, as well as coordinates, radio structure, angular size and position angle determined from the radio map indicated in the last column.
- ID:
- ivo://CDS.VizieR/J/A+A/452/739
- Title:
- ULX sources and FIRST radio sources
- Short Name:
- J/A+A/452/739
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We search for ultra luminous X-ray source (ULXs) radio counterparts located in nearby galaxies in order to constrain their physical nature. Our work is based on a systematic cross-identification of the most recent and extensive available ULX catalogues and archival radio data. A catalogue of 70 positional coincidences is reported. Most of them are located within the galaxy nucleus. Among them, we find 11 new cases of non-nuclear ULX sources with possibly associated radio emission.
- ID:
- ivo://CDS.VizieR/J/ApJS/249/1
- Title:
- 500um risers with HerMES & SPIRE drop-outs with S2CLS
- Short Name:
- J/ApJS/249/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our systematic search for the reddest far-infrared (FIR) and submillimeter (sub-mm) galaxies using the data from the Herschel Multi-tiered Extragalactic Survey (HerMES) and the SCUBA2 Cosmological Legacy Survey (S2CLS). The red FIR galaxies are "500{mu}m risers," whose spectral energy distributions increase with wavelength across the three FIR passbands of the Spectral and Photometric Imaging REceiver (SPIRE) of Herschel. Within 106.5deg^2^ of the HerMES fields, we have selected 629 500{mu}m risers. The red sub-mm galaxies are "SPIRE drop-outs," which are prominent detections in the S2CLS 850{mu}m data but are extremely weak or invisible in the SPIRE bands. Within the 2.98deg^2^ common area of HerMES and S2CLS, we have selected 95 such objects. These very red sources could be dusty starbursts at high redshifts (z>~4-6) because the peak of their cold-dust emission heated by star formation is shifted to the reddest FIR/sub-mm bands. The surface density of 500{mu}m risers is ~8.2deg^-2^ at the >=20mJy level in 500{mu}m, while that of SPIRE drop-outs is ~19.3deg^-2^ at the >=5mJy level in 850{mu}m. Both types of objects could span a wide range of redshifts, however. Using deep radio data in these fields to further select the ones likely at the highest redshifts, we find that the surface density of z>6 candidates is 5.5deg^-2^ among 500{mu}m risers and is 0.8-13.6deg^-2^ among SPIRE drop-outs. If this is correct, the dust-embedded star formation processes in such objects could contribute comparably as Lyman-break galaxies to the global SFR density at z>6.
- ID:
- ivo://CDS.VizieR/J/MNRAS/416/1135
- Title:
- Unbiased sample of CSS and GPS
- Short Name:
- J/MNRAS/416/1135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Compact Steep Spectrum (CSS) and Gigahertz Peaked Spectrum (GPS) sources are classes of compact, powerful, extragalactic objects. These sources are thought to be the earliest stages in the evolution of radio galaxies, capturing the ignition (or, in some cases, re-ignition) of the active galactic nucleus. As well as serving as probes of the early stages of large-scale radio sources, these sources are good, stable, amplitude calibrators for radio telescopes. We present an unbiased flux density limited (>1.5Jy at 2.7GHz) catalogue of these objects in the Southern hemisphere, including tabulated data, radio spectra, and where available, optical images and measurements. The catalogue contains 26 sources, consisting of two new candidates and 15 known CSS sources, and nine known GPS sources. We present new Australia Telescope Compact Array (ATCA) data on 10 of these 26 sources, and data on a further 42 sources which were excluded from our final sample. This bright sample will serve as a reference sample for comparison with subsequent faint (mJy level) samples of CSS and GPS candidates currently being compiled.
- ID:
- ivo://CDS.VizieR/J/ApJS/207/4
- Title:
- Unidentified {gamma}-ray sources. III. Radio
- Short Name:
- J/ApJS/207/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- About one-third of the {gamma}-ray sources listed in the second Fermi Large Area Telescope catalog (2FGL) have no firmly established counterpart at lower energies and so are classified as unidentified {gamma}-ray sources (UGSs). Here, we propose a new approach to find candidate counterparts for the UGSs based on the 325 MHz radio survey performed with the Westerbork Synthesis Radio Telescope in the northern hemisphere. First, we investigate the low-frequency radio properties of blazars, the largest known population of {gamma}-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS, Rengelink et al. 1997, Cat. J/A+AS/124/259; superseded by Cat. VIII/62) with those of the NRAO Very Large Array Sky Survey (NVSS, Condon et al. 1998, Cat. VIII/65). We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in the literature to look for infrared and optical counterparts of the {gamma}-ray blazar candidates selected using the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research, we identify 23 new {gamma}-ray blazar candidates out of the 32 UGSs investigated. Comparison with previous results on the UGSs is also presented. Finally, we speculate on the advantages of using low-frequency radio observations to associate UGSs and to search for {gamma}-ray pulsar candidates.
