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VLASS821P4 - VLA SDSS Stripe 82 Survey 1.4-GHz Source Catalog

HEASARC
Archive

Overview

This table contains results from a high-resolution radio survey of the Sloan Digital Sky Survey (SDSS) Southern Equatorial Stripe, also known as Stripe 82. This 1.4-GHz survey was conducted with the Very Large Array (VLA) primarily in the A configuration, with supplemental B configuration data to increase sensitivity to extended structure. The survey has an angular resolution of 1.8 arcseconds and achieves a median rms noise of 52 microJy/beam (uJy/beam) over 92 deg2. This is the deepest 1.4-GHz survey to achieve this large of an area, filling a gap in the phase space between small, deep and large, shallow surveys. It also serves as a pilot project for a larger high-resolution survey with the Expanded Very Large Array (EVLA). The authors discuss the technical design of the survey and details of the observations, and outline their method for data reduction, in the reference paper. They present a catalog of 17,969 isolated radio components, for an overall source density of ~195 sources deg-2. The astrometric accuracy of the data is excellent, with an internal check utilizing multiply observed sources yielding an rms scatter of 0.19 arcseconds in both Right Ascension and Declination. A comparison to the SDSS DR7 Quasar Catalog further confirms that the astrometry is well-tied to the optical reference frame, with mean offsets of 0.02" +/- 0.01" in Right Ascension, and 0.01" +/- 0.02" in Declination. A check of their photometry reveals a small, negative CLEAN-like bias on the level of 35 uJy. The authors report on the catalog completeness, finding that 97% of FIRST-detected quasars are recovered in the new Stripe 82 radio catalog, while faint, extended sources are more likely to be resolved out by the resolution bias. In their paper, they conclude with a discussion of the optical counterparts to the catalog sources, including 76 newly detected radio quasars. The full catalog as well as a search page and cutout server are available online at http://third.ucllnl.org/cgi-bin/stripe82cutout.

The SDSS Stripe 82 observations were made with the National Radio Astronomy Observatory's (NRAO's) VLA. The data were collected over two VLA cycles, 2007-2008 and 2008-2009. The majority of the observations were taken in the A configuration, but the authors also obtained B-configuration coverage of the area in order to improve the sampling of the Fourier (U-V) plane and to increase sensitivity to the extended structure. Area 1 (delineated in black in Figure 1(a) of the paper) was covered in the A and B configurations in 2007-2008, and Area 2 (delineated in purple in Figure 1(a) of the paper) in the A and B configurations in 2008-2009. Area 1 is made up of 275 pointings, and Area 2 has 374, coming to 649 fields, and 92 deg2 covered in total.


Catalog Bibcode

2011AJ....142....3H

References

High-resolution Very Large Array imaging of Sloan Digital Sky Survey Stripe 82
at 1.4 GHz.
    Hodge J.A., Becker R.H., White R.L., Richards G.T., Zeimann G.R..
   <Astronomical Jornal, Volume 142, Issue 1, article id. 3, 17 pp. (2011)>
   =2011AJ....142....3H

Provenance

This table was created by the HEASARC in August 2013 based on a complete machine-readable version of Table 1 from the reference paper which was kindly provided by the first author.

Parameters

Source_Number
A running source number in order of decreasing J2000.0 Declination, i.e., from north to south which uniquely identifies the radio source. This parameter was created by the HEASARC.

Name
The name of the radio source using the '[HBW2011] VLA' prefix (for Hodge, Becker, White, 2011) and the J2000 coordinates of the source in the standard position-based nomenclature 'JHHMMSS.ss+DDMMSS.s'. Thus, the source number 1 is '[HBW2011] VLA J014931.74+012403.6'. This parameter was created by the HEASARC.

RA
The Right Ascension of the radio source in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 0.001 seconds of time in the original table. The positional errors are a function of source brightness, size,and noise in the map. They are best found using a simple rule-of-thumb approach, as the errors derived from the source-finding algorithm used in this study, HAPPY (see White et al. 1997, ApJ, 475, 479) tend to be underestimated. An empirical equation for the accuracy at 90% confidence is fSize x (1/(S/N)+ (1/20), where fSize is the fitted major or minor axis size, and S/N is the signal-to-noise ratio (White et al. 1997, ibid.). Systematic errors are smaller than 0.05 arcseconds..

Dec
The Declination of the radio source in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 0.01 arcseconds in the original table. The positional errors are a function of source brightness, size,and noise in the map. They are best found using a simple rule-of-thumb approach, as the errors derived from the source-finding algorithm used in this study, HAPPY (see White et al. 1997, ApJ, 475, 479) tend to be underestimated. An empirical equation for the accuracy at 90% confidence is fSize x (1/(S/N)+ (1/20), where fSize is the fitted major or minor axis size, and S/N is the signal-to-noise ratio (White et al. 1997, ibid.). Systematic errors are smaller than 0.05 arcseconds.

LII
The Galactic Longitude of the radio source.

BII
The Galactic Latitude of the radio source.

Prob_No_Source
The probability P(S) that the source is spurious, most likely because it is a sidelobe of a nearby bright source. Low values of P(S) mean the source is unlikely to be spurious. The probabilities are computed using an algorithm based on multiple voting oblique decision tree classifiers, which were trained on deep VLA fields. The algorithm was developed for the FIRST survey and will be described in more detail in a future paper on the final FIRST catalog. Note that the algorithm is optimized for the FIRST survey, whereas the rms computation for this catalog has changed significantly. The values of P(S) are therefore considered to be not very reliable for this catalog.

Flux_1p4_GHz
The peak flux density Fpeak, in mJy beam-1, derived by fitting an elliptical Gaussian model to the radio source.

Int_Flux_1p4_GHz
The integrated flux density Fint, in mJy, derived from the elliptical Gaussian model fit. The uncertainty in Fint can be considerably greater than that of Fpeak depending on source size and morphology. An expression to estimate the uncertainty can be found in Schinnerer et al. (2004, AJ, 128, 1974). For point sources, the relative uncertainty (sigmaI /I) reduces to sqrt [2.5 * (sigma/I)2 + 0.012], where sigma is the local rms noise..

Flux_1p4_GHz_Error
The rms error in the peak flux density defined as the local noise estimate at the source position, in mJy. The rms is calculated by combining the measured noise from all grid images contributing to the co-added map at the source position.

Major_Axis
The major axis Maj (FWHM in arcseconds) derived from the elliptical Gaussian model for the source after the elliptical Gaussian PSF has been deconvolved. Noise can cause the fitted values of the major and minor axes prior to deconvolution to be smaller than the beam, and the deconvolved size is given as zero in that case. The uncertainties in the deconvolved sizes depend on both brightness and size.

Minor_Axis
The minor axis Min (FWHM in arcseconds) derived from the elliptical Gaussian model for the source after the elliptical Gaussian PSF has been deconvolved. Noise can cause the fitted values of the major and minor axes prior to deconvolution to be smaller than the beam, and the deconvolved size is given as zero in that case. The uncertainties in the deconvolved sizes depend on both brightness and size

Position_Angle
The position angle PA (in degrees measured eastwards from north) derived from the elliptical Gaussian model for the source after the elliptical Gaussian PSF has been deconvolved.

Fit_Major_Axis
The major axis fMaj (FWHM in arcseconds) derived from the elliptical Gaussian model for the source as fitted before deconvolution of the 1.8-arcseconds circular clean beam.

Fit_Minor_Axis
The minor axis fMin (FWHM in arcseconds) derived from the elliptical Gaussian model for the source as fitted before deconvolution of the 1.8-arcseconds circular clean beam.

Fit_Position_Angle
The position angle fPA (in degrees measured eastwards from north) derived from the elliptical Gaussian model for the source as fitted before deconvolution of the 1.8-arcseconds circular clean beam.

Field_Name
The field name, i.e., the name of the co-added image containing the source. Note that the field name encodes the center of the field, viz., field hhmmm+ddmmm is centered at RA = hh mm.m, Dec = +dd mm.m. The letter appended to the field name indicates the last catalog release in which the image was modified.

Num_SDSS_Matches
This parameter contains information on optical counterparts of the radio source from the SDSS DR6, which were found using the CasJobs Web interface: in this case, the number of matches within a radius of 8 arcseconds.

Min_Vla_SDSS_Offset
This parameter contains information on optical counterparts of the radio source from the SDSS DR6, which were found using the CasJobs Web interface: in this case, the separation in arcseconds of the closest SDSS match.

Imag
This parameter contains information on optical counterparts of the radio source from the SDSS DR6, which were found using the CasJobs Web interface: in this case, the i-band magnitude of the closest closest SDSS counterpart to the radio source position. If the closest counterpart was not detected in band, the i-magnitude is set to -1.0.

SDSS_Morph_Class
This parameter contains information on optical counterparts of the radio source from the SDSS DR6, which were found using the CasJobs Web interface: in this case, the SDSS morphological class code, where 's' = stellar and 'g' = non-stellar/galaxy.


Contact Person

Questions regarding the VLASS821P4 database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 8-Aug-2013