2008AJ....136..684K Kimball, Amy E.; Ivezic, Zeljko A Unified Catalog of Radio Objects Detected by NVSS, First, WENSS, GB6, and SDSS Affiliation: AA(Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA), AB(Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA) Publication: The Astronomical Journal, Volume 136, Issue 2, pp. 684-712 (2008). Abstract We construct a catalog of radio sources detected by the Green Bank 6 cm survey GB6, Faint Images of the Radio Sky at Twenty cm (FIRST) and NRAO VLA Sky Survey (NVSS) (20 cm), and Westerbork Northern Sky Survey (WENSS) (92 cm) radio surveys, and the Sloan Digital Sky Survey (SDSS) optical survey. The 2.7 million entries in the publicly-available master catalog are comprised of the closest three FIRST to NVSS matches (within 30'') and vice versa, and unmatched sources from each survey. Entries are supplemented by data from the other radio and optical surveys, where available. All objects with even a small probability of physical association are included, such that catalog users can easily implement their own selection criteria for data analysis. We perform data analysis in the ~ 3000 deg2 region of sky where the surveys overlap, which contains 140,000 NVSS-FIRST sources, of which 64,000 are detected by WENSS and 12,000 by GB6. About one third of each sample is detected by the SDSS. An automated classification method based on 20 cm fluxes defines three radio morphology classes: complex, resolved, and compact. Radio color-magnitude-morphology diagrams for these classes show structure suggestive of strong underlying physical correlations. Complex and resolved sources tend to have a steep spectral slope (? ~ 0.8) that is nearly constant from 6 to 92 cm, while the compact class (unresolved on ~5'' scale by FIRST) contains a significant number of flat-spectrum (? ~ 0) sources. In the optically-detected sample, quasars dominate the flat-spectrum compact sources while steep-spectrum and resolved objects contain substantial numbers of both quasars and galaxies. Differential radio counts of quasars and galaxies are similar at bright flux levels (>100 mJy at 20 cm), while at fainter levels the quasar counts are significantly reduced below galaxy counts. The optically-undetected sample is strongly biased toward steep-spectrum sources. In samples of quasars and galaxies with SDSS spectra (2885 and 1288 respectively), we find that radio properties such as spectral slope, morphology, and radio loudness are correlated with optical color and luminosity. The FIRST-NVSS-WENSS-GB6-SDSS Radio Object Catalog Supported by NSF grant AST-0507259 Summary We present here a combined catalog of radio objects drawn from four radio catalogs (FIRST, NVSS, WENSS, and GB6) and the optical SDSS. The two primary surveys used in creating the matched catalog are the two 20 cm surveys, FIRST and NVSS: a row in the matched catalog is either a FIRST object with an NVSS match, an NVSS object with a FIRST match, or an isolated object from either survey. All FIRST/NVSS catalog sources were than matched to the other two radio surveys, GB6 at 6cm and WENSS at 92cm. The complete catalog contains 2,724,343 entries in the region of the sky north of -40deg declination covered by the NVSS (which completely contains the part of sky observed by FIRST). A 2955 deg2 "overlap region" is defined by the area observed by all four radio surveys and photometrically with the SDSS. The overlap region contains 178,000 FIRST-NVSS matches (within 30"), 110,000 isolated FIRST sources, and 23,000 isolated NVSS sources. The catalog includes data parameters (from the original source surveys) for the closest positional matches. In addition, the catalog has "matching parameters" which give the distance to, and total number of, positional matches found within the chosen search radii. The catalog is available for download at the bottom of the page. A detailed description of the calibration and a preliminary science analysis is presented in Kimball & Ivezic (2008) (hereafter Paper I). Individual files with high-resolution figures are available here. Please see the section below on recent changes for updates. The radio source surveys The four radio surveys used to create this catalog are FIRST (Faint Images of the Radio Sky at Twenty Centimeters), NVSS (NRAO-VLA Sky Survey, 20cm), GB6 (Green Bank Telescope, 6cm) and WENSS (Westerbork Northern Sky Survey, 92cm). Matching procedure The first step in the catalog production was to match FIRST and NVSS. We undertook this step in two parts by first positionally matching FIRST objects to NVSS objects (using NVSS positions as search centers), then matching NVSS objects to FIRST objects (using FIRST positions as search center). For each FIRST and NVSS source, we store in the catalog the closest three neighbors from the other catalog, within 30". Most FIRST-NVSS matches show up twice in the catalog, once with the FIRST detection as the primary and once with the NVSS detection as the primary. Catalog users therefore have the option to examine matching results separately for either catalog. It is easy to distinguish between the two searches (NVSS to FIRST or FIRST to NVSS) using the catalog's matchflag parameters. In addition to storing data for the three closest matches within 30", we also provide the total number of neighbors found with 5", 10", 30", and 120" (matchtot parameters). We then positionally matched to neighboring sources in GB6 and WENSS using a 120" search radius. When available, we used the more accurate position of the FIRST source in each catalog row for this step. For NVSS objects with no nearby FIRST neighbor, the NVSS position was used for this step. (See note below on positions.) Each catalog entry contains data describing the closest WENSS and GB6 neighbor; the total number of GB6 and WENSS matches within 120" is stored in the respective matchtot parameter. GB6 and WENSS each cover a different portion of the sky than the 20cm surveys; for primary sources outside GB6 or WENSS survey coverage, the respective matchtot parameter is set to -1. We also matched the radio catalog with the SDSS photometric survey: we retain photometric metadata, and also spectroscopic metadata for objects observed by the SDSS spectroscopically. Due to the very different astrometric accuracy of NVSS and FIRST, we chose two different search radii for positional matching to FIRST (where available) and NVSS (when no FIRST match available). We used a search radius of 60". Due to the high density of photometric SDSS sources (about 7.5 arcmin-2), it is easy to find serendipitous line-of-sight matches between intrinsically unrelated objects. We therefore provide data separately for both the nearest and the brightest SDSS photometric matches. If the nearest source is within 3" of the primary object (see Matchflags below), we also find the brightest object within 3". If the nearest object is further than 3" but within 10", we find the brightest object within 10". If no photometric neighbors were found within 10", we used a 30" search radius. If that failed, we used a 60" search radius. In 98.8% of cases where an SDSS match was found within 3", the nearest object and the brightest object are the same source. The Catalog Format Data Field Units Format Description -- Row Identifiers -- 1 uniq_id long integer Unique catalog row identifier 2 ra degree double Designated right ascension of entry (see note on positions) 3 dec degree double Designated declination of entry -- FIRST data -- 4 first_id long integer unique FIRST identifier 5 first_ra degree double right ascension (J2000) values from FIRST survey; for details see the FIRST website 6 first_dec degree double declination (J2000) 7 first_wflag char warning: possible sidelobe of nearby bright source 8 first_peak_flux mJy/beam float peak flux at 20cm 9 first_flux mJy float integrated flux density at 20cm 10 first_sky mJy/beam float local noise estimate at source position 11 first_major arcsec float FWHM of major axis (after PSF deconvolution) 12 first_minor arcsec float FWHM of minor axis(after PSF deconvolution) 13 first_posangle degree float position angle east of north (after PSF deconvolution) 14 first_fmajor arsec float fitted major axis (before PSF deconvolution) 15 first_fminor arsec float fitted minor axis (before PSF deconvolution) 16 first_fposangle degree float fitted position angle east of north (before PSF deconvolution) 17 first_field char name of source field -- NVSS data -- 18 nvss_id long integer unique NVSS identifier 19 nvss_ra degree double right ascension (J2000) values from NVSS survey; for details see the NVSS website. Also, please see note on NVSS corrections. 20 nvss_dec degree double declination (J2000) 21 nvss_peak_int mJy/beam float peak intensity at 20cm (Stokes I) 22 nvss_flux mJy float integrated flux at 20cm 23 nvss_major arcsec float FWHM major axis after deconvolution (please see note on NVSS corrections) 24 nvss_minor arcsec float FWHM minor axis after deconvolution (please see note on NVSS corrections) 25 nvss_posangle degree float position angle east of north 26 nvss_q mJy/beam float interpolated Stokes Q value at position of I peak 27 nvss_u mJy/beam float interpolated Stokes U value at position of I peak 28 nvss_p_flux mJy float integrated linear polarized flux 29 nvss_i_rms mJy/beam float RMS noise in Stokes I image 30 nvss_pol_rms mJy/beam float RMS noise in Stokes Q,U images 31 nvss_res_rms mJy/beam float RMS Stokes I residual 32 nvss_res_peak mJy/beam float peak Stokes I residual 33 nvss_res_flux mJy/beam float integrated Stokes I residual 34 nvss_xpixel pixel float "X" pixel of source center 35 nvss_ypixel pixel float "Y" pixel of source center 36 nvss_field char name of (4x4 deg) field 37 nvss_jd_processed day long integer Julian date of processing -- WENSS data -- 38 wenss_id long integer unique WENSS identifier 39 wenss_ra degree double right ascension values from the WENSS survey; for details see the WENSS paper 40 wenss_dec degree double declination 41 wenss_type char label: Single, Component, Multiple, or Extended 42 wenss_flag char set to "*" when source-finding algorithm failed 43 wenss_peak_flux mJy/beam float peak flux density at 92cm 44 wenss_flux mJy float integrated source flux at 92cm 45 wenss_major arcsec float source major axis size 46 wenss_minor arcsec float source minor axis size 47 wenss_posangle degree float source angle on sky east of north 48 wenss_sky mJy/beam float local rms noise level 49 wenss_frame char name of WENSS frame -- GB6 Data -- 50 gb6_id long integer unique GB6 identifier 51 gb6_ra degree double right ascension (J2000) values from GB6 survey; for details see the GB6 catalog paper 52 gb6_dec degree double declination (J2000) 53 gb6_ra_err degree float error in right ascension 54 gb6_dec_err degree float error in declination 55 gb6_peak_flux mJy/beam float peak flux at 6cm 56 gb6_peak_flux_err mJy/beam float error in peak flux 57 gb6_major arcsec float FWHM major axis 58 gb6_minor arcsec float FWHM minor axis 59 gb6_flux mJy float integrated source flux 60 gb6_posangle degree float fitted major axis position east of north 61 gb6_sky mJy float local sky level 62 gb6_xpixel pixel float "X" pixel of object center 63 gb6_ypixel pixel float "Y" pixel of object center 64 gb6_eflag char flag indicating significantly extended source 65 gb6_wflag char warning flag 66 gb6_cflag char flag indicating confusion -- SDSS photometric data (nearest) -- 67 near_ra degree double right ascension values from SDSS photometric survey; for details see www.sdss.org 68 near_dec degree double declination 69 near_type integer indicates source photometric type 70 near_flags char SDSS quality flags 71 near_modelmag_u magnitude float u,g,r,i,z magnitudes 72 near_modelmag_g magnitude float 73 near_modelmag_r magnitude float 74 near_modelmag_i magnitude float 75 near_modelmag_z magnitude float 76 near_modelmagerr_u magnitude float u,g,r,i,z magnitude errors 77 near_modelmagerr_g magnitude float 78 near_modelmagerr_r magnitude float 79 near_modelmagerr_i magnitude float 80 near_modelmagerr_z magnitude float -- SDSS photometric data (brightest) -- 81 bright_ra degree double right ascension values from SDSS photometric survey; for details see www.sdss.org 82 bright_dec degree double declination 83 bright_type integer indicates source photometric type 84 bright_flags char SDSS quality flags 85 bright_modelmag_u magnitude float u,g,r,i,z magnitudes 86 bright_modelmag_g magnitude float 87 bright_modelmag_r magnitude float 88 bright_modelmag_i magnitude float 89 bright_modelmag_z magnitude float 90 bright_modelmagerr_u magnitude float u,g,r,i,z magnitude errors 91 bright_modelmagerr_g magnitude float 92 bright_modelmagerr_r magnitude float 93 bright_modelmagerr_i magnitude float 94 bright_modelmagerr_z magnitude float -- SDSS data (spectroscopic) -- 95 spec_type integer indicates source spectroscopic type values from SDSS spectroscopic survey; for details see www.sdss.org 96 spec_mjd day long integer Julian date of observation 97 spec_plate integer SDSS plate # 98 spec_fiber integer SDSS fiber # 99 spec_redshift double spectroscopic redshift 100 spec_redshifterr double error in spectroscopic redshift 101 spec_redshift_warning long integer warning flag for redshift calculation -- Matching parameters -- 102 matchflag_first integer set to -1 if FIRST is primary; otherwise equals rank of FIRST match (see matchflag note below) 103 matchflag_nvss integer set to -1 if NVSS is primary; otherwise equals rank of NVSS match (see matchflag note below) 104 distance arcsec double distance between NVSS and FIRST source in this row. 105 overlap integer set to 1 if row entry falls within overlap region; 0 otherwise (see note on positions) 106 spec_overlap integer set to 1 if row entry falls within SDSS spectroscopic overlap region; 0 otherwise (see note on positions) 107 matchtot5 integer # of NVSS or FIRST neighbors within 5" of primary source 108 matchtot10 integer # of NVSS or FIRST neighbors within 10" of primary source 109 matchtot30 integer # of NVSS or FIRST neighbors within 30" of primary source 110 matchtot120 integer # of NVSS or FIRST neighbors within 120" of primary source 111 wenss_distance arcsec double distance between primary and nearest WENSS source within 120" (see note on positions) 112 wenss_matchtot120 integer # of WENSS neighbors within 120" of primary source (see note on positions) 113 gb6_distance arcsec double distance between primary and nearest GB6 source within 120" (see note on positions) 114 gb6_matchtot120 integer # of GB6 neighbors within 120" of primary source (see note on positions) 115 near_distance arcsec double distance between primary and nearest SDSS photometric source within 60" (see note on positions) 116 bright_distance arcsec double distance between primary and nearest bright SDSS photometric source within 3", 10", 30", or 60" (see notes on positions and SDSS photometry) 117 sdss_matchtot integer # of photometric neighbors within 60" of primary (see notes on positions and recent changes) Overlap regions We have defined a region, about 2955 deg2, where the sky coverage of the four radio surveys and the SDSS photometric survey overlap. The SDSS spectroscopic survey is not yet complete; the spec_overlap parameter refers to a slightly smaller 2894 deg2 region defined by the overlap of the four radio surveys and the SDSS spectroscopic survey as of SDSS public Data Release 5. The data parameters overlap and spec_overlap are set to 1 if the row entry lies within the relevant sky region and is set to 0 otherwise. NVSS corrections The integrated NVSS fluxes and the NVSS major and minor axis sizes were calculated according to Condon et al. 1998 (available from the the NVSS website), where the FWHM of the beamsize is ? = 45" everywhere. However, the code used by the NVSS catalog browser to calculate angular sizes has since been updated to account for a non-circular beam. The values in the original version 1.0 of the Unified Catalog were calculated using the earlier circular beam approximation. Now available for download is an updated version 1.1, with the following changes: * The corrected flux values are lower than the values in version 1.0, with discrepancy as large as 10% in the case of unresolved sources. * The non-circular beam calculation can result in negative angular sizes for unresolved sources. We therefore provide an auxiliary file with angular sizes as output by the NVSS catalog browser. For resolved sources, the value given is the angular size. For unresolved sources, the value given is an upper limit only. Flags indicate whether the values are upper limits (0) or real (1). A future version of the Unified Catalog will include these values. * Modifications to some of the figures and tables in Paper I are outlined here. The original version 1.0 of the Unified Catalog is available here. Positions Because FIRST has more accurate astrometry than NVSS, we use the FIRST position to designate the right ascension and declination for each row, where available. For an NVSS source with no FIRST match, we use the NVSS position to designate ra and dec parameters for the corresponding row in the catalog. This decision results in the following: each FIRST source will have the same near and bright optical matches every time it appears in the catalog; an NVSS source can have different designated optical neighbors if it appears in several catalog rows with different FIRST matches. SDSS spectroscopic type The type or class of an SDSS spectroscopic source is determined from the spectrum by the survey's spectroscopic pipeline. * -1: unclassifiable * 0: no spectroscopic match> * 1: star * 2: galaxy * 3: quasar * 4: high-redshift quasar * 6: late-type star SDSS photometry: nearest vs. brightest Parameters labeled near correspond to the closest SDSS photometric match within 60". If that object is within 3" the parameters labeled bright correspond to the brightest neighbor within 3", and sdss_matchtot records the total number of neighbors within 3". If the nearest neighbor is further than 3" away but within 10" (or 30" or 60"), the bright and sdss_matchtot parameters correspond to neighbors within 10" (or 30" or 60", respectively). SDSS photometric type SDSS photometric type is determined morphologically in a simple way: objects whose light distribution matches the point-spread function are classified as unresolved (type=1 in this catalog); extended objects are classified as resolved (type=2 in this catalog). SDSS magnitudes The SDSS uses inverse hyperbolic sine ("asinh") magnitudes, often referred to as "luptitudes". For >10? detections, "luptitudes" are practically the same as standard magnitudes. For more details, please see the SDSS website and the Lupton et al. 1999 AJ paper. Matchflags The FIRST-NVSS matching was done in two ways: we both positionally matched NVSS objects to FIRST sources, and positionally matched FIRST objects to NVSS sources. If a FIRST detection was the primary object, matchflag_first = -1. If an NVSS object was the primary, then matchflag_first = 1 for the row containing the nearest FIRST match, matchflag_first = 2 for the row containing the second closest FIRST match, and matchflag_first = 3 for the row containing the third closest FIRST match (within 30"). Any remaining matches within 30" are not stored, although the number of such matches can be recovered from the matchtot30 parameter. Equivalent rules govern matchflag_nvss. Download the catalog in fits or csv (text) format Version 1.1 of the catalog is available below. Click here for version 1.0. See the note above on NVSS corrections for a discussion of the changes. For details regarding the selection of sources for each file, see Paper I. The file extension .csv refers to a comma-separated-variable text file. To unzip a .gz file, type "gunzip filename" at the command line (exclude quotation marks). 1. The complete catalog (version 1.1) is available as a compressed, tarred archive of files each with a 5deg width in right ascension. There are 2,724,343 rows. File names have the format Complete_0RA5 (containing sources between 0 and 5deg in right ascension). The data have the format described in the above table. To unzip the compressed archives, type Download the fits archive (271M compressed; 1.4G uncompressed) or the csv archive (227M compressed; 1.3G uncompressed 2. A small subset of the catalog could be useful for familiarizing yourself with the catalog format and for testing code. It covers a region of the sky about 106 deg2 in the range 150deg < R.A. < 165deg 40 1) galaxy candidates detected by FIRST, NVSS, WENSS (and not SDSS). These objects were selected based on their lack of an optical counterpart, and their steep radio spectra (? 9220 < -0.5). (See notes on recent changes.) Please note: the correct selection of these sources is given in Section 5.2 of Paper I; Table 8 does not list the selection criteria correctly. These objects: are a subset of item D in Table 8, have no SDSS match within 3", have compact radio morphology, and have steep radio spectra (? 9220 < -0.5). Download the fits file (2.5M compressed; 5.0M uncompressed) or the csv file (5.8M). 10. An auxiliary text file containing NVSS angular sizes in agreement with the NVSS catalog browser. See the note above on NVSS corrections for details. The file contains one row for each NVSS source in the Unified Catalog. Parameters include: NVSS id, major axis [arcsec], major axis flag, minor axis [arcsec], minor axis flag. Flags are 0 for unresolved (upper limit only), 1 for resolved (actual angular size). Download the csv file (12M compressed; 38M uncompressed). Recent changes (Posted 10 Oct 2008) Correction: The parameter sdss_matchtot records the total number of SDSS neighbors within 60", not within the pre-defined search radius as was previously stated (see note on SDSS photometry). (Posted 11 Oct 2008) Correction: The original set of high-redshift (z > 1) galaxy candidates for download mistakenly included sources with flat spectra and uncorrected NVSS fluxes. The version currently posted here is correct. Note that the corrected version is smaller than the dataset referred to in Paper I. (Posted 9 March 2009) Now available: version 1.1 of the catalog contains corrected NVSS fluxes and major/minor axis sizes. See the note above on NVSS corrections for details. The original version 1.0 is still available for download here. We thank Dr. Haida Liang (Nottingham Trent University), Dr. Hui Shi (NAOC), and Dr. Jess Broderick (University of Sydney) for bringing this issue to our attention. If you use this catalog in your research, we would greatly appreciate it if you add a link to this site and a reference to Kimball & Ivezic 2008, AJ, 136, 684 in your publications. Amy Kimball Zeljko Ivezic Department of Astronomy Box 351580, U.W. Seattle, WA 98195-1580 USA Please send us your questions, comments or suggestions. Version 1.1, last updated 5 May 2009 Click for catalog Version 1.0 Free counter and web stats