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GLXSDSSQSO - GALEX/SDSS Quasar Catalog

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Overview

This table contains the result of an analysis of the broad-band UV and optical properties of z ~< 3.4 quasars matched in the Galaxy Evolution Explorer (GALEX) General Data Release 1 (GR1) and the Sloan Digital Sky Survey (SDSS) Data Release 3 (DR3). Of the 6371 SDSS DR3 quasars covered by 204 GALEX GR1 tiles and listed in this table, 5380 (84%) have near-UV detections, while 3034 (48%) have both near-UV and far-UV detections using a matching radius of 7 arcseconds. Most of the DR3 sample quasars are detected in the near-UV until z ~ 1.7, with the near-UV detection fraction dropping to ~50% by z ~ 2. Statistical tests performed on the distributions of nondetections indicate that the optically selected quasars missed in the UV tend to be optically faint or at high redshift. The GALEX positions are shown to be consistent with the SDSS astrometry to within an rms scatter of 0.6 - 0.7 arcsecs in each coordinate, and the empirically determined photometric errors from multiepoch GALEX observations significantly exceed the Poissonian errors quoted in the GR1 object catalogs. The UV-detected quasars are well separated from stars in UV-optical color-color space, with the UV-optical relative colors suggesting a marginally detected population of reddened objects due to absorption along the line of sight or dust associated with the quasar. The resulting spectral energy distributions (SEDs) cover ~350 - 9000 Angstroms (rest frame), where the overall median SED peaks near the Lyman-Alpha emission line, as found in other UV quasar studies. The large sample size allows the authors to construct median SEDs in small bins of redshift and luminosity, and they find that the median SED becomes harder (bluer) at UV wavelengths for quasars with lower continuum luminosity. The detected UV-optical flux as a function of redshift is qualitatively consistent with attenuation by intervening Lyman-absorbing clouds.

Catalog Bibcode

2007AJ....133.1780T

References

The UV properties of SDSS-selected quasars.
    Trammell G.B., Vanden Berk D.E., Schneider D.P., Richards G.T., Hall P.B.,
    Anderson S.F., Brinkmann J.
   <Astron. J., 133, 1780-1794 (2007)>
   =2007AJ....133.1780T

Provenance

This table was created by the HEASARC in October 2009 based on the electronic version of Table 2 from the reference paper which was obtained from the CDS (their catalog J/AJ/133/1780 file table2.dat).

Parameters

Name
The SDSS DR3 object designation from the quasar catalog (Schneider et al. 2005, AJ, 130, 367) in the format SDSS Jhhmmss.ss+ddmmss.s

GALEX_Name
The GALEX GR1 object designation from the merged object catalog. The same object identified on multiple GALEX tiles can have more than one object ID. Thus, one should always use object coordinates and not object designations to identify individual objects as such. DR3 quasars without a UV detection (see Section 2.3 of the reference paper) have blank values for this parameter.

RA
The Right Ascension of the object from the SDSS DR3 quasar catalog, in the selected equinox. This was given in J2000.0 coordinates to a precision of 10-6 degrees in the original table. For a significant majority of the objects, the SDSS astrometric accuracy of each coordinate is 0.1 arcsecs, with the largest errors expected not to exceed 0.2 arcsecs (see Pier et al. 2003, AJ, 125, 1559).

Dec
The Declination of the object from the SDSS DR3 quasar catalog, in the selected equinox. This was given in J2000.0 coordinates to a precision of 10-6 degrees in the original table. For a significant majority of the objects, the SDSS astrometric accuracy of each coordinate is 0.1 arcsecs, with the largest errors expected not to exceed 0.2 arcsecs (see Pier et al. 2003, AJ, 125, 1559).

LII
The Galactic Longitude of the object from the SDSS DR3 quasar catalog.

BII
The Galactic Latitude of the object from the SDSS DR3 quasar catalog.

RA_GALEX
The Right Ascension from the GALEX GR1 merged object catalogs, in the selected equinox. This was given in J2000.0 coordinates to a precision of 10-6 degrees in the original table. The authors' empirical analysis in Section 2.3 of the reference paper demonstrates the derived rms of ~ 0.6 - 0.7 arcsecs for each GALEX coordinate. DR3 quasars without any UV detection will have blank GALEX coordinates.

Dec_GALEX
The Declination from the GALEX GR1 merged object catalogs, in the selected equinox. This was given in J2000.0 coordinates to a precision of 10-6 degrees in the original table. The authors' empirical analysis in Section 2.3 of the reference paper demonstrates the derived rms of ~ 0.6 - 0.7 arcsecs for each GALEX coordinate. DR3 quasars without any UV detection will have blank GALEX coordinates.

Offset
The coordinate offset between the GALEX and SDSS positions (GALEX - SDSS), given in arcseconds. Objects with separations > 7 arcsecs or nondetections have a blank entry for this parameter.

Redshift
The quasar redshift from the DR3. For any given object, the estimated redshift uncertainty is <0.01, except for broad absorption-line quasars (e.g., Trump et al. 2006, ApJS, 165, 1).

Umag
The DR3 PSF magnitude for the quasar (no Galactic extinction correction applied), given in AB magnitudes for the SDSS photometric u band. The magnitudes are those derived from BEST photometry (or TARGET if BEST is unavailable; see Schneider et al. [2005, AJ, 130, 367] and references therein).

Umag_Error
The error in the SDSS PSF u-band magnitude.

Gmag
The DR3 PSF magnitude for the quasar (no Galactic extinction correction applied), given in AB magnitudes for the SDSS photometric g band. The magnitudes are those derived from BEST photometry (or TARGET if BEST is unavailable; see Schneider et al. [2005, AJ, 130, 367] and references therein)

Gmag_Error
The error in the SDSS PSF g-band magnitude.

Rmag
The DR3 PSF magnitude for the quasar (no Galactic extinction correction applied), given in AB magnitudes for the SDSS photometric r band. The magnitudes are those derived from BEST photometry (or TARGET if BEST is unavailable; see Schneider et al. [2005, AJ, 130, 367] and references therein)

Rmag_Error
The error in the SDSS PSF r-band magnitude.

Imag
The DR3 PSF magnitude for the quasar (no Galactic extinction correction applied), given in AB magnitudes for the SDSS photometric i band. The magnitudes are those derived from BEST photometry (or TARGET if BEST is unavailable; see Schneider et al. [2005, AJ, 130, 367] and references therein)

Imag_Error
The error in the SDSS PSF i-band magnitude.

Zmag
The DR3 PSF magnitude for the quasar (no Galactic extinction correction applied), given in AB magnitudes for the SDSS photometric z band. The magnitudes are those derived from BEST photometry (or TARGET if BEST is unavailable; see Schneider et al. [2005, AJ, 130, 367] and references therein)

Zmag_Error
The error in the SDSS PSF z-band magnitude.

Fmag
The GALEX calibrated magnitude of the quasar, in units of AB magnitude for the far-UV (FUV) photometric band (f band). The effective wavelength of the FUV channel is 1528 Angstroms (Morrissey et al. 2005, ApJ, 619, L7).

Fmag_Error
The error in the GALEX GR1 FUV magnitude as quoted in the GR1 object catalog.

Fmag_Alt_Err
The error in the GALEX GR1 FUV magnitude, as derived by the authors' empirical analysis of the photometry .

Nmag
The GALEX calibrated magnitude of the quasar, in units of AB magnitude for the near-UV (NUV) photometric band (n band). The effective wavelength of the NUV channel is 2271 Angstroms (Morrissey et al. 2005, ApJ, 619, L7).

Nmag_Error
The error in the GALEX GR1 NUV magnitude as quoted in the GR1 object catalog.

Nmag_Alt_Err
The error in the GALEX GR1 NUV magnitude, as derived by the authors' empirical analysis of the photometry .

Gal_Abs_U
The Galactic extinction in the SDSS u band (A_u) in the direction of the quasar, derived from Schlegel et al. (1998, ApJ, 500, 525). The extinction in the remaining SDSS bands can be expressed as A_g, A_r, A_i, and A_z with values corresponding to 0.736, 0.534, 0.405, and 0.287 times A_u. For the GALEX f and n bands, the corrections A_f and A_n are 1.584 and 1.684 times A_u, respectively (Wyder et al. 2005, ApJ, 619, L15). All correction factors assume an R_V = 3.1 absorbing medium.

Log_NH_Gal
The logarithm of the neutral hydrogen column density, in atoms cm-2, along the Galactic line of sight to the quasar, interpolated via 21-cm data (see also Schneider et al. [2005, AJ, 130, 367] and references therein).

Abs_Imag
The absolute i-band magnitude, calculated after correcting for Galactic extinction and assuming a power-law continuum index of alpha = -0.5 (f_nu ~ nu^alpha) and a Lambda-dominated flat cosmology with Omega_Lambda = 0.7, Omega_m = 0.3, and H_0 = 70 km s-1 Mpc-1 (the same as for this paper).

Log_2200a_Lum
The logarithmic monochromatic quasar luminosity (nu x L_nu) computed at 2200 Angstroms (rest frame), in erg s-1. A blank entry is given if there is no wavelength coverage.

Log_5100a_Lum
The logarithmic monochromatic quasar luminosity (nu x L_nu) computed at 5100 Angstroms (rest frame), in erg s-1; only computed for those quasars for which 5100 Angstroms has not been redshifted out of the SDSS z band. A blank entry is given if there is no wavelength coverage.

GI_Color
The Delta(g - i) relative color of the quasar (see Section 3.3 of the reference paper), defined as the (g - i) color minus the corresponding median color at the redshift of the quasar, given in units of AB magnitude.

FN_Color
The Delta(f - n) relative color of the quasar (see Section 3.3 of the reference paper), defined as the (f - n) color minus the corresponding median color at the redshift of the quasar, given in units of AB magnitude.

Off_Axis
The object distance from the GALEX field center, in arcminutes (this was given in the original table in decimal degrees). Note that for the case of objects with multiepoch observations across multiple GALEX fields, the entry from the tile with the highest effective NUV exposure time ("NUV_WEIGHT" in the GR1 catalog) is used (see Section 2.3 of the reference paper).

NUV_Exposure
The GALEX NUV effective exposure time, in seconds. The nondetections have blank entries for this parameter. For the 991 DR3 quasars covered by a GALEX tile for which no NUV source was found within 7 arcsecs (they have blank entries for nmag), the NUV effective exposure time for the next nearest near-UV source to the DR3 quasar is given in seconds.

FUV_Exposure
The GALEX FUV effective exposure time, in seconds. The nondetections have blank entries for this parameter. Of the 3072 FUV detections, 38 are only detected in the FUV (they have blank entries for fmag), and are not analyzed as true matches in this study (see the discussion in Section 2.3 of the reference paper).

GALEX_Svy_Flag
The GALEX survey flag. The possible values are integers from 1 to 4 that specify the survey from which the UV identification of the SDSS quasar was drawn (4 = AIS, 3 = NGS, 2 = MIS, and 1 = DIS; see Section 2.1 of the reference paper for the GALEX data/survey descriptions).


Contact Person

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Page Author: Browse Software Development Team
Last Modified: 28-Oct-2009