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RASS6DFGS - ROSAT All-Sky Survey/6dF Galaxy Survey Catalog of X-Ray Selected AGN

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Overview

This table contains a catalog of 3405 X-ray sources from the ROSAT All Sky Survey (RASS) Bright Source Catalog which fall within the area covered by the 6dF Galaxy Survey (6dFGS). The catalog is count-rate limited at 0.05 ct s-1 in the X-ray and covers the area of sky with Declination < 0 degrees and |b| > 10 degrees. The RASS-6dFGS sample was one of the additional target catalogs of the 6dFGS and as a result the authors obtained optical spectra for 2224 (65 per cent) RASS sources. Of these, 1715 (77%) have reliable redshifts with a median redshift of z = 0.16 (excluding the Galactic sources). For the optically bright sources (b_J <= 17.5) in the observed sample, over 90% have reliable redshifts. The catalog mainly comprises quasi-stellar objects (QSOs) and active galaxies but also includes 238 Galactic sources. Of the sources with reliable redshifts, the majority are type 1 active galactic nuclei (AGN, 69%), while 12% are type 2 AGN, 6% absorption-line galaxies and 13% are stars. The authors also identify a small number of optically faint, very low redshift, compact objects which fall outside the general trend in the b_J - z plane. The RASS-6dFGS catalog complements a number of Northern hemisphere samples, particularly the ROSAT Bright Source Catalogue-NRAO VLA Sky Survey (RBSC-NVSS) sample (Bauer et al. 2000, ApJS, 129, 547), and furthermore, in the same region of sky (-40 degrees < Declination < 0 degrees) reveals an additional 561 sources that were not identified as part of that sample.

The authors detect 918 sources (27%) of the RASS-6dFGS sample in the radio using either the 1.4 GHz NVSS or the 843 MHz Sydney University Molonglo Sky Survey (SUMSS) catalogues and find that the detection rate changes with redshift. At redshifts larger than 1 virtually all of these sources have radio counterparts and with a median flux density of 1.15 Jy, they are much stronger than the median flux density of 28.6 mJy for the full sample. The authors attribute this to the fact that the X-ray flux of these objects is being boosted by a jet component, possibly Doppler boosted, that is only present in radio-loud AGN.

The RASS-6dFGS sample provides a large set of homogeneous optical spectra ideal for future studies of X-ray emitting AGN.


Catalog Bibcode

2010MNRAS.401.1151M

References

The RASS-6dFGS catalogue: a sample of X-ray selected AGN from the 6dF Galaxy
Survey
    Mahony E.K., Croom S.M., Boyle B.J., Edge A.C., Mauch T., Sadler E.M.
   <Monthly Notices of the Royal Astronomical Society, Volume 401, Issue 2,
    pp. 1151-1165 (2010)>
   =2010MNRAS.401.1151M

Provenance

This table was created by the HEASARC in April 2010 based on an electronic version of Table 3 from the reference paper obtained from the MNRAS web site.

Parameters

Name
The 6dFGS name of the source using the J2000.0 RA and Declination position-based nomenclature as recommended by the CDS Dictionary of Nomenclature of Celestial Objects, viz. '6dFGS JHHMMSSS-DDMMSS'. Notice that this differs from the style in the published paper where a non-standard form '6dFGS gHHMMSSS-DDMMSS' was suggested.

RA
The Right Ascension of the optical source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original table.

Dec
The Declination of the optical source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 arcseconds in the original table.

LII
The Galactic Longitude of the optical source.

BII
The Galactic Latitude of the optical source.

BJ_Mag
The b_J magnitude of the optical source from the USNO database.

Rmag
The R magnitude of the optical source from the USNO database.

RASS_Name
The RASS name of the source using the J2000.0 RA and Declination position-based nomenclature as recommended by the CDS Dictionary of Nomenclature of Celestial Objects, viz. '1RXS JHHMMSS.s-DDMMSS'. Notice that this differs from the style in the published paper where a non-standard form 'RHHMMSSS-DDMMSS' was suggested.

Extended_Flag
This flag parameter is set to 'E' to signify that the X-ray source is considered to be exetended. This is determined if the source extent given in the RASS-BSC is larger than 35 arcseconds.

RASS_Count_Rate
The RASS 0.1-2.4 keV X-ray count rate, in ct/s.

RASS_Count_Rate_Error
The uncertainty in the RASS 0.1-2.4 keV X-ray count rate, in ct/s.

NH_Gal
The Galactic Hydrogen column density in the direction of the source, in cm-2. This was calculated using the N(H) program in the HEASARC collection which uses data from Dickey and Lockman (1990) and Kalberla et al. (2005).

RASS_Flux
The unabsorbed 0.1-2.4 keV flux of the RASS source, in erg s-1 cm-2, calculated from the HEASARC PIMMS tool using a fixed photon index of 1.7 and the Galactic Hydrogen column density.

RASS_Flux_Error
The uncertainty in the unabsorbed 0.1-2.4 keV flux of the RASS source, in erg s-1 cm-2.

Flux_20_cm
The NVSS flux density of the radio counterpart at 20 cm, in mJy.

Flux_36_cm
The SUMSS flux density of the radio counterpart at 36 cm, in mJy.

Redshift
The redshift of the optical object, taken from the 6dFGS.

Redshift_Error
The uncertainty in the redshift of the optical object, taken from the 6dFGS.

Redshift_Quality_Flag
The redshift quality flag Q from the 6dFGS. Redshifts were measured from the 6dFGS spectra using the runz package and assigned a quality, Q, based on the reliability of the redshift. A quality Q= 1 or 2 denotes an unreliable redshift, Q= 3 signifies a probable redshift and Q= 4 implies a certain redshift. Galactic sources were assigned a quality Q= 6. During the redshifting process, unusual spectra or features were flagged with comments (see Comments parameter).

Qualities Q >= 3 are regarded as reliable and Q=0 means that the source was not observed as part of the 6dFGS. In Table 1 of the reference paper (reproduced below), percentages are given with respect to the full catalog in Column 3 (3405 sources) and with respect to only the sources in the observed sample in Column 4 (2224 sources).

  Q       No.     % full  % obs.

  0       1181    34.7    ---
  1       412     12.1    18.5
  2       97      2.8     4.4
  3       123     3.6     5.5
  4       1354    39.8    60.9
  6       238     7.0     10.7
  

Program_Id_6dFGS
The program identification of the 6dFGS spectrum. (See Section 7.5 of the reference paper). A value of '0' once again signifies that the source was not observed.

NED_Class
The classification of the object taken from the NED database, e.g., 'AbLS' for an absorption-line system, 'G' for galaxy, 'QSO' for quasi-stellar object, or 'UvES' for ultraviolet excess source.

NED_Redshift
The redshift of the object taken from the NED database.

Ref_NED_Redshift
The coded reference for the NED redshift. The HEASARC has created a parameter bibcode_ned_redshift using a table of the codes and their corresponding ADS bibliographic codes (bibcodes) which was obtained from the MNRAS web site.

Bibcode_NED_Redshift
The ADS bibcode of the reference from which the NED redshift was taken.

Comments
This comments parameter contains a brief note regarding any feature in the 6dFGS spectrum. To prevent these comments from being unnecessarily complicated they are generally self-explanatory, one-word entries as follows (a question mark signifies uncertainty in the comments. These comments were added during the visual inspection of the 6dFGS redshifts and should be used as a guide only):

  'broad'        - the spectrum features broad emission lines.

  'narrow'       - the spectrum has narrow emission features.

  'abs'          - the spectrum exhibits only absorption lines.

  'BLLac'        - a featureless spectrum with strong continuum.

  'active_M-star'- characteristic M-star spectrum with strong Balmer
                    emission at z= 0 .

  'WD'           - white dwarf star.

  'CV'           - cataclysmic variable star.

  'neb'          - spectrum displays z= 0 nebula emission lines.

  'bad_splicing' - refers to an error in the data reduction process when the two
                   arms of the spectrum (blue and red) were not matched together
                   correctly in the final spectrum.

  'fringing'     - fringing occasionally occurs causing strong oscillations in
                   the spectrum. This is due to either a small air pocket or
                   damage in the fibre which causes it to act like a fabry-perot
                   filter. Some redshifts could still be distinguished
                   accurately.

  'blue/red_arm_only'
                 - an error with either the red or blue arm during observations
                    resulting in only half of the spectrum being available.

  'contamination'- a nearby source (generally a foreground star) dominates the
                   spectrum, masking any optical signature of the RASS source.
  

Class
The HEASARC Browse object classification of the object. This was based on classification information given in the comments, or, if none were provided, the NED classification.


Contact Person

Questions regarding the RASS6DFGS database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 22-Apr-2010