TWODFQSOZ - 2dF QSO Redshift (2QZ) Survey

Overview

The final catalog of the 2dF QSO Redshift Survey (2QZ) is based on Anglo-Australian Telescope 2dF spectroscopic observations of 44,576 color-selected (u, b_J, r) objects with 18.25 < b_J < 20.85 selected from automated plate measurement scans of UK Schmidt Telescope (UKST) photographic plates. The 2QZ comprises 23,338 quasi-stellar objects (QSOs), 12,292 galactic stars (including 2,071 white dwarfs) and 4,558 compact narrow emission-line galaxies. The authors obtained a reliable spectroscopic identification for 86 per cent of objects observed with 2dF. They also report on the 6dF QSO Redshift Survey (6QZ), based on UKST 6dF observations of 1,564 brighter (16 < b_J < 18.25) sources selected from the same photographic input catalog. In total, the authors identified 322 QSOs spectroscopically in the 6QZ. The completed 2QZ is, by more than a factor of 50, the largest homogeneous QSO catalog ever constructed at these faint limits (b_J < 20.85) and high QSO surface densities (35 QSOs/deg²). As such, it represents an important resource in the study of the Universe at moderate-to-high redshifts.

The survey area comprised 30 UKST fields, arranged in two 75 degrees by 5 degrees declination strips, one passing across the South Galactic Gap centered on Dec = -30 degrees (the SGP strip), and the other across the North Galactic Gap centered on Dec = 0 degrees (referred to in the reference paper as the equatorial strip, but also known as the NGP strip. The total survey area is 721.6 deg², when allowance is made for regions of sky excised around bright stars.

Spectroscopic observations of the input catalogue were made with the 2dF instrument at the Anglo-Australian Telescope (AAT; the 2QZ sample) and the 6dF instrument at the UKST (the 6QZ sample). 2dF spectroscopic observations began in January 1997 and were completed in April 2002. Six-degree Field observations were performed over the period 2001 March-2002 September.

Catalog Bibcode

2004MNRAS.349.1397C

References

The 2dF QSO Redshift Survey (2QZ)
     Croom S.M., Smith R.J., Boyle B.J., Shanks T., Miller L., Outram P.J.,
     Loaring N.S.
    <Mon. Not. R. Astron. Soc. 349, 1397 (2004)>
    =2004MNRAS.349.1397C

Provenance

This online catalog was created by the HEASARC in October 2010 based on the machine-readable table 2qz.dat obtained from the CDS (their catalog VII/241).

Parameters

Name
The 2QZ Catalog source designation in the recommended J2000.0-based format, e.g., '2QZ JHHMMSS.S+DDMMSS'. Note that the object names may in some cases not correspond exactly to the listed source position as the authors improved the astrometry of the catalog after the object names were first defined, but decided not to change the names so as to avoid confusion with previously published lists.

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

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

LII
The Galactic Longitude of the object.

BII
The Galactic Latitude of the object.

Source_Number
The internal catalog object number. Objects should generally be referenced not by this designation, but by their position-based name.

Internal_Name
The internal catalog object name. Objects should generally be referenced not by this designation, but by their position-based name.

Sector_Name
The name of the sector which this object inhabits. A sector is defined as the intersection of overlapping 2dF fields (see Section 3 of the reference paper). The format of the sector name is, for example, 'S_200_201_247', where S denotes the SGP strip and the numbers indicate that the sector is formed by the overlap of fields 200, 201 and 247. There are no sectors defined for the 6QZ, and the 1,657 such objects in this table all have sector_name values of 'S_'.

UKST_Field_Number
The UKST survey field number. The survey area comprised 30 UKST fields, arranged in two 75 degrees by 5 degrees declination strips, one passing across the South Galactic Gap centered on Dec = -30 degrees (the SGP strip), and the other across the North Galactic Gap centered on Dec = 0 degrees (referred to in the reference paper as the equatorial strip, but also known as the NGP strip. The total survey area is 721.6 deg², when allowance is made for regions of sky excised around bright stars.

APM_X_Pos
The automated plate measurement (APM) scan X-position (1 pixel ~ 8 um)

APM_Y_Pos
The automated plate measurement (APM) scan Y-position (1 pixel ~ 8 um)

BJ_Mag
The b_J magnitude of the object.

U_Bj_Color
The u-b_J color index of the object.

Bj_R_Color
The b_J-r color index of the object. Sources which had only upper limits, i.e., non-detections, in the r plates were also included in this catalog and have a listed b_J color of (b_J-r_lim)-10, the -10 being used to differentiate upper limits from normal colors (objects with real r-band detections have colors in the range -1.4 < b_J-r < 3.4, while upper limits have b_J-r < -9.8).

Num_Obs
The number of independent spectral observations of the object. In a number of cases, there are two or more 2dF observations of the same source. The first and second observations (arranged in quality order) are listed in this table. (When there are more than 2 spectra, details of the additional spectra are given in the files ngp_rep.dat, sgp_rep.dat and 6qz_rep.dat, for North and South galactic poles, and 6QZ, respectively, which are not contained in the present table but are available at http://cdsarc.u-strasbg.fr/ftp/cats/VII/241/ ). These are useful to assess the quality of the final catalog. The identification and redshift that the authors adopt is that from the observation with the numerically lowest quality value (where the quality value is identification quality times 10 + redshift quality), and if there are equal quality values, the highest S/N value. In all cases, the final adopted ID is listed as observation #1, with the lower quality observation being listed as observation #2.

Redshift_1
The redshift of the object from the first spectrum.

Quality_Flag_1
The quality flag of the first observation, defined as (the identification quality times 10 + redshift quality). As part of the classification process a quality flag was attached to each identification and redshift measurement as follows:

  Quality = 1: High-quality identification or redshift
  Quality = 2: Poor-quality identification or redshift
  Quality = 3: No identification or redshift assignment

The quality flag was determined independently for the identification and redshift of an object. For example, a quality 1 QSO identification could have a quality 1 or 2 redshift, resulting in quality flag values of 11 and 12, respectively.

Broad_Type_1
The identification of the nature of the object based on the first spectrum. 2QZ spectra were classified using the AUTOZ program (see Croom et al. 2001, MNRAS, 322, L29) which uses a chi²-minimization technique to fit each spectrum to a number of QSO [including broad absorption line (BAL) QSOs], galaxy and stellar templates and to measure a redshift for all extragalactic identifications. The QSO template was based on the composite spectrum of Francis et al. (1991, ApJ, 373, 465). AUTOZ produces a single identification based on the best-fitting template in one of six categories based on the following spectral criteria:

   QSO: Broad (> 1000 km s^-1) emission lines
  NELG (Narrow Emission-Line Galaxy): Narrow (< 1000 km s^-1) emission lines only
   gal: Redshifted galaxy absorption features, no emission lines
  star: Stellar absorption features at rest, i.e., a Galactic star
  cont: No identifiable emission or absorption features (high S/N > 10)
    ??: Unclassifiable; no identified emission or absorption features (low S/N)

Sub-classes are contained within parentheses after the main classifications:

    DA = a DA white dwarf
    DB = a DB white dwarf
    DO = a DO white dwarf
    DZ = a DZ white dwarf
    CV = a star with strong hydrogen Balmer emission lines
   DAM = a DA white dwarf - M-dwarf binary
   DBM = a DB white dwarf - M-dwarf binary
   BAL = a broad absorption line QSO

For example QSO(BAL), star(DA), star(CV), etc. If the identification has a class 2 quality then there is a ? appended to the end of the identification.

Spectrum_1_Date
The date of the observation of the first spectrum of the object.

Field_Spect_Number_1
The 2dF field/spectrograph number for the first spectral observation of the object. This is defined as the actual 2dF field number times 10 plus the spectrograph number (1 or 2 for 2dF, 6 for 6dF), e.g., field number 218 and spectrograph 2 gives a value of 2182 for this parameter. Sources with spectra from the Keck observations of 2QZ radio sources all have field number values of 8881. Sources from the follow-up of close pairs have field number values of 7771. Sources from the 6QZ with double-beam spectrograph (DBS) observations all have field number values of 6666.

Fiber_Number_1
The 2dF fiber number within the spectrograph for the first spectral observation of the object.

SNR_Spectrum_1
The signal-to-noise ratio for the first spectrum of the object in the 4000-5000 Angstrom band.

Redshift_2
The redshift of the object from the second spectrum.

Quality_Flag_2
The quality flag of the second observation, defined as (the identification quality times 10 + redshift quality). As part of the classification process a quality flag was attached to each identification and redshift measurement as follows:

  Quality = 1: High-quality identification or redshift
  Quality = 2: Poor-quality identification or redshift
  Quality = 3: No identification or redshift assignment

Broad_Type_2
The identification of the nature of the object based on the second spectrum. 2QZ spectra were classified using the AUTOZ program (see Croom et al. 2001, MNRAS, 322, L29) which uses a chi²-minimization technique to fit each spectrum to a number of QSO [including broad absorption line (BAL) QSOs], galaxy and stellar templates and to measure a redshift for all extragalactic identifications. The QSO template was based on the composite spectrum of Francis et al. (1991, ApJ, 373, 465). AUTOZ produces a single identification based on the best-fitting template in one of six categories based on the following spectral criteria:

   QSO: Broad (> 1000 km s^-1) emission lines
  NELG (Narrow Emission-Line Galaxy): Narrow (< 1000 km s^-1) emission lines only
   gal: Redshifted galaxy absorption features, no emission lines
  star: Stellar absorption features at rest, i.e., a Galactic star
  cont: No identifiable emission or absorption features (high S/N > 10)
    ??: Unclassifiable; no identified emission or absorption features (low S/N)

Sub-classes are contained within parentheses after the main classifications:

    DA = a DA white dwarf
    DB = a DB white dwarf
    DO = a DO white dwarf
    DZ = a DZ white dwarf
    CV = a star with strong hydrogen Balmer emission lines
   DAM = a DA white dwarf - M-dwarf binary
   DBM = a DB white dwarf - M-dwarf binary
   BAL = a broad absorption line QSO

For example QSO(BAL), star(DA), star(CV), etc. If the identification has a class 2 quality then there is a ? appended to the end of the identification.

Spectrum_2_Date
The date of the observation of the second spectrum of the object.

Field_Spect_Number_2
The 2dF field/spectrograph number for the second spectral observation of the object. This is defined as the actual 2dF field number times 10 plus the spectrograph number (1 or 2 for 2dF, 6 for 6dF), e.g., field number 218 and spectrograph 2 gives a value of 2182 for this parameter. Sources with spectra from the Keck observations of 2QZ radio sources all have field number values of 8881. Sources from the follow-up of close pairs have field number values of 7771. Sources from the 6QZ with double-beam spectrograph (DBS) observations all have field number values of 6666.

Fiber_Number_2
The 2dF fiber number within the spectrograph for the second spectral observation of the object.

SNR_Spectrum_2
The signal-to-noise ratio for the second spectrum of the object in the 4000-5000 Angstrom band.

Previous_Redshift
The previously known redshift of the object. This is given when a 2QZ/6QZ source matches the position (to within 6 arcseconds) of a previously known QSO/active galactic nucleus (AGN) in the catalog of Veron-Cetty & Veron (9th edition: 2000).

Flux_20_cm
The flux density of the radio counterpart at 1.4 GHz (from the NVSS) which lies within 15 arcseconds of the 2QZ/6QZ source, in mJy.

RASS_Flux
The flux in the soft X-ray (0.1-2.4 keV) band from the RASS of any counterpart which lies within 30 arcseconds of the 2QZ/6QZ source, in erg s^-1 cm^-2. This was converted from the RASS counts per second into flux using a conversion factor of 1.2 x 10^-11 erg cm^-2 ct^-1 assuming a power-law spectrum with a photon index of -2.

Reddening
An estimate of the galactic reddening E(B-V) to the source, as taken from the work of Schlegel, Finkbeiner & Davis (1998, ApJ, 500, 525). In order to convert from E(B-V) to extinction values, the reader should multiply the value of E(B-V) by 5.434, 4.035 and 2.673 in order to obtain the extinction in the u, b_J, and r bands, respectively.

Comment_Spectrum_1
Comments about the first observation which might flag the object or spectrum as unusual.

Comment_Spectrum_2
Comments about the second observation which might flag the object or spectrum as unusual.

Class
The HEASARC Browse object classification based on the value of the broad_type_1 parameter, except if the value of the broad_type_2 parameter disagrees, in which case we have set the class value to unidentified.

Contact Person

Questions regarding the TWODFQSOZ database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:35:51 EDT