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J/MNRAS/391/369     New z≥3.6 QSOs from FIRST-SDSS DR5      (Carballo+, 2008)
Use of neural networks for the identification of new z ≥ 3.6 QSOs from
FIRST-SDSS DR5.
    Carballo R., Gonzalez-Serrano J.I., Benn C.R., Jimenez-Lujan F.
   <Mon. Not. R. Astron. Soc., 391, 369-382 (2008)>
   =2008MNRAS.391..369C
ADC_Keywords: QSOs ; Redshifts ; Radio sources ; Photometry, SDSS

Keywords: methods: data analysis - surveys - galaxies: high-redshift -
          quasars: general - early Universe - radio continuum: galaxies

Abstract:
    We aim to obtain a complete sample of redshift z≥3.6 radio
    quasi-stellar objects (QSOs) from the Faint Images of the Radio Sky at
    Twenty cm survey (FIRST) sources (S1.4GHz>1mJy) having star-like
    counterparts in the Sloan Digital Sky Survey (SDSS) Data Release 5
    (DR5) photometric survey (rAB≤20.2). Our starting sample of 8665
    FIRST-DR5 pairs includes 4250 objects with spectra in DR5, 52 of
    these being z≥3.6 QSOs. We found that simple supervised neural
    networks, trained on the sources with DR5 spectra, and using optical
    photometry and radio data, are very effective for identifying high-z
    QSOs in a sample without spectra. For the sources with DR5 spectra the
    technique yields a completeness (fraction of actual high-z QSOs
    classified as such by the neural network) of 96 per cent, and an
    efficiency (fraction of objects selected by the neural network as
    high-z QSOs that actually are high-z QSOs) of 62 per cent. Applying
    the trained networks to the 4415 sources without DR5 spectra we found
    58 z≥3.6 QSO candidates. We obtained spectra of 27 of them, and 17
    are confirmed as high-z QSOs. Spectra of 13 additional candidates from
    the literature and from SDSS Data Release 6 (DR6) revealed seven more
    z≥3.6 QSOs, giving an overall efficiency of 60 per cent (24/40).

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
table2.dat        62       52   FIRST-DR5 sources with SDSS spectra, and
                              classified by SDSS as z≥3.6 QSOs
table5.dat        79       58   z≥3.6 QSO candidates identified by the NN in
                              the FIRST-SDSS DR5 unlabelled sample


See also:
  II/276 : The SDSS Photometric Catalog, Release 5 (Adelman-McCarthy+, 2007)
  J/MNRAS/348/857 : Radio-loud QSOs at z∼4 (Holt+, 2004)
  J/MNRAS/370/1034 : FIRST-APM-SDSS survey for high-z radio QSOs 
                     (Carballo+, 2006)


Byte-by-byte Description of file: table2.dat

   Bytes Format Units   Label     Explanations

   1-  2  I2    h       RAh       SDSS Right ascension (J2000)
   4-  5  I2    min     RAm       SDSS Right ascension (J2000)
   7- 11  F5.2  s       RAs       SDSS Right ascension (J2000)
      13  A1    ---     DE-       SDSS Declination sign (J2000)
  14- 15  I2    deg     DEd       SDSS Declination (J2000)
  17- 18  I2    arcmin  DEm       SDSS Declination (J2000)
  20- 23  F4.1  arcsec  DEs       SDSS Declination (J2000)
  25- 29  F5.2  mag     rmag      SDSS dereddened PSF rAB magnitude
  31- 36  F6.2  mJy     S1.4GHz   FIRST total radio flux density
  39- 43  F5.3  ---     z         SDSS redshift
      44  A1    ---     n_z       [a] a = revised redshift from DR5Q,
                                          see Section 2
  47- 50  F4.2  ---     NN        [0.1,1] Neuronal network (NN) output 
                                          (ymed≥.01) see Section 4.2)
  52- 58  A7    ---     PSamp     Included in previous samples (1)
  60- 62  A3    ---     Notes     Notes (G1)

Note (1): Previous samples are:
      1 = QSOs included in the samples of Benn et al. (2002MNRAS.329..221B)
      2 = QSOs included in the samples of Holt et al. 2004, Cat. J/MNRAS/348/857
      3 = QSOs included in the samples of Carballo et al. 2006,
               Cat. J/MNRAS/370/1034


Byte-by-byte Description of file: table5.dat

   Bytes Format Units   Label     Explanations

   1-  2  I2    h       RAh       SDSS Right ascension (J2000)
   4-  5  I2    min     RAm       SDSS Right ascension (J2000)
   7- 11  F5.2  s       RAs       SDSS Right ascension (J2000)
      13  A1    ---     DE-       SDSS Declination sign (J2000)
  14- 15  I2    deg     DEd       SDSS Declination (J2000)
  17- 18  I2    arcmin  DEm       SDSS Declination (J2000)
  20- 23  F4.1  arcsec  DEs       SDSS Declination (J2000)
  25- 29  F5.2  mag     rmag      SDSS dereddened PSF rAB magnitude
  31- 36  F6.2  mJy     S1.4GHz   FIRST total radio flux density
  38- 41  F4.2  ---     NN        [0.1,1] Neuronal network (NN) output 
                                          (ymed≥.01) see Section 4.2)
  43- 47  F5.3  ---     zNED      ? Redshift from NED
  48- 51  F4.2  ---     z         ? Redshift from William Herschel Telescope
  53- 57  F5.3  ---     zDR6      ? Redshift from SDSS DR6
  59- 75  A17   ---     Notes     Notes (G1)
  77- 79  A3    ---     Flag      [Yes] indicates sources located within the
                                        spectroscopic plates available in DR6

Note (G1): Notes include:
     BAL = broad absorption line QSO
     abs = Lyα line appears to be self-absorbed


History:
    From electronic version of the journal
(End)                                      Patricia Vannier [CDS]    27-Mar-2009