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 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:
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FileName Lrecl Records Explanations
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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
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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
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Bytes Format Units Label Explanations
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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)
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Note (1): Previous samples are:
1 = QSOs included in the samples of Benn et al. (2002MNRAS.329..221B 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
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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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
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Note (G1): Notes include:
BAL = broad absorption line QSO
abs = Lyα line appears to be self-absorbed
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 27-Mar-2009