J/MNRAS/405/2302 Improved redshifts for SDSS quasar spectra (Hewett+, 2010)
Improved redshifts for SDSS quasar spectra.
Hewett P.C., Wild V.
<Mon. Not. R. Astron. Soc., 405, 2302-2316 (2010)>
=2010MNRAS.405.2302H 2010MNRAS.405.2302H
ADC_Keywords: Surveys ; QSOs ; Redshifts
Keywords: catalogues - surveys - quasars: emission lines - quasars: general
Abstract:
A systematic investigation of the relationship between different
redshift estimation schemes for more than 91000 quasars in the Sloan
Digital Sky Survey (SDSS) Data Release 6 is presented. The publicly
available SDSS quasar redshifts are shown to possess systematic biases
of Δz/(1+z)≥0.002 (600km/s) over both small (δz~=0.1) and
large (δz~=1) redshift intervals. Empirical relationships
between redshifts based on (i) CaII H&K host galaxy absorption, (ii)
quasar [OII] λλ3728, (iii) [OIII] λλ 4960,
5008 emission and (iv) cross-correlation (with a master-quasar
template) that includes, at increasing quasar redshift, the prominent
MgII λλ 2799, CIII] λλ 1908 and CIV
λλ 1549 emission lines are established as a function of
quasar redshift and luminosity. New redshifts in the resulting
catalogue possess systematic biases, a factor of ~=20 lower compared
to the SDSS redshift values; systematic effects are reduced to the
level of Δz/(1+z) (30km/s) per unit redshift or ≤2.5x10-5 per
unit absolute magnitude. Redshift errors, including components due
both to internal reproducibility and to the intrinsic quasar-to-quasar
variation among the population, are available for all quasars in the
catalogue. The improved redshifts and their associated errors have
wide applicability in areas such as quasar absorption outflows, quasar
clustering, quasar-galaxy clustering and proximity-effect
determinations.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 93 91665 Quasar redshift catalogue
table5.dat 37 7978 Quasar cross-correlation templates
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See also:
VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)
http://www.sdss.org : Home Page
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- --- [SDSS]
5- 23 A19 --- SDSS SDSS object name (JHHMMSS.ss+DDMMSS.s)
25- 33 F9.5 deg RAdeg Right ascension (J2000)
35- 43 F9.5 deg DEdeg Declination (J2000)
45- 52 F8.6 --- z Redshift
54- 61 F8.6 --- e_z Redshift error
63- 64 I2 --- Det [-1/1] FIRST Detection status: 1=detected,
-1=not detected, 0=outside FIRST footprint
66- 76 F11.6 --- z1 ?=-999.0 Alternate redshift for objects with
Det=0 and cross-correlation redshift
estimate >1.1
78 I1 --- n_z [1/7] Redshift estimation method code (2)
80- 83 I4 --- Plate SDSS spectroscopic plate
85- 89 I5 d MJD SDSS MJD of spectroscopic observation
91- 93 I3 --- Fiber SDSS spectroscopic fibre number
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Note (2): Redshift estimation method code as follows:
1 = [OIII]
2 = [OII]
3 = MgII_cc
4 = CIII]_cc
5 = CIV_cc
6 = extra_cc
7 = SDSS
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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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2- 8 F7.2 0.1nm lambda Wavelength (Angstroms)
10- 15 F6.3 --- rFlux1 Relative flux (per unit wavelength) for the
master quasar cross-correlation template (1)
17- 21 I5 --- Nqso1 Number of quasars contributing at given
wavelength
24- 31 F8.3 --- rFlux2 ?=-999.000 Relative flux (per unit wavelength)
for the FIRST-detected quasar cross-correlation
template (1)
33- 37 I5 --- Nqso2 Number of quasars contributing at given
wavelength
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Note (1): Both quasar templates were constructed for use in cross-correlation
estimates of quasar redshifts. The templates are NOT suitable for use
in investigations related to spectral energy distributions of quasars
or AGN. The value "-999.000" indicates no spectrum at given wavelength.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 16-Dec-2010