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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
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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table4.dat 93 91665 Quasar redshift catalogue table5.dat 37 7978 Quasar cross-correlation templates
See also: VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010) : Home Page Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 4 A4 --- --- [SDSS] 5- 23 A19 --- SDSS SDSS object name ( 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
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
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
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
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.
History: From electronic version of the journal
(End) Patricia Vannier [CDS] 16-Dec-2010
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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