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J/ApJ/675/1002 Proximate damped Lyα systems in SDSS-DR5 (Prochaska+, 2008)

The SDSS-DR5 survey for proximate damped Lyα systems. Prochaska J.X., Hennawi J.F., Herbert-fort S. <Astrophys. J., 675, 1002-1013 (2008)> =2008ApJ...675.1002P
ADC_Keywords: QSOs ; Redshifts Keywords: quasars: absorption lines Abstract: Using the Sloan Digital Sky Survey Data Release 5 (SDSS-DR5), we survey proximate damped Lyα systems (PDLAs): absorption-line systems with HI column density NH≥2x1020cm-2 at velocity separation δv<2999km/s from their background quasar. Many of these absorbers may be physically associated with their background quasars, and their statistics allow us to study quasar environments out to z∼5. However, the large ionizing flux emitted by a quasar can ionize the neutral gas in a nearby galaxy, possibly giving rise to a "proximity effect", analogous to the similar effect observed in the Lyα forest. From a sample of 108 PDLAs, we measure the HI frequency distribution f(NH,X) incidence, and gas mass density of the PDLAs near luminous quasars over the redshift interval z=2.2-5. The incidence and mass density of PDLAs at z∼3 is approximately twice that of intervening DLAs, while at z<2.5 and >3.5 the f(NHX) distribution is enhanced but statistically consistent with the intervening population. We interpret the observed enhancement of PDLAs around quasars in terms of quasar-galaxy clustering and compare the strength of the clustering signal to the expectation from independent measures of the respective clustering strengths of DLAs and quasars, as well as a complementary analysis of the clustering of absorbers around quasars in the transverse direction. We find that there are a factor of 5-10 fewer PDLAs around quasars than expected and interpret this result as evidence for the hypothesis that the ionizing flux from the quasars photoevaporates HI in nearby DLA galaxies, thus reducing their cross section for DLA absorption. This constitutes the first detection of a "proximity effect" for DLAs. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 55 10397 SDSS-DR5 quasar sample for proximate DLA table2.dat 63 107 SDSS-DR5 proximate DLA statistical sample table3.dat 63 40 SDSS-DR5 proximate DLA nonstatistical sample
See also: J/ApJ/651/61 : Optically thick absorbers near luminous quasars (Hennawi+ 2006) J/AJ/133/2222 : Clustering of high-redshift QSOs from SDSS (Shen+, 2007) http://www.sdss.org : SDSS Home Page Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 4 I4 --- Plate SDSS Plate number 6- 10 I5 d MJD Modified Julian Date of the observation 12- 14 I3 --- Fiber SDSS Fiber identification number 16- 34 A19 --- SDSS SDSS source name, JHHMMSS.ss+DDMMSS.s 36- 40 F5.3 --- zQSO Quasar redshift reported in SDSS-DR5 42- 47 F6.4 --- znew ? New quasar redshift (1) 49 I1 --- fmtl [0/3]? Absorption flag (2) 51- 55 F5.3 --- zinit ? Starting redshift for the PDLA search (3)
Note (1): Estimated using the algorithms developed by Hennawi et al. (2006, Cat. J/ApJ/651/61) and Shen et al. (2007, Cat. J/AJ/133/2222). This analysis was performed on quasars with PDLA candidates lying within 10000km/s of the SDSS-DR5 redshift. Note (2): Flag as follows: 0 = No intrinsic absorption 1 = Mild intrinsic absorption (WCIV<3Å), included in analysis 2 = Strong intrinsic absorption (WCIV>3Å), excluded Note (3): Assuming an offset of vprox=3000km/s from the quasar, allowing for the revised redshifts in z-new.
Byte-by-byte Description of file: table2.dat table3.dat
Bytes Format Units Label Explanations
1- 18 A18 --- QSO Quasar name (JHHMMSS.s+DDMMSS.s) 20- 25 F6.4 --- zabs Absorption redshift 27 I1 --- fmtl [0/2] Flag for metal absorption (1) 29- 33 F5.2 [cm-2] logNH Hydrogen column density 35- 38 F4.2 [cm-2] E_logNH Error on logNH (upper limit) 40- 43 F4.2 [cm-2] e_logNH Error on logNH (lower limit) 45- 63 A19 --- SDSS Full SDSS name (added at CDS)
Note (1): Flag as follows: 0 = no metal absorption observed in the SDSS spectrum 1 = weak metal absorption (∼3σ) detected in the SDSS spectrum 2 = metals detected at >5σ significance
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 10-Jul-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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