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 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:
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FileName Lrecl Records Explanations
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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
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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
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Bytes Format Units Label Explanations
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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)
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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.
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Byte-by-byte Description of file: table2.dat table3.dat
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Bytes Format Units Label Explanations
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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)
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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
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 10-Jul-2010