J/MNRAS/455/1043 SDSS DLA and absorber quasar samples (Murphy+, 2016)
The dust content of damped Lyman α systems in the
Sloan Digital Sky Survey.
Murphy M.T., Bernet M.L.
<Mon. Not. R. Astron. Soc., 455, 1043-1059 (2016)>
=2016MNRAS.455.1043M 2016MNRAS.455.1043M (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Redshifts ; Equivalent widths
Keywords: dust, extinction - galaxies: high redshift - intergalactic medium -
galaxies: ISM - quasars: absorption lines
Abstract:
The dust content of damped Lyman α systems (DLAs) is an
important observable for understanding their origin and the neutral
gas reservoirs of galaxies. While the average colour excess of DLAs,
E(B-V), is known to be ≲15-millimagnitude (mmag), both detections and
non-detections with ∼2mmag precision have been reported. Here we find
3.2σ statistical evidence for DLA dust-reddening of 774 Sloan
Digital Sky Survey (SDSS) quasars by comparing their fitted spectral
slopes to those of ∼7000 control quasars. The corresponding E(B-V) is
3.0±1.0mmag, assuming a Small Magellanic Cloud (SMC) dust extinction
law, and it correlates strongly (3.5σ) with the metal content,
characterized by the SiII λ1526 absorption-line equivalent
width, providing additional confidence that the detection is due to
dust in the DLAs. Evolution of E(B-V) over the redshift range
2.1<z<4.0 is limited to <2.5mmag per unit redshift (1σ),
consistent with the known, mild DLA metallicity evolution. There is
also no apparent relationship with neutral hydrogen column density,
NHI, though the data are consistent with a mean
E(B-V)/NHI=(3.5±1.0)*10-24mag*cm2, approximately the ratio
expected from the SMC scaled to the lower metallicities typical of
DLAs. We implement the SDSS selection algorithm in a portable code to
assess the potential for systematic, redshift-dependent biases
stemming from its magnitude and colour-selection criteria. The effect
on the mean E(B-V) is negligible (<5 per cent) over the entire
redshift range of interest. Given the broad potential usefulness of
this implementation, we make it publicly available.
Description:
Using spectral slope fits of the SDSS DR7 quasar spectra, and the
DLA/sub-DLA identifications of Noterdaeme et al. (2009, Cat.
J/A+A/505/1087), we found that the 774 selected quasars with a single
foreground DLA are significantly (3.2σ) redder, on average, than
carefully selected control groups drawn from a sample of ∼7000 quasars
without foreground DLAs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 113 774 The DLA quasar sample (774 quasars)
table2.dat 113 1069 The absorber quasar sample (1069 quasars)
table3.dat 57 7105 The non-DLA quasar sample (7105 quasars)
table4.dat 57 6733 The non-absorber quasar sample (6733 quasars)
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See also:
J/A+A/505/1087 : DLAs in SDSS-DR7 (Noterdaeme+, 2009)
Byte-by-byte Description of file: table1.dat table2.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- SDSS SDSS name (HHMMSS.ss+DDMMSS.s)
20- 25 F6.4 --- zem Emission redshift
27- 32 F6.4 --- zmin Minimun value for the redshift search path
for DLAs
33- 38 F6.4 --- zmax Maximum value for the redshift search path
for DLAs
39- 44 F6.3 --- beta Measured spectral index
46- 50 F5.3 --- e_beta 1-sigma uncertainty
52- 57 F6.3 --- betanw Spectral index measured with an unweighted
power-law fit
59- 63 F5.3 --- zabs Absorption redshift
65- 69 F5.2 [cm-2] logNHI logarithmic HI column density
71- 77 F7.2 0.1nm EWSII ?=-999.00 Rest-frame equivalent widths
of SiII 1526 (1)
79- 85 F7.2 0.1nm EWCII ?=-999.00 Rest-frame equivalent width of
CII 1334 (1)
87- 92 F6.3 --- dbeta Measured difference between the DLA quasar's
beta and the mean beta of its control
distribution
94-100 F7.4 mag E(B-V)SMC Corresponding colour excess for SMC-like dust
102-108 F7.4 mag E(B-V)LMC Corresponding colour excess for LMC-like dust
111-113 I3 --- Nctrl Number of control quasars
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Note (1): non-detections indicated by -999.00.
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Byte-by-byte Description of file: table3.dat table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 A18 --- SDSS SDSS name (HHMMSS.ss+DDMMSS.s)
20- 25 F6.4 --- zem Emission redshift
27- 32 F6.4 --- zmin Minimun value for the redshift search path
for DLAs
33- 38 F6.4 --- zmax Maximum value for the redshift search path
for DLAs
39- 44 F6.3 --- beta Measured spectral index
46- 50 F5.3 --- e_beta 1-sigma uncertainty
52- 57 F6.3 --- betanw Spectral index measured with an unweighted
power-law fit
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 28-Jul-2016