J/MNRAS/392/998 Damped Lymanα systems (Ellison+, 2009)
The kinematic signature of damped Lyman alpha systems: using the D-index to
screen for high column density HI absorbers.
Ellison S.L., Murphy M.T., Dessauges-Zavadsky M.
<Mon. Not. R. Astron. Soc., 392, 998-1007 (2009)>
=2009MNRAS.392..998E 2009MNRAS.392..998E
ADC_Keywords: QSOs ; Redshifts ; Equivalent widths
Keywords: galaxies: high redshift - quasars: absorption lines
Abstract:
Using a sample of 21 damped Lyman alpha systems (DLAs) and 35
sub-DLAs, we evaluate the D-index=[EW(Å)/Δv(km/s)]x1000 from
high-resolution spectra of the MgII λ2796 profile. This sample
represents an increase in the sub-DLA statistics by a factor of 4 over
the original D-index sample. We investigate various techniques to
define the velocity spread (Δv) of the MgII line to determine an
optimal D-index for the identification of DLAs. The success rate of
DLA identification is 50-55 per cent, depending on the velocity
limits used, improving by a few per cent when the column density of
FeII is included in the D-index calculation. We recommend the set of
parameters that are judged to be most robust, have a combination of
high DLA identification rate (57 per cent) and low DLA miss rate (6
per cent) and most cleanly separate the DLAs and sub-DLAs
(Kolmogorov-Smirnov probability 0.5 per cent).
These statistics demonstrate that the D-index is the most efficient
technique for selecting low-redshift DLA candidates.
Description:
We selected sub-DLAs from the compilation of Rao et al. (2006, Cat.
J/ApJ/636/610) for follow-up spectroscopy at high resolution,
obtaining new echelle spectra of 13 quasi-stellar objects (QSOs)
with 17 absorbers along their lines of sight. Nine of these QSOs
were observed with UVES at the VLT and four with the High-Resolution
Echelle Spectrograph (HIRES) at the Keck telescope. The observations
and data reduction are described in detail in Dessauges-Zavadsky et
al. (in preparation).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 72 56 *MgII 2796 equivalent widths (and errors) and
dV for the 3 approaches used in this paper
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Note on table4.dat: In all cases, only the central absorption component is
considered.
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See also:
J/ApJ/636/610 : Damped Lyα systems at z<1.65 (Rao+, 2006)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- QSO QSO name
12- 16 F5.2 [cm-2] logNHI HI column density
18- 21 F4.2 [cm-2] e_logNHI rms uncertainty on logNHI
23- 26 F4.2 0.1nm EW(ew) Equivalent width at 90% EW
28- 31 F4.2 0.1nm e_EW(ew) rms uncertainty on EW(ew)
33- 38 F6.2 km/s DV(ew) Velocity spread (DeltaV) at 90% EW
40- 43 F4.2 km/s EW(vel) Equivalent width at 90% vel
45- 48 F4.2 km/s e_EW(vel) rms uncertainty on EW(vel)
50- 55 F6.2 km/s DV(vel) Velocity spread (DeltaV) at 90% of the
velocity range
57- 60 F4.2 km/s EW(3s) Equivalent width at 3σ
62- 65 F4.2 km/s e_EW(3s) rms uncertainty on EW(3s)
67- 72 F6.2 km/s DV(3s) Velocity spread (DeltaV) at bounds set
by 3σ absorption
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 07-May-2009