J/MNRAS/392/998 Damped Lyman{alpha} 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. =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({AA})/{Delta}v(km/s)]x1000 from high-resolution spectra of the MgII {lambda}2796 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 ({Delta}v) 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. ) 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: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table4.dat 72 56 *MgII 2796 equivalent widths (and errors) and dV for the 3 approaches used in this paper -------------------------------------------------------------------------------- Note on table4.dat: In all cases, only the central absorption component is considered. -------------------------------------------------------------------------------- See also: J/ApJ/636/610 : Damped Ly{alpha} systems at z<1.65 (Rao+, 2006) Byte-by-byte Description of file: table4.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 3{sigma} 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 3{sigma} absorption -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Patricia Vannier [CDS] 07-May-2009