Abstract
We present the study of a sample of nine QSO fields, with damped-Ly-alpha (DLA) or sub-DLA systems at z~0.6, observed with the X-Shooter spectrograph at the Very Large Telescope. By suitably positioning the X-Shooter slit based on high spatial resolution images of HST/ACS we are able to detect absorbing galaxies in 7 out of 9 fields (~ 78\% success rate) at impact parameters from 10 to 30 kpc. In 5 out of 7 fields the absorbing galaxies are confirmed via detection of multiple emission lines at the redshift of DLAs where only 1 out of 5 also emits a faint continuum. In 2 out of these 5 fields we detect a second galaxy at the DLA redshift. Extinction corrected star formation rates (SFR) of these DLA-galaxies, estimated using their H-alpha fluxes, are in the range 0.3-6.7 M_sun yr^-1. The emission metallicities of these five DLA-galaxies are estimated to be from 0.2 to 0.9 Z_sun. Based on the Voigt profile fits to absorption lines we find the metallicity of the absorbing neutral gas to be in a range of 0.05--0.6 Z_sun. The two remaining DLA-galaxies are quiescent galaxies with SFR < 0.4 M_sun yr^-1 (3-sigma) presenting continuum emission but weak or no emission lines. Using X-Shooter spectrum we estimate i-band absolute magnitude of -19.5+/-0.2 for both these DLA-galaxies that indicates they are sub-L* galaxies. Comparing our results with that of other surveys in the literature we find a possible redshift evolution of the SFR of DLA-galaxies.
Highlights
Intergalactic medium (IGM) gas accretion and galactic outflows are processes invoked in large-scale structure simulations to regulate the galaxy growth (Springel et al 2005; Sijacki et al 2007; Booth & Schaye 2009; Oppenheimer et al 2010; Haas et al 2013; Vogelsberger et al 2014; Schaye et al 2015)
These quasi-stellar objects (QSOs) are selected based on Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) observations that indicate they have a damped Lyman α (DLA) or sub-DLA in their spectra at z ∼ 0.6
A point spread function (PSF) subtraction of high spatial resolution prism images obtained from these HST/ACS observations provide us with 24 candidate DLA galaxies in nine fields at low impact parameters
Summary
Intergalactic medium (IGM) gas accretion and galactic outflows are processes invoked in large-scale structure simulations to regulate the galaxy growth (Springel et al 2005; Sijacki et al 2007; Booth & Schaye 2009; Oppenheimer et al 2010; Haas et al 2013; Vogelsberger et al 2014; Schaye et al 2015). CGM study using DLA galaxies at z ∼ 0.6 981 et al 2012) Such results are limited by the low success rates in detection of DLA galaxies which is usually attributed to the faint nature of DLA galaxies near the position of bright background QSOs. The identification of a substantially large sample of DLAs at low redshifts is difficult because the Lyman α still lies in the ultraviolet (UV) wavelengths and the incidence of DLAs is low. Turnshek et al (2015) used the Advanced Camera for Surveys (ACS) HRC-P200L prism aboard the Hubble Space Telescope (HST) to obtain UV spectra of QSOs with strong Mg II absorbers They found ≈35 high-probability DLAs. They found ≈35 high-probability DLAs The dispersion of this prism is non-linear and extremely low at red wavelengths.
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