Journal Article

Galaxy group at <i>z</i>=0.3 associated with the damped Lyman α system towards quasar Q1127–145

Glenn G. Kacprzak, Michael T. Murphy and Christopher W. Churchill

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 1, pages 445-459
Published in print July 2010 | ISSN: 0035-8711
Published online July 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16667.x
Galaxy group at z=0.3 associated with the damped Lyman α system towards quasar Q1127–145

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We performed a spectroscopic galaxy survey, complete to mF814W≤ 20.3 (LB > 0.15LB at z= 0.3), within 100 × 100 arcsec2 of the quasar Q1127–145 (zem= 1.18). The Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph (UVES) quasar spectrum contains three zabs < 0.33 Mg ii absorption systems. We obtained eight new galaxy redshifts, adding to the four previously known, and galaxy star formation rates (SFRs) and metallicities were computed where possible. A strong Mg ii system [Wr(2796) = 1.8Å], which is a known damped Lyman α absorber (DLA), had three previously identified galaxies; we found two additional galaxies associated with this system. These five galaxies form a group with diverse properties, such as a luminosity range of 0.04 ≤LB≤ 0.63 LB, an impact parameter range of 17 ≤D≤ 241 kpc and a velocity dispersion of σ= 115 km s−1. The DLA group galaxy redshifts span beyond the 350 km s−1 velocity spread of the metallic absorption lines of the DLA itself. The two brightest group galaxies have SFRs of ∼few M yr−1 and should not have strong winds. We have sufficient spectroscopic information to directly compare three of the five group galaxies’ (emission-line) metallicities with the DLA (absorption) metallicity: the DLA metallicity is one-tenth solar, substantially lower than the three galaxies’ metallicity which ranges between less than 1/2 solar to solar. Hubble Space Telescope (HST)/Wide Field Planetary Camera 2 (WFPC-2) imaging shows perturbed morphologies for the three brightest group galaxies, with tidal tails extending ∼25 kpc. We favour a scenario where the DLA absorption originates from tidal debris in the group environment.

Another absorber exhibits weak Mg ii absorption [Wr(2796) = 0.03Å] and had a previously identified galaxy at a similar redshift. We have identified a second galaxy associated with this system. Both galaxies have solar metallicities and unperturbed morphologies in the HST/WFPC-2 image. The SFR of one galaxy is much lower than that expected for strong outflows. Finally, we have also identified five galaxies at large impact parameters with no associated Mg ii absorption [Wr(2796) ≲ 5.7 mÅ, 3σ] in the spectrum of Q1127–145.

Keywords: galaxies: haloes; galaxies: interactions; galaxies: ISM; quasars: absorption lines

Journal Article.  10285 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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