A survey of interstellar Ca II absorption in the haloes of low-redshift galaxies

David V. Bowen, Max Pettini, Michael V. Periston, Chris Blades

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We present medium-resolution observations of nine QSOs whose lines-of-sight pass within 45 h-1 kpc of low-redshift (zgal<0.2) galaxies. We fail to detect Can absorption at the galaxies' redshift down to 2 a equivalent-width limits of between 38 and 164 mÅ in all but one quasar spectrum, 1543 + 489. With these data, supplemented by previously published results, we attempt to establish the Can absorption cross-sections of present-day galaxies by defining an unbiased sample of QSO-galaxy pairs for which all observations have been reported, regardless of the success or otherwise of the search for absorption. With the exception of the very weak lines seen in the spectrum of 1543 + 489, we find that Ca n absorption - when observed - is strong (Wλ ≧ 350 mÅ) and occurs within approximately 11 h-1 kpc or 2.3 Holmberg radii from the centre of the galaxy. There exist, however, several examples of QSO-galaxy pairs with separations less than this which do not show absorption. By considering the six systems in which absorption is already known, we conclude that Can is confined either to galaxy discs, or distributed inhomogeneously around a galaxy, at least at the equivalent-width limits currently detectable. We conclude that there is no evidence for spherical, calcium-absorbing haloes with unity covering factor around present-day galaxies. We briefly contrast these conclusions with the observations of Mg n haloes at intermediate redshifts. In the case of 1543 + 489, we observe K and H absorption at a redshift of 0.075, with equivalent widths of 62±22 and 82±22 mÅ, respectively. These are the weakest Ca ii lines from an external galaxy yet detected in a quasar spectrum. They appear to be due to a bright, anonymous galaxy 45 h-1 kpc from the quasar sight-line, the largest separation of all QSO-galaxy pairs known to show Ca ii absorption. We speculate, however, that the absorber may actually be a dwarf galaxy only 6 h-1 kpc away from the line-of-sight.

Original languageEnglish (US)
Pages (from-to)145-158
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - 1991
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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