SIMBAD references

We present results from a spectroscopic and imaging survey of galaxies in the fields of quasars from the Hubble Space Telescope (HST) Quasar Absorption Line Key Project. The aim of this survey is to identify galaxies within 3.5' from the quasar sightline, to a limiting, integrated r-band magnitude m_r=22.5. The data are then compared to the HST homogeneous sample of Lyα-only absorbers in order to put constraints on the nature of these absorbers, and in particular on their relation to galaxies. We have obtained spectra for 81 objects in three quasar fields and identified 66 galaxies (success rate of 81%) at redshifts in the range z=0.0500-0.7974, and at linear impact parameters to the quasar sightlines spanning D=57-2380h₅₀^–1kpc. Among these galaxies, 19 are at less than 750km/s from a Lyα absorber, and only one clearly does not give rise to any absorption. Three other galaxies are at the redshifts of metal-rich absorption systems, of which one belongs to a cluster with altogether 19 identified galaxies at the quasar redshift. The analysis of our sample combined with those of previous studies shows that: 1) the redshift agreements of the Lyα absorber-galaxy associations cannot be due to chance coincidence; 2) there is no clear anti-correlation between the Lyα rest-frame equivalent width and the impact parameter for the whole sample (w_r, min_=0.10A). When only the strongest lines are considered (w_r≥0.24A), w_r(Lyα) and D are marginally anti-correlated. Lanzetta et al. (1995) found a stronger anti-correlation which could be due, at least in part, to the existence of metal-rich absorbers in their sample. Our results suggest that most Lyα absorbers are not gaseous clouds that belong in a strict sense to galaxies, as is the case for MgII absorbers. The size of Lyα galactic halos can be inferred from the variation with D of the fraction of associations to the total number of galaxies at impact parameters < D. This fraction drops from 1 to ∼0.65 at D∼200h₅₀^–1kpc and flattens at larger values of D (>300h₅₀^–1kpc). This leads to Lyα galactic halos sizes about three times larger than the inner MgII halo region; 3) there is no correlation between the galaxy luminosity and the impact parameter. This again suggests that significant Lyα clouds do not belong to individual galaxies, but instead are distributed in the local large-scale structure. For the smaller impact parameters, this could reflect a link between D and the total galaxy mass rather than its luminous mass; 4) the HWHM=120km/s of the relative velocity distribution of the Lyα absorber-galaxy associations is consistent with either galaxy rotation velocities or the local velocity dispersion in large-scale structures.