On the connection between the intergalactic medium and galaxies: the H i-galaxy cross-correlation at z ≲ 1

International audienceWe present a new optical spectroscopic survey of 1777 `star-forming' ('SF') and 366 `non-star-forming' ('non-SF') galaxies at redshifts z similar to 0-1 (2143 in total), 22 AGN and 423 stars, observed by instruments such as the Deep Imaging Multi-Object Spectrograph, the Visible Multi-Object Spectrograph and the Gemini Multi-Object Spectrograph, in three fields containing five quasi-stellar objects (QSOs) with Hubble Space Telescope (HST) ultraviolet spectroscopy. We also present a new spectroscopic survey of 173 `strong' (10(14) N-HI less than or similar to 10(17) cm(-2)) and 496 `weak' (10(13) less than or similar to N-HI 10(14) cm(-2)) intervening H i (Ly alpha) absorption-line systems at z less than or similar to 1 (669 in total), observed in the spectra of eight QSOs at z similar to 1 by the Cosmic Origins Spectrograph and the Faint Object Spectrograph on the HST. Combining these new data with previously published galaxy catalogues such as the Very Large Telescope Visible Multi-Object Spectrograph Deep Survey and the Gemini Deep Deep Survey, we have gathered a sample of 654 H i absorption systems and 17 509 galaxies at transverse scales less than or similar to 50 Mpc, suitable for a two-point correlation function analysis. We present observational results on the H i-galaxy (xi(ag)) and galaxy-galaxy (xi(gg)) correlations at transverse scales r(perpendicular to) less than or similar to 10 Mpc, and the H i-H i autocorrelation (xi(aa)) at transverse scales r(perpendicular to) less than or similar to 2 Mpc. The two-point correlation functions are measured both along and transverse to the line of sight, xi(r(perpendicular to), r(\textlessparallel to\textgreater)). We also infer the shape of their corresponding `real-space' correlation functions, xi(r), from the projected along the line-of-sight correlations, assuming power laws of the form xi(r) = (r/r(0))(-gamma). Comparing the results from xi(ag), xi(gg) and xi(aa), we constrain the H i-galaxy statistical connection, as a function of both H i column density and galaxy star formation activity. Our results are consistent with the following conclusions: (i) the bulk of H i systems on similar to Mpc scales have little velocity dispersion (less than or similar to 120 km s(-1)) with respect to the bulk of galaxies (i.e. no strong galaxy outflow/inflow signal is detected); (ii) the vast majority (similar to 100 per cent) of `strong' H i systems and `SF' galaxies are distributed in the same locations, together with 75 +/- 15 per cent of `non-SF' galaxies, all of which typically reside in dark matter haloes of similar masses; (iii) 25 +/- 15 per cent of `non-SF' galaxies reside in galaxy clusters and are not correlated with `strong' H i systems at scales less than or similar to 2 Mpc; and (iv) \textgreater 50 per cent of `weak' H i systems reside within galaxy voids (hence not correlated with galaxies), and are confined in dark matter haloes of masses smaller than those hosting `strong' systems and/or galaxies. We speculate that H i systems within galaxy voids might still be evolving in the linear regime even at scales less than or similar to 2 Mpc