MUSE searches for galaxies near very metal-poor gas clouds at z ∼ 3: new constraints for cold accretion models

We report on the search for galaxies in the proximity of two very metal-poor gas clouds at z similar to 3 towards the quasar Q0956+122. With a 5-hour Multi-Unit Spectroscopic Explorer (MUSE) integration in a similar to 500 x 500 kpc(2) region centred at the quasar position, we achieve a >= 80 per cent complete spectroscopic survey of continuum-detected galaxies with m(R) <= 25 mag and Ly alpha emitters with luminosity L-Ly alpha >= 3 x 10(41) erg s(-1). We do not identify galaxies at the redshift of a z similar to 3.2 Lyman limit system (LLS) with log Z/Z(circle dot) = -3.35 +/- 0.05, placing this gas cloud in the intergalactic medium or circumgalactic medium of a galaxy below our sensitivity limits. Conversely, we detect five Ly alpha emitters at the redshift of a pristine z similar to 3.1 LLS with log Z/Z(circle dot) <= -3.8, while similar to 0.4 sources were expected given the z similar to 3 Ly alpha luminosity function. Both this high detection rate and the fact that at least three emitters appear aligned in projection with the LLS suggest that this pristine cloud is tracing a gas filament that is feeding one or multiple galaxies. Our observations uncover two different environments for metal-poor LLSs, implying a complex link between these absorbers and galaxy haloes, which ongoing MUSE surveys will soon explore in detail. Moreover, in agreement with recent MUSE observations, we detected a similar to 90 kpc Ly alpha nebula at the quasar redshift and three Ly alpha emitters reminiscent of a 'dark galaxy' population.