MusE GAs FLOw and Wind (MEGAFLOW)

We present the design, rationale, properties, and catalogues of the MusE Gas FLOw and Wind survey (MEGAFLOW) of cool gaseous halos of z ≃ 1.0 galaxies, using low-ionisation Mg II absorption systems. The survey consists of 22 quasar fields selected from the Sloan Digital Sky Survey (SDSS), including multiple (≥3) strong Mg II absorption lines over the redshift range of 0.3 1; this amounts to more than 60 galaxies per arcmin 2 . They were identified using a dual detection algorithm based on both continuum and emission line objects. The achieved O II 50% completeness is 3.7 −0.6 +0.8 × 10 −18 erg s −1 cm −2 (corresponding to an SFR of > 0.01 M ⊙ yr −1 at z = 1) using realistic mock O II emitters and the 50% completeness is m F 775 W ≈ 26 AB magnitudes for continuum sources. We find that (i) the fraction of O II emitting galaxies that have no continuum is ∼15%; (ii) the success rate in identifying at least one galaxy within 500 km s −1 and 100 kpc is ≈90% for Mg II absorptions with W r 2796 ≳ 0.5 Å; (iii) the mean number of galaxies per Mg II absorption is 2.9 ± 1.6 within the MUSE field-of-view; (iv) of the 80 Mg II systems at 0.3 10 9 M ⊙ and star formation rates of > 1 M ⊙ yr −1 .