MusE GAs FLOw and Wind (MEGAFLOW) XII. Rationale and design of a MgII survey of the cool circum-galactic medium with MUSE and UVES: The MEGAFLOW Survey

Abstract

We present the design, rationale, properties and catalogs of the MusE Gas FLOw and Wind survey (MEGAFLOW), a survey of the cool gaseous halos of $z\sim 1$ galaxies using low-ionization MgII absorption systems. The survey consists of 22 quasar fields selected from the Sloan Digital Sky Survey (SDSS) having multiple ($\ge 3$) strong MgII absorption lines over the redshift range $0.3<z<1.5$. Each quasar was observed with the Multi-Unit Spectroscopic Explorer (MUSE) and the Ultraviolet and Visual Echelle Spectrograph (UVES), for a total of 85~hr and 63~hr, respectively. The UVES data resulted in 127 MgII absorption lines over $0.25<z<1.6$, with a median rest-frame equivalent width (REW) $3\ddot{I}ƒ$ limit of $\approx 0.05$~à . The MUSE data resulted in $\sim$2400 galaxies of which 1403 with redshift confidence ZCONF$>1$, i.e. more than 60 galaxies per arcmin${}^2$. They were identified using a dual detection algorithm based on both continuum and emission line objects. The achieved [OII] 50\%\ completeness is 3.7$\times 10^{-18}$ erg/s/cm${}^2$ (corresponding to SFR$>0.01$ M${}_{\odot }$ yr${}^{-1}$ at $z=1$) using realistic mock [OII] emitters and the 50\%\ completeness is $m_{F775W}\approx 26$ AB magnitudes for continuum sources. We find that (i) the fraction of [OII] emitting galaxies which have no continuum is $\sim 15$\%; (ii) the success rate in identifying at least one galaxy within 500 km/s and 100 kpc is $\approx 90$\%\ for MgII absorptions with $W_r^{2796}\gtrsim 0.5$~à ; (iii) the mean number of galaxies per MgII absorption is $2.9\pm 1.6$ within the MUSE field-of-view; (iv) of the 80 MgII systems at $0.3<z<1.5$, 40 (20) have 1 (2) galaxies within 100 kpc, respectively; (v) all but two host galaxies have stellar masses $M_{\star }>10^9$ M${}_{\odot }$, and star-formation rates $>1$ M${}_{\odot }$ yr${}^{-1}$.

23 pages; 16 figures; in press for publication in A&A; accepted version