MusE GAs FLOw and Wind (MEGAFLOW)

XII. Rationale and design of a Mg II survey of the cool circum-galactic medium with MUSE and UVES: The MEGAFLOW Survey

¹ Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon (CRAL) UMR5574, F-69230 Saint-Genis-Laval, France
² Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
³ Institute for Computational Astrophysics and Department of Astronomy & Physics, Saint Mary’s University, 923 Robie Street Halifax, Nova Scotia B3H 3C3, Canada
⁴ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, Centre National de la Recherche Scientifique, Centre National d’Etudes Spatiales, 31028 Toulouse, France
⁵ European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
⁶ Inter-University Centre for Astronomy & Astrophysics (IUCAA), Post Bag 04, Pune 411007, India
⁷ Leiden Observatory, Leiden University, PO Box 9513 NL-2300 RA Leiden, The Netherlands
⁸ Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
⁹ Canada-France-Hawaii Telescope, 65-1238 Mamalahoa Highway, Kamuela, HI 96743, USA
¹⁰ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

^⋆ Corresponding author; nicolas.bouche@univ-lyon1.fr

Received: 12 June 2024
Accepted: 24 October 2024

Abstract

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 < 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 hours and 63 hours, respectively. The UVES data resulted in 127 Mg II absorption lines over 0.25 < z < 1.6, with a median rest-frame equivalent width (REW) 3σ limit of ≈0.05 Å. The MUSE data resulted in ∼2400 galaxies, of which 1403 are characterised by a redshift confidence of ZCONF >  1; this amounts to more than 60 galaxies per arcmin². 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_F775W ≈ 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_r²⁷⁹⁶ ≳ 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 < z < 1.5, 40 (20) have 1 (2) galaxies within 100 kpc, respectively; and, finally, (v) all but two host galaxies have stellar masses of M_⋆ > 10⁹ M_⊙ and star formation rates of > 1 M_⊙ yr⁻¹.