MEGAFLOW (MusE GAs FLOw and Wind)

A study of the surrounding gas around galaxies using background quasars

Gas flows around galaxies: the baryon cycle


In the era of precision cosmology, astronomers still need to understand how intergalactic gas flows into galaxy halos [inflows], and how supernovae eject gas, metals, and energy back into the intergalactic medium [outflows]. Regarding inflows, a variety of observations indirectly indicated that continuous replenishment of the gas reservoir of galaxies must occur, but direct evidence for accretion remains elusive. In contrast, evidence of outflows or galactic-winds is ubiquitous, but our knowledge of their physical origin and properties is still in its infancy after decades of research in this area.

These gas in- and out-flows processes play a critical role in regulating the growth of galaxies, but our limited knowledge on their properties prevents our ability to produce accurate numerical simulations. This project aims at putting direct constraints on both in- and out-flow processes through innovation around 2 fronts:

  • through observations using the non-conventional technique of background quasars whose line of sight passes near star-forming galaxies;
  • through an observational campaign using novel techniques to spatially map outflows in emission using state-of-the-art IFUs
  • which will yield hundreds of star-forming galaxies across cosmic times, enabling us a new view on galactic winds;

    The MEGAFLOW survey

    The Muse GAs FLow and Wind [MEGAFLOW] survey aims at observing a statistical number (80+) of galaxy-quasar pairs to allow analysis of the relation between the absorption and the host galaxy properties. From the Zhu and Ménard Mg II catalog based on SDSS (Zhu & Ménard 2013), we selected quasars with multiple (N≥3) Mg II λλ 2796,2802 absorption lines with redshifts between 0.4 and 1.4 and with a Mg II λ2796 rest-equivalent width (REW) Wλ2796 > ~0.5A. The former criteria of having multiple absorbers in one quasar field, ensures that a large number of galaxy-quasar pairs of 80+ is reachable with 20−25 quasar fields. The latter criteria ensures that the host galaxies are within 100 kpc from the quasar LOS (at z ≈ 1), i.e. within the MUSE field-of-view, given the well known anti-correlation between the impact parameter and Wλ2796r (Lanzetta & Bowen 1990; Steidel 1995).
    Overall, the MEGAFLOW survey is made of 22 quasar fields, with each quasar spectrum having at least 3 strong (Wλ2796r >0.5A) Mg ii absorbers, over the redshift range between 0.4 and 1.5. Including a few serendipitous systems with 0.3 < Wλ2796r < 0.5 A, the survey containts a total of 79 Mg ii absorbers with Wλ2796r >0.3 A


  • Zabl et al. 2022, MNRAS, 507, 4294. MusE GAs FLOw and Wind (MEGAFLOW) VIII. Discovery of a Mg+ emission nebula probed by a quasar sightline
  • Press release CNRS.2021-09 on galactic winds and the missing baryons

  • Wendt et al. 2021, MNRAS, 502, 3733 MusE GAs FLOw and Wind (MEGAFLOW) V. The dust/metallicity-anisotropy of the circum-galactic medium
  • 2016

  • ANR funding ANR-17-CE31-0017 3DGasFLows
  • 2014:

  • First MUSE Observations!
  • Science

    MEGAFLOW provides the following science cases:
  • Gas ouflowing from galaxies
  • Gas inflowing onto galaxies
  • The metallicity distribution around galaxies
  • The covering fraction of the gas
  • The dust and metallicity anisotropy of the circumn-galactic medium
  • Study the molecular gas of the circumn-galactic medium
  • ...
  • Published papers:

    1. Schroetter et al. 2016ApJ…833…39S Muse Gas Flow and Wind (MEGAFLOW). I. First MUSE Results on Background Quasars
    2. Zabl et al. 2019MNRAS.485.1961Z MusE GAs FLOw and Wind (MEGAFLOW) II. A study of gas accretion around z ≈ 1 star-forming galaxies with background quasars
    3. Schroetter et al. 2019, MNRAS.490.4368S MusE GAs FLOw and Wind (MEGAFLOW) III. galactic wind properties using background quasars
    4. Zabl et al. 2020, MNRAS, 492, 3 MusE GAs FLOw and Wind (MEGAFLOW) IV. A two sight-line tomography of a galactic wind
    5. Wendt et al. 2021, MNRAS, 502, 3733. MusE GAs FLOw and Wind (MEGAFLOW) V. The dust/metallicity-anisotropy of the circum-galactic medium
    6. Schroetter et al. 2021, MNRAS, 506, 1355. MusE GAs FLOw and Wind (MEGAFLOW) VI. The CIV/MgII covering fraction
    7. Freundlich et al. 2021, MNRAS, 501, 1900. MusE GAs FLOw and Wind (MEGAFLOW) VII. A NOEMA pilot program to probe molecular gas in galaxies with measured circum-galactic gas flows
    8. Zabl et al. 2021, MNRAS, 507, 4294. MusE GAs FLOw and Wind (MEGAFLOW) VIII. Discovery of a Mg+ emission nebula probed by a quasar sightline »

    In preparation papers

    1. Langan et al. (in prep.), MusE GAs FLOw and Wind (MEGAFLOW) IX. The impact of gas flows on the mass-metallicity relation
    2. Schroetter et al. (in prep.), The MusE GAs FLOw and Wind (MEGAFLOW) X. Wind scaling relations
    3. Bouché et al. (in prep.), The MusE GAs FLOw and Wind (MEGAFLOW) XI. The survey

    Data release

    wil be available here

    MEGAFLOW Fields