Thesis title
Tracing molecular gas and star formation in super spiral galaxies — A case study of failed quenching
Composition of the jury
Benoit Semelin (LUX), président
Samuel Boissier (LAM), referee
Miguel Querejeta (Madrid Observatory), referee
Laure Ciesla (LAM), examiner
David Elbaz (CEA), examiner
Annie Hughes (IRAP), examiner
Philippe Salomé (LUX), co-supervisor
Damien Le Borgne (IAP), co-supervisor
Abstract
Super-spiral galaxies are among the most massive and extended star-forming disk galaxies in the local Universe. Their existence raises an important question : at such high masses, galaxy-evolution models typically predict that star formation should gradually decline—or already have ceased. This is the so-called quenching. Yet, these galaxies are still forming stars. This PhD thesis aims at investigating how they sustain their star-forming activity and what such sources can reveal about the evolution of massive galaxies.
Based on the first spatially resolved study of molecular gas in 19 super-spiral galaxies, observed with the IRAM NOEMA interferometer and combined with multi-wavelength data, this work shows that these objects are analogous to giant spiral galaxies rather than a distinct galaxy population. They contain abundant reservoirs of molecular gas that fuel ongoing star formation, which are distributed in very large rotation-dominated disks whose extent scales with that of the stellar disk. The local star-formation efficiency remains comparable to that of more typical lower-mass spiral galaxies. Their continued star formation therefore seem to not result from unusually efficient star formation, but rather from the persistence of a vast and stable cold gas reservoir. These findings suggest that the absence of quenching in these galaxies is linked to insufficient feedback, thus unable to disperse or heat their molecular gas across the full extent of the disk.
