MOLECULAR GAS IN SUPER SPIRAL GALAXIES
Encadrement de la thèse Philippe SALOME (philippe.salome@observatoiredeparis.psl.eu)
Co-Encadrant Françoise COMBES-BOTTARO
Mots clés – Keywords Galaxies, Observations, Retro-action, Formation d’étoilesGalaxies, Observations, Feedback, Star Formation
Profil et compétences recherchées – Profile and skills required
– Skills : ISM / Galaxies / Telescopes and instrumentation (ie interferometry)
– Data reduction and analysis; modeling
– Observations (visitor / remote)
Description
Very massive galaxies with stellar masses > 10E11 Msun are in general red and dead galaxies, ie Peng et al. (2010). They are preferably found in clusters or groups. The environment is thought to be a possible reason for the suppression of star formation in these objects (dynamical pressure, collisions, tidal effects). The presence of an AGN is also a possible reason for the suppression of star formation in very massive galaxies. Indeed, these 2 mechanisms can affect the gas content and prevent galaxies from forming stars. Yet, Ogle et al. (2016; 2019) found that 6% of the most luminous galaxies (in optical terms) at redshift <0.3 are extremely massive giant spiral super galaxies, with a very high SFR for their mass. As such, they resemble gigantic massive unquenched galaxies (55-140 kpc in optical diameter). These objects are therefore perfect sources to challenge mass-quenching scenarios. A key question is whether these galaxies have massive gas reservoirs and are as efficient at forming stars as their smaller version, the main sequence spirals. The millimeter observing window (ALMA/NOEMA) offers a unique opportunity to measure the gas content of these objects: the fuel for star formation is in the form of molecular gas, visible in the mm/submm range. Understanding star formation in these objects requires a better knowledge of their gas content, which has never been studied in these sources.
A pilot project has been designed to observe 5 super spiral galaxies with the NOEMA interferometer at IRAM. The observations are in progress and one source has already been detected in CO(1-0). The gas is clearly present and is in a molecular disk. These 5 sources are also currently observed in the cm-domain with the Nancay Radio Telescope (NRT), in order to search for atomic gas via the HI emission. This is much more difficult because of the interference at these frequencies, which are outside the protected domain (1.4 GHz redshifted).
The objective of this thesis will be to question the mechanisms that prevent the extinction of star formation in these massive galaxies and to discuss more generally the efficiency of feedback processes in galaxies. It will start with the reduction and analysis of data from NOEMA and NRT observations in order to (i) derive resolved galactic properties of the cold gas (mass, depletion time, kinematics and morphology) and (ii) compare them with stellar masses and SFR properties (from complementary data in the optical). This first step can be the subject of an M2 internship (see Master 2 internship proposals). The results of this first step will pave the way for a more important observational work on these objects. The PhD student will be responsible for submitting proposals for follow-ups with NOEMA and the 30m telescope, as well as for projects with MeerKAT, ALMA, VLT and JWST.
Thématique / Domaine / Contexte Galaxies, Feedback, Gas, Star Formation, Galaxy Formation and Evolution, Observations, Modeling
