Thesis Topic: Unlocking the astrophysics of the circum-galactic medium

Thesis Supervisors: Celine Peroux and Harald Kuntschner


Baryons from the cosmic web accrete onto galaxies, cool into a dense neutral then a molecular phase which fuels star formation, expelling material from these galaxies in powerful outflows which transform the surrounding circum-galactic medium (CGM). Today, the lack of observational constraints limits our understanding and our capacity to simulate this so-called baryon cycle. Quasar absorption features associated with foreground galaxies provide a unique tool to probe the gas properties of galaxies. The main advantage of absorption over emission from galaxies is the ability to reach low gas densities. To establish the connection of the circum-galactic medium gas probed to the underlying galaxy, it is essential to complement the absorption spectroscopy with imaging of the galaxies. A powerful technique is 3D spectroscopy.

The project uses a dataset already in hand from a 24-hr program with the MUSE 3D spectrograph on the Very Large Telescope (VLT) in Chile (PI: Peroux). We have carefully selected targets from HST spectroscopy to cover prominent emission lines with MUSE. The observations provide impact parameter, star formation rate, metallicity, and kinematics of a statistical sample an order of magnitude larger than any other currently available at any redshift. The dataset has been recently augmented with a now completed Hubble Space Telescope (HST) 40-orbit Medium Program (PI: Peroux). These remarkable observations will provide a measure of their stellar mass, dust content, age of their stellar population, constrain their resolved morphology and large-scale environment. The MUSE and HST data are fully reduced. Together, this unique sample comprises 19 VLT/MUSE quasar fields, comprising 40 z<0.85 absorbers and 120 associated galaxies, as well as an additional sample of 200 z<1.2 galaxies with MgII coverage from quasar spectroscopy. Furthermore, we have secured mm ALMA observations (PI: Peroux) of similar fields to measure the molecular masses, velocity fields and star formation efficiencies of the sources detected in CO. These observations are ideal to relate the neutral atomic gas, molecular gas and stars in the same objects resulting in a full baryon census of complex galaxy structures. This ambitious survey will help solve a major unknown in current galaxy evolution models: unlocking the physical conditions of the circum-galactic medium.