Master Thesis defense by Han Lei
Title: Molecular Gas in a Massive Main-sequence Galaxy at z = 3
Abstract: Since molecular hydrogen is the fuel of star formation, the reservoir of molecular hydrogen mass is the key to understand the star formation processes in galaxies and the galaxy evolution across cosmic time. The traditional gas mass tracer is carbon monoxide. Its line luminosity can be converted into molecular gas mass with a conversion factor. With the observational difficulty at higher redshift and the dependence of conversion factor on various conditions, other tracers should also receive attention. The neutral atomic carbon is an alternative due to its multiple advantages to carbon monoxide.
As a typical main-sequence star-forming galaxy at z ≈ 3, the study of D49 can hopefully provide knowledge of the Cosmic Noon and the main-sequence at a higher redshift. With the new observations and measurements on D49, its spectral energy distribution is fitted with a novel algorithm Stardust. The result is consistent with previous study and does not support a strong active galactic nucleus existing in D49.
A high CO(7-6)-to-IR ratio is found in D49, indicating there are more CO emissions than those from star formation activities. Such high ratios are also found in local galaxy NGC 6240 and distant galaxy BX610 at z ≈ 2, in both of which the CO emissions are believed to be enhanced by shocks. The similar scenario can possibly exist in D49.
With new detections of [CI] lines, molecular gas mass in D49 can be estimated from their line ratio and line luminosities. In addition to the gas mass estimation from Stardust fitting, seven estimates of molecular gas mass in D49 have been derived. They are consistent within a factor of three or less.
Supervisors:
- Georgios Magdis, University of Copenhagen, Niels Bohr Insitute
- Francesco Valentino, University of Copenhagen, Niels Bohr Insitute
Censor:
- Allan Hornstrup, DTU Space