The transition between atomic and molecular gas in the spiral arm of a Milky Way-like galaxy

Abstract

I have performed line radiative transfer to see emission at the frequency of 115 GHz for CO 1 → 0 line (under large velocity gradient (LVG) approximation) and the 1.5 GHz emission produced by the spin-flip transition of atomic hydrogen (HI) (under local thermodynamic equilibrium (LTE) assumption). I look at emission from different spiral arms (including inter-arm filaments) on a galactic model which is similar to the Milky Way. The line radiative transfer has been performed by using the RADMC-3D software. The input data for the modelling has been taken from a galactic model created by Dr. Rowan Smith using the AREPO moving mesh code. The emission data was further used to calculate intrinsic inter-stellar medium (ISM) gas properties like integrated emission and velocity dispersion. I then compared these properties as seen for different species of gas (like CO and HI) as well as for different position profiles of the same gas (like emitting from a galactic arm or an inter-arm filament). CO is used as a tracer to estimate molecular hydrogen and I made maps of observable molecular hydrogen and CO-dark molecular gas in the model. I further used output data in combination with the binary input files available to me to draw various interesting conclusions about the galactic model.

Date of Award	1 Aug 2017
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Rowan Smith (Supervisor) & Gary Fuller (Supervisor)