HI mock observations of galaxies in cosmological simulations

Supervisor: Sylvia Plöckinger

Contact information: sylvia.ploeckinger@univie.ac.at

Additional collaborator: Kyle Oman (Durham University)

Expected duration: 9 months

Project description & Goals:  

Observed dwarf galaxies show a large variety of rotation curve shapes, even within the same mass range: from steeply rising rotation curves indicative of a cuspy total mass profile (e.g. NFW dark matter profile) to very slowly rising rotation curves that are better fit by a central density core. Depending on the implemented subgrid models, simulations either produce cusps or cores for a given galaxy mass, but fail - so far - to reproduce the observed rotation diversity ("rotation curve diversity problem", Oman et al. 2015).

This master project is investigating if this discrepancy between simulated and observed dwarf galaxies is due to inaccuracies in the simulations or due to simplifications in the tilted-ring models used in observations, as suggested by Oman et al. (2019). The student will analyse a modern set of cosmological simulations, run with the SWIFT code. In one simulation box, the interstellar medium (ISM) is modelled as a single phase, as is still the norm in large-scale cosmological simulations (see e.g. Vogelsberger et al. 2020 for a review). This simplification has been speculated to be responsible for unrealistically thick galaxy discs and therefore a larger contribution of non-circular motions. In a second simulation box, the ISM is multi-phase and the neutral atomic (HI) and molecular phases (H2, CO) are clearly kinematically separated.

Using the software package Martini (https://github.com/kyleaoman/martini), mock observation of the HI disk (full datacubes of HI line observations) will be produced for the galaxies in each simulation box. The resulting rotation curves are fit with cusp and core profiles to address the following questions: Does the fraction of cusp/core profiles depend on the ISM model? Is the rotation curve diversity increased with a multi-phase ISM model? How does the rotation curve from the HI mock observation compare to the rotation curve derived from the total mass profile? 

Working plan & Milestones (including final thesis):

  1. Become familiar with how the objectives of this master thesis relate to the relevant literature and the broader fields of (computational) galaxy formation.
  2. Use the software Martini to create HI mock observations (velocity maps) of individual galaxies from two simulation boxes.
  3. Fit cusp and core profiles to the velocity fields created by Martini.
  4. Comparative analysis of the galaxy populations in the two simulation boxes
  5. Write master thesis

Requirements / special skills:

1) Should have followed lectures on galaxy formation. 2) Python programming skills are a bonus. 

References:

[1] Oman et al. (2015) "The unexpected diversity of dwarf galaxy rotation curves" https://ui.adsabs.harvard.edu/abs/2015MNRAS.452.3650O/abstract 

[2] Oman et al. (2019) "Non-circular motions and the diversity of dwarf galaxy rotation curves" https://ui.adsabs.harvard.edu/abs/2019MNRAS.482..821O/abstract 

[3] Vogelsberger et al. (2020) "Cosmological simulations of galaxy formation" (Review) https://ui.adsabs.harvard.edu/abs/2020NatRP...2...42V/abstract 

Links: SWIFT: www.swiftsim.com martini: https://github.com/kyleaoman/martini