Presentasjon av masteroppgave: Espen Hodne

Modelling Lyman-α Emission from Star Forming Galaxies at High Redshift Using Cosmological Simulations

Abstract

I study Lyman-α emission from high-redshift galaxies using the high-resolution smoothed particle hydrodynamics (SPH) galaxy simulation "Ponos" at redshift z = 6.5. The focus of my study is the luminosity from hydrogen recombination and the corresponding surface brightness.

I calculate an intrinsic luminosity for the galaxy using parameters from the simulation; as well as a self-shielding scheme that neutralizes all gas where temperature T < 104 K and hydrogen number density ηH > 0.1 cm-3. The data is then interpolated onto a grid, where I apply ionization from active galactic nuclei and radiating stars.

I make some general observations and calculations about the galaxy simulation as a whole, before reducing my study to a 50 × 50 × 50 kpc box around the main dark matter halo in order to do more detailed observations of the area encompassed by and immediately surrounding its 21,97 kpc virial radius. The final Lyman-α luminosity found in this area is 7,68 x 1043 erg s-1. The emission is sent through a scattering scheme in order to give a more realistic image of the galaxy. Finally I make Lyman-α surface brightness maps, surface brightness profiles and spectra as seen from six directions. The scattering smears out the Lyman-α radiation, giving larger and more extended maps, better representing observations. The accompanying spectra shows peaks at blue- and redshifted wavelengths. Doppler shifted photons have a smaller chance of scattering, making them more likely to escape. The high values in the center of the spectra represents scattering in the less dense outskirts of the galaxy.

I make comparisons to galaxies at redshifts 5 < z < 6, as well as to giant Lyman-α nebulae. The findings are that the surface brightness profile is around two orders of magnitude larger than for typical galaxies at similar redshifts, and more akin in values to the observed superluminous Lyman-α nebulae.

My findings indicate that the main reason of this high luminosity is the large star formation rate of 42,41M⨀ yr-1. This is the result of an ongoing starburst, starting approximately 150 million years before redshift z = 6,5. I postulate two possible reasons for this starburst: i) it is due to lack of feedback from the AGN, or ii) the simulation is experiencing a galaxy merger. The latter is the most likely due to the main galaxy’s proximity to another galaxy.

 

Veileder: Førsteamanuensis Sijing Shen, Institutt for teoretisk astrofysikk, UiO

Medveileder: Postdoktor Petter Laursen, Institutt for teoretisk astrofysikk, UiO

Intern sensor: Professor Øystein Elgarøy, Institutt for teoretisk astrofysikk, UiO

Ekstern sensor: Professor MSO Johan Peter Uldall Fynbo, Niels Bohr Instituttet, Københavns Universitet

Publisert 11. juni 2019 13:28 - Sist endret 11. juni 2019 13:58