Master thesis defense by Clara Giménez Arteaga

Abstract:

To understand how galaxy formation and evolution proceed, spectral energy distributions (SEDs) of hundreds of thousands of galaxies are modelled, in order to estimate their redshifts and study the properties of their gas, dust and stellar population. To derive these intrinsic properties, one must have an in-depth understanding of the dust content of the sources, since it modifies the galaxies’ inherent SEDs in a wavelength-dependent way, in terms of both extinction and reddening. In this work, we use recently obtained and processed images from the Hubble Space Telescope to study the properties of a sample of 53 nearby star-forming galaxies at z < 0.05. Of these objects, 24 are local infrared-luminous galaxies (LIRGs) in the GOALS survey and are likely reasonable analogues of dusty star-forming galaxies in the early Universe. We conduct this study with Hubble images of the local galaxies because this allows us to resolve structures on the scale of tens of parsecs that are unresolved in more distant galaxies. We obtain high spatial resolution dust extinction maps of the nearby galaxies by imaging them in narrow-band filters centered on the redshifted H and Paschen  (Pa) Hydrogen recombination lines. By measuring the Balmer decrement with H and Pa emission line maps, we can probe sites of ongoing star formation activity and dust reddening. We fit stellar population synthesis models to the spatially resolved HST photometry to derive physical properties across the sample galaxies, such as the star formation rate, the stellar mass surface densities and continuum dust attenuation. By comparing the continuum attenuation to the one obtained with the decrement, we demonstrate that the diffuse dust in the interstellar medium is not the only source of extinction, and accounting for the birth cloud attenuation is also required. We compare results from two population synthesis fitting codes, EAZY and Prospector, which yield somewhat distinct results. These differences are driven by differing parametrisations of star formation histories. Finally, we investigate how the resolution of our photometric measurements affects the derived stellar masses and star formation rates of our galaxies by comparing the ensemble of spatially resolved measurements to quantities derived from integrated measurements of the galaxies as a single source. We conclude that we obtain distinct estimates for these quantities depending on the resolution of our observations. The integrated measurements underestimate the stellar masses and overestimate the SFRs, with respect to the spatially resolved photometry.

Supervisor: Gabriel Brammer, Niels Bohr Insitute, DAWN

Censor: Maximillian Stritzinger (Aarhus University)