A Family Album: The Growth and Evolution of Milky Way Analogues from Z=5 to the Local Universe

Abstract

We present a breakdown of the evolutionary history of Milky Way-like galaxies up to redshift z=5, using multi-wavelength optical and NIR photometry from the Hubble Space Telescope and the James Webb Space Telescope. We use abundance matching to find progenitors of Milky Way Analogs (MWAs) by evolving the cumulative number density of the current Milky Way backwards through time, and matching the stellar mass to the expected number density with stellar mass functions obtained from large-scale galaxy surveys. We determine resolved physical properties of MWA progenitors such as stellar mass density, star-formation rate (SFR), age, and metallicity, via SED-fitting to spatially resolved pixel bins of their photometry.

In the first part of this thesis, we use photometric data from the Hubble Frontier Fields DeepSpace catalog, a survey of six lensing clusters and their flanking fields in order to chart the mass assembly of MWA progenitors up to z=2.

In the second part of this thesis, we extend the study of the mass assembly of MWA progenitors to z=5 with the data from the Canadian NIRISS Unbiased Cluster Survey (CANUCS), using JWST NIRCam and NIRISS imaging. In the early universe, MWA progenitors show clear inside-out mass assembly with specific star-formation rates more enhanced on the outskirts than the inner regions, and more stellar mass added to the outskirts. They are also increasing in size but morphologically remain disk-dominated. Merger fractions increase with increasing redshift, pointing to hierarchical assembly at early times.

In the third part of this thesis, we examine the resolved age and stellar metallicities of the MWA progenitors in CANUCS to uncover details of their star-formation history. The slopes of the radial gradients of non-merging galaxies are in line with inside-out growth. The slopes of the radial gradients for ongoing and late stage mergers show enhanced star-formation across the entire galaxy. Metallicity evolves slowly with redshift for MWA progenitors, and mergers contribute to overall mass growth both through their added mass and their enhancement of star-formation, but do not meaningfully alter the chemical evolution history of the galaxy until z~1.5.