Quantification of Disk Galaxy Formation through Ultraviolet Light at 0.8 < z < 1.2

Nicholas Rosner

2020

In this study, our goal was to produce evidence that would suggest how galaxydisks form, with the leading two theories being inside-out growth and outside-in growth. To accomplish this task, we selected a sample of 2,094 galaxies inthe GOODS-South field that were in the peak star formation redshift range of 0.8 to 1.2. These galaxies also had to have images in rest-frame visible light (using the F105W filter or F125W filter aboard the Hubble Space Telescope) and in ultraviolet light (using the F275W filter or F336W filter) because rest-frame visible light tells us where established star populations are and rest-frame ultraviolet light tells us where new stars are forming. We then cut out postage stamps of each galaxy in both types of light. Bad-pixel masks were created for each postage stamp to eliminate light sources other than the target galaxies. After this, we used GALFIT to model the light distribution and extract themorphological information about each galaxy. After limiting the sample to galaxies with successful and accurate models, our final sample contained 288 galaxies. We compared the effective radii of our final sample of galaxies in rest-frame ultraviolet versus rest-frame visible light to determine where new stars were forming in galaxy disks. We found that 75%, or 216, of our 288 galaxies had larger effective radii in rest-frame visible light than in rest-frame ultraviolet light, supporting the theory that galaxy disks form outside-in. This means that only 25%, or 72, of our 288 galaxies had larger effective radii in rest-frame ultraviolet light than in rest-frame visible light, supporting the theory that galaxy disks form inside-out.