Using Color Gradients to Study the Inside-Out Formation of Disk Galaxies at 0.8 ≤ z ≤ 1.0

In this study, we investigated the inside-out galaxy disk formation theory by deriving U - V rest-frame color gradients of a sample of 408 disk galaxies at 0.8 ≤ z ≤ 1.0. Using HST WFC3 images of the GOODS-N region from the CANDELS and UVCANDELS surveys, U - V color maps were created using PSF convolved postage stamps of galaxies in both the F275W and F125W filters, and surrounding objects in the images were masked out for analysis. Color gradients were analyzed through radial profiling using concentric annuli with widths of 0.5 kpc out to a full radius of ∼25 kpc. We find that 98.8% of the 408 galaxies have negative gradients, 45.3% of which had entire color profiles < 0.5 mag indicating that they are likely dominated by young stars, and 53.5% had profiles that had positive centers (> 0.5 mag centrally) and grew negative with radius. Our results suggest at least that an outside-in disk formation is not supported and at most that an inside-out disk formation is possible. Another potential conclusion is that there are fewer old stars in the galactic disk as radius from the center increases. The remaining 1.2% of galaxies had unusually shaped profiles. In the future, a determination of each galaxy's full radius is necessary to separate the galaxy's faint edge from the background.