Tracking the Formation of Thick Stellar Disks over the Last 10 Billion Years

In disk galaxies such as our Milky Way, older stars generally inhabit a thicker disk than their younger counterparts. Two competing models have attempted to explain this result: one in which stellar disks form thin and thicken internally with time, and one in which disks form thick then progressively thin as galaxies age. A direct measure of the thickness of stellar disks at high redshift is needed to discriminate these scenarios. Using archival UV-IR HST imaging from CANDELS, we have measured the stellar scale heights of 508 disk galaxies spanning over 10 billion years of cosmic time (0 < z < 2). In this talk, I will show how the scale heights of galaxies evolve with time and as a function of galaxy mass – and discuss what these results reveal about the formation history of today’s disks.