I am an assistant professor of astronomy & astrophysics at The Pennsylvania State University. My research interests focus on understanding the processes of galaxy formation through the use of large surveys and statistics.
In particular, I specialize in fitting flexible models to galaxy photometry and spectra, in building and exploring analytical and theoretical models of galaxy evolution, and in learning about and applying astrostatistics. I've harnessed millions of hours of supercomputer time running specialized code to build a more complete picture of how galaxies form and evolve. I've collaborated on a wide range of projects ranging from understanding the stellar origins of kilonova explosions to developing new methods for wide-field IR surveys. I am very proud to have been afforded the deep privilege of asking the big questions of the Universe!
Simple Models of Galaxy Assembly
I started my Ph.D in 2010 at Yale University with Professor Pieter van Dokkum. This was an exciting time to be studying galaxy evolution. We were in the middle of the first wide, deep, and unbiased (mass-selected) surveys of galaxy evolution at "cosmic noon", spear-headed by ambitious programs with the Hubble Space Telescope such as 3D-HST and CANDELS. As a result, astronomers had now surveyed the vast majority of the galaxy population over the majority of cosmic time for the very first time. My advisor and I thought that it was now the ideal time to "put it all together" and write down how galaxies grew up in a simple analytical model. This was the beginning of my thesis.
However, after constructing and testing our analytical framework, we found a serious problem with this plan. Applying our model to two independent measurements of galaxy mass growth (the current rate of star formation and the current mass locked up in stars) resulted in galaxy growth rates which were systematically offset by a factor of two. This was a big problem. To put it in persepctive, our model suggested that a typical ancestor of the Milky Way would grow by a factor of 4-16 from z~2, a confidence interval so large as to be almost useless!
2015: Even after changing the SFR(M), observed masses and SFRs disagreed
A New Method to Measure Galaxy Properties
The problem lay in the models we used to convert galaxy observations into galaxy properties. While these models had had many successes over many years, they were not quite precise enough to answer the questions we needed to answer. We identified three specific problems:
- The models did not include enough of the relevant physics, e.g. emission from black holes or nebulae.
- The assumptions built into them were not physically self-consistent.
- The models needed to use more clever statistics to translate the weak observational constraints into very broad parameter estimates
2017: Here Prospector fits our new galaxy SED model Prospector-α to photometry
A New Cosmic ConsensusWe applied this new Prospector-α model to a mass-complete sample of 58,461 galaxies across 0.5 < z < 2.5 from the 3D-HST survey. These new inferences lowered the observed cosmic star formation rate density by ∼0.2 dex and increase the observed stellar mass growth by ∼0.1 dex, finally bringing these two measurements into agreement and implying an older, more quiescent Universe than found in previous work.
2019: A new consensus in the older, more quiescent Universe from Prospector-α
In additional to my professional mentoring, I believe that knowing more about science and the scientific process improves the lives of everyone (and -- talking to folks about it is lots of fun!).
Flipped Science Fair
I host an annual reverse science fair, where professional researchers present their research to students from local elementary and middle schools. The students serve as “judges” and announce a winner at the end of the event. This encourages and develops outreach skills among researchers while simultaneously engaging the middle school students in a critical form of active learning.
Visitint URJ 6 Points Sci-Tech Academy
Giving talks to middle schoolers at science summer camp about my thesis research, and talking to them in their classrooms!
My office is Davey 515. You can reach me electronically at (firstname).(lastname)@psu.edu.