Research

My research focuses on the formation and evolution of galaxies. More specifically, I am interested in the stellar kinematics and structures, stellar populations, dust properties, and black hole accretion rates of galaxies across cosmic time. I am currently involved in several large observing programs, among which the MOSFIRE Deep Evolution Field (MOSDEF) Survey and 3D-HST. Below I describe several of my recent and current efforts in a bit more detail.

Stellar Kinematics and structures of distant galaxies

One of the most surprising discoveries in extra-galactic astronomy in the past years is the finding that early-type galaxies may have been significantly smaller in the past. However, these studies were all based on the photometric properties of galaxies, and independent spectroscopic measurements are needed to confirm these exciting results. Together with Leiden graduate student Jesse van de Sande, I am studying the stellar kinematics of a sample of distant compact galaxies. Our findings support that these galaxies were indeed more compact and dense when the universe was only 20-25% its current age, and we are currently studying the structural evolution of these galaxies in detail (van de Sande, Kriek et al. 2011, 2013).

In order the explain the large size of nearby early-type galaxies, these distant compact galaxies must have grown in size significantly. Several theories have been proposed to explain this size growth. One theory is that the number of early-type galaxies is growing over time, and that galaxies that join this population at later times are larger. This would increase the average size of the early-type population with time. Kate Whitaker (now a postdoctoral fellow at NASA-Goddard) and I assessed this theory by comparing the sizes of early-type galaxies of different ages. Interestingly, we found that galaxies that joined the early type galaxy population at a certain time were not larger than the early type galaxies that already existed at that time, and thus we ruled out this theory for the size growth of early type galaxies (Whitaker, Kriek et al. 2012).

Dust and stellar populations across cosmic time

Most of my recent work on this topic has been based on the NEWFIRM Medium-Band Survey (NMBS, Whitaker et al. 2011). Using the exquisite quality of the NMBS photometric data, we have constructed composite spectral energy distributions (SEDs), by combining galaxies of similar SED shapes over a range of redshifts (Kriek et al. 2011). These SEDs exhibit a tremendous improvement in spectral sampling and S/N when compared to normal broadband SEDs, and show many absorption and emission features. Each SED represents a different spectral type, and together they span nearly the full galaxy population at 0.5<z<2.0. I have used these SEDs to study stellar populations and star formation histories of galaxies, and to constrain the thermally-pulsing asymptotic giant branch (TP-AGB) phase (Kriek et al. 2010). Currently, I am using the composite SEDs to investigate the variation in the dust attenuation curve (Kriek & Conroy, in prep). I am also using data from the 3D-HST survey to study dust and stars in distant galaxies. Together with UC Berkeley graduate student Sedona Price, I am studying how dust extinction toward star-forming regions relates to the total integrated dust attenuation of the entire galaxy.

The MOSFIRE Deep Evolution Field Survey

Together with five faculty members at the University of California (Alison Coil; Bahram Mobasher; Naveen Reddy; Alice Shapley; Brian Siana) I have started a large galaxy survey with the new instrument MOSFIRE on the Keck I Telescope. Using MOSFIRE we plan to study galaxy evolution over the past 12 billion years. We have been approved 44 night over 4 spring semesters (2013A-2016A) to observe about 2000 galaxies. We are in particular interested in the time period starting 12 billion years ago until about 5 billion years ago (1.5 < z < 3.5), as both black holes and galaxies experienced most growth during this epoch. The scientific goals of this survey are broad, ranging from the growth of galaxies and their black holes to the chemical enrichment histories of galaxies.