Mariska Kriek

University of California, Berkeley

 

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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. This result poses the question of how these galaxies have grown in size over the past 11 billion years, while not forming appreciable numbers of stars. Together with Leiden graduate student Jesse van de Sande, I am studying the stellar kinematics of a sample of distant compact galaxies. Our findings confirm previous photometric studies, that these galaxies were indeed more compact and dense when the universe was only 20-25% its current age. We are currently using our kinematic galaxy sample to study the structural evolution of these galaxies in detail, in order to understand how these distant compact galaxies must have grown in size (van de Sande, Kriek et al. 2011, 2013).

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. Together with Kate Whitaker (now a postdoctoral fellow at NASA-Goddard), I have 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 later 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 redshift (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) and dust attenuation curve (Kriek & Conroy 2013). Among the main results are that the contribution from TP-AGB phase to galaxy spectra is not as dominant as initially thought and that the dust attenuation law in distant galaxies varies with spectral type. Together with UC Berkeley graduate student Dyas Utomo I am currently extending the composite SEDs to the MIR, in order to model the stellar and dust emission simultaneously. 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 are studying galaxy evolution over the past 12 billion years. We have been awarded 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.