The major research areas studied in the Whitaker Research Group are summarized below, though we continue to branch into new areas of galaxy formation and evolution. You can download public Data Products from various public surveys: James Webb Space Telescope UNCOVER Treasury Survey, Hubble Legacy Survey, 3D-HST, and the NEWFIRM Medium-Band Survey.
NEW(EST) Projects
(i.e., recruiting new students and/or postdoctoral researchers)
Large Millimeter Telescope (funded by NSF CAREER grant)
Ultra-Deep Galaxy Survey - 3-band confusion limited mm wavelength imaging of deep fields with the TolTEC instrument
James Webb Space Telescope (funded by JWST grants)
Deep Dive Survey - Cycle 2 spectroscopic program targeting quiescent galaxies at z>3 (PI: Francesco Valentino)
UNCOVER Survey - Ultra-deep JWST NIRCam/NIRISS imaging and NIRSpec spectroscopy of a Frontier Field cluster
PANORAMIC Survey - Pure-parallel NIRCam imaging program covering wide area
PRIMER Survey - Deep JWST NIRCam and MIRI imaging program in two CANDELS fields
3D-Herschel Project (no funding remains, but undergraduate projects possible)
Several possible projects using the combined 3D-HST and Herschel catalogs with Prospector Bayesian modeling.
Discovery of Ancient Relics in a Distant Evolved Galaxy
Whitaker et al. (2025)
Globular clusters (GCs) are some of the oldest bound structures in the Universe, holding clues to the earliest epochs of star formation and galaxy assembly. However, accurate age measurements of these ancient clusters are challenging due to the age-metallicity degeneracy. Using deep data from the UNCOVER/MegaScience JWST Surveys, we have discovered a remarkable population of compact stellar systems within ‘The Relic', a massive, quiescent galaxy that exists only 2.5 billion years after the Big Bang. The Relic resides in an overdensity behind the Abell 2744 cluster, with a prominent tidal tail extending towards two low-mass companions. When taking the cluster-based star formation history together with the spatial distribution and low inferred metallicities of the younger age clusters, we may be seeing direct evidence for the accretion of star clusters, in addition to the early in-situ formation of older clusters. This unique laboratory enables the first connection between long-lived, high-redshift clusters and local stellar populations, offering insights into the early stages of GC evolution and the broader processes of galaxy assembly. Stay tuned for upcoming results from a Cycle 3 spectroscopic follow-up program (PI: Cutler, co-PI: Whitaker)!
Understanding Cold Dust in Quiescent Galaxies
Whitaker et al. (2021a, 2021b), Caliendo et al. (2021)
We are still in a data-limited stage of understanding the cold dust properties of ‘red and dead’ (quiescent) galaxies. It especially remains a mystery how massive galaxies quench at such early times given that their dark matter halos contain large gas reservoirs. This gas should cool efficiently, sustaining star formation over long periods; if the molecular gas is there, standard molecular-gas-to-dust mass conversions suggest we should also see cold dust. The plot thickens - recent predictions from cosmological simulations coupled with predictive dust modeling find exotic (high) molecular-gas-to-dust mass ratios in the quiescent population and stand in tension with low-resolution millimeter stacking results. In this work, we explore the cold dust content from a fresh perspective by leveraging a premier sample of strong gravitationally lensed quiescent galaxies at cosmic noon. Ongoing work with ALMA and LMT programs, when coupled with mock observations from simulations, will inform the future prospects for using the cold dust continuum to trace molecular gas reservoirs.
Morphological Studies Informing Galaxy Formation Theories
Cutler et al. (2022, 2024); Wright et al. (2023); Bodansky et al. (2025)
Measurements of the galaxy size–mass relation can help inform galaxy formation and evolution theories. Our work is focused primarily at cosmic noon (z~2), using both high-resolution Hubble and James Webb Space Telescope imaging. We confirm an unambiguous flattening of the low-mass quiescent size–mass relation (Cutler et al. 2022), which results from the separation of the quiescent galaxy sample into two distinct populations (Cutler et al. 2024): low-mass quiescent galaxies that are notably younger and have disky structures, and massive galaxies consistent with spheroidal morphologies and older median stellar ages. These separate populations imply mass quenching dominates at the massive end while other mechanisms, such as environmental or feedback-driven quenching, form the low-mass end. While these quiescent galaxies are already known to be remarkably compact, we find that this trend only becomes more dramatic when we push to z>3 (Wright et al. 2023). Furthermore, we can connect this compact population of quenched galaxies to their possible progenitors, dusty mm-selected star-forming galaxies (Bodansky et al. in prep).
The Star Formation Sequence: Redshift Evolution and the Connection to Galactic Structure
Whitaker et al. (2012, 2014b, 2015, 2017ab)
A wealth of data from deep extragalactic surveys have revealed a picture where star-forming galaxies follow a tight relation between star formation rate (SFR) and stellar mass (M*), known as the “star formation sequence” (see figure to right from Whitaker et al. 2014b; note the erratum and updated Table 1 values). In Whitaker et al. (2012b), we showed that this relation has a roughly constant scatter with cosmic time, and that galaxies show strong trends of increasing dust attenuation with stellar mass. By leveraging the factor of ten lower mass-completeness limits in the 3D-HST photometric catalogs, we further constrained the low-mass slope of this relation in Whitaker et al. (2014b). For the first time, we showed that while the slope of the star formation sequence is unity for low-mass galaxies out to z=2.5, it becomes increasingly shallower towards later times for massive galaxies, indicating either less efficient star formation or decreasing gas accretion. These self-consistent empirical measurements of the evolving relation between star formation rate and stellar mass enable powerful constraints on theoretical models across different mass regimes. Most recently, we have explored the correlations between the star formation sequence and various metrics of galactic structure, including the Sersic index (Whitaker et al. 2015) and size and central density (Whitaker et al. 2017).
The Quenching of Star Formation in Massive Galaxies
Whitaker et al. (2010, 2011, 2012a, 2013), Clausen et al. (2024, 2025)
My research is focused on mapping the stellar population properties and spatial structures of galaxies, in order to reconstruct their life cycles and identify their driving mechanism. How do massive galaxies grow? And what regulates their star formation? Unifying both of these questions, one of the most outstanding problems in galaxy formation theory is understanding how actively star-forming galaxies quench their star formation. To make sense of the formation and evolution of the most massive galaxies in our universe, we must directly observe these galaxies at the pivotal epoch of 1<z<3 when they are most rapidly shutting off star formation. At these early times, roughly half of massive galaxies had already stopped forming new stars within the last one to two gigayears (see figure on left from Whitaker et al. 2012a). One approach to illuminating the dominant quenching mechanism requires first discriminating the distant galaxies that most recently shut off. This is now possible with the technique of Whitaker et al. (2010). Using this color-color selection, we are working to quantify the rest-frame optical, observed in the near-infrared (NIR), structural and stellar population properties of these recently quenched galaxies relative to star-forming and older quiescent galaxies (Whitaker et al. 2012a, 2013). The next step, and ongoing research, involves spatially resolving the stellar populations to disentangle the unique observational signatures that different quenching models predict.
Semi-Resolved Stellar Populations in Distant Galaxies
Whitaker et al. (2014a), Akhshik et al. (2020, 2021, 2023)
RCS0327 is one of the best-studied star-forming galaxies at the peak of cosmic star formation. Due to the strong gravitational lensing magnification and enhanced star formation from an ongoing interaction (see figure to right from Whitaker et al. 2014a), RCS0327 provides a unique opportunity to study a distant galaxy in detail on the ∼100 pc spatial scales characteristic of star-forming regions. In Whitaker et al. (2014a), we use HST/WFC3 grism observations to spatially-resolved the Hγ/Hβ, [OIII]λ5007/Hβ and HeIλ5887/Hβ emission line ratios, mapping the variations in the extinction and ionization conditions for 7 individual star-forming regions at z=1.7. Working with the Sloan Giant Arcs Survey collaboration (PI: M. Gladders), we are now performing a detailed census of the stellar populations of a pilot sample of distant gravitationally lensed galaxies. Synergizing the science possible with the large representative 3D-HST galaxy sample and the high spatial resolution case-studies of lensed galaxies will have durable value and guide the focus of the next generation of telescopes.