# Katherine Whitaker, Ph.D.

Assistant Professor, Department of Physics | University of Connecticut

Storrs, CT, United-States

Katherine Whitaker, Ph.D., is an expert in star and galaxy formation.

## Biography

Katherine Whitaker is an Assistant Professor in the Department of Physics at the University of Connecticut.

## Areas of Expertise (3)

Stars Physics Galaxies

## Affiliations (1)

• American Astronomical Society, Member

## Accomplishments (3)

Yale University

#### FAMOUS Travel Grant

American Astronomical Society

## Media Appearances (2)

#### Hubble Finds Patches of Newborn Stars in Galaxy 11 Billion Light-Years from Earth

Science News  online

2017-07-07

Astronomers using the NASA/ESA Hubble Space Telescope have captured a detailed image of an extremely distant, gravitationally lensed galaxy they believe contains two dozen patches of newborn stars.

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#### Free talk about the mysteries of the galaxies

The Weston Forum  online

2017-07-11

"UCONN astrophysicist Dr. Katherine E. Whitaker is giving a talk about the mysteries of galaxy formation and evolution on Tuesday, July 18 at 8 p.m., at the Westport Astronomical Society." (...)

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## Articles (5)

The Mass, Color, and Structural Evolution of Today's Massive Galaxies Since z ~ 5 The Astrophysical Journal

Allison R. Hill, Adam Muzzin, Marijn Franx, Bart Clauwens, Corentin Schreiber, Danilo Marchesini, Mauro Stefanon, Ivo Labbe, Gabriel Brammer, Karina Caputi, Johan Fynbo, Bo Milvang-Jensen, Rosalind E. Skelton, Pieter van Dokkum, and Katherine E. Whitaker

2017

In this paper, we use stacking analysis to trace the mass growth, color evolution, and structural evolution of present-day massive galaxies ($\mathrm{log}({M}_{* }/{M}_{\odot })=11.5$) out to z = 5. We utilize the exceptional depth and area of the latest UltraVISTA data release, combined with the depth and unparalleled seeing of CANDELS to gather a large, mass-selected sample of galaxies in the NIR (rest-frame optical to UV). Progenitors of present-day massive galaxies are identified via an evolving cumulative number density selection, which accounts for the effects of merging to correct for the systematic biases introduced using a fixed cumulative number density selection, and find progenitors grow in stellar mass by $\approx 1.5\,\mathrm{dex}$ since z = 5. Using stacking, we analyze the structural parameters of the progenitors and find that most of the stellar mass content in the central regions was in place by $z\sim 2$, and while galaxies continue to assemble mass at all radii, the outskirts experience the largest fractional increase in stellar mass. However, we find evidence of significant stellar mass build-up at $r\lt 3\,\mathrm{kpc}$ beyond $z\gt 4$ probing an era of significant mass assembly in the interiors of present-day massive galaxies. We also compare mass assembly from progenitors in this study to the EAGLE simulation and find qualitatively similar assembly with z at $r\lt 3\,\mathrm{kpc}$. We identify $z\sim 1.5$ as a distinct epoch in the evolution of massive galaxies where progenitors transitioned from growing in mass and size primarily through in situ star formation in disks to a period of efficient growth in r e consistent with the minor merger scenario.

Predicting Quiescence: The Dependence of Specific Star Formation Rate on Galaxy Size and Central Density at 0.5 < z < 2.5 The Astrophysical Journal

Katherine E. Whitaker, Rachel Bezanson, Pieter G. van Dokkum, Marijn Franx, Arjen van der Wel, Gabriel Brammer, Natascha M. Förster-Schreiber, Mauro Giavalisco, Ivo Labbé, Ivelina G. Momcheva, Erica J. Nelson, and Rosalind Skelton

2017

In this paper, we investigate the relationship between star formation and structure, using a mass-complete sample of 27,893 galaxies at 0.5 < z < 2.5 selected from 3D-HST. We confirm that star-forming galaxies are larger than quiescent galaxies at fixed stellar mass (${M}_{\star }$). However, in contrast with some simulations, there is only a weak relation between star formation rate (SFR) and size within the star-forming population: when dividing into quartiles based on residual offsets in SFR, we find that the sizes of star-forming galaxies in the lowest quartile are 0.27 ± 0.06 dex smaller than the highest quartile. We show that 50% of star formation in galaxies at fixed ${M}_{\star }$ takes place within a narrow range of sizes (0.26 dex). Taken together, these results suggest that there is an abrupt cessation of star formation after galaxies attain particular structural properties. Confirming earlier results, we find that central stellar density within a 1 kpc fixed physical radius is the key parameter connecting galaxy morphology and star formation histories: galaxies with high central densities are red and have increasingly lower SFR/${M}_{\star }$, whereas galaxies with low central densities are blue and have a roughly constant (higher) SFR/${M}_{\star }$ at a given redshift. We find remarkably little scatter in the average trends and a strong evolution of >0.5 dex in the central density threshold correlated with quiescence from z ~ 0.7–2.0. Neither a compact size nor high-n are sufficient to assess the likelihood of quiescence for the average galaxy; instead, the combination of these two parameters together with ${M}_{\star }$ results in a unique quenching threshold in central density/velocity.

Near-infrared Spectroscopy of Five Ultra-massive Galaxies at 1.7 < z < 2.7 The Astrophysical Journal

Erin Kado-Fong, Danilo Marchesini, Z. Cemile Marsan, Adam Muzzin, Ryan Quadri, Gabriel Brammer, Rachel Bezanson, Ivo Labbé, Britt Lundgren, Gregory Rudnick, Mauro Stefanon, Tomer Tal, David Wake, Rik Williams, Katherine Whitaker, and Pieter van Dokkum

2017

We present the results of a pilot near-infrared spectroscopic campaign of five very massive galaxies ($\mathrm{log}({M}_{\star }/{M}_{\odot })\gt 11.45$) in the range of $1.7\lt z\lt 2.7$. We measure an absorption feature redshift for one galaxy at ${z}_{\mathrm{spec}}=2.000\pm 0.006$. For the remaining galaxies, we combine the photometry with the continuum from the spectra to estimate continuum redshifts and stellar population properties. We define a continuum redshift (${z}_{\mathrm{cont}}$ ) as one in which the redshift is estimated probabilistically from the combination of catalog photometry and the observed spectrum using EAZY. We derive the uncertainties on the stellar population synthesis properties using a Monte Carlo simulation and examine the correlations between the parameters with and without the use of the spectrum in the modeling of the spectral energy distributions. The spectroscopic constraints confirm the extreme stellar masses of the galaxies in our sample. We find that three out of five galaxies are quiescent (star-formation rate of $\lesssim 1{M}_{\odot }\,{\mathrm{yr}}^{-1}$) with low levels of dust obscuration (${A}_{{\rm{V}}}\lt 1$) , that one galaxy displays both high levels of star formation and dust obscuration ($\mathrm{SFR}\approx 300{M}_{\odot }\,{\mathrm{yr}}^{-1}$, ${A}_{{\rm{V}}}\approx 1.7$ mag), and that the remaining galaxy has properties that are intermediate between the quiescent and star-forming populations.

Hierarchical Star Formation in Turbulent Media: Evidence from Young Star Clusters The Astrophysical Journal

K. Grasha, B. G. Elmegreen, D. Calzetti, A. Adamo, A. Aloisi, S. N. Bright, D. O. Cook, D. A. Dale, M. Fumagalli, J. S. Gallagher, D. A. Gouliermis, E. K. Grebel, L. Kahre, H. Kim, M. R. Krumholz, J. C. Lee, M. Messa, J. E. Ryon, and L. Ubeda

2017

We present an analysis of the positions and ages of young star clusters in eight local galaxies to investigate the connection between the age difference and separation of cluster pairs. We find that star clusters do not form uniformly but instead are distributed so that the age difference increases with the cluster pair separation to the 0.25–0.6 power, and that the maximum size over which star formation is physically correlated ranges from ~200 pc to ~1 kpc. The observed trends between age difference and separation suggest that cluster formation is hierarchical both in space and time: clusters that are close to each other are more similar in age than clusters born further apart. The temporal correlations between stellar aggregates have slopes that are consistent with predictions of turbulence acting as the primary driver of star formation. The velocity associated with the maximum size is proportional to the galaxy's shear, suggesting that the galactic environment influences the maximum size of the star-forming structures.

Star Formation at z = 2.481 in the Lensed Galaxy SDSS J1110 = 6459. I. Lens Modeling and Source Reconstruction* The Astrophysical Journal

Traci L. Johnson, Keren Sharon, Michael D. Gladders, Jane R. Rigby, Matthew B. Bayliss, Eva Wuyts, Katherine E. Whitaker, Michael Florian, and Katherine T. Murray

2017

Using the combined resolving power of the Hubble Space Telescope and gravitational lensing, we resolve star-forming structures in a $z\sim 2.5$ galaxy on scales much smaller than the usual kiloparsec diffraction limit of HST. SGAS J111020.0+645950.8 is a clumpy, star-forming galaxy lensed by the galaxy cluster SDSS J1110+6459 at $z=0.659$, with a total magnification $\sim 30\times$ across the entire arc. We use a hybrid parametric/non-parametric strong lensing mass model to compute the deflection and magnification of this giant arc, reconstruct the light distribution of the lensed galaxy in the source plane, and resolve the star formation into two dozen clumps. We develop a forward-modeling technique to model each clump in the source plane. We ray-trace the model to the image plane, convolve with the instrumental point-spread function (PSF), and compare with the GALFIT model of the clumps in the image plane, which decomposes clump structure from more extended emission. This technique has the advantage, over ray-tracing, of accounting for the asymmetric lensing shear of the galaxy in the image plane and the instrument PSF. At this resolution, we can begin to study star formation on a clump-by-clump basis, toward the goal of understanding feedback mechanisms and the buildup of exponential disks at high redshift.