I am a third year graduate student at the Center for Astrophysics of Harvard University. Currently I study star formation in galaxies and how it affects their structure and evolution using observations and numerical simulations. I have a Bachelor of Science in physics with a minor in astronomy from Case Western Reserve University and a master of philosophy in physics from the Institute of Astronomy of the University of Cambridge. My time at the IoA was funded by a Churchill Foundation scholarship.

A few pictures.

Simulations of XUV Disks
The outer regions of disk galaxies show a drop-off in optical and Halpha emission, suggesting a star formation threshold radius, assumed to owe to a critical surface density below which star formation does not take place. GALEX recently challenged this picture with the discovery that 30% of disk galaxies show UV emission, indicating star formation, out to 2-3 times the optical radius of the galaxy, well beyond this threshold. Analysis of the UV star formation profiles of these galaxies suggests that the Kennicutt-Schmidt relation could hold beyond the traditional density threshold for the galaxy. However, it has been suggested that local over-densities in outer H~I disks drive star formation at large radii when they exceed the star formation threshold density. We run smooth particle hydrodynamics simulations of disk galaxies with extended gas disks to test whether over-densities owing to spiral structure in the outer disk can reproduce the observed star formation. We indeed find that spiral density waves from the inner disk propagate into the outer gas disk and raise local gas regions above the star formation density threshold, yielding features similar to those observed. Because the amount of star formation is low, we expect to see little optical emission in outer disks, as observed. Our results indicate that XUV disks can be simulated simply by adding an extended gas disk to an isolated galaxy and evolving it with fiducial star formation parameters. This illustrates that a star formation threshold density is not equivalent to a star formation threshold radius.
Adviser: Dr. Lars Hernquist
Submitted to ApJL: Bush, S., Cox, T.J., Hernquist, L., Thilker, D., and Younger, J.D. 2008.

Testing Star Formation Prescriptions with the Antennae
NGC 4038/4039, nicknamed "the Antennae," is a prototypical galaxy merger whose close proximity (D ~ 20 Mpc) and relatively simple morphology have made it a favorite target of observational and theoretical studies. Two long, symmetric tidal tails extend off two overlapping disk galaxies and cross to give the merger the appearance of a pair of antennae. The most recent model of the Antennae reproduces many of its key morphological features using collisionless N-Body simulations including a disk, bulge and a King model dark matter halo (Barnes 1988). However, in the last 20 years there have been large advances in both modeling and observations which have not yet been implemented in an updated model. Detailed optical (Whitmore & Schweizer 1995), infrared (Wang et al. 2004) and HI (Hibbard et al. 2001, Gordon et al. 2001) observations give new constraints on the morphology and kinematics of the Antennae and improved simulations allow us to implement more realistic galaxy models. We intend to revisit the Antennae with GADGET simulations, implementing a Hernquist profile for the dark matter halo and adding gas to update the simulations of this system. We will examine which galaxy models are consistent with creating a system such as the Antennae, and comment on the outlook for constraining disk and halo models with detailed simulations of nearby mergers. Finally, we will implement two different star formation prescriptions, shock induced and Kennicutt-Schmidt law, and examine how the distribution of young stars in the Antennae depends on star formation prescription. We will then use observations of the Antennae to constraints on how much each type of star formation contributes to the overall stellar population of the antennae.
Advisers: Dr. Lars Hernquist and Dr. Giovanni Fazio
Collaborators: Dr. T.J. Cox, Dr. John Hibbard, Dr. Josh Barnes and Dr. Zhong Wang

A New Picture of NGC 6240
We have taken a new look at the canonical merger remnant and luminous infrared galaxy (LIRG) NGC 6240 using multiwavelength archive data and new Spitzer/IRAC data. NGC 6240 is a unique merger remnant that has double nuclei detectable in the optical and x-ray and is on the border between LIRG and ULIRG classes. We use photometry to analyze the distributions of the stars and dust in NGC 6240 and to search for AGN indicators in the nucleus. We use these results to compile a consistent picture of the structure of NGC 6240 and discuss possibilities for the future of the remnant.
Adviser: Dr. Giovanni Fazio
Submitted to ApJ: Bush, S., Wang, Z., Korovska, M. and Fazio, G. 2008