Below are a selection of research projects from the past, present and future that have (or will be) carried out by students in my research group.

Graduate Students

I'm currently looking for graduate students interested in working on high redshift galaxy and structure formation theory projects. Please contact me (or just stop by my office) if you're interested - the list below give some examples of possible projects, but there are always others available. My research usually involves a significant amount of computational physics. While expertize in any particular programming language is not a prerequisite for these projects, an interest in computational physics and a willingness to learn how to use complex modeling software is highly beneficial.

Summer Work/SURF

I usually take on one (occasionally two) undergradraduate(s) each summer. Please contact me if you are interested. SURF proposals are usually due by the last week of February, so I accept inquiries until the fourth Monday of January and then choose students who will submit SURF applications.

Current Projects

Testing the Validity of the Adiabatic Contraction Approximation in Dark Matter Halos
Laura Book (Caltech)

The formation of galaxies within dark matter halos leads to compression of the central regions of the halo due to the galaxy's gravitational pull. This process is usually modelled as an adiabatic process in a spherical halo. However, numerical simulations show that this approach does not work as accurately as we might like. We are investigating some of the approximations which enter into the adiabatic contraction calculation to assess which of these may be responsible for its failures.

Cosmological Shock Growth and Environmental Effects
Laura Book (Caltech)

Galaxies show a transition in their properties from the field into clusters. This transition begins to become apparent significantly beyond the virial radii of clusters. We are investigating if the formation shock surrounding each cluster provides a more natural radius for various environmental effects to come into play and whether this can quantitatively explain the observed transitions in galaxy properties.

A Model of the Internal Structure of NFW Halos
Dan Grin (Caltech)

We're attempting to construct a model which explains how the internal structure (basically the scale length) of NFW dark matter halos is changed as a result of mergers between halos. Such a model could be applied to dark matter halo merger trees to predict how the NFW concentration parameter should depend on halo mass (and formation history).

Future Projects

Cosmological Ionization Fronts

Stars and AGN in galaxies can create large-scale ionized bubbles in the intergalactic medium. This project would compute the ionization and thermal structure of such bubbles, with particular emphasis on the double ionization of helium and the effects of X-ray photons which cause secondary ionizations.

Black Hole Growth During Galaxy Formation

The presence of supermassive black holes in the centers of galaxies is thought to play a significant role in their evolution. Current modelling of the growth of blacks holes during galaxy formation are overly simplistic. This project would aim to self-consistently follow the growth of the black hole's mass and spin during the process of galaxy formation, including calculating the power in outflows from the black hole and how this influences the formation of the surrounding galaxy.

Past Projects

Testing Massive Galaxy Growth Rates in Hierarchical Models with AGN Feedback

Martin Stringer (University of Oxford/Caltech)

In collaboration with Richard Ellis and Kevin Bundy, we are making the most careful and detailed comparison to date between theoretical predictions for the rate of massive galaxy growth and observations of the same. The Galform semi-analytic model of galaxy formation is being used to predict galaxy growth rates, and to determine the effects of cosmic variance and mass-estimation uncertainties in the observational data to provide the most accurate test possible of the theory.

Clustering of Luminous Red Galaxies
Lauren Porter (Caltech)

We are computing the expected clustering signal of luminous red galaxies at high redshifts with the aim of using observational data to place constraints on the distribution of such galaxies between dark matter halos.

Predictions for the JWST Galaxy Formation Science Goals
Tom Fox (University of Nottingham, UK)

This project began the first phase of adapting Galform to the high-redshift Universe (including following the thermal and ionization state of the IGM) to permit calculations to be made for JWST science.

Effects of Stochastic SNe Events on Early Galaxy Formation
Justin Chen (Caltech)

Semi-analytic models of galaxy formation have typically employed simple rules to describes the rates of star formation and feedback in forming galaxies. Typically, feedback (assumed to be due to SNe and stellar winds) is modelled as an outflowing of gas at a rate proportional to the current rate of star formation. This project is investigating what happens if we apply feedback due to individual, stochastically occuring SNe events and how this affects the properties of the first generations of galaxies to form.