Alex Fry alex_header_info

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I am an astronomy graduate student at the University of Washington. I did my undergraduate work in physics and astronomy at the University of Texas where I worked on the Hetdex project studying dark energy.

I am broadly interested in cosmology, extragalactic astronomy, and astrophysics. Specific topics of interest include, but are not limited to: baryonic acoustic oscillations, 21 cm cosmology, the Sunyaev Zeldovich effect, epoch of reionization, dark matter, Lyman alpha emitters, formation of large scale structure, pulsars, and the formation an evolution of super massive black holes.

My thesis work is exploring a major outstanding problem in astrophysics - dark matter. The dominant form of mass in the standard cosmological model is collisionless cold dark matter (CDM) which due to primordial random Gaussian density perturbations has collapsed into virialized halos in the evolved universe. Baryonic matter aggregates in these dark matter overdensities and forms luminous galaxies, like our own Milky Way. Simulations and observations on cosmological scales are in strong agreement with the CDM theory. However the distribution of dark matter is poorly understood on smaller galactic scales as indicated by a lack of concordance between CDM predictions and observations: 1) The inner density profile of galaxies inside the scale radius is much shallower than expected. Additionally the central density of dark matter halos is observed to be constant (with intrinsic scatter) independent of halo mass. This is the so called core/cusp problem. 2) The number of observed galaxies in the Local Group is an order of magnitude lower than that predicted by CDM simulations. This is the so called missing satellite problem. 3) The shape of halos is predicted to be triaxial by CDM models, but observations of halos indicate nearly spherical shapes. All of these issues would be ameliorated by mechanisms which lower the central density of galaxies and or raise the phase space density of dark matter. Mechanisms which are relevant include baryonic feedback and collisional dark matter. Evidence is mounting that including the effects of baryons in high resolution numerical simulations such as gas cooling, star formation, and gas outflows driven by supernovae can better match the observations such as flatter cores in dwarf galaxies. The possibility of cold, nondissipative, but collisional and self-interacting dark matter is also being raised. A dark matter interaction with a mean free path between 1 kpc and 1 Mpc would only alter the evolution of cold dark matter in high density galaxy environments and large scale power spectrum measurements would be insensitive to the this modification of dark matter. The purpose of my work is to test the galactic scale distribution of dark matter by using detailed numerical simulations (including a full range of baryonic physics including gas cooling, star formation, and supernovae driven gas outflows) to explore the effects of cosmologically consistent self-interacting dark matter models.

You may reach me by email at .washington.edu




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