Introduction

It is predicted that a large fraction of the total baryons in the universe reside outside the well studied dense clusters of galaxies. Cosmological simulations show a universe where rich clusters and super-clusters of galaxies are connected by a diffuse "cosmic web" of sheets and filaments, but these regions are difficult to detect precisely because they are such low density environments. My research, in collaboration with Prof. Larry Rudnick, focuses on using non-thermal emission to detect and characterize these low density regions, using powerful telescopes such as the Very Large Array, the Greenbank Telescope, and the Westerbork Synthesis Radio Telescope array. Our current focus is on using polarization observations to detect very low surface brightness emission purportedly cause by shocks related to large scale structure formation. I am also working on a project with Professor Lawrence Rudnick and senior graduate student Kisha Delain to detect diffuse radio emission in groups and clusters of galaxies using the Westerbork Synthesis Radio Telescope (see Kisha's compilation of known relics and halos). I am utilizing a novel technique called rotation measure synthesis (Brentjens, M. A., de Bruyn, A. G., 2005, A&A, 441, 1217) that circumvents the confounding problems of Faraday rotation. I have also recently gotten involved with the Alfalfa project at Arecibo Observatory as a part time observer. Alfalfa is an extremely deep neutral hydrogen survey of the entire Arecibo sky.

GBT Super-Cluster Mapping

We were recently awarded 80 hrs on the Green Bank Telescope to map the polarized synchrotron emission around three super-clusters of galaxies: Coma/A1367, Abell 576, and Abell 907. The observations are now well underway, and the hard part of reducing and calibrating the data is about to begin! Here is a pdf version of our GBT Proposal. Here are some notes on our GBT L-band polarization observations and a collection of our raw scans; this is all proprietary stuff, but if you can make sense of it you're probably a collaborator anyway!

Update!
We are now producing calibrated maps (in all Stokes) with the GBT data. Here is an example.

1.4 GHz Green Bank Telescope Stokes I map of the Coma Cluster. The image has been convolved to 12', point-source subtracted, and a median weight filter applied.

Giant Void in the Universe

We recently reported a discovery of a ~280 Mpc void in the direction of the famous WMAP "Cold Spot". Look here for a site describing the largest void ever discovered. This project was a collaboration with Professors Lawrence Rudnick and Liliya Williams, and received a fair amount of press. It combines cosmology and radio astronomy, two of my favorite things to work on.

More to come soon!

Rotation Measure Synthesis

Diffuse synchrotron emission in low mass systems

0809+39

Fig. 1: Left: Not done yet...part of an RM cube made from the Stokes Q and U maps of 0809+39, going from a Faraday depth of -25 rad/m^2 to 25 rad/m^2. You can see how the galactic synchrotron emission starts to fade away at higher Faraday depth. There are still some calibration issues that need to be worked out, but much more on this later. Right: I image of 0809+39; to the same scale as the cube.

Theoretical Interests

Last Updated: (October 25, 2007).