Tracy E. Clarke

Postdoctoral Research Associate

Curriculum Vitae

B.Sc., University of New Brunswick, (Honours) Physics, (1993)

M.Sc., University of Toronto, Astronomy, (1994)

Ph.D., University of Toronto, Astronomy, (2000)

Jansky Fellow, National Radio Astronomy Observatory (1999-2002)

Present Position:

Postdoctoral Research Associate, University of Virginia

Research Interests:

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Interaction of cluster-center radio sources and the thermal ICM:

The cores of cooling flow clusters typically contain giant cD galaxies which are often host to powerful, steep-spectrum radio galaxies. The Chandra X-ray Observatory has revealed complex interactions between cluster-center radio galaxies and the thermal intracluster medium.

The adaptively smoothed Chandra image of the central 72 x 72 kpc region of Abell 2029 is shown in colour with the 1490 MHz radio contours of PKS 1508+059 from Taylor et al. (1994) overlaid (Clarke et al. 2004).

Adaptively smoothed Chandra image of the central 36 x 36 kpc region of Abell 2029 with the 8350 MHz radio contours from Taylor et al. (1994) overlaid (Clarke et al. 2004).

X-ray residual image of the central 500 x 550 kpc region of Abell 2029 obtained by subtracting a smooth elliptical fit to the Chandra data. The large spiral excess is estimated to contain at least 6 x 10^12 Solar masses of material. The most likely origins of the excess are either stripping of gas from a group of dark matter potential merging with Abell 2029, or sloshing motions in the cluster core due to a past merger event. (Clarke et al. 2004).

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Cluster mergers and the connection to diffuse synchrotron emission:

Clusters of galaxies are thought to form through multiple mergers at the intersection of large-scale filaments. A large cluster merger can release enormous amounts of energy into the intracluster medium. This energy is dissipated through the compression of magnetic fields, particle acceleration, and heating. In the presence of magnetic fields the accelerated (relativistic) particles will emit synchrotron emission.

ROSAT X-ray contours of Abell 754 overlaid on the greyscale 74 Mhz VLA observations of the cluster. The radio data reveal a central radio halo to the west of the X-ray bar as well as a radio relic to the east of the bar (Kassim et al. [2001]).

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Magnetic fields in galaxy clusters:

Combining multi-frequency radio observations of polarized radio sources viewed through the intracluster medium with X-ray observations of the thermal gas to determine the magnetic field strength in the intracluster medium.

Galaxy-corrected rotation measure (RM) plotted as a function of impact parameter of the radio source from the cluster center (b). Open circles represent sources viewed through the thermal cluster gas and filled points are the control sample at larger radii. There is a clear increase in the RM toward low impact parameters indicating the presence of intracluster magnetic fields (from Clarke et al. [2001])

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Other Stuff:

During the analysis of the Abell 2029 Chandra data we discovered an east-west depression in the X-ray gas roughly 1.5 arcminutes south of the cluster core.

Top panel shows the optical I-band image of UZC J151054.6+054313. This galaxy is a redshift z=0.0221 edge-on spiral galaxy viewed 1.5 arcminutes south of the core of the z=0.0767 galaxy cluster Abell 2029. The middle panel shows the 0.3-1.0 keV soft X-ray image from Chandra while the bottom panel shows the hard-band 1.0-7.0 keV data. The X-ray deficit at low eneregies is consistent with photoelectric absorption. ( Clarke et al. [2004] ).

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Selected Papers:

The Complex Cooling Core of Abell 2029: Radio and X-ray Interactions, Tracy E. Clarke, Elizabeth L. Blanton, and Craig L. Sarazin, ApJ in press

Chandra Observation of the Central Region of the Cooling Flow Cluster Abell 262: A Radio Source that is a Shadow of its Former Self?, Elizabeth L. Blanton, Craig L. Sarazin, Brian R. McNamara, Tracy E. Clarke, ApJ in press

Soft X-ray Absorption due to a Foreground Edge-On Spiral Galaxy Toward the Core of Abell 2029, Tracy E. Clarke, Juan M. Uson, Craig L. Sarazin, Elizabeth L. Blanton, 2004, ApJ, 601, 798

Hydra A at Low Radio Frequencies, Wendy M. Lane, Tracy E. Clarke, Gregory B. Taylor, Rick A. Perley, Namir, E. Kassim, 2004, AJ, 127, 48

Are the Faraday Rotating Magnetic Fields Local to Intracluster Radio Galaxies?, Torsten Ensslin, Corina Vogt, Tracy Clarke, Gregory Taylor, 2003, ApJ 597, 870

Low-Frequency VLA Observations of Abell 754: Evidence for a Cluster Radio Halo and Possible Radio Relics, Namir Kassim, Tracy Clarke, Torsten Ensslin, Aaron Cohen, Doris Neumann, 2001, ApJ, 559, 785

A New Radio-X-Ray Probe of Galaxy Cluster Magnetic Fields, Tracy Clarke, Hans Boehringer, Phil Kronberg, 2001, ApJL, 547, 111

A Search for Flux Density Variations in 24 Compact Radio Sources in M82, P.P. Kronberg, R.A. Sramek, G.T. Birk, Q.W. Dufton, T.E. Clarke, M.L. Allen, 2000, ApJ, 535, 706

The Distance to the Draco Intermediate-Velocity Cloud, M.D. Gladders, T.E. Clarke, C.R. Burns, A. Attard, M.P. Casey, D. Hamilton, G. Mallén-Ornelas, J.L. Karr, S.M. Poirier, M. Sawicki, L.F. Barrientos, S.W. Mochnacki, 1998, ApJ, 507, 161

Do gamma-ray bursts come from the Oort cloud?, Tracy Clarke, Omer Blaes, Scott Tremaine, 1994, AJ, 107, 1873