I work with Prof. Ned Wright on the foreground cleaning of maps taken by the Wilkinson Microwave Anisotropy Probe (WMAP). My thesis focuses on the investigations of two foregrounds in the WMAP data: Extragalactic Point Sources, and the Zodiacal Light Emission.


Overview of point source distribution in the sky. Sources are
detected in the ILC map of the five-year 41, 61, and 94 GHz bands.

Extragalactic Point Sources

The most important foreground at small angular scales is due to extragalactic radio sources. In the past, sources were generally found by searching for bright spots that approximate the beam profile in the maps. However, due to the limited angular resolution of WMAP, it is possible to confuse positive CMB excursions with point sources. To circumvent this CMB “noise”, we have developed a new source-finding technique, which involves forming internal linear combinations (ILC) of the multi-frequency WMAP maps to suppress the CMB. Applying this technique to the WMAP 41, 61 and 94 GHz temperature maps, we made new detections as well as recovered previous detections with independent methods. The number of sources detected in the 61 and 94 GHz maps alone varied as N ~ t^0.72 from first year to five years, indicating that the ILC technique improves rapidly with increased observing time. Point source catalogs from this work can be found here:

  • Extragalactic Point-Source Search in WMAP 61 and 94 GHz Data, Chen, X. and Wright, E. L., 2008, ApJ, 681, 747C
  • The Wilkinson Microwave Anisotropy Probe (WMAP) Source Catalog, Wright, E. L., Chen, X., Odegard, N., Bennett, C. L., Hill, R. S., Hinshaw, G., Jarosik, N., Komatsu, E., Nolta, M. R., Page, L., Spergel, D. N., Weiland, J. L., Wollack, E., Dunkley, J., Gold, B., Halpern, M., Kogut, A., Larson, D., Limon, M., Meyer, S. S., Tucker, G. S., ApJS, in press
  • Extragalactic Point Source Search in Five-year WMAP 41, 61 and 94 GHz Maps, Chen, X. and Wright, E. L., ApJ, in press

    Zodiacal Light Emission

    The Zodiacal Light Emission (ZLE) comes from scattered light and thermal emission from the interplanetary dust in our Solar System. Unlike other foregrounds usually considered in CMB studies, the ZLE is special because its surface brightness depends not only on the pointing direction but also on the instantaneous position of the observer within the Solar System. Therefore it appears as a time-dependent foreground. If not accounted for properly, the ZLE will directly cause incorrect extraction of dust foreground from the CMB map, which will then lead to an inaccurate calculation of the CMB power spectrum.

    To set the limits of ZLE contamination in the WMAP data, I am performing a simultaneous fit of the Kelsall et al. (1998) zodiacal light model plus low-l CMB components (l = 1 to 4) to five years of WMAP time-ordered data (TOD) stream at 94 GHz. If ZLE signal is confirmed to be at a substantial level in the WMAP data, a careful treatment of ZLE will be required for precision cosmology.