Physics Student Research


The Surface Brightness Fluctuation Distance to the Coma Cluster

Document Type



American Astronomical Society


Seattle, WA

Publication Date



The Coma cluster, as one of the closest very rich clusters of galaxies, is commonly used as a reference point in the cosmic distance ladder. We measured the surface brightness fluctuation (SBF) distance to NGC 4874, the cD galaxy in the Coma cluster, using the F160W (H-band) filter in the WFC3/IR camera on the Hubble Space Telescope. To compute the distance to NGC 4874, we relied on a calibration of the F160W SBF distance scale derived from WFC3/IR measurements of 12 galaxies in the Virgo and Fornax clusters. We present this new IR SBF calibration, which is based on optical SBF distances calibrated using Cepheid variable stars. The Cepheid/SBF calibration gives a distance of 96 +/- 5 Mpc to the Coma cluster. We also measured SBF in the disk of NGC 4258. The discovery of water masers in NGC 4258 provided a precise and accurate geometrical distance measurement, making it a popular first rung on the extragalactic distance ladder. While the SBF measurement for this galaxy is not very reliable due to the presence of young stars and dust lanes, it is useful to better understand stellar population variations and their effects on SBF measurements.

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