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Session 81 - Dwarf Galaxies.
Display session, Friday, January 09
Exhibit Hall,
The Hydra I galaxy cluster (Abell 1060, richness-class 1) is at a redshift of z = 0.012, about half of the distance to the Coma cluster. I have analyzed deep CTIO 4-m CCD images (in the Washington C and T_1 filters) of the Hydra cluster core. The Hydra I cluster is sufficiently close that on these images, the cluster dE galaxies are well resolved. For the brightest eight cluster dEs, I constructed isophotal models using the isophote package within IRAF/STSDAS. These tasks implement iterative modeling of elliptical isophotes, and allow for variable center position, ellipticity and position angle at each semimajor axis radius. In all cases the models created were excellent over the entire radial range, with the exception of the center-most few pixels. The surface photometry derived from these models was used to measure color gradients and structural parameters for each individual dE. Both red and blue color gradients are observed within this sample of dEs, yet there is no preference for one over the other. As well, their radial surface brightness profiles are well described by a modified exponential profile, I(r) = I_0 \exp \left[ -(r/r_0)^n \right]. Analysis of the dE galaxy sequence reveals a linear metallicity-luminosity relationship with a slope comparable to that observed for the dE populations in Coma and Fornax. These candidate dE galaxies will be reobserved spectroscopically, to determine ages and abundances from the analysis of spectral line indices.
