A NICMOS survey of early-type galaxy centers: The relation between core properties, gas and dust content, and environment

We present a NICMOS 1.6 mu m imaging isophotal study of 27 early-type galaxies. Core galaxies have reduced ellipticity and boxiness near and within their core or break radius. This supports a core formation mechanism that mixes or scatters stars such as scattering caused by a binary black hole. We find the same trends between central surface brightness and luminosities as the WPFC studies. We find no correlation between core properties and dust mass or X-ray luminosity, suggesting that processes determining the current gas content (e.g., such as minor mergers and cooling flows) are unrelated to processes occurring during core formation. Core galaxies exist in a variety of environments ranging from poor groups to large clusters. A combined sample suggests that galaxy groups may harbor more luminous power-law galaxies than clusters such as Virgo and Fornax.