Dependence of Galaxy Shape on Environment in the Sloan Digital Sky Survey

Using a sample of galaxies from the Sloan Digital Sky Survey (SDSS) DataRelease 4, we study the trends relating surface brightness profile type andapparent axis ratio to the local galaxy environment. We use the SDSS parameter`fracDeV' to quantify the profile type. We find that galaxies with M_r > -18are mostly described by exponential profiles in all environments. Galaxies with-21 < M_r < -18 mainly have exponential profiles in low density environmentsand de Vaucouleurs profiles in high density environments. The most luminousgalaxies, with M_r < -21, are mostly described by de Vaucouleurs profiles inall environments. For galaxies with M_r < -19, the fraction of de Vaucouleursgalaxies is a monotonically increasing function of local density, while thefraction of exponential galaxies is monotonically decreasing. For a fixedsurface brightness profile type, apparent axis ratio is frequently correlatedwith environment. As the local density of galaxies increases, we find that for-20 < M_r < -18, galaxies of all profile types become slightly rounder, onaverage; for -22 < M_r < -20, galaxies with exponential profiles tend to becomeflatter, while galaxies with de Vaucouleurs profiles become rounder; for M_r <-22, galaxies with exponential profiles become flatter, while the deVaucouleurs galaxies become rounder in their inner regions, yet exhibit nochange in their outer regions. We comment on how the observed trends relate tothe merger history of galaxies.Comment: 23 pages, 7 figures, accepted by Ap