Surface photometry of the Shell Galaxy NGC 2865

Abstract

This thesis presents independently calibrated CCD surface photometry derived from 12 images of the shell galaxy NGC 2865 in the B, V, and R passbands. Short exposures were used to permit accurate sky subtraction. Mean isophotes were derived for each passband over the radial distance range 3"-60". The isophotes are presented in the form of their best-fit (lease-squares) ellipse parameters. The parameters for the best-fit de Vaucouleurs surface brightness law were determined for the mean profile in each passband and deviations of the actual surface brightness profile from the r[superscript 1/4] law are discussed in terms of the galaxy's shell structure. From the best-fit ellipse parameters, the amplitudes of the cos(4[theta]) component of the isophotes could be measured. They do not show the boxiness often observed in a galaxy which had experienced a recent merger. A peak amplitude of about +1 percent (2[sigma]) over the interval of 25"-40" suggests only the presence of a weak disk. If the disk is real it indicates that NGC 2865 is an S0, rather than an elliptical, galaxy. Also, both (B - V) and (B - R) colour gradients were measured and show that the galaxy becomes bluer with increasing radius. (Abstract shortened by UMI.)