Surface photometry of edge-on galaxies: IC 5249 and ESO 404-G18

We present the results of BRI CCD surface photometry of two late type edge-on galaxies, IC 5249 and ESO 404-G18, which are very thin and almost perfectly edge-on. Surface brightness and color profiles along the major and minor axes, and vertical profiles at various distances from the galactic center are examined. Unlike most other edge-on spirals, both galaxies show no sign of a dust lane. From the color profiles, the overall contribution of dust turns out to be very weak in these systems. The vertical profiles have been found to demonstrate clearly an excess of light at small z over the isothermal model suggested by van der Kruit and Searle. A simple exponential distribution model seems to give a better fit for the overall trend of the z dependence of light. The scale height of their disks does not change with distance from the galactic center like other spirals. However a thick disk component found in earlier type disk galaxies is not seen in either of these systems. The major axis profile of IC 5249 demonstrates a peculiar two-component structure with an exponential inner disk where the change of surface brightness is slow and an exponential outer disk with a steep change of surface brightness. The very large scale length of the inner disk is considered in relation to its low surface brightness. A systematic further study of low surface brightness disk galaxies is required for a firm conclusion regarding the correlation between large disk scale length and overall surface brightness.