Luminous halos surrounding edge-on disk galaxies in the Sloan Digital Sky Survey

We present the first measurement of both major-axis and minor-axis average surface brightness profiles of low-redshift (0.009 ≤ z ≤ 0.1), edge-on Sc-Sd galaxies. The 906 objects in our sample have 90% Petrosian radii between 5 kpc and 15 kpc and were selected from the Fourth Data Release of the Sloan Digital Sky Survey. The minor-axis profile extends to 20 kpc above the disk and a limiting surface brightness of 30 mag/arcsec 2. We demonstrate that this surface brightness profile is best fit by an exponential+power-law with slope 2.3 1 0.3 in agreement with simulations and star counts around individual galaxies. We attribute the power-law component to a diffuse stellar halo and present the first measurement of such around isolated, late-type galaxies. We also divide our sample according to physical size and show that the minor-axis power-law slopes of the two size categories do not differ by more than 2sigma, also in agreement with simulations. We find that the average major-axis scale length is reap = 4.37 10.012 kpc, somewhat larger than the typical value for face-on galaxies (see, for example, Kent (1985)). We also present the first measurement of the ratio of the disk luminosity to that of the halo, and provide a context for this ratio.