BEYOND 31 mag arcsec-2: THE FRONTIER OF LOW SURFACE BRIGHTNESS IMAGING WITH THE LARGEST OPTICAL TELESCOPES

The detection of structures in the sky with optical surface brightnesses fainter than 30 mag arcsec(-2) (3 sigma in 10 x 10 arcsec boxes; r-band) has remained elusive in current photometric deep surveys. Here we show how present-day telescopes of 10 m class can provide broadband imaging 1.5-2 mag deeper than most previous results within a reasonable amount of time (i.e., <10 hr on-source integration). In particular, we illustrate the ability of the 10.4 m Gran Telescopio de Canarias telescope to produce imaging with a limiting surface brightness of 31.5 mag arcsec(-2) (3s in 10 x 10 arcsec boxes; r-band) using 8.1 hr on source. We apply this power to explore the stellar halo of the galaxy UGC 00180, a galaxy analogous to M31 located at similar to 150 Mpc, by obtaining a radial profile of surface brightness down to mu(r) similar to 33 mag arcsec(-2). This depth is similar to that obtained using the star-counts techniques for Local Group galaxies, but is achieved at a distance where this technique is unfeasible. We find that the mass of the stellar halo of this galaxy is similar to 4 x 10(9) M-circle dot, i.e., (3 +/- 1)% of the total stellar mass of the whole system. This amount of mass in the stellar halo is in agreement with current theoretical expectations for galaxies of this kind.