Galactic structure from photometric surveys

Seventeen of twenty known or suspected dwarf galaxy satellites of the Milky Way were discovered through photometric images. Six significant tidal streams are known in the Galactic spheroid, all of which were discovered through photometric surveys. At present, only photometric surveys provide enough sky coverage and depth to probe the shape of the Milky Way. We argue that the Virgo Stellar Stream, which might be a stream or a disrupting dwarf galaxy, has a center 14-19 kpc from the Sun in the direction (l, b) = (300◦, 64◦), using photometry from the Sloan Digital Sky Survey (SDSS) and the Sloan Extension for Galactic Understanding and Exploration (SEGUE). In the process, we demonstrate the importance of large, deep, multi-color, public photometric sky surveys with precision color information. Currently, the most urgent need is for data in the southern hemisphere and at low Galactic latitude. Deeper surveys would also be useful.