AAS 202nd Meeting, May 2003
Session 26 Galactic Center, Galactic Halo
Poster, Tuesday, May 27, 2003, 10:00am-6:30pm, West Exhbit Hall

## [26.05] Tidal Tails and Ptolemy: a New View of Galactic Streams

D. F. Bartlett (University of Colorado)

Astronomers have recently delineated three tidal streams in the halo of the Milky Way: the Sagittarius (Ibata et al 1994), the Pal 5 (Odenkirchen et al 2001), and the Monoceros (Yanny et al 2003). During the same time I have been developing an alternative to Newtonian gravity; one which ameliorates the need for dark matter (Bartlett 2001 & posters at AAS 199, 200, & 201). Here the usual Newtonian potential is replaced with \phi = -(GM/r) cos (2 \pi r/\lambdao), where \lambdao = 425 pc.

A consequence of this ''sinusoidal potential'' is that stars far from the galactic center must be traveling in nearly circular orbits. Otherwise they cannot be bound to the Galaxy. Alternatively, their azimuthal velocity, v\phi, need not be near the canonical 225 km/s. I shall show how the observed tidal structures for Pal 5 and Monoceros are consistent with the sinusoidal potential. A deeply plunging "rosette" orbit for the Sagittarius dwarf spheroidal is not. The observed Northern stream requires a separate progenitor. This possibility has already been suggested elsewhere (Martinez-Delgado et al 2001).

I also will discuss how the strong tidal forces of the sinusoidal potential help in understanding structures in external galaxies. These include the classic Whirlpool and Cartwheel galaxies and the newly discoverd ring in NGC 5907 (Shang et al 1998).

Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.