Can Galactic Tides Inflate the Apparent $M/L$'s of Dwarf Galaxies?

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Session 57 -- Galaxies III
Oral presentation, Thursday, January 13, 10:15-11:45, Salon IV Room (Crystal Gateway)

[57.01] Can Galactic Tides Inflate the Apparent $M/L$'s of Dwarf Galaxies?

S. Piatek, C. Pryor (Rutgers University)

Dwarf spheroidal galaxies (dSph's; hereafter), companions of the Milky Way, have unusually high apparent mass-to-light ratios, ($M/L$'s; hereafter). For example, the two closest dSph's, Draco and Ursa Minor, have $M/L$'s $\sim 100$. Such large apparent $M/L$'s may indicate that dSph's contain a great deal of dark matter or that they are not in a virial equilibrium, e.g., due to galactic tides. In this work we investigate whether galactic tides can elevate the apparent $M/L$'s in dwarf spheroidals. We find that tides can affect the structure, the kinematics, and the apparent $M/L$ in a dSph, however, only under very special circumstances: the dSph must have an intrinsic $M/L$ of about 1.0, it must be very near its perigalacticon, and it must be just disintegrating; it is unlikely that four out of eight dSph's should exist in these special circumstances. However, the ultimate test of the importance of tides in dSph's will come from searches for the kinematic signatures of tides in these galaxies. Tides produce large ordered motions rather than large random motions. A clear signature of these motions is apparent rotation.

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