The dangers of artificially fixing the Milky Way's center of mass

F. A. GÓMEZ; G. BESLA; D. D. CARPINTERO; Á. VILLALOBOS; B. W. O'SHEA; E. F. BELL

Santiago

Congreso; VI Reunión de Astronomía Dinámica en Latinoamérica; 2014

Conicyt - Fondo Gemini - Inst. Milenio de Astrofísica

Motivated by recent studies suggesting that the LMC could be significantly more massive than previously thought, we explore whether the approximation of an inertial Galactocentric reference frame is still valid in the presence of such a massive LMC. We find that previous estimates of the LMC?s orbital period and apocentric distance derived assuming a fixed Milky Way are significantly shortened for models where the Milky Way is allowed to move freely in response to the gravitational pull of the LMC. Holding other parameters fixed, the fraction of models favoring first infall is reduced. Due to this interaction, the Milky Way center of mass within the inner 50 kpc can be significantly displaced in phase-space in a very short period of time that ranges fom 0.3 to 0.5 Gyr by as much as 20 kpc and 70 km/s. Furthermore, we show that the gravitational pull of the LMC and response of the Milky Way are likely to make significant differences to the orbit and phase space distribution of tidal debris from the Sgr dwarf galaxy, and are larger than previous estimates based on accounting for the torque of the LMC alone. As a result, Sgr deposits debris in regions of the sky that are not aligned with the present-day Sgr orbital plane. In addition, we find that properly accounting for the movement of the Milky Way around its common center of mass with the LMC significantly modifies the angular distance between apocenters and tilts its orbital pole, possibly alleviating tensions between previous models and observations. While these models are preliminary in nature, they highlight the central importance of accounting for the mutual gravitational interaction between theMWand LMC when modeling the kinematics of objects in the MilkyWay and local group.