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Collaborators : Nitya Kallivayalil Lars Hernquist Brant Robertson T.J. Cox

The Orbital Evolution of the Magellanic Clouds and the Implications for the Formation of the Stream. Gurtina Besla Harvard CfA. Collaborators : Nitya Kallivayalil Lars Hernquist Brant Robertson T.J. Cox Roeland P. van der Marel Charles Alcock. Putman et al (2003).

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Collaborators : Nitya Kallivayalil Lars Hernquist Brant Robertson T.J. Cox

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  1. The Orbital Evolution of the Magellanic Clouds and the Implications for the Formation of the Stream Gurtina Besla Harvard CfA Collaborators: Nitya Kallivayalil Lars Hernquist Brant Robertson T.J. Cox Roeland P. van der Marel Charles Alcock Putman et al (2003) The Globular Cluster-Dwarf Galaxy Connection, August 2007

  2. Outline • Motivation: New PM and halo models • Results: Clouds are on their first passage • Implications for the Magellanic Stream S L

  3. LMC Proper Motions: K1 measurement is accurate to 5% N is not consistent with 0 New velocity ~1.3 times higher

  4. Implications of the K1 results for the Classical Picture GN96, vdM02 : Apo = 110-120 kpc T = 1.5 Gyr Isothermal sphere model K1 mean: Apo = 220 kpc T = 3 Gyr An isothermal sphere model is likely inaccurate at large distances.

  5. 4-component MW model Mvir = 1012 M Consistent with Klypin et al (2002) Consistent with known obs. constraints Knapp et al 1985

  6. New MW model (static)+ new PM: New MW model: how do the old orbits change? Fiducial 378 km/s 450 km/s T~6-10 Gyr Apo~400 kpc Only one previous passage 310 km/s The LMC is on its FIRST passage about the MW

  7. Implications for the Formation of the Magellanic Stream 1) The LMC’s past orbit does NOT trace the current location of the MS on the plane of the sky 1) Orbit traces the MS on the plane of the sky (uniquely requires LMC’s N = 0) (W, N) K1; vdM02 N Magellanic Stream LMC GN96 W E Orbit deviates from the MS by ~ 10º SMC This result is independent of the new HST measurements AND the MW model. Putman et al (2003) S

  8. 2) Vlsr orbit ≠ Vlsr MS Putman et al (2003; P03)

  9. Implications for the Magellanic Stream (MS) Issue: the strength of the MW/L/SMC interaction is severely limited Tidal Stripping: NOT VIABLE - No stars & tidal radius is too large along fiducial orbits. - Most of the mass is lost at PERICENTER Ram Pressure Stripping (v2): LIKELYNOT VIABLE - Requires high gas densities & no Leading Arm Feature - Instantaneous ram pressure is insufficient without tides. ALTERNATIVES Stellar Feedback: Olano (2004), Nidever et al (2007), Lehner & Howk (2007) Intercloud Region: Tides+ram pressure; timescale is ~300 Myr (formation of Magellanic Bridge)

  10. Conclusions The new PM measurements by Kallivayalil et al (2006) strongly suggest that the Clouds are on their first passage about the MW. OR The MW is substantially more massive than previously believed (>2 x 1012 M) and the proper motions are discrepant by 4. The past orbits of the Clouds DO NOT trace the line of sight velocities or location of the MS. This result is independentof the halo model and the new velocities. All formation scenarios for the MS need to be re-evaluated in light of the new orbital history.

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