The Many Streams of the Magellanic Stream

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We present results from neutral hydrogen (H I) observations of the tip of the Magellanic Stream (MS), obtained with the Arecibo telescope as a part of the ongoing survey by the consortium for Galactic studies with the Arecibo L-band Feed Array. We find four large-scale, coherent H I streams, extending continuously over a length of 20°, each stream possessing different morphology and velocity gradients. The newly discovered streams provide strong support for the tidal model of the MS formation by Connors et al. (2006), who suggested a spatial and kinematic bifurcation of the MS. The observed morphology and kinematics suggest that three of these streams could be interpreted as a three-way splitting of the main MS filament, while the fourth stream appears much younger and may have originated from the Magellanic Bridge. We find an extensive population of H I clouds at the tip of the MS. Two-thirds of clouds have an angular size in the range 3.5'-10'. We interpret this as being due to thermal instability, which would affect a warm tail of gas trailing through the Galactic halo over a characteristic timescale of a few Myr to a few hundred Myr. We show that thermal fragments can survive in the hot halo for a long time, especially if surrounded by a <106 K halo gas. If the observed clumpy structure is mainly due to thermal instability, then the tip of the MS is at a distance of ~70 kpc. A significant fraction of H I clouds at the tip of the MS show multiphase velocity profiles, indicating the coexistence of cooler and warmer gas.