2010ApJ...723.1618N

We establish with certainty that the Magellanic Stream (MS) is some 40° longer than previously known and that the entire MS and Leading Arm system is thus at least 200° long. With the Green Bank Telescope (GBT), we conducted a ∼200 deg², 21 cm survey at the tip of the MS to substantiate the continuity of the MS between the Hulsbosch & Wakker data and the MS-like emission reported by Braun & Thilker. Our survey, in combination with the Arecibo survey by Stanimirovic et al., shows that the MS gas is continuous in this region and that the MS is at least ∼140° long. The MS tip is composed of a multitude of forks and filaments. We identify a new filament on the eastern side of the MS that significantly deviates from the equator of the MS coordinate system for more than ∼45°. Additionally, we find a previously unknown velocity inflection in the MS tip near MS longitude L_MS~-120° at which the velocity reaches a minimum and then starts to increase. We find that five compact high-velocity clouds cataloged by de Heij et al. as well as Wright's Cloud are plausibly associated with the MS because they match the MS in position and velocity. The mass of the newly confirmed ∼40° extension of the MS tip is ∼2x10⁷ M_☉(d/120 kpc)² (including Wright's Cloud increases this by ∼50%) and increases the total mass of the MS by ∼4%. However, projected model distances of the MS at the tip are generally quite large and, if true, indicate that the mass of the extension might be as large as ∼10⁸ M_☉. From our combined map of the entire MS, we find that the total column density (integrated transverse to the MS) drops markedly along the MS and follows an exponential decline with L_MS of = 5.9 x 10²¹exp(L_MS/19°.3)/cm2. Under the assumption that the observed sinusoidal velocity pattern of the LMC filament of the MS is due to the origin of the MS from a rotating LMC, we estimate that the age of the ∼140° long MS is ∼2.5 Gyr. This coincides with bursts of star formation in the Magellanic Clouds and a possible close encounter of these two galaxies with each other that could have triggered the formation of the MS. These newly observed characteristics of the MS offer additional constraints for MS simulations. In the Appendix, we describe a previously little discussed problem with a standing wave pattern in GBT H I data and detail a method for removing it.