THE 200° LONG MAGELLANIC STREAM SYSTEM

Abstract

We establish that the Magellanic Stream (MS) is some 40 degrees longer than previously known with certainty and that the entire MS and Leading Arm (LA) system is thus at least 200 degrees long. With the GBT, we conducted a ~200 square degree, 21-cm survey at the MS-tip 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 degrees long. 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 degrees. Additionally, we find a previously unknown velocity inflection in the MS-tip near MS longitude L_MS=-120 degrees 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 degree extension of the MS-tip is ~2x10^7 Msun (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 ~10^8 Msun. 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. We estimate that the age of the ~140 degree-long MS is ~2.5 Gyr which 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. [Abridged]