M.E. Putman, PASA, 17 (1), 1.
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Magellanic Complexes
The three high velocity complexes which are classified as Magellanic debris are the Magellanic Bridge, the Magellanic Stream and the Leading Arm (see Putman (2000) for a review). The Magellanic Bridge (see Figure 1) is a M filament of neutral hydrogen which joins the two Magellanic Clouds and has a velocity gradient which proceeds from 125 km at the tail of the SMC or Shapley's Wing, to km at the extended arm of the LMC. Tidal models predict that the Bridge was pulled from the SMC during a close encounter between the two Clouds 0.2 Gyr ago (Gardiner & Noguchi 1996). The HIPASS data reveal new structure along the Bridge, as well as an extension from the LMC which suggests that the Bridge is made of both SMC and LMC material. The Bridge is the only high-velocity cloud which is known to contain stars, and the age of many of the stellar concentrations (10 - 25 Myr) indicates that the Bridge is a star forming region (Grondin, Demers and Kunkel 1992).
The HIPASS map of the Magellanic Stream is shown in Figure 2. The Stream trails the Magellanic Clouds for over 100 and is not a confined filament as previous maps depict (Mathewson, Cleary and Murray 1974), but a complex network of filaments and clumps. The beginning of the Stream consists of multiple filaments and bow-shock structures as it spews from the northern side of the SMC and Bridge at
vlsr = 90 - 240 km . Most of these filaments end at declination
, but the main filament of the Stream continues to march northward, its bifurcated structure diminishing towards the northern tip1. Dense clumps follow the Stream in position and velocity, except for the region of the Sculptor Group which will be discussed in the next section. There are no stars in the Stream (e.g. Guhathakurta & Reitzel 1998), but H appears to be detectable at every location along the Stream with a column density greater than 1019 M (Weiner & Williams 1996; Bland-Hawthorn & Maloney 1999a). These detections, together with the fact that no [OIII] has been detected from the Stream, indicates that the Stream is being ionized by photons escaping from the Galaxy (Bland-Hawthorn & Maloney 1999b).
The third Magellanic complex is a natural tidal counterpart to the Stream, and is called the Leading Arm (see Figure 3). This feature is more diffuse than the Stream and its leading position indicates that tidal forces are the dominant mechanism responsible for forming the Magellanic Stream. This complex was only recently confidently defined as Magellanic debris (Putman et al. 1998), as the course resolution and observing grid used in the previous surveys missed the filaments between the clumps and the connection to the Magellanic Clouds. Further evidence that this feature is of Magellanic origin is the metallicity determination of Lu et al. (1998), using the background galaxy NGC 3783.
Next Section: Is it all Magellanic
Title/Abstract Page: The Magellanic System's Interactive
Previous Section: Introduction
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