The Large‐Scale Bipolar Wind in the Galactic Center

Abstract

During a 9-month campaign (1996--1997), the Midcourse Space Experiment (MSX)\nsatellite mapped the Galactic Plane at mid-infrared wavelengths (4.3--21.3um).\nHere we report evidence for a spectacular limb- brightened, bipolar structure\nat the Galactic Center extending more than a degree (170 pc at 8.0 kpc) on\neither side of the plane. The 8.3um emission shows a tight correlation with the\n3, 6 and 11 cm continuum structure over the same scales. Dense gas and dust are\nbeing entrained in a large-scale bipolar wind powered by a central starburst.\nThe inferred energy injection at the source is ~10^54/kappa erg for which\n\\kappa is the covering fraction of the dusty shell (kappa <= 0.1).\n There is observational evidence for a galactic wind on much larger scales,\npresumably from the same central source which produced the bipolar shell seen\nby MSX. Sofue has argued that the North Polar Spur -- a thermal x-ray/radio\nloop which extends from the Galactic Plane to b = +80 deg -- was powered by a\nnuclear explosion (1-30 x 10^55 erg) roughly 15 Myr ago. We demonstrate that an\nopen-ended bipolar wind (~10^55 erg), when viewed in near-field projection,\nprovides the most natural explanation for the observed loop structure. The\nROSAT 1.5 keV diffuse x-ray map over the inner 45 deg provides compelling\nevidence for this interpretation. Since the faint bipolar emission would be\nvery difficult to detect beyond the Galaxy, the phenomenon of large-scale\ngalactic winds may be far more common than has been observed to date.\n