HVC131+1-200: A collision of a high-velocity cloud with the galactic plane

Abstract

We report HI observations from Effeisberg, using the 100-m radiotelescope of the Max-Planck Institut fur Radioastronomie, which show evidences of a High Velocity Cloud (HVC) - Galaxy collision, in a region around l = 131°, b = +1°. They show a) a HVC, named HVC131 +1-200; b) a hole in the gas distribution at velocities around v ≃ -12 km/s; c) a HI shell surrounding the hole and d) intermediate velocity gas in the velocity range -30 < v < -25 km/s. All these features are found in the same region of the sky We believe that a possible interpretation for all these phenomena is that they were produced by a collision of HVC131 +1-200 with the galactic plane. The consequences of such a collision, predicted by several authors (Tenorio-Tagle, 1987; Meyerdierks, 1991; Comeron & Torra, 1992), are the formation of a) a forward shock moving into the galactic gas ahead; b) a dense layer of shocked gas between the HVC and the galactic gas; and c) a cavity which, due to the thermal energy originated in the forward shock, will be filled with hot low-density gas and will expand laterally. All these effects are present in the studied region in the form of the mentioned features.