HIGH-VELOCITY CLOUDS IMPACTING ONTO THE GALACTIC DISK - A NEW CLASS OF X-RAY EMITTING OBJECTS

We present observational evidence in ROSAT all-sky survey data that la rge parts of the high-velocity cloud (HVC) complex C are associated wi th soft X-ray radiation. Moreover the new Leiden/Dwingeloo northern-sk y survey shows very faint H I 21-cm line emission which connects the H VC velocity regime with the low-velocity atomic hydrogen of the galact ic disk by velocity bridges. Finally we find a close positional correl ation of soft X-ray enhancements and the atomic hydrogen velocity brid ges. Thus we obtain for the first time direct evidence that large part s of the HVC complex C are impacting onto the galactic disk. As a cons equence, the HVCs of complex C are closer to the galactic disk than pr eviously assumed. Most probably the gas of the Reynolds and/or Lockman layers are the collision partners of the HVCs.