First detection of the [CII] 158 mum line in the intermediate-velocity cloud Draco

High-latitude intermediate-velocity clouds (IVCs) are part of the Milky Way's halo and originate from either a galactic fountain process or extragalactic gas infall. They are partly molecular and can most of the time be identified in CO. Some of these regions also exhibit high-velocity cloud (HVC) gas, which is mostly atomic, and gas at local velocities (LVCs), which is partly atomic and partly molecular. We conducted a study on the IVCs Draco and Spider, both were exposed to a very weak UV field, using the spectroscopic receiver upGREAT on the Stratospheric Observatory for Infrared Astronomy (SOFIA). The 158 mu m fine-structure line of ionized carbon ( was observed, and the results are as follows: In Draco, the line was detected at intermediate velocities (but not at local or high velocities) in four out of five positions. No emission was found at any velocity in the two observed positions in Spider. To understand the excitation conditions of the gas in Draco, we analyzed complementary CO and data as well as dust column density and temperature maps from Herschel . The observed intensities suggest the presence of shocks in Draco that heat the gas and subsequently emit in the cooling line. These shocks are likely caused by the fast cloud's motion toward the Galactic plane that is accompanied by collisions between clouds. The nondetection of in the Spider IVC and LVC as well as in other low-density clouds at local velocities that we present in this paper (Polaris and Musca) supports the idea that highly dynamic processes are necessary for excitation in UV-faint low-density regions.