Optical and 21-cm observations of high-velocity gas towards subdwarfs in the halo and early-type stars in the disk.

We present a study of high-velocity gas in the direction of 13 halo sub-dwarfs located at |z|=~0.5-2kpc and of 8 early-type stars in the Galactic disk at d=~1-4kpc. For each line of sight of our sample we collected Caii and Nai absorption spectra with the 2.5-m Isaac Newton Telescope at La Palma (Spain) and HI 21-cm emission profiles with the 100-m radiotelescope at Effelsberg (Germany). The faint sub-dwarfs (m_V_=~11-14) are observed for the first time at relatively high spectral resolution (=~25-30km/s) in the optical. By comparing the optical absorptions (or upper limits) with the 21-cm emissions, we constrain the distances to the concentrations of neutral gas at high velocity named Complex C, Complex H, and for high velocity gas located between the Cohen Stream and the Magellanic Stream. We find new evidence for gas at intermediate velocity in the halo and in the disk of our Galaxy.