Disk-Halo interaction: The molecular clouds in the Galactic center region

Abstract

From a large-scale study of the Galactic center (GC) region in SiO(2 - 1), HCO+(1 - 0), and H13CO+(1 - 0), we identify shock regions as traced by the enhancement of SiO emission. We selected 9 positions called by us as "interaction regions", because they mark the places where gas in the GC could be interacting with gas coming from higher latitude ("disk-halo interaction") or from larger galactocentric radius. These positions were studied using the 12C/13C isotopic ratio to trace gas accretion/ejection. We found a systematically higher 12C/13C isotopic ratio (> 40) toward the interaction regions than for the GC "standard" molecular clouds (20 - 25). These high isotopic ratios are consistent with the accretion of the gas from higher galactic latitudes or from larger galactocentric distances. There are two kinetic temperature regimes (one warm at ∼ 200 K and one cold at ∼ 40 K) for all the positions, except for the positions associated to the giant molecular loops where only the warm component is present. Relative molecular abundances suggest that the heating mechanism in the GC is related to shocks. We mapped one molecular cloud placed at the foot points of the giant molecular loops in 3-mm molecular lines to reveal the morphology, chemical composition and the kinematics of the shocked gas.