EVIDENCE OF A CLOUD-CLOUD COLLISION FROM OVERSHOOTING GAS IN THE GALACTIC CENTER

Abstract

We observed a cloud near the Galactic Center at (𝓁, b) = (+5.4, −0.4) with the ALMA/ACA. We took measurements of the spectral lines 12CO J = 2 → 1 , 13CO J = 2 → 1 , C18O J = 2 →_ 1, H2CO J = 303 → 202 , H2CO J = 322 → 221 , CH3OH J = 422 → 312 , OCS J = 18 → 17 and SiO J = 5 → 4. We observed a velocity bridge, evidence of a cloud-cloud collision, between two clouds at ~50 km s−1 and ~150 km s−1 in our position-velocity diagram. We found evidence of strong shocks due to the presence of SiO and weak shocks due to enhanced abundances of CH −1 3OH. We believe that the ~50 km s cloud came from gas which overshot the CMZ as it flowed in and that the cloud is colliding with the ~150 km s −1 cloud on the opposite side of the galaxy’s dust lane.