Distance to the Low-velocity Cloud in the Direction of the High-velocity Compact Cloud CO--0.40--0.22

Abstract

CO--0.40--0.22 is a peculiar molecular cloud that is compact and has an extraordinary broad velocity width. It is found in the central molecular zone of our Galaxy. In this direction, there is another cloud with an H$_2$O maser spot at a lower velocity. Collision with this low-velocity cloud could be responsible for the broad velocity width of CO--0.40--0.22. We performed phase-referencing VLBI astrometry with VERA and detected the annual parallax of the H$_2$O maser spot in the low-velocity cloud to be $0.33 \pm 0.14$ mas, which corresponds to a distance of $3.07^{+2.22}_{-0.91}$ kpc from the Sun. This implies that the low-velocity cloud is located in the Galactic disk on the near side of the central molecular zone.