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

## TL;DR

This study measures the distance to a low-velocity molecular cloud near the Galactic center using VLBI astrometry, revealing its location in the Galactic disk and suggesting a collision with a peculiar high-velocity cloud as the cause of its broad velocity width.

## Contribution

First direct distance measurement to the low-velocity cloud near the Galactic center using VLBI astrometry, clarifying its position relative to the central molecular zone.

## Key findings

- Low-velocity cloud is approximately 3.07 kpc away from the Sun.
- The cloud is located in the Galactic disk on the near side of the central molecular zone.
- The distance supports the collision hypothesis for the broad velocity width of 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.