A new distance to the Brick, the dense molecular cloud G0.253+0.016

TL;DR

This study precisely measures the distance to the dense molecular cloud G0.253+0.016 (The Brick) using near-infrared observations, revealing it is closer than previously assumed, which impacts understanding of star formation in the Galactic center.

Contribution

The paper provides a new, more accurate distance measurement to the Brick cloud using stellar observations, challenging prior assumptions based on dynamical models.

Findings

The Brick cloud is at 7.20 kpc from the Sun, closer than the assumed 8.2 kpc.

The cloud is significantly offset from the Galactic center, affecting star formation models.

The cloud's lack of star formation contradicts the Kennicutt-Schmidt relation.

Abstract

We analyse the near infrared colour magnitude diagram of a field including the giant molecular cloud G0.253+0.016 (a.k.a. The Brick) observed at high spatial resolution, with HAWK-I at the VLT. The distribution of red clump stars in a line of sight crossing the cloud, compared with that in a direction just beside it, and not crossing it, allow us to measure the distance of the cloud from the Sun to be 7.20, with a statistical uncertainty of +/-0.16 and a systematic error of +/-0.20 kpc. This is significantly closer than what is generally assumed, i.e., that the cloud belongs to the near side of the central molecular zone, at 60 pc from the Galactic center. This assumption was based on dynamical models of the central molecular zone, observationally constrained uniquely by the radial velocity of this and other clouds. Determining the true position of the Brick cloud is relevant because this is the densest cloud of the Galaxy not showing any ongoing star formation. This puts the cloud off by 1 order of magnitude from the Kennicutt-Schmidt relation between the density of the dense gas and the star formation rate. Several explanations have been proposed for this absence of star formation, most of them based on the dynamical evolution of this and other clouds, within the Galactic center region. Our result emphasizes the need to include constraints coming from stellar observations in the interpretation of our Galaxy central molecular zone.