In this work, we computed the distances to three molecular clouds in the central molecular zone (CMZ), the 50 kms-1 , 20 kms-1, and the Brick clouds, and investigated their CMZ membership. We used the colour magnitude diagrams Ks versus H−Ks to compare stars detected towards the target clouds with stars detected towards three reference regions in the nuclear stellar disc (NSD) and the Galactic bulge. We used red clump (RC) stars to estimate the distance to each region.
Target regions over-plotted on a Spitzer/IRAC image at 3.6μm.
We found that all the clouds present a double RC feature. Such a double RC has been reported in previous work for the NSD, but not for the bulge adjacent to it. We exclude the possibility that the different RC features are located at significantly different distances. The obtained absolute and relative distances are compatible with the Galactic centre distance (∼8 kpc).
Histograms corresponding to the de-reddened RC stars in the analysed regions. The solid lines show a Gaussian fit to the bright RC.The numbers 1 and 2 indicate the double RC features observed in the data.
Colour magnitude diagrams Ks vs. H−Ks of the target regions: the 50 km s−1 cloud (panel a), the 20 km s−1 cloud (b), the Brick cloud (c), Control 1 (d), Control 2 (e), and the bulge region (f). The red and orange points indicate the detected double feature for the RC. The solid violet line corresponds to the reddening line of RC stars at an 8.2 kpc distance following the extinction curve from Nogueras-Lara et al. (2020b). The dashed blue line shows the extinction curve from Minniti et al. (2020). The black, violet, and blue error bars correspond to the systematics of the data and the two extinction curves, respectively.
