Distance to the Galactic centre 7$^\prime$ halo from HI absorption
Abstract
Using archival data, we have made an HI absorption study of the 7 halo surrounding the Sgr A complex, observed towards the Galactic centre (GC) region. We find strong HI absorption near velocities of 53 km s, which is due to the 3-kpc arm, placing it beyond 5 kpc from us. We further examined the HI absorption properties towards 5 different parts of the 7 halo. Absorption by +50 km s GC cloud is seen towards only 3 parts of the halo, but not towards the other 2 regions. Strong emissions in CO and CS are, however, identified toward all the above 5 parts of the halo by the +50 km s GC molecular cloud. This does show that the 7 halo is partly behind, and partly in front of the +50 km s cloud. To our knowledge, this, for the first time clearly shows the 7 halo to be located at the same distance as the +50 km s molecular cloud, i.e., at the GC region.
Cite
@article{arxiv.2506.02799,
title = {Distance to the Galactic centre 7$^\prime$ halo from HI absorption},
author = {Debangan Maji and Subhashis Roy},
journal= {arXiv preprint arXiv:2506.02799},
year = {2025}
}
Comments
Accepted for publication in ApJ