Where is the Western Part of the Galactic Center Lobe Located really?

TL;DR

This paper investigates the true location of the Western Part of the Galactic Center Lobe, concluding it is a nearby giant HII region in the Galactic disk rather than part of the central structure.

Contribution

The study combines radio observations and visual extinction maps to determine the WPGCL's position, challenging previous assumptions of its location in the Galactic Center.

Findings

WPGCL is located within a few kpc from us.

It is likely a giant HII region in the Galactic disk.

The structure is not part of the Galactic Center region.

Abstract

The Galactic Center Lobe (GCL) is a peculiar object widely protruding from the Galactic plane toward the positive Galactic latitude, which had been found toward the Galactic Center (GC) in the early days of the radio observation. The peculiar shape has suggested any relation with historical events, star burst, large explosion and so on in the GC. However, the issue whether the GCL is a single large structure located in the GC region is not yet settled conclusively. In the previous observations, the silhouette against the low frequency emission was found in the western part of the GCL (WPGCL), This suggests that the part is located in front of the GC region. On the other hand, the LSR velocity of the radio recombination line toward it was found to be as low as 0 kms$^{-1}$. However, these observations cannot determine the exact position on the line-of-sight. There is still another possibility that it is in the near side area of the GC region. In this analysis, we compare these results with the visual extinction map toward the GC. We found that the distribution of the visual extinction larger than 4 mag. clearly corresponds to the silhouette of the WPGCL. The WPGCL must be located at most within a few kpc from us and not in the GC region. This would be a giant HII region in the Galactic disk.