The ATCA/VLA OH 1612 MHz survey. III. Northern Galactic Plane

TL;DR

This survey of the northern Galactic Plane using the VLA and ATCA detected 286 OH maser sources, including many new detections, providing valuable data on galactic structure and maser properties.

Contribution

It presents the final part of a comprehensive OH 1612 MHz survey of the northern Galactic Plane, with systematic observations, data analysis, and source identification, expanding the catalog of galactic masers.

Findings

Detected 286 OH maser sources, 161 new detections.

Found evidence for the Galactic Bar extending to higher longitudes.

Achieved 75% detection efficiency compared to previous surveys.

Abstract

We present observations of the region between 5deg < l < 45deg and |b| < 3deg, in the OH 1612 MHz line, taken from 1993 to 1995 with the VLA. These observations are the last part of a larger survey, covering |l| < 45deg and |b| < 3deg, with the ATCA and the VLA. The region was systematically observed on a 30'x30' grid in (l,b) and the resulting coverage was 92%, with 965 pointings. We found 286 OH--masing objects, 161 of which are new detections and 207 have reliable IRAS point-source identifications. The outflow velocity was determined for 276 sources. A total of 766 sources were detected in the combined ATCA/VLA survey, of which 29 were detected in two regions of the survey. The source tables and spectra may be downloaded from http://msowww.anu.edu.au/~msevenst/pubs.html In this article we analyse the data statistically and give identifications with known sources where possible. The efficiency of this VLA survey is 75% of that of the ATCA Bulge survey. This efficiency was determined by comparing the detections in the region where the two surveys overlap. The completeness- and error characteristics are similar, though less homogeneous, except for the much larger errors in the flux densities. The relatively large surface number density found in the northern disk, suggests that we can see the Bar extending to higher longitudes on this side of the galactic Centre.