The VLBA Galactic Plane Survey -- VGaPS

TL;DR

This paper reports a new survey using the VLBA at 24 GHz to identify and precisely locate compact extragalactic sources near the Galactic plane, developing a new software tool and providing a valuable catalog for calibration.

Contribution

Introduction of PIMA, a new software for low detection limit group delay determination, and creation of a comprehensive catalog of 327 sources for VLBI calibration near the Galactic plane.

Findings

Detected 327 sources out of 487 observed targets.

Half of the sources were also observed at 8.6 GHz and 2.3 GHz.

Position differences across frequencies are within uncertainties, with some complex sources showing different components.

Abstract

This paper presents accurate absolute positions from a 24 GHz Very Long Baseline Array (VLBA) search for compact extragalactic sources in an area where the density of known calibrators with precise coordinates is low. The goals were to identify additional sources suitable for use as phase calibrators for galactic sources, determine their precise positions, and produce radio images. In order to achieve these goals, we developed a new software package, PIMA, for determining group delays from wide-band data with much lower detection limit. With the use of PIMA we have detected 327 sources out of 487 targets observed in three 24 hour VLBA experiments. Among the 327 detected objects, 176 are within 10 degrees of the Galactic plane. This VGaPS catalogue of source positions, plots of correlated flux density versus projected baseline length, contour plots, as well as weighted CLEAN images and calibrated visibility data in FITS format, are available on the Web at http://astrogeo.org/vgaps. Approximately one half of objects from the 24 GHz catalogue were observed at dual band 8.6 GHz and 2.3 GHz experiments. Position differences at 24 GHz versus 8.6/2.3 GHz for all but two objects on average are strictly within reported uncertainties. We found that for two objects with complex structure positions at different frequencies correspond to different components of a source.