HII Regions in the Pilot Ku-band Galactic Reconnaissance Survey

Abstract

This thesis presents data from the Ku-band Galactic Reconnaissance Survey (KuGARS), a large area survey observed on the Jansky Very Large Array (JVLA). KuGARS is the first galactic plane survey to explore the sub-arcsecond and sub-mJy regime at 14 GHz. We have described the development of the data reduction procedures in CASA for the On the Fly (OTF) mapping method used for KuGARS. Included in our discussion are the calibration and imaging processes: as the OTF mapping method has not been extensively explored we have gone through several steps to present quality assurance of the calibration. Due to the large volume of data, we focused on a pilot study of the area surrounding the W49A massive star forming region and a subset of the final frequency range.

Using an automated source finding algorithm, AEGEAN (Hancock et al., 2012), we have detected 35 islands with 57 components. We compared the brightest of these sources to the literature to determine their nature. In order to carry out a robust analysis, we compared our detections to observations over multiple frequencies. Comparing to GLIMPSE and Herschel showed our sources deeply embedded in 8μm and 70μm emission, respectively, which indicate heated dust and therefore infer star formation. We further, through the SIMBAD database, found several star formation tracers, including: Masers, YSOs, and HII regions, associated with our KuGARS detections. Our comparison with CORNISH and De Pree et al. (1997) revealed previous detections of these sources as HII regions with similar morphologies to KuGARS. We have detected and identified 2 spherical or unresolved HII regions, and 2 irregular HII regions in the ring of HII regions (W49 North), 1 isolated spherical/unresolved HII region, and 1 cometary HII region in W49 South. We find that one of the objects (source B) is recovered by KuGARS and De Pree et al. (1997) but not in CORNISH. This source, which is undetected at 5GHz and below has a steep positive spectrum (α = 1:1) and has broad radio recombination lines with line widths (> 45kmsð€€€1) (De Pree et al., 1997). It, therefore, must be a Hypercompact HII region and thus demonstrates KuGARS capability to detect Hypercompact HII regions.