Beyond the solar circle - trends in massive star formation between the inner and outer galaxy

Abstract

We have compiled the most complete compact and ultracompact HII region catalogue to date via multiwavelength inspection of survey data. We utilize data from the recently available SASSy 850 μm survey to identify massive star-forming clumps in the outer Galaxy (RGC > 8.5 kpc) and cross-match with infrared and radio data of known UC HII regions from the RMS database. For the inner Galaxy sample (RGC < 8.5 kpc), we adopt the compact HII regions from previous works that used similar methods to cross-match ATLASGAL with either CORNISH or RMS, depending on the location within the Galactic plane. We present a new UC HII region catalogue that more than doubles the original sample size of previous work, totalling 536 embedded HII regions and 445 host clumps. We examine the distance independent values of NLy/M and Lbol/M as proxies for massive star formation efficiency and overall star formation efficiency, respectively. We find a significant trend showing that Lbol/M decreases with increasing RGC, suggesting that the overall star formation per unit mass is less in the outer Galaxy.