# Beyond the Solar Circle $-$ Trends in Massive Star Formation Between the Inner and Outer Galaxy

## TL;DR

This study compiles a comprehensive catalog of HII regions across the Galaxy, revealing that star formation efficiency decreases with distance from the Galactic center, especially in the outer regions.

## Contribution

It provides the largest catalog of embedded HII regions to date and analyzes star formation trends across the inner and outer Galaxy.

## Key findings

- Star formation efficiency decreases with Galactocentric radius.
- The new catalog more than doubles previous sample sizes.
- Outer Galaxy regions show lower star formation per unit mass.

## Abstract

We have compiled the most complete compact and ultracompact HII region catalogue to date via multi-wavelength inspection of survey data. We utilise data from the recently available SASSy 850$\mu$m survey to identify massive star forming clumps in the outer Galaxy ($R_{\rm{GC}}>8.5$ kpc) and cross-match with infrared and radio data of known UC HII regions from the RMS database. For the inner Galaxy sample ($R_{\rm{GC}}<8.5$ 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, totaling 536 embedded HII regions and 445 host clumps. We examine the distance independent values of N$_{\rm{Ly}}/$M and L$_{\rm{bol}}/$M as proxies for massive star formation efficiency and overall star formation efficiency, respectively. We find a significant trend showing that L$_{\rm{bol}}/$M decreases with increasing $R_{\rm{GC}}$, suggesting that the overall star formation per unit mass is less in the outer Galaxy.