OGHReS: Star formation in the Outer Galaxy (ℓ = 250○-280○)

Abstract

Abstract We have used data from the Outer Galaxy High-Resolution Survey (OGHReS) to refine the velocities, distances, and physical properties of a large sample of 3 584 clumps detected in far infrared/submillimetre emission in the Hi-GAL survey located in the ℓ = 250○ − 280○ region of the Galactic plane. Using 12CO and 13CO spectra, we have determined reliable velocities to 3 412 clumps (95 per cent of the sample). In comparison to the velocities from the Hi-GAL catalogue, we find good agreement for 80 per cent of the sample (within 5 km s−1). Using the higher resolution and sensitivity of OGHReS has allowed us to correct the velocity for 632 clumps and provide velocities for 687 clumps for which no velocity had been previously allocated. The velocities are used with a rotation curve to refine the distances to the clumps and to calculate the clumps’ properties using a distance-dependent gas-to-dust ratio. We have determined reliable physical parameters for 3 200 outer Galaxy dense clumps (∼90 per cent of the Hi-GAL sources in the region). We find a trend of decreasing luminosity-to-mass ratio with increasing Galactocentric distance, suggesting the star formation efficiency is lower in the outer Galaxy or that it is resulting in more lower mass stars than in the inner Galaxy. We also find a similar surface density for protostellar clumps located in the inner and outer Galaxy, revealing that the surface density requirements for star formation are the same across the Galactic disc.