SEDIGISM-ATLASGAL: dense gas fraction and star formation efficiency across the Galactic disc

Abstract

By combining two surveys covering a large fraction of the molecular material in the Galactic disk we investigate the role the spiral arms play in the star formation process. We have matched clumps identified by ATLASGAL with their parental GMCs as identified by SEDIGISM, and use these giant molecular cloud (GMC) masses, the bolometric luminosities, and integrated clump masses obtained in a concurrent paper to estimate the dense gas fractions (DGFgmc = ∑Mclump/Mgmc) and the instantaneous star forming efficiencies (i.e., SFEgmc = ∑Lclump/Mgmc). We find that the molecular material associated with ATLASGAL clumps is concentrated in the spiral arms (∼60 per cent found within ±10 km s−1 of an arm). We have searched for variations in the values of these physical parameters with respect to their proximity to the spiral arms, but find no evidence for any enhancement that might be attributable to the spiral arms. The combined results from a number of similar studies based on different surveys indicate that, while spiral-arm location plays a role in cloud formation and H i to H2 conversion, the subsequent star formation processes appear to depend more on local environment effects. This leads us to conclude that the enhanced star formation activity seen towards the spiral arms is the result of source crowding rather than the consequence of a any physical process.

The formation and early evolution of embedded star clusters in spiral galaxies

“…Previous work has found that spiral arms do not typically make a large difference to the global star formation rate in numerical simulations galaxies (Dobbs et al 2011;Pettitt et al 2017;Tress et al 2020;Kim et al 2020), rather the gas is simply gathered together in the spiral arms (Elmegreen & Elmegreen 1986;Vogel et al 1988). Observations of nearby arms in our Galaxy suggest they do not have a significant role (Eden et al 2013(Eden et al , 2015Urquhart et al 2021), however there is some recent observational evidence that spiral arms have some impact on star formation rates over larger galaxy samples (Yu et al 2021). Colombo et al (2014) also find more massive, and strongly star forming GMCs in the spiral arms of M51 compared to the inter-arm regions.…”

The formation and early evolution of embedded star clusters in spiral galaxies

“…Previous work has found that spiral arms do not typically make a large difference to the global star formation rate in numerical simulations galaxies (Dobbs et al 2011;Pettitt et al 2017;Tress et al 2020;Kim et al 2020), rather the gas is simply gathered together in the spiral arms (Elmegreen & Elmegreen 1986;Vogel et al 1988). Observations of nearby arms in our Galaxy suggest they do not have a significant role (Eden et al 2013(Eden et al , 2015Urquhart et al 2021), however there is some recent observational evidence that spiral arms have some impact on star formation rates over larger galaxy samples (Yu et al 2021). Colombo et al (2014) also find more massive, and strongly star forming GMCs in the spiral arms of M51 compared to the inter-arm regions.…”

ATLASGAL -- Evolutionary trends in high-mass star formation

“…The SEDIGISM survey is a 13 CO and C 18 O (2-1) survey conducted with the APEX telescope. 1 In a previous paper, (Urquhart et al 2021) we combined the ATLASGAL sample of clumps with the reduced data cubes provided by the SEDIGISM catalogue to extract spectra towards clumps where the two surveys overlapped (i.e. 300 • < < 18 • and |b| < 0.5 • ).…”