ATLASGAL -- Evolutionary trends in high-mass star formation

Abstract

ATLASGAL is a 870-µm dust survey of 420 square degrees of the inner Galactic plane and has been used to identify ∼10 000 dense molecular clumps. Dedicated follow-up observations and complementary surveys are used to characterise the physical properties of these clumps, map their Galactic distribution and investigate the evolutionary sequence for highmass star formation. The analysis of the ATLASGAL data is ongoing: we present an up-todate version of the catalogue. We have classified 5007 clumps into four evolutionary stages (quiescent, protostellar, young stellar objects and HII regions) and find similar numbers of clumps in each stage, suggesting a similar lifetime. The luminosity-to-mass (L bol /M fwhm ) ratio curve shows a smooth distribution with no significant kinks or discontinuities when compared to the mean values for evolutionary stages indicating that the star-formation process is continuous and that the observational stages do not represent fundamentally different stages or changes in the physical mechanisms involved. We compare the evolutionary sample with other star-formation tracers (methanol and water masers, extended green objects and molecular outflows) and find that the association rates with these increases as a function of evolutionary stage, confirming that our classification is reliable. This also reveals a high association rate between quiescent sources and molecular outflows, revealing that outflows are the earliest indication that star formation has begun and that star formation is already ongoing in many of the clumps that are dark even at 70 µm.

The SEDIGISM survey: a search for molecular outflows

“…A comprehensive database of ∼ 10163 massive star-forming clumps has been compiled, the ATLASGAL compact source catalogue ( CSC; Contreras et al 2013;Csengeri et al 2014;Urquhart et al 2014), which allows us to undertake a search for CO outflow activity toward the clumps. Furthermore, the physical properties (e.g., distance, clump mass, column density, bolometric luminosity, density) have been measured and the evolutionary stages classified (König et al 2017;Urquhart et al 2018Urquhart et al , 2021b. We use this well-characterized sample of clumps to conduct a statistical analysis of correlations between outflow parameters and clump properties for a large and representative sample of massive star-forming clumps in different evolutionary stages.…”

“…1, we overlaid the surveyed region (white shaded), the coordinates of the total 4120 clumps (black dots), and the selected 2052 clumps (yellow circles) on the artist's impression image of the Galactic structure to put the sampled clumps into a Galactic context. The physical properties of these clumps are presented in Table 1, which were calculated in Urquhart et al (2018) and Urquhart et al (2021b). For the properties calculated in both Urquhart et al (2018) and Urquhart et al (2021b), we adopted the values in Urquhart et al (2021b), as they were recalculated using the FWHM sizes (determined from the pixels above the half-power level), to eliminate any observational bias that would make the clumps appear to increase in size and have decreasing volume densities with evolution.…”

“…The physical properties of these clumps are presented in Table 1, which were calculated in Urquhart et al (2018) and Urquhart et al (2021b). For the properties calculated in both Urquhart et al (2018) and Urquhart et al (2021b), we adopted the values in Urquhart et al (2021b), as they were recalculated using the FWHM sizes (determined from the pixels above the half-power level), to eliminate any observational bias that would make the clumps appear to increase in size and have decreasing volume densities with evolution. Full details are available in Fig.…”

“…The high-velocity outflow wings are defined by the velocities where the observed 13 CO profile is Notes. These physical properties are taken from Urquhart et al (2018) and Urquhart et al (2021b), with uncertainties of a factor of a few. The information of maser associations are from Billington et al (2020), with the detection levels of 15-167 mJy (1σ) for H 2 O (Walsh et al 2011(Walsh et al , 2014 and ∼170 mJy (1σ) for CH 3 OH maser (Green et al 2009).…”