ATLASGAL - star forming efficiencies and the Galactic star formation rate

Abstract

The ATLASGAL survey has characterised the properties of approximately 1000 embedded H ii regions and found an empirical relationship between the clump mass and bolometric luminosity that covers 3–4 orders of magnitude. Comparing this relation with simulated clusters drawn from an initial mass function and using different star formation efficiencies we find that a single value is unable to fit the observed luminosity to mass (L/M) relation. We have used a Monte Carlo simulation to generate 200,000 clusters using the L/M-ratio as a constraint to investigate how the star formation efficiency changes as a function of clump mass. This has revealed that the star formation efficiency decreases with increasing clump mass with a value of 0.2 for clumps with masses of a few hundred solar masses and dropping to 0.08 for clumps with masses of a few thousand solar masses. We find good agreement between our results and star formation efficiencies determined from counts of embedded objects in nearby molecular clouds. Using the star formation efficiency relationship and the infrared excess time for embedded star formation of 2 ± 1 Myr we estimate the Galactic star formation rate to be approximately 0.9 ± 0.45 M⊙yr−1, which is in good agreement with previously reported values. This model has the advantage of providing a direct means of determining the star formation rate and avoids the difficulties encountered in converting infrared luminosities to stellar mass that affect previous galactic and extragalactic studies.

Variation of the High-mass Slope of the Stellar Initial Mass Function: Theory Meets Observations

“…The stellar initial mass function (IMF), which is the distribution of the masses of stars at their birth, is of fundamental importance to almost all branches in astrophysics. The shape of the IMF affects the efficiency of star formation in molecular clouds (Dib 2011;Dib et al 2011;Dib et al 2013;Hony et al 2015;Wells et al 2022;Garduño et al 2023), and sets the amount of feedback from stars into the large-scale interstellar medium (Dib et al 2006(Dib et al , 2009Gatto et al 2017;Orr et al 2020;Dib et al 2021;Lara-López et al 2023). Furthermore, the IMF, and particularly its component at the high-mass end, determines the chemical and dynamical evolution of galaxies (Prantzos & Boissier 2000;Davé et al 2011;Brusadin et al 2013;Few et al 2014;Recchi & Kroupa 2015;Dariush et al 2016;Vincenzo et al 2016;Fontanot et al 2017;Diehl & Prantzos 2023).…”