ATLASGAL - Star forming efficiencies and the Galactic star formation rate

The ATLASGAL survey has characterised the properties of approximately 1000 embedded Hii 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

SEDIGISM-ATLASGAL: Dense Gas Fraction and Star Formation Efficiency Across the Galactic Disk

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 ($DGF_{gmc} = ∑M_{clump}/M_{gmc}$) and the instantaneous star forming efficiencies (i.e., $SFE_{gmc} = ∑L_{clump}/M_{gmc}$). 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 HI to H$_2$ 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 geological significance of some Triassic microfossils from the South Orkney Islands, Scotia Ridge

Late Triassic Radiolaria have been recovered from a bedded chert collected early in 1977 in the South Orkney islands. This is the first reliable palaeontological evidence for the age of the so-called basement complex that forms most of the exposed rock of a microcontinent on the southern limb of the Scotia Ridge. The fossils place a lower limit on the age of deformation of at least part of the complex as post-Karnian or Norian. The basement is overlain by undeformed Jurassic to Cretaceous conglomerates, which suggests this event took place during the early Mesozoic Gondwanian orogeny. The new data are consistent with the interpretation that the basement complex of the South Orkney Islands represents part of a subduction complex and was accreted to the Pacific margin of Gondwanaland during the late Triassic or early Jurassic time