Despite recent progress, the question of what regulates the star formation efficiency in galaxies remains one of the most debated problems in astrophysics. According to the dominant picture, star formation is regulated by turbulence and feedback, and the star formation efficiency is 1-2% per local free-fall time. In an alternate scenario, the star formation rate in galactic disks is linearly proportional to the mass of dense gas above a critical density threshold. In new research, Université Paris-Sacla astrophysicist Michael Mattern and his colleagues aimed to discriminate between these two pictures thanks to high-resolution observations from the Atacama Pathfinder Experiment (APEX) tracing dense gas and young stellar objects for a comprehensive sample of 49 nearby dense molecular clouds.
This composite image shows RCW 106, a star-forming region located in the southern constellation Norma, approximately 12,000 light-years away from Earth. The image imposes a red map of dense gas, imaged with the ArTéMiS camera at APEX, over an optical image taken with ESO’s VLT Survey Telescope. Image credit: ESO / M. Mattern et al.
Understanding what regulates the star formation efficiency in the giant molecular clouds of galaxies is a fundamental open question in star formation research.
The rate of star formation on multiple scales in galaxies is known to be strongly correlated with the mass of available molecular gas.
Overall, star formation is observed to be a very inefficient process.
“The glowing red clouds seen in the image above show dense gas regions where new stars are being born in the RCW 106 region,” the astronomers said in a statement.
“But only 1% of this gas will actually go on to create stars, and we don’t know why this percentage is so low.”
“We do know that star formation takes place when regions of these huge clouds of cold gas are able to clump together and eventually collapse into newborn stars, which happens at a critical density.”
“But once we go past that density, do even denser regions produce even more stars, and could this help to explain the 1% mystery?”
Their new results suggest this is not the case: denser regions are not more efficient at forming stars.
According to the team, this is perhaps explained by the way these denser clouds fragment into filamentary structures and cores out of which stars will form, but leaves many questions still to be answered.
“Our results suggest that the star formation efficiency does not increase with density above the critical threshold and support a scenario in which the star formation efficiency in dense gas is approximately constant,” the researchers said.
“However, the star formation efficiency measurements traced by Class I young stellar objects in nearby clouds are more inconclusive, since they are consistent with both the presence of a density threshold and a dependence on density above the threshold.”
“Overall, we suggest that the star formation efficiency in dense gas is primarily governed by the physics of filament fragmentation into protostellar cores.”
The study will appear in the journal Astronomy & Astrophysics.
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M. Mattern et al. 2024. Understanding the Star Formation Efficiency in Dense Gas: Initial Results from the CAFFEINE Survey with ArTéMiS. A&A, in press; arXiv: 2405.15713
