Inefficient star formation through turbulence, magnetic fields and feedback

By Christoph Federrath. 2015

172 citations recorded by the source corpus.

Star formation is inefficient. Only a few percent of the available gas in molecular clouds forms stars, leading to the observed low star formation rate (SFR). The same holds when averaged over many molecular clouds, such that the SFR of whole galaxies is again surprisingly low. Indeed, considering the low temperatures, molecular clouds should be highly gravitationally unstable and collapse on their global mean freefall timescale. And yet, they are observed to live about 10-100 times longer, i.e., the SFR per freefall time (SFR_ff) is only a few percent. Thus, other physical mechanisms must counteract the quick global collapse. Turbulence, magnetic fields and stellar feedback have been proposed as regulating agents, but it is still unclear which of these processes is the most important and what their relative contributions are. Here we run high-resolution simulations including gravity, turbulence, magnetic fields, and jet/outflow feedback. We confirm that clouds collapse on a mean freefall time, if only gravity is considered, producing stars at an unrealistic rate. In contrast, if turbulence, magnetic fields, and feedback are included step-by-step, the SFR is reduced by a factor of 2-3 with each additional physical ingredient. When they all act in concert, we find a constant SFR_ff = 0.04, currently the closest match to observations, but still about a factor of 2-4 higher than the average. A detailed comparison with other simulations and with observations leads us to conclude that only models with turbulence producing large virial parameters, and including magnetic fields and feedback can produce realistic SFRs.

Subfields: Astronomy and Astrophysics, Fluid Flow and Transfer Processes

View Paper: https://www.semanticscholar.org/paper/015762cefaa157ff8235ef3a14f4b883ebdd00bb

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Fluid Flow and Transfer Processes

Citations in the corpus

On the diversity and statistical properties of protostellar discs (2018, background): “Missing outflows are likely to result in protostellar and disc masses that are higher than they should be (e.g. Hansen et al. 2012; Krumholz et al. 2012; Federrath et al. 2014; Federrath 2015), but the magnitude of this effect is likely to be small (∼ 10 − 20”
A unified model for galactic discs: star formation, turbulence driving, and mass transport (2017, background): “…by The Australian N ational U niversity user on 16 O ctober 2018 relation as the sum of small-scale relations (Krumholz & McKee 2005; Krumholz, McKee & Tumlinson 2009b; Federrath & Klessen 2012, 2013; Padoan, Haugbølle & Nordlund 2012; Krumholz 2013; Federrath 2015; Burkhart 2018).”
FIRE-2 simulations: physics versus numerics in galaxy formation (2017, background): “Later, Federrath et al. (2010) and many subsequent authors (e.g. Padoan & Nordlund 2011; Myers et al. 2013; Gong & Ostriker 2013; Federrath 2015; Skinner & Ostriker 2015) pointed out that one can instead use this criterion to determine when local fragmentation is unresolved, and assign the mass to…”
Raining on black holes and massive galaxies: the top-down multiphase condensation model (2016, background): “…turbulent pressure is the dominant mechanism counterbalancing the self-gravitational collapse, thus helping to explain the low star formation efficiencies, ε∗ 5 per cent, although magnetic fields and stellar feedback may play an important role (Federrath 2015) and will be studied in the future.”
On the universality of interstellar filaments: theory meets simulations and observations (2015, background): “Columns 11 and 12: number of detected filaments (Nfilaments) and derived width (Wfil) of the filaments. the structure of their parent molecular cloud and to potentially control star formation in a feedback loop (Federrath 2015).”