On the compressive nature of turbulence driven by ionizing feedback in the pillars of the Carina Nebula

Abstract

The ionizing radiation of massive stars sculpts the surrounding neutral gas into pillar-like structures. Direct signatures of star formation through outflows and jets are observed in these structures, typically at their tips. Recent numerical simulations have suggested that this star formation could potentially be triggered by photoionising radiation, driving compressive modes of turbulence in the pillars. In this study we use recent high-resolution ALMA observations of 12CO, 13CO, and C18O, J = 2 − 1 emission to test this hypothesis for pillars in the Carina Nebula. We analyse column density and intensity-weighted velocity maps, and subtract any large-scale bulk motions in the plane of the sky to isolate the turbulent motions. We then reconstruct the dominant turbulence driving mode in the pillars, by computing the turbulence driving parameter b, characterised by the relation $\sigma _{\rho /\rho _0} = b \mathcal {M}$ between the standard deviation of the density contrast $\sigma _{\rho /\rho _0}$ (with gas density ρ and its average ρ0) and the turbulent Mach number $\mathcal {M}$. We find values of b ∼ 0.7–1.0 for most of the pillars, suggesting that predominantly compressive modes of turbulence are driven in the pillars by the ionising radiation from nearby massive stars. We find that this range of b values can produce star formation rates in the pillars that are a factor ∼3 greater than with b ∼ 0.5, a typical average value of b for spiral-arm molecular clouds. Our results provide further evidence for the potential triggering of star formation in pillars through compressive turbulent motions.

Blowing Bubbles around Intermediate-Mass Stars: Feedback from Main-Sequence Winds is not Enough

“…Stellar feedback alters the mass density and dynamics of gas in star-forming environments (e.g., Lopez et al 2014;Menon et al 2021;Gallegos-Garcia et al 2020;Olivier et al 2021). Figure 4 shows normalized histograms of the gas density (left panel), velocity magnitude (middle panel), and momentum (right panel) for IsoRun (teal dashed lines) and AdiaRun (pink dotdashed lines) for the final snapshots at t = 0.2 Myr with the initial histograms over-plotted (gray solid lines).…”

Impact of relativistic jets on the star formation rate: a turbulence-regulated framework

“…Here we assume a value of 𝑏 = 0.5, corresponding to a common mixed mode of driving of the turbulence. However, variations do exist between different regions and clouds (Federrath et al 2016;Menon et al 2020Menon et al , 2021.…”

The Effects of Magnetic Fields and Outflow Feedback on the Shape and Evolution of the Density PDF in Turbulent Star-Forming Clouds

“…The turbulent driving parameter, b, describes the mix of solenoidal and compressive modes of the turbulent driving and ranges from b ≈ 1/3 for purely solenoidal driving, to b ≈ 1 for purely compressive driving (Federrath et al 2008;Federrath et al 2010b). Values of b for real clouds occupy the full range from b ∼ 0.3-1 (see e.g., Brunt 2010; Price et al 2011;Ginsburg et al 2013;Federrath et al 2016;Menon et al 2021), depending on the physical conditions and location of the clouds. For the simulations used in this work, which are driven with a natural mix of forcing modes, resulting in b ∼ 0.4 (Federrath et al 2010b) and M s = 5, Eq.…”