2024/06/11 by Nir Mandelker, Mandelker, Nir, Omry Ginzburg +11 · 2 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.48550/arxiv.2406.07633
openalex publication_date 2024/06/11 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
We address the formation of giant clumps in violently unstable gas-rich disc galaxies at cosmic noon. While these are commonly thought to originate from gravitational Toomre instability, cosmological simulations have indicated that clumps form even in regions where the Toomre Q parameter is well above unity, which should be stable according to linear Toomre theory (Inoue et al., 2016). Examining one of these cosmological simulations, we find that it exhibits an excess in compressive modes of turbulence with converging motions. The energy in converging motions within proto-clump regions is ∼ 70% of the total turbulent energy, compared to ∼ 17% expected in equipartition. When averaged over the whole disc, ∼ 32% of the turbulent energy is in converging motions, with a further ∼ 8% in diverging motions. Thus, a total of ∼ 40% of the turbulent energy is in compressive modes, with the rest in solenoidal modes, compared to the (1/3)-(2/3) division expected in equipartition. By contrast, we find that in an isolated-disc simulation with similar properties, resembling high-z star-forming galaxies, the energy in the different turbulence modes are in equipartition, both in proto-clump regions and over the whole disc. We conclude that the origin of the excessive converging motions in proto-clump regions is external to the disc, and propose several mechanisms that can induce them. This is an additional mechanism for clump formation, complementary to and possibly preceding gravitational instability.