2020/09/30 by Hitesh Kishore Das, Prakriti Pal Choudhury, Prateek Sharma
Earth and Planetary Sciences · Physics and Astronomy · #Astro and Planetary Science #Astrophysics #Geology and Paleoclimatology Research #High-pressure geophysics and materials #Instability #Isobaric process #Isochoric process #Mechanics #Metallicity #Physics #Thermodynamics #astro-ph.GA
paper · pdf · doi:10.1093/mnras/stab382
18 pages, 18 figures (including 1 in the appendix), 2 tables. Accepted in MNRAS
openalex publication_date 2021/02/08 · arxiv created 2021/03/10 · arxiv updated 2021/03/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
ABSTRACT We test how metallicity variation (a background gradient and fluctuations) affects the physics of local thermal instability using analytical calculations and idealized, high-resolution 1D hydrodynamic simulations. Although the cooling function (Λ[T, Z]) and the cooling time (tcool) depend on gas temperature and metallicity, we find that the growth rate of thermal instability is explicitly dependent only on the derivative of the cooling function relative to temperature (∂ln Λ/∂ln T) and not on the metallicity derivative (∂ln Λ/∂ln Z). For most of 104 K ≲ T ≲ 107 K, both the isobaric and isochoric modes (occurring at scales smaller and larger than the sonic length covered in a cooling time [cstcool], respectively) grow linearly, and at higher temperatures (≳107 K) the isochoric modes are stable. We show that even the non-linear evolution depends on whether the isochoric modes are linearly stable or unstable. For the stable isochoric modes, we observe the growth of small-scale isobaric modes but this is distinct from the non-linear fragmentation of a dense cooling region. For unstable isochoric perturbations we do not observe large density perturbations at small scales. While very small clouds (∼min[cstcool]) form in the transient state of non-linear evolution of the stable isochoric thermal instability, most of them merge eventually.