Thermal instability through the outer half of quasi-static spherically symmetric molecular clumps and cores

Abstract

Thermal instability (TI) is a trigger mechanism, which can explain formation of condensations through some regions of the interstellar clouds. Our goal here is to investigate some conditions for occurrence of TI and formation of pre-condensations through the outer half a quasi-static spherical molecular clump or core. The inner half is nearly singular and ambiguous so out of scope of this research. We consider a spherically symmetric molecular cloud in quasi-static and thermally equilibrium state, and we use the linear perturbation method to investigate occurrence of TI through its outer half. The origin of perturbations are assumed to be as Inside-Rush-Perturbation (IRP) with outward perturbed velocity at inner region of the cloud, and Outside-Rush-Perturbation (ORP) with inward perturbed velocity originated at the outer parts of the cloud. The local thermal balance at the outer half of the molecular cloud leads to a local loosely constrained power-law relation between the pressure and density as $p\propto {\rho }^{1+\chi }$, where $-0.4\lesssim \chi \lesssim 0.05$ depends on the functional form of the net cooling function. Physically, the value of $\chi$ depends on the power of dependence of magnetic field to the density, $\eta$, and also on the value of magnetic field gradient, $\zeta$. For strong magnetic field (smaller $\eta$) and/or large field gradient (greater $\zeta$), the value of $\chi$ decreases, and vice versa. The results show that increasing of the value of $\chi$ leads to form a flatter density profiles at the thermally equilibrium outer half of the molecular clump or core, and to occur more thermally unstable IRP and ORP with smaller growth time-scales, and vice versa.

21 pages, 6 figures, accepted by Ap&SS

References in corpus (14)

• Magnetic Fields in Dark Cloud Cores: Arecibo OH Zeeman Observations
• The central 1000 AU of a pre-stellar core revealed with ALMA. I. 1.3 mm continuum observations
• Revealing H2D+ depletion and compact structure in starless and protostellar cores with ALMA
• Warm CO gas generated by possible turbulent shocks in a low-mass star-forming dense core in Taurus
• Investigating fragmentation of gas structures in OB cluster-forming molecular clump G33.92+0.11 with 1000 AU resolution observations of ALMA
• Gravitationally unstable condensations revealed by ALMA in the TUKH122 prestellar core in the Orion A cloud
• Early science with the Large Millimetre Telescope: An LMT/AzTEC 1.1 mm Survey of Dense Cores in the Monoceros R2 Giant Molecular Cloud
• Stellar mass spectrum within massive collapsing clumps III. Effects of temperature and magnetic field
• Star Cluster Formation from Turbulent Clumps. II. Gradual Star Cluster Formation
• Turbulence decay and cloud core relaxation in molecular clouds
• Modified Bonnor-Ebert spheres with ambipolar diffusion heating
• Dense core compression and fragmentation induced by the scattering of hydromagnetic waves
• An ALMA archival study of the clump mass function in the Large Magellanic Cloud
• The effect of magnetic field morphology on the structure of massive IRDC clumps