The Formation and Destruction of Molecular Clouds and Galactic Star Formation

Abstract

We describe an overall picture of galactic-scale star formation. Recent high-resolution magneto-hydrodynamical simulations of twofluid dynamics with cooling/heating and thermal conduction have shown that the formation of molecular clouds requires multiple episodes of supersonic compression. This finding enables us to create a scenario in which molecular clouds form in interacting shells or bubbles on a galactic scale. First we estimate the ensemble-averaged growth rate of molecular clouds over a timescale larger than a million years. Next we perform radiation hydrodynamics simulations to evaluate the destruction rate of magnetized molecular clouds by the stellar FUV radiation. We also investigate the resultant star formation efficiency within a cloud which amounts to a low value (a few percent) if we adopt the power-law exponent ∼ −2.5 for the mass distribution of stars in the cloud. We finally describe the time evolution of the mass function of molecular clouds over a long timescale (>1Myr) and discuss the steady state exponent of the power-law slope in various environments.

Three-dimensional magnetic fields of molecular clouds

“…Moreover, 3D magnetic field observations allow comparison of their morphologies to cloud-formation model predictions, enabling us to investigate ISM evolution and molecular-cloud formation. While observed magnetic field morphologies are consistent with some cloud-formation models (e.g., Inoue and Fukui, 2013;Inutsuka et al, 2015Inutsuka et al, , 2016Gómez et al, 2018;Inoue et al, 2018;Abe et al, 2021), observing the 3D magnetic fields of a large number of clouds is required to study their formation scenario and determine how magnetic fields influence the evolution of these clouds into filaments, cores, and, eventually, stars.…”

Filamentary Network and Magnetic Field Structures Revealed with BISTRO in the High-mass Star-forming Region NGC 2264: Global Properties and Local Magnetogravitational Configurations

“…Consequently, a dynamic filament model is desirable to more accurately describe the stability of this system. Assessing the proportion of mass within a cloud that resides in filaments is essential to evaluate the final star formation efficiency (Inoue & Inutsuka 2012;Inutsuka et al 2016). To accomplish this, we employ two different methods to calculate the total mass of the identified filaments.…”

“…(2) The evolved YSOs might have formed from filaments that have been dissipated. Inutsuka et al (2016) argue that present YSOs can have partially formed within filaments that existed in the past. This is suggested because the total mass of the observed YSOs often exceeds the product of the total filament mass and the star formation efficiency.…”