Mathesis of star formation – from kpc to parsec scales

Abstract

In this thesis I present a series of studies aiming to understand the formation of stars from gas in the Milky Way. Generally speaking, I will progress from larger to smaller scales. <br /> The kilo-parsec scale (1000 parsec ~ 10^21 cm) is the scale at which dynamics of the molecular clouds is coupled to dynamics of the Milky Way disk. Here we present an observational study of molecular gas at 49.5 deg <l < 52.5 deg and -5 km/s <vlsr < 17.4 km/s. The molecular gas is found in the form of a huge ~ 500 pc filamentary gas wisp. It has a large physical extent and a velocity dispersion of ~ 5 km/s. The filamentary gas wisp is composed of two molecular clouds and an expanding bubble. The length of the gas wisp exceeds by much the thickness of the molecular disk of the Milky Way, and this is consistent with the cloud-formation scenario in which gas is cold prior to the formation of molecular clouds.<br /> Molecular clouds (1 - 100 parsec) are the nurseries of the stars. There are many indications that molecular clouds are turbulence-dominated objects. However, it is not clear what role gravity plays. We propose a new method (G-virial) to quantify the role of gravity in molecular clouds. Our new method takes the gravitational interactions between all pixels in 3D position-position-velocity data cube into account, and generates maps of the importance of gravity in 3D position-position-velocity space. With our method we demonstrate that gravity plays an importance role in the individual regions in the Perseus and Ophiuchus molecular cloud, and find that high values of G-virial are reached in cluster-bearing regions. We also demonstrate the capability of our method in finding regions and quantifying the properties of the regions in the clouds.<br /> Protostellar outflow ~ 1 pc is a prominent process accompanying the formation of stars. In this work, we theoretically investigate the possibility that the outflow results from interaction between the wind and the ambient gas in the form of turbulent entrainment. In our model, the ram-pressure of the wind balances the turbulent ram-pressure of the ambient gas, and the outflow consists of the ambient gas entrained by the wind. We demonstrate that the outflow phenomena can be naturally generated through this process, and discuss the potential usage of outflows as a probes of the dynamical state of the turbulent molecular gas.