From star formation to regional distribution: Influences on the embedded cluster mass function

Abstract

In this work we study the embedded cluster mass function (ECMF), meaning the mass distribution function of embedded clusters. Embedded clusters are fully or partially enclosed in interstellar gas, dust and molecular clouds and represent the earliest stage in the life-time of a formed star cluster. They may be the forerunners to the open clusters and are therefore valuable probes for cluster formation. It has been observed that while the ECMF locally has the form of a power-law, the galaxy-wide ECMF has a Schechter-like turn down. This work looks into possible explanations for the difference between the local ECMF and the galaxy-wide ECMF. The main assumption in this work is that the local star formation rate creates an upper mass limit on the ECMF. As the star formation rate varies over the galaxy the upper mass limit would also vary. This would naturally cause turn down similar to a Schechter turn down. <br> In this work we apply different models for the radial distribution of the star formation rate in a galaxy and how it effects the ECMF. Like a simple Kennicutt-Schmidt power-law relation between the gas surface density and star formation surface density while assuming a thin radially symmetric exponential gas disk. We also make a theoretical derivation of a Kennicutt-Schmidt-like relation from the free-fall time of the gas in a galaxy and thus getting a more detailed star formation rate profile of the galaxy. Finally we also look into the disruptive force created by the gradient of angular velocity caused by a galaxy’s flat rotation curve: the shear effect. This effect can further limit the areas of a galaxy in which star formation is possible and could also cause indirectly a size and mass limit on embedded star clusters. In the last we chapter we look whether the ECMF proposed in the second chapter can be applied to the Andromeda galaxy.