The Structure and Evolution of Young Stellar Clusters

TL;DR

This study analyzes the properties and structures of young stellar clusters within 1 kiloparsec, revealing a continuum of star-forming environments, cluster morphologies, and the limited impact of massive stars on disk truncation.

Contribution

It provides a comprehensive analysis of embedded cluster properties using new infrared data, highlighting the continuum of environments and the influence of cluster morphology on star formation.

Findings

Clusters show a continuum from isolation to dense groups.

Cluster size correlates with number of members, with surface density varying little.

Protostar distribution mirrors dense molecular gas, indicating fragmentation.

Abstract

We examine the properties of embedded clusters within 1 kiloparsec using new data from the Spitzer Space Telescope, as well as recent results from 2MASS and other ground-based near-infrared surveys. We use surveys of entire molecular clouds to understand the range and distribution of cluster membership, size and surface density. The Spitzer data demonstrate clearly that there is a continuum of star- forming environments, from relative isolation to dense clusters. The number of members of a cluster is correlated with the cluster radius, such that the average surface density of clusters having a few to a thousand members varies by a factor of only a few. The spatial distributions of Spitzer-identified young stellar objects frequently show elongation, low density halos, and sub-clustering. The spatial distributions of protostars resemble the distribution of dense molecular gas, suggesting that their morphologies result directly from the fragmentation of the natal gas. We also examine the effects of the cluster environments on star and planet formation. Although Far-UV and Extreme-UV radiation from massive stars can truncate disks in a few million years, fewer than half of the young stars in our sample (embedded clusters within 1 kpc) are found in regions of strong FUV and EUV fields. Typical volume densities and lifetimes of the observed clusters suggest that dynamical interactions are not an important mechanism for truncating disks on solar system size scales.