A CO Line and Infrared Continuum Study of the Active Star-Forming Complex W51

TL;DR

This study investigates the molecular gas properties and star formation activity in the W51 complex using CO line observations, infrared data, and statistical modeling, revealing triggered star formation and cloud interactions.

Contribution

It provides new insights into the physical conditions of molecular clouds and the mechanisms driving star formation in W51, including the role of HII region expansion and cloud collisions.

Findings

Different CO line ratios inside and outside star-forming regions

Evidence of star formation triggered by HII region expansion

Approximately 1% of cloud mass is in YSOs

Abstract

We present the results of an extensive observational study of the active star-forming complex W51 that was observed in the J=2-1 transition of the 12CO and 13CO molecules over a 1.25 deg x 1.00 deg region with the University of Arizona Heinrich Hertz Submillimeter Telescope. We use a statistical equilibrium code to estimate physical properties of the molecular gas. We compare the molecular cloud morphology with the distribution of infrared (IR) and radio continuum sources, and find associations between molecular clouds and young stellar objects (YSOs) listed in Spitzer IR catalogs. The ratios of CO lines associated with HII regions are different from the ratios outside the active star-forming regions. We present evidence of star formation triggered by the expansion of the HII regions and by cloud-cloud collisions. We estimate that about 1% of the cloud mass is currently in YSOs.