MUSCLE W49: A multi-scale continuum and line exploration of the most luminous star formation region in the Milky Way. I. Data and the mass structure of the giant molecular cloud

Abstract

The Multi-Scale Continuum and Line Exploration of W49 (MUSCLE W49) is a comprehensive gas and dust survey of the giant molecular cloud (GMC) of W49A, the most luminous star-formation region in the Milky Way. The project covers, for the first time, the entire GMC at different scales and angular resolutions. In this paper we present: 1) an all-configuration SMA mosaic in the 230-GHz (1.3-mm) band covering the central ∼ 3′×3 ′ ( ∼ 10 pc, known as W49N), where most of the embedded massive stars reside; and 2) PMO 14m telescope observations in the 90-GHz band, covering the entire GMC with maps of up to ∼ 35′ × 35 ′ in size, or ∼ 113 pc. We also make use of archival data from the VLA, JCMT-SCUBA, IRAM 30m, and the CSO BOLOCAM Galactic Plane Survey. We derive the basic physical parameters of the GMC at all scales. Our main findings are as follows: 1) The W49 GMC is one of the most massive in the Galaxy, with a total mass Mgas ∼ 1.1×106 M within a radius of 60 pc. Within a radius of 6 pc, the total gas mass is Mgas ∼ 2×105 M. At these scales only ∼ 1% of the material is photoionized. The mass reservoir is sufficient to form several young massive clusters (YMCs) as massive as a globular cluster. 2) The mass of the GMC is distributed in a hierarchical network of filaments. At scales < 10 pc, a triple, centrally condensed structure peaks toward the ring