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 \sim 3 \arcmin \times 3 \arcmin ( \sim 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 \sim 35 \arcmin \times 35 \arcmin in size , or \sim 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 M _ { \mathrm { gas } } \sim 1.1 \times 10 ^ { 6 } M _ { \odot } within a radius of 60 pc .
Within a radius of 6 pc , the total gas mass is M _ { \mathrm { gas } } \sim 2 \times 10 ^ { 5 } M _ { \odot } .
At these scales only \sim 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 of HC HII regions in W49N .
This structure extends to scales from \sim 10 to 100 pc through filaments that radially converge toward W49N and its less prominent neighbor W49S .
The W49A starburst most likely formed from global gravitational contraction with localized collapse in a ” hub-filament ” geometry .
3 ) Currently , feedback from the central YMCs ( with a present mass M _ { \mathrm { cl } } \gtrsim 5 \times 10 ^ { 4 } M _ { \odot } ) is still not enough to entirely disrupt the GMC , but further stellar mass growth could be enough to allow radiation pressure to clear the cloud and halt star formation .
4 ) The resulting stellar content will probably remain as a gravitationally bound massive star cluster , or a small system of bound clusters .