CO J=2-1 Observations toward the Supernova Remnant G54.1+0.3
  We present 12CO J = 2-1 line observations of G54.1+0.3, a composite supernova remnant with a mid-infrared (MIR) loop surrounding the central pulsar wind nebula (PWN). We mapped an area of 12' x 9' around the PWN and its associated MIR loop. We confirm two velocity components that had been proposed to be possibly interacting with the PWN/MIR-loop; the +53 km/s cloud that appears in contact with the eastern boundary of the PWN and the +23 km/s cloud that has CO emission coincident with the MIR loop. We have not found a direct evidence for the interaction in either of these clouds. Instead, we detected an 5'-long arc-like cloud at +15-+23 km/s with a systematic velocity gradient of ~3 km/s/arcmin and broad-line emitting CO gas having widths (FWHM) of <7 km/s in the western interior of the supernova remnant. We discuss their association with the supernova remnant. 
Jung-Won Lee, Bon-Chul Koo, Jeong-Eun Lee
astro-ph.GA