Detection of Shocked Molecular Gas by Full-Extent Mapping of the Supernova Remnant W44

Abstract

Molecular gas toward the supernova remnant (SNR) W44 (G34.7� 0.4) was extensively mapped in CO J ¼ 1 0 emission with the 17 0 beam of the Nobeyama 45 m radio telescope. We detected high-velocity (>25 km s � 1 ) CO line wings. They are confined to compact (� 1.5 pc) spots, and they are located adjacent to bright radio filaments or knots. The low 13 CO/ 12 CO intensity ratio of 0.03 and high HCO + / 12 CO intensity ratio of 0.3 suggest that the wing-emitting gas has a moderate 12 CO opacity of � 1 and a high density of n(H2 )>1 0 5 cm � 3 . This gas might be shocked molecular gas that has been accelerated and compressed by the expanding blast waves of W44. In addition, the high spatial resolution CO maps reveal several other features that may reveal the interaction between the SNR and the surrounding interstellar gas. The giant molecular cloud CO G34.8� 0.6 (vLSR ¼ 48 km s � 1 ) has a sharp edge coincident with the eastern radio continuum rim of W44, which may indicate that we observe the SNR/cloud interaction almost edge-on. The existence of the ‘‘edge’’ suggests that most of the molecular mass resides in smaller clumps that evaporate rapidly after the passage of the supernova blast wave. We also find spatially extended moderately broad emission (SEMBE) with a moderately large intensity of � 30 K km s � 1 in CO J ¼ 1 0 and a typical line width of � 10 km s � 1 (FWHM). Its extent coincides with the brighter region of the radio synchrotron emission. We discuss the SEMBE in terms of molecular clumps shocked and disturbed by the compressed shell of the SNR.