2017A&A...604A..13C

Context. The investigation of the interaction between the supernova remnants (SNRs) and interstellar gas is not only necessary to improve our knowledge of SNRs, but also to understand the nature of the progenitor systems.
Aims. As a part of the Milky Way Imaging Scroll Painting CO line survey, the aim is to study the interstellar gas surrounding the Galactic historical SNRs. In this work, we present the CO results of Tycho's SNR.
Methods. Using the 3x3 Superconducting Spectroscopic Array Receiver (SSAR) at the PMO 13.7-m telescope, we performed large-field (3°x2°) and high-sensitivity CO (1-0) molecular line observations toward Tycho's SNR.
Results. The CO observations reveal large molecular clouds, stream-like structures, and an inner rim around the remnant. We derived the basic properties (column density, mass, and kinematics) of these objects based on the CO observations. The large molecular clouds individually show an arc toward the remnant center, outlining a large cavity with radii of ∼0.3°x0.6° (or 13pcx27pc at a distance of 2.5kpc) around the remnant. The CO line broadenings and asymmetries detected in the surrounding clouds, the observed expansion of the cavity, in concert with enhanced ¹²CO (2-1)/(1-0) intensity ratio detected in previous studies, suggest the interaction of the large cavity with a wind in the region. After excluding the scenario of a large bubble produced by bright massive stars, we suggest that the large cavity could be explained by accretion wind from the progenitor system of Tycho's supernova. Nevertheless, the possibility of the random distribution of a large cavity around Tycho's SNR cannot be ruled out thus far. Further observations are needed to confirm the physical association of the large cavity with Tycho's SNR.