Large-field CO(1--0) observations toward the Galactic historical supernova remnants: a large cavity around Tycho's supernova remnant

TL;DR

This study uses large-field CO(1-0) observations to identify a large cavity around Tycho's supernova remnant, suggesting it may result from the progenitor system's accretion wind, advancing understanding of SNR-ISM interactions.

Contribution

First high-sensitivity, large-field CO(1-0) mapping around Tycho's SNR revealing a large cavity likely caused by progenitor wind, not a stellar bubble, providing new insights into SNR progenitor environments.

Findings

Discovered a large cavity (~13x27 pc) around Tycho's SNR.

Detected molecular cloud structures indicating cavity expansion.

Suggested cavity formation by progenitor accretion wind, not massive star activity.

Abstract

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. As a part of the Milky Way Imaging Scroll Painting CO line survey (MWISP), we study the interstellar gas surrounding the Galactic historical SNRs, using the PMO 13.7-meter telescope. In this work, we present large-field (3$^\circ$$\times$2$^\circ$) and high-sensitivity CO(1-0) molecular line observations toward Tycho's SNR. The CO observations reveal, from the outside in, large molecular clouds, stream-like structures, and an inner rim around Tycho's SNR. We derived the basic properties (column density, mass, and kinematics) of these objects based on the CO observations. The large molecular clouds individually show an arc toward the remnant center, outlining a large cavity with radii of $\sim$0.3$^\circ$$\times$0.6$^\circ$ (or 13 pc $\times$27 pc at a distance of 2.5 kpc) around the remnant. The CO line broadenings and asymmetries detected in the surrounding clouds, the observed expansion of the cavity, in concert with enhanced $^{12}$CO(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.