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

¹ Purple Mountain Observatory & Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 2 West Beijing Road, 210008 Nanjing, PR China
e-mail: xpchen@pmo.ac.cn
² University of Chinese Academy of Sciences, No. 19A Yuquan Road, 100049 Beijing, PR China

Received: 3 November 2016
Accepted: 17 April 2017

Abstract

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 3 × 3 Superconducting Spectroscopic Array Receiver (SSAR) at the PMO 13.7-m telescope, we performed large-field (3° × 2°) 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° × 0.6° (or 13 pc × 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 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.