Dark Supernova Remnants revealed by CO-line Bubbles in the W43 Molecular Complex along the 4-kpc Arm

TL;DR

This study identifies dark CO-line bubbles in the W43 molecular complex, interpreted as evolved supernova remnants, providing insights into turbulence and star formation activity in giant molecular clouds.

Contribution

It reveals a new class of dark supernova remnants in molecular clouds, observed as CO bubbles with unique properties, advancing understanding of supernova impacts on GMCs.

Findings

CO bubbles are dark in radio and infrared, unlike typical SNRs.

These bubbles are likely evolved supernova remnants within molecular clouds.

Detection of dark SNRs can improve supernova rate estimates in the Milky Way.

Abstract

Fine structure of the density distribution in giant molecular clouds (GMC) around W43 (G31+00+90 km/s at $\sim 5.5$ kpc) was analyzed using the FUGIN$^*$ CO-line survey at high-angular ($20''\sim 0.5$ pc) and velocity (1.3 km/s) resolutions ($^*$Four-receiver-system Unbiased Galactic Imaging survey with the Nobeyama 45-m telescope). The GMCs show highly turbulent structures, and the eddies are found to exhibit spherical bubble morphology appearing in narrow ranges of velocity channels. The bubbles are dark in radio continuum emission, unlike usual supernova remnants (SNR) or HII regions, and in infrared dust emission, unlike molecular bubbles around young stellar objects. The CO bubbles are interpreted as due to fully evolved buried SNRs in molecular clouds after rapid exhaustion of the released energy in dense molecular clouds. The CO bubbles may be a direct evidence for exciting and maintaining the turbulence in GMCs by SN origin. Search for CO bubbles as "dark SNRs" (dSNR) will have implication to estimate the supernova rate more accurately, and hence the star formation activity in the Milky Way.