A Systematic Survey for Broadened CO Emission Toward Galactic Supernova Remnants

TL;DR

This systematic survey of 50 Galactic supernova remnants using millimeter-wave spectroscopy identified nineteen with broad molecular line regions, providing insights into SNR-MC interactions and their role in star formation and cosmic ray acceleration.

Contribution

The paper presents the first large-scale systematic survey detecting broad molecular lines in SNRs, expanding the known interactions and challenging existing theories on star formation triggers and cosmic ray origins.

Findings

Nineteen SNRs show broad molecular line regions, including nine newly identified.

Few SNRs exhibit detectable broadened CO lines, indicating low interaction frequency.

No significant correlation found between TeV gamma-ray sources and molecular cloud interactions.

Abstract

We present molecular spectroscopy toward 50 Galactic supernova remnants (SNRs) taken at millimeter wavelengths in 12CO and 13CO J=2-1 with the Heinrich Hertz Submillimeter Telescope as part of a systematic survey for broad molecular line (BML) regions indicative of interactions with molecular clouds (MCs). These observations reveal BML regions toward nineteen SNRs, including nine newly identified BML regions associated with SNRs (G08.3-0.0, G09.9-0.8, G11.2-0.3, G12.2+0.3, G18.6-0.2, G23.6+0.3, 4C-04.71, G29.6+0.1, G32.4+0.1). The remaining ten SNRs with BML regions confirm previous evidence for MC interaction in most cases (G16.7+0.1, Kes 75, 3C 391, Kes 79, 3C 396, 3C 397, W49B, Cas A, IC 443), although we confirm that the BML region toward HB 3 is associated with the W3(OH) HII region, not the SNR. Based on the systemic velocity of each MC, molecular line diagnostics, and cloud morphology, we test whether these detections represent SNR-MC interactions. One of the targets (G54.1+0.3) had previous indications of a BML region, but we did not detect broadened emission toward it. Although broadened 12CO J=2-1 line emission should be detectable toward virtually all SNR-MC interactions we find relatively few examples; therefore, the number of interactions is low. This result favors mechanisms other than SN feedback as the basic trigger for star formation. In addition, we find no significant association between TeV gamma-ray sources and MC interactions, contrary to predictions that SNR-MC interfaces are the primary venues for cosmic ray acceleration.