Absorption in the Spectrum of a Background AGN by C ii* by the Supernova Remnant G354-33

Abstract

A number of very large, very faint supernova remnants (SNRs) have been discovered in the past few years. Those in the Galactic halo occur in low density gas, so they might be more easily observed in absorption than in emission. The SNR G354-33 is a shell of faint UV and optical filaments about 10° in diameter. Here we point out that a spectrum of the QSO J2017-4516 used study the galaxy cluster J2016-4517 shows an absorption line from the excited fine structure level of C ii at −50 km s−1. Absorption features of Si ii and Si iii are also seen at this velocity. The observed column density compares well with shock wave models. Doppler shifted C ii* absorption features provide an excellent means to find and characterize SNR shocks because they arise from compressed gas.