Detection of 3.3 Micron Aromatic Feature in the Supernova Remnant N49 with AKARI

TL;DR

This study reports the first detection of the 3.3 micron aromatic feature in a supernova remnant, revealing insights into PAH presence and characteristics in shock-affected environments using AKARI and archival Spitzer data.

Contribution

First detection of the 3.3 micron aromatic feature in a supernova remnant, linking PAH emission to shock and pre-shock conditions with multi-wavelength analysis.

Findings

Detection of 3.3 μm aromatic feature in N49

PAHs are mostly neutral and small in size

PAH emission likely from surviving or pre-shock heated PAHs

Abstract

We present an infrared study of the supernova remnant (SNR) N49 in the Large Magellanic Cloud with the near-infrared (NIR; 2.5 - 5 {\mu}m) spectroscopic observations performed by AKARI. The observations were performed as a coarse spectral mapping to cover most of the bright region in the east, which enables us to compare the distribution of various line emission and to examine their correlation. We detect the 3.3 {\mu}m aromatic feature in the remnant, which is for the first time to report the presence of the 3.3 {\mu}m aromatic feature related to a SNR. In the line maps of H2 1-0 O(3), 3.3 {\mu}m feature, and Br{\alpha}, the distribution of the aromatic feature shows overall correlation with those of other emissions together with regional differences reflecting the local physical conditions. By comparison with other archival imaging data at different wavelengths, the association of the aromatic emission to other ionic/molecular emission is clarified. We examine archival Spitzer IRS data of N49 and find signatures of other polycyclic aromatic hydrocarbon (PAH) features at 6.2, 7.7, and 11.3 {\mu}m corresponding to the 3.3 {\mu}m aromatic feature. Based on the band ratios of PAHs, we find that PAHs in N49 are not only dominantly neutral but also small in size. We discuss the origin of the PAH emission in N49 and conclude that the emission is either from PAHs that have survived the shock or PAHs in the preshock gas heated by radiative precursor.