Near-infrared [P II] and [Fe II] line mapping of Galactic supernova remnants

TL;DR

This study maps near-infrared [P II] and [Fe II] lines in 26 Galactic supernova remnants to investigate phosphorus production and dust destruction, revealing diverse P/Fe ratios and potential asymmetric P ejection during supernovae.

Contribution

First near-infrared line mapping of P II and Fe II in multiple supernova remnants, providing new insights into P origins and dust processing in these environments.

Findings

Detected line emissions in 5 SNRs, only Fe II in 15, none in 6.

P/Fe abundance ratios vary by up to two orders of magnitude.

High P/Fe ratios in Cassiopeia A and Crab Nebula likely reflect asymmetric P ejection.

Abstract

Phosphorus (P) is one of the key ingredients for life, yet its origins in galaxies remain poorly understood. In order to investigate the production of P by supernovae, we performed near-infrared (IR) [P II] and [Fe II] line mapping of 26 Galactic supernova remnants (SNRs) with the Infrared Survey Facility and Kanata telescopes, using the narrow-band filters tuned to these lines. By combining our data with archival [Fe II] maps from UKIRT, we detected both the [P II] and [Fe II] emissions in five SNRs, only the [Fe II] emission in 15 SNRs, and no line emissions in the remaining six. Using the observed [P II]/[Fe II] ratios and upper limits for non-detections, we derived the P/Fe abundance ratios, which vary by up to two orders of magnitude among our sample SNRs. This suggests that the production rate of P and/or the degree of dust destruction may differ from remnant to remnant, the latter being due to the fact that P is volatile while Fe is mostly locked in dust grains. We used the mid- and far-IR maps to examine the dust content for the five SNRs where both the line emissions are detected. As a result, we find that high P/Fe abundance ratios in the northern and southeastern regions of Cassiopeia A and the Crab Nebula, respectively, are not likely due to dust destruction but may reflect an asymmetric ejection of P during supernova explosions. In the Crab Nebula, it is also possible that near-IR [Ni II] emission contaminates the observed flux in the southeastern region, suggesting that the Ni/Fe abundance ratio, rather than the P/Fe abundance ratio, is relatively high in this part of the remnant.