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

TL;DR

This study uses large-area near-infrared mapping of [P II] 1.189 μm and [Fe II] lines across 26 Galactic SNRs to probe in-situ phosphorus production and dust destruction in radiative shocks. By deriving P/Fe abundances from the [P II]/[Fe II] flux ratios, it finds that X(P/Fe) varies by up to two orders of magnitude among remnants, with Cas A and the Crab showing regionally elevated values that may reflect asymmetric P ejection. The authors combine IR line maps with mid-/far-IR dust emission data to assess the role of dust destruction, revealing anti-correlations between gas-phase Fe and dust-phase Fe in several remnants, while deviations in Cas A and the Crab suggest additional processes such as ejecta asymmetry or Ni II contamination. Overall, the work provides new observational constraints on the production and processing of phosphorus in supernova explosions and their impact on the ISM, highlighting the need for high-resolution spectroscopy to disentangle complex ejecta-dust interactions.

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.

Figures (8)

• Figure 1: Continuum-subtracted [P II], [Fe II]$_{1.26}$, and [Fe II]$_{1.64}$ maps of Cas A (top), the Crab Nebula (middle), and RCW 103 (bottom). The [Fe II]$_{1.64}$ map of Cas A is taken from koo18. The color levels are in units of erg s$^{-1}$ cm$^{-2}$ sr$^{-1}$. Alt text: Nine maps.
• Figure 2: Top: continuum-subtracted [P II] and [Fe II]$_{1.26}$ maps of IC 443. The [Fe II]$_{1.26}$ map is taken from kok13, where white boxes represent the target regions in our study. White contours in the [P II] maps represent the [Fe II]$_{1.26}$ emission. Bottom: $843$ GHz and continuum-subtracted [P II], [Fe II]$_{1.26}$, and [Fe II]$_{1.64}$ maps of Puppis A. The $843$ GHz map is taken from the SUMSS survey (mau03), where a white box represents the target region in our study. White contours in the [P II] and [Fe II] maps represent the $843$ GHz emission. The color levels are in units of Jy/beam and erg s$^{-1}$ cm$^{-2}$ sr$^{-1}$ for the radio and near-IR line maps, respectively. Alt text: Seven maps.
• Figure 3: Continuum-subtracted [Fe II]$_{1.64}$ and radio continuum maps of Kepler, MSH 15--52, G337.2--0.7, G344.7--0.1, G349.7$+$0.2, and RCW 86. The radio continuum maps at $843$ MHz and $1.5$ GHz are taken from the SUMSS survey mau03 and NRAO VLA archive survey at $\langle$http://www.vla.nrao.edu/astro/nvas$\rangle$, respectively. White boxes in the radio maps of G344.7--0.1 and RCW 86 show the target region in our study. White contours in the [Fe II]$_{1.64}$ maps represent the radio continuum emission. The color levels are in units of Jy/beam and erg s$^{-1}$ cm$^{-2}$ sr$^{-1}$ for the radio and [Fe II]$_{1.64}$ maps, respectively. Alt text: 13 maps.
• Figure 4: Scatter plot between the extinction-corrected [P II] and [Fe II] fluxes. Circle and triangle represent core-collapse and Type Ia SNRs, respectively. Blue, green, and red represent the SNR ages of $<5000$ (young), $5000$--$10000$ (middle-age), and $>10000$ yr (old), respectively. The black data point corresponds to G41.5$+$0.4, for which the age is not estimated in previous studies. Filled and open symbols indicate exposure times longer and shorter than 30 minutes, respectively. Arrows represent $3{\sigma}$ upper limits. Gray lines represent the relation expected from corresponding $X$(P/Fe) (see text for details). Alt text: A scatter plot with three lines.
• Figure 5: Relations between the extinction-corrected [P II]/[Fe II]$_{1.26}$ flux ratio and $n_e$ of our sample SNRs detected in both the line emissions. Each SNR is represented by a circle in a different color, while the Orion bar is shown as a black cross for comparison wam00. Gray lines represent relations expected from corresponding $X$(P/Fe). Alt text: A scatter plot with two lines.