The Extinction Distance of Supernova Remnants in Combination with the CO Line Measurements

Abstract

Accurate distance measurements to supernova remnants (SNRs) are crucial for understanding their physical properties and evolution. We present a novel method that combines CO line observations with three-dimensional (3D) extinction maps to determine distances to SNRs (G93.7$-$0.2, G109.1$-$1.0, G156.2+5.7, and G166.0+4.3) through their associated molecular clouds. For each SNR, candidate CO velocity components corresponding to interacting molecular clouds are identified based on previous observational evidence with refinements: [$-$19, $-$3] km s$^{-1}$ for G93.7$-$0.2, [$-$51, $-$46] km s$^{-1}$ for G109.1$-$1.0, [$-$10, 0] km s$^{-1}$ for G156.2+5.7, and [$-$27, $-$15] km s$^{-1}$ for G166.0+4.3. By examining extinction-distance profiles along the sightlines and identifying extinction jumps that spatially coincide with CO emission features, we derive distances of 1.82$\pm$0.13 kpc for G93.7$-$0.2, 3.05$\pm$0.15 kpc for G109.1$-$1.0, 0.60$\pm$0.15 kpc for G156.2+5.7, and 3.44$\pm$0.23 kpc for G166.0+4.3. Our extinction-based distances are largely consistent with previous estimates while with better accuracy and robustness.

Figures (15)

• Figure 1: The averaged $\rm ^{12}CO$ ($J$ = 1$-$0) spectra extracted from the regions of G93.7$-$0.2, G109.1$-$1.0, G156.2+5.7, and G166.0+4.3 by blue lines. Red shaded regions indicate the velocity components identified as associated with SNR-MC interactions, while gray shaded regions denote other unassociated velocity components along the sightline.
• Figure 2: Integrated intensity maps of $\rm ^{12}CO$ for G93.7$-$0.2 corresponding to the velocity ranges of $[-55, -30]$$\,{\rm km\, s^{-1}}$, $[-19, -3]$$\,{\rm km\, s^{-1}}$, $[-3, 6]$$\,{\rm km\, s^{-1}}$, and [7, 15] $\,{\rm km\, s^{-1}}$ respectively (see Figure \ref{['fig1']}(a)). Purple contours represent the 1420 MHz radio continuum emission, with the levels from 7.5 to 9.5 K with an interval of 0.5 K. Red triangles mark the representative $\rm ^{12}CO$ emission positions selected for extracting extinction-distance profiles.
• Figure 3: The color excess $E(B-V)$ as a function of distance for G93.7$-$0.2 derived from 3D extinction map. Different colored lines correspond to the red positions marked in Figure \ref{['fig2']}. Vertical gray shaded regions indicate the extinction jump for the corresponding MC: 7.5--10.0 kpc for $[-55, -30]$$\,{\rm km\, s^{-1}}$, 1.5--2.0 kpc for $[-19, -3]$$\,{\rm km\, s^{-1}}$, and 0.2--0.55 kpc for both $[-3, 6]$$\,{\rm km\, s^{-1}}$ and $[7, 15]$$\,{\rm km\, s^{-1}}$.
• Figure 4: Differential extinction maps ($\Delta E(B-V)$) toward G93.7$-$0.2 for the distance bins of 0--0.55 kpc, 0.55--1.5 kpc, 1.5--2.0 kpc, 2.0--4.2 kpc, 4.2--7.5 kpc, and 7.5--10.0 kpc respectively. Blue contours in the 1.5--2.0 kpc and 7.5--10.0 kpc bins represent $\rm ^{12}CO$ emission integrated over $[-19, -3]$$\,{\rm km\, s^{-1}}$ and $[-55, -30]$$\,{\rm km\, s^{-1}}$ respectively. In the 0--0.55 kpc bin, contours show $\rm ^{12}CO$ emission for the [7, 15] $\,{\rm km\, s^{-1}}$ (green) and $[-3, 6]$$\,{\rm km\, s^{-1}}$ (blue) components. Contours are plotted at levels of 6.0, 13.0, 21.0, and 28.0 $\,{\rm K~ km\, s^{-1}}$ for $[-55, -30]$$\,{\rm km\, s^{-1}}$ component; 3.0, 10.0, 17.0, and 24.0 $\,{\rm K~ km\, s^{-1}}$ for $[-19, -3]$$\,{\rm km\, s^{-1}}$ component; 4.5, 9.5, and 14.5 $\,{\rm K~ km\, s^{-1}}$ for $[-3, 6]$$\,{\rm km\, s^{-1}}$ component; 4.5, 11.5, and 18.5 $\,{\rm K~ km\, s^{-1}}$ for [7, 15] $\,{\rm km\, s^{-1}}$ component. The color bar indicates $\Delta E(B-V)$ values ranging from 0.1 to 1.2 mag.
• Figure 5: Integrated intensity maps of $\rm ^{12}CO$ for G109.1$-$1.0 corresponding to the $[-51, -46]$$\,{\rm km\, s^{-1}}$ and $[-12, -6.5]$$\,{\rm km\, s^{-1}}$ components (see Figure \ref{['fig1']}(b)). Purple contours represent the 1420 MHz radio emission shell of SNR, with the levels from 0 to 24.0 K with an interval of 3.0 K. The red triangles are used for the same purpose as in Figure \ref{['fig2']}.