Interstellar molecules containing noble gases in the diffuse and superhot region
Abstract
Naturally occurring noble gas molecules are rare in the Earth. But in the superhot region and favorable density of the space, noble gases can lead to the formation of some molecules. Recently two molecules containing the noble gases (HeH$^+$ and NeH$^+$) are identified in space. The elemental abundance of neon is much more than that of the argon. However, the presence of NeH$^+$ is yet to be confirmed in space. The hydroxyl radicals (-OH) are found to be significantly abundant around the similar region either in neutral or in the cationic form, hydroxyl cations of such noble gases (i.e., ArOH$^+$, HeOH$^+$, and NeOH$^+$) are yet to be identified. We employ a spectral synthesis code to examine the chemical evolution of the hydride and hydroxyl cations of the various isotopes of Ar, Ne, and He in the Crab Nebula filamentary region and calculate their line emissivity and intrinsic line surface brightness under such environment. We successfully explain the observed surface brightness of two transitions of ArH$^+$ (617 and 1234 GHz), one transition of OH$^+$ (971 GHz), and one transition of H$_2$ (2.12 $\mu$m). We explain the observed surface brightness ratios between various molecular and atomic transitions. We find that our model reproduces the overall observed features when a hydrogen number density of $\sim 10^4 - 10^5$ cm$^{-3}$ and a cosmic-ray ionization rate per H$_2$ of $\sim 10^{-11} - 10^{-9}$ s$^{-1}$ are chosen. The possibility of detecting some hydride and hydroxyl cations in the Crab nebula environment will also be highlighted.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1993D