Herschel observations of ortho- and para-oxidaniumyl (H2O+) in spiral arm clouds toward Sgr B2(M)

TL;DR

This study reports Herschel telescope observations of H2O+ in different spin states toward Sgr B2(M), revealing an average ortho/para ratio of 4.8 in spiral arm clouds, with implications for understanding the physical conditions of interstellar gas.

Contribution

First detection and analysis of ortho- and para-H2O+ in spiral arm clouds toward Sgr B2(M), providing insights into their spin temperature and formation conditions.

Findings

Average o/p ratio of 4.8 indicating a spin temperature of 21 K

Detection of absorption in all spiral arm clouds between Sun and Sgr B2

Possible variation in o/p ratio below unity in certain velocity intervals

Abstract

H2O+ has been observed in its ortho- and para- states toward the massive star forming core Sgr B2(M), located close to the Galactic center. The observations show absorption in all spiral arm clouds between the Sun and Sgr B2. The average o/p ratio of H2O+ in most velocity intervals is 4.8, which corresponds to a nuclear spin temperature of 21 K. The relationship of this spin temperature to the formation temperature and current physical temperature of the gas hosting H2O+ is discussed, but no firm conclusion is reached. In the velocity interval 0 to 60 km/s, an ortho/para ratio of below unity is found, but if this is due to an artifact of contamination by other species or real is not clear.