New upper limits on the interstellar O2 abundance

TL;DR

This study sets new, lower upper limits on the abundance of molecular oxygen in an interstellar cloud at z=0.685, challenging previous assumptions about oxygen chemistry in space.

Contribution

It provides the most stringent upper limits to date on interstellar O2 abundance using multi-telescope observations and analysis of absorption lines at high redshift.

Findings

O2/CO ratio $oxed{ ext{less than } 2 imes 10^{-3}}$ at 1$\sigma$

Oxygen abundance is at least seven times lower than previous limits

Implications for interstellar oxygen chemistry and molecular cloud composition

Abstract

We report new observations of molecular oxygen in absorption at z=0.685 in front of the radio source B0218+357. The lines at 56.3 and 118.7 GHz have been observed, redshifted to 33.4 and 70.5 GHz respectively, with the 12m at Kitt Peak, 43m at Green Bank telescopes, and the 45m Nobeyama radio telescope. Deriving the surface filling factor of the absorbing dark cloud with other lines detected at nearby frequencies, we deduce from the upper limits on the O2 lines a relative abundance of molecular oxygen with respect to carbon monoxyde of O2/CO $\la$ 2 10$^{-3}$ at 1$\sigma$, seven times lower than the previous limit. The consequences of this result are discussed.