Letter to the Editor

Detection of interstellar hydrogen peroxide^⋆

P. Bergman¹, B. Parise², R. Liseau³, B. Larsson⁴, H. Olofsson¹, K. M. Menten² and R. Güsten²

¹ Onsala Space Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden
e-mail: per.bergman@chalmers.se
² Max Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Department of Earth and Space Sciences, Chalmers University of Technology, 439 92 Onsala, Sweden
⁴ Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden

Received: 2 May 2011
Accepted: 25 May 2011

Abstract

Context. The molecular species hydrogen peroxide, HOOH, is likely to be a key ingredient in the oxygen and water chemistry in the interstellar medium.

Aims. Our aim with this investigation is to determine how abundant HOOH is in the cloud core ρ Oph A.

Methods. By observing several transitions of HOOH in the (sub)millimeter regime we seek to identify the molecule and also to determine the excitation conditions through a multilevel excitation analysis.

Results. We have detected three spectral lines toward the SM1 position of ρ Oph A at velocity-corrected frequencies that coincide very closely with those measured from laboratory spectroscopy of HOOH. A fourth line was detected at the 4σ level. We also found through mapping observations that the HOOH emission extends (about 0.05 pc) over the densest part of the ρ Oph A cloud core. We derive an abundance of HOOH relative to that of H₂ in the SM1 core of about 1 × 10^-10.

Conclusions. To our knowledge, this is the first reported detection of HOOH in the interstellar medium.