Deuterium fractionation across the infrared-dark cloud G034.77−00.55 interacting with the supernova remnant W44

¹ Department of Space, Earth and Environment, Chalmers University of Technology, 412 96 Gothenburg, Sweden
e-mail: giuliana.cosentino@chalmers.se
² Department of Astronomy, University of Virginia, 530 McCormick Road Charlottesville, 22904-4325, USA
³ Centro de Astrobiología (CSIC/INTA), Ctra. de Torrejón a Ajalvir km 4, Madrid, Spain
⁴ INAF Osservatorio Astronomico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁵ Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching bei München, Germany
⁶ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
⁷ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁸ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
⁹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁰ Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
¹¹ Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹² Star and Planet Formation Laboratory, Cluster for Pioneering Research, RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan

Received: 17 April 2023
Accepted: 31 May 2023

Abstract

Context. Supernova remnants (SNRs) may regulate star formation in galaxies. For example, SNR-driven shocks may form new molecular gas or compress pre-existing clouds and trigger the formation of new stars.

Aims. To test this scenario, we measured the deuteration of N₂H⁺, D_frac^N₂H+ – a well-studied tracer of pre-stellar cores – across the infrared-dark cloud (IRDC) G034.77-00.55, which is known to be experiencing a shock interaction with the SNR W44.

Methods. We use N₂H⁺ and N₂D⁺J = 1−0 single pointing observations obtained with the 30m antenna at the Instituto de Radioas-tronomia Millimetrica to infer D_frac^N₂H+ towards five positions across the cloud, namely a massive core, different regions across the shock front, a dense clump, an₊d ambient gas.

Results. We find D_frac^N₂H+ in the range 0.03−0.1, which is several orders of magnitude larger than the cosmic D/H ratio (~10⁻⁵). The D_frac^N₂H+ across the shock front is enhanced by more than a factor of 2 (D_frac^N₂H+ ~ 0.05 - 0.07) with respect to the ambient gas (≤0.03) and simila₊r to that measured generally in pre-stellar cores. Indeed, in the massive core and dense clump regions of this IRDC we measure D_frac^N₂H+ ~ 0.01.

Conclusions. We find enhanced deuteration of N₂H⁺ across the region of the shock, that is, at a level that is enhanced with respect to regions of unperturbed gas. It is possible that this has been induced by shock compression, which would then be indirect evidence that the shock is triggering conditions for future star formation. However, since unperturbed dense regions also show elevated levels of deuteration, further, higher-resolution studies are needed to better understand the structure and kinematics of the deuterated material in the shock region; for example, to decipher whether it is still in a relatively diffuse form or is already organised in a population of low-mass pre-stellar cores.