Extended emission of D2H+ in a prestellar core

Parise, Berengere, Belloche, A., Du, F., Güsten, R. and Menten, K. M. 2011. Extended emission of D2H+ in a prestellar core. Astronomy and Astrophysics 526 , A31. 10.1051/0004-6361/201015475

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Abstract

Context. In the past years, the H2D+ and D2H+ molecules have gained attention as probes of cold and depleted dense molecular cloud cores. These ions are the basis of molecular deuterium fractionation, a common characteristic observed in star-forming regions. H2D+ is now routinely observed, but the search for its isotopologue D2H+ is still difficult because of the high frequency of its ground para transition (692 GHz). Aims. We observed molecular transitions of H2D+ and D2H+ in a cold prestellar core to characterize the roots of deuterium chemistry. Methods. Thanks to the sensitive multi-pixel CHAMP+ receiver on the APEX telescope where the required excellent weather conditions are met, we not only successfully detect D2H+ in the H-MM1 prestellar core located in the L1688 cloud, but also obtain information on the spatial extent of its emission. We also detect H2D+ at 372 GHz in the same source. We analyze these detections using a non-LTE radiative transfer code and a state-of-the-art spin-dependent chemical model. Results. This observation is the first secure detection of D2H+ in space. The emission is moreover extended over several pixels of the CHAMP+ array, i.e. on a scale of at least 40′′, corresponding to ~4800 AU. We derive column densities on the order of 1012–1013 cm-2 for both molecules in the LTE approximation depending on the assumed temperature, and up to two orders of magnitude higher based on a non-LTE analysis. Conclusions. Our modeling suggests that the level of CO depletion must be extremely high (>10, and even >100 if the temperature of the core is around 10 K) at the core center, contradicting CO depletion levels directly measured in other cores. Observation of the H2D+ spatial distribution and direct measurement of the CO depletion in H-MM1 will be essential to confirm whether present chemical models investigating the basis of deuterium fractionation of molecules need to be revised.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Subjects:	Q Science > QB Astronomy
Uncontrolled Keywords:	astrochemistry ; line: identification ; stars: formation ; ISM: molecules
Additional Information:	Pdf uploaded in accordance with publisher's policy at http://www.sherpa.ac.uk/romeo/issn/0004-6361/ (accessed 16/04/2014)
Publisher:	EDP Sciences
ISSN:	0004-6361
Related URLs:	http://dx.doi.org/10.1051/0004-6361/2010...
Date of First Compliant Deposit:	30 March 2016
Last Modified:	06 May 2023 22:34
URI:	https://orca.cardiff.ac.uk/id/eprint/52782

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