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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+, DfracN2H+– 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 DfracN2H+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 DfracN2H+in the range 0.03−0.1, which is several orders of magnitude larger than the cosmic D/H ratio (~10−5). The DfracN2H+across the shock front is enhanced by more than a factor of 2 (DfracN2H+~ 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 DfracN2H+~ 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.
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This content will become publicly available on January 1, 2026
Interaction between the supernova remnant W44 and the infrared dark cloud G034.77-00.55: Shock induced star formation
Context. We have studied the dense gas morphology and kinematics towards the infrared dark cloud (IRDC) G034.77-00.55, shock-interacting with the SNR W44, to identify evidence of early-stage star formation induced by the shock. Aims. We used high angular resolution N2H+(1−0) images across G034.77-00.55, obtained with the Atacama Large Millimeter/sub-Millimeter Array. N2H+is a well-known tracer of dense and cold material, optimal for identifying gas that has the highest potential to harbour star formation. Methods. The N2H+emission is distributed in two elongated structures, one towards the dense ridge at the edge of the source and one towards the inner cloud. Both elongations are spatially associated with well-defined mass-surface density features. The velocities of the gas in the two structures (i.e. 38–41 km s−1and 41–43 km s−1) are consistent with the lowest velocities of the J- and C-type parts, respectively, of the SNR-driven shock. A third velocity component is present at 43–45.5 km s–1. The dense gas shows a fragmented morphology with core-like fragments at scales consistent with the Jeans lengths, masses of ~1–20 M⊙, densities of (n(H2)≥105cm–3) sufficient to host star formation in free-fall timescales (a few 104yr), and with virial parameters that suggest a possible collapse. Results. The W44 driven shock may have swept up the encountered material, which is now seen as a dense ridge, almost detached from the main cloud, and an elongation within the inner cloud, well constrained in both N2H+emission and mass surface density. This shock compressed material may have then fragmented into cores that are either in a starless or pre-stellar stage. Additional observations are needed to confirm this scenario and the nature of the cores.
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- Award ID(s):
- 2009674
- PAR ID:
- 10569830
- Publisher / Repository:
- EDP Sciences
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 693
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A199
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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