Dense molecular outflows traced by HCO + (1-0) and HNC (1-0) in massive star-forming regions

Authors:
Open Access
Publisher website
Google Scholar
Abstract
Context. Molecular outflows are important signposts of star formation since they provide critical feedback to molecular clouds. Aims. We systematically investigate the dynamical and energetic characteristics of dense molecular outflows in 22 massive star-forming regions with high-precision parallax distances. Methods. We present on-the-fly mapping observations of HCO + , HNC, and their optically thin isotopologs H 13 CO + and HN 13 C ( J = 1-0) using the IRAM 30 m telescope aimed toward our sample targets. Results. Dense molecular outflows were identified through line-wing analysis, which yielded high detection rates of 81.8% for HCO + and 77.3% for HNC; most sources exhibit distinct bipolar morphologies. A robust scaling relation is established between the dense outflow mass ( M out ) and the core mass ( M core ), M out ∝ M core α . The HCO + tracer yields a sublinear index of α = 0.68, indicating that the efficiency of generating dense outflows relative to the total mass reservoir decreases at the high-mass end. In contrast, HNC exhibits a steeper slope ( α = 1.13), likely reflecting temperature-dependent abundance increases in massive star-forming regions. Conclusions. These results highlight the complex, multiphase nature of stellar feedback and underscore the necessity of sourcespecific chemical modeling of high-mass star-forming environments. Excitation analysis indicates that HCO + J=1-0 traces extended, cooler outflow gas due to its lower critical density, while HCO + J=3-2 traces warmer, denser gas near the protostar, which is consistent with the derived spatial separations between the red and blue peaks of the two transitions in the same sources.
Funding Information
  • National Natural Science Foundation of China (12503031)
  • the Postdoctoral Fellowship Program of CPSF (GZC20252099)
  • Shanghai Post-doctoral Excellence Program (No. 2024379)
  • Natural Science Foundation of Shanghai (No. 25ZR1402267)

This publication has 35 references indexed in Scilit: