Singly- and doubly-deuterated formaldehyde in massive star-forming regions

Abstract

Deuterated molecules are good tracers of the evolutionary stage of star-forming cores. During the star formation process, deuterated molecules are expected to be enhanced in cold, dense pre-stellar cores and to deplete after protostellar birth. In this paper we study the deuteration fraction of formaldehyde in high-mass star-forming cores at different evolutionary stages to investigate whether the deuteration fraction of formaldehyde can be used as an evolutionary tracer. Using the APEX SEPIA Band 5 receiver, we extended our pilot study of the $J$=3$\to$2 rotational lines of HDCO and D${}_2$CO to eleven high-mass star-forming regions that host objects at different evolutionary stages. High-resolution follow-up observations of eight objects in ALMA Band 6 were performed to reveal the size of the H${}_2$CO emission and to give an estimate of the deuteration fractions HDCO/H${}_2$CO and D${}_2$CO/HDCO at scales of $\sim$6" (0.04-0.15 pc at the distance of our targets). Our observations show that singly- and doubly deuterated H${}_2$CO are detected toward high-mass protostellar objects (HMPOs) and ultracompact HII regions (UCHII regions), the deuteration fraction of H${}_2$CO is also found to decrease by an order of magnitude from the earlier HMPO phases to the latest evolutionary stage (UCHII), from $\sim$0.13 to $\sim$0.01. We have not detected HDCO and D${}_2$CO emission from the youngest sources (high-mass starless cores, HMSCs). Our extended study supports the results of the previous pilot study: the deuteration fraction of formaldehyde decreases with evolutionary stage, but higher sensitivity observations are needed to provide more stringent constraints on the D/H ratio during the HMSC phase. The calculated upper limits for the HMSC sources are high, so the trend between HMSC and HMPO phases cannot be constrained.

15 pages, 4 figures, 4 tables, accepted for publication in A&A

References in corpus (11)

• Survey of ortho-H2D+(1_{1,0}-1_{1,1}) in dense cloud cores
• The N2D+/N2H+ ratio as an evolutionary tracer of Class 0 protostars
• SEPIA - a new single pixel receiver at the APEX Telescope
• Deuteration and evolution in the massive star formation process: the role of surface chemistry
• DCO${}^{+}$, DCN and N${}_2$D${}^{+}$ reveal three different deuteration regimes in the disk around the Herbig Ae star HD163296
• A Hunt for Massive Starless Cores
• Decrease of the organic deuteration during the evolution of Sun-like protostars: the case of SVS13-A
• Deuteration around the ultracompact HII region Mon R2
• The ALMA-PILS survey: Gas dynamics in IRAS 16293$-$2422 and the connection between its two protostars
• H${}_2$ ortho-to-para conversion on grains: A route to fast deuterium fractionation in dense cloud cores?
• Gas vs. solid phase deuterated chemistry: HDCO and D${}_2$CO in massive star-forming regions