Journal
ASTROPHYSICAL JOURNAL
Volume 718, Issue 2, Pages 666-682Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/718/2/666
Keywords
ISM: kinematics and dynamics; ISM: molecules; ISM: structure; radio lines: ISM; stars: formation
Categories
Funding
- University of Victoria
- National Research Council Canada
- National Science and Engineering Research Council of Canada
- National Science Foundation [0708158]
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [0708158] Funding Source: National Science Foundation
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We present N2D+ 3-2 (IRAM), and H2D+ 1(11)-1(10) and N2H+ 4-3 (JCMT) maps of the small cluster-forming Ophiuchus B2 core in the nearby Ophiuchus molecular cloud. In conjunction with previously published N2H+ 1-0 observations, the N2D+ data reveal the deuterium fractionation in the high-density gas across Oph B2. The average deuterium fractionation R-D = N(N2D+)/N(N2H+) similar to 0.03 over Oph B2, with several small scale R-D peaks and a maximum R-D = 0.1. The mean RD is consistent with previous results in isolated starless and protostellar cores. The column density distributions of both H2D+ and N2D+ show no correlation with total H-2 column density. We find, however, an anticorrelation in deuterium fractionation with proximity to the embedded protostars in Oph B2 to distances greater than or similar to 0.04 pc. Destruction mechanisms for deuterated molecules require gas temperatures greater than those previously determined through NH3 observations of Oph B2 to proceed. We present temperatures calculated for the dense core gas through the equating of non-thermal line widths for molecules (i.e., N2D+ and H2D+) expected to trace the same core regions, but the observed complex line structures in B2 preclude finding a reasonable result in many locations. This method may, however, work well in isolated cores with less complicated velocity structures. Finally, we use RD and the H2D+ column density across Oph B2 to set a lower limit on the ionization fraction across the core, finding a mean x(e,lim) greater than or similar to few x 10(-8). Our results show that care must be taken when using deuterated species as a probe of the physical conditions of dense gas in star-forming regions.
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