N2H+ and C18O Depletion in a Cold Dark Cloud

By E. Bergin, Joao F. Alves, T. Huard, C. Lada. 2002

148 citations recorded by the source corpus.

We present sensitive, high angular resolution molecular line observations of C18O and N2H+ toward the dark globule B68. We directly compare these data with the near-infrared extinction measurements of Alves, Lada, & Lada to derive the first evidence for the depletion of N2H+, and by inference N2, in a prestellar dark cloud. We also find widespread C18O depletion throughout the centrally condensed core of the B68 cloud. Specifically, we find the N2H+ emission to peak in a shell partially surrounding the peak of dust extinction. Moreover, N2H+ peaks inside the much larger C18O depletion hole and has a smaller depletion zone, confirming theoretical predictions. These data are analyzed through a direct coupling of time-dependent chemical models to a radiation transfer code. This analysis highlights the importance of photodissociation at cloud edges and suggests that the CO abundance declines by 2 orders of magnitude from edge to center. In contrast, N2H+ declines in abundance, at minimum, by at least a factor of 2. Indeed, it is entirely possible that both N2H+ and N2 are completely absent from the central regions of the B68 core. The depletion of N2H+, and its parent molecule N2, opens up the possibility that the centers of dense cores, prior to the formation of a star, may evade detection by conventional methods of probing cores using molecular emission. Under these conditions, H2D+ may be the sole viable molecular probe of the innermost regions of star-forming cores.

Subfields: Astronomy and Astrophysics, Instrumentation, Organic Chemistry

View Paper: https://www.semanticscholar.org/paper/d5f1a3e1c227f46fb3e15a6405d48642e8a41bfa

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Citations in the corpus

On The Internal Structure Of Starless Cores. Physical and Chemical Properties of L1498 and L1517B (2004, unknown): “To derive the temperature, kinematics, and chemical structure of L1498 and L1517B, we now analyze their molecular emission.”
Physical Processes in the Interstellar Medium (2014, background): “…from nitrogen-bearing species, such as N2H+, more closely follows the dust emission, while emission f om carbon-bearing molecules, such as C18O or CS, often appears s a “ ing-lik ” str cture arou th dust emissi n peak (Bergin et al., 2002; Tafalla et al., 2002; L d t al , 2003; Maret et al., 2007).”
Probing the Evolutionary Status of Starless Cores through N2H+ and N2D+ Observations (2004, methodology): “Moreover, a 1.2 mm map of B68 taken with SIMBA (the facility bolometer at SEST) was published in Bianchi et al. (2003).”
ON THE STAR FORMATION RATES IN MOLECULAR CLOUDS (2010, background): “However such comparisons do exist for N2H + emission in three clouds, IC 5146, (Bergin et al. 2001) B68 (Bergin et al. 2002) and FeSt 1-457 (Aguti et al. 2007).”
Our astrochemical heritage (2012, background): “Nitrogen-bearing species have also been found to deplete from the gas phase, although not as much as CO (e.g., Bergin et al. 2002; Tafalla et al. 2006; Friesen et al. 2010).”