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Chemical modeling of Infrared Dark Clouds: the Role of Surface Chemistry | | T. Vasyunina
; A. I. Vasyunin
; E. Herbst
; H. Linz
; | | Date: |
26 Mar 2012 | | Abstract: | We simulate the chemistry of infrared dark clouds (IRDCs) with a model in
which the physical conditions are homogeneous and time-independent. The
chemistry is solved as a function of time with three networks: one purely
gas-phase, one that includes accretion and desorption, and one, the complete
gas-grain network, that includes surface chemistry in addition. We compare our
results with observed molecular abundances for two representative IRDCs --
IRDC013.90-1 and IRDC321.73-1 -- using the molecular species N$_2$H$^+$,
HC$_3$N, HNC, HCO$^+$, HCN, C$_2$H, NH$_3$ and CS. IRDC013.90-1 is a cold IRDC,
with a temperature below 20 K, while IRDC321.73-1 is somewhat warmer, in the
range 20 - 30 K. We find that the complete gas-grain model fits the data very
well, but that the goodness-of-fit is not sharply peaked at a particular
temperature. Surface processes are important for the explanation of the high
gas-phase abundance of N$_2$H$^+$ in IRDC321.73-1. The general success of the
0-D model in reproducing single-dish observations of our limited sample of 8
species shows that it is probably sufficient for an explanation of this type of
data. To build and justify more complicated models, including spatial
temperature and density structure, contraction, and heating, we require
high-resolution interferometric data. | | Source: | arXiv, 1203.5561 | | Services: | Forum | Review | PDF | Favorites | |
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