It is crucial to estimate the elemental depletion in the interstellar medium (ISM) to successfully and accurately simulate the chemical evolution in various astrophysical environments such as molecular clouds or star forming regions.
Current investigations show a depletion of nearly all elements as the density of the clouds increases. The majority of the depleted elements can be found in the gas phase (molecular form) and in the icy grain mantles. However, the process of sulfur depletion in dense cores has remained an unanswered question for decades, with nearly 99% of depleted sulfur still unaccounted for. This is called as sulfur depletion or the missing sulfur problem in dark clouds or star forming regions.
IQBAL Wasim, of Astrochemistry group (lead by LI Xiaohu) at Xinjiang Astronomical Observatory (XAO) of the Chinese Academy of Sciences (CAS), together with TUO Juan and her supervisors and collaborators, used data obtained from the Nanshan 26 m Radio Telescope (NSRT 26 m) to study carbon chain sulfur bearing species (C2S and C3S) toward a molecular cloud TMC-1.
Their study was published in Chinese Physics Letters.
The researchers found that depending on the type of dense core, as determined by the C/O ratio, sulfur depletion could occur in sources where the C/O ratio exceeds 0.75.
Their findings indicate that C/O ratio is a crucial parameter, and plays a key role in determining the evolution of sulfur bearing species in molecular clouds. In Figure 1, simulated gas phase abundances for C2S and C3S are shown as a function of time (detailed description is given in the figure caption). Therefore, the C/O ratio should be chosen carefully based on the source type; otherwise, it could result in significant inaccuracies in the simulation results.Furthermore, better observational constrains on the exact C/O ratio are required for the successful astronomical simulations of C2S and C3S abundances, as well as the abundances of other sulfur bearing species.
The results of this research provide more insights into the sulfur depletion or the missing sulfur problem in dark clouds or star forming region.
Figure 1: Left panel: Impact of varying C/O ratio on the simulated gas-phase abundances of C2S (blue lines) and C3S (red lines), with fo(S+) = 1.5 × 10-5. Right panel: Impact of Sulfur depletion on the simulated abundance of C2S (blue lines) and C3S (red lines), with C/O = 1. Simulated abundance are compared with observed values within the time range of 2× 105 to 106 years, which are lower and upper limits for suggested age of TMC-1 cloud.
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