Search for High-Extinction Regions in the Small Magellanic Cloud

We have applied the unsharp-masking technique to the 24 μm image of the SMC, obtained with the Spitzer, to search for high-extinction regions. Fifty-five candidate regions of high-extincion (namely high-contrast regions, HCRs) have been identified from the decremental contrast image. HCRs have a size of 8 - 14 pc and a peak contrast at 24 μm of 2 - 2.5%. To constrain physical properties of HCRs, we have performed observations of NH₃, N₂H⁺, HNC, HCO⁺, and HCN toward one of the HCRs, HCR LIRS36-east, using the ATCA and the Mopra telescope. No molecular line emission detected, but upper limits to column densities of molecular species suggest that HCRs are moderately dense with n ~ 10³ cm^-3. Two interesting properties of HCRs are shown below.