Spatial Distribution of C4H and c-C3H2 in Cold Molecular Cores

C₄H and c-C₃H₂, as unsaturated hydrocarbon molecules, are important for forming large organic molecules in the interstellar medium. We present mapping observations of C₄H (N=9-8) lines, c-C₃H₂ (J₊₀, ₊₁=2₁, ₂-1₀, ₁) %at 85338. 894 MHz and H^13CO^+ (J=1-0) %at 86754. 2884 MHz toward 19 nearby cold molecular cores in the Milky Way with the IRAM 30m telescope. C₄H 9--8 was detected in 13 sources, while c-C₃H₂ was detected in 18 sources. The widely existing C₄H and c-C₃H₂ molecules in cold cores provide material to form large organic molecules. Different spatial distributions between C₄H 9--8 and c-C₃H₂ 2--1 were found. The relative abundances of these three molecules were obtained under the assumption of local thermodynamic equilibrium conditions with a fixed excitation temperature. The abundance ratio of C₄H to c-C₃H₂ ranged from 0. 34 0. 09 in G032. 93+02 to 4. 65 0. 50 in G008. 67+22. A weak correlation between C₄H/H^13CO^+ and c-C₃H₂/H^13CO^+ abundance ratios was found, with a correlation coefficient of 0. 46, which indicates that there is no tight astrochemical connection between C₄H and c-C₃H₂ molecules.