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 Ka,Kb = 21,2-10,1), and (HCO+ )-C-13(J = 1-0) toward 19 nearby cold molecular cores in the Milky Way with the IRAM 30 m 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/(HCO)-C-13+ and c-C3H2/(HCO)-C-13+ 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.