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

C _4 H and c -C _3 H _2 , as unsaturated hydrocarbon molecules, are important for forming large organic molecules in the interstellar medium. We present mapping observations of C _4 H ( N = 9−8) lines, c -C _3 H _2 ( J _Ka _, _Kb = 2 _1,2 –1 _0,1 ), and H ^13 CO ^+ ( J = 1−0) toward 19 nearby cold molecular cores in the Milky Way with the IRAM 30 m telescope. C _4 H 9–8 was detected in 13 sources, while c -C _3 H _2 was detected in 18 sources. The widely existing C _4 H and c -C _3 H _2 molecules in cold cores provide material to form large organic molecules. Different spatial distributions between C _4 H 9–8 and c -C _3 H _2 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 C _4 H to c -C _3 H _2 ranged from 0.34 ± 0.09 in G032.93+02 to 4.65 ± 0.50 in G008.67+22. A weak correlation between C _4 H/H ^13 CO ^+ and c -C _3 H _2 /H ^13 CO ^+ abundance ratios was found, with a correlation coefficient of 0.46, which indicates that there is no tight astrochemical connection between C _4 H and c -C _3 H _2 molecules.