2024ApJ...969...33L

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 = 2_1,2-1_0,1), and H¹³CO⁺ (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/H¹³CO⁺ and c-C₃H₂/H¹³CO⁺ 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.