射电天文研究室知识库

We present 2.5-square-degree C2H N = 1-0 and N2H+ J = 1-0 maps of the rho Ophiuchi molecular cloud complex. These are the first large-scale maps of the rho Ophiuchi molecular cloud complex with these two tracers. The C2H emission is spatially more extended than the N2H+ emission. One faint N2H+ clump, Oph-M, and one C2H ring, OphRingSW, are identified for the first time. The observed C2H-to-N2H+ abundance ratio ([C2H]/[N2H+]) varies between 5 and 110. We modeled the C2H andN(2)H(+) abundances with 1D chemical models, which show a clear decline of [C2H]/ [N2H+] with chemical age. Such an evolutionary trend is little affected by temperatures when they are below 40 K. At high density (n(H) > 10(5) cm(-3)), however, the time it takes for the abundance ratio to drop at least one order of magnitude becomes less than the dynamical time (e.g., turbulence crossing time of similar to 10(5) yr). The observed [C2H]/[N2H+] difference between L1688 and L1689 can be explained by L1688 having chemically younger gas in relatively less dense regions. The observed [C2H]/[N2H+] values are the results of time evolution, accelerated at higher densities. For the relatively low density regions in L1688 where only C2H emission was detected, the gas should be chemically younger.