Distribution of the [C I] emission in the ρ Ophiuchi dark cloud

The P-l(1)-P-3(0) fine-structure line of the neutral carbon atom ([C I]) has been mapped over the 1.degrees8 x 1.degrees3 area of the L1688 cloud in the rho Ophiuchi region with the Mount Fuji submillimeter-wave telescope. The P-3(2)-P-3(1) line of [C I] has also been observed toward two representative positions to evaluate the excitation temperature of the [C I] lines. The overall extent of the [C I] distribution generally resembles that of the (CO)-C-13 distribution. The [C I] distribution has two major peaks; one ( peak I) is at rho Oph A, and the other (peak II) is toward the east side of the (CO)-O-18 core in the southern part of L1688. Peak II is located beyond the (CO)-O-18 core with respect to the exciting star HD 147889. The C-0 column density is 5.0 x 10(17) cm(-2) toward peak II. The spatial distribution of the [C I] emission is compared with plane-parallel photodissociation region (PDR) models, which suggest that peak II is associated with a lower density PDR front, adjacent to the dense cloud cores observed in the (CO)-O-18 line emission. Alternatively, peak II is in the early stage of chemical evolution, where C-0 has not been completely converted to CO. In this case, the difference in the [C I] and (CO)-O-18 distributions represents an evolutionary sequence. This is consistent with a picture of a shock-compressed formation of the dense cores in this region due to influences from the Sco OB2 association.