ALMA view of the $\rho$ Ophiuchi A PDR with a 360-au beam: the [CI] emission originates from the plane-parallel PDR and extended gas

Abstract

We present the results of data analysis of the [CI] (${}^3{P}_1$-${}^3{P}_0$) emission from the $\rho$ Ophiuchi A photon-dominated region (PDR) obtained in the ALMA ACA stand-alone mode with a spatial resolution of 2.''6 (360 au). The [CI] emission shows filamentary structures with a width of $\sim$1000 au, which are adjacent to the shell structure seen in the 4.5 $\mu$m map. We found that the 4.5 $\mu$m emission, C${}^0$, and CO are distributed in this order from the excitation star (S1) in a complementary pattern. These results indicate that [CI] is emitted from a thin layer in the PDR generated by the excitation star, as predicted in the plane-parallel PDR model. In addition, extended [CI] emission was also detected, which shows nearly uniform integrated intensity over the entire field-of-view (1.'6$\times$1.'6). The line profile of the extended component is different from that of the above shell component. The column density ratio of C${}^0$ to CO in the extended component was $\sim$2, which is significantly higher than those of Galactic massive star-forming regions (0.1-0.2). These results suggest that [CI] is emitted also from the extended gas with a density of $n_{{\mathrm{H}}_2}\sim 10^3$ cm${}^{-3}$, which is not greatly affected by the excitation star.

11 pages, 4 figures, ApJL accepted

References in corpus (5)

• The distance to the Orion Nebula
• The Gould's Belt Distances Survey (GOBELINS) I. Trigonometric parallax distances and depth of the Ophiuchus complex
• Revealing the physical properties of molecular gas in Orion with a large scale survey in J=2-1 lines of 12CO, 13CO and C18O
• Observations of the [CI] (${}^3{P}_1$-${}^3{P}_0$) emission toward the massive star-forming region RCW38: further evidence for highly-clumped density distribution of the molecular gas
• ALMA observations of layered structures due to CO selective dissociation in the $\rho$ Ophiuchi A plane-parallel PDR

Cited by in corpus (3)

• The subthermal excitation of the C{\sc i} lines in the molecular gas reservoirs of galaxies: its significance and potential utility
• Emergence of high-mass stars in complex fiber networks (EMERGE) II. The need for data combination in ALMA observations
• CI and CO in Nearby Spiral Galaxies -- I. Line Ratio and Abundance Variations at ~ 200 pc Scales