Detection of C I in Absorption toward PKS 1830 – 211 with the eSMA

Abstract

We report the first science observations and results obtained with the "extended" SMA (eSMA), which is composed of the SMA (Submillimeter Array), JCMT (James Clerk Maxwell Telescope), and CSO (Caltech Submillimeter Observatory). Redshifted absorptions at z = 0.886 of C I (3P1-3P0) were observed with the eSMA with an angular resolution of 0".55 × 0".22 at 1.1 mm toward the southwestern image of the remarkable lensed quasar PKS 1830–211, but not toward the northeastern component at a separation of ~1". Additionally, SMA observations of CO, 13CO, and C18O (all J = 4-3) were obtained toward this object: CO was also detected toward the southwest component, but none of the isotopologues were. This is the first time [C I] has been detected in this object, allowing the first direct determination of relative abundances of neutral atomic carbon to CO in the molecular clouds of a spiral galaxy at z > 0.1. The [C I] and CO profiles can be decomposed into two and three velocity components, respectively. We derive C/CO column density ratios ranging from ≾ 0.5 (representative of dense cores) to ~2.5 (close to translucent cloud values). This could indicate that we are seeing environments with different physical conditions or that we are witnessing the chemical evolution of regions where C has not completely been converted into CO.

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