Detection of CI in absorption towards PKS 1830-211 with the eSMA

TL;DR

This paper reports the first detection of neutral atomic carbon ([CI]) in absorption toward the lensed quasar PKS 1830-211 using the eSMA, providing new insights into the molecular cloud composition in a galaxy at z>0.1.

Contribution

First detection of [CI] in absorption in a high-redshift galaxy, enabling direct measurement of C/CO ratios and analysis of physical conditions in molecular clouds.

Findings

[CI] detected at z=0.886 with high angular resolution.

C/CO ratios vary from <0.5 to ~2.5, indicating diverse environments.

First direct measurement of atomic carbon abundance in this galaxy.

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 CI (^3P_1 - ^3P_0) were observed with the eSMA with an angular resolution of 0.55"x0.22" 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 SW component, but none of the isotopologues were. This is the first time [CI] is 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 [CI] 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 clouds values). This could indicate that we are seeing environments with different physical conditions or that we are witnessing chemical evolution of regions where C has not completely been converted into CO.