The kinetic temperature of a molecular cloud at redshift 0.9: Ammonia in the gravitational lens PKS1830-211

TL;DR

This study detects ammonia inversion lines in a galaxy at redshift 0.9, revealing a complex temperature structure with a dominant 80 K component and a warmer gas at least 600 K, providing insights into molecular cloud conditions in a spiral arm.

Contribution

First detection of high-excitation ammonia lines in a galaxy at redshift 0.9, revealing detailed kinetic temperature structure of molecular gas in a spiral arm.

Findings

Majority of ammonia gas at ~80 K

Presence of significantly warmer gas at ≥600 K

Column densities of ammonia are (5-10) x 10^14 cm^-2

Abstract

Using the Green Bank Telescope (GBT), we have detected the (J,K) = (1,1) to (10,10) ammonia inversion lines, up to 1030 K above the ground state, in a face-on spiral galaxy viewed against the radio continuum of the lensed background source PKS 1830-211. The ammonia absorption lines, seen at redshift 0.886, appear to be optically thin with absolute peak flux densities up to 2.5 percent of the total continuum of the background source. Measured intensities are consistent with a kinetic temperature of 80 K for 80-90 percent of the ammonia column. The remaining gas is warmer, reaching at least 600 K. Column density and fractional abundance are of order (5-10) x 10^14 cm^-2 and (1.5-3.0) x 10^-8. Similarities with a hot ammonia absorption component observed toward the Sgr B2 region close to the Galactic center may suggest that the Sgr B2 component also originates from warm diffuse low-density molecular gas. The warm ammonia column observed toward PKS 1830-211 is unique in the sense that it originates in a spiral arm.