An ALMA Early Science survey of molecular absorption lines toward PKS1830-211 -- Analysis of the absorption profiles

TL;DR

This ALMA survey of the z=0.89 absorber toward PKS1830-211 reveals extensive molecular absorption, indicating complex gas dynamics and composition, with potential for high-redshift diffuse gas detection.

Contribution

First comprehensive ALMA spectral survey of molecular absorption lines in this system, providing new insights into gas structure, composition, and dynamics at high redshift.

Findings

Detected 42 species and 14 isotopologues toward SW image.

Absorption over large velocity intervals suggests complex galaxy structure.

Ground-state water lines are promising for high-redshift diffuse gas detection.

Abstract

We present the first results of an ALMA spectral survey of strong absorption lines for common interstellar species in the z=0.89 molecular absorber toward the lensed blazar PKS1830-211. The dataset brings essential information on the structure and composition of the absorbing gas in the foreground galaxy. In particular, we find absorption over large velocity intervals (gtrsim 100 km/s) toward both lensed images of the blazar. This suggests either that the galaxy inclination is intermediate and that we sample velocity gradients or streaming motions in the disk plane, that the molecular gas has a large vertical distribution or extraplanar components, or that the absorber is not a simple spiral galaxy but might be a merger system. The number of detected species is now reaching a total of 42 different species plus 14 different rare isotopologues toward the SW image, and 14 species toward the NE line-of-sight. The abundances of CH, H2O, HCO+, HCN, and NH3 relative to H2 are found to be comparable to those in the Galactic diffuse medium. Of all the lines detected so far toward PKS1830-211, the ground-state line of ortho-water has the deepest absorption. We argue that ground-state lines of water have the best potential for detecting diffuse molecular gas in absorption at high redshift.