CO investigation of z=0.4-1.5 galaxies

TL;DR

This study used IRAM-30m observations to search for CO emission in intermediate-redshift galaxies, highlighting the challenges in detecting molecular gas in this redshift range.

Contribution

First attempt to constrain molecular content in z=0.4-1.5 infrared-bright galaxies using CO lines, addressing a poorly explored redshift range.

Findings

No CO detections achieved in the three targeted galaxies.

Upper limits on molecular gas mass are between 4 and 8 billion solar masses.

Highlights difficulties in selecting sources with detectable molecular content at these redshifts.

Abstract

We report on the results of an IRAM-30m search for CO emission lines in three galaxies at intermediate redshifts. The idea was to investigate the molecular content of galaxies bright in the infrared at z=0.4-1.5, a redshift desert for molecular line studies, poorly investigated as of yet. We integrated 8-10h per source and did not succeed in detecting any of the sources. From our upper limits, we are able to constrain the molecular gas content in these systems to less than 4 to 8 x 10^9 Mo, assuming a CO-to-H_2 conversion factor (\alpha=0.8 Mo/(K km s^-1 pc^2)). We stress the current difficulty of selecting sources with a detectable molecular content, a problem that will be faced by the ALMA First Science projects.