CO emission in optically obscured (type-2) quasars at redshifts z=0.1-0.4

TL;DR

This study detects CO emission in half of a sample of type-2 quasars at z=0.1-0.4, revealing their molecular gas content and suggesting similarities with type-1 quasars, while also noting signs of past or ongoing mergers.

Contribution

First detection of CO emission in a sample of type-2 quasars at intermediate redshifts, providing insights into their molecular gas properties and merger activity.

Findings

CO detected in 5 out of 10 sources with gas masses of (2-16)x10^9 Msun

Line profiles are narrow and single-peaked, indicating no strong merger signatures in most cases

At least one source shows optical signs of a merger, suggesting diverse evolutionary states

Abstract

We present a search for CO emission in a sample of ten type-2 quasar host galaxies with redshifts of z=0.1-0.4. We detect CO(J=1-0) line emission with >=5sigma in the velocity integrated intensity maps of five sources. A sixth source shows a tentative detection at the ~4.5sigma level of its CO(J=1-0) line emission. The CO emission of all six sources is spatially coincident with the position at optical, infrared or radio wavelengths. The spectroscopic redshifts derived from the CO(J=1-0) line are very close to the photometric ones for all five detections except for the tentative detection for which we find a much larger discrepancy. We derive gas masses of ~(2-16)x10^9Msun for the CO emission in the six detected sources, while we constrain the gas masses to upper limits of Mgas<=8x10^9Msun for the four non-detections. These values are of the order or slightly lower than those derived for type-1 quasars. The line profiles of the CO(J=1-0) emission are rather narrow (<=300km/s) and single peaked, unveiling no typical signatures for current or recent merger activity, and are comparable to that of type-1 quasars. However, at least one of the observed sources shows a tidal-tail like emission in the optical that is indicative for an on-going or past merging event. We also address the problem of detecting spurious ~5sigma emission peaks within the field of view.