Unveiling the mask on the ULIRG-to-QSO transition object [H89]1821+643 at z = 0.3: A gas-poor/gas-rich galaxy merger and the implications for co-based dynamical mass estimates

Abstract

We report the detection of the 12CO J = 1-0 emission line in [H89]1821+643, one of the most optically luminous quasi-stellar objects (QSOs) in the local universe, and a template ULIRG-to-QSO transition object, located in a rich, cool-core cluster at z = 0.297. The CO emission is likely to be extended, highly asymmetric with respect to the center of the host elliptical where the QSO resides, and correspond with a molecular gas mass of ∼8.0 × 109 M⊙. The dynamical mass enclosed by the CO emission-line region could amount to ∼1.7 × 1012 M ⊙ (80% of the total mass of the elliptical host). The bulk of the CO emission is located at ∼9kpc southeast from the nuclei position, close to a faint optical structure, suggesting that the CO emission could either represent a gas-rich companion galaxy merging with the elliptical host or a tail-like structure reminiscent of a previous interaction. We argue that the first scenario is more likely given the large masses implied by the CO source, which would imply a highly asymmetric elliptical host. The close alignment between the CO emission's major axis and the radio plume suggests a possible role in the excitation of the ambient gas reservoir by the latter. The stacking technique was used to search for CO emission and 3-mm continuum emission from galaxies in the surrounding cluster. However, no detection was found toward individual galaxies or the stacked ensemble of galaxies, with a 3σ limit of <1.1 × 109 M⊙ for the molecular gas. © 2011 The American Astronomical Society. All rights reserved.