Complex molecular gas kinematics in the inner 5 kpc of 4C12.50 as seen by ALMA^⋆

¹ Department of Astrophysics, Astronomy & Mechanics, Faculty of Physics, National and Kapodistrian University of Athens, Panepistimiopolis, Zografos 15784, Greece
² Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
e-mail: constant@mpa-garching.mpg.de
³ Institute for Astronomy, Astrophysics, Space Applications, and Remote Sensing, National Observatory of Athens, 15236 Penteli, Greece
⁴ Observatoire de Paris, LERMA, 61 Av. de l’Observatoire, 75014 Paris, France

Received: 11 October 2018
Accepted: 19 July 2019

Abstract

The nearby system 4C12.50, also known as IRAS 13451+1217 and PKS 1345+12, is a merger of gas-rich galaxies with infrared and radio activity. It has a perturbed interstellar medium (ISM) and a dense configuration of gas and dust around the nucleus. The radio emission at small (∼100 pc) and large (∼100 kpc) scales, as well as the large X-ray cavity in which the system is embedded, are indicative of a jet that could have affected the ISM. We carried out observations of the CO(1−0), (3−2), and (4−3) lines with the Atacama Large Millimeter Array (ALMA) to determine basic properties (i.e., extent, mass, and excitation) of the cold molecular gas in this system, including its already-known wind. The CO emission reveals the presence of gaseous streams related to the merger, which result in a small (∼4 kpc-wide) disk around the western nucleus. The disk reaches a rotational velocity of 200 km s⁻¹, and has a mass of 3.8(±0.4) × 10⁹ M_⊙. It is truncated at a gaseous ridge north of the nucleus that is bright in [O III]. Regions with high-velocity CO emission are seen at signal-to-noise ratios of between 3 and 5 along filaments that radially extend from the nucleus to the ridge and that are bright in [O III] and stellar emission. A tentative wind detection is also reported in the nucleus and in the disk. The molecular gas speed could be as high as 2200 km s⁻¹ and the total wind mass could be as high as 1.5(±0.1) × 10⁹ M_⊙. Energetically, it is possible that the jet, assisted by the radiation pressure of the active nucleus or the stars, accelerated clouds inside an expanding bubble.