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

## TL;DR

This study uses ALMA observations to analyze complex molecular gas kinematics in the inner 5 kpc of the merger system 4C12.50, revealing a rotating disk, high-velocity gas streams, and potential nuclear wind driven by jet activity.

## Contribution

First detailed ALMA analysis of molecular gas dynamics in 4C12.50, identifying a rotating disk, high-velocity filaments, and possible nuclear wind in a merging galaxy system.

## Key findings

- Detected a 4 kpc-wide rotating molecular gas disk with 3.8×10^9 M⊙ mass.
- Observed high-velocity gas filaments extending from the nucleus, with speeds up to 2200 km/s.
- Tentative evidence of a nuclear wind with a mass up to 1.5×10^9 M⊙, possibly driven by jet activity.

## 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 ($\sim$100 pc) and large ($\sim$100 kpc) scales, as well as the large X-ray cavity in which the system is embedded, are indicative of a jet that could have affected the ISM. We carried out observations of the CO(1-0), (3-2), and (4-3) lines with the Atacama Large Millimeter Array (ALMA) to determine basic properties (i.e., extent, mass, and excitation) of the cold molecular gas in this system, including its already-known wind. The CO emission reveals the presence of gaseous streams related to the merger, which result in a small ($\sim$4kpc-wide) disk around the western nucleus. The disk reaches a rotational velocity of 200 $kms^{-1}$ , and has a mass of 3.8($\pm$0.4)$\times$10${^9}M_{\odot}$. 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 $kms^{-1}$ and the total wind mass could be as high as 1.5($\pm$0.1)$\times$10$^9M_{\odot}$. 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.