Jets blowing bubbles in the young radio galaxy 4C 31.04

• Published in: arXiv.org 2019-02
• Main Authors: Zovaro, Henry R M, Sharp, Robert, Nesvadba, Nicole P H, Bicknell, Geoffrey V, Mukherjee, Dipanjan, Wagner, Alexander Y, Groves, Brent, Shreyam Krishna
• Format: Article
• Language: English
• Subjects: Active galactic nuclei; Adaptive optics; Bubbles; Clumps; Compact galaxies; Ejection; Galaxies; Infrared imaging; Infrared spectroscopy; Molecular gases; Near infrared radiation; Phase transitions; Plasma; Radio emission; Radio galaxies; Spatial resolution; Vapor phases
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1811.08971

We report the discovery of shocked molecular and ionized gas resulting from jet-driven feedback in the compact radio galaxy 4C 31.04 using near-IR imaging spectroscopy. 4C 31.04 is a \(\sim 100\) pc double-lobed Compact Steep Spectrum source believed to be a very young AGN. It is hosted by a giant elliptical with a \(\sim 10^{9}~\rm M_\odot\) multi-phase gaseous circumnuclear disc. We used high spatial resolution, adaptive optics-assisted \(H\)- and \(K\)-band integral field Gemini/NIFS observations to probe (1) the warm (\(\sim 10^3~\rm K\)) molecular gas phase, traced by ro-vibrational transitions of \(\rm H_2\), and (2), the warm ionized medium, traced by the [Fe II]\(_{1.644~\rm \mu m}\) line. The [Fe II] emission traces shocked gas ejected from the disc plane by a jet-blown bubble \(300-400~\rm pc\) in diameter, whilst the \(\rm H_2\) emission traces shock-excited molecular gas in the interior \(\sim 1~\rm kpc\) of the circumnuclear disc. Hydrodynamical modelling shows that the apparent discrepancy between the extent of the shocked gas and the radio emission can occur when the brightest regions of the synchrotron-emitting plasma are temporarily halted by dense clumps, whilst less bright plasma can percolate through the porous ISM and form an energy-driven bubble that expands freely out of the disc plane. This bubble is filled with low surface-brightness plasma not visible in existing VLBI observations of 4C 31.04 due to insufficient sensitivity. Additional radial flows of jet plasma may percolate to \(\sim \rm kpc\) radii in the circumnuclear disc, driving shocks and accelerating clouds of gas, giving rise to the \(\rm H_2\) emission.