MAGNUM survey: Compact jets causing large turmoil in galaxies Enhanced line widths perpendicular to radio jets as tracers of jet-ISM interaction

Abstract

Context. Outflows accelerated by active galactic nuclei (AGN) are commonly observed in the form of coherent, mildly collimated high-velocity gas directed along the AGN ionisation cones and kinetically powerful (≳1044 − 45 erg s−1) jets. Recent works found that outflows can also be accelerated by low-power (≲1044 erg s−1) jets, and the most recent cosmological simulations indicate that these are the dominant source of feedback on sub-kiloparsec scales, but little is known about their effect on the galaxy host.

Aims. We study the relation between radio jets and the distribution and kinematics of the ionised gas in IC 5063, NGC 5643, NGC 1068, and NGC 1386 as part of our survey of nearby Seyfert galaxies called Measuring Active Galactic Nuclei Under MUSE Microscope (MAGNUM). All these objects host a small-scale (≲1 kpc) low-power (≲1044 erg s−1) radio jet that has small inclinations (≲45°) with respect to the galaxy disc.

Methods. We employed seeing-limited optical integral field spectroscopic observations from the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope to obtain flux, kinematic, and excitation maps of the extended ionised gas. We compared these maps with archival radio images and in one case, with Chandra X-ray observations.

Results. We detect a strong (up to ≳800–1000 km s−1) and extended (≳1 kpc) emission-line velocity spread perpendicular to the direction of the AGN ionisation cones and jets in all four targets. The gas excitation in this region of line-width enhancement is entirely compatible with shock ionisation. These broad and symmetric line profiles are not associated with a single coherent velocity of the gas. A ‘classical’ outflow component with net blueshifted and redshifted motions is also present, but is directed along the ionisation cones and jets.

Conclusions. We interpret the observed phenomenon as due to the action of the jets perturbing the gas in the galaxy disc. These intense and extended velocity spreads perpendicular to AGN jets and cones are indeed currently only observed in galaxies hosting a low-power jet whose inclination is sufficiently low with respect to the galaxy disc to impact on and strongly affect its material. In line with cosmological simulations, our results demonstrate that low-power jets are indeed capable of affecting the host galaxy.