We present the results of 3D relativistic hydrodynamic simulations of interaction of active galactic nucleus jets with a dense turbulent two-phase interstellar medium, which would be typical of high-redshift galaxies. We describe the effect of the jet on the evolution of the density of the turbulent interstellar medium (ISM). The jet-driven energy bubble affects the gas to distances up to several kiloparsecs from the injection region. The shocks resulting from such interactions create a multiphase ISM and radial outflows. One of the striking result of this work is that low-power jets (P_jet ≲ 10⁴³ ergs⁻¹), although less efficient in accelerating clouds, are trapped in the ISM for a longer time and hence affect the ISM over a larger volume. Jets of higher power drill through with relative ease. Although the relativistic jets launch strong outflows, there is little net mass ejection to very large distances, supporting a galactic fountain scenario for local feedback.

The interstellar medium of the radio galaxy IC 5063 is highly perturbed by an AGN jet expanding in the gaseous disc of the galaxy. We model this interaction with relativistic hydrodynamic simulations and multiphase initial conditions for the interstellar medium and compare the results with recent observations. As the jets flood through the intercloud channels of the disc, they ablate, accelerate, and disperse clouds to velocities exceeding 400 km s⁻¹. Clouds are also destroyed or displaced in bulk from the central regions of the galaxy. Our models with jet powers of 10⁴⁴ and 10⁴⁵ erg s⁻¹ are capable of reproducing many of the observed features in the position velocity diagram of IC 5063, and confirm the notion that the jet is responsible for the strongly perturbed gas dynamics seen in the ionized, neutral, and molecular gas phases. In our simulations, we also see strong venting of the jet plasma perpendicular to the disc, which entrains clumps and diffuse filaments into the halo of the galaxy. Our simulations are the first 3D hydrodynamic simulations of the jet and interstellar matter of IC 5063.

We have performed a search over 3440 deg² of Epoch 1 (2017–2019) of the Very Large Array Sky Survey to identify unobscured quasars in the optical (0.2 < z < 3.2) and obscured active galactic nuclei (AGNs) in the infrared that have brightened dramatically in the radio over the past one to two decades. These sources would have been previously classified as “radio-quiet” quasars based on upper limits from the Faint Images of the Radio Sky at Twenty cm survey (1993–2011), but they are now consistent with “radio-loud” quasars ( ). A quasi-simultaneous, multiband (∼1–18 GHz) follow-up study of 14 sources with the VLA has revealed compact sources (<0.″1 or 2500%) but roughly steady fluxes over a few months at 3 GHz are inconsistent with extrinsic variability due to propagation effects, thus favoring an intrinsic origin. We conclude that our sources are powerful quasars hosting compact/young jets. This challenges the generally accepted idea that “radio-loudness” is a property of the quasar/AGN population that remains fixed on human timescales. Our study suggests that frequent episodes of short-lived AGN jets that do not necessarily grow to large scales may be common at high redshift. We speculate that intermittent but powerful jets on subgalactic scales could interact with the interstellar medium, possibly driving feedback capable of influencing galaxy evolution.

We propose that Gigahertz Peak Spectrum (GPS) and Compact Steep Spectrum (CSS) radio sources are the signposts of relativistic jet feedback in evolving galaxies. Our simulations of relativistic jets interacting with a warm, inhomogeneous medium, utilizing cloud densities and velocity dispersions in the range derived from optical observations, show that free–free absorption can account for the ∼ GHz peak frequencies and low-frequency power laws inferred from the radio observations. These new computational models replace a power-law model for the free–free optical depth a more fundamental model involving disrupted log-normal distributions of warm gas. One feature of our new models is that at early stages, the low-frequency spectrum is steep but progressively flattens as a result of a broader distribution of optical depths, suggesting that the steep low-frequency spectra discovered by Callingham et al. may possibly be attributed to young sources. We also investigate the inverse correlation between peak frequency and size and find that the initial location on this correlation is determined by the average density of the warm ISM. The simulated sources track this correlation initially but eventually fall below it, indicating the need for a more extended ISM than presently modelled. GPS and CSS sources can potentially provide new insights into the phenomenon of AGN feedback since their peak frequencies and spectra are indicative of the density, turbulent structure, and distribution of gas in the host galaxy.

We present a study of a luminous, z = 0.15, type-2 quasar (⁠|$L_{[\rm O III]}$|=10^42.8 erg s⁻¹) from the Quasar Feedback Survey. It is classified as ‘radio-quiet’ ( L_1.4 GHz=10^23.8 W Hz⁻¹); however, radio imaging reveals ∼ 1 kpc low-power jets (P_jet= 10⁴⁴ erg s⁻¹) inclined into the plane of the galaxy disk. We combine MUSE and ALMA observations to map stellar kinematics and ionised and molecular gas properties. The jets are seen to drive galaxy-wide bi-conical turbulent outflows, reaching W₈₀ = 1000 - 1300 km s⁻¹, in the ionised phase (traced via optical emission-lines), which also have increased electron densities compared to the quiescent gas. The turbulent gas is driven perpendicular to the jet axis and is escaping along the galaxy minor axis, reaching 7.5 kpc on both sides. Traced via CO(3–2) emission, the turbulent material in molecular gas phase is one-third as spatially extended and has 3 times lower velocity-dispersion as compared to ionised gas. The jets are seen to be strongly interacting with the interstellar medium (ISM) through enhanced ionised emission and disturbed/depleted molecular gas at the jet termini. We see further evidence for jet-induced feedback through significantly higher stellar velocity-dispersion aligned, and co-spatial with, the jet axis (< 5 ^○). We discuss possible negative and positive feedback scenarios arising due to the interaction of the low-power jets with the ISM in the context of recent jet-ISM interaction simulations, which qualitatively agree with our observations. We discuss how jet-induced feedback could be an important feedback mechanism even in bolometrically luminous ‘radio-quiet’ quasars.