###### Abstract

Radio activity in AGN (Active Galactic Nuclei) produce feedback on the host
galaxy via the impact of the relativistic jets on the circumnuclear gas.
Although radio jets can reach up to several times the optical radius of the
host galaxy, in this review we focus on the observation of the feedback
deposited locally in the central region of the host galaxies, in the form of
outflows due to the jet-gas interaction. We begin by discussing how galaxy
mergers and interactions are the most favored scenario for triggering radio
AGN after gas accretion to the nuclear supermassive black hole and star
formation enhancement in the nuclear region, observed in particular in the
most luminous sources. We then discuss observational signatures of the process
of jet-gas coupling, in particular the resulting outflows and their effects on
the host galaxy. These include the presence of shock signatures and the
detection of outflows not only along the radio jet but perpendicular to it in
many sources. Although most of the studies are done via the observation of
ionized gas, molecular gas is also being increasingly observed in outflow,
contributing to the bulk of the mass outflow rate. Even though most radio
sources present outflow kinetic powers that do not reach $1\%\,L_{bol}$, and
thus do not seem to provide an immediate impact on the host galaxy, they act
to heat the ISM gas, preventing star formation, slowing the galaxy mass build-
up process and limiting the stellar mass growth, in a “maintenance mode"
feedback.

###### keywords:

Active galaxies; galaxy evolution; galaxy jets; galaxy kinematics and
dynamics; ISM

1 1 0 https://doi.org/ The interplay between radio AGN activity and their host
galaxies The interplay between radio AGN activity and their host galaxies
Guilherme S. Couto 1 and Thaisa Storchi-Bergmann 2 Guilherme S. Couto and
Thaisa Storchi-Bergmann Couto, G.S.; Storchi-Bergmann, T.

##  1 Introduction

The Active Galactic Nuclei (AGN) population can be represented by two main
categories. In the first category, Quasars and Seyfert galaxies, sources of
high bolometric luminosities, capable of generating winds through radiation
pressure due to their accretion rate close to Eddington, usually found in
wide-angle outflows, are commonly distinguished as radiative-mode (or
sometimes also called quasar-mode) AGNs. In the second category, the so called
radio-mode AGN (or jet-mode, or kinetic-mode), the central engine launches
powerful collimated jets of relativistic particles accelerated in the inner
regions of the accretion disk due to its intense magnetic fields. The origin
of the difference between these two categories is believed to happen within
the accretion disk structure and internal thermodynamics, and the resulting
mass accretion rates (Heckman and Best, 2014) (and references therein).

Radio emission is one of the most distinctive tracers of nuclear activity in
galaxies. The radio jets can be extremely powerful, extending up to Mpc scales
and producing strong feedback in the surrounding medium of early-type galaxy
hosts in the center of galaxy clusters (McNamara and Nulsen, 2012; Hlavacek-
Larrondo et al., 2013; Tremblay et al., 2018; Hardcastle and Croston, 2020).
But do radio jets produce feedback in its host galaxies? This is the central
topic of this short review of the interplay between radio-emission from AGN
and its host galaxies. Fast ($\gtrsim 1000\,$km s-1) H i 21 cm absorption
outflows observed using WSRT (Morganti et al., 2005, 2016) and X-ray
detections related to shocks signatures due to the jet-gas interactions, e.g.,
observed with Chandra (Jetha et al., 2008; Thimmappa et al., 2022) illustrate
how multi-wavelength analysis is fundamental to properly characterize the role
of radio feedback.

With the emergence of Integral Field Spectroscopy (hereafter IFS) optical
instruments in the past years, such as the Gemini GMOS (Allington-Smith et
al., 2002), VLT MUSE (Bacon et al., 2010) and GTC MEGARA (Carrasco et al.,
2018), along with deep observations in other wavelength instruments such as
ALMA (Wootten and Thompson, 2009) and most recently JWST, recent studies of
outflows in local AGN have been able to characterize and constrains the
outflow properties, resolving their kinematics and determining its extent
within the host galaxies. High resolution spectra allow to extract information
in the ionized and molecular gas phases, such as velocity dispersion and
emission line ratios, helping understand how gas excitation works. This has
been proven useful in radio-loud AGN, characterized by shock-driven outflows
due to jet-gas interactions.

We begin by discussing the role of interactions in the triggering of radio
activity in galaxies in Section 2, since there is plenty of evidence that the
host galaxies of the most powerful radio galaxies show morphological
disturbances characteristic of interactions e.g. (Ramos Almeida et al., 2011).
In Section 3 we discuss the signatures of radio-mode feedback within galaxies,
as evidenced by the disturbed ionized gas kinematics in association with radio
sources e.g. (Jarvis et al., 2019). This association is most frequently
observed in the optical, in particular in recent studies IFS of the host
galaxies (Couto et al., 2020; Comerón et al., 2021). These signatures point to
an important role of shocks associated to the radio jets in producing feedback
in the host galaxies.

A recent development in the study of AGN feedback is the observation of
enhanced velocity dispersion perpendicular to the ionization axis and radio
jet, and this is discussed in Section 4 e.g. (Ruschel-Dutra et al., 2021;
Venturi et al., 2021). In Section 5 we discuss how the increasing sensitivity
of radio antennas is allowing us to find radio jets down to very low powers,
as observed in the so-called “Red Geysers" (Cheung et al., 2016). These
galaxies show a faint AGN with mild ionized gas winds but that extend to large
distances from the nucleus. The frequent presence of a radio source at the
nucleus (Roy et al., 2021), suggests an association of the radio source with
the winds, that seem to provide a “maintenance mode" feedback. In this kind of
feedback, the impact of the outflows is mild, but enough to heat and disturb
the surrounding gas precluding the formation of new stars, as also been argued
to happen in the central galaxies of clusters, halting the so-called “cooling
flows" e.g. (McNamara and Nulsen, 2012).

##  2 Galaxy interactions as triggers of radio AGN activity

We begin the discussion of radio activity in galaxies via its triggering, and
one of the possible mechanisms are galaxy interactions and mergers. While the
occurrence of minor mergers seems to be frequent in galaxies hosting low-
luminosity AGNs (LAGN $\leq 10^{44}$ erg s-1), major mergers are dominant in
the AGN high-mass regime SMBH masses $\geq 10^{8}$ M⊙, (Treister et al., 2012;
Menci et al., 2014; Storchi-Bergmann and Schnorr-Müller, 2019). For the case
of AGN radio activity, these sources are usually related to early-type hosts,
which makes it easier to find morphological disturbances in images, non-
orbital motions in the kinematics, and support a connection with galaxy
interactions as they are found in the center of galaxy clusters (Colina and de
Juan, 1995; Véron-Cetty and Véron, 2001; Inskip et al., 2010).

Galaxy interactions as a mechanism to produce dynamical destabilization of
large amounts of gas have been considered a possible trigger of the AGN
feeding, driving the gas from kpc-scale distances to the nucleus of the galaxy
(Ellison et al., 2008; Davies et al., 2022). In a broad scenario, a major
merger of gas-rich progenitors could be the responsible to concentrate gas in
the central regions of the resulting galaxy, possibly triggering a starburst
event close to the nucleus, while part of the gas makes its way to the central
SMBH, initiating AGN activity. This scenario has been proposed in a number of
powerful AGN, suggesting a link between galaxy mergers and both starburst and
AGN activities (Emonts et al., 2006; Urrutia et al., 2008; Bessiere et al.,
2017; Calabrò et al., 2019).

Using Gemini GMOS broad-band images of a sample of 46 2 Jy radio galaxies,
Ramos Almeida et al. (2011) performed one of the first qualitative studies of
host galaxy morphologies of radio-loud AGNs at redshifts in the range
$0.05<z<0.7$. Peculiar morphologies including fan-like structures, tails,
bridges, shells and others were observed in 85$\%$ of the sample galaxies, a
considerably higher fraction than observed in quiescent elliptical galaxies
(van Dokkum, 2005; Tal et al., 2009). When dividing the sample into Weak- and
Strong-Line Radio Galaxies (WLRGs and SLRGs, respectively, with WLRGs
presenting an [O iii]$\lambda 5007\AA$ emission line equivalent width below
10Å), the authors find an incidence of disturbed morphologies in $94\%$ of the
SLRGs, while WLRGs present merger signatures in only $27\%$ of the galaxies,
indicating there is a correlation between the AGN power and the incidence of
mergers.

More recent studies are in agreement with these results (Gordon et al., 2019).
With deep imaging observations of 30 intermediate radio power AGNs, Pierce et
al. (2019) have found that the most radio-powerful half of the sample displays
a higher incidence of interaction signatures than the less-powerful half
($67\pm 12\%$ and $40\pm 13\%$, respectively, with corresponding radio
luminosities of $23.06<$ log (L${}_{1.4~{}\mathrm{GHz}}$) $<24.0$ W Hz-1and
$22.5<$ log (L${}_{1.4~{}\mathrm{GHz}}$) $<23.06$ W Hz-1). Even though there
is no clear correlation between L${}_{1.4~{}\mathrm{GHz}}$ and L[OIII]
luminosities, the same fractions are observed when separating the sample in
terms of L[OIII].

In this context, Ultra Luminous Infrared Galaxies (ULIRGs) are also important
as they support the scenario of luminous nuclear starbursts triggered by
merging galaxies that evolve to become luminous AGN (as will be further
explored in the next section). As shown by Sanders and Mirabel (1996) using
IRAS observations, the properties of ULIRGS indicate that the incidence of
mergers correlate with that of AGN at the highest IR luminosities (see their
Table 3). The mean projected separation of the nuclei also decreases with the
increase of AGN and merger fraction, suggesting that the AGN activity is more
likely to happen at latter phases of the galaxy merger due to gas migration to
the central regions, which also feeds the very high star formation rates
observed in ULIRGs of up to $\sim 1000\,$M⊙ yr-1.

### Individual Studies

Clear signatures of galaxy interactions in radio-loud AGNs have been largely
observed in individual studies. This is the case of B2 0648 + 27, an early-
type galaxy presenting interacting signatures such as tail-like structures in
low-surface brightness emission (Heisler and Vader, 1994). Emonts et al.
(2006) found three main events in the galaxy’s history while studying its
neutral gas, optical spectroscopy, and radio continuum: a major merger that
happened $\gtrsim$1.5 Gyr ago; a starburst $\sim$0.3 Gyr ago; and the AGN
activity that must have started $\gtrsim$0.001 Gyr ago. The starburst event
was succeeded by the AGN activity after the removal of angular momentum from
the gas driven towards the nucleus. B2 0648 + 27 seems to be between a
starburst and a normal elliptical galaxy in an evolutionary sequence triggered
by galaxy interaction and where the AGN activity happens in between.

Another interesting study case is the host galaxy of the radio-loud AGNs 4C
+29.30. This galaxy seems to be a merger system in its late stages, with a
characteristic dust lane passing in front of the central region, in a similar
fashion to Centaurus A, a well studied radio galaxy with clear signatures of
past interactions (Beasley et al., 2008; Wang et al., 2020). As in Centaurus
A, 4C +29.30 also presents several phases of recurrent radio activity, with
structures corresponding to different time periods, from $\gtrsim$200 Myr to a
very young activity of only $10^{4}$ yr (Jamrozy et al., 2007; Liuzzo et al.,
2009), which could relate to different feeding events during the merger
process. As shown in Figure 1, 4C +29.30 shows a very complex morphology not
only in the optical, but also related to the jet in X-rays and radio
wavelengths. As we discussed in a paper detailing Gemini-GMOS IFU data (Couto
et al., 2020), powerful ionized gas outflows are being launched due to the
interaction between the relativistic jet and the circumnuclear gas, a scenario
quite common in radio-loud AGNs that we will explore in the following
sections. Several other studies on individual sources display a possible
relation between radio AGN activity and galaxy interactions, which may be
related ultimately to the fueling of the SMBH, or at least driving gas to the
nuclear vicinity e.g. (Frank et al., 2016; Couto et al., 2016; Salomé et al.,
2021).

Figure 1: Composite image of radio-loud AGNs 4C +29.30, with Chandra X-ray,
HST optical and VLA radio observations (Siemiginowska et al., 2012; Sobolewska
et al., 2012). Three different time periods of radio activity have been
detected studying the radio-jet emission in this galaxy, which can be related
to the galaxy interaction history (with clear signatures observed in the
optical) and the feeding of the central SMBH.

NGC 3801 is one of the few radio-loud AGNs where shock-induced X-ray emission
due to jet–gas interaction was observed, and it seems to be in a rare
evolutionary stage where the enhanced star formation from a merger event has
declined, and a young, powerful AGN activity is taking place (Croston et al.,
2007; Hota et al., 2012). In this scenario, early stages of the radio source
expansion such as in Fanaroff-Riley I objects (Fanaroff and Riley, 1974) have
a more dramatic effect on the interstellar medium (ISM) when compared to
larger scale extended sources such as FR II objects. The decline of star
formation and the role of radio feedback in heating the gas seem to be
important mechanisms to drive this type of object in the ‘red sequence,’ or
‘red-and-dead’ elliptical type galaxies.

The relation between radio-loud AGNs and galaxy interactions seems to hold
true also for higher redshift sources. Making use of high sensitivity HST
imaging, Chiaberge et al. (2015) studied the dependence of merger fractions in
radio-loud and radio-quiet AGNs for redshifts $1<z<2.5$ when the AGN activity
has peaked over cosmic history. The authors find that
$92\%\begin{subarray}{c}+8\%\\\ -14\%\end{subarray}$ of the powerful radio-
loud galaxies ($P_{1.4~{}\mathrm{GHz}}>10^{30}$erg s-1 Hz-1) are merging
systems, while only $38\%\begin{subarray}{c}+16\%\\\ -15\%\end{subarray}$ of
the radio-quiet galaxies present merger signatures.

Another possible influence of mergers on the radio loudness of active galaxies
is its impact on the spin of the SMBH. As discussed in Chiaberge et al.
(2015), if gas accretion resulting from a merging galaxy occurs with a similar
angular momentum axis as that of the SMBH, it may result in an increase in the
SMBH spin velocity, while if the accretion happens in a different direction,
the SMBH spin can be slowed. These different orientations may then affect the
nature of the radio-loudness of the AGN, as it is expected that faster
spinning SMBHs generate more powerful radio jets, and the radio-loud/quiet
characteristics could be explained by different accretion and SMBH spins
(Wilson and Colbert, 1995; Tchekhovskoy et al., 2010). Of course, this effect
is expected to be more prominent at high redshifts ($z\gtrsim 2$), as gas-rich
mergers were more common in the younger Universe (Volonteri et al., 2013).

The close environment of a radio-loud AGN, within its dark matter haloes (of
radius $\sim$1 Mpc $h^{-1}$) is denser than that of radio-quiet galaxies
overall, but this also happens when the galaxies are matched by stellar mass
and redshift (Donoso et al., 2010; Wylezalek et al., 2013). The fact that
galaxies with high stellar masses do not necessarily host a radio-loud AGN
indicates that the presence of radio-loud jets could be influenced by the
environment of the host galaxy (Hatch et al., 2014). In response, AGN radio
jets seem to be important to control the star formation within the dark matter
halo of its host galaxy, resulting in a slower stellar mass build-up process,
and the hosts would have lower stellar masses if the radio-mode feedback were
not present (Izquierdo-Villalba et al., 2018).

##  3 Radio-Mode Feedback in Galaxies

As pointed out in the Introduction, radio jets from giant elliptical galaxies
at the center of clusters can extend up to Mpc scales and produce strong
feedback in the surrounding medium, e.g. (McNamara and Nulsen, 2012;
Hardcastle and Croston, 2020). However, as this topic is being discussed
elsewhere in this volume, we focus here on the effect of radio-mode feedback
inside galaxies. In this section, we present some of the characteristic
features of the radio-mode feedback and how the interactions between the
relativistic jets and the gas in its path manifest themselves within active
galaxies.

###  3.1 Complex Gas Kinematics

The relativistic jets present in a radio-loud AGN, when coupled with the
circumnuclear gas either in the narrow-line region (within the radius of
influence of the AGN ionizing radiation) or further out in the ISM (within the
inner few kpcs), can be responsible for the heating and acceleration of this
gas resulting in outflows. These outflows are usually detected in the
turbulent ionized emitting gas by measuring its kinematics and isolating the
kinematic components linked to the AGN feedback, e.g. (Cecil, 1988; Lena et
al., 2015; Mahony et al., 2016). The superposition of one or more kinematic
components to that originating in gas rotating in the galaxy potential can
result in a complex ionized gas spectrum, with many components, making the
decomposition process hard to constrain (Wylezalek et al., 2020). With the
advent of better spatial and spectral resolutions IFUs, the number of
resolvable kinematic components has increased, and the interpretation of these
components and their origin has also increased in complexity.

The case of the Seyfert 2 galaxy NGC 7130 is a clear example of such
complexity, as discussed in Comerón et al. (2021), using MUSE narrow-field
adaptive optics observations. Even though the radio jet in this Seyfert galaxy
is not powerful, one or maybe two outflowing ionized gas components seem to be
interacting with the radio jet, as revealed by the very detailed emission-line
decomposition performed by the authors, which comprises a total of nine
components, with six being connected to outflows. It is important to note that
the fitting of several components should be statistically justified so that
the decomposition does not introduce artificial components into the emission-
line fit.

Usually, a rotation component is observed in the gas velocity field of radio-
loud AGN, but alongside more complex kinematics, as illustrated in the study
performed in the MURALES survey (Balmaverde et al., 2019, 2021), in which a
sample of 37 radio galaxies from the Third Cambridge Catalog (3C) were
observed with the MUSE IFS. As shown in Figure 2, the ionized gas velocity
maps of these radio galaxies appear to show some rotation, but present a much
more disturbed pattern than the expected “web diagram” characteristic of the
isovelocity curves of ordered rotation. Although these complex kinematics may
not be the case for all radio-loud AGNs, they are commonly observed, as
several other studies of individual galaxies have also shown, such as in 4C
+29.30 (Couto et al., 2020), Cygnus A (Riffel, 2021), and UGC 05771 (Zovaro et
al., 2019), and are usually caused by the interaction between the radio jet
and the circumnuclear gas.

Figure 2: Velocity maps in the indicated emission-lines of the radio-loud AGNs
3C 076, 3C 079, 3C 018 and 3C 017 clockwise from top left, (Balmaverde et al.,
2019, 2021). Although some rotation seems to be present, disturbed kinematics
dominate the velocity field of these galaxies, attributed to the interaction
of the ambient gas with the radio jet. Velocity units are km s-1.

An alternative method for tracking different kinematic components is to probe
the velocity field along channel maps, which is possible when using IFS
observations. Arp 102B is one case in which the channel maps can aid in the
interpretation of how the radio jet interacts with the surrounding emitting
gas. In Couto et al. (2013), we have used Gemini-GMOS IFU observations to
analyze the ionized gas kinematics in this galaxy. H$\alpha$ channel maps,
shown in Figure 3, indicate that a spiral arm-like structure correlates
spatially with the radio jet, and the emitting gas is observed both in
blueshifted and redshifted velocities. We have interpreted that these
velocities trace the outflowing gas pushed by the radio jet oriented very
close to the plane of the sky. The channel maps show emission from the “walls”
surrounding the outflow being pushed aside, seen in both blueshifted and
redshifted velocities. The use of channel maps to interpret the relationship
between the jet and the gas in individual galaxies studies has been proven
useful in the past years, as displayed in other papers by our group, such as
in Schnorr-Müller et al. (2014); Lena et al. (2015); Riffel et al. (2015).

Figure 3: Channel maps along the H$\alpha$ emission-line profile of the radio
galaxy Arp 102B, with velocities displayed in white at the top right corner of
each map in units of km s-1, (Couto et al., 2013). The flux distribution maps
show a spatial correlation with the radio jet, represented by the green
contours from VLA observations at 8.4 GHz. We have interpreted this emission
to be related to outflowing gas pushed aside by the jet moving close to the
sky plane, thus displaying blueshifted and redshifted velocities originating
in the gas surrounding the radio jet. X and Y-axis are in arcsec and are
centered at the galaxy nucleus.

###  3.2 Radio Bubbles

When the jet collimation is lost due to interaction with dense gas or jet
precession, sometimes a gas bubble is formed, and the inflation of the bubble
by the outflow also impacts the ISM. A nuclear starburst leading to numerous
supernovae explosions can also produce outflowing bubbles from galaxy centers.
The bubble serves as a shock front between the outflow and the ISM gas, and
when it erupts, several galaxy properties can be altered, including its
chemical composition. Perhaps the most famous case is of our own galaxy.
Bipolar bubbles at the Galaxy center have been observed in several
wavelengths, including in the radio at 1.3 GHz with MeerKAT (Heywood et al.,
2019), and it is still debatable whether these bubbles originate from AGNs or
star formation feedback. A similar case where there is ambiguity in the
feedback origin is NGC 3079 (Cecil et al., 2001). While studying the AGN-
starburst composite galaxy NGC 6764, Hota and Saikia (2006) also found an
inconclusive origin for the feedback, and compared it to 10 other sources.
These are all associated with AGN activity, but the radio and optical
emissions could be also affected by central starbursts. Pure starburst sources
do not seem to present the same structures, indicating that AGNs must be
present to produce the large-scale bubbles.

###  3.3 Molecular Gas

Besides the effect on the ionized gas phase that traces the hot and turbulent
outflows, molecular gas can also show signatures of jet–gas interaction. As
the ionized gas represents only a fraction of the total gas mass, which is
dominated by the molecular gas in the galaxy’s inner regions, the outflow gas
mass should also be dominated by the molecular gas, especially in low AGN
bolometric luminosities (Carniani et al., 2015). Mass outflow rates observed
in molecular gas are about 2–3 orders of magnitude higher than those traced in
the ionized gas phase ($\sim$1000 M⊙ yr-1as compared to $\sim$1–10 M⊙ yr-1,
respectively) in AGNs with bolometric luminosity $\sim$$10^{46}$ erg s-1e.g.
(Fiore et al., 2017). As a comparison, star-formation rates of 10–100 M⊙
yr-1(see Figure 3 in Fiore et al. (2017)) are estimated for AGNs in the same
luminosity range demonstrating that these outflows must indeed originate from
AGN activity.

As shown in a study of the galaxy IC 5063 by Dasyra et al. (2022), by
estimating the internal and external pressures of the molecular clouds, one
can infer the impact of the radio jet in the star formation processes within
the galaxy, where both suppression and enhancement can simultaneously happen.
In NGC 613, disturbed gas can be traced in the nucleus due to molecular
outflows mainly boosted by the radio jet (Audibert et al., 2019). While
modeling the molecular gas outflows in the young radio galaxy 4C 31.04, Zovaro
et al. (2019) could reproduce the observed kinematics by assuming that the gas
was being pushed and expanded by the radio jet in an energy bubble while
generating shocks within this bubble, originating the observed H2 emission. As
observed (and discussed above) for the ionized gas phase, rotation is also
usually observed in the molecular gas phase but with distortions commonly
found in the inner few hundred pc, as analyzed by Ruffa et al. (2019) in a
sample of six low excitation radio galaxies using ALMA observations. However,
in the case of this sample, the authors interpreted that these non-rotating
components were related to inflowing gas since they seem to be correlated with
structures such as spirals or bars, known for being mechanisms causing the gas
to lose angular momentum to reach the nucleus and feed the SMBH. This
illustrates that other signatures, besides the gas velocities should be used
in the search for outflows, such as velocity dispersion and line ratios and
their relation to the observed kinematics. Other cases of galaxies presenting
jet–gas interaction signatures through the analysis of their molecular gas
kinematics include NGC 1377 (Aalto et al., 2016), ESO 420-G13 (Fernández-
Ontiveros et al., 2020), and NGC 7319 (Pereira-Santaella et al., 2022), among
others.

###  3.4 Models and Simulations

Detailed 3D hydro-dynamical simulations indicate that, indeed the gas can be
perturbed by the radio jet within the host galaxy. Not only is the jet
responsible for disturbing and shaping the emitting gas distribution, as
discussed in Wagner and Bicknell (2011), but the path taken by the jet and its
morphology is also affected by the inhomogeneity of the gas density. In this
scenario, the jet collimation, its power, and how it spatially couples with
the gas are important parameters to estimate the feedback energetics. One
example of such simulations is displayed in Figure 4, where the gas density
distribution is shown while the radio jet evolves with time: the jet carves
its way through the gas, pushing it both aside and forward to larger distances
while heating it and possibly creating shock ionization. How easy and straight
the path of the jet is through the gas depends on its density and porosity
distributions. We refer the reader interested in learning more about
simulations of jet–gas interactions to papers by Mukherjee et al. (2018,
2018); Talbot et al. (2021); Meenakshi et al. (2022) for further details.

Figure 4: Figure 2 from Wagner and Bicknell (2011), showing the time evolution
of the jet–gas interaction in one of the simulations performed in the paper.
Colors represent the different gas densities as the jet makes its way through
it, being deflected towards regions of less resistance and finally creating a
bubble of expanding gas. Some of the dispersed gas may reach velocities of up
to $\sim$$1000~{}$km s-1.

###  3.5 Signatures of Shocks Due to Radio Jets

During the interaction between the relativistic jet and the surrounding gas,
gas ionization through fast shocks can occur, with the excited gas emitting
characteristic spectra that provide information about the physical parameters
of the shock ionization. Observed line ratios in the narrow-line region (NLR)
indicating the presence of shocks usually lie in the Low-Ionization Emission
Line Region LINER, (Heckman, 1980) part of optical diagnostic diagrams, such
as the well-known BPT diagrams (Baldwin et al., 1981), depending on parameters
such as the shock velocity and gas density (Dopita and Sutherland, 1995; Allen
et al., 2008). Although photoionization models have a considerable overlap
with shock models in the BPT diagrams, high values of low-ionization line
ratios such as [N ii]/H$\alpha$ and [S ii]/H$\alpha$ are usually interpreted
as tracers of shocks when gas emission is observed due to jet influence.

The presence of shocked gas also commonly correlates with broader emission
lines, which trace the increase of gas turbulence. This is the case of 3C 293
(Mahony et al., 2016), where jet-driven outflows are detected along the radio
emission, and two kinematic components are needed to reproduce the ionized gas
emission-line profiles. A clear increase in the [N ii]/H$\alpha$ and [S
ii]/H$\alpha$ line ratios is observed in the regions where a broader component
is required to reproduce the emission lines [see Figure 6 in (Mahony et al.,
2016)], indicating that the shock velocity increases in the regions where the
highest ratios are observed.

Another interesting case is the gas excitation observed in 3C 33 (Couto et
al., 2017). As displayed in Figure 5, velocity dispersion increases in a
region surrounding the nucleus, perpendicular to the radio jet (a discussion
that we will explore further in Section 5), in the same orientation where
high-velocity residuals are observed when a rotating disk model is subtracted
from the H$\alpha$ velocity field. This correlation indicates that this region
is dominated by a non-rotating kinematic component. Using channel maps of the
[N ii]/H$\alpha$ line ratio, we could detect the increase of this line ratio
with the velocity residuals since the regions presenting the highest
blueshifted and redshifted residuals show high [N ii]/H$\alpha$ values with
the same velocity shift. Other shock-driven outflow signatures, such as an
increase of gas temperature (obtained using the [O iii]$\lambda
4959+5007/4363$ line ratio) and density, strengthen the scenario that the
excitation of this component is (at least partially) due to kinetic-mode
feedback.

Figure 5: Gemini-GMOS IFS observations of the radio galaxy 3C 33. H$\alpha$
velocity dispersion (top left), velocity residuals (top right, observed
velocity field minus disk-like rotation model) and [N ii]/H$\alpha$ line ratio
channel maps (middle and bottom panels) adapted from Couto et al. (2017).
Channel map velocities ($-84$, $-21$, 42 and 106 km s-1, clockwise from the
top left) are displayed in the top right corner of the panels. The blue line
displays the large-scale radio jet orientation. An increase in the velocity
dispersion is observed in the same region where velocity residuals are
highest. The same velocities are spatially correlated with an increase of the
[N ii]/H$\alpha$ line ratio (delineated by contours), indicating that shock-
driven outflows are present in these regions, probably due to the jet–gas
interaction.

Shock excitation has been found in several other objects presenting radio
jets, such as M51 (Cecil, 1988), Coma A (Morganti et al., 2002), the Beetle
galaxy (Villar-Martín et al., 2017), PKS B1934-63 (Santoro et al., 2018), 3C
320 (Vagshette et al., 2019), 4C 31.04 (Zovaro et al., 2019), 3C 433 (Murthy
et al., 2020), J1220 + 3020 (Molina et al., 2021), and Cygnus A (Riffel,
2021), among others. Shock excitation has been found not only in the ionized
gas phase but also sometimes in molecular or neutral gas. High gas velocities
of up to $\sim$1000 km s-1, or even higher, are commonly found in these
sources, and an increase of velocity dispersion is also a good tracer of the
regions presenting shocks.

###  3.6 Feedback Power and Scaling Relations

After characterizing gas outflows due to the AGN jet feedback, it is useful to
estimate its kinetic power in order to quantify its impact on the host galaxy
and compare it with models and other sources of feedback. The kinetic power of
the outflow attributed to the kinematic disturbance produced by the radio jet
can be calculated via (Holt et al., 2006):

$\dot{E}=6.34\times 10^{35}\frac{\dot{M}_{out}}{2}(v^{2}_{out}+3\sigma^{2}),$
(1)

where $\dot{M}_{out}$ is the mass outflow rate, $v_{out}$ is the deprojected
outflow velocity, and $\sigma$ is the outflow velocity dispersion. The mass
outflow rate is dependent on the assumed outflow geometry, and can be
expressed through:

$\dot{M}=1.4n_{e}m_{p}v_{out}Af,$ (2)

where $n_{e}$ is the gas density, $A$ is the assumed geometric cross-section
area of the outflow, $f$ is the filling factor within the outflow volume, and
$m_{p}$ is the proton mass ($m_{p}=1.7\times 10^{-24}$g), while the factor 1.4
accounts for the contribution of elements heavier than hydrogen.

The calculations above are not restricted to radio-loud AGNs but are general
to any type of outflow. For the ionized gas, the gas density is usually
estimated using the [S II]$\lambda 6717,31\AA$ line ratio, and the filling
factor can be obtained using a measured hydrogen emission-line luminosity,
such as H$\alpha$ (Peterson, 1997):

$f=2.6\times 10^{59}\frac{L_{41}(\textrm{H}\alpha)}{Vn_{3}^{2}},$ (3)

where $L_{41}(\textrm{H}\alpha)$ is the H$\alpha$ luminosity in units of
$10^{41}$ erg s-1, $V$ is the assumed geometry volume, and $n_{3}$ is the gas
density in units of $10^{3}$cm-3.

Scaling relations using the estimated mass outflow rates $\dot{M}$ and outflow
kinetic power $\dot{E}$ of AGN-driven feedback have been the object of studies
in the past few years. Fiore et al. (2017) investigated the relation between
the bolometric luminosity and both the mass outflow rate and outflow kinetic
power for 94 AGNs covering a large range of redshifts (from local Universe up
to z$\sim$6) compiling observational data from the literature and
homogeneously calculating the mass outflow rates and powers. Ionized and
molecular gas show clear correlations between $L_{bol}$ and both $\dot{M}$ and
$\dot{E}$, with somewhat higher $\dot{M}$ and $\dot{E}$ for the molecular gas
that seems to reach the coupling efficiency in the range 1–10% $L_{bol}$, as
required in models e.g. (Di Matteo et al., 2005; Hopkins and Elvis, 2010) to
have a significant impact on the host galaxy (e.g., by pushing the gas out of
the galaxy and halting star-formation) while for the ionized gas only
$\approx$30% of the galaxies reach this efficiency.

More recent studies, e.g. (Baron and Netzer, 2019; Dall’Agnol de Oliveira et
al., 2021) and references therein on kinematic feedback via ionized gas
outflows have obtained higher gas densities and resulting lower powers than
those estimated in Fiore et al. (2017) for most AGNs. In some cases, like in
the radio-galaxy 4C +29.30 (Couto et al., 2020), the outflow power can reach a
few percent of the AGN power $L_{AGN}$, implying strong feedback, but in most
cases, this power is below 1%$L_{AGN}$. The kinematic feedback is usually
present, heating and disturbing the gas—a “maintenance mode feedback,” but not
high enough to push the gas out of the galaxy or immediately halt star
formation. On the other hand, AGN feedback occurs not only via outflows, with
recent model estimates suggesting that at most 20% of the AGN feedback is in
kinetic form, e.g. (Richings and Faucher-Giguère, 2018).

The relations between $\dot{E}$ and $L_{AGN}$ and $\dot{M}$ and $L_{AGN}$
discussed above seem to apply both to radio-loud and radio-quiet AGN. In the
case of the latter, Villar Martin et al. (2021) have shown that, for a sample
of 13 nearby ($z<0.2$) radio quiet QSOs, most of which showed signatures of
interactions, 10 had extended radio emission. In addition, they found this
radio emission was correlated with the optical H$\alpha$ emission, indicating
jet–gas interaction. Thus radio-mode feedback is also present in radio-quiet
AGNs when the jet is spatially coupled with the ISM gas.

##  4 Statistical Studies and Higher Redshift Sources

There are a number of statistical studies of an AGN feedback effect in general
(not restricted to radio AGN) on host galaxy properties. Wylezalek and
Zakamska (2016) gathered a large sample of radio-quiet AGNs at $z<1$ with SDSS
observations to investigate the relation between AGN feedback and star
formation quenching. Measuring the [O iii]$\lambda 5007\AA$velocity width as
an outflow tracer, the authors find no correlation between mass outflow rates
and star formation rates; however, in galaxies with high specific star
formation rates (sSFR), they found a negative correlation between outflow
strength and sSFR, indicating that in these galaxies with the highest gas
content, there is quenching due to AGN outflows.

Studying a much larger sample of SDSS AGN, Mullaney et al. (2013) performed a
multiple-component fit to the optical emission lines and found that AGNs with
moderate radio luminosities (L${}_{1.4~{}\textrm{GHz}}=10^{123}-10^{25}$ W
Hz-1) present the most disturbed gas kinematics with the highest incidence of
extremely broad [O iii]$\lambda 5007\AA$emission. This suggests that young and
compact radio sources seem to more effectively drive gas turbulence in the
host galaxies than powerful extended jets of the most radio luminous sources.

At higher redshifts, we cite the work of Delvecchio et al. (2017), where they
performed a multi-wavelength analysis of 7700 radio selected AGNs from the
COSMOS field with VLA observations with redshifts up to $z\lesssim 6$. They
divided the sample into moderate-to-high and low-to-moderate radiative
luminosity AGNs (MLAGNs and HLAGNs, respectively). The authors found that the
HLAGNs had systematically higher radiative luminosities and the AGN power
occurred predominantly in radiative form, while for MLAGN, the AGN power also
had a large mechanical component. They also found that at $z<1.5$, MLAGNs
resided in more massive and less star-forming galaxies compared to HLAGN. At
$z>1.5$, the opposite was found: the HLAGNs seemed to occur in more massive
galaxies. The authors interpreted their findings as evidence of downsizing,
with the most massive galaxies triggering AGNs earlier than the less massive
galaxies. At lower redshifts, the HLAGNs faded to MLAGNs.

##  5 Feedback Perpendicular to the Radio Jet Orientation

Even though gas outflows are usually expected to be found along the AGN radio
jet, this is not always the case. Recent studies have been showing different
orientations between the radio jet axis and the direction of an observed
increase of the gas velocity dispersion related to outflowing gas. In many
cases, the direction of the enhanced velocity dispersion is approximately
perpendicular to that of the radio jet. Perhaps the first observational
evidence of such orientation in an IFS analysis was the case of Arp 102B
(Couto et al., 2013). In this radio galaxy, we observed an increase in the gas
velocity dispersion in the [O iii]$\lambda 5007\AA$ emission line, close to
the nucleus, approximately perpendicular to the radio jet. The jet then bends
with increasing distance to the nucleus.

Ionized gas velocity dispersion maps of Arp 102B and other galaxies presenting
enhanced values approximately perpendicular to radio jets are shown in Figure
6. Arp 102B, NGC 1386 (Lena et al., 2015), NGC 5643 (Venturi et al., 2021), 3C
33 (Couto et al., 2017) and NGC 3393 (Finlez et al., 2018) show very clear
signatures of the misalignment between the radio jet and the extended high-
velocity dispersion emission, very close to perpendicularity. In a very
detailed study of this phenomenon, Venturi et al. (2021) used VLT MUSE
observations to trace the outflowing gas in four galaxies displaying a
mismatch relative to the orientation of the radio jets, including NGC 5643,
shown in Figure 6. Extended emission ($\gtrsim$1 kpc) is observed with
increased velocity dispersion (W70 $\gtrsim$ 800–1000 km s-1) perpendicularly
to the jet. The authors also found that the gas excitation in these regions
was consistent with shock ionization, similar to the results we have found in
3C 33 (as discussed in Section LABEL:sec:_shock, where higher shock-related
line ratio values ([S ii]/H$\alpha$ in their case) are observed. Further
evidence of this phenomenon was observed in the AGNIFS survey (Ruschel-Dutra
et al., 2021), comprising 30 local AGNs observed with GMOS-IFU, in which
outflows perpendicular to the ionization axis (via enhanced W80 values) were
detected in 7 sources out of 21 that presented outflows. The same was found in
the MURALES survey (Balmaverde et al., 2019), where at least 6 of the initial
20 observed galaxies present some indication of turbulent ionized gas
perpendicular to the radio jet. NGC 5929 (Riffel et al., 2015) is another case
where the velocity dispersion of the ionized gas is found to be enhanced
perpendicularly to the radio jet (see their Fig. 8).

Figure 6: Gas kinematics of several active galaxies displaying increased gas
velocity dispersion – attributed to outflowing components – perpendicularly
(or close to being perpendicular) to the radio jet orientation. Top left: Arp
102B Gemini GMOS-IFU [O iii] velocity dispersion map, with VLA 8.4 GHz
contours displaying the radio jet emission (Couto et al., 2013). Top middle:
NGC 1386 GMOS-IFU [N ii] velocity dispersion map, with the dark region along
the north–south axis tracing the jet emission (not shown here) and enhanced
integrated flux (Lena et al., 2015). Top right: NGC 5643 VLT-MUSE [O iii] W70
map showing highest values perpendicular to the radio jet shown via VLA 8.4
GHz emission contours (Venturi et al., 2021). Bottom left: 3C 33 H$\alpha$
velocity dispersion map, with the large scale VLA 1.4 GHz radio jet
orientation represented by the blue line (Couto et al., 2017). Bottom right:
NGC 3393 GMOS-IFU [N ii] velocity dispersion map also displaying VLA 8.4 GHz
radio emission as black contours (Finlez et al., 2018). Velocity dispersion
and W70 units are in km s-1. Figure 7: One of the simulated interactions
between the jet and the gas by Mukherjee et al. (2018), in this case within
$45^{\circ}$ inclination between the jet axis and the galaxy disk plane. The
left panels display the time evolution of the gas density along the radio axis
plane. The right panel shows the projected velocity of the gas, where a clear,
enhanced component is observed perpendicularly to the jet. As a result of the
enhanced interaction with the ISM, in comparison to scenario with the jets
being launched perpendicularly to the disk, the jet is decelerated and
generates higher turbulence dispersion, mainly towards the path of less
resistance perpendicularly to it.

As discussed in Venturi et al. (2021), the galaxies presenting outflows
perpendicular to the radio jet are usually hosts of either compact or low-
power radio jets (with some exceptions, like 3C 33), and thus the bulk of the
jet emission is close to the nucleus, within the inner kpc or less. These jets
are also not perpendicular to the galaxy disk, with low inclination angles
between these structures, resulting in a larger impact of the jet in the ISM.
Galaxies that present jets oriented perpendicularly to the galaxy disk plane
do not display the same behavior. The spatial correlation of the regions with
high gas velocity dispersion with high line ratios related to shocks (as shown
in Figure 5) indicates that these outflows are shock-driven due to the jet
interaction with the galaxy disk gas. In galaxies with large-scale jets,
usually FR II objects, with lobes extending tens of kpcs from the galaxy
nucleus, the jet could have already cleared much of the gas in its path.
Additionally, high-power jets ($\gtrsim 10^{45}\,$ erg s-1) penetrate the
clumpy ISM and dig their way out through the gas easier when compared to low-
power jets (Wagner and Bicknell, 2011; Mukherjee et al., 2018).

A similar scenario has been reproduced with radio-mode feedback models. The
jet power and its inclination relative to the galaxy disk determines how the
jet affects the gas in the NLR and ISM, as discussed in Mukherjee et al.
(2018). Jets inclined closer to the disk influence the gas more than when its
orientation is perpendicular to it, generating shock-driven wide-angle
outflows along the disk’s minor axis and enhancing turbulent dispersion along
the disk. As shown by the gas density evolution along the jet axis in Figure
7, with a jet axis inclination of $45^{\circ}$ with the disk plane, the jet
interacts strongly with the gas, and the denser gas (when compared to higher
disk latitudes) deflect the jets, which is decelerated. The direction of least
resistance is where the turbulence is propagated, which is along the direction
perpendicular to the radio jet.

##  6 Maintenance Mode Feedback—Red Geysers

In Comerford et al. (2020), the authors have identified in the MaNGA/SDSS
galaxy survey (Mapping Nearby Galaxies with the Apache Point Observatory of
the Sloan Digital Sky Survey) (Bundy et al., 2015) a number of low-luminosity
AGNs in radio using the NVSS and FIRST radio surveys, many of which were not
detected in the optical observations. They separated the sample into radio-
mode and radio-quiet AGNs and, comparing the two subsamples, found that the
radio-mode ones are preferably hosted by early-type galaxies, have older
stellar populations, and lower star-formation rates. Such galaxies are
sometimes referred to as being “red and dead,” and in Comerford et al. (2020)
the authors suggest that feedback from radio jets could be the source of the
suppression of star formation.

But the authors also point out that one caveat of the conclusion above is the
fact that early-type galaxies have less gas in the inner region, implying low
mass accretion rates to the nuclear SMBH, which leads to advection-dominated
accretion flows, e.g. (Narayan and McClintock, 2008; Nemmen et al., 2014). It
is well known that such accretion flows favor the formation of radio jets.
Thus, instead of radio jets being the source of feedback that would lead to
red and dead galaxies, they are more a consequence of the low accretion rates
to their SMBH, resulting from the scarcity of gas in the nuclear region of
early-type galaxies. In addition, while radio activity in AGNs are short-lived
phenomena a few million years old, continuum optical and IR galaxy features,
as well as the central stellar populations, are hundreds of millions to
billions of years old, which means that the radio feedback has little to none
effect in these structures. On the other hand, there is still mass loss due to
the process of stellar evolution that could still lead to some star formation
that seems not to be there, and this could indeed be attributed to
feedback—even if mild, produced by low-power radio jets, precluding new star
formation. It is also important to take into consideration recurrent radio
activity where relic emission is observed, mainly in merger remnants such as
Centaurus A or NGC 3801. In these galaxies, the older activity could indeed
have had an impact on the past star formation history of the host galaxy.

Low-power jets can produce a mild outflow, producing what is being called
“maintenance mode feedback,” also observed in a class of galaxies that have
been called Red Geysers, in which a low-luminosity AGN seems to be the source
of large-scale but mild outflows that were discovered in observations with the
MaNGA (Cheung et al., 2016). The Red Geysers frequently show a radio-source at
the nucleus (Roy et al., 2021), and recent optical IFS of the inner region at
a resolution at the galaxies of a few 100 pc using the Gemini telescopes (Ilha
et al., 2022) have revealed nuclear outflows that are misaligned relative to
the larger scale outflows discovered in the MaNGA survey. This misalignment
has been argued by Riffel et al. (2019) as being due to the precession of a
nuclear outflow/jet, as illustrated in Figure 8.

Using MaNGA/SDSS datacubes of a sample AGN, Wylezalek et al. (2020) have also
shown that low-luminosity AGNs can introduce mild kinematic disturbances over
most of the galaxy extension as mapped via the $W_{80}$ kinematic parameter,
which measures the width of line profiles comprising 80% of their fluxes.
Using a control sample, Gatto et al. [in preparation] confirms the larger
$W_{80}$ in AGNs than controls down to the lowest AGN luminosities,
configuring a mild, maintenance mode feedback.

Figure 8: Outflow orientation of the prototype Red Geyser Akira Figure 4 in
(Riffel et al., 2019). SDSS MaNGA (left panels) and Gemini-GMOS IFS (right
panels) display different scales of the galaxy (Gemini FoV represented by the
red rectangle in the top left panel), with top and middle panels showing the
H$\alpha$ equivalent width and velocity maps, respectively. Circles represent
the orientation of outflowing gas after interpreting that these regions cannot
be reproduced by disk-like rotation, where open and closed circles are using
MaNGA and GMOS data, respectively. Redshifted and blueshifted velocities
obtained from the stellar kinematics are identified along the line of the
nodes measured in the stellar velocity field. The bottom panel displays the
outflow orientation relation with distance to the nucleus. The variation in
outflow orientation is interpreted as precessing winds due to the orientation
of the accretion disk in relation to the SMBH spin.

Another possible scenario for the misalignment between the small and large-
scale ionized gas is the radio detection limit from observations using
telescopes and arrays such as the VLA. Recent and future radio telescopes such
as LOFAR and SKA will explore further the faint emission of older jet
feedback, which may correlate with the large-scale ionized gas orientation,
while the gas closer to the nucleus is affected by younger and more compact
activity. Example cases of these phenomena are NGC 5813 (Randall et al., 2011)
and Mkr 6 (Mingo et al., 2011). A recent report of LOFAR observations by
Webster et al. (2021) describes a large sample of intermediate scale radio
sources in low luminosity AGNs at 150 MHz. As these new observations expand
the samples of faint sources, we will be able to further constrain how the
radio feedback interacts with its galaxy hosts.

##  7 Summary

AGN radio activity and its relation with the host galaxy has been the subject
of detailed studies in the context of galaxy evolution. With the further
development of IFS instruments, we have been able to trace and characterize
gas outflows originating in jet–gas interactions in nearby radio galaxies. In
this review, we focused on the discussion of the interplay of radio jets with
the circumnuclear gas of radio AGNs, displaying clear examples of where these
jets have an impact on the galaxy’s ISM. We showed how galaxy interactions
seem to have an important role in the triggering radio activity, usually found
in early-type galaxies, via the feeding of the nuclear SMBH.

Feedback in the form of outflows produced via the interaction of the radio-jet
with the circumnuclear gas is observed not only in ionized gas phases, but
also in molecular gas, which should represent the bulk of the gas mass within
the outflows, as discussed in the context of AGN scaling relations. Jet–gas
coupling and orientation of the outflows are important parameters to
understand the produced feedback, as even low power radio jets can be well
coupled with the gas and generate outflows. These outflows are observed both
in the direction of the radio jet but also perpendicularly to it, usually
traced with enhanced velocity dispersions perpendicular to the radio jet.

Although there are a few radio AGNs that produce strong feedback on the host
galaxies, most radio sources in the near Universe present outflow kinetic
powers that do not reach $1\%L_{bol}$, and thus do not provide a strong and
immediate impact on the host galaxy. Instead, they act to heat the ISM gas,
preventing star formation, slowing the galaxy mass build-up process, and
limiting the stellar mass growth in a “maintenance mode” feedback.

The era of the James Webb Space Telescope will allow us to perform similar
spatially resolved studies at higher redshifts, revealing important
information on AGN feedback across cosmic time. With the aid of incoming
surveys such as 4MOST and WEAVE and the future IFS generation (such as
ELT/HARMONI), we will be in a better condition to establish the role of radio
feedback on galaxy evolution, not only in high-power jets but also in low
radio luminosity AGNs, which also seem to be an important piece of the puzzle.

All authors have read and agreed to the published version of the manuscript.

This research received no external funding

The data underlying this article will be shared on reasonable request to the
authors.

###### Acknowledgements.

The authors thank the anonymous referees for their valuable contributions on
improving this review. The authors declare no conflict of interest. References

## References

  * Heckman and Best (2014) Heckman, T.M.; Best, P.N.  The Coevolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe.  Annu. Rev. Astron. Astrophys. 2014, 52, 589–660.  https://doi.org/10.1146/annurev-astro-081913-035722.
  * McNamara and Nulsen (2012) McNamara, B.R.; Nulsen, P.E.J.  Mechanical feedback from active galactic nuclei in galaxies, groups and clusters.  New J. Phys. 2012, 14, 055023.  https://doi.org/10.1088/1367-2630/14/5/055023.
  * Hlavacek-Larrondo et al. (2013) Hlavacek-Larrondo, J.; Fabian, A.C.; Edge, A.C.; Ebeling, H.; Allen, S.W.; Sanders, J.S.; Taylor, G.B.  The rapid evolution of AGN feedback in brightest cluster galaxies: Switching from quasar-mode to radio-mode feedback.  Mon. Not. R. Astron. Soc. 2013, 431, 1638–1658.  https://doi.org/10.1093/mnras/stt283.
  * Tremblay et al. (2018) Tremblay, G.R.; Combes, F.; Oonk, J.B.R.; Russell, H.R.; McDonald, M.A.; Gaspari, M.; Husemann, B.; Nulsen, P.E.J.; McNamara, B.R.; Hamer, S.L.; et al.  A Galaxy-scale Fountain of Cold Molecular Gas Pumped by a Black Hole.  Astrophys. J. 2018, 865, 13.  https://doi.org/10.3847/1538-4357/aad6dd.
  * Hardcastle and Croston (2020) Hardcastle, M.J.; Croston, J.H.  Radio galaxies and feedback from AGN jets.  New Astron. Rev. 2020, 88, 101539.  https://doi.org/10.1016/j.newar.2020.101539.
  * Morganti et al. (2005) Morganti, R.; Tadhunter, C.N.; Oosterloo, T.A.  Fast neutral outflows in powerful radio galaxies: A major source of feedback in massive galaxies.  Astron. Astrophys. 2005, 444, L9–L13.  https://doi.org/10.1051/0004-6361:200500197.
  * Morganti et al. (2016) Morganti, R.; Veilleux, S.; Oosterloo, T.; Teng, S.H.; Rupke, D.  Another piece of the puzzle: The fast H I outflow in Mrk 231.  Astron. Astrophys. 2016, 593, A30.  https://doi.org/10.1051/0004-6361/201628978.
  * Jetha et al. (2008) Jetha, N.N.; Hardcastle, M.J.; Ponman, T.J.; Sakelliou, I.  Shock heating in the group atmosphere of the radio galaxy B2 0838+32A.  Mon. Not. R. Astron. Soc. 2008, 391, 1052–1062.  https://doi.org/10.1111/j.1365-2966.2008.13959.x.
  * Thimmappa et al. (2022) Thimmappa, R.; Stawarz, Ł.; Neilsen, J.; Ostrowski, M.; Reville, B.  X-Ray Spectral Analysis of the Jet Termination Shock in Pictor A on Subarcsecond Scales with Chandra.  Astrophys. J. 2022, 941, 204.  https://doi.org/10.3847/1538-4357/aca472.
  * Allington-Smith et al. (2002) Allington-Smith, J.; Murray, G.; Content, R.; Dodsworth, G.; Davies, R.; Miller, B.W.; Jorgensen, I.; Hook, I.; Crampton, D.; Murowinski, R.  Integral Field Spectroscopy with the Gemini Multiobject Spectrograph. I. Design, Construction, and Testing.  Publ. Astron. Soc. Pac. 2002, 114, 892–912.  https://doi.org/10.1086/341712.
  * Bacon et al. (2010) Bacon, R.; Accardo, M.; Adjali, L.; Anwand, H.; Bauer, S.; Biswas, I.; Blaizot, J.; Boudon, D.; Brau-Nogue, S.; Brinchmann, J.; et al.  The MUSE second-generation VLT instrument.  In Proceedings of the Ground-Based and Airborne Instrumentation for Astronomy III, San Diego, CA, USA, 14 July 2010; Conference Series; McLean, I.S., Ramsay, S.K., Takami, H., Eds.; Society of Photo-Optical Instrumentation Engineers (SPIE): Bellingham, WA, USA, 2010; Volume 7735, p. 773508.  https://doi.org/10.1117/12.856027.
  * Carrasco et al. (2018) Carrasco, E.; Gil de Paz, A.; Gallego, J.; Iglesias-Páramo, J.; Cedazo, R.; García Vargas, M.L.; Arrillaga, X.; Avilés, J.L.; Bouquin, A.; Carbajo, J.; et al.  MEGARA, the R=6000-20000 IFU and MOS of GTC.  In Proceedings of the Ground-Based and Airborne Instrumentation for Astronomy VII, Austin, TX, USA, 10–15 June 2018; Conference Series; Evans, C.J., Simard, L., Takami, H., Eds.; Society of Photo-Optical Instrumentation Engineers (SPIE): Bellingham, WA, USA, 2018; Volume 10702, p. 1070216.  https://doi.org/10.1117/12.2313040.
  * Wootten and Thompson (2009) Wootten, A.; Thompson, A.R.  The Atacama Large Millimeter/Submillimeter Array.  IEEE Proc. 2009, 97, 1463–1471.  https://doi.org/10.1109/JPROC.2009.2020572.
  * Ramos Almeida et al. (2011) Ramos Almeida, C.; Tadhunter, C.N.; Inskip, K.J.; Morganti, R.; Holt, J.; Dicken, D.  The optical morphologies of the 2 Jy sample of radio galaxies: Evidence for galaxy interactions.  Mon. Not. R. Astron. Soc. 2011, 410, 1550–1576.  https://doi.org/10.1111/j.1365-2966.2010.17542.x.
  * Jarvis et al. (2019) Jarvis, M.E.; Harrison, C.M.; Thomson, A.P.; Circosta, C.; Mainieri, V.; Alexander, D.M.; Edge, A.C.; Lansbury, G.B.; Molyneux, S.J.; Mullaney, J.R.  Prevalence of radio jets associated with galactic outflows and feedback from quasars.  Mon. Not. R. Astron. Soc. 2019, 485, 2710–2730.  https://doi.org/10.1093/mnras/stz556.
  * Couto et al. (2020) Couto, G.S.; Storchi-Bergmann, T.; Siemiginowska, A.; Riffel, R.A.; Morganti, R.  Powerful ionized gas outflows in the interacting radio galaxy 4C+29.30.  Mon. Not. R. Astron. Soc. 2020, 497, 5103–5117.  https://doi.org/10.1093/mnras/staa2268.
  * Comerón et al. (2021) Comerón, S.; Knapen, J.H.; Ramos Almeida, C.; Watkins, A.E.  The complex multi-component outflow of the Seyfert galaxy NGC 7130.  Astron. Astrophys. 2021, 645, A130.  https://doi.org/10.1051/0004-6361/202039382.
  * Ruschel-Dutra et al. (2021) Ruschel-Dutra, D.; Storchi-Bergmann, T.; Schnorr-Müller, A.; Riffel, R.A.; Dall’Agnol de Oliveira, B.; Lena, D.; Robinson, A.; Nagar, N.; Elvis, M.  AGNIFS survey of local AGN: GMOS-IFU data and outflows in 30 sources.  Mon. Not. R. Astron. Soc. 2021, 507, 74–89.  https://doi.org/10.1093/mnras/stab2058.
  * Venturi et al. (2021) Venturi, G.; Cresci, G.; Marconi, A.; Mingozzi, M.; Nardini, E.; Carniani, S.; Mannucci, F.; Marasco, A.; Maiolino, R.; Perna, M.; et al.  MAGNUM survey: Compact jets causing large turmoil in galaxies. Enhanced line widths perpendicular to radio jets as tracers of jet-ISM interaction.  Astron. Astrophys. 2021, 648, A17.  https://doi.org/10.1051/0004-6361/202039869.
  * Cheung et al. (2016) Cheung, E.; Bundy, K.; Cappellari, M.; Peirani, S.; Rujopakarn, W.; Westfall, K.; Yan, R.; Bershady, M.; Greene, J.E.; Heckman, T.M.; et al.  Suppressing star formation in quiescent galaxies with supermassive black hole winds.  Nature 2016, 533, 504–508.  https://doi.org/10.1038/nature18006.
  * Roy et al. (2021) Roy, N.; Moravec, E.; Bundy, K.; Hardcastle, M.J.; Gürkan, G.; Diego Baldi, R.; Leslie, S.K.; Masters, K.; Gelfand, J.; Riffel, R.; et al.  Radio Morphology of Red Geysers.  Astrophys. J. 2021, 922, 230.  https://doi.org/10.3847/1538-4357/ac24a0.
  * Treister et al. (2012) Treister, E.; Schawinski, K.; Urry, C.M.; Simmons, B.D.  Major Galaxy Mergers Only Trigger the Most Luminous Active Galactic Nuclei.  Astrophys. J. 2012, 758, L39.  https://doi.org/10.1088/2041-8205/758/2/L39.
  * Menci et al. (2014) Menci, N.; Gatti, M.; Fiore, F.; Lamastra, A.  Triggering active galactic nuclei in hierarchical galaxy formation: Disk instability vs. interactions.  Astron. Astrophys. 2014, 569, A37. https://doi.org/10.1051/0004-6361/201424217.
  * Storchi-Bergmann and Schnorr-Müller (2019) Storchi-Bergmann, T.; Schnorr-Müller, A.  Observational constraints on the feeding of supermassive black holes.  Nat. Astron. 2019, 3, 48–61.  https://doi.org/10.1038/s41550-018-0611-0.
  * Colina and de Juan (1995) Colina, L.; de Juan, L.  Collisions of Ellipticals and the Onset of Fanaroff-Riley Type I Radio Sources.  Astrophys. J. 1995, 448, 548.  https://doi.org/10.1086/175985.
  * Véron-Cetty and Véron (2001) Véron-Cetty, M.P.; Véron, P.  Are all radio galaxies genuine ellipticals?  Astron. Astrophys. 2001, 375, 791–796.  https://doi.org/ 10.1051/0004-6361:20010902.
  * Inskip et al. (2010) Inskip, K.J.; Tadhunter, C.N.; Morganti, R.; Holt, J.; Ramos Almeida, C.; Dicken, D.  A near-IR study of the host galaxies of 2 Jy radio sources at 0.03 <~z <~0.5 - I. The data.  Mon. Not. R. Astron. Soc. 2010, 407, 1739–1766.  https://doi.org/10.1111/j.1365-2966.2010.17002.x.
  * Ellison et al. (2008) Ellison, S.L.; Patton, D.R.; Simard, L.; McConnachie, A.W.  Galaxy Pairs in the Sloan Digital Sky Survey. I. Star Formation, Active Galactic Nucleus Fraction, and the Mass-Metallicity Relation.  Astron. J. 2008, 135, 1877–1899.  https://doi.org/10.1088/0004-6256/135/5/1877.
  * Davies et al. (2022) Davies, J.J.; Pontzen, A.; Crain, R.A.  Galaxy mergers can initiate quenching by unlocking an AGN-driven transformation of the baryon cycle.  Mon. Not. R. Astron. Soc. 2022, 515, 1430–1443.  https://doi.org/10.1093/mnras/stac1742.
  * Emonts et al. (2006) Emonts, B.H.C.; Morganti, R.; Tadhunter, C.N.; Holt, J.; Oosterloo, T.A.; van der Hulst, J.M.; Wills, K.A.  Timescales of merger, starburst and AGN activity in radio galaxy B2 0648+27.  Astron. Astrophys. 2006, 454, 125–135.  https://doi.org/10.1051/0004-6361:20054753.
  * Urrutia et al. (2008) Urrutia, T.; Lacy, M.; Becker, R.H.  Evidence for Quasar Activity Triggered by Galaxy Mergers in HST Observations of Dust-reddened Quasars.  Astrophys. J. 2008, 674, 80–96.  https://doi.org/10.1086/523959.
  * Bessiere et al. (2017) Bessiere, P.S.; Tadhunter, C.N.; Ramos Almeida, C.; Villar Martín, M.; Cabrera-Lavers, A.  Young stellar populations in type II quasars: Timing the onset of star formation and nuclear activity.  Mon. Not. R. Astron. Soc. 2017, 466, 3887–3917.  https://doi.org/10.1093/mnras/stw3175.
  * Calabrò et al. (2019) Calabrò, A.; Daddi, E.; Puglisi, A.; Oliva, E.; Gobat, R.; Cassata, P.; Amorín, R.; Arimoto, N.; Boquien, M.; Carraro, R.; et al.  Deciphering an evolutionary sequence of merger stages in infrared-luminous starburst galaxies at z $\sim$ 0.7.  Astron. Astrophys. 2019, 623, A64.  https://doi.org/10.1051/0004-6361/201834522.
  * van Dokkum (2005) van Dokkum, P.G.  The Recent and Continuing Assembly of Field Elliptical Galaxies by Red Mergers.  Astron. J. 2005, 130, 2647–2665.  https://doi.org/10.1086/497593.
  * Tal et al. (2009) Tal, T.; van Dokkum, P.G.; Nelan, J.; Bezanson, R.  The Frequency of Tidal Features Associated with Nearby Luminous Elliptical Galaxies From a Statistically Complete Sample.  Astron. J. 2009, 138, 1417–1427.  https://doi.org/10.1088/0004-6256/138/5/1417.
  * Gordon et al. (2019) Gordon, Y.A.; Pimbblet, K.A.; Kaviraj, S.; Owers, M.S.; O’Dea, C.P.; Walmsley, M.; Baum, S.A.; Crossett, J.P.; Fraser-McKelvie, A.; Lintott, C.J.; et al.  The Effect of Minor and Major Mergers on the Evolution of Low-excitation Radio Galaxies.  Astrophys. J. 2019, 878, 88.  https://doi.org/10.3847/1538-4357/ab203f.
  * Pierce et al. (2019) Pierce, J.C.S.; Tadhunter, C.N.; Ramos Almeida, C.; Bessiere, P.S.; Rose, M.  Do AGN triggering mechanisms vary with radio power? - I. Optical morphologies of radio-intermediate HERGs.  Mon. Not. R. Astron. Soc. 2019, 487, 5490–5507.  https://doi.org/10.1093/mnras/stz1253.
  * Sanders and Mirabel (1996) Sanders, D.B.; Mirabel, I.F.  Luminous Infrared Galaxies.  Annu. Rev. Astron. Astrophys. 1996, 34, 749.  https://doi.org/10.1146/ annurev.astro.34.1.749.
  * Heisler and Vader (1994) Heisler, C.A.; Vader, J.P.  Galaxies With Spectral Energy Distribution Peaking Near 60microns. II. Optical Broadband Properties.  Astron. J. 1994, 107, 35.  https://doi.org/10.1086/116834.
  * Siemiginowska et al. (2012) Siemiginowska, A.; Stawarz, Ł.; Cheung, C.C.; Aldcroft, T.L.; Bechtold, J.; Burke, D.J.; Evans, D.; Holt, J.; Jamrozy, M.; Migliori, G.  Deep Chandra X-Ray Imaging of a nearby Radio Galaxy 4C+29.30: X-Ray/Radio Connection.  Astrophys. J. 2012, 750, 124.  https://doi.org/10.1088/0004-637X/750/2/124.
  * Sobolewska et al. (2012) Sobolewska, M.A.; Siemiginowska, A.; Migliori, G.; Stawarz, Ł.; Jamrozy, M.; Evans, D.; Cheung, C.C.  Nuclear X-Ray Properties of the Peculiar Radio-loud Hidden AGN 4C+29.30.  Astrophys. J. 2012, 758, 90.  https://doi.org/10.1088/0004-637X/758/2/90.
  * Beasley et al. (2008) Beasley, M.A.; Bridges, T.; Peng, E.; Harris, W.E.; Harris, G.L.H.; Forbes, D.A.; Mackie, G.  A 2dF spectroscopic study of globular clusters in NGC 5128: Probing the formation history of the nearest giant elliptical.  Mon. Not. R. Astron. Soc. 2008, 386, 1443–1463.  https://doi.org/10.1111/j.1365-2966.2008.13123.x.
  * Wang et al. (2020) Wang, J.; Hammer, F.; Rejkuba, M.; Crnojević, D.; Yang, Y.  A recent major merger tale for the closest giant elliptical galaxy Centaurus A.  Mon. Not. R. Astron. Soc. 2020, 498, 2766–2777.  https://doi.org/10.1093/mnras/staa2508.
  * Jamrozy et al. (2007) Jamrozy, M.; Konar, C.; Saikia, D.J.; Stawarz, Ł.; Mack, K.H.; Siemiginowska, A.  Intermittent jet activity in the radio galaxy 4C29.30?  Mon. Not. R. Astron. Soc. 2007, 378, 581–593.  https://doi.org/10.1111/j.1365-2966.2007.11782.x.
  * Liuzzo et al. (2009) Liuzzo, E.; Giovannini, G.; Giroletti, M.; Taylor, G.B.  The Bologna complete sample of nearby radio sources. II. Phase referenced observations of faint nuclear sources.  Astron. Astrophys. 2009, 505, 509–520.  https://doi.org/10.1051/0004-6361/200912586.
  * Frank et al. (2016) Frank, B.S.; Morganti, R.; Oosterloo, T.; Nyland, K.; Serra, P.  A rare example of low surface-brightness radio lobes in a gas-rich early-type galaxy: The story of NGC 3998.  Astron. Astrophys. 2016, 592, A94.  https://doi.org/10.1051/0004-6361/201628282.
  * Couto et al. (2016) Couto, G.S.; Storchi-Bergmann, T.; Robinson, A.; Riffel, R.A.; Kharb, P.; Lena, D.; Schnorr-Müller, A.  Integral field spectroscopy of the circum-nuclear region of the radio Galaxy Pictor A.  Mon. Not. R. Astron. Soc. 2016, 458, 855–867.  https://doi.org/10.1093/mnras/stw399.
  * Salomé et al. (2021) Salomé, Q.; Longinotti, A.L.; Krongold, Y.; Feruglio, C.; Chavushyan, V.; Vega, O.; García-Burillo, S.; Fuente, A.; Olguín-Iglesias, A.; Patiño-Álvarez, V.M.; et al.  Evidence of galaxy interaction in the narrow-line Seyfert 1 galaxy IRAS 17020+4544 seen by NOEMA.  Mon. Not. R. Astron. Soc. 2021, 501, 219–228.  https://doi.org/10.1093/mnras/staa3626.
  * Croston et al. (2007) Croston, J.H.; Kraft, R.P.; Hardcastle, M.J.  Shock Heating in the Nearby Radio Galaxy NGC 3801.  Astrophys. J. 2007, 660, 191–199.  https://doi.org/10.1086/513500.
  * Hota et al. (2012) Hota, A.; Rey, S.C.; Kang, Y.; Kim, S.; Matsushita, S.; Chung, J.  NGC 3801 caught in the act: A post-merger star-forming early-type galaxy with AGN-jet feedback.  Mon. Not. R. Astron. Soc. 2012, 422, L38–L42.  https://doi.org/10.1111/j.1745-3933.2012.01231.x.
  * Fanaroff and Riley (1974) Fanaroff, B.L.; Riley, J.M.  The morphology of extragalactic radio sources of high and low luminosity.  Mon. Not. R. Astron. Soc. 1974, 167, 31P–36P.  https://doi.org/10.1093/mnras/167.1.31P.
  * Chiaberge et al. (2015) Chiaberge, M.; Gilli, R.; Lotz, J.M.; Norman, C.  Radio Loud AGNs are Mergers.  Astrophys. J. 2015, 806, 147.  https://doi.org/10.1088/ 0004-637X/806/2/147.
  * Wilson and Colbert (1995) Wilson, A.S.; Colbert, E.J.M.  The Difference between Radio-loud and Radio-quiet Active Galaxies.  Astrophys. J. 1995, 438, 62.  https://doi.org/10.1086/175054.
  * Tchekhovskoy et al. (2010) Tchekhovskoy, A.; Narayan, R.; McKinney, J.C.  Black Hole Spin and The Radio Loud/Quiet Dichotomy of Active Galactic Nuclei.  Astrophys. J. 2010, 711, 50–63.  https://doi.org/10.1088/0004-637X/711/1/50.
  * Volonteri et al. (2013) Volonteri, M.; Sikora, M.; Lasota, J.P.; Merloni, A.  The Evolution of Active Galactic Nuclei and their Spins.  Astrophys. J. 2013, 775, 94.  https://doi.org/10.1088/0004-637X/775/2/94.
  * Donoso et al. (2010) Donoso, E.; Li, C.; Kauffmann, G.; Best, P.N.; Heckman, T.M.  Clustering of radio galaxies and quasars.  Mon. Not. R. Astron. Soc. 2010, 407, 1078–1089.  https://doi.org/10.1111/j.1365-2966.2010.16907.x.
  * Wylezalek et al. (2013) Wylezalek, D.; Galametz, A.; Stern, D.; Vernet, J.; De Breuck, C.; Seymour, N.; Brodwin, M.; Eisenhardt, P.R.M.; Gonzalez, A.H.; Hatch, N.; et al.  Galaxy Clusters around Radio-loud Active Galactic Nuclei at 1.3 < z < 3.2 as Seen by Spitzer.  Astrophys. J. 2013, 769, 79.  https://doi.org/10.1088/0004-637X/769/1/79.
  * Hatch et al. (2014) Hatch, N.A.; Wylezalek, D.; Kurk, J.D.; Stern, D.; De Breuck, C.; Jarvis, M.J.; Galametz, A.; Gonzalez, A.H.; Hartley, W.G.; Mortlock, A.; et al.  Why z > 1 radio-loud galaxies are commonly located in protoclusters.  Mon. Not. R. Astron. Soc. 2014, 445, 280–289.  https://doi.org/10.1093/mnras/stu1725.
  * Izquierdo-Villalba et al. (2018) Izquierdo-Villalba, D.; Orsi, Á.A.; Bonoli, S.; Lacey, C.G.; Baugh, C.M.; Griffin, A.J.  The environment of radio galaxies: A signature of AGN feedback at high redshifts.  Mon. Not. R. Astron. Soc. 2018, 480, 1340–1352.  https://doi.org/10.1093/mnras/sty1941.
  * Cecil (1988) Cecil, G.  Kinematics of Spatially Extended High-Velocity Outflow from the Nucleus of M51.  Astrophys. J. 1988, 329, 38.  https://doi.org/10.1086/166356.
  * Lena et al. (2015) Lena, D.; Robinson, A.; Storchi-Bergman, T.; Schnorr-Müller, A.; Seelig, T.; Riffel, R.A.; Nagar, N.M.; Couto, G.S.; Shadler, L.  The Complex Gas Kinematics in the Nucleus of the Seyfert 2 Galaxy NGC 1386: Rotation, Outflows, and Inflows.  Astrophys. J. 2015, 806, 84.  https://doi.org/10.1088/0004-637X/806/1/84.
  * Mahony et al. (2016) Mahony, E.K.; Oonk, J.B.R.; Morganti, R.; Tadhunter, C.; Bessiere, P.; Short, P.; Emonts, B.H.C.; Oosterloo, T.A.  Jet-driven outflows of ionized gas in the nearby radio galaxy 3C 293\.  Mon. Not. R. Astron. Soc. 2016, 455, 2453–2460.  https://doi.org/10.1093/mnras/stv2456.
  * Wylezalek et al. (2020) Wylezalek, D.; Flores, A.M.; Zakamska, N.L.; Greene, J.E.; Riffel, R.A.  Ionized gas outflow signatures in SDSS-IV MaNGA active galactic nuclei.  Mon. Not. R. Astron. Soc. 2020, 492, 4680–4696.  https://doi.org/10.1093/mnras/staa062.
  * Balmaverde et al. (2019) Balmaverde, B.; Capetti, A.; Marconi, A.; Venturi, G.; Chiaberge, M.; Baldi, R.D.; Baum, S.; Gilli, R.; Grandi, P.; Meyer, E.; et al.  The MURALES survey. II. Presentation of MUSE observations of 20 3C low-z radio galaxies and first results.  Astron. Astrophys. 2019, 632, A124.  https://doi.org/10.1051/0004-6361/201935544.
  * Balmaverde et al. (2021) Balmaverde, B.; Capetti, A.; Marconi, A.; Venturi, G.; Chiaberge, M.; Baldi, R.D.; Baum, S.; Gilli, R.; Grandi, P.; Meyer, E.T.; et al.  The MURALES survey. III. Completing the MUSE observations of 37 3C low-z radio galaxies.  Astron. Astrophys. 2021, 645, A12.  https://doi.org/10.1051/0004-6361/202039062.
  * Riffel (2021) Riffel, R.A.  Powerful multiphase outflows in the central region of Cygnus A.  Mon. Not. R. Astron. Soc. 2021, 506, 2950–2962.  https://doi.org/10.1093/mnras/stab1877.
  * Zovaro et al. (2019) Zovaro, H.R.M.; Nesvadba, N.P.H.; Sharp, R.; Bicknell, G.V.; Groves, B.; Mukherjee, D.; Wagner, A.Y.  Searching for signs of jet-driven negative feedback in the nearby radio galaxy UGC 05771.  Mon. Not. R. Astron. Soc. 2019, 489, 4944–4961.  https://doi.org/10.1093/mnras/stz2459.
  * Couto et al. (2013) Couto, G.S.; Storchi-Bergmann, T.; Axon, D.J.; Robinson, A.; Kharb, P.; Riffel, R.A.  Kinematics and excitation of the nuclear spiral in the active galaxy Arp 102B.  Mon. Not. R. Astron. Soc. 2013, 435, 2982–3000.  https://doi.org/10.1093/mnras/stt1491.
  * Schnorr-Müller et al. (2014) Schnorr-Müller, A.; Storchi-Bergmann, T.; Nagar, N.M.; Robinson, A.; Lena, D.; Riffel, R.A.; Couto, G.S.  Feeding and feedback in the inner kiloparsec of the active galaxy NGC 2110.  Mon. Not. R. Astron. Soc. 2014, 437, 1708–1724.  https://doi.org/10.1093/mnras/stt2001.
  * Riffel et al. (2015) Riffel, R.A.; Storchi-Bergmann, T.; Riffel, R.  Feeding versus feedback in active galactic nuclei from near-infrared integral field spectroscopy - X. NGC 5929.  Mon. Not. R. Astron. Soc. 2015, 451, 3587–3605.  https://doi.org/10.1093/mnras/stv1129.
  * Heywood et al. (2019) Heywood, I.; Camilo, F.; Cotton, W.D.; Yusef-Zadeh, F.; Abbott, T.D.; Adam, R.M.; Aldera, M.A.; Bauermeister, E.F.; Booth, R.S.; Botha, A.G.; et al.  Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by an energetic event.  Nature 2019, 573, 235–237.  https://doi.org/10.1038/s41586-019-1532-5.
  * Cecil et al. (2001) Cecil, G.; Bland-Hawthorn, J.; Veilleux, S.; Filippenko, A.V.  Jet- and Wind-driven Ionized Outflows in the Superbubble and Star-forming Disk of NGC 3079.  Astrophys. J. 2001, 555, 338–355.  https://doi.org/10.1086/321481.
  * Hota and Saikia (2006) Hota, A.; Saikia, D.J.  Radio bubbles in the composite AGN-starburst galaxy NGC6764.  Mon. Not. R. Astron. Soc. 2006, 371, 945–956.  https://doi.org/10.1111/j.1365-2966.2006.10738.x.
  * Carniani et al. (2015) Carniani, S.; Marconi, A.; Maiolino, R.; Balmaverde, B.; Brusa, M.; Cano-Díaz, M.; Cicone, C.; Comastri, A.; Cresci, G.; Fiore, F.; et al.  Ionised outflows in z ~2.4 quasar host galaxies.  Astron. Astrophys. 2015, 580, A102.  https://doi.org/10.1051/0004-6361/201526557.
  * Fiore et al. (2017) Fiore, F.; Feruglio, C.; Shankar, F.; Bischetti, M.; Bongiorno, A.; Brusa, M.; Carniani, S.; Cicone, C.; Duras, F.; Lamastra, A.; et al.  AGN wind scaling relations and the co-evolution of black holes and galaxies.  Astron. Astrophys. 2017, 601, A143.  https://doi.org/10.1051/0004-6361/201629478.
  * Dasyra et al. (2022) Dasyra, K.M.; Paraschos, G.F.; Bisbas, T.G.; Combes, F.; Fernández-Ontiveros, J.A.  Insights into the collapse and expansion of molecular clouds in outflows from observable pressure gradients.  Nat. Astron. 2022, 6, 1077–1084.  https://doi.org/10.1038/s41550-022-01725-9.
  * Audibert et al. (2019) Audibert, A.; Combes, F.; García-Burillo, S.; Hunt, L.; Eckart, A.; Aalto, S.; Casasola, V.; Boone, F.; Krips, M.; Viti, S.; et al.  ALMA captures feeding and feedback from the active galactic nucleus in NGC 613.  Astron. Astrophys. 2019, 632, A33.  https://doi.org/10.1051/0004-6361/201935845.
  * Zovaro et al. (2019) Zovaro, H.R.M.; Sharp, R.; Nesvadba, N.P.H.; Bicknell, G.V.; Mukherjee, D.; Wagner, A.Y.; Groves, B.; Krishna, S.  Jets blowing bubbles in the young radio galaxy 4C 31.04.  Mon. Not. R. Astron. Soc. 2019, 484, 3393–3409.  https://doi.org/10.1093/mnras/stz233.
  * Ruffa et al. (2019) Ruffa, I.; Davis, T.A.; Prandoni, I.; Laing, R.A.; Paladino, R.; Parma, P.; de Ruiter, H.; Casasola, V.; Bureau, M.; Warren, J.  The AGN fuelling/feedback cycle in nearby radio galaxies - II. Kinematics of the molecular gas.  Mon. Not. R. Astron. Soc. 2019, 489, 3739–3757.  https://doi.org/10.1093/mnras/stz2368.
  * Aalto et al. (2016) Aalto, S.; Costagliola, F.; Muller, S.; Sakamoto, K.; Gallagher, J.S.; Dasyra, K.; Wada, K.; Combes, F.; García-Burillo, S.; Kristensen, L.E.; et al.  A precessing molecular jet signaling an obscured, growing supermassive black hole in NGC 1377?  Astron. Astrophys. 2016, 590, A73.  https://doi.org/10.1051/0004-6361/201527664.
  * Fernández-Ontiveros et al. (2020) Fernández-Ontiveros, J.A.; Dasyra, K.M.; Hatziminaoglou, E.; Malkan, M.A.; Pereira-Santaella, M.; Papachristou, M.; Spinoglio, L.; Combes, F.; Aalto, S.; Nagar, N.; et al.  A CO molecular gas wind 340 pc away from the Seyfert 2 nucleus in ESO 420-G13 probes an elusive radio jet.  Astron. Astrophys. 2020, 633, A127.  https://doi.org/10.1051/0004-6361/201936552.
  * Pereira-Santaella et al. (2022) Pereira-Santaella, M.; Álvarez-Márquez, J.; García-Bernete, I.; Labiano, A.; Colina, L.; Alonso-Herrero, A.; Bellocchi, E.; García-Burillo, S.; Hönig, S.F.; Ramos Almeida, C.; et al.  Low-power jet-interstellar medium interaction in NGC 7319 revealed by JWST/MIRI MRS.  Astron. Astrophys. 2022, 665, L11.  https://doi.org/10.1051/0004-6361/202244725.
  * Wagner and Bicknell (2011) Wagner, A.Y.; Bicknell, G.V.  Relativistic Jet Feedback in Evolving Galaxies.  Astrophys. J. 2011, 728, 29.  https://doi.org/10.1088/0004-637X/728/1/29.
  * Mukherjee et al. (2018) Mukherjee, D.; Wagner, A.Y.; Bicknell, G.V.; Morganti, R.; Oosterloo, T.; Nesvadba, N.; Sutherland, R.S.  The jet-ISM interactions in IC 5063.  Mon. Not. R. Astron. Soc. 2018, 476, 80–95.  https://doi.org/10.1093/mnras/sty067.
  * Mukherjee et al. (2018) Mukherjee, D.; Bicknell, G.V.; Wagner, A.Y.; Sutherland, R.S.; Silk, J.  Relativistic jet feedback - III. Feedback on gas discs.  Mon. Not. R. Astron. Soc. 2018, 479, 5544–5566.  https://doi.org/10.1093/mnras/sty1776.
  * Talbot et al. (2021) Talbot, R.Y.; Bourne, M.A.; Sijacki, D.  Blandford-Znajek jets in galaxy formation simulations: Method and implementation.  Mon. Not. R. Astron. Soc. 2021, 504, 3619–3650.  https://doi.org/10.1093/mnras/stab804.
  * Meenakshi et al. (2022) Meenakshi, M.; Mukherjee, D.; Wagner, A.Y.; Nesvadba, N.P.H.; Bicknell, G.V.; Morganti, R.; Janssen, R.M.J.; Sutherland, R.S.; Mandal, A.  Modelling observable signatures of jet-ISM interaction: Thermal emission and gas kinematics.  Mon. Not. R. Astron. Soc. 2022, 516, 766–786.  https://doi.org/10.1093/mnras/stac2251.
  * Heckman (1980) Heckman, T.M.  An Optical and Radio Survey of the Nuclei of Bright Galaxies - Activity in the Normal Galactic Nuclei.  Astron. Astrophys. 1980, 87, 152.
  * Baldwin et al. (1981) Baldwin, J.A.; Phillips, M.M.; Terlevich, R.  Classification parameters for the emission-line spectra of extragalactic objects.  Publ. Astron. Soc. Pac. 1981, 93, 5–19.  https://doi.org/10.1086/130766.
  * Dopita and Sutherland (1995) Dopita, M.A.; Sutherland, R.S.  Spectral Signatures of Fast Shocks. II. Optical Diagnostic Diagrams.  Astrophys. J. 1995, 455, 468.  https://doi.org/10.1086/176596.
  * Allen et al. (2008) Allen, M.G.; Groves, B.A.; Dopita, M.A.; Sutherland, R.S.; Kewley, L.J.  The MAPPINGS III Library of Fast Radiative Shock Models.  Astrophys. J. 2008, 178, 20–55.  https://doi.org/10.1086/589652.
  * Couto et al. (2017) Couto, G.S.; Storchi-Bergmann, T.; Schnorr-Müller, A.  Gas rotation, shocks and outflow within the inner 3 kpc of the radio galaxy 3C 33.  Mon. Not. R. Astron. Soc. 2017, 469, 1573–1586.  https://doi.org/10.1093/mnras/stx962.
  * Morganti et al. (2002) Morganti, R.; Oosterloo, T.A.; Tinti, S.; Tadhunter, C.N.; Wills, K.A.; van Moorsel, G.  Large-scale gas disk around the radio galaxy Coma A.  Astron. Astrophys. 2002, 387, 830–837.  https://doi.org/10.1051/0004-6361:20020350.
  * Villar-Martín et al. (2017) Villar-Martín, M.; Emonts, B.; Cabrera Lavers, A.; Tadhunter, C.; Mukherjee, D.; Humphrey, A.; Rodríguez Zaurín, J.; Ramos Almeida, C.; Pérez Torres, M.; Bessiere, P.  Galaxy-wide radio-induced feedback in a radio-quiet quasar.  Mon. Not. R. Astron. Soc. 2017, 472, 4659–4678.  https://doi.org/10.1093/mnras/stx2209.
  * Santoro et al. (2018) Santoro, F.; Rose, M.; Morganti, R.; Tadhunter, C.; Oosterloo, T.A.; Holt, J.  Probing multi-phase outflows and AGN feedback in compact radio galaxies: The case of PKS B1934-63.  Astron. Astrophys. 2018, 617, A139.  https://doi.org/10.1051/0004-6361/201833248.
  * Vagshette et al. (2019) Vagshette, N.D.; Naik, S.; Patil, M.K.  Cavities, shocks and a cold front around 3C 320.  Mon. Not. R. Astron. Soc. 2019, 485, 1981–1989.  https://doi.org/10.1093/mnras/stz476.
  * Murthy et al. (2020) Murthy, S.; Morganti, R.; Emonts, B.; Villar-Martín, M.; Oosterloo, T.; Peletier, R.  Disc galaxy resolved in H I absorption against the radio lobe of 3C 433: Case study for future surveys.  Astron. Astrophys. 2020, 643, A74.  https://doi.org/10.1051/0004-6361/202039114.
  * Molina et al. (2021) Molina, M.; Reines, A.E.; Greene, J.E.; Darling, J.; Condon, J.J.  Outflows, Shocks, and Coronal Line Emission in a Radio-selected AGN in a Dwarf Galaxy.  Astrophys. J. 2021, 910, 5.  https://doi.org/10.3847/1538-4357/abe120.
  * Holt et al. (2006) Holt, J.; Tadhunter, C.; Morganti, R.; Bellamy, M.; González Delgado, R.M.; Tzioumis, A.; Inskip, K.J.  The co-evolution of the obscured quasar PKS 1549-79 and its host galaxy: Evidence for a high accretion rate and warm outflow.  Mon. Not. R. Astron. Soc. 2006, 370, 1633–1650.  https://doi.org/10.1111/j.1365-2966.2006.10604.x.
  * Peterson (1997) Peterson, B.M.  An Introduction to Active Galactic Nuclei; IOP Publishing Ltd.: Bristol, UK, 1997.
  * Di Matteo et al. (2005) Di Matteo, T.; Springel, V.; Hernquist, L.  Energy input from quasars regulates the growth and activity of black holes and their host galaxies.  Nature 2005, 433, 604–607.  https://doi.org/10.1038/nature03335.
  * Hopkins and Elvis (2010) Hopkins, P.F.; Elvis, M.  Quasar feedback: More bang for your buck.  Mon. Not. R. Astron. Soc. 2010, 401, 7–14.  https://doi.org/10.1111/j.1365-2966.2009.15643.x.
  * Baron and Netzer (2019) Baron, D.; Netzer, H.  Discovering AGN-driven winds through their infrared emission - II. Mass outflow rate and energetics.  Mon. Not. R. Astron. Soc. 2019, 486, 4290–4303.  https://doi.org/10.1093/mnras/stz1070.
  * Dall’Agnol de Oliveira et al. (2021) Dall’Agnol de Oliveira, B.; Storchi-Bergmann, T.; Kraemer, S.B.; Villar Martín, M.; Schnorr-Müller, A.; Schmitt, H.R.; Ruschel-Dutra, D.; Crenshaw, D.M.; Fischer, T.C.  Gauging the effect of supermassive black holes feedback on quasar host galaxies.  Mon. Not. R. Astron. Soc. 2021, 504, 3890–3908.  https://doi.org/10.1093/mnras/stab1067.
  * Richings and Faucher-Giguère (2018) Richings, A.J.; Faucher-Giguère, C.A.  Radiative cooling of swept-up gas in AGN-driven galactic winds and its implications for molecular outflows.  Mon. Not. R. Astron. Soc. 2018, 478, 3100–3119.  https://doi.org/10.1093/mnras/sty1285.
  * Villar Martin et al. (2021) Villar Martin, M.; Emonts, B.H.C.; Cabrera Lavers, A.; Bellocchi, E.; Alonso Herrero, A.; Humphrey, A.; Dall’Agnol de Oliveira, B.; Storchi-Bergmann, T.  Interactions between large-scale radio structures and gas in a sample of optically selected type 2 quasars.  Astron. Astrophys. 2021, 650, A84.  https://doi.org/10.1051/0004-6361/202039642.
  * Wylezalek and Zakamska (2016) Wylezalek, D.; Zakamska, N.L.  Evidence of suppression of star formation by quasar-driven winds in gas-rich host galaxies at z < 1?  Mon. Not. R. Astron. Soc. 2016, 461, 3724–3739.  https://doi.org/10.1093/mnras/stw1557.
  * Mullaney et al. (2013) Mullaney, J.R.; Alexander, D.M.; Fine, S.; Goulding, A.D.; Harrison, C.M.; Hickox, R.C.  Narrow-line region gas kinematics of 24 264 optically selected AGN: The radio connection.  Mon. Not. R. Astron. Soc. 2013, 433, 622–638.  https://doi.org/10.1093/mnras/stt751.
  * Delvecchio et al. (2017) Delvecchio, I.; Smolčić, V.; Zamorani, G.; Lagos, C.D.P.; Berta, S.; Delhaize, J.; Baran, N.; Alexander, D.M.; Rosario, D.J.; Gonzalez-Perez, V.; et al.  The VLA-COSMOS 3 GHz Large Project: AGN and host-galaxy properties out to z $\lesssim$ 6\.  Astron. Astrophys. 2017, 602, A3.  https://doi.org/10.1051/0004-6361/201629367.
  * Finlez et al. (2018) Finlez, C.; Nagar, N.M.; Storchi-Bergmann, T.; Schnorr-Müller, A.; Riffel, R.A.; Lena, D.; Mundell, C.G.; Elvis, M.S.  The complex jet- and bar-perturbed kinematics in NGC 3393 as revealed with ALMA and GEMINI-GMOS/IFU.  Mon. Not. R. Astron. Soc. 2018, 479, 3892–3908.  https://doi.org/10.1093/mnras/sty1555.
  * Riffel et al. (2019) Riffel, R.A.; Nemmen, R.S.; Ilha, G.S.; Rembold, S.B.; Roy, N.; Storchi-Bergmann, T.; Riffel, R.; Bundy, K.A.; Machado, A.D.; Mallman, N.D.; et al.  Precessing winds from the nucleus of the prototype Red Geyser?  Mon. Not. R. Astron. Soc. 2019, 485, 5590–5597.  https://doi.org/10.1093/mnras/stz841.
  * Comerford et al. (2020) Comerford, J.M.; Negus, J.; Müller-Sánchez, F.; Eracleous, M.; Wylezalek, D.; Storchi-Bergmann, T.; Greene, J.E.; Barrows, R.S.; Nevin, R.; Roy, N.; et al.  A Catalog of 406 AGNs in MaNGA: A Connection between Radio-mode AGNs and Star Formation Quenching.  Astrophys. J. 2020, 901, 159.  https://doi.org/10.3847/1538-4357/abb2ae.
  * Bundy et al. (2015) Bundy, K.; Bershady, M.A.; Law, D.R.; Yan, R.; Drory, N.; MacDonald, N.; Wake, D.A.; Cherinka, B.; Sánchez-Gallego, J.R.; Weijmans, A.M.; et al.  Overview of the SDSS-IV MaNGA Survey: Mapping nearby Galaxies at Apache Point Observatory.  Astrophys. J. 2015, 798, 7.  https://doi.org/10.1088/0004-637X/798/1/7.
  * Narayan and McClintock (2008) Narayan, R.; McClintock, J.E.  Advection-dominated accretion and the black hole event horizon.  New Astron. Rev. 2008, 51, 733–751.  https://doi.org/10.1016/j.newar.2008.03.002.
  * Nemmen et al. (2014) Nemmen, R.S.; Storchi-Bergmann, T.; Eracleous, M.  Spectral models for low-luminosity active galactic nuclei in LINERs: The role of advection-dominated accretion and jets.  Mon. Not. R. Astron. Soc. 2014, 438, 2804–2827.  https://doi.org/10.1093/mnras/stt2388.
  * Ilha et al. (2022) Ilha, G.S.; Riffel, R.A.; Ricci, T.V.; Rembold, S.B.; Storchi-Bergmann, T.; Riffel, R.; Roy, N.; Bundy, K.; Nemmen, R.; Schimoia, J.S.; et al.  Active galactic nuclei signatures in Red Geyser galaxies from Gemini GMOS-IFU observations.  Mon. Not. R. Astron. Soc. 2022, 516, 1442–1461.  https://doi.org/10.1093/mnras/stac2233.
  * Randall et al. (2011) Randall, S.W.; Forman, W.R.; Giacintucci, S.; Nulsen, P.E.J.; Sun, M.; Jones, C.; Churazov, E.; David, L.P.; Kraft, R.; Donahue, M.; et al.  Shocks and Cavities from Multiple Outbursts in the Galaxy Group NGC 5813: A Window to Active Galactic Nucleus Feedback.  Astrophys. J. 2011, 726, 86.  https://doi.org/10.1088/0004-637X/726/2/86.
  * Mingo et al. (2011) Mingo, B.; Hardcastle, M.J.; Croston, J.H.; Evans, D.A.; Hota, A.; Kharb, P.; Kraft, R.P.  Markarian 6: Shocking the Environment of an Intermediate Seyfert.  Astrophys. J. 2011, 731, 21.  https://doi.org/10.1088/0004-637X/731/1/21.
  * Webster et al. (2021) Webster, B.; Croston, J.H.; Mingo, B.; Baldi, R.D.; Barkus, B.; Gürkan, G.; Hardcastle, M.J.; Morganti, R.; Röttgering, H.J.A.; Sabater, J.; et al.  A population of galaxy-scale jets discovered using LOFAR.  Mon. Not. R. Astron. Soc. 2021, 500, 4921–4936.  https://doi.org/10.1093/mnras/staa3437.