# Galactic-Scale Feedback Observed in the 3C 298 Quasar Host Galaxy

Andrey Vayner Department of Physics, University of California San Diego, 9500
Gilman Drive La Jolla, CA 92093 USA  Center for Astrophysics & Space Sciences,
University of California San Diego, 9500 Gilman Drive La Jolla, CA 92093 USA
Shelley A. Wright Department of Physics, University of California San Diego,
9500 Gilman Drive La Jolla, CA 92093 USA  Center for Astrophysics & Space
Sciences, University of California San Diego, 9500 Gilman Drive La Jolla, CA
92093 USA  Norman Murray  Canadian Institute for Theoretical Astrophysics,
University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada
Canada Research Chair in Theoretical Astrophysics  Lee Armus Spitzer Science
Center, California Institute of Technology, 1200 E. California Blvd.,
Pasadena, CA 91125 USA  James E. Larkin  Department of Physics and Astronomy,
University of California, Los Angeles, CA 90095 USA  Etsuko Mieda  NRC
Herzberg Astronomy and Astrophysics, 5071 West Saanich Rd, Victoria, BC, V9E
2E7, Canada

(Received September 10, 2017; Accepted November 15, 2017)

###### Abstract

We present high angular resolution multi-wavelength data of the 3C 298 radio-
loud quasar host galaxy (z=1.439) taken using the W.M. Keck Observatory OSIRIS
integral field spectrograph (IFS) with adaptive optics, Atacama Large
Millimeter/submillimeter Array (ALMA), Hubble Space Telescope (HST) WFC3, and
the Very Large Array (VLA). Extended emission is detected in the rest-frame
optical nebular emission lines H$\beta$, [OIII], H$\alpha$, [NII], and [SII],
as well as molecular lines CO (J=3-2) and (J=5-4). Along the path of 3C 298’s
relativistic jets we detect conical outflows in ionized gas emission with
velocities up to 1700 km s-1 and outflow rate of 450-1500 M⊙ yr-1 extended
over 12 kpc. Near the spatial center of the conical outflow, CO (J=3-2)
emission shows a molecular gas disc with a rotational velocity of $\pm$150km
s-1and total molecular mass ($\rm M_{H_{2}}$) of 6.6$\pm 0.36\times
10^{9}~{}$M⊙. On the molecular disc’s blueshifted side we observe broad
extended emission due to a molecular outflow with a rate of 2300 M⊙ yr-1 and
depletion time scale of 3 Myr. We detect no narrow H$\alpha$ emission in the
outflow regions, suggesting a limit on star formation of 0.3 M⊙ yr-1 kpc-2.
Quasar driven winds are evacuating the molecular gas reservoir thereby
directly impacting star formation in the host galaxy. The observed mass of the
supermassive black hole is $10^{9.37-9.56}~{}$M⊙ and we determine a dynamical
bulge mass of M$\rm{}_{bulge}=$ 1-1.7$\rm\times 10^{10}\frac{R}{1.6kpc}~{}$M⊙.
The bulge mass of 3C 298 resides 2-2.5 orders of magnitude below the expected
value from the local galactic bulge - supermassive black hole mass
(M$\rm{}_{bulge}-M_{BH}$) relationship. A second galactic disc observed in
nebular emission is offset from the quasar by 9 kpc suggesting the system is
an intermediate stage merger. These results show that galactic scale negative
feedback is occurring early in the merger phase of 3C 298, well before the
coalescence of the galactic nuclei and assembly on the local
M$\rm{}_{bulge}-M_{BH}$ relationship.

galaxies: active, galaxies: high-redshift, galaxies: kinematics and dynamics —
quasars: emission lines, quasars: supermassive black holes, quasars:
individual (3C 298)

††facilities: Keck(OSIRIS-LGSAO), ALMA (Band 4 and 6), HST(WFC3),
VLA††software: Scipy: (Jones et al., 2001–), CASA: (McMullin et al., 2007),
OSIRIS Data Reduction Pipeline:(Larkin et al., 2013), Matplotlib (Hunter,
2007)

December 20, 2017

##  1 Introduction

Quasars are the most luminous active galactic nuclei (AGN), whose supermassive
black holes (SMBHs) are often fueled by large galaxy mergers (Treister et al.,
2012). AGN accretion discs are thought to drive energetic winds (Murray et
al., 1995) and/or relativistic jets that suppress star formation (Hopkins &
Elvis, 2010; Zubovas & King, 2014; Costa et al., 2015), thereby impacting
galactic structure and evolution. This is one of the leading theoretical (Di
Matteo et al., 2005; Faucher-Giguère et al., 2012; Barai et al., 2017; Anglés-
Alcázar et al., 2017) pictures used to explain correlations between SMBH
masses and galactic stellar masses (Magorrian et al., 1998; Gebhardt et al.,
2000; Ferrarese & Merritt, 2000; Kormendy & Ho, 2013) and luminosity function
of local massive galaxies (Benson et al., 2003). The sphere of influence of
SMBHs, inside of which their gravity dominates that of the stars, gas, and
dark matter, range from a few 10s to 100 pc, while the local scaling relations
of M$\rm{}_{bulge}-M_{BH}$ apply on stellar bulge scales, i.e., several kpc.
The SMBH energy output can be orders of magnitude higher than the binding
energy of galactic bulges; therefore energy injected by active SMBHs into the
interstellar medium (ISM) could be efficient at impacting the stellar mass
history of its host galaxy. Since the bulk of stellar mass is formed at high-
redshift (z$>1$) (Gallazzi et al., 2008), it is critical to study the effects
of AGN activity during the assembly periods of their host galaxies at high-
redshift.

Observational studies have found that nearby quasars and ULIRGs (Ultra-
Luminous Infrared Galaxies) show evidence of large scale ionized (Greene et
al., 2012; Rupke & Veilleux, 2011; Liu et al., 2013a; Harrison et al., 2014)
and molecular outflows (e.g., Cicone et al. 2014; Sun et al. 2014; Stone et
al. 2016; Veilleux et al. 2017) allowing for detailed studies of feedback
physics. However the computed outflow rates in nearby systems are not
sufficient to impact the stellar mass assembly history since these galaxies
have already done the bulk of their growth. In contrast, there is minimal
observational evidence for AGN activity directly affecting star formation at
the peak epoch (1$<$z$<$3) of galaxy formation and black hole accretion
(Delvecchio et al., 2014; Madau & Dickinson, 2014). Recent studies of distant
quasars and radio-loud galaxies have shown evidence of large scale (5-20 kpc)
outflows driven by AGN activity that theoretically should be powerful enough
to quench star formation (Nesvadba et al., 2008; Steinbring, 2011; Cano-Díaz
et al., 2012; Harrison et al., 2012; Brusa et al., 2016; Carniani et al.,
2015). Although it has still remained challenging to directly associate large
scale outflows with the suppression of star formation of AGN host galaxies
(Cano-Díaz et al., 2012; Cresci et al., 2015; Carniani et al., 2016). These
studies have provided intriguing clues as to the nature of quasar feedback.
Yet compared to nearby quasars there is little known about z $>$ 1 host
galaxies (i.e., stellar mass, dynamics, and morphologies) and the true effects
of feedback on host galaxy star formation. A key missing result is one that
connects quasar and jet driven outflows with the observed galactic scale
winds, star formation activity, and molecular gas properties.

Quasars outshine their host galaxies by an order of magnitude or more, making
it observationally challenging to detect and study their faint underlying
galaxies (Lehnert et al., 1999; Hutchings et al., 2002; Jahnke et al., 2004;
Falomo et al., 2005; Floyd et al., 2013; Glikman et al., 2015). The sizes of
distant (z $>$ 1; look-back time of 9.25 Gyr) galaxies are small ($\sim$ 1″),
roughly the same angular size as ground-based “seeing” and space-based
instrument resolution and contrast sensitivity. The combination of near-
infrared integral field spectroscopy (IFS) with laser-guide star adaptive
optics (LGS-AO) allows for the effective separation of quasar emission from
the host galaxy. This is achieved by using a pristine point spread function
(PSF) generated by the quasar broad-line and continuum emission from the IFS
data cube (Inskip et al., 2011; Vayner et al., 2016).

We have started the QUART (Quasar hosts Unveiled by high Angular Resolution
Techniques) survey of high-redshift (1.3$<$z$<$2.6) quasars using W.M Keck
Observatory laser guide star adaptive optics (LGS-AO) observations to resolve
and study quasar host galaxy properties with a rich multi-wavelength data
sets. Herein we present the first paper of this survey on the individual
z=1.439 (look-back time 9.3 Gyr) radio loud quasar 3C 298. We combine high
spatial resolution observations to reveal the complex morphology, dynamics,
and energetics of the 3C 298 host galaxy. Using OSIRIS and Keck LGS-AO, we are
able to map the kinematics and intensity of galactic nebular emission lines
H$\beta$, [OIII], H$\alpha$, [NII]and [SII] at$\sim$1.4 kiloparsec (kpc)
resolution. We present the multi-wavelength data sets in §2 and describe the
data reduction and analysis techniques for each instrument in §3. We discuss
the dynamics and energetics of ionized and molecular gas in §4, and in §5 we
discuss our results and overall interpretation. We suggest the reader refers
to Figure 11 while reading the manuscript, which summarizes the observed
structure and properties of the 3C 298 host galaxy. Throughout the paper we
assume a $\Lambda$-dominated cosmology (Planck Collaboration et al., 2014)
with $\Omega_{M}$=0.308, $\Omega_{\Lambda}$=0.692, and Ho=67.8 km s-1 Mpc-1

##  2 Observations

We present new observations of 3C 298 using Keck OSIRIS AO and ALMA band 4 and
6. These observations are coupled with archival Hubble Space Telescope (HST)
WFC3 and Very Large Array (VLA) imaging data.

###  2.1 Keck: OSIRIS

Observations were taken using the integral field spectrograph OSIRIS (Larkin
et al., 2006) with the upgraded grating (Mieda et al., 2014) behind the laser
guide star adaptive optics (LGS-AO) system at W.M. Keck Observatory on May 19
and 20, 2014 (UT). The quasar was used for tip/tilt correction while the laser
tuned to 589.2 nm created an artificial star on-axis for higher order
corrections. We used the Hn3 (May 19) and Jn1 (May 20) filters with a plate
scale of 100 milli-arcseconds (mas) per lenslet with a position-angle of 103∘.
In these modes OSIRIS has a field of view of 3.2″$\times$6.4″in Jn1 and
4.8″$\times$6.4″in Hn3. We took four 600s exposures on-source in each filter,
plus an additional 600s pure-sky frame. Each night immediately after the
quasar observations we observed the standard star HD136754 for telluric and
flux calibrations. Both nights were photometric with near-infrared seeing of
0.4-0.5″.

###  2.2 ALMA: Band 4 and 6

Early ALMA science (cycle 2, 3) band 4 and 6 observations (2013.1.01359.S,
2015.1.01090.S, PI: Vayner) were aimed at observing the rotational molecular
transition of CO J=3-2 and J=5-4 in emission to map the distribution and
kinematics of the molecular gas in 3C 298. One 1.8745 GHz spectral window was
centered on CO (J=3-2) (141.87 GHz) and CO (J=5-4) (236.43 GHz) while three
additional spectral windows set up to map the continuum in each band. The
effective velocity bandwidth per spectral window was approximately 4,000 km
s-1 for band 4 and 2,400 km s-1 for band 6. Observations were taken in an
extended configuration with an approximate angular resolution of $\sim$0.4″
and $\sim 0.3$″ for band 4 and 6, respectively. In Table 1 we summarize the
observational setup for each band.

Table 1: ALMA Cycle 2 and 3 observations summary Date | Band | Central frequencies | Integration | PWV | Antennae | Beam | LineaaComputed per 34km s-1 channels | Continuum
---|---|---|---|---|---|---|---|---
|  | (GHz) | Time (min) | (mm) | $\\#$ | Size |  $\sigma$/beam (mJy) |  $\sigma$/beam ($\mu$Jy)
2015 Aug 6 | 4 | 141.86 | 27.84 | 4.5 | 39 | 0.44″$\times$0.41″ | 0.5 | 48
2016 Sep 9 | 4 | 141.85, 140.00, 129.97, 128.01 | 24.19 | 2.5 | 37 | 0.39″$\times$0.30″ | 0.22 | 46
2016 Sep 17 | 6 | 236.42, 234.5, 220.99, 219.11 | 19.65 | 0.7 | 38 | 0.28″$\times$0.18″ | 0.37 | 44

##  3 Data reduction and Analysis

###  3.1 OSIRIS: Data reduction

The data was reduced with the OSIRIS data reduction pipeline version 3.2,
which performs standard near-infrared IFS reduction procedures: dark
subtraction; adjust channel levels; remove crosstalk; glitch identification;
clean cosmic rays; extract spectra; assemble data cube; and correct
dispersion. We used the scaled sky subtraction routine for the Jn1 data cubes,
which uses families of atmospheric OH-emission lines between multiple frames
for a cleaner subtraction. For Hn3 data we used our own custom sky subtraction
routine that scales only the nearest three OH lines in proximity to the quasar
H$\alpha$ emission line. This produced better residuals compared to the
pipeline’s scaled sky routine in Hn3. Inspection of individual spaxels in the
scaled sky subtracted data cubes still revealed strong OH-sky line residuals,
typically over 2-3 spectral pixels in the wings of the H$\alpha$ emission
line. These spectral pixels were linearly interpolated using the slope from
the neighboring two pixels around the strong residuals. The telluric spectrum
of the calibration star was extracted over the seeing halo and had its
continuum divided by a 9400K blackbody function with its hydrogen absorption
lines removed. The 1D telluric spectrum was normalized and divided into the
quasar data cubes. Individual data cubes were then shifted to a common
position and combined using a $3\sigma$ clipping algorithm, which is part of
the OSIRIS data reduction pipeline. Finally we applied flux calibration to all
quasar data cube by using the telluric corrected standard star spectrum and
scaling the DN/s/channel to match the expected Jn1 and Hn3 band flux
(erg/s/cm2).

###  3.2 OSIRIS: PSF construction and subtraction

Both the quasar broad line emission (H$\beta$ and H$\alpha$) and quasar
continuum originate from gas on parsec scales from the SMBH, and are therefore
spatially unresolved in our OSIRIS observations. Wavelength channels of the
broad line emission and/or continuum can be used to construct a pristine
quasar image that can then be used for PSF subtraction in the reduced data
cube. In Vayner et al. (2016) we discuss in greater detail our PSF subtraction
routine and its performance on a set of luminous type-1 radio quiet quasars at
z$\sim$2\. In brief, we used broad emission line/continuum channels that
should not overlap with the host galaxy emission with spectral channels offset
by 5,000-10,000 km s-1 from the quasar redshift. We carefully select spectral
channels that do not coincide with OH-emission lines or regions of low
transparency in the near-infrared. PSFs are generated by combining individual
data channels and are scaled to the peak pixel values. This empirical PSF is
then subtracted from the entire data cube while re-scaling to the peak pixel
value of the quasar emission per wavelength channel.

After data reduction, the 100 mas mode in OSIRIS suffers from flux mis-
assignment between adjacent spaxels given its enlarged pupil size in the
instrument. The reductions still conserve the integrated flux of the source,
but neighboring pixels can receive a $\sim$10% mis-assignment of flux. This
effect is seen in bright stars (H $<$ 16 mag) with excellent AO correction,
where flux is mis-assigned from the bright central spaxel to the row above and
below the centroid position of the point source. This effect can be easily
identified by evidence of spaxels with an inaccurate spectral shape. Our PSF
subtraction routine removes a significant portion of flux from the PSF in
these spaxels but they generally have stronger post-PSF subtraction residuals.
We masked the affected spaxles with background flux values calculated by
taking a standard deviation in a 1″$\times$1″sky region. We fit a 2D Gaussian
to the PSF image and measure a full-width half-maximum (FWHM) of 0.127″and
0.113″in Hn3 and Jn1, respectively. After PSF subtraction of the quasar data
cubes, we smooth the Hn3 and Jn1 data sets to a common resolution with a beam
FWHM of 0.2″ to improve the signal-to-noise (SNR) in the diffuse parts of the
host galaxy.

###  3.3 OSIRIS: Kinematics

In this section we investigate the kinematics properties of nebular emission
lines in the host galaxy of 3C 298. We inspect all individual spectra that
overlap between the two observing modes (Jn1 and Hn3), which amounts to
approximately 2,640 spectra. An emission line is identified to be real if the
peak intensity is at least 3$\times$ greater than the noise per wavelength
channel, and the emission line dispersion is larger than the instrumental
resolution (0.206 nm for Hn3 and 0.174 nm for Jn1).

A single Gaussian profile provides a good fit to the 486.1 nm H$\beta$
emission line that is redshifted into Jn1 at an observed wavelength of 1186
nm. The 495.9, 500.7 nm [OIII] lines are redshifted into Jn1 band at an
observed wavelength of 1210 and 1221 nm. The 495.9, 500.7 nm [OIII] lines are
fit simultaneously, each with a single Gaussian profile. The position and
width of the 495.9 nm line are held fixed to the redshift and width of 500.7
nm line at each spaxel. The line ratio between the [OIII] lines are held fixed
at 1:2.98 (Storey & Zeippen, 2000). The 495.9, 500.7 [OIII] lines in several
spaxels in the north-west and south-east regions require two Gaussian profiles
for a good fit. The [NII] 654.9, 658.5 nm, H$\alpha$ 656.3 nm, and [SII] 671.7
673.1 nm are redshifted into the Hn3 filter. Spaxels with detected H$\alpha$
and both [NII] emission lines are fit together with three Gaussian profiles.
The position and width of the [NII] lines are fixed to the H$\alpha$ redshift
and width, with a flux ratio between [NII] 654.9, 658.5 nm of 1:2.95.
Generally a single Gaussian profile fit to H$\alpha$ and each [NII] line
provide a satisfactory fit ($\chi^{2}_{R}\sim 1-2$), with the exception of
several spaxels in the south-east region, where an additional broad H$\alpha$
component is necessary. The H$\alpha$, H$\beta$ and [OIII] broad-line
components have similar velocity dispersions and offsets. The lower SNR of the
[SII] doublet make it challenging to fit a single Gaussian profile to each
emission line, therefore each spaxel where [SII] is detected we fit a single
Gaussian profile to the combined signal. Regions where no [NII] or [SII] lines
are detected have only a single Gaussian fit to H$\alpha$. Limits on [NII] and
[SII] lines are derived by inserting a Gaussian profile with the same width as
H$\alpha$ at the expected location of the emission line based on H$\alpha$’s
redshift, with a peak flux 2$\times$ greater than the standard deviation of
the noise. Similarly to a real detection we integrate the inserted emission
line to obtain a limit.

To construct 2D flux maps we integrate each emission line from $-3\sigma$ to
$+3\sigma$, where $\sigma$ is derived from the line fit. Error on the line
flux is calculated by taking a standard deviation of every 3 spectral channels
and summing in quadrature over the same spectral region where the nebular
emission line is integrated. Velocity maps for each emission line are relative
to the redshift of the quasar’s broad line region, which is calculated by
fitting a single Gaussian profile to the broad H$\beta$ line constructed by
spatially integrating the cube over the seeing halo before PSF subtraction.
The velocity dispersion map has the instrumental PSF subtracted out in
quadrature using the width of OH emission sky lines. Errors on velocity
offsets and dispersions are based on 1$\sigma$ errors associated with the
least squares fit.

In Figure 1 we show the line integrated emission of H$\alpha$, [OIII] and
[SII] in a three colour image composite alongside the [OIII] radial velocity
and dispersion maps of 3C 298. A distinct extended broad velocity emission
region is co-spatial with radio synchrotron emission emanating from extended
jet/lobes. The radio VLA observations are taken from Mantovani et al. (2013)
(Project code: AJ206). We downloaded fully reduced clean map of 3C 298 at
8485.100 MHz 111http://db.ira.inaf.it/aj206-fm/. The centroid of the point
source with the flattest spectral slope is associated with the optical
location of the quasar. We extract the image centered on the quasar and rotate
to a position angle of 103∘ to match our OSIRIS observations.

Figure 1: OSIRIS observations of 3C 298 nebular emission line intensities and
[OIII] kinematic maps. (a) Three colour intensity map of nebular emission
lines: H$\alpha$(red), [OIII](green), and [SII](blue). FWHM of the OSIRIS beam
is shown as a white circle on the bottom left. (b) Radial velocity offset (km
s-1) of the [OIII] line relative to the redshift of the quasar. The white star
shows the location of the subtracted luminous quasar. (c) Velocity dispersion
(km s-1) map of [OIII]emission. The black contours are 8485.100 MHz VLA
observations of radio synchrotron emission from the quasar jet and lobes. The
largest velocity offset and dispersion corresponds to the location of jet and
lobes. This spatial correspondence provides evidence of a quasar driven
outflow in the ionized ISM with an ionized outflow rate of 450-1500 M⊙ yr-1.

We generate integrated spectra for three distinct outflow regions identified
based on their radial velocity ($\pm$400 km/s) and dispersion
(V${}_{\sigma}>$500km s-1), see Figure 1. For the purposes of the figure, the
north-western outflow will be identified as the redshifted outflow or
“Outflow-R”, and the north-eastern outflow will be identified as the
blueshifted outflow or “Outflow-B”, and the third outflow in the south-eastern
direction will be identified as “AGN-Outflow”. We believe AGN-outflow belongs
to a secondary nucleus in the 3C 298 system due to its isolated nature, and
since the ionized emission does not extend from the quasar and does not
coincide with the quasar jet/lobes. The AGN-outflow is in close proximity to
the dynamical center of a rotating disc in the 3C 298 system that belongs to a
second merging galaxy (see section 3.5 for further discussion). Each spectra
are then fit with multiple Gaussian profiles. Outflow-R is best fit with a
combination of two relatively broad (V${}_{\sigma}\sim$500 km/s) Gaussian
profiles in both [OIII] lines, H$\alpha$, and [NII], which we interpret as a
signature of outflowing gas along the line of sight. The 500.7 nm [OIII] line
requires an additional relatively narrow (V${}_{\sigma}\sim$ 80 km/s)
component for a good fit that has no counterpart in H$\alpha$, [NII], or
[SII]. A faint H$\beta$ line is detected, and is fit with a single Gaussian
component that potentially matches the broad components of [OIII] and
H$\alpha$. See the top row of Figure 2 for the integrated spectrum in J and H
band along with the fit. Components A (green curve) and B (red curve) are the
broad lines, while component C (blue curve) is the narrow line found only in
[OIII]. The white contour in the right column shows the region over which the
data cube is spatially integrated. The spectrum of the blueshifted outflow
(Outflow-B) region is best fit with a single broad Gaussian component in
H$\beta$, [OIII], H$\alpha$ and [NII]; second row of Figure 2 shows the
spectra along with the fit. In the redshifted outflow region the lines are
very broad, so the [SII] doublet blends together, making it very hard to fit
the individual lines. The lines are slightly narrower in the blueshifted
outflow region, and each emission line in [OIII] and H$\alpha$ require only a
single Gaussian component. This made it possible to fit the [SII] doublet
using a single Gaussian profile for each emission line.

We construct a high SNR spectrum over the entire AGN-Outflow region. H$\alpha$
and [OIII] are fit with two components: a broad-line blueshifted Gaussian for
the outflow and a narrow component that we interpret as part of the AGN/quasar
narrow-line region. H$\beta$, [NII], and [SII] are fit with a single Guassian
narrow-line component.

Figure 2: OSIRIS near-infrared spectra for distinct photoionized regions in
the host galaxy of 3C 298. J and H band spectra are shown in the left and
middle panels, respectively, with observed wavelengths (nm) and calibrated
flux (Fλ). The three-colour composite image (right) shows the regions over
which the spectra were extracted. Multiple Gaussian functions are fit to each
of the emission lines: H$\beta$, [OIII], H$\alpha$, and [NII] in all the
spectra. The green curves show the combined fit to each spectrum, and each
dotted line represents an individual component of the fit. The redshifted
outflow region is best fit with a double Gaussian component (labeled A and B
in top panel) to each nebular emission line, that suggests conical expansion
of the gas along the line-of-sight. The blueshifted outflow region is best
modeled with a single Gaussian component to each emission line. The presence
of broad, blueshifted emission lines in [OIII] and H$\alpha$ (labeled ‘AGN
Outflow’, third panel from top), indicating outflowing gas, roughly coincident
with the dynamical center of the secondary galaxy in the merger. This outflow
region is not associated with strong star formation, based on line ratio
diagnostics in Figure 3. The star forming region is best fit with a single
narrow Gaussian component to each emission line.

###  3.4 OSIRIS: Nebular Emission line Diagnostics

In this section we investigate potential ionizing sources for distinct regions
of the host galaxy. Line ratio maps are constructed by taking ratios of
integrated flux maps [OIII], H$\alpha$, [NII], and [SII]. The H$\beta$ line is
only detected in a small number of individual spaxels; sensitivity and dust
obscuration prohibits us from detecting this line over similar sized regions
to other detected nebular emission lines. We construct an H$\beta$ map over
the region where H$\alpha$ is detected by assuming case B recombination
($F_{H\beta}=F_{H\alpha}/2.89$).

We create three line ratio maps log([OIII]/H$\beta$), log([NII]/H$\alpha$),
and log([SII]/H$\alpha$). In Figure 3 we plot the line ratios on a standard
BPT diagram, log([OIII]/H$\beta$) vs log([NII]/H$\alpha$). Empirical
(Kauffmann et al., 2003) and theoretical (Kewley et al., 2001) curves
separating photoionization by O-stars versus quasar ionization are shown.
Generally, values that lie above these curves represent photo-ionization by an
AGN, while points below represent photoionization by newly formed O-type
stars, tracing regions of active/recent star formation. Points on the BPT
diagram are colour coded to match the line ratio map of log([OIII]/H$\beta$)
(middle Figure 3). The 1″ central region (red and orange in Figure 3) is
mainly photoionized by the quasar in an extended narrow line region (ENLR), as
shown by very high log([OIII]/H$\beta$)$\gtrsim$ 0.8 values. 658.5[NII] is
detected over the red region in individual spaxels while over the orange
region we place a 2$\sigma$ flux limit. Even within the limits the orange
region fall in the AGN photoionzation portion of the BPT diagram due to very
high log([OIII]/H$\beta$) values. The star formation region (blue) has low
log([OIII]/H$\beta$)$<$0.8 and log([NII]/H$\alpha$)$<$0.5 values,
corresponding to ionization from newly formed stars. We generate a spectrum
over the Star Formation region and easily identify and fit a single Gaussian
to [OIII], H$\alpha$, [NII] and a H$\beta$ line with a SNR of 2 identified
(bottom panel of Figure 2).

Figure 3: Photoionization diagnostics of ionized gas in the 3C 298 system.
(LEFT) The log([OIII]/H$\beta$) vs log([NII]/H$\alpha$) nebular line ratio
diagram of the 3C 298 host galaxy with empirical (Kauffmann et al., 2003) and
theoretical (Kewley et al., 2001) curves that delineate the separation between
star formation and AGN. Nebular line ratios that lie above and to the right of
the curves are considered to be photoionzed by a hard radiation source such as
a quasar/AGN or shocks, and values below the curves are considered to be
ionized by O-stars in HII regions. (MIDDLE) Galaxy map coloured to match the
line ratio diagnostic diagram. Red and orange colours represent regions
photoionization by the quasar and secondary AGN in an extended narrow line
region (ENLR). Regions with upper limits on log([NII]/H$\alpha$) are labelled
orange, while red regions have directly measured 658.4nm [NII]line. The blue
region shows gas whose line ratios are consistent with ionization by young
massive stars. The green region is the redshifted outflow, and the yellow
region is the blueshifted outflow. The redshifted outflow (green) shows a
blend of photoionization from the quasar and radiative shocks due to
interactions of the ISM with large scale outflows. This is further confirmed
with the log([OIII]/H$\beta$) vs. log([SII]/H$\alpha$) diagnostic diagram as
seen in Figure 4. (RIGHT) The log([OIII]/H$\beta$) ratio map illustrating
different photoionization levels across the galaxy. The colours clearly
cluster in distinct regions in the resolved host galaxy. The beam size is
given by the solid white circle. The white star represents the location of the
quasar and the red star and circle represents the location of the dynamical
center of the secondary galaxy, where a potential secondary obscured, AGN
exists.

Star forming regions are spatially offset from the large outflows, and their
kinematics and morphologies agree with a potential tidal feature induced by
the merging galaxies. Outflow regions (yellow and green) correspond to the
highest log([OIII]/H$\beta$) line ratios. These regions are inconsistent with
ionization by young stars, and are photoionized by quasars and shocks. Gas in
outflow regions is moving at sufficiently high velocity so the Mach number of
the wind is high and strong radiative shocks are expected. Using shock models
from (Allen et al., 2008) we find that a large portion of observed line ratios
agree with shock models for gas with electron density between
$10^{2}-10^{3}$cm-3 and shock velocities of 1000 km/s. In Figure 4 we plot the
log([OIII]/H$\beta$) vs log([SII]/H$\alpha$) values over regions where [SII]
was detected in individual spaxels. We overlay shock models on this BPT
diagram, a large fraction of the nebular line ratios in the redshifted outflow
region (green) and blueshifted outflow region (yellow) are consistent with
these models. Dark red/blue lines in the model represent higher velocity gas
and stronger magnetic parameter (see Allen et al. (2008) for further details).
Furthermore the region photoionized by AGN shows a spatial profile that drops
off as $\rm 1/R^{2}$ in nebular emission, while in the region where we see
powerful outflows the profile is more complex suggesting multiple ionizing
sources. Both regions show similar extinction values as we discuss below.

Figure 4: Photoionzation diagnostics of ionized gas in the 3C 298 system.
(LEFT) We show diagram of log([OIII]/H$\beta$) vs log([SII]/H$\alpha$) with
empirical dash curve(Kauffmann et al., 2003) that separates photoionization of
star forming regions and AGN. The theoretical position of shocked ionization
is overlaid on the BPT diagram (Allen et al., 2008). Dark red/blue lines in
the model represent higher velocity gas and stronger magnetic parameter.
(RIGHT) Coloured values match the spatial regions of the host galaxy, where
the green and yellow points are from the redshifted and blueshifted outflow
regions. Ionization in these outflow regions are due to shocks moving at
speeds of $\sim$1000km s-1. The red region is consistent with values primarily
ionized by AGN.

In order to investigate how dust can alter our photoioniziation measurements,
we construct a high SNR spectrum over the ENLR (red in Figure 3) to estimate
the amount of dust obscuration from the H$\alpha$/H$\beta$ ratio. Using the
Calzetti et al. (2000) law, we find an average ${\rm A_{v}}=0.07$ over the
ENLR (the red region in Figure-3), based on an H$\alpha$/H$\beta$ ratio of
2.9. This would on average increase the ratio of log([OIII]/H$\beta$) only by
a factor of 1.05 for the ENLR; this is not large enough to alter our results.
We find that in portions of the the ENLR and redshifted outflow region the Av
value is consistent with zero extinction in the ionized gas. Similar results
are found over the outflow regions suggesting negligible extinction in the
ionized gas. Over the star forming region (blue region in Figure-3) we measure
an ${\rm A_{v}}$ value of 1.2 based on H$\alpha$/H$\beta$ ratio of 4.0. The
observed non-detection of H$\beta$ in individual spaxels is consistent with
the derived integrated extinction value and given the expected H$\beta$ SNR
relative to [OIII] and H$\alpha$ emission lines.

###  3.5 OSIRIS: Velocity field modeling

To the south-east of the quasar there is a kinematic feature resembling a
rotating galactic disc that is offset by $\sim 200$ km s-1 from the quasar
BLR, with a projected rotational velocity of $\pm$170 km s-1. In this section
we outline the modeling done on the radial velocity map of [OIII] emission to
confirm the rotating disc nature of this feature. We isolate this feature for
the disc fitting, using a box size of 0.7″$\times$1.7″centered on the gradient
feature in the [OIII] radial velocity map. The boxed region is selected to not
include any strong broad emission from the conical outflow. The [OIII]
velocity field is modelled by fitting a two dimensional arc-tangent disc model
given by

$V(r)=\frac{2}{\pi}V_{max}\arctan\Big{(}\frac{r}{r_{dyn}}\Big{)},$ (1)

where V(r) is rotation velocity at radius r from the dynamical center,
$V_{max}$ is plateau velocity, and $r_{dyn}$ is the radius at which the arc-
tangent function has a turn over to a decreasing slope. The measured line-of-
sight velocity from our observations relates to V(r) as

$V=V_{0}+\sin i\cos\theta V(r),$ (2)

where

$\cos\theta=\frac{(\sin\phi(x_{0}-x))+(\cos\phi(y_{0}-y))}{r}.$ (3)

Radial distance from the dynamical center to each spaxel is given by

$r=\sqrt{(x-x_{0})^{2}+\Big{(}\frac{y-y_{0}}{\cos i}\Big{)}^{2}},$ (4)

where $x_{0},y_{0}$ is spaxel location of the dynamical center, $V_{0}$ is
velocity offset at the dynamical center relative to the redshift of the quasar
broad line region, $\phi$ is position angle in spaxel space, and $i$ is the
inclination of the disc.

We fit the seven parameter velocity field model to a selected region of our
observed [OIII] velocity map using a non-linear least squares routine. The
selected box region tries to exclude broad emission from the extended quasar
outflow and a tidal feature that seems to show its own distinct kinematic
structure. Our best fit has a $\chi_{R}^{2}=$0.7 with the following values:
$x_{0},y_{0}=$ -0.49″, +0.94″ relative to the centroid of the quasar,
$V_{max}$= 209$\pm 33$ km s-1, $r_{dyn}=$ 2.2 $\pm 0.98$ kpc, $i=72\pm
4^{\circ}$, $\phi=-109\pm 6^{\circ}$, and $V_{0}=170\pm 9$ km s-1 relative to
the redshift of the quasar broad line region. Figure 5 shows the region
selected for disc fitting with the modeled 2D velocity profile and residuals
between the model and observed velocities. The disc is offset from the quasar
by 1.06 ″ or $\sim$ 9 kpc, which is evidence of a merging disc system in 3C
298. We obtain a dynamical mass of $1.3\pm 0.8\times 10^{10}$M⊙ within a
radius of $r_{dyn}=2.2$ kpc. The dynamical center of this disc is in the
vicinity of the isolated AGN outflow identified in Figure 2. With currently
available archival Chandra ACIS observations we are unable to explore the
X-ray properties of this secondary AGN candidate. Unfortunately there is
strong asymmetry in the Chandra PSF along this position angle from the quasar.
Future Chandra observations at a specific spacecraft roll angle will allow us
to search for X-ray emission from this secondary AGN and explore the potential
dual AGN nature of this system.

Figure 5: Observed and modeled galactic rotation disc, detected in the nebular
[OIII] line in the 3C 298 system. (LEFT) The entire [OIII] radial velocity map
with overlaid region used for the modeled disc fit. (MIDDLE LEFT) Observed
[OIII] velocities with the spider diagram overlaid from the disc model.
(MIDDLE RIGHT) The best fit 2D disc model. (RIGHT) The residual map shows the
observed velocities subtracted by the disc model fit. The dynamical center is
at 0,0.

###  3.6 ALMA: Data reduction

Data reduction was performed using CASA (Common Astronomy Software
Applications (McMullin et al., 2007)) version 4.4 and 4.7. At the observed
frequencies, synchrotron emission from the quasar dominates over molecular CO
or dust emission, and has sufficient SNR to perform self calibrations directly
on the science source. We used the CASA CLEAN function to establish a model
for the synchrotron continuum through several interactive runs with clean
masks centered on high SNR features. Cleaning is performed with Briggs
weighting using a robust value of 0.5 with a pixel scale of 0.05″. We used the
gaincal function to perform phase corrections. The self-calibrated data was
then cleaned again with further phase corrections until we did not see a
significant improvement in the SNR on the continuum. The final root mean
square (rms) improved by a factor of 6-8 in the continuum images. We perform
continuum subtraction in UV-space by fitting a first order polynomial to
channels free of line emission from the host galaxy, and subtract this fit
from the rest of the channels.

Data cubes were imaged using clean with a plate scale of 0.05″ per pixel,
spectral channel size of 34 km s-1 and natural weighting to improve SNR in
diffuse structure of the host galaxy at cost of angular resolution. For cycle
3 data, clean masks were placed on CO emission with SNR$>$5 with the same mask
applied to all channels. The resulting beam sizes and rms values are reported
in Table 1.

We find the cycle 2 band 4 data cube is a factor of 2 noisier due to poorer
weather conditions at the time of observations. Faint emission is detected
with a peak SNR of 3.6$\sigma$ for CO (J=3-2) emission over a number of
spaxels in the east/north-east direction from the quasar. Applying UV tapering
to a resolution of 0.98″$\times$0.8″with Briggs weighting (robust = 0.5)
improves the SNR to 5 however the line is not spatially resolved. Therefore
for the analysis of CO (J=3-2) we defer to cycle 3 data taken under superior
weather conditions.

We align the ALMA and OSIRIS data cubes by matching the position of the
optical quasar emission to the unresolved quasar synchrotron emission centroid
in the continuum map. The centroid of the quasar matches the location of the
unresolved point source with the flattest spectra seen using high resolution
cm observation of 3C 298 with MERLIN (component B1/B2 in (Fanti et al.,
2002)). This location is typically associated with the quasar core. Finally,
we rotate the ALMA data cube to a position angle of 103∘ to match the OSIRIS
observations.

###  3.7 ALMA: Analysis

In this section we describe the analysis of resolved CO (3-2) and (5-4) 3D
spectroscopy. Initial inspection revealed high SNR $\gtrsim 5$ detection of CO
(J=3-2) and (J=5-4) emission. We extracted spectra over the beam size centered
on the detected regions. We then collapsed the data cube over spectral
channels where the CO features are detected, and constructed SNR maps by
dividing the integrated emission by the standard deviation computed in an
empty sky region. Spaxels that showed an emission line with a SNR $\geq$ 3 are
fit with a Gaussian profile. We constructed a flux map by integrating over the
line ($-3\sigma$ to $+3\sigma$). We created a velocity map by computing the
Doppler shift of the emission line centroid relative to the redshift (z=1.439)
of the broad line region (calculated from H$\beta$), and generated a velocity
dispersion map from the Gaussian fit. Figure 6 shows the CO emission, radial
velocity, and dispersion maps.

Figure 6: ALMA band 4 and 6 CO (J=3-2) and (J=5-4) observations of 3C 298.
(LEFT) Integrated emission shown in red for CO (3-2) and teal for CO (5-4)
with white contours representing the lowest surface brightness of the
integrated H$\alpha$ map. (MIDDLE) Radial velocity map (km s-1) for CO (3-2)
data relative to the redshift of the quasar. (RIGHT) Radial velocity
dispersion map (km s-1) of CO (3-2) emission. We find that majority of the
molecular gas resides in a disc centered on the quasar and in a molecular
clump 16 kpc away from the quasar where active star formation is present as
indicated by the log([OIII]/H$\beta$) and log([NII]/H$\alpha$) line ratios
(blue region in Figure 3). The synthesized beam is shown in the lower left
corner. White star marks the location of the quasar

####  3.7.1 Molecular gas velocity field modeling

In this section we outline modeling performed on the CO (3-2) radial velocity
map to derive a dynamical mass for the inner $\sim$2 kpc of the host galaxy.
We find the majority of the CO emission to be concentrated at the spatial
location of the quasar and with a secondary peak offset by 16 kpc spatially
coincident with the recent star formation from OSIRIS BPT analysis (see Figure
3 and section 3.4). CO (3-2) emission concentrated on the quasar shows a
distinct velocity gradient resembling a rotating disc, with an extent of about
0.8″ with a velocity difference of $\pm$150 km s-1. Similar to section 3.5 we
model the molecular disc with a hyperbolic arctangent function and derive the
following properties about the disc: $\chi_{R}^{2}=$0.6: $x_{0},y_{0}=$ 0.05″,
0.0″ relative to the centroid of the quasar, $V_{max}$= 392$\pm 65$ km s-1,
$r_{dyn}=$ 2.1 $\pm 0.9$ kpc, $i=54.37\pm 6.4^{\circ}$, $\phi=5.3\pm
1.28^{\circ}$, and $V_{0}=-13.0\pm 3.15$km s-1. Fit of the disc along with the
residuals are shown in Figure 7. We derive a dynamical mass 1.7$\pm 0.9\times
10^{10}$M⊙within $r_{dyn}=$2.1 kpc using the disc inclination derived from the
velocity modeling.

Figure 7: (TOP LEFT) Velocity field modeling of the molecular disc. CO (3-2)
radial velocity map with a box highlighting the location of the molecular
disc. (MIDDLE LEFT) Boxed region with spider diagram of the disc model.
(MIDDLE RIGHT) The best fit rotating disc model. (RIGHT) The residuals between
the observed velocity and model fit. The quasar is located at 0,0. The fitting
was done on data at the ALMA observation position angle of 0∘ to avoid any
pixel interpolation that may cause a difference in the fitting results.
(BOTTOM) Position velocity (PV) diagram along the major axis of the ALMA disc,
which illustrates the the velocity field and plateau velocity on kiloparsec
scale. Broad blue shifted emission that is not associated with the disc’s
rotation is observed in the PV diagram from -400 to 200 km s-1as the large
molecular outflow.

Alternatively, we collapsed the data cube along the spectral direction from
-150 km s-1 to +150 km s-1 to produce a CO (3-2) image of the molecular disk.
Using a 2D Gaussian we obtain a major axis value of 0.374$\pm 0.05$″and a
minor axis of 0.155$\pm$0.098″ corrected for the beam size. Assuming the
molecular disc can be approximated by an oblate spheroid we derive the
inclination angle using the following formula (Holmberg, 1946):

$\rm i=cos^{-1}\sqrt{\frac{(b/a)^{2}-q_{0}^{2}}{1-q_{0}^{2}}},$ (5)

where a and b are the major and minor axes, and $\rm q_{0}$ is the axial ratio
for an edge on disc taken to be 0.13. We derive a dynamical mass of $1.0\pm
0.5\times 10^{10}$ M⊙ using a major axis radius of 1.6$\pm 0.215$ kpc and an
inclination angle of $66.6\pm 17.8^{\circ}$. The dynamical masses and disc
inclination angles obtained with these two methods agree within the error.
With two distinct galactic discs (see section 3.5) in the 3C 298 system we are
finding evidence for an intermediate-late stage merger.

Shen et al. (2011) determined a single epoch black hole mass for 3C 298 using
three calibration methods: $10^{9.57\pm 0.03}$ M⊙ using the MgII-black hole
mass relationship calibrated from their study; $10^{9.37\pm 0.03}$ M⊙ using
the Vestergaard & Osmer (2009) calibration; and $10^{9.56\pm 0.01}$ M⊙ using
McLure & Dunlop (2004) relation. The systematic differences between black hole
mass measurements are typically due to differing quasar samples, and
properties of the emission lines (e.g., H$\beta$) used for the SMBH mass
calculation.

With both the derived dynamical and black hole mass we can compare the nuclear
region of 3C 298 to the local black hole M$\rm{}_{bulge}-M_{BH}$ relationship.
In Figure 8 we plot the 3C 298 black hole and bulge dynamical mass relative to
the local scaling relation from Häring & Rix (2004); Sani et al. (2011);
McConnell & Ma (2013). Compared to all three relationships the 3C 298 bulge
dynamical mass is either $\sim$2-2.5 orders of magnitude lower than what is
expected or the black hole is $\sim$ 2 orders of magnitude higher than what is
expected for its bulge mass. If one assumes the 3C 298 bulge is more extended
than what is measured by ALMA, then we can use the tidal feature at 21.5 kpc
as an estimate for the total enclosed mass. To do this, we integrate all
spaxels with a detected CO (3-2) line and remove the outflow contribution by
simultaneously fitting a broad and a narrow Gaussian component to the outflow
region. We measure a maximum line width of 369.3 km s-1 at 90$\%$ intensity,
and find the maximum circular velocity of 184.6/$\sin(i)$ km s-1at 21.5 kpc
from the quasar. Using this maximum circular velocity, we obtain a total
enclosed mass at this radius of $\sim 2.7\times 10^{11}$ M⊙ assuming the
smallest measured inclination angle from the molecular disc. This value should
be considered as a maximum limit for the total enclosed mass of the 3C 298
system. This enclosed dynamical mass at 21.5 kpc from the quasar still places
3C 298 an order of magnitude above from the local scaling relation. Also, the
radius used for this calculation is significantly larger than the typical
bulge radius at this redshift (Bruce et al., 2014; Sachdeva et al., 2017), and
there is no guarantee that the entire enclosed stellar mass will end up in the
newly created bulge once the merger is finished. This implies a delay in
growth of the galactic bulge for the 3C 298 host galaxy with respect to its
SMBH. Averaging SMBH masses and dynamical masses determined for 3C 298 we
obtain the following values: $\rm M_{dyn,bulge}=1.35\pm 0.5\times 10^{10}$,
$\rm M_{SMBH}=3.23\pm 1.1\times 10^{9}$. Errors are added in quadrature with
the SMBH mass standard deviation included to address the systematic
uncertainty associated with using various calibration methods.

Figure 8: Local SMBH vs galactic bulge dynamical mass relationship compared to
3C 298 measured values. The black star represents the average dynamical mass
derived from the intensity and kinematic molecular gas disc modeling and the
average black hole mass derived with McLure & Dunlop (2004); Vestergaard &
Osmer (2009); Shen et al. (2011) relationships. Errors are added in quadrature
from the various methods used to derive the dynamical mass of the disc and the
black hole mass. Local scaling laws from various studies (Häring & Rix, 2004;
Sani et al., 2011; McConnell & Ma, 2013) are shown in solid lines with their
respective 1$\sigma$ errors shown with dotted curves. The observed black hole
mass and dynamical mass of the bulge of 3C 298 resides $\sim$2-2.5 orders of
magnitude away from the local scaling relation. Points from literature (Wang
et al., 2013; Willott et al., 2015; Venemans et al., 2016) for z$>5.7$ quasars
are also included. There is line of evidence that some of these high redshifts
systems also reside off the local scaling laws.

####  3.7.2 Molecular gas mass

In this section we derive the molecular gas mass from spatially integrated CO
(3-2) and (5-4) emission presented in Table 2.

Table 2: Measured molecular line intensities Region | $\rm I_{CO(3-2)}$ | $\rm I_{CO(5-4)}$
---|---|---
Molecular disc | 0.63$\pm$0.035 Jy km s-1 | 1.26$\pm$0.063 Jy km s-1
Tidal FeatureaaMolecular gas associated with star forming region labeled in blue in Figure 3 | 0.13$\pm$0.013 Jy km s-1 | 0.1$\pm$0.025 Jy km s-1

In order to measure the molecular gas in the 3C 298 system we convert the CO
(3-2) flux into $L^{{}^{\prime}}_{CO(3-2)}$ using the following equation from
Carilli & Walter (2013),

$\rm L^{{}^{\prime}}_{CO(3-2)}=3.25\times 10^{7}S_{CO(3-2)}\Delta
v\frac{D^{2}_{L}}{(1+z)^{3}\nu_{obs}^{2}}K~{}km~{}s^{-1}~{}pc^{2}.$ (6)

We convert to CO (1-0) luminosity (L${}^{{}^{\prime}}_{CO(1-0)}$) using a
ratio $L^{{}^{\prime}}_{\rm CO(3-2)}/L^{{}^{\prime}}_{\rm CO(1-0)}$ of 0.97
(Carilli & Walter, 2013). Using the typical $\alpha_{\rm CO}$ value from
nuclear star bursts and quasars (0.8 K km s-1$\rm pc^{2}$)-1), we derive a
total molecular gas mass equal to $8.75\pm 0.4\times 10^{9}$M⊙. The total
molecular gas includes all regions with a fitted CO (3-2) line in Figure 6.
The molecular gas disc contains 6.6$\pm 0.36\times 10^{9}$M⊙, while the active
star formation region that resides 16 kpc away contains 1.44$\pm 0.14\times
10^{9}$M⊙. We measure a 2$\sigma$ molecular gas limit of $\rm 1\times
10^{9}$M⊙$\rm(\frac{\alpha_{CO}}{0.8})(\frac{V_{FWHM}}{200kms^{-1}})$ per
beam. This corresponds to a molecular gas surface density of 104 M⊙$\rm
pc^{-2}(\frac{\alpha_{CO}}{0.8})(\frac{V_{FWHM}}{200kms^{-1}})$. These
estimates are valid for the inner few arcseconds around the phase center
(quasar).

CO (3-2) and (5-4) emission in some spaxels shows relatively broad
($V_{\sigma}>270$km s-1) emission, greater than the escape velocity
$\sqrt{2}V_{rotational}\sim$270 km s-1 at the observed edge of the rotating
disc. In the position-velocity diagram (Figure 7) broad blue-shifted emission
is seen with velocities ranging from -400 to 200 km s-1 that spatially resides
away from the ordered $\pm$150km s-1 rotation profile. Integrating over these
spaxels the CO (3-2) and (5-4) emission profiles resemble both an outflow with
broad emission, and narrow emission that is likely emanating from the
molecular disc. We fit a double Gaussian component to the CO (3-2) line and a
single Gaussian to the CO (5-4) data. We measure FWHM of 624$\pm$49 km s-1 for
the broad line emission in CO (3-2) and 687$\pm$18 km s-1in CO (5-4). The
broad emission line represents either an extended outflow originating from the
nuclear region of 3C 298 quasar or from the molecular disc itself. Figure 9
shows spectra of the CO (3-2) and (5-4) emission regions with their
corresponding Gaussian fits. The broad emission in both lines is predominantly
found on the blue shifted side of the rotating disc. The total molecular gas
in the outflow is 3.3$\pm 0.1\times 10^{9}$ M⊙. In section 4 we measure the
molecular gas outflow rate, kinetic energy, and momentum to understand its
impact on the galaxy.

Figure 9: Spectra of molecular CO (3-2) and (5-4) emission in distinct regions
of the host galaxy. Left and middle columns show CO (3-2) and (5-4) emission
spectra respectively, while the right column showcases a three colour
composite from nebular emission lines [OIII], H$\alpha$, [SII] with an overlay
of CO (3-2) emission in orange. White contours represent the region over which
the cubes were spatially integrated to construct the spectra. (TOP) Spectrum
constructed by integrating over region with broad ($\rm V_{\sigma}>270$km s-1)
emission implying a molecular outflow. Both lines are fit with a broad
Gaussian profile, CO (3-2) requires a second narrow component that is likely
emission from the disc. (MIDDLE) Spectrum constructed over region with narrow
emission in the molecular disc, both spectra are well fit with a single
Gaussian component. (BOTTOM) Integrated spectrum over the molecular reservoir
in the star forming region identified in Figure 3. Both CO (3-2) and (5-4)
spectra are fit with a narrow component.

###  3.8 HST WFC3: PSF Subtraction

We obtain archival Hubble Space Telescope (HST) observations of 3C 298 to
quantify properties of the stellar populations of the host galaxy (GO13023,
P.I. Chiaberge). Detailed description of the observations are available in
(Hilbert et al., 2016). In summary, observations were taken in the F606W
($\lambda_{p}$=588.7 nm, width = 218.2 nm) and F140W ($\lambda_{p}$=1392.3 nm,
width=384.0 nm) filters which cover the rest frame wavelength range of 196.6
nm - 286.1 nm and 492.1-649.6 nm, respectively. These wavelength ranges
bracket the 4000Å break feature in galaxy spectra. Two observations were taken
in each filter for a total exposure time of 1100.0s (F606W) and 498.46s
(F140W).

We utilize the nearby star SDSS J141908.18+062834.7 to construct a PSF for the
F606W filter. The PSF star and quasar have a similar magnitude in the F606W
filter with a similar g-r colour as measured in SDSS. Both the PSF star and
quasar are saturated, so they share similar bleeding and diffraction patterns
on the detector. In the F140W filter the quasar is unsaturated and is about
0.8 magnitudes brighter, so we combine two unsaturated stars in the field to
produce a final PSF with matching SNR in the diffraction spikes structure. We
extract a 12″$\times$12″ box centered on the quasar and the PSF, and scale the
flux of the PSF image to match the peak of the quasar emission and then
subtract the two images. We also tried to match only the flux in the
diffraction spikes that do not overlap with the structure in the host galaxy,
and obtained a similar scaling factor. In both filters the inner 1″ is
dominated by noise from the PSF subtraction, the diffraction spikes at
position angles of 0∘, 180∘, 225∘ and along the bleeding pattern in the F606W
filter that extends about 0.5” along PA 0∘ from the quasar. However, the
majority of the host galaxy lies between position angles of 45∘ and 170∘ where
the structure is least affected by residual noise. The quoted residual
structure are for an image at a PA of 103∘ matching the observations of OSIRIS
and ALMA.

We convert electron counts at each pixel into flux density (Jy) using the
’PHOTFNU’ header value. We resize the pixels to 100 milliarcsecond plate scale
to match OSIRIS and ALMA data by using the flux conserving IDL frebin routine.
We convert the maps into AB magnitude/arcsec2 and construct a colour map of
the host galaxy. Reliable colours are extracted down to a surface brightness
limit of 23.5 AB mag/arcsecond2 for the majority of the host galaxy, with the
exception of the redshifted outflow region that falls in the area dominated by
residual noise from PSF subtraction.

Figure 10 presents the WFC3 F606W (left) and F140W (middle) after PSF
subtraction in 0.1″/pixel scale. The right panel shows the resolved host
galaxy colours (F606W-F140W). Overlaying H$\alpha$ contours on the colour map
shows that the star forming regions identified in OSIRIS (blue region in
Figure 3) nicely aligns to regions with bluer colours. Additionally we overlay
the ALMA CO (3-2) observation. The molecular clump offset 16 kpc from the
quasar matches with bluer regions where clumpy structure is seen in the F606W
observations, yielding evidence for young stellar populations over these
regions as would be expected from on-going star formation.

Figure 10: HST WFC3 Rest-frame near-UV (F606W) and approximately rest frame V
band (F140W) images of the stellar light in the host galaxy of 3C 298. The
images have had the bright unresolved quasar emission subtracted from them.
(LEFT) Rest frame near-UV image representing light from young massive stars in
the 3C 298 system. Orange contours represent the CO 3-2 ALMA observations of
the molecular gas. The UV morphology appears clumpy as in H$\alpha$,
indicating regions heated by young stars. (MIDDLE) Rest frame V band image
which traces light from a combination of young and older stellar populations.
The units are in AB magnitude/arcsec2. (RIGHT) Colours (F606W-F140W) of stars
in the host galaxy of 3C 298 representing the ages of the stellar populations.
White contours represent integrated H$\alpha$ luminosity tracing the ionized
gas; note the similarity between the morphology of the ionized emission and
the stellar light. Bluer regions contain younger stars, and are typically
found where clumpy structure exists in H$\alpha$, CO and UV light; these
regions are sights of active star formation. Red star represents the location
of the dynamical center of the second merging galaxy in the system.

###  3.9 HST WFC3: Stellar population

Two available filters for the 3C 298 system are ideally placed to bracket the
break feature at rest-frame wavelength of 4000Å found in galaxy spectra. Thus
we can easily identify young ($<$100 Myr) stellar populations without any
ambiguity, as we attribute blue colours (F606W-F140W $<$1.5) in these filters
to stellar populations dominated by young O and B stars. Redder colours in
these filters can come from older stellar populations (100 Myr - 1 Gyr) or
from young dusty star forming regions, and thus we are unable to say much
about older stellar populations without additional filters.

HST colours provide strong constraints on the resolved star formation and
stellar population history across the 3C 298 system. We approximate the HST
colour map with the flexible stellar population synthesis (FSPS) code (Conroy
et al., 2009; Conroy & Gunn, 2010), using a five parameter star formation
history model. We start the FSPS code with an exponential star formation
history that is followed by a burst of star formation 2 Gyr later, using a
solar metallicity and Salpeter IMF. Using the FSPS code, we find that varying
the star formation history and e-folding time scale $\tau$ from 0.1 to 102
prior to the starburst does not significantly affect the age of the stellar
population post starburst.

The average F606W-F140W colour over the blueshifted outflow region is best
explained with a stellar population that has an age of 25 Myr after the burst.
According to ionized gas emission, dust does not affect the age estimated in
this region since the H$\alpha$ and H$\beta$ ratio suggests a low
E(B-V)$\sim$0 value. However ALMA observations reveal that part of the
molecular disc centered on the quasar has extened emission into the
blueshifted outflow region suggesting that a part of the region can have
higher dust extinction. The age of the outflow region and the modelled rest
frame U-V colour imply that the stellar population resides in the transition
zone between the red sequence and blue cloud in the U-V vs MV colour diagram
(Hopkins et al., 2008; Sánchez et al., 2004; Bell et al., 2004). Furthermore
u-r modelled colours at this age suggest that the region lies where post
starburst galaxies reside in the u-r vs Mstellar diagram (Wong et al., 2012).
The extracted 3C 298 model spectra shows strong Balmer absorption lines with a
strong 4000Å break, characteristic of a post-starburst galaxy. Stellar colours
over the blueshifted outflow region are consistent with a strong episode of
star formation that was abruptly halted.

In the region where star formation is identified in Figure 3 based on BPT
diagnostics and in the molecular gas clump found in CO, using the same initial
conditions in the FSPS code with the outflow region, we find a stellar
population with an age of 20 Myr after a burst of star formation. Without any
dust correction this age should be taken as an upper limit. Ahead of the
jet/blueshifted outflow we find an even younger stellar population. From the
H$\alpha$ emission we can place a limit of 0.3 M⊙ yr-1 kpc-2 across this
region. ALMA observation of the CO (3-2) transition yields a limit of 1$\times
10^{9}$M⊙ on the molecular gas. This suggests that the current star formation
rate is relatively low. However the blue colours indicate recent star
formation activity. The stellar populations in this region would then be
associated with a young age of 7 Myr after the burst. It is likely that the
star formation event was very recent and short (6-10 Myr) due to lack of
H$\alpha$ emission that would otherwise be present if star formation persisted
for a time longer than 6 Myr.

Ages quoted in this analysis could be altered by additional quasar emission
from light scattered off dust grains or electrons in the ISM making the
colours systemically bluer. However polarimetric observations of 3C 298 reveal
that the source is not heavily polarized, with an optical polarization of only
0.77$\pm$0.39$\%$ (Stockman et al., 1984). Given that the bluest regions also
show star formation from other indicators (e.g, H$\alpha$ and CO (3-2)
emission), this implies that the majority of UV emission comes from young
massive stars and not from scattered quasar light. The young stellar
population observed $>$16 kpc beyond the blueshifted outflow is even further
away than the region photoionized by the quasar, indicating that ionizing
radiation from the quasar does not reach this region.

##  4 Dynamics and energetics of outflow regions

In this section we explore the dynamics and energetics of the ionized and
molecular outflows identified in sections 3.3, 3.4, and 3.7. We explore the
energy budget from a broad absorption line (BAL) wind and from the quasar jets
to investigate the origin of the galactic scale winds.

###  4.1 Outflow rates

The redshifted and blueshifted outflow regions resemble a cone-like structure.
For a conical outflow with constant density ($\overline{\rho}$) we use the
outflow rate equation from (Cano-Díaz et al., 2012),

$\dot{M}=vR^{2}\Omega\overline{\rho},$ (7)

where $v$ is the velocity of the material in the outflow assumed to be moving
at a constant rate over the cone, $R$ is the radial extent of the cone and
$\Omega$ is the opening angle of the cone. For
$\overline{\rho}=M/V=\frac{3M}{R^{3}\Omega}$ the outflow rate equation
simplifies to

$\dot{M}=3\frac{Mv}{R}.$ (8)

Assuming individual ionizing clouds in the outflow have the same density, we
can derive an ionized gas mass from line-integrated H$\alpha$ luminosity and
average electron density over the outflow using (Osterbrock & Ferland, 2006),

$\rm M_{\rm gas~{}ionized}=0.98\times
10^{9}\bigg{(}\frac{L_{H\alpha}}{10^{43}~{}ergs^{-1}}\bigg{)}\bigg{(}\frac{n_{e}}{100~{}cm^{-3}}\bigg{)}^{-1}.$
(9)

The electron density is derived from the line ratio of the [SII] lines in the
blueshifted outflow region through using a Gaussian fit to each component of
the doublet. We find a ratio of ([SII] 6717/[SII]6731=1.14), which yields an
electron density of 272 cm-3 using the getTempDen code part of PyNeb
(Luridiana et al., 2015) package. We calculate the ionized gas mass from the
[OIII] line using methodology presented in (Cano-Díaz et al., 2012). This
method requires knowledge of the ionized gas-phase metallicity at the site of
the outflow region. We assume a metallicity value set to solar for a
conservative estimate (i.e., for less than solar the gas mass increases). For
the outflow velocity we use the v10 parameter, which is the velocity value
where 10$\%$ of the line is integrated. This value is calculated from the
model fits to the spatially integrated [OIII] and H$\alpha$ lines for each
outflow region. The wings of the emission lines most likely give the true
average velocity of the outflow, as the lower velocities seen in the line
profiles are probably due to projection effects of the conical structure
(Cano-Díaz et al., 2012; Greene et al., 2012). Measured properties of the the
outflow regions are presented in Table 3.

For the redshited and blueshifted outflow regions we obtain a combined outflow
rate of 467 M⊙ yr-1 and 1515 M⊙ yr-1 for [OIII] and H$\alpha$, respectively,
while for the AGN outflow region we obtain an outflow rate of 9 M⊙ yr-1 and
115 M⊙ yr-1 for [OIII] and H$\alpha$. The H$\alpha$ outflow rate is likely a
better representation of the ionized outflow rate, since H$\alpha$ is capable
of probing denser regions where [OIII] would be collisionally de-excited. The
observed H$\alpha$ outflow rate is similar to what is observed in other quasar
surveys (Carniani et al., 2015), where they measure a larger outflow rate in
H$\alpha$ compared to [OIII]. The total kinetic energy and luminosity of the
ionized outflow are 3.5$\times 10^{58}$ erg and 1.2$\times 10^{45}$ erg s-1.
The kinetic luminosity is consistent with the value usually invoked in
theoretical models (Hopkins & Elvis, 2010) as necessary to affect star forming
properties in the host galaxy. Over the outflow regions we measure a 2$\sigma$
star formation rate upper limit of 0.3 M⊙ yr-1 kpc-2, by using a Gaussian
profile with 2$\sigma$ peak flux and FWHM of 200 km s-1, with the multi-
Gaussian fit of the outflowing gas subtracted. The properties of the multiple
outflow components are summarized in Table 3

Similarly using equation 8 we compute the molecular outflow rate. As found in
section 3.7 the extent of the broad molecular emission from CO (3-2) and (5-4)
lines is approximately 1.6kpc, the total molecular gas mass in the outflow
region is 3.3$\times 10^{9}$M⊙ with an outflow velocity of 400km s-1as
measured by $V_{10}$ parameter. This yields a total molecular outflow rate of
2300M⊙ yr-1. The kinetic energy and luminosity of the molecular outflow are
5.1$\times 10^{57}$ erg and 1$\times 10^{44}$ erg/s.

Table 3: 3C 298 Ionized Outflow Properties Region | LHα | L[OIII] | MHα | M[OIII] | $v$ | $R$ | $\dot{\rm M_{H\alpha}}$ | $\dot{\rm M_{[OIII]}}$
---|---|---|---|---|---|---|---|---
|  $\times 10^{44}$ erg s-1 |  $\times 10^{44}$ erg s-1 |  $\times 10^{8}$M⊙ |  $\times 10^{8}$M⊙ | km s-1 | kpc | M⊙ yr-1 | M⊙ yr-1
Outflow-R | 0.29 | 1.8 | 10 | 3.5 | 1703 | 4.7 | 1110 | 390
Outflow-B | 0.09 | 0.3 | 3.2 | 0.6 | 1403 | 3.4 | 405 | 77
Outflow-AGN | 0.03 | 0.04 | 0.8 | 0.064 | 1400 | 3 | 115 | 9

###  4.2 Virial parameters & gas pressure

Using the virial parameter, a ratio of the free fall time scale to the
dynamical time scale we can investigate whether the gas is gravitationally
bound or unbound in the outflow regions and molecular disc. A value of unity
or below would suggest that the gas is bound and is able to collapse to form
stars. A value much greater than one would suggest that the gas is unbound and
therefore at present time should not be collapsing to form stars. Over the
outflow region we measure a virial parameter

$\alpha_{\rm vir}=5{\sigma^{2}R\over GM}\approx 164\left({\sigma\over
500\,{\rm km\,s}^{-1}}\right)^{2},$ (10)

using an average velocity dispersion of $\sigma=500\,{\rm km\,s}^{-1}$ seen in
the ionized outflow, a radius of $R=3$ kpc, and the ionized gas mass
(1.32$\times 10^{9}$ M⊙). Using the molecular gas mass of 6.6$\times 10^{9}$
M⊙ an average velocity dispersion of 270 km s-1 seen in the molecular outflow
and a radius of 1.6 kpc yields $\alpha_{\rm vir}$ of 20.5. Both of these
virial parameter estimates suggest that at the present time, the physical
conditions in the ionized and molecular outflow regions and in the molecular
disc are stable against gravitational collapse, hindering star formation. In
contrast, the molecular gas clump in the star forming region observed in CO
(3-2) yields a virial parameter value of $\alpha_{\rm vir}\approx 0.7$. A
value close to unity suggests that star formation should be able to proceed in
this region, where there are no powerful outflows.

If the quasar-driven wind does not efficiently cool and adiabatically expands,
then the initial driving mechanism is capable of transferring its kinetic
energy into mechanical energy in the galactic-scale outflow. The momentum flux
of the outflow should therefore be greater than $L_{\rm bol}$/c (Zubovas &
King, 2012). We measure total momentum flux ($\dot{P}_{\rm
outflow}=\dot{M}\times v$) of 2.1$\times 10^{37}$ dynes over the entire
outflow region. We use the 3000Å quasar luminosity to compute a bolometric
luminosity value of 1.04$\times 10^{47}$ erg s-1 (Runnoe et al., 2012).
Comparing the outflow momentum flux to the quasar radiation momentum flux
($L_{\rm bol}$/c) of 3.5$\times 10^{36}$ dynes, yields a ratio $\dot{P}_{\rm
outflow}/\dot{P}_{\rm quasar}$ (loading factor) of 6. In principle this ratio
is a lower limit, since there can still be diffuse molecular gas in the
ionized outflow regions whose CO emission is below the sensitivity of ALMA.
Based on theoretical work by Faucher-Giguère et al. 2012; Zubovas & King 2012
the measured loading factor of $>$6 suggests that the wind is energy-
conserving. The total kinetic luminosity of the outflow is also about 2$\%$ of
$\rm L_{bol}$, consistent with the above theoretical prediction. 3C 298
observed extended outflow properties strongly suggests that radiation pressure
by itself is unable to drive the outflow. Star formation is also incapable of
driving the observed outflow as the expected terminal velocity for a supernova
driven galactic scale wind is only $\sigma\sim$200 km s-1(Murray et al.,
2005), far lower than the observed velocities ($\sigma\sim 500$km s-1) seen in
the bi-conical wind.

The outflow could be induced by either the jet and/or broad-absorption line
(BAL) winds from the quasar. We infer a jet pressure

$\rm P_{jet}\approx\frac{L_{jet}\times t}{3V},$ (11)

of $3\times 10^{-8}$ dynes cm-2 using the jet kinetic luminosity of 1.4$\times
10^{47}$ erg/s, derived using the 1.4 GHz (570 MHz observed) radio flux-jet
power relation (Bîrzan et al., 2008; Cavagnolo et al., 2010), assuming
spherical volumes at a radius of 9 kpc and a time scale of 3 Myr. This is an
order of magnitude calculation given the approximations in the jet luminosity,
lifetime (t) of the jet, and volume. Observations of other BAL quasars
indicate that the kinetic luminosity of outflows can get as high as $10^{46}$
erg s-1(Chamberlain et al., 2015), which is close to the kinetic luminosity
for the 3C 298 jet and would exert a pressure of $10^{-8}$ dynes cm-2. This
means that a BAL-type wind could potentially drive the extended 3C 298
outflow. However, there is no observed BAL in the optical and infrared spectra
of 3C 298. The lack of an observed BAL in 3C 298 could be due to an
orientation effect where our line-of-sight does not overlap with the absorbing
outflowing gas. If this is not the case, and there is no BAL, the jet of 3C
298 still has the necessary ram pressure capable of inducing a large scale
outflow.

The gas pressure ($P=nkT$) in the ionized ([SII]) gas is $\sim 4\times
10^{-10}$ dynes cm-2. From the ALMA CO (3-2) observations we measure a
molecular gas surface density of 490 M⊙pc-1 indicating a molecular gas
pressure ($P=(\pi/2)G\Sigma_{molecular}^{2}$) of $\sim 1\times 10^{-9}$ dynes
cm-2. Both the BAL wind and quasar jet pressures are 2-3 orders of magnitude
higher than the current pressure of the ionized and molecular ISM. The fact
that the ionized gas pressure is comparable to or smaller than the weight per
unit area of the molecular gas shows that the jet is not currently producing
an overpressure (which would be reflected in the thermal gas pressure of the
ionized gas in the ISM) relative to the overburden of the molecular gas. This
suggests that the jet is now venting out of the galaxy. The interaction
between the ISM and the jet and/or BAL wind in the past was likely in a denser
environment, and thus confined to a smaller volume with a higher pressure, to
initially generate the outflows.

Both a BAL quasar wind and jet have enough kinetic energy to drive galactic
scale winds. These large outflows in 3C 298 supply the necessary energy and
momentum to hinder star formation along their path and expel large amounts of
gas out of the galaxy. If the sources of turbulence were to halt at the
present time, the shocks would dissipate on a dynamical time scale of 3-6 Myr.
By that time the majority of the gas in the ionized outflow will have already
escaped into the intergalactic medium with most of the molecular gas in the
disc removed from the inner few kpc and potentially swept up into the ionized
outflow. Any left over gas in the galaxy would quickly cool back into a
molecular state. Taken together this shows both negative and ejective feedback
occurring along the outflow region, thereby impacting the stellar mass growth
of the quasar host.

##  5 Discussion

To generate a comprehensive picture of 3C 298, we combine multi-wavelength
data to spatially resolve the ionized gas, molecular gas, and stellar light
distribution of the host galaxy. This allows a unique comparison between the
star formation histories, photo-ionization mechanisms, and gas-phase
properties in a high-redshift quasar host galaxy. In Figure 11 we generalize
the multi-wavelength analysis of the 3C 298 system in a schematic diagram and
summarize its properties in Table 4.

We make use of observations from VLA to probe the quasar radio jets, WFC3 data
from HST to study the stellar contribution, ALMA to measure the resolved
molecular gas morphology and dynamics, and Keck LGS-AO to determine the
resolved ionized gas properties. These data show clear evidence of a conical
outflow in the host galaxy of 3C 298, driven by quasar jets and/or winds, that
directly impact the ISM of the host galaxy. VLA images of 3C 298 reveal
synchrotron radio jets feeding lobes that extend over $\sim$ 18 kpc from the
quasar in the east-west direction (Figure 1). Along the radio lobes, OSIRIS
kinematic maps reveal broad ($\sigma\sim 800$ km/s) emission lines that are
offset up to 600 km s-1 from the quasar’s systemic redshift, indicating an
outflow extending over a significant swathe of the galaxy.

We find direct evidence of negative feedback along the path of the jet and
outflow regions of the host galaxy. The term “negative feedback” has been used
loosely in the astronomical literature; herein we define negative feedback as
injected energy and momentum in the ISM that inhibits the normal thermal
cooling and/or decay of turbulence, thereby extending the time scale for star
formation to occur. Galactic-scale feedback may also occur when high velocity
outflows remove large fractions of the ISM, thereby impacting the star
formation and stellar mass history of the host galaxy. The latter might be
called “ejective feedback”. Both negative and ejective feedback may occur
simultaneously. The 3C 298 ionized outflow region has a bi-conical shape with
a primarily blueshifted approaching side and redshifted receding side of the
cone (Figures 1 and 3). Emission line ratios (e.g., [NII]/H$\alpha$ and
[OIII]/H$\beta$) allow us to distinguish between various photo-ionization
modes of 3C 298’s ISM, which is illustrated in the nebular diagnostic diagram
Figure 3. In both of the outflow regions we detect high nebular emission-line
ratios that imply a combination of hard photoionizing radiation from the
quasar and shock ionization. We find a total ionized mass outflow rate
($\dot{M}$) of 450-1500 M⊙ yr-1 combined for both outflow regions. ALMA
observations of molecular gas reveal a disc centered on the quasar. A large
fraction of gas in the molecular disc reveals broad emission associated with a
molecular outflow with a rate of 2300M⊙ yr-1. Unlike the ionized outflow the
molecular outflow emanates in a single direction from the blueshifted side of
the molecular disc. The molecular outflow either originates from the 3C 298
quasar nuclear region or from the disc itself. In the rest-frame of the
redshifted ionized receding cone, two broad Gaussian functions are required to
fit the profiles of the nebular emission lines (Figure 2). This indicates an
approaching and receding component corresponding to the front and back of a
hollow cone that suggests expansion of the outflow along our line-of-sight.

Combining kinematic maps from OSIRIS and ALMA reveals that the ionized outflow
gas most likely originates from the molecular disc since the blue/red-shifted
outflow matches the blue/red-shifted region of the disc. Furthermore the
blueshifted molecular outflow is on the same side as the ionized. We find no
narrow ($\sigma$ $<$200 km/s) H$\alpha$ emission in either of the outflow
regions, suggesting that the majority of the ionized gas is in a turbulent
phase. The outflow carries a significant amount of kinetic energy and it is
capable of removing the majority of the galaxy’s gas on a time scale of 3 Myr.
The virial parameter deduced from the ionized and molecular gas over the
outflow regions are much greater than one, implying that the ISM is not self-
gravitating, and hence will not collapse to form stars. Similarly, the
molecular outflow is both stirring the molecular gas and removing it from the
inner regions of the galaxy. Ionization occurring over the outflow region is
dominated by shocks, which drives intense heating into the ISM that further
inhibits star formation. Over the conical outflow region we derive a
conservative limit for H$\alpha$ emission due to star formation of $<$ 14 M⊙
yr-1(2$\sigma$), or $\sim$0.3 M⊙ yr-1 kpc-2 using the empirical H$\alpha$
luminosity-star formation rate (Kennicutt, 1998). Colours of the stellar light
as seen in HST data projected on the blueshifted outflow region are also
consistent with a stellar population that had its star formation abruptly
halted within the last $\sim$25 Myr (see Figure 10).

In the 3C 298 host galaxy we observe star forming regions that are offset from
the outflows. The youngest (7 Myr) stellar populations observed with HST
(Figure 10) imply that a recent burst of star formation has occurred. These
regions are found 10-16 kpc east of the quasar. In addition, beyond the
extended narrow-line and outflow regions, using OSIRIS and HST we resolve star
forming clumps that reside $\sim$10-22 kpc (blue in Figure 3) away from the
quasar. These clumps have an integrated star formation rate of 88$\pm$9 M⊙
yr-1, based on the observed H$\alpha$ luminosity and empirical star formation
rate relation (Kennicutt, 1998). ALMA CO (3-2) and (5-4) data reveal a
molecular clump in the vicinity of this region with a total molecular gas mass
of 1.4$\times 10^{9}$M⊙. Using the HST-measured colours, we find a young
stellar population with an age of $\sim$20 Myr in these star forming regions.
Therefore, combining results from the resolved molecular gas, stellar
populations, and ionized gas yields a consistent picture; we find star
formation occurring away from large scale outflows, where the quasar winds
and/or jets are stirring the ISM and removing gas.

The kinematic map of the ionized gas in 3C 298 shows a systematic velocity
gradient across a large portion of the system. We fit this region with a
rotating disc model (Figure 5). We find evidence for a second rotating disc in
the system that is offset by $\sim$8.6 kpc and $\sim$170 km s-1from the quasar
centroid and central velocity of the broad line region. The dynamical center
of the second disc is in the vicinity of a secondary outflow region,
suggesting for the presence of a candidate second nucleus. The offset between
the dynamical center of the second disc and the secondary outflow is on the
order of 3kpc. We note that this is a typical separation that is found between
the stellar centroid and AGN location in local late stage mergers (Liu et al.,
2013b; Comerford et al., 2015; Barrows et al., 2016). We infer that the 3C 298
system likely has two massive galaxies with distinct rotating discs that are
currently experiencing a close passage, where their galactic nuclei and SMBHs
have yet to merge.

We calculated the enclosed dynamical mass of the molecular disc at the
location of the quasar to be 1-1.7$\times 10^{10}$M⊙. With the measured SMBH
mass ($10^{9.37-9.56}$M⊙) 3C 298 resides off the local scaling
M$\rm{}_{bulge}-M_{BH}$ relationship, which indicates that black hole growth
must occur earlier than stellar mass assembly. These results are similar to
what has been recently observed in nearby ultraluminous infrared galaxies
(ULIRGs) in gas-rich merger stages by Medling et al. 2015, where they find
that these ULIRGs predominantly have early black hole growth and have yet to
form the bulk of their stellar mass. Similar results have been found for a
small number of z$>6$ quasar host galaxies observed with ALMA, where the black
hole to galaxy bulge mass ratio is higher by a factor of 3-4 (Wang et al.,
2013; Venemans et al., 2016) compared to local galaxies. This is counter to
previous theoretical simulations that imply star formation and stellar mass
build-up should occur during the gas-rich-merger phase, before the SMBH does
its predominant growth when AGN feedback is suspected to transpire (i.e., Di
Matteo et al. 2005; Hopkins 2012; Hopkins et al. 2016).

Models are still unclear about whether distant quasars should reside above,
below or even on an extension of the local SMBH-galaxy scaling relations.
Hydrodynamical simulations of $\rm z>6$ quasars by Barai et al. 2017 suggest
that negative feedback may drive quasars above the local scaling SMBH-galaxy
relations. Barai et al. 2017 argue that conical, symmetric outflows can remove
gas efficiently from galactic discs, while still allowing gas to accrete on to
the SMBH perpendicular to the bi-conical outflow. Furthermore, the same
simulations without quasar feedback tend to grow their stellar mass ahead of
the SMBH, driving galaxies below the local correlations. Anglés-Alcázar et al.
2017 also find that the stellar bulges outpace the SMBH in the absence of
feedback. Anglés-Alcázar et al. 2017 include feedback from bursty star
formation, which can limit the growth of the SMBH and keeps the system lying
below local SMBH-galaxy scaling relation.

3C 298 at z=1.439 (age 4.47 Gyr) has quasar negative feedback occurring in a
conical outflow early in the gas-rich merger-phase, implying that the majority
of the nucleus’ stellar mass assembly must occur in later phases if it is to
reach the scaling relations of today. Since the majority of the current gas
supply in the host galaxy of 3C 298 is incapable of forming stars and will
soon be removed from the galaxy through the quasar driven winds, perhaps this
assembly happens through dry mergers or newly supplied IGM molecular gas. Even
if all of the current gas supply in the molecular disc (6.6$\times 10^{9}$M⊙)
turns into stars it will still be insufficient to bring the bulge of the 3C
298 host galaxy onto the local scaling relation. For the 3C 298 system this
means that the SMBH mass is formed earlier and more efficiently than the host
galaxy’s stellar mass.

The host galaxy of 3C 298 could be a precursor to local galaxies that are
significantly offset from the local scaling relation (e.g, NGC 1277). If there
is insufficient accretion from the intergalactic medium to fuel future star
formation or if 3C 298 resides in a less dense environment than a typical
quasar it could fail to form/accrete enough stars to fall on the local scaling
laws. A natural way to limit the growth of the stellar bulge in a system with
a powerful AGN is to have strong feedback on the ISM through a bi-polar
outflow early in the lifetime of the system (Fabian et al., 2013).

Figure 11: Cartoon illustration of the merger in the 3C 298 system that
includes the results from OSIRIS, ALMA, HST, and VLA. The location of the
quasar is distinguished by a yellow star. The large blue and red-shifted
outflows emanating from the quasar observed in the nebular emission lines are
co-aligned with the radio jet (indicated by a grey dashed arrow), where
negative feedback is observed. The locations of the ALMA CO (3-2) and (5-4)
emission are shown with red-brown ovals, representing molecular gas
reservoirs. A molecular disc centered on the quasar is shown with a blue-red
gradient. We find strong evidence for molecular outflow on the blueshifted
side of the disc. The dynamical center of the secondary merging galaxy is
shown with a black ’x’ sign. The radial velocity map of this galaxy is well-
fit to disc model. A secondary outflow region is found to reside near the
dynamical center of the merging galaxy, providing tentative evidence for a
secondary AGN in the system. The secondary AGN has spatially-concentrated
elevated emission line ratios that are consistent with ionization from an AGN.
A large area of the 3C 298 system is observed to have extended narrow line
region (ENLR; grey) between both the quasar and putative AGN. The majority of
the star formation (green) is occurring in compact clumps offset from both
galaxies, which would be consistent with a tidal feature being induced by the
merger. A young stellar population (purple) measured from the HST WFC3 colours
is offset from both the outflows and molecular gas of the system.

In summary, the 3C 298 system shows strong evidence of negative feedback from
powerful conical outflows that are halting star formation by driving extremely
high velocity turbulence in the ISM and by ejecting large amounts of gas. The
dynamical time scale of the outflow is $\sim$3-6 Myr, suggesting that
quenching of star formation must occur rapidly. In the 3C 298 system, strong
feedback has started fairly early in the merger process, well before the final
coalescence of the two galactic nuclei. The system shows multiple concurrent
phases of the standard merger model (Sanders et al., 1988; Hopkins et al.,
2008; Alexander & Hickox, 2012), with the co-existence of a luminous type-1
quasar, star formation in merger host galaxies, and candidate secondary AGN
that is offset from the quasar. This implies that removal of gas and dust
surrounding the SMBHs occurred rapidly and early during the merger phase. This
early and short onset of quasar feedback compared to total time scale of the
merger ($\sim$ 1 Gyr) may also partially explain why it has been difficult for
measuring its effect on the star-forming ISM in distant galaxies.

##  6 Conclusion

We present integral field spectroscopy of resolved nebular emission lines;
H$\beta$, [OIII], H$\alpha$, [NII], [SII]together with rotational CO (3-2) and
(5-4) spatially resolved emission spectroscopy in the host galaxy of the radio
loud quasar 3C 298 (z=1.439). These data are supplemented with archival HST-
WFC3 and VLA observations of the rest frame UV and optical stellar continuum
and jet/lobe synchrotron emission, respectively.

  * •

We find strong evidence for negative feedback in the host galaxy of 3C 298.
Dynamics of ionized gas traced through nebular emission lines show a
significant quasar-driven outflow encompassing a large area of the host
galaxy. We derive an ionized outflow rate of 467-1515M⊙ yr-1.

  * •

Co-spatial with the powerful ionized gas outflow VLA imaging shows extended
synchrotron emission from the quasar jet/lobes. Radio data suggests that the
jet has sufficient energy to drive the outflow. A BAL wind also has the
necessary energetics for potentially driving the outflow.

  * •

We detect a molecular gas disc centered on the quasar with a total molecular
gas of 6.6$\times 10^{9}$M⊙ and effective radius of 1.6 kpc.

  * •

A powerful quasar driven molecular outflow is detected in the molecular disc
with an $\rm\dot{M}_{H_{2}}$ outflow rate of 2300 M⊙ yr-1. The molecular gas
in the disc will be depleted by the outflow on a time scale of 3 Myr.

  * •

Dynamical modeling of the molecular disc reveals that total mass enclosed in
the disc is 2-2.5 orders of magnitude below the expected value from local $\rm
M_{stellar-bulge}-M_{BH}$ relationship using the measured SMBH mass of the 3C
298 quasar.

  * •

Several kiloparsecs away from the outflow path we find evidence of star
forming regions based on BPT diagnostics, strong UV emission from O and B
stars, and evidence for a molecular reservoir with a total mass of 1.4$\times
10^{9}$M⊙.

  * •

Disc modeling of the velocity field traced by [OIII] emission shows a second
rotating disc with a dynamical center offset from the quasar by 9 kpc. This
suggests evidence for a late stage merger where the disc traces the second
merging galaxy in the system. The dynamical center of the disc aligns well
with a secondary outflow region seen in nebular emission that does not extend
from the quasar and does not align with any structure in the radio map. This
suggests a candidate secondary AGN in the 3C 298 system.

  * •

These observations taken together imply an early onset of negative feedback
with a short quenching time compared to time scale of the galactic merger.
Feedback is also happening early in the 3C 298 merger process and is occurring
well before the assembly of the 3C 298 host galaxy on the local $\rm
M_{stellar-bulge}-M_{BH}$ relationship.

Table 4: 3C 298 Properties & Results  Parameter | Value
---|---
zquasar | 1.439
RA | 14:19:08.181
DEC |  $+$06:28:34.79
$\lambda$LλaaComputed at rest-frame 3000 Å | 2.0$\times 10^{46}$erg s-1
SFR H$\alpha$ | 88$\pm$9M⊙ yr-1
SFR IR bbValue from (Podigachoski et al., 2015) | 930${}^{+40}_{-40}$M⊙ yr-1
MdustbbValue from (Podigachoski et al., 2015) | 3.8${}^{+0.3}_{-0.4}\times 10^{8}$M⊙
M$\rm{}_{H_{2}}^{Total}$ | 8.75$\pm 0.4$$\times 10^{9}$ M⊙
M$\rm{}_{H_{2}}^{MolDisc}$ | 6.6$\pm 0.36$$\times 10^{9}$ M⊙
M$\rm{}_{H_{2}}^{SFRegion}$ | 1.4$\pm 0.14$$\times 10^{9}$ M⊙
$\rm\dot{M}_{[OIII]}$ | 467 M⊙ yr-1
$\rm\dot{M}_{H\alpha}$ | 1515 M⊙ yr-1
$\rm\dot{M}_{H_{2}}$ | 2300 M⊙ yr-1
Outflow $\rm n_{e}$ccValue based on [SII] line ratio measurment over blueshifted outflow region. | 272 cm-3
$\rm M_{dyn,bulge}$ | $1.35\pm 0.5\times 10^{10}$
$\rm M_{SMBH}$ | $3.23\pm 1.1\times 10^{9}$

The authors wish to thank Randy Campbell and Jim Lyke with their assistance at
the telescope to acquire the Keck OSIRIS data sets. We also appreciate
valuable discussions with Dusan Keres and the constructive comments made by
the anonymous referee. The data presented herein were obtained at the W.M.
Keck Observatory, which is operated as a scientific partnership among the
California Institute of Technology, the University of California and the
National Aeronautics and Space Administration. The Observatory was made
possible by the generous financial support of the W.M. Keck Foundation. The
authors wish to recognize and acknowledge the very significant cultural role
and reverence that the summit of Maunakea has always had within the indigenous
Hawaiian community. We are most fortunate to have the opportunity to conduct
observations from this mountain. This paper makes use of the following ALMA
data: ADS/JAO.ALMA[2013.1.01359.S]. ALMA is a partnership of ESO (representing
its member states), NSF (USA) and NINS (Japan), together with NRC (Canada),
NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the
Republic of Chile. Based on observations made with the NASA/ESA Hubble Space
Telescope, obtained from the Data Archive (Program GO13023) at the Space
Telescope Science Institute, which is operated by the Association of
Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
A portion of the research was conducted at The Dunlap Institute for Astronomy
and Astrophysics that is funded through an endowment established by the David
Dunlap family and the University of Toronto. This research has made use of the
NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion
Laboratory, California Institute of Technology, under contract with the
National Aeronautics and Space Administration.

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