# A Polarimetric Study of 9 PG Quasars with the VLA

Janhavi Baghel,1 P. Kharb,1 Silpa S.,1 Luis C. Ho,2,3 C. M. Harrison4
1National Centre for Radio Astrophysics (NCRA) - Tata Institute of Fundamental
Research (TIFR), S. P. Pune University Campus, Ganeshkhind, Pune 411007, India
2Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing
100871, China
3Department of Astronomy, School of Physics, Peking University, Beijing
100871, China
4School of Mathematics, Statistics and Physics, Newcastle University,
Newcastle upon Tyne NE1 7RU, UK E-mail<EMAIL_ADDRESS>
###### Abstract

We present polarization images of 9 radio-loud (RL) quasars from the VLA
B-array at 6 GHz. These quasars belong to the Palomar-Green (PG) “blazar”
sample comprising 16 RL quasars and 8 BL Lac objects. Extensive polarization
is detected in the cores, jets and lobes of all the quasars, with cores
primarily displaying magnetic (B-) fields transverse to, and jets displaying
fields aligned with the jet direction. Hotspots display either transverse
B-fields signifying B-field compression at terminal shocks or more complex
structures. The fractional polarization in the cores ranges from 1-10% and
jets/lobes from 10-40%. Several of the quasars show distorted or hybrid
FRI/FRII radio morphologies with indications of restarted AGN activity. We
attribute this to the optical/UV selection criteria of the PG sample that
remains unbiased at radio frequencies. The in-band spectral indices of the
radio cores are relatively flat while they are steep in the hotspots. This is
consistent with the polarization structures where the hotspots appear to be
locations of jet bends or bow-shocks. We present global properties for the
entire PG “blazar” sample. We find that jet powers correlate with accretion
rates for the quasars; higher accretion rates result in more powerful radio
jets. A correlation between the radio core fractional polarization and the 150
MHz total radio luminosity for the 9 quasars studied here may imply that more
organized B-fields at the jet bases lead to higher core fractional
polarization and to more powerful radio jets.

###### keywords:

galaxies: active – (galaxies:) quasars: general – (galaxies:) BL Lacertae
objects: general – galaxies: jets – techniques: interferometric – techniques:
polarimetric

††pagerange: A Polarimetric Study of 9 PG Quasars with the VLA–References

##  1 Introduction

Active Galactic Nuclei (AGN) are highly energetic and luminous non-stellar
sources in the centres of galaxies that are powered by an actively accreting
supermassive black hole (SMBH; Rees, 1984; Rawlings & Saunders, 1991). Radio-
loud AGN (RL AGN) are AGNs with collimated, bipolar, relativistic jets
(Blandford & Rees, 1974), parameterised as having
$\mathrm{R=(S_{5~{}GHz}/S_{{\it B}-band})\geq 10}$ where R is the ratio of
radio (5 GHz) to optical (B-band) flux densities (Kellermann et al., 1989).
Only around $\mathrm{15-20\%}$ of AGN are radio-loud (Kellermann et al., 1989;
Urry, 2003) but these kpc–Mpc scale jetted AGN have a major impact on their
host galaxy and surrounding environments, stimulating and limiting the growth
of galaxies, star-formation, and heating the circumgalactic medium (Blandford
et al., 2019). The different classes of RL AGN are radio galaxies (RGs),
quasars and BL Lac objects. RGs and quasars are distinguished by the presence
of narrow, as opposed to broad (velocity widths of $\sim 1000$ km s-1) optical
emission lines respectively (Osterbrock, 1980; Wills & Browne, 1986), whereas
the optical spectra of BL Lacs is mostly featureless and dominated by the
continuum emission (Stickel et al., 1991; Stocke et al., 1991).

The prevailing jet based RL AGN model is intrinsically anisotropic and
orientation based RL unification postulates that observational properties of
RL AGNs (and in general of Type 1 and 2 AGN) are explained by the different
orientation of an opaque dust distribution (torus) relative to an observer and
the effects of relativistic beaming (Barthel, 1989; Antonucci, 1993; Urry &
Padovani, 1995). The torus lies in the radio axis equatorial plane,
surrounding the central engine and broad emission line region (BLR) obscuring
them from view for certain viewing angles, resulting in Type 1 (broad + narrow
optical emission lines; broad line RGs and quasars) and Type 2 (narrow line
RGs) AGN. Relativistic beaming of jets oriented at small angles to the
observer leads to superluminal velocities, one-sided core-jet morphologies,
depolarization asymmetry, and high source brightness. However, there are other
phenomenological differences in RL AGN unrelated to the viewing angle. A
morphological divide in radio jets of RGs was first noted by Fanaroff & Riley
(1974) and hence they are denoted as Fanaroff & Riley Type I (FRI) and Type II
(FRII). The lower-luminosity FRI RGs exhibit plume-like radio lobes whereas
the higher-luminosity FRII RGs exhibit collimated jets with terminal
“hotspots”. A division in total radio power found to occur at
$\mathrm{L_{178~{}MHz}=2\times 10^{25}~{}W~{}Hz^{-1}~{}sr^{-1}}$ (Fanaroff &
Riley, 1974).

The RL unification posits that quasars are the pole-on counterparts of FRII
RGs while BL Lac objects are the pole-on counterparts of FRI RGs (Barthel,
1989; Urry & Padovani, 1995). Blazars have been historically characterised as
AGN with high luminosities, rapid variability, high and variable polarization,
superluminal jet motion, and intense non-thermal emission across the
electromagnetic spectrum. These properties are understood to be now largely
explained by their relativistic jets being oriented at small angles to the
line of sight, where both Doppler and projection effects become prominent. In
addition, blazar spectral energy distributions (SEDs) exhibit double peaks,
attributed to synchrotron radiation and inverse Compton (IC) radiation,
respectively (e.g., Abdo et al., 2010). While quasars are found to have low
synchrotron peak frequency $\mathrm{(\nu_{peak}<10^{14.5}~{}Hz)}$, BL Lacs are
found to span the entire range, with low-, intermediate-, and high-frequency-
peaking BL Lacs (LBL, IBL, and HBL; Ghisellini et al., 2011).

The origin of the FR dichotomy in radio power and morphology is still an
unresolved question. As is the question of the dramatically different optical
spectra and broad-band SEDs in the blazar subclasses, aka the blazar divide.
Various hypotheses have been put forth to explain the differences between the
FR radio galaxies as well as the blazar sub-classes. Two popular suggestions
include “intrinsic differences” between FRIs and FRIIs in terms of jet kinetic
power, driven by differences in the SMBH spins (e.g., Baum et al., 1995;
Celotti et al., 1997; Bhattacharya et al., 2016), or efficiency of accretion
(e.g., Meier et al., 1997; Marchesini et al., 2004; Ghisellini et al., 2010),
and “extrinsic differences” in jet-medium interaction that results from
differences in the surrounding medium (e.g., Gopal-Krishna et al., 1996; Urry
& Padovani, 1995; Prestage & Peacock, 1988).

High-excitation radio galaxies (HERGs) displaying strong optical emission
lines are associated with high-rate, radiatively-efficient (Shakura & Sunyaev,
1973) accretion whereas low-excitation radio galaxies (LERGs) with faint or
absent lines are linked to low-rate, radiatively-inefficient (Narayan & Yi,
1995) accretion. FRI and FRII classes have been frequently associated with RI
and RE accretion states, respectively (Jackson & Rawlings, 1997). Almost all
FRIs are LERGs and most FRIIs are HERGs. However, there are few known examples
of FRI HERGs (Gürkan et al., 2022), and a significant population of FRII LERGs
(Hine & Longair, 1979). This association is also contradicted by the discovery
of FRII-like BL Lacs, and FRI-like quasars (Landt et al., 2006; Kharb et al.,
2010). Jet deceleration and subsequent decollimation in FRI jets, which likely
occurs on kpc scales (Bicknell, 1994; Laing & Bridle, 2002) could be
controlled by a combination of jet power and environmental density (Ledlow &
Owen, 1996). This suggestion has found support in recent LOFAR observations
(Mingo et al., 2019; Mingo et al., 2022).

Jet formation mechanisms, either through the Blandford-Znajek (BZ; Blandford &
Znajek, 1977) or the Blandford-Payne (BP; Blandford & Payne, 1982) mechanisms,
or a combination of both, may also be driving the FR/blazar divide. Several
theoretical models of AGN jets predict the generation of helical B-fields
propagating outward with the jet plasma (Meier et al., 2001; Lyutikov et al.,
2005; Hawley et al., 2015). Polarization observations are therefore important
to understand and differentiate between different jet formation mechanisms.
Earlier polarization studies of AGN jets have revealed that fractional
polarization up to 40% are common in radio jets at low radio frequencies
(Bridle & Perley, 1984). The inferred B-field structures (inferred to be
perpendicular to the electric vector positions angles, EVPA, for optically
thin emission, and parallel to the EVPA for optically thick emission;
Pacholczyk, 1970) can be categorised as (i) B-fields predominantly parallel to
the jet axis, (ii) B-fields predominantly perpendicular to the jet axis, and,
(iii) B-fields perpendicular to the jet axis at the centre of the jet, but
parallel near one or both of its edges. More powerful FRII sources tend to
have B-fields parallel to the jet axis whereas FRI sources typically display
jets with the other two B-field configurations (Willis et al., 1981; Bridle,
1982). In the jets of most powerful quasars, the inferred B-field direction
after correction for Faraday rotation is normally along the jet, often
following bends in the jet very closely (Bridle et al., 1994).

Very long baseline interferometry (VLBI) observations of blazars have found
differences in magnetic (B-) field structures as well as rotation measures
(RM) on parsec-scales (Cawthorne et al., 1993). BL Lacs tend to have their
parsec-scale electric vector position angles (EVPA) parallel to the jet
direction whereas RL quasars tend to show a perpendicular relative orientation
(Lister & Homan, 2005; Lister et al., 2013). Also, BL Lacs have been found to
show systematically higher parsec-scale RM relative to the quasars (Zavala &
Taylor, 2005). However, it is not clear if these differences extend to kpc-
scales.

In this paper, we present polarization-sensitive Karl G. Jansky Very Large
Array (VLA) images for the jets and lobes of 9 RL quasars to study their kpc-
scale B-field structures. The selection criteria for our sample is discussed
in Section (2). We have detailed the radio data reduction and calibration and
imaging details in Section (3). Results from our observations are discussed in
Section (4) along with a discussion on previous observations of our sources.
Global correlations for the entire Palomar Green (PG) “blazar” sample have
also been discussed in Section (5). We discuss our results and findings in
Section (6) and summarize and present our final conclusions in Section (7).

Throughout this paper, we have adopted $\Lambda$CDM cosmology with
$\mathrm{H_{0}=73~{}km~{}s^{-1}Mpc^{-1}}$, $\mathrm{\Omega_{m}=0.3}$ and
$\mathrm{\Omega_{v}=0.7}$ and used flat $\Lambda$CDM subroutine of
astropy.cosmology subpackage (Astropy Collaboration et al., 2013, 2018). The
spectral index $\alpha$ is defined such that flux density at frequency $\nu$,
$S_{\nu}\propto\nu^{\alpha}$.

##  2 The PG “Blazar” Sample

The Palomar Green UV-excess photographic survey was carried out in the U and B
bands with the Palomar 18 inch Schmidt telescope in the late 1970s (Green et
al., 1986). The PG UV-excess survey remains the largest complete optically
selected survey for unobscured AGN at low redshift and therefore has no radio
selection biases. This makes this a good sample to examine the FR dichotomy,
which was originally observed in the radio-selected 3C sample. The PG sample
is one of the most well studied samples of AGN (Boroson & Green, 1992;
Kellermann et al., 1989; Miller et al., 1993) having extensive supplementary
multi-band data available in the literature, including accurate black hole
(BH) masses, accretion rates, galactic properties including star-formation
rates (SFR), etc. (e.g., Shangguan et al., 2018; Davis & Laor, 2011; Xie et
al., 2021). While the PG sample is well studied at optical/UV wavebands,
sensitive high-resolution polarimetric radio observations have been lacking
for most of the sources. These high-resolution polarimetric data are meant to
fill that gap and provide a means to adequately resolve jet structures and to
probe the environment through which jets are propagating.

The complete PG sample includes 1715 objects and covers a region of the sky
that is 10,714 square degrees. The limiting B-band magnitude for the PG sample
is B = 16.1 mag. The sample was 84% complete in 1986. Only 9% of the PG sample
sources are extragalactic in origin. Quasi-stellar objects (QSOs) constitute
5.4% of the sample. QSOs include both RL and RQ quasars, with the latter
making the vast majority ($>80$%). Only 4 BL Lac objects were initially
identified in the PG sample. These are: PG0851+203 (OJ287), PG1218+304,
PG1418+546, PG1553+113. Padovani & Giommi (1995) revised this list to 9: apart
from the original 4, 3 BL Lacs were identified by Fleming et al. (1993) :
PG1246+586, PG1424+240 and PG1437 +398; and the two identified by Padovani &
Giommi (1995) were PG1101+384 (Mrk421) and PG2254+075. Padovani & Giommi
(1995) also noted that the PG sample may be missing 40% of BL Lacs based on
its U-B color limit.

Figure 1: Distribution of redshifts $z$ w.r.t. the radio extents in kpc for
the PG “blazar” sample.

The PG “blazar” sample presented in this paper comprises 16 RL quasars and 8
BL Lac objects. Historically, blazars include only BL Lac objects and flat
spectrum radio quasars (FSRQs). We have also included steep spectrum radio
quasars (SSRQs) in our present study, and loosely referred to the BL Lacs,
FSRQs and SSRQs collectively as “blazars”. This was chosen to increase the
sample size while still including only Type 1 sources, where the jets are
inclined relatively close to our lines of sight. Given that the half-opening
angle of the dusty obscuring tori is $\leq 50\degr$ (Simpson et al., 1996),
our selection restricts the quasar jet orientations to be $\leq 50\degr$ while
displaying broad ($\geq 1000$ km s-1 velocity widths) emission lines in their
optical/UV spectra. Nearly 1/3 of our sample quasars are optically-violently-
variable (OVV) quasars. In the paper, when we refer to FSRQs and BL Lacs
exclusively, we call them “classical” blazars. Our PG “blazar” sample was
chosen using the following selection criteria.

  1. 1.

Redshift $z<0.5$

  2. 2.

Projected core-to-lobe extents $\gtrsim 15\arcsec$

The projected lobe extents were chosen so that the $\sim 5\arcsec$ uGMRT Band
4 ($\mathrm{\sim 600~{}MHz}$) observations can sample the lobes three or more
times. This results in the $\sim 1\arcsec$ VLA 6 GHz B-array observations
probing at least $\sim 5$ kpc scale regions at the distance of these sources.
1 BL Lac object, viz., PG1246+586, was excluded due to the redshift cutoff and
1 PG RL quasar, viz., PG1211+143, was excluded as it was unresolved on kpc-
scales (Danehkar et al., 2018). In general, Type 1 AGN are good candidates for
carrying out polarimetric observations as smaller inclination angles and
Doppler boosting effects are conducive to reduced depolarising effects from
intervening media as well as radio flux density brightening. Figure 1 presents
the range of redshifts and spatial extents in kpc of the PG “blazar” sample.
In this paper, we present the VLA images of 9 sample RL quasars which we had
already acquired data for from our PG blazar sample111 New VLA observations
have recently been approved for the remaining 15 sources.. Silpa et al.
(2021a) have already discussed source PG0007+106 using this data but we
mention those results as this source is also part of our sample and we also
provide the in-band spectral index image of the same.

Table 1: The PG “Blazar” Sample S.No. | Name | Other Name | RA | DEC | Redshift | Radio Extent ($\arcsec$ | kpc) | Type
---|---|---|---|---|---|---|---
1 | PG0851+203 | OJ 287 | 08h54m48.87s | +20d06m30.64s | 0.306501 | 20 | 87 | BL Lac
2 | PG1101+384 | Mrk 421 | 11h04m27.31s | +38d12m31.79s | 0.030893 | 30 | 18 | BL Lac
3 | PG1218+304 | RBS 1100 | 12h21m21.94s | +30d10m37.16s | 0.184537 | 45 | 134 | BL Lac
4 | PG1418+546 | OQ +530 | 14h19m46.59s | +54d23m14.78s | 0.152845 | 45 | 115 | BL Lac
5 | PG1424+240 | OQ +240 | 14h27m00.39s | +23d48m00.03s | 0.160680∗ | 45 | 290 | BL Lac
6 | PG1437+398 | RBS 1414 | 14h39m17.47s | +39d32m42.80s | 0.344153 |  25 | 117 | BL Lac
7 | PG1553+113 | RBS 1538 | 15h55m43.04s | +11d11m24.36s | 0.360365 | 60 | 290 | BL Lac
8 | PG 2254+075 | OY +091 | 22h57m17.30s | +07d43m12.30s | 0.188765 | 60 | 181 | BL Lac
9 | PG0007+106 | Mrk 1501 | 00h10m31.00s | +10d58m29.50s | 0.086032 | 60 | 93 | FSRQ
10 | PG1226+023 | 3C 273 | 12h29m06.69s | +02d03m08.59s | 0.159492 | 25 | 66 | FSRQ
11 | PG1302$-$102 | RBS 1212 | 13h05m33.01s | -10d33m19.43s | 0.27949 | 15 | 61 | FSRQ
12 | PG1309+355 | Ton 1565 | 13h12m17.75s | +35d15m21.08s | 0.183734 |  15 | 44 | FSRQ
13 | PG2209+184 | II Zw 171 | 22h11m53.88s | +18d41m49.85s | 0.06873 |  12 | 15 | FSRQ
14 | PG0003+158 | 4C +15.01 | 00h05m59.23s | +16d09m49.02s | 0.449711 | 35|194 | SSRQ
15 | PG1004+130 | 4C +13.41 | 10h07m26.09s | +12d48m56.18s | 0.24186 | 115|421 | SSRQ
16 | PG1048$-$090 | 3C 246 | 10h51m29.91s | -09d18m10.19s | 0.346528 | 83|392 | SSRQ
17 | PG1100+772 | 3C 249.1 | 11h04m13.86s | +76d58m58.19s | 0.31163 | 44|193 | SSRQ
18 | PG1103$-$006 | 4C -00.43 | 11h06m31.77s | -00d52m52.38s | 0.424968 | 22|119 | SSRQ
19 | PG1425+267 | Ton 202 | 14h27m35.60s | +26d32m14.54s | 0.364262 | 218|1060 | SSRQ
20 | PG1512+370 | 4C +37.43 | 15h14m43.06s | +36d50m50.35s | 0.370922 | 58|287 | SSRQ
21 | PG1545+210 | 3C 323.1 | 15h47m43.53s | +20d52m16.61s | 0.264659 | 70|275 | SSRQ
22 | PG1704+608 | 3C 351 | 17h04m41.37s | +60d44m30.52s | 0.371411 | 66|325 | SSRQ
23 | PG2251+113 | 4C +11.72 | 22h54m10.42s | +11d36m38.74s | 0.32427 | 15 | 68 | SSRQ
24 | PG2308+098 | 4C +09.72 | 23h11m17.75s | +10d08m15.75s | 0.432064 | 83|447 | SSRQ
Note. Column (1): Serial Number. Column (2): PG names of sources. Column (3):
Other common names of sources. Column (4): Right Ascension.
Column (5): Declination. Column (6): Redshift†. Column (7): Radio extents in
arcsec and kpc. Column (9): Type of blazar
∗ $z=0.60468$ has been suggested by Paiano et al. (2017). We have used this
updated value in our calculations
† All redshift values reported are corrected to the reference frame defined by
the 3K CMB on NASA NED222The NASA/IPAC Extragalactic Database (NED) is
operated by the Jet Propulsion Laboratory, California Institute of Technology,
under contract with the National Aeronautics and Space Administration..
Radio extents derived from Miller et al. (1993) at 5 GHz or from 1.4 GHz VLA
FIRST / NVSS images for sources unresolved at 5 GHz.

##  3 Radio Data: Reduction and Analysis

The radio data were acquired using the VLA in the C-band (6 GHz) B-array
configuration from 2020, August 10 to 2020, October 15 (Project ID: 20A-182)
with a resolution of 1.1$\arcsec$. 16 spectral windows with 64 channels each
were chosen to span the frequency range of 4.5 - 6.6 GHz. The average time on
source was around 10 min. Polarization calibrators 3C286 and 3C138 were used.
For more details see table 3. We used the CASA calibration pipeline for VLA
data reduction for the initial calibration and flagging. This was followed by
manual polarization calibration.

First, the model of a polarized calibrator was set manually using the task
SETJY in CASA. For this, we provided the model parameters such as the
reference frequency, Stokes I flux density at the reference frequency, the
spectral index and the coefficients of the Taylor expansion of fractional
polarization and polarization angle as a function of frequency about the
reference frequency. The coefficients were estimated by fitting a first-order
polynomial to the values of fractional polarization and polarization angle as
function of frequency, which were obtained from the NRAO VLA observing
guide333
https://science.nrao.edu/facilities/vla/docs/manuals/obsguide/modes/pol.
Stokes I flux density values were calculated from the Perley & Butler (2017)
scale and used to estimate the spectral index by fitting and provided the
coefficients for Stokes I flux density at reference frequency, the spectral
index (alpha), and curvature (beta).

Table 2: The PG “Blazar” Sample Properties S.No. | Name | Type | $\mathrm{\log_{10}(M_{BH}/M_{\sun})}$ | Ref | R | ${\log_{10}\dot{M}\mathrm{(M_{\sun}/yr)}}$ | Ref | $\mathrm{\log_{10}SFR(M_{\sun}/yr)}$ | Ref |  $\bar{Q}$ ($10^{42}$erg/s)
---|---|---|---|---|---|---|---|---|---|---
1 | PG0851+203 | BL Lac | 8.5 | 1 | … | … | … | … | … | 210
2 | PG1101+384 | BL Lac | 8.23 | 1 | … | … | … | … | … | 6.58
3 | PG1218+304 | BL Lac | 8.47 | 1 | … | … | … | … | … | 9.23
4 | PG1418+546 | BL Lac | 8.74 | 1 | … | … | … | … | … | 61.80
5 | PG1424+240 | BL Lac | 6.42 | 1 | … | … | … | … | … | 988
6 | PG1437+398 | BL Lac | 8.95 | 1 | … | … | … | … | … | 165
7 | PG1553+113 | BL Lac | 7.25 | 1 | … | … | … | … | … | 120
8 | PG 2254+075 | BL Lac | 8.85 | 1 | … | … | … | … | … | 43
9 | PG0007+106 | FSRQ | 8.87 | 2 | 197 | -0.42 | 3 | 0.92 | 5 | 7.01
10 | PG1226+023 | FSRQ | 9.18 | 2 | 1138 | 1.18 | 3 | 1.56 | 6 | 4850
11 | PG1302$-$102 | FSRQ | 9.05 | 2 | 187 | 0.92 | 3 | 1.82 | 5 | 161
12 | PG1309+355 | FSRQ | 8.48 | 2 | 18 | 0.37 | 3 | 1.06 | 5 | 9.92
13 | PG2209+184 | FSRQ | 8.89 | 2 | 141 | -0.98 | 3 | 0.46 | 5 | 1.50
14 | PG0003+158 | SSRQ | 9.45 | 2 | 175 | 0.79 | 3 | $<1.25$ | 5 | 2380
15 | PG1004+130 | SSRQ | 9.43 | 2 | 228 | -0.37 | 4 | 1.42 | 5 | 847
16 | PG1048$-$090 | SSRQ | 9.37 | 2 | 377 | 0.3 | 3 | $<1.15$ | 5 | 2690
17 | PG1100+772 | SSRQ | 9.44 | 2 | 322 | 0.29 | 3 | 1.83 | 5 | 3540
18 | PG1103$-$006 | SSRQ | 9.49 | 2 | 272 | 0.21 | 3 | $<1.15$ | 5 | 2250
19 | PG1425+267 | SSRQ | 9.9 | 2 | 53.6 | 0.07 | 3 | 1.79 | 5 | 519
20 | PG1512+370 | SSRQ | 9.53 | 2 | 190 | 0.2 | 3 | 1.19 | 5 | 1920
21 | PG1545+210 | SSRQ | 9.47 | 2 | 418 | 0.01 | 3 | $<1.15$ | 5 | 1930
22 | PG1704+608 | SSRQ | 9.55 | 2 | 645 | 0.38 | 3 | 1.94 | 5 | 4640
23 | PG2251+113 | SSRQ | 9.15 | 2 | 365 | 0.66 | 3 | 0.46 | 5 | 1760
24 | PG2308+098 | SSRQ | 9.76 | 2 | 188 | 0.22 | 3 | $<1.25$ | 5 | 2000
Note. Column (1): Serial Number. Column (2): PG names. Column (3): Blazar
type. Column (4): Black hole masses. Column (5): References for black hole
masses.
Column (6): Radio loudness parameter from Kellermann et al. (1994). Column
(7): Accretion rates. Column (8): References for accretion rates. Column (9):
Star
Formation Rates (SFR). Column (10): References for SFR. Column (11): Jet
Power.
References- 1: Wu et al. (2009), 2: Shangguan et al. (2018), 3: Davis & Laor
(2011), 4: Luo et al. (2013), 5: Xie et al. (2021), 6: Westhues et al. (2016)
Table 3: VLA Observational Details of the 9 PG quasars Source | Observation Date | Time on source | Flux Calibrator | Phase Calibrator | Leakage Calibrator | Polarization Angle Calibrator
---|---|---|---|---|---|---
PG0003+158 | 20-Aug-2020 | 10m42s | 3C138 | J0010+1724 | 3C84 | 3C138
PG0007+106 | 20-Aug-2020 | 10m54s | 3C138 | J0010+1724 | 3C84 | 3C138
PG1004+130 | 25-Aug-2020 | 10m42s | 3C138 | J1016+2037 | 3C84 | 3C138
PG1048-090 | 27-Sep-2020 | 10m51s | 3C138 | J1130-1449 | 3C84 | 3C138
PG1100+772 | 22-Aug-2020 | 10m24s | 3C138 | J1044+8054 | 3C84 | 3C138
PG1103-006 | 22-Aug-2020 | 10m30s | 3C138 | J1058+0133 | 3C84 | 3C138
PG1226+023 | 15-Oct-2020 | 10m36s | 3C286 | J1150-0023 | 3C286 | 3C286
PG1309+355 | 12-Oct-2020 | 10m30s | 3C286 | J1310+3220 | 3C286 | 3C286
PG1704+608 | 10-Aug-2020 | 07m06s | 3C286 | J1740+5211 | 3C286 | 3C286
Note. Column(1): PG source name. Column(2): Observation date. Column(3): Time
on source. Column(4): Flux calibrator.
Column(5): Phase calibrator. Column(6): Leakage calibrator Column(7):
Polarization angle calibrator

Polarization calibration was carried out in three steps: (i) the cross-hand
(RL, LR) delays, were solved using a polarized calibrator with strong cross-
polarization (either 3C138 or 3C286). This was carried out using the task
GAINCAL with gaintype = KCROSS in CASA. (ii) the instrumental polarization
(i.e, the frequency dependent leakage terms or ‘D-terms’), was solved using a
polarized calibrator with good parallactic angle coverage. We used the task
POLCAL in CASA to solve for instrumental polarization with with poltype = Df +
QU while using the polarized calibrators (either 3C138 or 3C286) and poltype =
Df while using the unpolarized calibrator (3C84). The average value of the
D-term amplitude turned out to be $\approx$ 7% (iii) the frequency-dependent
polarization angle was solved using a polarized calibrator with known electric
vector position angle, EVPA (either 3C138 or 3C286). This was carried out
using the task POLCAL in CASA with poltype = Xf.

The calibration solutions were then applied to the multi-source dataset. The
CASA task SPLIT was used to extract the calibrated visibility data for the
sources from the multi-source dataset while averaging the spectral channels
such that the bandwidth (BW) smearing effects were negligible. The total
intensity or the Stokes I image of the sources created using the multiterm-
multifrequency synthesis (MT-MFS; Rau & Cornwell, 2011) algorithm of TCLEAN
task in CASA. Three rounds of phase-only self-calibration followed by one
round of amplitude and phase self-calibration were carried out for almost all
the datasets, except those for PG1704+608 and PG1309+355 for which only two
rounds of phase-only self-calibration were carried out. Images were made using
natural weighting with robust=+0.5 in CASA. For PG1048$-$090, we created the
images using robust=+2 in order to reduce the Y-shaped deconvolution errors
that showed up around the hotspots. Stokes Q and U images were created from
the final self-calibrated visibility data.

Linear polarized intensity $\mathrm{P=\sqrt{Q^{2}+U^{2}}}$ and the EVPA
$\chi=0.5~{}\mathrm{{tan}^{-1}(U/Q)}$ images were obtained by combining the
Stokes Q and U images using the AIPS444Astronomical Image Processing System;
Wells (1985) task COMB with opcode = POLC (which corrects for Ricean bias) and
POLA respectively. Regions with intensity values less than 3 times the rms
noise in the $P$ image and with values greater than $10^{\circ}$ error in the
$\chi$ image were blanked using COMB. Fractional polarization
$\mathrm{FP=P/I}$ images were obtained in COMB with opcode = DIV. Regions with
fractional polarization errors $\gtrsim$10% were blanked in the image. While
imaging with the MT-MFS algorithm of the TCLEAN task in CASA, we used two
Taylor terms to model the frequency dependence of the sky emission by setting
the parameter nterms = 2. This produced in-band spectral index images and
spectral index noise images for individual sources. We blanked the pixels with
spectral index errors greater than 0.3.

The average r.m.s. noise in the Stokes I images is $3\times 10^{-5}$ mJy
beam-1 (except for the outlier PG1226+023 or 3C273). The results from these
images are presented in Table 4. We note that PG1048$-$090 was imaged with a
circular convolved beam of size of $3.17\arcsec$ to minimise the imaging
artefacts, which were difficult to get rid of completely with different
weighting schemes. Flux density values reported in the paper were obtained
using the Gaussian-fitting AIPS task JMFIT for compact components like the
core, and AIPS verb TVSTAT for extended emission. The FP and spectral index
values noted are the mean values over the noted region. The rms noise values
were obtained using AIPS tasks TVWIN and IMSTAT. AIPS procedure TVDIST was
used to obtain spatial extents.

We note that Faraday rotation effects are not expected to be significant at 5
GHz in the kpc-scale observations of jets and lobes (e.g., Saikia et al.,
1987; Pudritz et al., 2012). For several of the sample sources, viz.,
PG1004+130, PG1048$-$090, PG1100+772, and PG1226+023, the average integrated
kpc-scale RM values are, respectively, $-16\pm 5$, $+0\pm 3$, $+29\pm 1$,
$+2.0\pm 0.2$ rad m-2 (Simard-Normandin et al., 1981). Integrated RM $\lesssim
50$ rad m-2 result in rotation of $\lesssim 10\degr$ at 5 GHz. RM values can
indeed be higher than the integrated RM values in smaller local regions, which
can influence the local inferred B-field directions (e.g., McKean et al.,
2016; Silpa et al., 2021b). However, the absence of strong Faraday effects is
supported by the observed polarization in the jets in these sources which tend
to lie either parallel or perpendicular to the local jet direction, with the
inferred B field directions being perpendicular to the direction of the EVPA
vectors for optically-thin regions of emission; such orientations could be
indicative of organised B-field structures (see Pudritz et al., 2012). We had
estimated the bandwidth depolarization in 5 GHz VLA data by comparing the
ratios of polarized flux density of individual sub-bands (of 512 MHz BW each)
to that of the full band (of 2 GHz BW); this turned out to be around a factor
of 0.5 (Silpa et al., 2022).

Table 4: Observational Results Source |  $I_{rms}$(Jy/beam) |  $P_{rms}$(Jy/beam) | Region |  | P (Jy) | I (Jy) | FP (%) | $\alpha$
---|---|---|---|---|---|---|---|---
PG0003+158 | 2.752E-05 | 2.390E-06 | Core |  | (3.6 $\pm$ 0.8) E-04 | 1.65E-01 | 8 $\pm$ 2%† | -0.13$\pm$0.13
|  |  | Hotspot region | NW | (1.8$\pm$ 0.2) E-03 | 3.3264E-02 | 9 $\pm$ 2% | -1.0$\pm$0.2
|  |  |  | SE | (4.0 $\pm$ 0.2) E-03 | 7.3481E-02 | 11 $\pm$ 2% | -1.2$\pm$0.3
|  |  | Lobes | NW | (3.5 $\pm$ 0.8) E-03 | 2.8033E-02 | 23 $\pm$ 5% | -1.2$\pm$0.4
|  |  |  | SE | (4.4 $\pm$ 0.8) E-03 | 4.5004E-02 | 17 $\pm$ 4% | -1.5$\pm$0.6
|  |  | SE jet knot |  | (1.04 $\pm$ 0.05)E-03 | 6.3260E-03 | 17.7 $\pm$ 0.8% | -1.3$\pm$0.1
PG0007+106 | 1.559E-05 | 2.770E-06 | Core |  | (1.2 $\pm$ 0.3) E-04 | 1.26E-01 | 0.8 $\pm$ 0.3% | 0.12$\pm$0.03
|  |  | Lobes | W | (2.3 $\pm$ 0.5) E-04 | 4.18E-03 | 16 $\pm$ 4% | -1.0$\pm$0.3
PG1004+130 | 2.641E-05 | 4.769E-06 | Core |  | (2.7 $\pm$ 0.8) E-05 | 2.90E-02 | 3 $\pm$ 1%∗ | -0.3 $\pm$ 0.2
|  |  | Lobes | NW | (2.9$\pm$ 0.3) E-02 | 1.2465E-01 | 28 $\pm$ 4% | -2.0 $\pm$ 0.2
|  |  |  | SE | (1.3 $\pm$ 0.3) E-02 | 4.9203E-02 | 31 $\pm$ 9% | -2 $\pm$ 1
|  |  | SE jet |  | (3.0 $\pm$ 0.5) E-03 | 1.5625E-02 | 24 $\pm$ 5 % | -2.4 $\pm$ 0.5
|  |  | NW jet knot /hotspot |  | (1.6 $\pm$ 0.5) E-04 | 1.8104E-03 | 26 $\pm$ 8% | -1.8 $\pm$ 0.7
PG1048-090 | 9.089E-04 | 5.375E-05 | Core |  | (8 $\pm$ 2) E-05 | 4.9798E-02 | 2.1 $\pm$ 0.4 % | 0.2 $\pm$ 0.4
|  |  | Hotspot region | NW | (1.4 $\pm$ 0.1) E-02 | 2.4785E-01 | 10 $\pm$ 2 % | -0.64 $\pm$ 0.13
|  |  |  | SE | (3.1 $\pm$ 0.1) E-02 | 2.8795E-01 | 14 $\pm$ 2% | -1.2 $\pm$ 0.1
PG1100+772 | 3.292E-05 | 4.032E-06 | Core |  | (1.17 $\pm$ 0.05) E-03 | 1.17E-01 | 2.7 $\pm$ 0.4% | 0.55$\pm$0.006
|  |  | Hotspot region | W | (1.751 $\pm$ 0.009) E-02 | 2.1315E-01 | 10.48 $\pm$ 0.08% | -1.051$\pm$0.003
|  |  |  | E | (1.314 $\pm$ 0.007) E-02 | 1.1189E-01 | 14.3 $\pm$ 0.7% | -0.938$\pm$0.004
|  |  | Lobes | W | (3.5 $\pm$ 0.2) E-02 | 1.9166E-01 | 23 $\pm$ 2% | -0.86$\pm$0.07
|  |  |  | E | (1.8 $\pm$ 0.3) E-02 | 8.5160E-02 | 25 $\pm$ 4% | -1.2$\pm$0.2
|  |  | Jet |  | (6.4 $\pm$ 0.3) E-03 | 5.7812E-02 | 15 $\pm$ 4% | -0.86$\pm$0.07
|  |  | Ridge | E | (1.05 $\pm$ 0.07) E-02 | 4.173E-02 | 23 $\pm$ 3% | -0.68$\pm$0.07
PG1103-006 | 2.511E-05 | 2.511E-05 | Core |  | (2.08 $\pm$ 0.07) E-03 | 1.37E-01 | 5.8 $\pm$ 0.3 % | -0.319$\pm$0.004
|  |  | Hotspot region | NW | (2.18 $\pm$ 0.08) E-03 | 3.1218E-02 | 13 $\pm$ 1 % | -0.76$\pm$0.03
|  |  |  | SE | (1.11 $\pm$ 0.02) E-02 | 8.8719E-02 | 18.5 $\pm$ 0.8% | -0.93$\pm$0.02
|  |  | Lobes | NW | (1.47 $\pm$ 0.07) E-02 | 1.3515E-01 | 19 $\pm$ 2 % | -0.7$\pm$0.3
|  |  |  | SE | (7.2 $\pm$ 0.7) E-03 | 1.2988E-01 | 20 $\pm$ 2 % | -0.6$\pm$0.2
|  |  |  | SW | (2.4 $\pm$ 0.5) E-03 | 1.3785E-02 | 25 $\pm$ 6% | -1.9$\pm$0.2
|  |  |  | NE | (9 $\pm$ 2) E-04 | 2.7121E-03 | 20 $\pm$ 5% | -0.9$\pm$0.3
|  |  | NW jet |  | (7.6 $\pm$ 0.2) E-03 | 1.1045E-01 | 10.2 $\pm$ 0.5 % | -0.806$\pm$0.008
PG1226+023 | 2.237E-03 | 2.439E-04 | Core |  | (2.128 $\pm$ 0.009)E+00 | 2.16E+01 | 11 $\pm$ 2% | -0.327 $\pm$ 0.004
|  |  | Hotspot region | SW | (5.6 $\pm$ 0.2)E-01 | 5.19E+00 | 15 $\pm$ 2% | -0.902 $\pm$ 0.03
PG1309+355 | 8.706E-05 | 9.592E-06 | Core |  | (1.3 $\pm$ 0.2)E-04 | 4.69E-02 | 0.37 $\pm$ 0.07% | 0.17 $\pm$ 0.06
PG1704+608 | 4.671E-05 | 1.014E-05 | Core |  | (1.36 $\pm$ 0.08) E-03 | 2.12E-02 | 8.2 $\pm$ 0.9% | -0.8$\pm$0.7
|  |  | Hotspot region | NE (up) | (4.54 $\pm$ 0.02) E-02 | 5.2227E-01 | 11.5 $\pm$ 0.4% | -0.96$\pm$0.02
|  |  |  | NE (lw) | (3.75 $\pm$ 0.02) E-02 | 2.1331E-01 | 15.4 $\pm$ 0.9% | -1.06$\pm$0.04
|  |  |  | SW | (1.8 $\pm$ 0.2) E-03 | 9.6707E-03 | 16 $\pm$ 2% | -2.0$\pm$0.2
|  |  | Lobes | NW | (2.0 $\pm$ 0.5) E-03 | 2.3813E-02 | 23 $\pm$ 7% | -0.2$\pm$0.7
|  |  |  | NE | (1.4 $\pm$ 0.1) E-02 | 1.6121E-01 | 13 $\pm$ 2% | -1.2$\pm$0.5
|  |  |  | SW | (2.2 $\pm$ 0.7) E-03 | 4.1280E-02 | 14$\pm$ 3% | -1.9$\pm$0.5
Note. Column (1): PG source name. Column (2): R.M.S noise in Stokes I (total
intensity) image. Column (3): R.M.S noise in polarized intensity image. Column
(4):
Region of the source and location. Column (5): Polarized flux density. Column
(6): Total flux density. Column (7): Fractional Polarization. Column (8):
Spectral index
† FP at intensity peak position is 0.9 $\pm$ 0.3%. ∗ FP at intensity peak
position is 0.27 $\pm$ 0.09%.

##  4 Results

We have presented the total intensity and polarization images, as well as the
in-band spectral index images in Figures 2-12. The quantitative results have
been noted in Table 4 where we have adopted the definitions of a jets, knots
and hotspots as detailed by Bridle & Perley (1984). We find extensive
polarization in the cores, jets, lobes and hotspots of all the quasars, with
the exception of PG1309+355 which remains largely unresolved but shows core
polarization (see Table 4). The radio morphology shows distortions and
complexities. The spectral indices are typically flat/inverted for the radio
cores, with the sole exception of PG1704+608, but steep in the jets and
hotspots (Table 4). Below we describe these details for the individual
sources.

###  4.1 Notes on individual sources

####  4.1.1 PG0003+158

This SSRQ (aka 4C+15.01) was imaged with the VLA A-array at 5 GHz by Miller et
al. (1993) who detected only the bright and compact regions (i.e., core and
hotspots) of this large double radio source. Our image detects the diffuse
lobe emission as well and shows extensive polarization in its core, lobes and
hostpots (Figure 2). The inferred B-field is transverse to the jet direction
for the optically thick radio core. The southern jet knot has an inferred
B-field morphology inconsistent with a shocked region; the B-field vectors are
aligned with the jet flow rather than perpendicular. This jet knot could be a
site for particle re-acceleration/energizing which should show a relatively
flat spectral index without B-field enchancement. However, the spectral index
of the jet knot is $-1.3\pm 0.1$, making it steeper than the $\alpha$ of the
hotspots ($-1.2\pm 0.3$ for the southern hotspot and $-1.0\pm 0.2$ for the
northern hotspot), suggesting this to be a portion of the jet itself. This is
then consistent with the findings of Bridle et al. (1994) who found that jet
knots that are elongated in directions close to that of the jet, the EVPA
vectors tend to be orthogonal to the jet axis. The inferred B-fields in the
lobes are largely aligned with the local jet direction assuming optically thin
emission. A jet region entering the southern hotspot is highly polarized,
exhibiting parallel inferred B-fields. The inferred B-fields are aligned with
the edges of the hotspot regions. Recent VLBI results from Wang et al. (2022)
indicate that the parsec-scale approaching jet is towards the south-east but
offset from the straight line connecting the core to the southern hotspot,
indicating jet curvature.

Figure 2: VLA 6 GHz contour image of quasar PG0003+158 (4C 15.01) superimposed
with red (top) polarized intensity vectors and (bottom) in-band spectral index
image. The inferred B-fields are perpendicular to the polarization vectors
assuming optically thin emission. The beam is $1.71\arcsec\times 1.13\arcsec$
with a PA of $55.18^{\circ}$. The peak surface brightness, $I_{P}$ is 161.0
mJy beam-1. The contour levels in percentage of the peak surface brightness
$I_{P}$ are
$(-0.045,~{}0.045,~{}0.09,~{}0.18,~{}0.35,~{}0.7,~{}1.4,~{}2.8,~{}5.6,~{}11.25,~{}22.5,~{}45,~{}90)$
Jy beam-1. The length of the EVPA vectors is proportional to polarized
intensity with $5\arcsec$ corresponding to 1.25 mJy beam-1.

####  4.1.2 PG0007+106

This SSRQ (aka III Zw 2) has been classified as a radio intermediate quasar by
(Miller et al., 1993; Falcke et al., 1996b, a). It’s host galaxy has prominent
tidal tails and arms indicative of a recent merger systems (Surace et al.,
2001; Dunlop et al., 1993). The source is known to be variable at both radio
and optical wavelengths (e.g. Schnopper et al., 1978; Terasranta et al.,
1992). Using the 685 MHz uGMRT and 6 GHz VLA polarimetric observations, Silpa
et al. (2021a) were able to identify the signatures of a jet+wind-like
stratification in the radio outflow of this PG quasar (see Figure 3). The
possible stratification in the outflow was revealed by the presence of
different inferred B-field structures in the different frequency and different
resolution images; uGMRT images sampled the outer sheath of the jet/lobe while
the VLA images sampled the inner spine of the jet/lobe. The VLBI image from
Wang et al. (2022) shows an unresolved core.

####  4.1.3 PG1004+130

This SSRQ (aka 4C+13.41) appears to be a restarted source as observed in the
bright jet-core-counterjet emission on the 30$\arcsec$-scales (Figure 4). A
clear surface brightness discontinuity is observed between the jet-counterjet
and the larger lobe emission. The inferred B-field is transverse to the jet
direction for the optically thick radio core. The terminal region on the
western side does not show a typical B-field configuration in its hotspot
(i.e., transverse to the jet direction). This could indicate weakening of the
hotspot as the previous episode of activity has died down. The jet seen inside
the south eastern lobe shows B-field vectors parallel to the jet direction
(assuming optically thin emission) ending in a weak hotspot with B-field
vectors nearly perpendicular to the jet direction. This B-field structure is
similar to the one seen in 3C219 by Clarke et al. (1992) for its restarting
jet. The south eastern lobe shows diffuse emission that is not well detected
in our higher resolution images. The VLBA image from Wang et al. (2022)
indicates that the parsec-scale (approaching) jet is aligned well with the
south-eastern inner jet.

Gopal-Krishna & Wiita (2000) have classified this quasar as a hybrid FRI/FRII
morphology source and Miller et al. (2006) found an X-ray counterpart a little
upstream of the radio FR I jet, with a flat photon index and a concave SED
more typical of FR II quasar jets than FR I jets. Gopal-Krishna & Wiita (2000)
have explained this hybrid nature as resulting from environmental differences
in density, i.e. the density of the surrounding medium is higher towards the
SE causing decollimation. This source is also a broad absorption line (BAL)
QSO (Wills et al., 1999).

####  4.1.4 PG1048$-$090

This SSRQ (aka 3C246) is a member of a galaxy cluster (Yates et al., 1989). It
is relatively poorly imaged at radio frequencies compared to the other
sources. Previous VLA images show the presence of a core and two hotspots;
however the jet and lobe emission is very faint (Miller et al., 1993; Dennett-
Thorpe et al., 2000; Kellermann et al., 1994). We find a similar structure in
our images (Figure 5). The Y-shaped ears around the north-western hotspot are
due to deconvolution errors that remain in spite of self-calibration and must
be regarded as image artefacts. We find that the core and two hotspots show
extensive polarization; however their fractional polarization is low. This
would be consistent with the presence of X-ray emitting gas in the galaxy
cluster (e.g., Sarazin, 1986). The inferred B-field is transverse to the jet
direction for the optically thick radio core. The western hotspot shows a
polarization structure (B-field aligned along the jet direction) consistent
with the jet entering the hotspot region. The in-band spectral index image
(Figure 5) shows that the core has an inverted spectrum while the hotspots
have steep spectra. The VLBA image from Wang et al. (2022) indicates that the
parsec-scale (approaching) jet is in the north-west direction.

####  4.1.5 PG1100+772

This SSRQ (aka 3C249.1) is a candidate restarted source (Marecki, 2012;
Fernini, 2007, Figure 6). The western lobe is FRII-like while the eastern one
does not have a terminal hotspot and is FRI-like. This makes the source a
hybrid FRI/FRII radio source. The inferred B-field is transverse to the jet
direction for the optically thick radio core. The polarization features in the
inner “hotspot” are consistent with a terminal shock in that the B-vectors are
transverse to the jet direction here (Figure 7). Further down the eastern
lobe, the B-field vectors resemble the bubble-like lobe structures observed in
several Seyfert galaxies (Kharb et al., 2006; Sebastian et al., 2020) and is
relatively flat in spectral index. The VLBI image from Wang et al. (2022)
shows an unresolved core.

This source was observed at VLA 5 GHz B/C array by Bridle et al. (1994) and
Gilbert et al. (2004) who identified that the two lobes are asymmetric in
size, intensity and surface brightness. The west lobe is edge-brightened with
a well resolved hotspot near its western end. The east lobe is edge-darkened
except for a resolved ridge along its southern boundary. Bridle et al. (1994)
note that a jet enters it on its extreme southern edge and terminates abruptly
at $7.7\arcsec$ ($\sim$34 kpc) from the central feature. The degree of
polarization is greatest at the edges of the lobes, particularly east of
eastern hotspot at the end of the jet, where it reaches 55% to 65%.
Interestingly, we have detected a polarization of 44$\pm$4% in this region
which is a $\sim$10 - 40% reduction. The EVPA vectors are roughly
perpendicular to the main ridge in the east lobe and to the outer boundaries
of the west lobe. At 0.35$\arcsec$ resolution from the combined A, B, and C
configuration data, all structures in the east lobe are fully resolved. The
jet bends at least twice on its path to the resolved terminal hot spot at its
east end.

Many different explanations have been proposed in the literature for the
peculiar morphology of PG1100+772, including a dense cluster environment
(Hintzen, 1984), cooling flows (Crawford et al., 1988), interacting systems
(Stockton & MacKenty, 1983), the “flip-flop” mechanism (Lonsdale & Morison,
1983) and restarted activity (Marecki, 2012). There is an emission line system
extending for several arcseconds around the quasar, plus an extended optical
continuum that may be of stellar origin (Richstone & Oke, 1977; Boroson & Oke,
1984).

Figure 3: VLA 6 GHz contour image of quasar PG0007+106 superimposed with red
(top) polarized intensity vectors and (bottom) in-band spectral index image.
The inferred B-fields are perpendicular to the polarization vectors assuming
optically thin emission. The beam is $2.04\arcsec\times 1.12\arcsec$ with a PA
of $53.54^{\circ}$. The peak surface brightness, $I_{P}$ is 123.98 mJy beam-1.
The contour levels in percentage of the peak surface brightness $I_{P}$ are
$(-0.045,~{}0.045,~{}0.09,~{}0.18,~{}0.35,~{}0.7,~{}1.4,~{}2.8,~{}5.6,~{}11.25,~{}22.5,~{}45,~{}90)$
Jy beam-1. The length of the EVPA vectors is proportional to polarized
intensity with $5\arcsec$ corresponding to 0.156 mJy beam-1 (see Silpa et al.,
2021a)

.

Figure 4: VLA 6 GHz contour image of quasar PG1004+130 (4C 13.41) superimposed
with red (top) polarized intensity vectors and (bottom) in-band spectral index
image. The beam is $1.35\arcsec\times 1.29\arcsec$ with a PA of
$-80.03^{\circ}$. The peak surface brightness, $I_{P}$ is 28.62 mJy beam-1.
The contour levels in percentage of the peak surface brightness $I_{P}$ are
$(-0.4,~{}0.4,~{}1.0,~{}2.0,~{}4.0,~{}8.0,~{}16,~{}32,~{}64)$ Jy beam-1. The
length of the EVPA vectors is proportional to polarized intensity with
$10\arcsec$ corresponding to 2.27 mJy beam-1. The inset shows a zoomed-in
image of the core and $0.5\arcsec$ corresponding to 0.05 mJy beam-1.

Figure 5: VLA 6 GHz contour image of quasar PG1048-090 (3C246) superimposed
with red (top) polarized intensity vectors and (bottom) in-band spectral index
image. The beam is $3.35\arcsec\times 3.35\arcsec$ with a PA of $0^{\circ}$.
The peak surface brightness, $I_{P}$ is 0.1836 Jy beam-1. The contour levels
in percentage of the peak surface brightness $I_{P}$ are
$(-2.5,~{}2.5,~{}5.0,~{}10.0,~{}20.0,~{}40.0,~{}80.0)$ Jy beam-1. The length
of the EVPA vectors is proportional to polarized intensity with $5\arcsec$
corresponding to 6.25 mJy beam-1.

Figure 6: VLA 6 GHz contour image of quasar PG1100+772 superimposed with red
(top) polarized intensity vectors and (bottom) in-band spectral index image.
The inferred B-fields are perpendicular to the polarization vectors assuming
optically thin emission. The beam is $1.79\arcsec\times 1.00\arcsec$ with a PA
of $67.35^{\circ}$. The peak surface brightness, $I_{P}$ is 107.6 mJy beam-1.
The contour levels in percentage of the peak surface brightness $I_{P}$ are
$(-0.09,~{}0.09,~{}0.18,~{}0.35,~{}0.7,~{}1.4,~{}2.8,~{}5.6,~{}11.25,~{}22.5,~{}45,~{}90)$
Jy beam-1. The length of the EVPA vectors is proportional to polarized
intensity with $5\arcsec$ corresponding to 3.57 mJy beam-1.  Figure 7:  VLA 6
GHz contour image of the core and eastern hotspot of quasar PG1100+772
(3C249.1) superimposed with red polarization vectors whose length is
proportional to fractional polarization, rotated by 90∘ to indicate the
B-field direction, assuming optically thin emission. The beam is
$1.79\arcsec\times 1.00\arcsec$ with a PA of $67.35^{\circ}$. The peak surface
brightness, $I_{P}$ is 107.6 mJy beam-1. The contour levels in percentage of
the peak surface brightness $I_{P}$ are
$(-0.09,~{}0.09,~{}0.18,~{}0.35,~{}0.7,~{}1.4,~{}2.8,~{}5.6,~{}11.25,~{}22.5,~{}45,~{}90)$
Jy beam-1. 1$\arcsec$ length of the vector corresponds to 25%. Figure 8:  VLA
6 GHz contour image of PG1103$-$006 (4C-00.43) superimposed with red
polarization vectors whose length is proportional to fractional polarization,
rotated by 90∘ to indicate the B-field direction, assuming optically thin
emission. The beam is $1.79\arcsec\times 1.15\arcsec$ with a PA of
$-51.79^{\circ}$. The peak surface brightness, $I_{P}$ is 128.7 mJy beam-1.
The contour levels in percentage of the peak surface brightness $I_{P}$ are
$(-0.045,~{}0.045,~{}0.09,~{}0.18,~{}0.35,~{}0.7,~{}1.4,~{}2.8,~{}5.6,~{}11.25,~{}22.5,~{}45,~{}90)$
Jy beam-1. 2$\arcsec$ length of the vector corresponds to 62.5%.

Figure 9: VLA 6 GHz contour image of quasar PG1103$-$006 superimposed with red
(top) polarized intensity vectors and (bottom) in-band spectral index image.
The beam is $1.79\arcsec\times 1.15\arcsec$ with a PA of $-51.79^{\circ}$. The
peak surface brightness, $I_{P}$ is 128.7 mJy beam-1. The contour levels in
percentage of the peak surface brightness $I_{P}$ are
$(-0.09,~{}0.09,~{}0.18,~{}0.35,~{}0.7,~{}1.4,~{}2.8,~{}5.6,~{}11.25,~{}22.5,~{}45,~{}90)$
Jy beam-1. The length of the EVPA vectors is proportional to polarized
intensity with $2\arcsec$ corresponding to 2.00 mJy beam-1.

####  4.1.6 PG1103$-$006

This RL quasar (aka 4C -00.43) is an X-shaped radio source (Figure 8,9). The
jets appear to be S-shaped, especially going North, which could be consistent
with jet precession. This quasar has been observed previously by the VLA by
Hutchings et al. (1998) who did not detect the X-shape as prominently.
Hutchings et al. (1996) studied this source as those residing inside galaxy
cluster environments. Rector et al. (1995) did not see any correlation between
galaxy density and quasar radio morphology in their sample of QSOs of which
PG1103$-$006 is one. Such a correlation is expected from jet-ICM interaction.
Our polarization structures in the inner lobes match those of Reid et al.
(1999); however, they also did not pick up the X-shaped lobe emission in their
VLA 4.9 GHz B-array images. The VLBI image from Wang et al. (2022) shows that
the parsec-scale (approaching) jet is aligned with the north-west jet
direction.

The inferred B-field structure in the north-western jet stays aligned with the
jet throughout, all the way to the north-western hotspot. The inferred B-field
in the radio core is transverse to the jet direction for the optically thick
core. The inferred B-field appears to be be bow-shock-like in both the
hotspots, as seen in the southern hotspot of III Zw 2. Extensive polarization
is observed in the X-shaped wings. Although the inferred B-fields are aligned
with the direction of the wings (see Figure 8), the vectors do not follow the
flow “around the corner” unambiguously. Nevertheless, we do find them to be
largely consistent with the “hydrodynamical backflow model” (see Cotton et
al., 2020). We discuss the models for X-shaped sources in section 6 ahead.

####  4.1.7 PG1226+023

This famous FSRQ (aka 3C273) is the first identified quasar (Schmidt, 1963).
It is one of the closest and most luminous of all quasars. Imaging of this
source has been done at multiple wavebands (e.g., Perley & Butler, 2017).
3C273 has a bright, flat-spectrum nucleus with highly variable flux density,
and a one-sided, highly polarized, narrow jet extending $\sim 23\arcsec$ to
the southwest of the nucleus. Our 5 GHz image (Figure 10) is consistent with
the previous total intensity, polarization and spectral index images of 3C273
(Perley & Butler, 2017). The inferred B-field is transverse to the jet
direction in the optically thick radio core, i.e., the unresolved base of the
jet. The inferred B-field is aligned with the jet direction along the jet and
becomes transverse to it at the position of the southern hotspot. The VLBI
image from Wang et al. (2022) indicates that the parsec-scale (approaching)
jet is towards the south-west and shows clear curvature.

####  4.1.8 PG1309+355

This radio-intermediate FSRQ (aka Ton1565) has been suggested to be a boosted
RQ quasar (Miller et al., 1993). It shows a compact radio morphology in VLA A
and D array 5 GHz data (Kellermann et al., 1994). Its host galaxy shows
evidence of a spiral-like substructure (Kim et al., 2008). In view of its
small viewing angle, strong UV absorption lines are observed in its HST
spectrum (Brandt et al., 2000). Brandt et al. (2000) note that it is
moderately X-ray weak for a radio-loud QSO. We had chosen this object as being
potentially extended based on its NVSS image. However, we detect only a
compact radio core in our 5 GHz data (Figure 11) which shows marginal
fractional polarization ($\sim 0.4$%). Our VLA data has failed to detect any
extended diffuse emission or hotspots on kpc-scales. An archival VLA A-array
image555http://www.vla.nrao.edu/astro/archive/pipeline/position/J131217.7+351521/
at 22 GHz (resolution $100\times 75$ mas) does indicate a faint jet-like
extension to the west of the core. If this is indeed the kpc-scale jet
direction in PG1309+355, the inferred B-field is transverse to the jet
direction for optically thick core emission. The VLBI image from Wang et al.
(2022) shows an unresolved core.

The in-band spectral index (Figure 11) also suggests a gradient to the south-
west which could hint at the presence of an unresolved core-jet structure. Its
EVN image, however, suggests a mas-scale core-jet structure to the south-east
(Falcke et al., 1996b). It is possible that the jet curves towards the south-
west on scales intermediate between the VLA and EVN+MERLIN. Large jet bents
going from parsec- to kpc-scale are commonly observed in blazars (Kharb et
al., 2010). Moreover, Falcke et al. (1996a) suggest that PG1309+355 might not
be a boosted radio-quiet quasar based on their observations.

####  4.1.9 PG1704+608

This SSRQ (aka 3C351) shows the presence of multiple hotspots and a one-sided
distored radio lobe in VLA and GMRT images (Bridle et al., 1994; Vaddi et al.,
2019). A 15 GHz image from the Cambridge 5-km telescope shows that in the
northern hotspot, the southern component is compact while the northern
component shows extended emission (Laing, 1981). Our 5 GHz image shows the
complex radio morphology in total intensity and polarization (Figure 12). The
inferred B-field is parallel to the jet direction for the optically thin radio
core. The southern hotspot shows the characteristic B-field morphology of a
hotspot (transverse to the jet direction). The jet direction appears to have
suddenly changed in this source as is also visible in the misaligned northern
radio lobe. In in-band spectral index image (Figure 12) shows similarly steep
spectrum in both the northern as well as southern hotspots. Both lobes show
diffuse emission that are not well detected in our higher resolution images.
The VLBA image from Wang et al. (2022) does not resolve the core.

Overall, we find that the fractional polarization in the radio cores ranges
from 0.8% to 10% and in the jets/lobes from 10% to 40% (see Table 4). The
radio cores primarily display inferred B-fields transverse to the jet
direction (assuming optically thick emission) except PG1704+608 where the core
emission is optically thin the B-field vectors are aligned along the jet
direction. The inferred B-fields are aligned parallel to the local jet
directions whenever a jet or a jet knot is observed. The inferred B-field
becomes transverse in the compact hotspot regions. However, several hotspots
like those in PG1004+130 and PG1100+772, show a more complex B-field
structure. We discuss these in greater detail in Section 6 ahead. The B-fields
in the radio lobes are almost always aligned with the lobe edges.

Figure 10: VLA 6 GHz contour image of quasar PG1226+023 (3C273) superimposed
with red (top) polarized intensity vectors and (bottom) in-band spectral index
image. The beam is $1.37\arcsec\times 1.09\arcsec$ with a PA of
$-0.43^{\circ}$. The peak surface brightness, $I_{P}$ is 21.05 Jy beam-1. The
contour levels in percentage of the peak surface brightness $I_{P}$ are
$(-0.045,~{}0.045,~{}0.09,~{}0.18,~{}0.35,~{}0.7,~{}1.4,~{}2.8,~{}5.6,~{}11.25,~{}22.5,~{}45,~{}90)$
Jy beam-1. The length of the EVPA vectors is proportional to polarized
intensity with $2\arcsec$ corresponding to 333.33 mJy beam-1.

Figure 11: VLA 6 GHz contour image of quasar PG1309+355 (Ton 1565)
superimposed with red (top) polarized intensity vectors and (bottom) in-band
spectral index image. The beam is $2.07\arcsec\times 1.19\arcsec$ with a PA of
$73.31^{\circ}$. The peak surface brightness, $I_{P}$ is 0.047415 Jy beam-1.
The contour levels in percentage of the peak surface brightness $I_{P}$ are
$(-0.7,~{}0.7,~{}1.4,~{}2.8,~{}5.6,~{}11.25,~{}22.5,~{}45,~{}90)$ Jy beam-1.
The length of the EVPA vectors is proportional to polarized intensity with
$1.0\arcsec$ corresponding to 0.23 mJy beam-1.

Figure 12: VLA 6 GHz contour image of quasar PG1704+608 (3C351) superimposed
with red (top) polarized intensity vectors and (bottom) in-band spectral index
image. The beam is $1.82\arcsec\times 0.97\arcsec$ with a PA of
$44.86^{\circ}$. The peak surface brightness, $I_{P}$ is 317.2 mJy beam-1. The
contour levels in percentage of the peak surface brightness $I_{P}$ are
$(-0.09,~{}0.09,~{}0.18,~{}0.35,~{}0.7,~{}1.4,~{}2.8,~{}5.6,~{}11.25,~{}22.5,~{}45,~{}90)$
Jy beam-1. The length of the EVPA vectors is proportional to polarized
intensity with $5\arcsec$ corresponding to 4.16 mJy beam-1.

##  5 Global correlations

We have looked at various global correlations for the PG “blazar” sample using
the most recent and reliable estimates of BH masses, accretion rates and SFR
values. As far as possible, we have relied on estimates that were obtained
uniformly for the various blazar sub-classes. These properties are listed in
Table 2. We have used the Kolmogorov-Smirnov (KS) test for evaluating
statistical differences between properties of various populations and the
Kendall-$\tau$ test to measure the significance of correlations between
different properties. We report the radio jet kinetic power $\bar{Q}$ without
errors as systematic uncertainties in the estimation methods dominate the
statistical uncertainty in the data. $M_{BH}$ and $\dot{M}$ do not have
reported errors in Shangguan et al. (2018); Wu et al. (2009) and Davis & Laor
(2011) due to the same. The errors in $R_{c}$ are smaller than the symbol
sizes in Figure 15.

Figure 13: Distribution of redshifts $z$ w.r.t. the log of BH masses
($M_{\mathrm{BH}}/M_{\sun}$) for the sample blazars.

###  5.1 Black Hole Mass

The SMBH masses of the sample blazars were obtained from Wu et al. (2009) and
Shangguan et al. (2018). We note that the BH masses were estimated from the
H$\beta$ line luminosity in Shangguan et al. (2018) and from the R-band host
galaxy magnitudes in Wu et al. (2009); these different mass estimation methods
might potentially be introducing biases between the blazar sub-classes. We
note that the BH mass estimates obtained by converting a single-band optical
luminosity using an empirical correlation, as obtained by Wu et al. (2009),
may be suspect. This may be the reason for the unusually small BH masses in
PG1424+240 and PG1553+113.

Figure 14: Log of radio core fractional polarization $\mathrm{FP_{C}}$ (%)
versus log of BH masses ($M_{BH}/M_{\sun}$) of the quasars.

The BH masses for the quasars in the current paper however, all come from
Shangguan et al. (2018). We discuss the possible selection biases affecting
the BH masses in the PG sample in Section 6. The distribution of BH masses
$\log_{10}(\mathrm{M_{BH}/M_{\sun}})$ and redshifts for the sample blazars are
shown in Figure 13. We find that the hypothesis that quasars and BL Lacs have
different BH masses cannot be ruled out at the 95% confidence level (KS test
p=0.0007). RL quasars have systematically larger BH masses compared to the BL
Lacs in our sample. However, we also find that the SSRQs have systematically
higher BH masses compared to the FSRQs (KS test p=0.0027), as well as BL Lacs
and FSRQs combined (KS test p=0.00009). So the major BH differences are
between the SSRQs and the classical blazars. We find that the BH masses seem
to be marginally correlated with the core fractional polarization
$\mathrm{FP_{C}}$ (Kendall $\tau$ test $p=0.044$) and anti-correlated with
radio core prominence $R_{C}$ (Kendall $\tau$ test $p=0.012$) for the 9
quasars studied here (Figures 14 and 15). We discuss the implications of these
findings in Section 6.

Figure 15: Log of radio core prominence $R_{C}$ versus log of BH masses
($M_{BH}/M_{\sun}$) of the quasars.

###  5.2 Star Formation Rate

The SFR for the PG quasars reported here have been obtained from Xie et al.
(2021) except for PG1226+023 which was obtained from (Westhues et al., 2016).
The conventional methods to determine SFR for non-active galaxies (which
include rest-frame UV-optical SED fitting, optical emission lines, mid
infrared (IR) flux density, e.g., Kennicutt, 1998; Kennicutt & Evans, 2012)
may not be reliable for galaxies hosting AGN, especially of Type I. Typically,
in the rest-frame far-IR, the contrast between the typical SED of a star
forming galaxy and an AGN SED is the largest and the thermal far-IR continuum
emission from cool dust grains primarily traces star formation from the host
galaxy and is used in most studies (e.g., Haas et al., 2003; Dai et al.,
2018). The total IR luminosity (LIR) of the host galaxy was calculated by
integrating the Draine & Li (2007) component of the best-fit LIR model. LIR
was obtained from 8-1000 $\mu$m measurements. The SFR derived from LIR can
only provide us with an upper limit for host galaxy SFR, especially for highly
beamed or high luminosity AGN. In the case of BL Lac objects, optical emission
from BL Lacs is often dominated by the nuclear source. The FIR and
submillimeter also show high flux densities and synchrotron contamination from
radio region due to jet triggering and beaming angle (Seal Braun, 2017).
Therefore, we cannot use LIR as a surrogate for SFR in the case of BL Lac
objects. We find that the SFR values are not significantly different between
FSRQs and SSRQs (KS test $p=0.27$).

Figure 16: Log of radio core fractional polarization $\mathrm{FP_{C}}$ (%)
versus core spectral index $\alpha_{C}$. Figure 17: Log of radio core
fractional polarization $\mathrm{FP_{C}}$ (%) versus log of total luminosity
at 150 MHz ($L_{150~{}MHz}$) of the quasars.

###  5.3 Jet Power

We find a correlation between the radio core fractional polarization and the
radio core spectral index (Kendall $\tau$ test $p=0.044$, see Figure 16) for
the 9 quasars; cores with relatively steep spectral indices have a higher
fractional polarization. We note that the core spectral indices are typically
flat/inverted with the exception of PG1704+608. This implies a relative
dominance of unresolved jet emission in the radio core emission.

We find a correlation between the radio core fractional polarization and the
150 MHz total radio luminosity (Kendall $\tau$ test $p=0.024$, see Figure 17)
for the 9 quasars; cores with higher fractional polarization also have higher
total radio luminosity at 150 MHz. This could imply that more organized
B-fields in the cores lead to higher core fractional polarization and to more
radio powerful sources. Interestingly, we found no correlation between the
radio core fractional polarization and the accretion rates for the 9 quasars
(Kendall $\tau$ test $p=0.180$).

We have estimated the long term, time-averaged bulk radio jet kinetic power
$\bar{Q}$ of jets using the radio luminosity at 151 MHz as a surrogate for the
luminosity of the radio lobes by using the relation given by Punsly et al.
(2018),

$\bar{Q}=3.8\times 10^{45}\it{f}~{}L_{151}^{6/7}~{}\mathrm{erg~{}s^{-1}}$

where $L_{151}$ is radio luminosity at 151 MHz in units of $10^{28}$ W Hz-1
sr-1 and $f\approx 15$ (Blundell & Rawlings, 2000). We obtained the $L_{151}$
from the TGSS survey flux densities (Intema et al., 2017) using the relation,
$L_{151}=[D_{L}^{2}~{}F_{151}]/[(1+z)^{(1+\alpha)}]$ W Hz-1 sr-1, 666We note
that there is no $4\pi$ factor because of the anisotropic jet emission, e.g.,
see Peacock (1999). where we have used the typical average $\alpha=-0.7$ for
the extended emission. We find that $\bar{Q}$ ranges from $1.50\times 10^{42}$
erg s-1 to $4.85\times 10^{45}$ erg s-1 for the PG blazar sample. In Figures
18-20, we have examined the relationship between $\bar{Q}$ and BH masses as
well as accretion rates. For the entire blazar sample, the jet power appears
to be significantly correlated with BH mass (Figure 18; Kendall $\tau$ test
$p=0.0025$). However, this correlation disappears when the blazar sub-samples
(of FSRQs, SSRQs and BL Lacs) are considered individually, suggesting that
there isn’t a strong correlation between these two parameters.

We looked for a correlation between jet power and accretion rates ($\dot{M}$)
for the blazars. We obtained $\dot{M}$ for the quasars from Davis & Laor
(2011), except for the BAL QSO, PG1004+130. For this source, we have adopted
an $\eta=0.1$ value and Eddington ratio $\dot{m_{Edd}}=0.09$ from Luo et al.
(2013) and used it to compute its accretion rate. Corresponding $\dot{M}$
values were not available for the BL Lacs. We find that the jet power is
correlated with accretion rate for both FSRQs (Kendall $\tau$ test $p=0.016$)
and SSRQs (Kendall $\tau$ test $p=0.060$) with the former being a stronger
correlation. Taken together, the jet power of quasars (FSRQs + SSRQs) remains
significantly correlated with the accretion rate (Figure 19; Kendall $\tau$
test $p=0.020$). Interestingly, we find that the jet power is correlated with
the galactic SFR when quasars are considered collectively, (Kendall $\tau$
test $p=0.0515$) but not when taken individually (Figure 20; FSRQ Kendall
$\tau$ test $p=0.0833$ and SSRQ Kendall $\tau$ test $p=0.4772$). We discuss
the implications of this finding in the next section.

Figure 18: Distribution of jet power in erg s-1 versus BH masses
$\mathrm{\log_{10}(M_{BH}/M_{\sun})}$ for the PG blazar sample. Figure 19:
Distribution of jet power in erg s-1 versus accretion rates $\dot{M}$ for the
PG blazar sample. Figure 20: Distribution of jet power in erg s-1 versus SFR
$\mathrm{\log_{10}(M_{\sun}/yr)}$ for the PG quasars.

##  6 Discussion

Our VLA observations reveals that most of the quasars have a disturbed or
hybrid FRI/FRII-type radio morphology. Some of them appear to be restarted
sources as well, showing clear surface brightness discontinuities between the
episodes. We find that in the 9 quasars studied here, the typical hotspot
B-field morphology signifying a terminal shock (i.e., B-field perpendicular to
the jet direction), is often seen in only one of the hotspots. The inferred
B-fields in the radio cores are transverse to the jet direction in all the
sources assuming optically thick emission with the exception of PG1704+608
where the B-field are aligned along the jet direction and the core emission is
optically thin. The inferred B-fields are aligned parallel to the local jet
directions whenever a jet or a jet knot is observed. The in-band spectral
index images show that while the radio cores in all sources exhibit
flat/inverted spectral indices (with the exception of PG1704+608), the
hotspots in several sources have relatively steep spectral indices. This is
also consistent with the polarization structures, where the hotspots appear to
not be compact terminal shocked regions, but rather locations of jet bends or
bow-shock like structures. Such bow-shock like features are consistent with
restarted jet activity (e.g., Clarke & Burns, 1991; Silpa et al., 2021a).

Assuming that the aligned B-fields in the jets signify the dominance of a
poloidal B-field component in them, and the transverse B-fields in the cores
signify a dominant toroidal B-field component at the unresolved bases of the
jets, then we see a transition from a toroidal field to a poloidal field along
the radio jets. However, it has been suggested that the toroidal B-field
component becomes more dominant and the poloidal component decays faster with
distance from the core, since the poloidal field varies as r-2 and the
toroidal field varies as r-1 v-1 (e.g., Begelman et al., 1984). One then needs
to invoke some mechanism that can sustain poloidal B-fields over large
distances, and explain the quasar results, such as the $\alpha$-turbulence
dynamo mechanism (Parker, 1955). Alternately, Silpa et al. (2021a) had
suggested that the transverse to poloidal B-field structure that they had
detected in the case of the radio-intermediate quasar III Zw 2 was an
indicator of a ‘jet+wind’ composite radio outflow. It is indeed interesting to
note that the majority of the quasars (5/9) would qualify as radio-
intermediate quasars (with R values $\lesssim 250$; Falcke et al., 1996a, see
Table 2).

The distorted/hybrid/restarted radio structures could be a consequence of the
selection criteria of the PG sample which relies on UV-excess and a star-like
nucleus. The PG quasar sample is biased towards luminous sources with high
Eddington ratios (Hooper et al., 1996; Laor, 2000; Jester et al., 2005). These
properties are closely related to the accretion disk state of the sources and
remains largely unbiased in terms of the radio properties of these sources. In
principle, this could be suggesting that the kpc-scale radio emission could be
influenced by the interaction with its environment. Sensitive low-frequency
observations with less restrictive selection effects than earlier studies are
also revealing a more complex extended source population, including candidate
hybrid radio galaxies, restarting and remnant radio galaxies (e.g., Kapińska
et al., 2017; Mingo et al., 2019; Jurlin et al., 2021).

The quasar PG1103$-$006 is an X-shaped source. Two primary models have been
invoked in the literature to explain such sources: (1) a reorientation of the
BH spin axes (Ekers et al., 1978; Dennett-Thorpe et al., 2002), (2)
superposition of two independent jets produced by two SMBHs residing in the
same host galaxy (Lal & Rao, 2007), and (3) hydrodynamical backflows from the
overpressured main jets deflected by the ellipsoidal hot interstellar medium
of the host galaxy (Leahy & Williams, 1984; Capetti et al., 2002). The
polarization structure observed in PG1103$-$006 is fully consistent with the
hydrodynamical backflow model as the inferred B-fields are aligned with the
flow of plasma along the X-shaped lobes. It is worth noting that the S-shaped
jets are consistent with jet precession, although precession cannot explain
the entire structure seen in PG1103$-$006.

We have looked at the total radio power at 150 MHz for the sample sources
w.r.t. the FR dividing line (Mingo et al., 2019) in Figure 21. We have not
corrected for Doppler boosting as we did not have reliable Doppler beaming
factors for all our sources. In terms of total radio power at 150 MHz, all the
9 quasars in this paper with the exception of PG0007+106 and PG1309+355 (and
PG2209+184 in the larger quasar sample), have FRII-like radio powers. However,
not all of them have FRII-like radio morphologies with clear terminal
hotspots. It is known that in other samples of radio-loud quasars, not all
possess FRII-like (with terminal hotspots) radio morphologies (e.g., Leahy &
Perley, 1991; Black et al., 1992; Kharb et al., 2010). Three BL Lac objects,
viz., PG0851+203, PG1424+240, and PG1437+398, have FRII-like radio powers. All
the remaining BL Lacs have FRI-like radio powers. Overall, the PG blazar
sample sources do not follow the simple unification scheme that suggests that
FRI radio galaxies are the parent population of BL Lac objects and FRII radio
galaxies are the parents population of radio-loud quasars.

Figure 21: Distribution of log of total luminosity at 150 MHz
($L_{150~{}MHz}$) for the PG “blazar” sample. The blue line indicates the
FRI/FRII luminosity divide derived by Mingo et al. (2019).

We find that PG quasars and BL Lacs have different BH masses, with the RL
quasars having systematically larger BH masses compared to the BL Lacs.
However, we also find that the SSRQs have systematically larger BH masses than
the FSRQs, as well as BL Lacs and FSRQs combined. Therefore, the major
difference in BH masses is between SSRQs and the “classical” blazars. Gu et
al. (2001) have shown that steep- and flat-spectrum quasars have similar
distributions of BH masses compared to radio luminosity and radio loudness
parameter $R$. However, as noted by Oshlack et al. (2002), disk-like line
emission could change the BH mass estimates by a large factor of 2. Indeed, we
find that a factor of 2 change in the BH masses of the FSRQs make them
indistinguishable from the BH masses of SSRQs (KS test $p=0.1$).

The optical selection criteria of the PG survey is biased against lower
optical luminosity RL quasars (Oshlack et al., 2002; Jester et al., 2005). The
RL quasars selected on the basis of UV excess tend to be optically luminous
with larger BH masses (Oshlack et al., 2002) due to the correlation between
the host’s bulge mass and the BH mass. We find an anti-correlation between BH
masses and radio core prominence $R_{C}$ for the 9 quasars studied in this
paper. This could be a consequence of the line emission originating in a disk
(e.g., Oshlack et al., 2002) which would then result in smaller BH masses for
larger face-on quasars (see above). BH masses seem to be marginally correlated
with the ${\mathrm{FP_{C}}}$. While this correlation could be suffering from
small number statistics, in principle, it could imply a relation between BH
mass and more organised/uniform B-fields in jets as they are launched from the
BHs. This correlation needs to be further examined with more data.

The jet power estimates for the PG quasars discussed here come from the
calculations of Punsly et al. (2018). These authors have corrected the Willott
et al. (1999) relation for use in blazars by introducing the parameter $\it f$
to account for deviations from 100% filling factor, minimum energy, a low-
frequency cutoff at 10 MHz, the jet axis at $60^{\circ}$ to the LOS, and no
protonic contribution, as well as energy lost expanding the lobe into the
external medium, back flow from the head of the lobe, and kinetic turbulence.
Willott et al. (1999) had estimated the long term, time-averaged bulk radio
jet kinetic power $\bar{Q}$ of jets using the radio luminosity at 151 MHz as a
surrogate for the luminosity of the radio lobes, motivated by the assumption
that the core emission is attenuated by synchrotron self-absorption at 151
MHz. Blundell & Rawlings (2000) had estimated $\it{f}$ to lie in the range of
$10<f<20$ for most FRII radio sources. We used an average value of 15 in this
paper. This relation was proposed for FR II radio galaxies and quasars. We
adopt this relation to estimate the power of jets in BL Lac objects following
Cao (2003) since BL Lac objects have similar radio properties as radio
quasars.

We have found a marginal correlation between the radio core fractional
polarization and the radio core spectral index for the 9 quasars; cores with
steeper spectral indices have a higher fractional polarization. This implies a
dominance of unresolved jet emission in the radio cores of these quasars.

For the entire blazar sample, the jet power appears to be significantly
correlated with BH mass (Kendall $\tau$ test $p=0.0025$). However, this
correlation disappears when the blazar sub-samples (of FSRQs, SSRQs and BL
Lacs) are considered individually, suggesting that there isn’t a strong
correlation between these two parameters. The jet power is correlated with
accretion rate for both FSRQs (Kendall $\tau$ test $p=0.016$) and SSRQs
(Kendall $\tau$ test $p=0.060$) with the former being a stronger correlation.
Taken together, the quasars (FSRQs +SSRQs) have their jet power correlated
with their accretion rates (Kendall $\tau$ test $p=0.020$).

We find that the jet power is correlated with the galactic SFR when quasars
are considered collectively (Kendall $\tau$ test $p=0.0515$), but not when
taken individually (FSRQ Kendall $\tau$ test $p=0.0833$ and SSRQ Kendall
$\tau$ test $p=0.4772$). While the marginal correlation between jet powers and
the SFR in the host galaxies of the quasars could in principle be consistent
with radio-mode feedback, many caveats remain (see Harrison, 2017; Scholtz et
al., 2018). For instance, Zhuang & Ho (2020); Zhuang et al. (2021) have found
a correlation between SFR and accretion rates. Additionally, as discussed by
Ward et al. (2022), specific SFR estimates are typically higher in galaxies
hosting higher Eddington ratio AGN (for e.g., the PG blazars). Therefore, we
cannot draw any conclusions about radio-mode AGN feedback from our current
data.

##  7 Summary and Conclusions

In this paper, we have presented results from 6 GHz VLA polarimetric
observations of 9 RL quasars. These quasars are a part of our well-selected PG
“blazar” sample comprising 6 RL quasars and 8 BL Lac objects. We summarise our
primary findings below.

  1. 1.

The quasars exhibit extensive polarization in their cores, jets/lobes and
hotspots, with the exception of PG1309+355, which remains largely unresolved
but shows core polarization. The fractional polarization in the cores ranges
from 0.8% to 10% and jets/lobes from 10% to 40%. The inferred B-fields in the
radio cores are transverse to the jet direction in all the quasars assuming
optically thick emission, with the exception of PG1704+608 where the B-fields
are aligned along the jet direction in the optically thin radio core. The
inferred B-field directions are largely aligned with the local jet direction
in the jets and jet knots of the quasars. The inferred B-fields are transverse
to the jet direction in several of the hotspots, consistent with B-field
compression in the terminal shock regions. The inferred B-fields in several
other hotspots are consistent with jet bends or bow-shock-like structures.
Such bow-shock like features are consistent with restarted jet activity. The
inferred B-fields in the radio lobes are mostly aligned with the lobe edges.

  2. 2.

A large fraction of the quasars show either distorted (S- or X-shaped)
morphologies, hybrid FR radio morphologies or restarted activity; the latter
is noted as a clear discontinuity in the surface brightness of different
features between different episodes. The polarization structures in several
hotspots are consistent with restarted jet activity. We attribute this
diversity in morphology to the optical/UV selection criteria of the PG sample
that remains unbiased at radio frequencies.

  3. 3.

The polarization structure observed in the X-shaped quasar PG1103$-$006 is
consistent with the hydrodynamical backflow model as the inferred B-fields are
aligned with the flow of plasma along the optically thin X-shaped wings.

  4. 4.

The in-band spectral index images of these 9 quasars show flat/inverted
spectral indices in the radio cores (with the exception of PG1704+608), while
the hotspots in several sources have relatively steep spectral indices. This
along with the complex polarization structures of the hotspots are also
consistent with restarted jet activity in these quasars.

  5. 5.

For the entire PG “blazar” sample (BL Lacs, FSRQs and SSRQs) we find that they
do not fit neatly into the different Fanaroff-Riley total power regime at 150
MHz, as well as Fanaroff-Riley radio morphologies. Several quasar lobes lack a
terminal hotspot typical of FRII radio galaxies. Correlations with BH masses
appear to be affected by various selection effects related to the mass
estimations for the different blazar sub-classes.

  6. 6.

We find that the jet mechanical powers correlate with accretion rates for the
16 PG quasars. Accretion rates were not available for the PG BL Lacs. This
correlation implies that higher accretion rates result in more powerful radio
jets. We also find a correlation between the radio core fractional
polarization and the 150 MHz total radio luminosity for the 9 quasars
considered here. That is, cores with higher fractional polarization also have
higher total radio luminosity at 150 MHz. This can imply that more organized
B-fields at the jet bases lead to higher core fractional polarization and to
more radio powerful jets.

## Acknowledgements

We thank the referee for their constructive suggestions that have
significantly improved this manuscript. JB, PK and SS acknowledge the support
of the Department of Atomic Energy, Government of India, under the project
12-R&D-TFR-5.02-0700. LCH acknowledges and was supported by the National
Science Foundation of China (11721303, 11991052, 12011540375) and the China
Manned Space Project (CMS-CSST-2021-A04, CMS-CSST-2021-A06). CMH acknowledges
funding from an United Kingdom Research and Innovation grant (code:
MR/V022830/1). For the purpose of open access, the authors has applied a
Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript
version arising. The National Radio Astronomy Observatory is a facility of the
National Science Foundation operated under cooperative agreement by Associated
Universities, Inc. 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. This research has made use of the VizieR catalogue
access tool, CDS, Strasbourg, France (DOI : 10.26093/cds/vizier). The original
description of the VizieR service was published in 2000, A&AS 143, 23.

## Data Availability

The data underlying this article will be shared on reasonable request to the
corresponding author. The VLA data underlying this article can be obtained
from the NRAO Science Data Archive
(https://archive.nrao.edu/archive/advquery.jsp) using the proposal ID:
20A-182.

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