![Figure 3. Spectra of the host galaxies of FRBs 190611, 190714, and 191001 (named with an HG prefix). FRBs 190711 and 200430 are not shown here because the poor signal-to-noise ratio (S/N) of the spectra does not allow us to model the line features with pPXF. The solid black lines show the dust-corrected spectra, with the associated error spectrum shown in gray. In the bottom panels, we show zoom-ins on the most prominent nebular emission lines from Hα, Hβ, [O III], and [N II], with the best-fit models from pPXF overplotted on the spectra shown as solid red lines. Strong telluric regions are masked out by the gray shaded regions.](/figures/figure-3-spectra-of-the-host-galaxies-of-frbs-190611-190714-352hfcp8.webp)
Host Galaxy Properties and Offset Distributions of Fast Radio Bursts: Implications for
Their Progenitors
Kasper E. Heintz
1
, J. Xavier Prochaska
2,3
, Sunil Simha
2
, Emma Platts
4
, Wen-fai Fong
5
, Nicolas Tejos
6
,
Stuart D. Ryder
7,8
, Kshitij Aggerwal
9,10
, Shivani Bhandari
11
, Cherie K. Day
11,12
, Adam T. Deller
12
,
Charles D. Kilpatrick
13
, Casey J. Law
14
, Jean-Pierre Macquart
15,17
, Alexandra Mannings
2
, Lachlan J. Marnoch
7,8,11
,
Elaine M. Sadler
11,16
, and Ryan M. Shannon
12
1
Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland; keh14@hi.is
2
University of California—Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
3
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), 5-1-5 Kashiwanoha, Kashiwa, 277-8583, Japan
4
High Energy Physics, Cosmology & Astrophysics Theory (HEPCAT) group, Department of Mathematics and Applied Mathematics, University of Cape Town,
South Africa
5
Center for Interdisciplinary Exploration and Research in Astrophysics and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road,
Evanston, IL 60208-3112, USA
6
Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla 4059, Valparaíso, Chile
7
Department of Physics & Astronomy, Macquarie University, NSW 2109, Australia
8
Astronomy, Astrophysics and Astrophotonics Research Centre, Macquarie University, Sydney, NSW 2109, Australia
9
Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, USA
10
Center for Gravitational Waves and Cosmology, West Virginia University, Chestnut Ridge Research Building, Morgantown, WV, USA
11
Australia Telescope National Facility, CSIRO Astronomy and Space Science, P.O. Box 76, Epping, NSW 1710, Australia
12
Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
13
Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
14
Cahill Center for Astronomy and Astrophysics, MC 249-17 California Institute of Technology, Pasadena, CA 91125, USA
15
International Centre for Radio Astronomy Research, Curtin University, Bentley WA 6102, Australia
16
Sydney Institute for Astronomy, School of Physics A28, The University of Sydney, NSW 2006, Australia
Received 2020 July 1; revised 2020 September 6; accepted 2020 September 8; published 2020 November 12
Abstract
We present observations and detailed characterizations of five new host galaxies of fast radio bursts (FRBs)
discovered with the Australian Square Kilometre Array Pathfinder (ASKAP) and localized to 1″. Combining these
galaxies with FRB hosts from the literature, we introduce criteria based on the probability of chance coincidence to
define a subsample of 10 highly confident associations (at z=0.03–0.52), 3 of which correspond to known repeating
FRBs. Overall, the FRB-host galaxies exhibit a broad, continuous range of color (M
u
−M
r
=0.9–2.0), stellar mass
(M
å
=10
8
−6×10
10
M
e
), and star formation rate (SFR=0.05–10 M
e
yr
−1
) spanning the full parameter space
occupied by z<0.5 galaxies. However, they do not track the color–magnitude, SFR–M
å
,norBPTdiagramsoffield
galaxies surveyed at similar redshifts. There is an excess of “green valley” galaxies and an excess of emission-line
ratios indicative of a harder radiation field than that generated by star formation alone. From the observed stellar mass
distribution, we rule out the hypothesis that FRBs strictly track stellar mass in galaxies (>99% c.l.). We measure a
median offset of 3.3 kpc from the FRB to the estimated center of the host galaxies and compare the host-burst offset
distribution and other properties with the distributions of long- and short-duration gamma-ray bursts (LGRBs and
SGRBs), core-collapse supernovae (CC-SNe), and SNe Ia. This analysis rules out galaxies hosting LGRBs (faint,
star-forming galaxies) as common hosts for FRBs (>95% c.l.). Other transient channels (SGRBs, CC-, and SNe Ia)
have host-galaxy properties and offsets consistent with the FRB distributions. All of the data and derived quantities
are made publicly available on a dedicated website and repository.
Unified Astronomy Thesaurus concepts: Galaxies (573); Interstellar medium (847); Star formation (1569);
Extragalactic radio sources (508); Radio bursts (1339); Magnetars (992)
1. Introduction
The transients classified as fast radio bursts (FRBs ) and their
progenitors constitute one of the major puzzles in contempor-
ary astrophysics (see Cordes & Chatterjee 2019; Petroff et al.
2019, for recent reviews). FRBs are brief (∼1ms), but bright
(>1Jyms) radio-pulse events, similar in nature to pulsars,
although their extragalactic origin
(Thornton et al. 2013)
implies much higher energies. Despite being first detected more
than a decade ago (Lorimer et al. 2007), the physical engines
powering FRBs still remain a mystery, but a plethora of
origins has been proposed (see e.g., Platts et al. 2019, for a
compendium).
Nevertheless, FRBs have already been demonstrated to be
powerful cosmological probes. Similar to how UV or optically
bright cosmic beacons such as quasars and gamma-ray burst
(GRB) afterglows have been paramount in the study of the
interstellar and intergalactic gas properties at high redshifts
(Wolfe et al. 2005; Fynbo et al. 2009), FRBs have revolutionized
the studies of the “cosmic web” between galaxies (Macquart et al.
2020; Simha et al. 2020), the diffuse ionized gas in extragalactic
halos (McQuinn 2014; Prochaska & Zheng 2019;Prochaska
et al. 2019a), and the interstellar and circumgalactic media of
their hosts (Tendulkar et al. 2017; Chittidi et al. 2020).Most
notably, FRBs can be used to provide a census of the baryonic
content that is in a highly diffuse state and therefore difficult to
detect with any other approach (Macquart et al. 2020).
The Astrophysical Journal, 903:152 (22pp), 2020 November 10 https://doi.org/10.3847/1538-4357/abb6fb
© 2020. The American Astronomical Society. All rights reserved.
17
Deceased.
1
Until recently, the main issue hindering any significant
progress has been the generally poor localizations of the events.
The first decade of FRB searches was undertaken with
telescopes that had localization regions ?1 arcmin
2
. This is
inhibited by the seeming lack of “afterglows” analogous to
those observed for GRBs (Petroff et al. 2017; Bhandari et al.
2018; Chen et al. 2020) and associated supernova-like transient
counterparts (Marnoch et al. 2020). A precise localization
(∼1″) of the burst itself is thus required to robustly identify the
associated host galaxy (Eftekhari & Berger 2017).
The first unique identification of an FRB-host galaxy was
based on direct interferometric localization of the repeat bursts
from FRB 121102 (Spitler et al. 2016). Follow-up observations
revealed a faint, actively star-forming (SF), low-mass galaxy at
z=0.1927 (Chatterjee et al. 2017; Tendulkar et al. 2017). The
resemblance to the hosts of long-duration GRBs and super-
luminous supernovae (SLSNe) promoted “young” flaring
magnetar models as the origin of the repeat bursts (e.g.,
Metzger et al. 2017; Margalit & Metzger 2018). However, it is
now clear that the host galaxy of FRB 121102 is anomalous
compared to other FRB hosts (e.g., Bannister et al. 2019;Li
et al. 2019; Bhandari et al. 2020b). Recently, another repeating
FRB, FRB 180916, was localized to an SF region in a nearby
spiral galaxy (Marcote et al. 2020), showing properties in stark
contrast to the host of FRB 121102.
The Commensal Real-Time ASKAP Fast Transients
(CRAFT; Macquart et al. 2010) survey has operated the
Australian Square Kilometre Array Pathfinder (ASKAP) in
incoherent-sum (ICS) mode since 2018, and now routinely
provides ∼arcsecond localizations of single-pulse FRBs. This
led to the discovery of the first two host galaxies associated
with apparently one-off FRBs (Bannister et al. 2019; Prochaska
et al. 2019a), and based on the first preliminary study of
ASKAP-detected FRBs (Bhandari et al. 2020b, see also Li &
Zhang 2020), it is now clear that the majority of FRB hosts are
instead massive galaxies with older stellar populations. This
suggests that FRBs reside in diverse environments, even for the
proposed subpopulation of repeating bursts. The progenitors of
FRBs (and astronomical transients in general) are likely linked
to specific stellar populations and galactic environments, so
detailed characterizations of their host galaxies allow us to
constrain the nature of these events and their likely progenitor
channels (akin to how the host properties of GRBs aided in
constraining their progenitors, e.g., Fruchter et al. 2006; Yoon
et al. 2006).
In this paper, we present the first comprehensive and
statistical analyses of the population of galaxies hosting FRBs.
These include detailed characterizations of five new host
galaxies of accurately localized FRBs detected by ASKAP.
Combined with all previously identified FRB hosts reported in
the literature, our sample comprises a total of 13 host galaxies.
We measure the physical properties of the majority of the FRB
hosts in our sample based on existing and newly obtained
spectroscopic and photometric data.
Throughout the paper, we distinguish between host galaxies
of repeating FRBs and apparently nonrepeating, one-off bursts
to investigate any distinct characteristics between the host
populations of the two apparent types of FRBs. We first
compare the observed FRB-host properties to those of field
galaxies to examine how the FRB hosts are drawn from the
underlying galaxy population. We then investigate any
connections between the FRB-host properties and host-burst
offset distributions to those of other astronomical transients
such as long-duration GRBs (LGRBs), short-duration GRBs
(SGRBs), core-collapse supernovae (
CC-SNe), and SNe Ia.
Recently, Li & Zhang (2020) and Bhandari et al. (2020b)
analyzed a sample of five and six FRB hosts, respectively, and
found that their physical properties are most consistent with
those of SGRBs and SNe Ia, excluding models in which the
majority of FRBs originate from SLSN/LGRB progenitors or
active galactic nuclei (AGNs). Here, we leverage our larger
sample to further narrow down and provide stronger constraints
on the most likely progenitor channels for the majority
of FRBs.
We have structured the paper as follows: in Section 2 we
define the FRB-host galaxy sample(s) and present the new host-
galaxy observations of the ASKAP-localized FRBs character-
ized here. We detail the modeling of the host-galaxy properties
in Section 3 and compare the typical host-galaxy environments
to field-selected galaxies in Section 4.InSection5 we compare
the FRBs to other types of astronomical transients and discuss
the implications of our results on the most likely FRB progenitor
channels. We conclude and summarize our work in Section 6.
Throughout the paper, we assume the concordance cosmological
model, with Ω
m
=0.308 and H
0
=67.8 km s
−1
Mpc
−1
(Planck
Collaboration et al. 2016).
2. Sample and Observations
In collaboration with the CRAFT (Macquart et al. 2010) and
realfast (Law et al. 2018) surveys, we have as part of the Fast
and Fortunate for FRB Follow-up (F
4
)
18
collaboration
endeavored to obtain dedicated photometric and spectroscopic
follow-up observations of all ∼arcsecond-localized FRBs.
These provide a secure identification of the associated host
galaxies and allow us to derive their main physical properties.
All the observational data products are available on the FRB
GitHub repository,
19
in addition to a large suite of FRB-related
scripts. As a front-end to these data repositories, we have also
launched an online FRB-host galaxy database,
20
with the goal
of collecting and sharing all currently known and future FRB
hosts and their basic properties.
In this section, we describe the identification of FRB-host
galaxies and define a set of sample criteria to describe the
robustness of the host associations. We then present the new
observations of five FRB-host galaxies and compile all
previously known FRB hosts reported in the literature, all
considered in our meta analysis. At the end, we summarize the
overall sample properties.
2.1. Host-galaxy Associations
An FRB signal alone cannot directly establish the redshift of
the source, and one relies on an association with a host galaxy
for a precise measurement. To date and in this work, the
association of the FRB with a host galaxy is primarily based on
probabilistic arguments given their position relative to coin-
cident or nearby galaxies. Following standard practice for other
transients (e.g., Bloom et al. 2002; Blanchard et al. 2016,
for GRBs), one may estimate the probability of a chance
coincidence (P
chance
) based on the angular offset, θ, of the FRB
position from the galaxy centroid, the uncertainty of the FRB
18
https://ucolick.org/f-4
19
https://github.com/FRBs/FRB
20
https://frbhosts.org
2
The Astrophysical Journal, 903:152 (22pp), 2020 November 10 Heintz et al.
localization, and the galaxy’s apparent magnitude. Further
work may adopt additional properties and priors for establish-
ing associations.
The derivation of P
chance
is based on galaxy number counts
and captures the fact that apparently faint galaxies are more
common on the sky. We adopt the formalism developed by
Bloom et al. (2002), derived from optical galaxy number
counts (Hogg et al. 1997), which gives the number density of
galaxies brighter than apparent r -band magnitude m
r
(not
taking into account clustering of galaxies),as
S=
´
´
-+ -
m
1
3600 0.334 log 10
10 arcsec . 1
r
e
m
2
0.334 22.963 4.320 2
r
()
()
()
()
We then calculate the probability of chance coincidence, given
by
h=- -P 1exp , 2
chance
() ()
where η ≡πθ
2
Σ(m
r
). We report the estimated chance
probabilities of each of the FRB-host galaxies in Table 1.
Here, we also provide the association radius δx, representing
the offset from a given galaxy with r-band magnitude m
r
within
which the FRB can be securely associated with the galaxy
(Tunnicliffe et al. 2014).
In previous works, we estimated the probability of chance
coincidence with an empirical approach (Bannister et al. 2019)
and reported
<
-
P 10
chance
3
for the first well-localized ASKAP-
detected FRBs (e.g., Bannister et al. 2019; Prochaska et al.
2019a). The formalism described above yields consistent
results. We note that Eftekhari & Berger (2017) have
developed a similar framework to quantify the robustness of
the FRB-host galaxy associations with a more recent number
count estimation. This generally provides lower chance
probabilities; here, we use the formalism described above to
be more conservative. In this work, we also estimate the
uncertainty on the offsets from the FRB to the host galaxy
center by integrating over the FRB localization ellipse.
Our approach is designed to (i) minimize the deleterious effect
of false positives on this somewhat small sample of events and
(ii) define a high-confidence sample that can be used in future
analyses to generate priors for a full Bayesian analysis. To do
this, we define four subsamples based solely on
P
chance
and the
quality of the galaxy redshift estimation. These are:
1. Sample A: The host-galaxy association is considered
highly probable (
<P 0.05
chance
) based on the FRB
localization and galaxy photometry. The galaxy has a
spectroscopically confirmed redshift
z
spec
.
2. Sample B: Same as Sample A, except that only a
photometric redshift
z
pho
t
has been estimated.
3. Sample C: The host-galaxy association is less secure due
to a poor FRB localization, multiple host candidates,
and/or because additional priors were adopted in the
association (e.g., the Macquart DM–z relation; Macquart
et al. 2020). A spectroscopic redshift
z
spec
has been
measured.
4. Sample D: Same as Sample C, except that only a
photometric redshift
z
pho
t
has been measured.
We consider all the FRB hosts compiled in this work
throughout the paper but caution about the potential pitfalls of
the uncertain host-galaxy identifications where relevant. For the
statistical analyses we only consider the FRBs in SampleA. In
the following section we introduce all of the candidate FRB-
host galaxies and enumerate the number in each sample type.
2.2. FRB-host Galaxy Observations
In continuation of the first four FRBs detected and accurately
localized by ASKAP/CRAFT (presented in Bhandari et al.
2020b), we here report the observations and basic properties of
five more recent FRB-host galaxies: those of FRBs 190611,
190711, 190714, 191001, and 200430.
2.2.1. FRB 190611
On UT 2019 June 11 at 05:45:43.3, the ASKAP telescope
recorded FRB 190611 as reported by Macquart et al. (2020),
who also briefly described its host-galaxy candidates. The FRB
position is at R.A., decl. (α, δ)=21
h
22
m
58 91, −79
d
23
m
51 3
(J2000), with an uncertainty of σ
α,δ
=0 7, 0 7.
We obtained deep Gemini-S/GMOS images in the r and i
bands (the latter shown in Figure 1) revealing a bright source
(r=22.65 mag) approximately 2″ to the northwest at α,
δ=21
h
22
m
58 28, −79
d
23
m
50 1 (J2000), identified as the
host galaxy by Macquart et al. (2020). We do not detect any
significant structure (e.g., spiral arms ) and measure an effective
half-light radius of R
eff
=0 40. We also tentatively detect a
considerably fainter source coincident within the FRB error
ellipse (r≈26 mag; at 21
h
22
m
58 97, −79
d
23
m
51 7) at a
smaller offset of 0
43 from the FRB position. We estimate
chance probabilities for the two galaxies to be unrelated to the
FRB host of
=P 0.017 and 0.10
chance
for the bright and faint
galaxy, respectively. Given the only tentative detection of the
faint source and that the bright source has
»P 2%
chance
,we
consider the more clearly offset, bright galaxy to be the host of
FRB 190611 and place it in our primary SampleA.
Spectroscopy of this host-galaxy candidate with the FORS2
instrument on the ESO Very Large Telescope (VLT ) was
reduced using the PypeIt reduction package (Prochaska et al.
2020), which optimally extracts a 1D spectrum from the flat-
fielded and sky-subtracted 2D spectral image. We additionally
performed a 2D coaddition of the spectra presented in
Macquart et al. (2020). This yields a spectroscopic redshift of
=
z
0.3778
spec
based on the Hα,Hβ, and [O III] line features.
At this redshift, the physical projected offset of the FRB from
the bright galaxy centroid is ≈11 kpc.
2.2.2. FRB 190711
On UT 2019 July 11 at 01:53:41.1, the ASKAP telescope
recorded FRB 190711 as reported by Macquart et al. (2020),
who also provided a brief description of its host galaxy. The
FRB position is at α, δ=21
h
57
m
40 68, −80
d
21
m
28 8
(J2000), with an uncertainty of σ
α,δ
=0 4, 0 3 (Day et al.
2020). This FRB has subsequently been found to repeat
(Kumar et al. 2020).
The FRB is coincident with an r≈23.5 mag galaxy at α,
δ=21
h
57
m
40 60, −80
d
21
m
29 25 (see Figure 1), with an
offset of 0
49. No clear morphological structures can be
identified in the GMOS imaging, and we measure an effective
half-light radius of R
eff
=0 46. We assert a secure association
of FRB 190711 to this galaxy, given the low chance probability
of
=P 0.011
chance
, and include it in SampleA.
3
The Astrophysical Journal, 903:152 (22pp), 2020 November 10 Heintz et al.
Table 1
Overview of the Main Sample of FRBs and Their Putative Hosts
FRB R.A.
FRB
Decl.
FRB
σ
R
Repeating R.A.
host
Decl.
host
θδxr
1/2
r
i
m Filter
P
chance
Sample
(deg)(deg)(″)(deg)(deg)(″)(″)(″)(″)(mag)
(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)
121102 82.9946 33.1479 0.100 y 82.9946 33.1480 0.17 1.2 0.2 0.44 23.73 GMOS_N_r 0.0023 A
180916 29.5031 65.7168 0.002 y 29.5012 65.7147 7.87 44.8 5.1 12.95 16.17 SDSS_r 0.0059 A
180924 326.1052 −40.9000 0.102 n 326.1052 −40.9002 0.71 4.7 0.6 1.35 20.50 DES_r 0.0018 A
181112 327.3485 −52.9709 1.626 n 327.3486 −52.9709 0.28 2.7 1.2 3.25 21.68 DES_r 0.0257 C
190102 322.4157 −79.4757 0.502 n 322.4150 −79.4757 0.45 4.1 1.0 2.02 20.77 VLT_FORS2_I 0.0050 A
190523 207.0650 72.4697 2.449 n 207.0643 72.4708 3.79 2.4 0.5 4.90 22.01 Pan-STARRS_r 0.0733 C
190608 334.0199 −7.8982 0.258 n 334.0204 −7.8989 3.00 20.5 1.3 3.96 17.55 SDSS_r 0.0016 A
190611 320.7455 −79.3976 0.671 n 320.7428 −79.3972 2.13 2.3 0.4 2.27 22.07 GMOS_S_r 0.0169 A
190614 65.0755 73.7067 0.566 n 65.0738 73.7064 2.22 1.4 1.0 2.99 23.25 GMOS_S_r 0.0708 D
190711 329.4195 −80.3580 0.350 y 329.4192 −80.3581 0.49 1.3 0.5 1.04 23.49 GMOS_S_r 0.0106 A
190714 183.9797 −13.0210 0.283 n 183.9796 −13.0211 0.49 4.3 1.0 2.09 20.69 Pan-STARRS_r 0.0050 A
191001 323.3516 −54.7477 0.149 n 323.3519 −54.7485 2.86 13.5 1.4 4.07 18.34 DES_r 0.0031 A
200430 229.7064 12.3769 0.546 n 229.7063 12.3766 1.04 3.0 0.6 1.55 21.51 Pan-STARRS_r 0.0051 A
Note. Column 1: FRB source. Columns 2 and 3: R.A. and decl. of the FRB (J2000). Column 4: Approximate FRB localization uncertainty
(geometric mean of R.A. and decl. axes). Column 5: FRB classification.
Repeating=yes(y)/no(n). Columns 6 and 7: R.A. and decl. of the associated host galaxy (J2000). Column 8: Projected angular offset of the FRB to the host-galaxy center. Column 9: Association radius δx (Tunnicliffe
et al. 2014). Column 10: Angular effective radius of the host measured from a Sérsic model using GALFIT (Peng et al. 2010) on the i -band images (or equivalent). Column 11: Effective search radius (Bloom et al. 2002).
Column 12: Measured apparent magnitude of the host. Column 13: Filter used for the magnitude measurement. Column 14: Probability of chance coincidence using the Bloom et al. (2002) formalism. Column 15:
Sample designations following the criteria outlined in Section 2.1.
4
The Astrophysical Journal, 903:152 (22pp), 2020 November 10 Heintz et al.
Using PypeIt, we have performed a 2D coaddition of the
VLT X-Shooter spectra presented in Macquart et al. (2020).
Based on the detection of Hβ and [O
III] in this spectrum, we
find
=
z
0.5220
spec
. At this redshift, the physical projected
offset of the FRB from the galaxy centroid is ≈3 kpc. We do
not detect Hα emission, but this feature lies at a lower
throughput portion of the spectrograph where there is also
significant telluric absorption.
2.2.3. FRB 190714
On UT 2019 July 14 at 05:37:12.9, the ASKAP telescope
recorded FRB 190714 at α, δ =12
h
15
m
55 12, −13
d
01
m
15 7
(J2000), with an uncertainty of σ
α,δ
=0 4, 0 3. This
localization places FRB 190714≈0
5 from the galaxy
J121555.0941−130116.004 (see Figure 1), which was pre-
viously cataloged by the Pan-STARRS (Chambers et al. 2016)
and the VISTA (Cross et al. 2012) surveys. It is a relatively
bright source (r=20.85 mag), and we estimate a chance
association of
P
chance
=0.005. We thus include this galaxy in
SampleA. We do not detect any distinct morphology of the
host galaxy in our FORS2 I-band image, but there might be
evidence of spiral arms based on preliminary results obtained
from imaging with the Hubble Space Telescope (A. Mannings
et al. 2020, in preparation). We measure an effective half-light
radius of R
eff
=1 02.
We obtained optical spectroscopy of the host of FRB 190714
on 2020 January 28 with the LRIS spectrometer (Oke et al.
1995) on the KeckI 10 m telescope. This dual-camera
instrument was configured with the 600/7500 grating, the
600/4000 grism, and a slit mask designed to observe the FRB-
host and additional galaxies in the field. We reduced these data
with PypeIt, and the extracted 1D spectrum was then flux-
calibrated through observations of a spectroscopic photometric
standard acquired on the same (clear ) night and scaled to the
Pan-STARRS photometry. The bright nebular emission lines of
Hβ, [O
III],Hα, and [N II] yield a spectroscopic redshift of
=
z
0.2365
spec
. This places FRB 190714 at a projected physical
separation of ≈2 kpc from the galaxy center.
2.2.4. FRB 191001
On UT 2019 October 01 at 16:55:36.0, the ASKAP
telescope recorded FRB 191001 at α, δ=21
h
33
m
24 373,
−54
d
44
m
51 4 (J2000), with an uncertainty of σ
α,δ
=0 17,
0
13 (Bhandari et al. 2020a). This position is ≈2 9 north of
the previously cataloged source DESJ213324.44−544454.65
(Figure 1; Abbott et al. 2018). Despite the relatively large
angular offset, the bright magnitude (r=18.41 mag) yields a
chance coincidence probability of only
=P 0.00
3
chance
.We
therefore include this galaxy in SampleA. The host galaxy of
this FRB shows clear spiral-arm features, with the FRB
occurring in the outskirts of the northern arm (see Bhandari
et al. 2020a, for a more detailed study of this FRB). The
estimated effective half-light radius is R
eff
=1 44.
On UT 2019 October 4, we obtained a GMOS spectrum of
the host of FRB 191001 with the Gemini-S telescope,
configured with a 1″ long slit and the R400 grating tilted to
cover λ≈5000–9900 Å with a full width at half maximum
(FWHM)≈
-
5
00 km s
1
. The data were reduced with the
PypeIt software package (see Section 2.2.1 for details) and
flux calibrated with a standard star obtained and scaled to
=
r
18.
4
mag. The detection of strong nebular emission lines
from Hβ, [O
III],Hα, and [N II] yield a spectroscopic redshift
Figure 1. Mosaic showing the I/i-band images of the host galaxies of FRBs 190611, 190711, 190714, 191001, and 200430. The dashed black lines represent the total
1σuncertainties on the FRB positions (statistical and systematic).
5
The Astrophysical Journal, 903:152 (22pp), 2020 November 10 Heintz et al.