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Resolving a dusty, star-forming SHiZELS galaxy at z=2.2 with
HST, ALMA and SINFONI on kiloparsec scales
Citation for published version:
Cochrane, RK, Best, PN, Smail, I, Ibar, E, Cheng, C, Swinbank, AM, Molina, J, Sobral, D & Dudzeviciute, U
2021, 'Resolving a dusty, star-forming SHiZELS galaxy at z=2.2 with HST, ALMA and SINFONI on
kiloparsec scales', Monthly Notices of the Royal Astronomical Society , vol. 503, no. 2, pp. 2622-2638.
https://doi.org/10.1093/mnras/stab467
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Resolving a dusty, star-forming SHiZELS galaxy at z = 2 .2 with HST,
ALMA and SINFONI on kiloparsec scales
R. K. Cochrane,
1,2★
P. N. Best,
2
I. Smail,
3
E. Ibar,
4
C. Cheng,
5,6,4
A. M. Swinbank,
3
J. Molina,
7
D. Sobral,
8
U. Dudzeviči
¯
ut
˙
e
3
1
Harvard-Smithsonian Center for Astrophysics, 60 Garden St. Cambridge, MA 02138, USA
2
SUPA, Institute for Astronomy, Royal Observatory Edinburgh, EH9 3HJ, UK
3
Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
4
Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso, Chile
5
Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing 100101, China
6
CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
7
Kavli Institute for Astronomy and Astrophysics, Peking University, 5 Yiheyuan Road, Haidian District, Beijing 100871, P.R. China
8
Department of Physics, Lancaster University, Lancaster, LA1 4YB
Accepted 2021 February 10. Received 2021 February 10; in original form 2020 August 21
ABSTRACT
We present ∼ 0.15
00
spatial resolution imaging of SHiZELS-14, a massive (𝑀
∗
∼ 10
11
M
), dusty, star-forming galaxy at
𝑧 = 2.24. Our rest-frame ∼ 1kpc-scale, matched-resolution data comprise four different widely used tracers of star formation:
the H𝛼 emission line (from SINFONI/VLT), rest-frame UV continuum (from HST F606W imaging), the rest-frame far-infrared
(from ALMA), and the radio continuum (from JVLA). Although originally identified by its modest H𝛼 emission line flux,
SHiZELS-14 appears to be a vigorously star-forming (SFR ∼ 1000 M
yr
−1
) example of a submillimeter galaxy, probably
undergoing a merger. SHiZELS-14 displays a compact, dusty central starburst, as well as extended emission in H𝛼 and the
rest-frame optical and FIR. The UV emission is spatially offset from the peak of the dust continuum emission, and appears to
trace holes in the dust distribution. We find that the dust attenuation varies across the spatial extent of the galaxy, reaching a
peak of at least 𝐴
H𝛼
∼ 5 in the most dusty regions, although the extinction in the central starburst is likely to be much higher.
Global star-formation rates inferred using standard calibrations for the different tracers vary from ∼ 10 − 1000 M
yr
−1
, and
are particularly discrepant in the galaxy’s dusty centre. This galaxy highlights the biased view of the evolution of star-forming
galaxies provided by shorter wavelength data.
Key words: galaxies: high redshift – galaxies: evolution – galaxies: starburst – galaxies: star formation – submillimetre: galaxies
– infrared: galaxies
1 INTRODUCTION
Galaxy surveys have long shown that star-formation rates within in-
dividual galaxies increase towards high redshift. At a given stellar
mass, typical star-formation rates increase by over an order of mag-
nitude between the present day and the peak of cosmic star formation
at 𝑧 ∼ 2 (Sobral et al. 2013a; Madau & Dickinson 2014; Speagle
et al. 2014). This is thought to reflect the large reservoirs of molec-
ular gas that cool from the high rates of gas accretion onto galaxies’
host halos in the early universe (Tacconi et al. 2010, 2013, 2017;
Papovich et al. 2016; Falgarone et al. 2017; Jiménez-Andrade et al.
2018; Dudzeviciute et al. 2020).
Although highly luminous dusty galaxies are rare at 𝑧 = 0 and
known as ‘ultra luminous infrared galaxies’ (ULIRGs, with total
infrared luminosities 𝐿
TIR
> 10
12−13
L
), galaxies with typical
ULIRG luminosities are more common around the peak of cosmic
star formation (Smail et al. 1997; Barger et al. 1998). Submillime-
★
E-mail: rachel.cochrane@cfa.harvard.edu
ter galaxies (SMGs; Blain et al. 2002) are ULIRGs at high redshift
with bright submillimeter fluxes that suggest star-formation rates
(SFRs) of ∼ 100 − 1000 M
yr
−1
. Sustained star-formation rates of
this magnitude have the potential to form massive galaxies (with
stellar masses of ∼ 10
11
M
) on sub-Gyr timescales (Simpson et al.
2014; Dudzeviciute et al. 2020). Chapman et al. (2005) found that
the volume density of SMGs increases by a factor of ∼ 1000 be-
tween 𝑧 = 0 and 𝑧 = 2.5, with the redshift distribution peaking at
𝑧 ∼ 2.0 − 2.5 (see also Koprowski et al. 2014; Simpson et al. 2014;
Danielson et al. 2017; Stach et al. 2019; recent studies using larger
samples derive a redshift distribution that peaks slightly higher).
SMGs at 1 < 𝑧 < 5 appear to account for ∼ 20 − 30 per cent of the
total comoving star-formation rate density at these redshifts (Swin-
bank et al. 2014; Smith et al. 2017; Dudzeviciute et al. 2020). Even
in less far-infrared (FIR)-luminous high redshift galaxies, a signif-
icant amount of star formation is obscured by dust. Dunlop et al.
(2017) combined long- and short-wavelength data from two premier
observatories: the Atacama Large Millimeter Array (ALMA, prob-
ing the dust continuum emission at 1.3mm) and the Hubble Space
© 2021 The Authors
arXiv:2102.07791v1 [astro-ph.GA] 15 Feb 2021
2 R.K. Cochrane et al.
Telescope (HST, Wide Field Camera 3, probing rest-frame UV), in
the well-studied Hubble Ultra Deep Field (e.g. Bouwens et al. 2010;
Oesch et al. 2010; Illingworth et al. 2013; Dunlop et al. 2013). These
complementary data enabled them to confirm that ∼ 85 per cent of
the total star formation at 𝑧 ∼ 1 − 3 is enshrouded in dust. Emis-
sion from the most massive galaxies is most highly attenuated: for
galaxies with 𝑀
∗
∼ 5 × 10
10
M
, they suggest a ratio of obscured
to unobscured star formation of ∼ 50. However, lower mass galaxies
are still affected, with the ratio decreasing to ∼ 5 for galaxies with
𝑀
∗
∼ 5 × 10
9
M
(see also Magnelli et al. 2020).
While studies of wide areas are important in tracking the evolving
properties of star-forming galaxies and the build-up of stellar mass
in the Universe, understanding the physical processes of star forma-
tion within individual galaxies requires higher angular resolution.
Until recently, resolved studies of distant star-forming (SF) galaxies
tended to be based on observations from near-infrared integral field
unit spectrographs, which probe rest-frame optical emission lines
such as H𝛼 and [OIII] at 𝑧 ∼ 2 (e.g. Genzel et al. 2008; Swinbank
et al. 2012a; Reddy et al. 2015; Stott et al. 2016; Simons et al. 2017),
or from HST at rest-frame UV wavelengths (e.g. Wuyts et al. 2012;
Fisher et al. 2017). These claim a physical picture in which star for-
mation takes place within massive clumps embedded in turbulent
disk structures (Genzel et al. 2008; Elmegreen et al. 2013; Genzel
et al. 2013; Guo et al. 2015, 2017; Soto et al. 2017). Emission at these
short wavelengths is, however, strongly attenuated by dust, and the
significant global obscuration of star formation at 𝑧 < 4 suggests that
our understanding of galaxy evolution from short-wavelength studies
is likely to be highly biased by dust, even at high spatial resolution.
As such, the importance and even the reality of these clumps has
been questioned (e.g. Hodge et al. 2016, 2019; Ivison et al. 2020).
Indeed, star formation in the dustiest regions of high redshift galaxies
is expected to be totally hidden from view (Simpson et al. 2017).
Recent work made possible by new submillimeter interferometers,
in particular ALMA, which offers both high sensitivity and spatial
resolution, has focused on characterising the spatially-resolved prop-
erties of high redshift galaxies at long wavelengths (see the recent
review by Hodge & da Cunha 2020). The spatial extent of dust emis-
sion and molecular gas has been of particular interest in recent years.
The dust continuum emission and CO emission appear very compact
for distant (𝑧 > 1), sub-millimeter-bright galaxies, with typical effec-
tive radii ∼ 1 − 2 kpc (Simpson et al. 2015; Tadaki et al. 2016, 2017,
2018; Hodge et al. 2016, 2019; Oteo et al. 2017; Strandet et al. 2017;
Calistro Rivera et al. 2018; Lang et al. 2019; Gullberg et al. 2019;
Dudzeviciute et al. 2020). A number of studies have shown that these
sizes are comparable to the optical sizes of 𝑧 ∼ 1 − 2 compact qui-
escent ellipticals, galaxies that must have formed a huge amount of
stellar mass and then quenched early (Krogager et al. 2014; Onodera
et al. 2015; Belli et al. 2016; Lang et al. 2019). This, together with
the large estimated stellar masses of SMGs (𝑀
∗
∼ 10
11
M
; Hodge
et al. 2019; Dudzeviciute et al. 2020) has fuelled speculation that the
SMGs detected at 𝑧 ∼ 3 − 6 are the progenitors of 𝑧 = 2 massive
ellipticals (e.g. Toft et al. 2014; Simpson et al. 2014; Oteo et al. 2017;
Gómez-Guijarro et al. 2018; Tadaki et al. 2020), possibly tracing a
rapid phase of bulge-building (e.g. Tadaki et al. 2016; Simpson et al.
2017; Nelson et al. 2019).
However, observations of compact dust continuum sizes are in
contrast to the extended, clumpy structures traced by HST imaging
(Chen et al. 2015; Barro et al. 2016; Hodge et al. 2015, 2016, 2019;
Rujopakarn et al. 2019). In some cases, kpc-scale offsets have been
found between the peaks of the FIR and UV emission (Hodge et al.
2015; Tadaki et al. 2016; Chen et al. 2017; Calistro Rivera et al.
2018). These offsets could potentially bias interpretations of global
measurements (particularly for fits to photometry that focus solely on
the rest-frame optical to near-infrared, but also for ‘energy-balance’
spectral energy distribution fitting). Indeed, Simpson et al. (2017)
argue that attenuation in the dusty regions of SMGs is so great that
essentially all the co-located stellar emission is obscured at optical-
to-near-infrared wavelengths; for ∼ 30 per cent of their sample, the
data available at these wavelengths is insufficient to put constraints
on photometric redshifts and stellar masses (see also work on ‘NIR-
dark’ sources; e.g. Simpson et al. 2014; Franco et al. 2018; Wang
et al. 2019; Dudzeviciute et al. 2020; Smail et al. 2020)
Overall, it has become clear that drawing conclusions from single-
wavelength surveys, especially in the rest-frame UV, is subject to sub-
stantial bias and uncertainty, even where data is at high angular reso-
lution. In this paper, we present multi-wavelength, 0.15
00
-resolution
imaging of SHiZELS-14, a highly star-forming, H𝛼-selected galaxy
at 𝑧 = 2.24. Of the ALMA-studied SHiZELS parent sample (which
is presented in a companion paper, Cheng et al. 2020), SHiZELS-14
is the most FIR luminous, with the largest of all H𝛼-derived effective
radii (4.6 ± 0.4 kpc) (Swinbank et al. 2012a,b; Gillman et al. 2019).
Although its H𝛼 flux is modest, it displays SMG-like dust continuum
emission. Our observations comprise matched-resolution imaging
of the H𝛼 emission line (from SINFONI/VLT), rest-frame UV and
optical continuum (from HST), and the rest-frame far-infrared (from
ALMA), as well as the radio continuum (from the Karl G. Jansky
Very Large Array; JVLA). We find bright, extended structures in the
multi-wavelength imaging, with clear clumps in H𝛼 and extended
dust continuum emission. Given this extended structure and the high
signal-to-noise that results from its high SFR, we have been able to
resolve star formation on kpc scales at multiple wavelengths.
The structure of this paper is as follows. In Section 2, we provide
an overview of the data available for our study of SHiZELS-14. We
review the high quality, but less well-resolved multi-wavelength data
available from imaging of the COSMOS field, and present the new
0.15
00
resolution imaging from SINFONI/VLT, HST, ALMA and
JVLA. We discuss the astrometric alignment of these data in Section
2.8. In Section 3, we present the global properties of SHiZELS-14
that may be inferred from spectral energy distribution (SED) fitting.
In Section 4, we present maps of the spatially-resolved SFRs in-
ferred from different SFR indicators, and derive a spatially-resolved
dust attenuation map. In Section 5, we compare the properties of
SHiZELS-14 to the submillimeter galaxy population. In Section 6,
we summarise our results.
We assume a ΛCDM cosmology with 𝐻
0
= 70 km s
−1
Mpc
−1
,
Ω
𝑀
= 0.3 and Ω
Λ
= 0.7. We use a Kroupa (2002) initial mass
function (IMF).
2 OBSERVATIONS AND DATA REDUCTION
The High-Redshift(Z) Emission Line Survey, HiZELS, used a com-
bination of narrow-band and broad-band filters to select star-forming
galaxies via their emission line fluxes (Sobral et al. 2013a, 2015)
in fields with high-quality multi-wavelength coverage (COSMOS,
UDS & SA22). This survey has yielded thousands of H𝛼 emitters
at 𝑧 = 0.4, 0.8, 1.47 & 2.23, providing sufficiently large samples to
constrain H𝛼 luminosity functions, stellar mass functions and halo
environments of typical star-forming galaxies around the peak of
cosmic star formation (Geach et al. 2008; Sobral et al. 2009, 2010,
2014; Cochrane et al. 2017, 2018).
As well as providing the sample sizes for population studies such
as these, HiZELS has also provided parent samples for more detailed
follow-up observations (Sobral et al. 2013b; Magdis et al. 2016;
MNRAS in press, 1–17 (2021)
SHiZELS-14: Resolving a dusty, star-forming galaxy at 𝑧 = 2.2 3
Stott et al. 2016; Molina et al. 2017, 2019; Gillman et al. 2019). In
particular, by exploiting the wide area HiZELS coverage, a sample
of bright H𝛼 emitters ( 𝑓
H𝛼
> 0.7 × 10
−16
erg s
−1
cm
−2
) which by
chance lie within 30
00
of bright natural guide stars (𝑅<15) could
be identified and targeted for IFU spectroscopy of the H𝛼 line us-
ing adaptive optics with the SINFONI Integral Field Unit on the
Very Large Telescope (VLT). This campaign, known as SINFONI-
HiZELS (SHiZELS), yielded high-resolution spectral maps for 20
galaxies at 𝑧 = 0.8, 𝑧 = 1.47 and 𝑧 = 2.23 at ∼ 0.15
00
(rest-frame
∼ 1 kpc) resolution (see Swinbank et al. 2012a,b; Molina et al. 2017;
Gillman et al. 2019).
We complemented these data with imaging at similar angular res-
olution but different wavelengths. Nine HiZELS galaxies were tar-
geted at ∼ 0.2
00
resolution with ALMA (Band 6 or 7, depending
on redshift), to map the dust continuum emission (see Cheng et al.
2020). UVIS Imaging in the rest-frame UV (F606W) and rest-frame
optical (F140W) filters obtained during HST Cycle 24 completes
this dataset. We now have FIR-UV-H𝛼 matched-resolution observa-
tions of a small sample of HiZELS galaxies. Since these galaxies
are H𝛼-selected, they are likely to be a less biased sub-sample of
the high-redshift star-forming galaxy population than UV-selected
samples, which target the bluest and least dusty galaxies, at an epoch
where dust is important (see Oteo et al. 2015).
Here, we present data for SHiZELS-14, which is the brightest,
most extended and more extreme source in our sample. SHiZELS-14
(10:00:51:6 +02:33:34.5) is a 𝑧 = 2.24 galaxy, with high stellar mass
(𝑀
∗
∼ 10
11
M
; Swinbank et al. 2012a; Laigle et al. 2016), and
a star-formation rate of ∼ 1000 M
yr
−1
These properties enable a
detailed investigation of the multi-wavelength extended structures of
this galaxy. In the following subsections, we provide details of the
new high-resolution imaging we have recently obtained as part of the
SHiZELS campaign. We present new radio continuum imaging from
the JVLA (at comparable angular resolution to the other new imag-
ing), which were obtained only for SHiZELS-14. We also describe
the existing data available for our multi-wavelength characterisation
of this galaxy.
2.1 Resolved H𝛼 emission from SINFONI
SINFONI observations of SHiZELS-14 took place in March 2010,
in good seeing and photometric conditions (∼ 0.6
00
), with total ex-
posure time 12ks (each individual exposure was 600s). This yielded
the sub-kpc resolution H𝛼 map shown in the lower left-hand panel
of Figure 1. SHiZELS-14 was the only 𝑧 ∼ 2.2 source resolved in
this initial Swinbank et al. (2012a,b) campaign (though note that five
more 𝑧 ∼ 2.2 galaxies were targeted in the campaign presented by
Molina et al. 2017).
Data reduction and analysis procedures are outlined in full in
Swinbank et al. (2012a,b) (see also Molina et al. 2017 and Gill-
man et al. 2019). In summary, the SINFONI ESOREX data reduction
pipeline was used to perform extraction, flat fielding and wavelength
calibration, and to create the data cube for each exposure. These
data cubes were then stacked and combined using an average with
a 3𝜎 clip, to reject cosmic rays and sky line residuals. Flux cal-
ibration was performed using observations of standard stars taken
immediately before/after science exposures, which were reduced in
the same way. H𝛼 and [Nii]𝜆𝜆6548, 6583 emission lines were fitted
on a pixel-by-pixel basis, using a 𝜒
2
minimisation procedure. This
yielded intensity, velocity, and velocity dispersion maps. An angular
resolution of ∼ 0.15
00
was achieved. The spectral resolution of the
instrument is 𝜆/Δ𝜆 ∼ 4500.
The H𝛼 flux derived from the SINFONI observations of SHiZELS-
14 was 1.6 ± 0.1 × 10
−16
erg s
−1
cm
−2
. The H𝛼-derived effective
radius is 4.6 ± 0.4 kpc (Swinbank et al. 2012b). Using the same
SINFONI data, Gillman et al. (2019) derive 𝑉
rot
/𝜎 = 0.6± 0.3 (indi-
cating that SHiZELS-14 is dispersion dominated), though, as noted
by (Swinbank et al. 2012a), this galaxy shows a substantial (in their
paper, 480 ± 40 km s
−1
) peak-to-peak velocity gradient. Swinbank
et al. (2012a) comment that the one- and two-dimensional velocity
fields are consistent with an early-stage prograde encounter. This
suggests that the disordered morphology and extreme star formation
may be related to a merger event.
2.2 Resolved UV and optical light from HST
SHiZELS-14 was observed over two HST orbits during Cycle 24
(Program 14719, PI: Best). One orbit (2700 s exposure) used the
WFC3/UVIS F606W filter, and the other used the WFC3/IR F140W
filter. Orbits were split into a 3-point dither pattern in the UVIS
channel, as a compromise between maximising sensitivity and sub-
sampling the point spread function (PSF). Since angular resolution
was preferred over sensitivity in the IR channel, a 4-point dither
pattern was used for these orbits. At 𝑧 = 2.24 (the redshift of
SHiZELS-14), the filters correspond to the rest-frame near-UV at
∼ 1900 Å, and the rest-frame optical at ∼ 4400 Å. Our observations
were designed to span the 4000 Å break, and therefore sample both
young and more evolved stellar populations, in line-free regions of
the galaxy spectrum. The HST images are made using standard HST
procedures and shown in the upper panels of Figure 1. We derive
the effective radius of the F140W image via a two-dimensional Sér-
sic profile fit, obtaining effective radius along the semi-major axis
𝑅
maj
𝑒, opt
= 4.6 ± 0.2 kpc (in good agreement with the H𝛼 measure-
ment) and axial ratio 𝑞 = 0.64 (with a Sérsic index fixed at 𝑛 = 1;
fitting this parameter gives 𝑛 = 0.9).
2.3 Resolved far-infrared emission from ALMA
SHiZELS-14 was observed with ALMA during August 2016 as part
of ALMA Cycle 3 (project code 2015.1.00026.S, PI: Ibar). Our ob-
servations, taken in configuration C36-5, used Band 6 (260 GHz,
7.5 GHz bandwidth). The time on-source was 26 minutes. We used
flux calibrator J1058+0133 and phase calibrator J0948+0022. These
observations resolved the rest-frame 840 GHz (367𝜇m) emission of
SHiZELS-14 at ∼ 0.2
00
resolution.
The image was manually cleaned down to 3𝜎 (rms ∼
25 𝜇Jy beam
−1
) at the source position. We used Briggs (robust=0.5)
visibility weighting, which assigns higher weights to longer base-
lines, producing an image with higher angular resolution (see the
image in the lower right-hand panel of Figure 1). To investigate the
impact of visibility weighting on the reduced ALMA image, we re-
imaged the ALMA data using a natural weighting, which weights
visibilities only by the rms noise (see the left-hand panel of Figure
2). This method minimises the noise level but provides poorer angu-
lar resolution, given that the density of visibilities falls towards the
outskirts of the 𝑢𝑣-plane and there is thus higher noise in the longer-
baseline visibilities. Using the re-reduced, lower angular resolution
natural-weighted image, we probe to slightly lower flux density per
beam. This will be used to assess the quality of our astrometric cali-
bration in Section 2.8.
SHiZELS-14 has an observed-frame 260 GHz flux density of
2.7 ± 0.2 mJy. It displays a compact, ∼ 3 kpc diameter core of dust
emission, with extended emission contributing substantially to the
flux. Its effective radius is notably larger, due to this extended faint
MNRAS in press, 1–17 (2021)
4 R.K. Cochrane et al.
2°33'35"
34"
33"
Dec
HST UV (F606W)
10
h
00
m
51.65
s
51.60
s
51.55
s
51.50
s
2°33'35"
34"
33"
RA
Dec
SINFONI H
1kpc
10
h
00
m
51.65
s
51.60
s
51.55
s
51.50
s
RA
ALMA beam
ALMA 260GHz
HST IR (F140W)
Figure 1: Astrometrically-calibrated, high-resolution observations of SHiZELS-14 in the rest-frame UV (HST F606W filter; upper left panel),
rest-frame optical (HST F140W filter; upper right panel), H𝛼 (SINFONI/VLT; lower left) and dust continuum (rest-frame 370 𝜇m imaging
from ALMA, reduced with Briggs weighting; lower right). The red contours on all panels outline the ALMA dust continuum emission at 50,
200, and 300 𝜇Jy beam
−1
. The green contours outline the 3𝜎 emission H𝛼 emission from SINFONI as described in Section 2.1. Pale grey
contours outline the peak of the F140W image. The emission imaged by SINFONI, ALMA and the HST F140W filter span the same extended
region, but display very different morphologies. The peaks of the short-wavelength emission are clearly offset from the peaks of the dust
continuum emission. This is particularly striking for the F606W UV emission, which is concentrated in regions with little dust emission and
does not extend down to the southern regions that are clearly probed by the other bands.
emission. We derive this radius using multiple methods. First, we
fit a Gaussian model with varying axis ratio in the 𝑢𝑣-plane, using
CASA’s uvmodelfit task (see Figure A1). The effective radius along
the semi-major axis, 𝑅
maj
𝑒
, is 4.5 ± 0.2 kpc, with fitted axial ratio
𝑞 = 0.36 ± 0.01. A two-dimensional Sérsic profile fit in the image
plane yields 𝑅
maj
𝑒,FIR
= 4.6 ± 0.2 kpc and 𝑞 = 0.47 (with the Sérsic
index fixed at 𝑛 = 1; allowing this to vary gives 𝑛 = 1.1). These
measurements of effective radius are broadly consistent with those
derived from the SINFONI H𝛼 and the HST rest-frame optical data.
2.4 Existing radio observations from COSMOS-VLA
We make use of the deep existing radio observations in the COSMOS
field from the VLA-COSMOS surveys. The VLA-COSMOS Large
Project (Schinnerer et al. 2007) surveyed 2 square degrees in VLA A-
and C-array configurations at 1.4 GHz (20 cm). The project yielded
images with rms noise ∼ 10 − 15 𝜇Jy beam
−1
at angular resolution
1.5
00
× 1.4
00
. The VLA-COSMOS Deep project (Schinnerer et al.
2010) added further A-array observations at 1.4 GHz in the central
region of the COSMOS field. The VLA-COSMOS 3 GHz Large
Project (Smolčić et al. 2017) subsequently surveyed 2.6 deg
2
at a
MNRAS in press, 1–17 (2021)
