Can Cosmological Simulations Reproduce the Spectroscopically Confirmed Galaxies Seen at z ≥ 10?

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DRAFT VERSION DECEMBER 27, 2022
Typeset using LATEX twocolumn style in AASTeX631
Can Cosmological Simulations Reproduce the Spectroscopically Confirmed Galaxies Seen at z ≥ 10?
B.W. KELLER,1 F. MUNSHI,2 M. TREBITSCH,3 AND M. TREMMEL4
1Department of Physics and Materials Science, University of Memphis, 3720 Alumni Avenue, Memphis, TN 38152, USA
2Department of Physics and Astronomy, George Mason University 4400 University Drive, MSN 3F3 Fairfax, VA 22030-4444, USA
3Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands
4Physics Department, University College Cork, T12 K8AF Cork, Ireland
ABSTRACT
Recent photometric detections of extreme (z > 10) redshift galaxies from the JWST have been shown to be
in strong tension with existing simulation models for galaxy formation, and in the most acute case, in tension
with ΛCDM itself. These results, however, all rest on the confirmation of these distances by spectroscopy.
Recently, the JADES survey has detected the most distant galaxies with spectroscopically confirmed redshifts,
with four galaxies found with redshifts between z = 10.38 and z = 13.2. In this paper, we compare simulation
predictions from four large cosmological volumes and two zoom-in protoclusters with the JADES observations
to determine whether these spectroscopically confirmed galaxy detections are in tension with existing models
for galaxy formation, or with ΛCDM more broadly. We find that existing models for cosmological galaxy
formation can generally reproduce the observations for JADES, in terms of galaxy stellar masses, star formation
rates, and the number density of galaxies at z > 10.
Keywords: Astronomical simulations (1857) – Galaxy Formation (595) – Protogalaxies (1298) – Cosmology
(343)
1. INTRODUCTION
The successful deployment of the JWST has already pro-
duced observations of the highest-redshift galaxies detected
to date. The first sets of detections reported (Finkelstein
et al. 2022; Labbe et al. 2022; Naidu et al. 2022a; Adams
et al. 2023; Rodighiero et al. 2023) have found galaxies with
M∗ > 108 M at zphot > 10. The most extreme of these
examples, with M∗ > 1010 M at zphot > 10 have already
been shown to be in strong tension with ΛCDM (Haslbauer
et al. 2022; Boylan-Kolchin 2022). These tensions have,
however, been clouded by the large uncertainty in fitting pho-
tometric redshifts at such extreme distances (Bouwens et al.
2022; Naidu et al. 2022b; Kaasinen et al. 2022). Naidu et al.
(2022b) and Zavala et al. (2022) found that breaks in the
Spectral Energy Distribution (SED) produced by dust obscu-
ration at z ∼ 5 can masquerade as a Lyman break at z ∼ 17
for recent JWST observations (see also (Fujimoto et al. 2022)
for a similar effect in ALMA observations).
As Boylan-Kolchin (2022) showed, if the comoving num-
ber density of galaxies at z = 10 with M∗ > 1010 M
bkeller1@memphis.edu
is as high as can be estimated from Labbe et al. (2022), it
would be a significant challenge for ΛCDM : analogous to
Haldane’s “fossil rabbits in the Precambrian” (Harvey et al.
1996). Haslbauer et al. (2022) has shown that the obser-
vations of galaxies with high stellar mass (M∗ > 109) at
high redshift z & 10 from Adams et al. (2023), Labbe et al.
(2022), Naidu et al. (2022a), and Naidu et al. (2022b) are in
extreme tension with the simulation predictions of EAGLE
(Schaye et al. 2015), TNG50, and TNG100 (Pillepich et al.
2018a; Nelson et al. 2019a). These tensions all rest on the es-
timations of stellar masses provided by SED fitting and, crit-
ically, on the distance estimates themselves. Without spec-
troscopic confirmation of the redshifts reported in these ob-
servations, these potential tensions may be illusory: artifacts
of overestimated distances, and thus overestimated intrinsic
luminosities. Indeed, as Behroozi et al. (2020) has shown,
semi-empirical modelling of galaxy formation in ΛCDM
predicts JWST-detectable galaxies with M∗ > 107 M to
at least z ∼ 13.5.
Spectroscopic confirmation has now arrived with the dis-
covery in the JADES survey of 4 galaxies with zspec > 10
and M∗ & 108 M (Curtis-Lake et al. 2022; Robertson
et al. 2022). By observing 65 arcmin2 of the GOODS-S
field with JWST NIRCam and NIRSpec, JADES has con-
arXiv:2212.12804v1  [astro-ph.GA]  24 Dec 2022
2
KELLER, MUNSHI, TREBITSCH & TREMMEL
firmed the four earliest detected galaxies: JADES-GS-z10-0
at z = 10.38+0.07
−0.06, JADES-GS-z11-0 at z = 11.58
+0.05
−0.05,
JADES-GS-z12-0 at z = 12.63+0.24
−0.08, and JADES-GS-z13-
0 at z = 13.2+0.04
−0.07. Curtis-Lake et al. (2022); Robertson
et al. (2022) have measured stellar masses and star forma-
tion rates for these galaxies using the Prospector SED-fitting
code (Johnson et al. 2021), finding them to be compact, star
forming galaxies with young stellar populations and rela-
tively high star formation surface densities.
In this letter, we compare the observed JADES galaxies
to predictions from an array of large cosmological hydrody-
namical simulations. These simulations reproduce observed
galaxy population statistics (such as the observed galaxy stel-
lar mass function and fundamental plane of star formation) at
low redshift. With JADES, we are able to test whether those
same models for galaxy formation fail to reproduce these new
observations of high redshift galaxy formation.
2. SIMULATION DATA
In order to probe the predictions of current galaxy forma-
tion models, we examine simulation data from the EAGLE
(Crain et al. 2015; Schaye et al. 2015; McAlpine et al. 2016),
Illustris (Vogelsberger et al. 2014a,b; Genel et al. 2014; Nel-
son et al. 2015), TNG100 (Pillepich et al. 2018b; Springel
et al. 2018; Nelson et al. 2018; Naiman et al. 2018; Mari-
nacci et al. 2018; Nelson et al. 2019b), and Simba (Davé et al.
2019) cosmological volumes. Each of these simulations has
a volume of ∼ 106 cMpc3, with baryonic mass resolution of
106 M − 107 M, which allows them to (marginally) re-
solve the formation of M∗ = 108 M − 109 M galaxies
(an M∗ = 5×108 M galaxy in EAGLE, Illustris, TNG100,
and Simba will contain 276, 384, 357, and 27 star particles
respectively). Each of these projects includes models for gas
cooling, star formation, and feedback from supernovae (SNe)
and active galactic nuclei (AGN) that are tuned to reproduce
the z ∼ 0 stellar mass function (among other low-redshift
population statistics). In Table 1 we list the cosmological pa-
rameters used for each simulation, as well as the size of the
simulation volume, the range and number of snapshots with
redshift between z ∼ 10 and z ∼ 14, and the mass resolution
for dark matter (DM) and baryonic particles. We rely on the
public releases of the halo catalogs from each simulation to
determine galaxy stellar masses and star formation rates in
these simulation data sets.
We have also included data from the cosmological zoom-
in simulations OBELISK (Trebitsch et al. 2021) and Romu-
lusC (Tremmel et al. 2019). OBELISK is a zoom-in of the
most massive halo at z = 2 in the HORIZON-AGN volume
(Dubois et al. 2014, 2016). This region is selected to include
all DM particles within 4Rvir of the halo center at z = 2. At
z = 0, this cluster has a halo mass ofMhalo ∼ 6.6×1014M.
RomulusC is a zoom-in simulation of a smaller galaxy clus-
10
11
12
13
14
redshift z
108
109
M
∗
(M

)
EAGLE
Illustris
TNG100
Simba
OBELISK
RomulusC
JADES
Figure 1. Stellar mass of galaxies from various simulation vol-
umes as a function of redshift. Black stars with error bars show the
Robertson et al. (2022) JADES observations, while colored points
show individual galaxies from different simulated volumes. Large
points show the most massive galaxy at each redshift for a given
simulation.
ter, with halo mass Mhalo = 1.5 × 1014 M at z = 0. It
is drawn from a 503 cMpc3 DM-only volume, and applies
the same modelling approach for cooling, star formation, su-
permassive black hole (SMBH) evolution, and feedback as
the Romulus volume (Tremmel et al. 2017). Unlike the other
data sets we examine here, these zooms do not include a full
resolution sample of a large volume; instead they offer an
higher-resolution picture of early collapsing overdensities.
3. RESULTS
We begin by simply showing the distribution of galaxy
stellar masses in each simulation volume as a function of red-
shift, shown in Figure 1. Not all of the simulations we exam-
ine here have well-sampled snapshots above z = 10 (EAGLE
in particular only includes one snapshot between z ∼ 10 and
z ∼ 14). However, as can be seen, all of the simulations
produce a large number of galaxies with M∗ > 108 M at
z ∼ 10. At all redshifts, Simba and OBELISK produce the
most massive galaxies of the simulations we examine, in part
due to the larger volume they simulate/are drawn from (∼ 2.4
times the comoving volume of TNG100, the next largest vol-
ume), as well as differences in the choice of subgrid physics
models. As we move to higher redshift, only Simba and
OBELISK produce even a single galaxy above the best-fit
stellar masses of JADES-GS-z11-0, JADES-GS-z12-0, and
JADES-GS-z13-0. Illustris and TNG100 are unable to pro-
duce galaxies at z ∼ 11.5 − 12 which reach even the lower
estimate for the stellar mass of JADES-GS-z11-0.
CAN COSMOLOGICAL SIMULATIONS REPRODUCE z ≥ 10 GALAXIES
3
Simulation Cosmology
Box Size (cMpc)
z range
Nsnap MDM ( M) Mbaryon( M)
EAGLE
Planck 2013 (Planck Collaboration et al. 2014)
100
9.99
1
9.7 × 106
1.81 × 106
Illustris
WMAP-9 (Hinshaw et al. 2013)
106.5
10.00-13.34
7
6.3 × 106
1.3 × 106
TNG100
Planck 2015 (Planck Collaboration et al. 2016)
110.7
10.00-11.98
3
7.5 × 106
1.4 × 106
Simba
Planck 2015 (Planck Collaboration et al. 2016)
147.7
9.96-13.70
10
9.7 × 107
1.82 × 107
OBELISK WMAP-7 (Komatsu et al. 2011)
142.0†
10.07-13.77
13
1.2 × 106
1 × 104
RomulusC
Planck 2015 (Planck Collaboration et al. 2016)
50†
9.97-12.88
2
3.4 × 105
2.1 × 105
Table 1. Simulation data compared in this study. Each cosmological volume has a box of side length ∼ 100 cMpc. We show the choice of
cosmological parameters, box size, redshift range between z ∼ 10 − 14, number of snapshot outputs in that range, and resolution for DM
and baryons. The (†) denotes that these are zoom-in simulations of an individual galaxy protocluster, drawn from a lower-resolution volume.
OBELISK is an Eulerian simulation, and thus the baryonic resolution reported here is given as the typical mass of a star particle and the mass
of a gas cell with ∆x = 35 pc at a density of n > 10 cm−3.
108
109
1010
M∗ (M)
10−3
10−2
10−1
100
101
102
SFR(M

/yr)
EAGLE
Illustris
TNG100
Simba
OBELISK
RomulusC
sSFR = 10 Gyr−1
JADES Observations
Figure 2. Star formation rate versus stellar mass for simulated
galaxies at z ∼ 10 and observed galaxies at z ≥ 10. Simulation
data are shown as colored points, while the JADES observations are
shown as black stars. A constant sSFR of 10 Gyr−1 is shown in the
grey line.
As Robertson et al. (2022) has also provided estimates for
the star formation rates (SFR) in the 4 JADES observations,
we show in Figure 2 the SFR-M∗ plane for simulated galax-
ies at z ∼ 10. All simulation volumes produce galaxies at
z ∼ 10 with sSFR = 10 Gyr−1, except for RomulusC,
which has an sSFR roughly half this value. An sSFR of
10Gyr−1 is approximately 4 times higher than the star form-
ing main sequence at z = 2 (Rodighiero et al. 2011), con-
sistent with the observed trend of increasing sSFR towards
higher z ∼ 6 redshift (Tasca et al. 2015; Santini et al. 2017).
The banding seen in the lower-mass Simba galaxies is sim-
ply a function of resolution, as these galaxies contain only
a handful of star particles. Interestingly, there appears to be
no noticeable trend in the SFR as a function of stellar mass
for the JADES observations. However, drawing strong con-
clusions as to the nature of the SFR−M∗ relation at z ≥ 10
is ill-advised given the small number of observations, their
relatively large uncertainties, and the intrinsic scatter in the
SFR-M∗ plane that the simulations predict. Beyond these,
the NIRSpec observations of the JADES galaxies are selected
from photometric observations, which are subject to a con-
tinuum flux (and therefore SFR) limit, introducing a poten-
tial observational bias. Overall, the SFRs measured from the
simulations match the JADES observations reasonably well,
though with perhaps higher SFRs for simulated galaxies at
masses above M∗ ∼ 5 × 108 M. Further observations will
help reveal if the flat SFR −M∗ curve is a real feature of
z ≥ 10 galaxy formation, or simply an artifact of the small
sample size of the spectroscopically confirmed JADES galax-
ies and/or uncertainties in the estimation of M∗ or SFR.
In order to make a more quantitative estimate of poten-
tial tension between simulated cosmological volumes and the
Robertson et al. (2022) observations, we now look to the co-
moving number density of galaxies at each of the redshifts
probed by JADES. The deep observing area of JADES, us-
ing the JWST NIRCam, (9.7 square arcmin), yields a volume
of V ∼ (9 × 9 × 494) cMpc3 ∼ 4 × 104 cMpc3 bounded
by the comoving distance of 494 Mpc between the JADES-
GS-z10-0 at z = 10.38 and JADES-GS-z13-0 at z = 13.2.
These candidates were, however, originally selected photo-
metrically from a wider field of 65 arcmin2, which yields
a volume of V ∼ 2.7 × 105 cMpc3. We can thus esti-
mate the number density of the JADES galaxy observations
as n ∼ 3.7 × 10−6 cMpc−3.
In Figure 3, we show the
comoving number density of galaxies above a given stel-
lar mass for simulation snapshots nearest in redshift to each
of the JADES observations (if the nearest snapshot is sepa-
rated by more than 0.5 in redshift, we omit it from the plot).
Each of the JADES observations above z > 10.38 implies
a slightly higher number density than what is produced by
the simulations. We also show the estimated number den-
sity assuming a constant stellar baryon conversion efficiency
(M∗ = εfBMhalo) of ε = 0.1, and the maximum expected
number density (with M∗ = fBMhalo), following Boylan-
Kolchin (2022) using a Sheth & Tormen (1999) halo mass
function. Each of the JADES galaxies lies outside of the
4
KELLER, MUNSHI, TREBITSCH & TREMMEL
108
109
M∗(M)
10−7
10−6
10−5
10−4
10−3
10−2
n(>M
∗
)(cMpc
−
3
)
JADES-GS-z10-0
108
109
M∗(M)
10−7
10−6
10−5
10−4
10−3
10−2
n(>M
∗
)(cMpc
−
3
)
JADES-GS-z11-0
108
109
M∗(M)
10−7
10−6
10−5
10−4
10−3
10−2
n(>M
∗
)(cMpc
−
3
)
JADES-GS-z12-0
108
109
M∗(M)
10−7
10−6
10−5
10−4
10−3
10−2
n(>M
∗
)(cMpc
−
3
)
JADES-GS-z13-0
EAGLE
Illustris
TNG100
Simba
ε = 0.1
M∗ > fBMhalo
Stefanon+ 21
JADES
Figure 3. Cumulative number density of galaxies above a given stellar mass for simulation snapshots (colored areas) at the nearest redshift to
the JADES observations. Snapshots are chosen such that no more than ∆z = 0.5 separates the simulation snapshot redshift from the observed
redshift. Black stars show the detections from Robertson et al. (2022). Filled area shows the uncertainty from Poisson sampling of each mass
bin. The grey dashed curve shows the expected number density for an integrated star formation efficiency ε of 10 per cent, and the shaded grey
are shows the excluded region where more stellar mass is produced in halos than their available baryon budget. Black circles at z ∼ 10 show
the estimated number density from observations by Stefanon et al. (2021). We exclude from this figure the data from zoom-in simulations.
excluded region of M∗ = fBMhalo, but the most extreme
two cases (JADES-GS-z11-0 and JADES-GS-z12-0) imply
integrated baryon conversion efficiencies near 10 per cent
(M∗/(fBMhalo) ∼ 0.1). For z ∼ 10, we also show the in-
dependent measurements for the galaxy stellar mass function
measured by the GREATS ALMA survey by Stefanon et al.
(2021). The highest predicted number density for massive
halos at these redshifts is from Simba, and only JADES-GS-
z11-0 and JADES-GS-z12-0 imply number densities higher
than in Simba for galaxies at their stellar mass. Even for
the most extreme case, JADES-GS-z11-0, the probability of
finding a galaxy with stellar mass above M∗ = 108.9 M at
z ∼ 11, in a random volume of 2.7 × 105 cMpc3 in Simba,
is 8%. If we instead take the lower estimate for the stellar
masses from JADES-GS-z11-0 (M∗ = 108.5 M), this prob-
ability rises to 92%. There does not appear to be any signif-
icant tension in the density of galaxies with M∗ ∼ 108 M
at z > 10 inferred from JADES and the number density
produced by at least one existing cosmological simulation
(Simba).
4. DISCUSSION
We have compared the recent detection of spectroscopi-
cally confirmed z > 10 galaxies from the JADES survey
to the EAGLE, Illustris, TNG100, and Simba surveys. We
show that all four simulation suites produce galaxies with
M∗ ∼ 108.5 M at z ∼ 10, and that Simba in particular
produces at least one galaxy with mass comparable to the
JADES observations at each observed redshift. The JADES
galaxies show a relatively flat SFR −M∗ trend, in contrast
to the constant sSFR of ∼ 5−10Gyr−1 for simulated galax-
ies at z ∼ 10. Comparing the estimated JADES galaxy
stellar mass functions to the simulation predictions shows
that these simulations are in reasonable agreement with the
number density of galaxies at z ∼ 10 observed by JADES
CAN COSMOLOGICAL SIMULATIONS REPRODUCE z ≥ 10 GALAXIES
5
and the earlier ALMA measurements from Stefanon et al.
(2021) (though Illustris and TNG100 appear to be slightly
under-predicting the formation of galaxies at z ∼ 10). At
z ∼ 11 − 12, JADES implies a slightly higher number den-
sity of galaxies at M > 108 M than are predicted by any of
the simulation volumes we examine here. We find, however,
that given the small number of objects confirmed in JADES
(in a volume of ∼ 2.7 × 105 cMpc3), none of the JADES
observations is in greater than 2σ tension for the best-fit stel-
lar mass, relative to the Simba simulation. JADES-GS-z11-0
implies a slightly higher density at z = 11 for galaxies with
M∗ ∼ 109 M, but the difference between Simba and den-
sity inferred from JADES is only slight. A randomly cho-
sen volume of 2.7 × 105 cMpc3 from Simba at z = 11.4
will contain a galaxy with stellar mass greater than that of
JADES-GS-z11-0 8% of the time. At the lower uncertainty
for the JADES-GS-z11-0 stellar mass, this probability grows
to 92%.
As future observations better constrain the stellar mass
function at z ∼ 11, this tension may strengthen or disap-
pear. In order to be in tension with all models for galaxy
formation in ΛCDM (by implying galaxy star formation ef-
ficiencies > 100%), the number density of M∗ = 109 M
galaxies at z ∼ 11 would need to be more than 3 orders
of magnitude higher than what is implied by the JADES-
GS-z11-0 detection. This tension may be resolved by fu-
ture refinements in the SED-fit stellar mass estimates low-
ering the stellar mass measured for JADES-GS-z11-0, or
simply by JADES-GS-z11-0 residing in a moderately rare
(P ∼ 8%) overdensity. For a mean cosmological mass den-
sity of ρm ∼ 4 × 1010 M cMpc−3, a comoving volume of
4×104 cMpc3 contains a total mass of ∼ 1015M. If the en-
tire volume covered by the deepest JADES observations is a
rare overdensity that will eventually collapse to form a z ∼ 0
cluster, it will be on the order of the most massive clusters
detected (Jee et al. 2014). It is unlikely that the entire JADES
volume is probing a single large overdensity (given the fact
that it is a pencil-beam volume with a comoving depth of
494 cMpc over an area on the sky of only (9 × 9) cMpc2),
but the possibility that one or more of the JADES galaxies
above z > 10 resides within one or more protoclusters such
as those simulated in OBELISK is still plausible.
One question that arises from this data is why the Simba
simulations predict more M∗ > 108 M galaxies at z > 10
than Illustris and TNG100. While the Simba volume is some-
what larger than Illustris and TNG100 (Simba’s volume is
∼ 2.4 times larger than TNG100), it also produces a higher
density of galaxies with M∗ > 108 M at all redshifts we
have examined here. Each of these simulations applies a
different set of models for star formation and feedback by
SNe and AGN. In Simba, SMBHs are seeded in galaxies with
M∗ > 109.5M, while in TNG100 SMBHs are seeded in ha-
los withMhalo > 7.4×1010M. This means that none of the
galaxies we show in Figure 1 or in Figure 3 contain SMBHs,
so the differences we find must be a function of the differ-
ent star formation and feedback recipes used in TNG100 and
Simba. Simba applies a tuned reduction in the SN-driven
outflow mass loadings η above z > 3 to better match obser-
vations of the galaxy stellar mass function at z > 6, lowering
the mass loadings by (a/0.25)2 (Davé et al. 2019). It ap-
pears that lower mass loadings at high redshift are not only
important to matching observations at z ∼ 6, but for z > 10
as well. Understanding how SNe regulate galaxy formation
and drive outflows in these early epochs will be an important
avenue of future simulation study.
While the results we have shown here show that there is
no strong tension between at least one existing large-volume
cosmological simulation and the spectroscopically confirmed
galaxy detections from JADES, it is important to note that the
cosmological volumes we have examined here are all rela-
tively low resolution: even a 109 M galaxy only contains
∼ 50 star particles in Simba. These simulations are also
tuned to reproduce z ∼ 0 galaxy properties. Star formation
and feedback at low redshift are still relatively poorly un-
derstood processes (Naab & Ostriker 2017), a problem that
becomes much more severe at epochs as early as z > 10
(Crosby et al. 2013; Jeon et al. 2014; Visbal et al. 2020).
An obvious direction for future studies is to search for
galaxies of similar mass in higher resolution, high redshift
simulation volumes. In particular, simulations designed to
study reionization such as Renaissance (O’Shea et al. 2015),
OBELISK (Trebitsch et al. 2021), SPHINX (Rosdahl et al.
2018), and FLARES (Lovell et al. 2021) all achieve res-
olutions significantly higher than any of the volumes we
have studied here. Many also feature more physically mo-
tivated models for stellar feedback, which are possible at
these higher resolutions. FLARES produces a stellar mass
function at z ∼ 10 consistent with Stefanon et al. (2021),
which we show here to be consistent with JADES. Zoom-in
simulations of protoclusters such as OBELISK will be par-
ticularly fruitful, as the earliest bright galaxies to form are
likely to be found in these environments. As we show in
Figure 1, OBELISK contains a number of simulated galaxies
with comparable stellar masses to each of the JADES detec-
tions at every redshift of the JADES sample, resolved with
> 1000 star particles. Zoom-in simulations such as these
will be a powerful tool for understanding the earliest phase
of galaxy formation at z > 10.
5. CONCLUSIONS
We have compared the recent observations of the highest
redshift galaxies with spectroscopically confirmed distances
from the JADES survey (Robertson et al. 2022) to simulated
galaxies from EAGLE, Illustris, TNG100, and Simba vol-
6
KELLER, MUNSHI, TREBITSCH & TREMMEL
umes and the OBELISK and RomulusC zoom-ins. In gen-
eral, we find that each of these simulations produces galax-
ies with comparable stellar masses to the JADES galaxies by
z ∼ 10. The most massive JADES galaxies have somewhat
lower SFRs than simulated galaxies at z ∼ 10, but lie within
the scatter of the simulations. The galaxy number density
implied by the JADES galaxies at z ∼ 10 is consistent with
both the simulations and past observations. At higher red-
shift, only Simba and OBELISK produce galaxies as massive
as are found in JADES. The number density of galaxies in-
ferred from JADES is slightly larger than what is predicted
by Simba at z = 11 and z = 12, but at a low level of signifi-
cance. Overall, there appears to be no strong tension between
models for galaxy formation in cosmological hydrodynamic
simulations and the most distant spectroscopically confirmed
galaxies.
ACKNOWLEDGEMENTS
BWK would like to thank Tessa Klettl for her incredible
support and help editing this manuscript. MT acknowledges
support from the NWO grant 0.16.VIDI.189.162 (“ODIN”).
We also would like to thank James Wadsley for useful discus-
sions, and for Jordan Van Nest in helping with the RomulusC
simulation data. We especially would like to thank the teams
behind EAGLE, Illustris, TNG, and Simba for providing pub-
lic access to their simulation datasets. This study would have
been impossible to complete in a timely fashion without the
community spirit behind these public releases.
We acknowledge the Virgo Consortium for making their
simulation data available. The EAGLE simulations were per-
formed using the DiRAC-2 facility at Durham, managed by
the ICC, and the PRACE facility Curie based in France at
TGCC, CEA, Bruyéresle-Châtel.
The IllustrisTNG simulations were undertaken with com-
pute time awarded by the Gauss Centre for Supercomput-
ing (GCS) under GCS Large-Scale Projects GCS-ILLU and
GCS-DWAR on the GCS share of the supercomputer Hazel
Hen at the High Performance Computing Center Stuttgart
(HLRS), as well as on the machines of the Max Planck Com-
puting and Data Facility (MPCDF) in Garching, Germany.
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