23 research outputs found
First Light and Reionisation Epoch Simulations (FLARES) X: Environmental Galaxy Bias and Survey Variance at High Redshift
Upcoming deep galaxy surveys with JWST will probe galaxy evolution during the
epoch of reionisation (EoR, ) over relatively compact areas
(e.g. 300\,arcmin for the JADES GTO survey). It is therefore
imperative that we understand the degree of survey variance, to evaluate how
representative the galaxy populations in these studies will be. We use the
First Light And Reionisation Epoch Simulations (FLARES) to measure the galaxy
bias of various tracers over an unprecedentedly large range in overdensity for
a hydrodynamic simulation, and use these relations to assess the impact of bias
and clustering on survey variance in the EoR. Star formation is highly biased
relative to the underlying dark matter distribution, with the mean ratio of the
stellar to dark matter density varying by a factor of 100 between regions of
low and high matter overdensity (smoothed on a scale of 14\,cMpc). This
is reflected in the galaxy distribution -- the most massive galaxies are found
solely in regions of high overdensity. As a consequence of the above, galaxies
in the EoR are highly clustered, which can lead to large variance in survey
number counts. For mean number counts (1000), in a unit
redshift slice of angular area 300\,arcmin (1.4\,deg), the 2-sigma
range in is roughly a factor of four (two). We present relations between
the expected variance and survey area for different survey geometries; these
relations will be of use to observers wishing to understand the impact of
survey variance on their results.Comment: 14 pages, 17 figures. Paper 10 in the First Light and Reionisation
Epoch Simulations (FLARES) serie
First Light and Reionisation Epoch Simulations (FLARES) - VI. The colour evolution of galaxies z=5-15
With its exquisite sensitivity, wavelength coverage, and spatial and spectral resolution, the James Webb Space Telescope (JWST) is poised to revolutionize our view of the distant, high-redshift (z > 5) Universe. While Webb's spectroscopic observations will be transformative for the field, photometric observations play a key role in identifying distant objects and providing more comprehensive samples than accessible to spectroscopy alone. In addition to identifying objects, photometric observations can also be used to infer physical properties and thus be used to constrain galaxy formation models. However, inferred physical properties from broad-band photometric observations, particularly in the absence of spectroscopic redshifts, often have large uncertainties. With the development of new tools for forward modelling simulations, it is now routinely possible to predict observational quantities, enabling a direct comparison with observations. With this in mind, in this work, we make predictions for the colour evolution of galaxies at z = 5-15 using the First Light And Reionisation Epoch Simulations (flares) cosmological hydrodynamical simulation suite. We predict a complex evolution with time, driven predominantly by strong nebular line emission passing through individual bands. These predictions are in good agreement with existing constraints from Hubble and Spitzer as well as some of the first results from Webb. We also contrast our predictions with other models in the literature: While the general trends are similar, we find key differences, particularly in the strength of features associated with strong nebular line emission. This suggests photometric observations alone should provide useful discriminating power between different models and physical states of galaxies.Peer reviewe
First Light And Reionisation Epoch Simulations (FLARES) VIII. The Emergence of Passive Galaxies at
Passive galaxies are ubiquitous in the local universe, and various physical
channels have been proposed that lead to this passivity. To date, robust
passive galaxy candidates have been detected up to , but it is
still unknown if they exist at higher redshifts, what their relative abundances
are, and what causes them to stop forming stars. We present predictions from
the First Light And Reionisation Epoch Simulations (FLARES), a series of zoom
simulations of a range of overdensities using the EAGLE code. Passive galaxies
occur naturally in the EAGLE model at high redshift, and are in good agreement
with number density estimates from HST and early JWST results at . Due to the unique FLARES approach, we extend these predictions to
higher redshifts, finding passive galaxy populations up to . Feedback
from supermassive black holes is the main driver of passivity, leading to
reduced gas fractions and star forming gas reservoirs. We find that passive
galaxies at are not identified in the typical UVJ selection
space due to their still relatively young stellar populations, and present new
rest--frame selection regions. We also present NIRCam and MIRI fluxes, and find
that significant numbers of passive galaxies at should be
detectable in upcoming wide surveys with JWST. Finally, we present JWST colour
distributions, with new selection regions in the observer--frame for
identifying these early passive populations.Comment: 21 pages, 20 figures. Accepted to MNRA
First light and reionization epoch simulations (FLARES) V : the redshift frontier
JWST is set to transform many areas of astronomy, one of the most exciting is the expansion of the redshift frontier to z > 10. In its first year, alone JWST should discover hundreds of galaxies, dwarfing the handful currently known. To prepare for these powerful observational constraints, we use the First Light And Reionization Epoch simulations (flares) to predict the physical and observational properties of the z > 10 population of galaxies accessible to JWST. This is the first time such predictions have been made using a hydrodynamical model validated at low redshift. Our predictions at z = 10 are broadly in agreement with current observational constraints on the far-UV luminosity function and UV continuum slope beta, though the observational uncertainties are large. We note tension with recent constraints z similar to 13 from Harikane et al. () - compared to these constraints, flares predicts objects with the same space density should have an order-of-magnitude lower luminosity, though this is mitigated slightly if dust attenuation is negligible in these systems. Our predictions suggest that in JWST's first cycle alone, around 600 galaxies should be identified at z > 10, with the first small samples available at z > 13.Peer reviewe
First Light And Reionization Epoch Simulations (FLARES) VII : The star formation and metal enrichment histories of galaxies in the early Universe
The star formation and metal enrichment histories of galaxies - at any epoch - constitute one of the key properties of galaxies, and their measurement is a core aim of observational extragalactic astronomy. The lack of deep rest-frame optical coverage at high redshift has made robust constraints elusive, but this is now changing thanks to JWST. In preparation for the constraints provided by JWST, we explore the star formation and metal enrichment histories of galaxies at z = 5-13 using the First Light And Reionization Epoch Simulations (FLARES) suite. Built on the EAGLE model, the unique strategy of FLARES allows us to simulate galaxies with a wide range of stellar masses (and luminosities) and environments. While we predict significant redshift evolution of average ages and specific star formation rates, our core result is mostly a flat relationship of age and specific star formation rate with stellar mass. We also find that galaxies in this epoch predominantly have strongly rising star formation histories, albeit with the normalization dropping with redshift and stellar mass. In terms of chemical enrichment, we predict a strong stellar mass-metallicity relation present at z = 10 and beyond alongside significant a-enhancement. Finally, we find no large-scale environmental dependence of the relationship between age, specific star formation rate, or metallicity with stellar mass.Peer reviewe
First Light And Reionisation Epoch Simulations (FLARES) XIV: The Balmer/4000~\AA\ Breaks of Distant Galaxies
With the successful launch and commissioning of JWST we are now able to
routinely spectroscopically probe the rest-frame optical emission of galaxies
at for the first time. Amongst the most useful spectral diagnostics used
in the optical is the Balmer/4000~\AA\ break; this is, in principle, a
diagnostic of the mean ages of composite stellar populations. However, the
Balmer break is also sensitive to the shape of the star formation history, the
stellar (and gas) metallicity, the presence of nebular continuum emission, and
dust attenuation. In this work we explore the origin of the Balmer/4000~\AA\
break using the SYNTHESIZER synthetic observations package. We then make
predictions of the Balmer/4000~\AA\ break using the First Light and
Reionisation Epoch Simulations (FLARES) at . We find that the average
break strength weakly correlates with stellar mass and rest-frame far-UV
luminosity, but that this is predominantly driven by dust attenuation. We also
find that break strength provides a weak diagnostic of the age but performs
better as a means to constrain star formation and stellar mass, alongside the
UV and optical luminosity, respectively.Comment: 9 pages, 9 figures, submitted to MNRA
First Light And Reionisation Epoch Simulations (FLARES) XIII: the Lyman-continuum emission of high-redshift galaxies
The history of reionisation is highly dependent on the ionising properties of
high-redshift galaxies. It is therefore important to have a solid understanding
of how the ionising properties of galaxies are linked to physical and
observable quantities. In this paper, we use the First Light and Reionisation
Epoch Simulations (FLARES) to study the Lyman-continuum (LyC, i.e.
hydrogen-ionising) emission of massive () galaxies
at redshifts . We find that the specific ionising emissivity (i.e.
intrinsic ionising emissivity per unit stellar mass) decreases as stellar mass
increases, due to the combined effects of increasing age and metallicity.
FLARES predicts a median ionising photon production efficiency (i.e. intrinsic
ionising emissivity per unit intrinsic far-UV luminosity) of
, with values
spanning the range . This is
within the range of many observational estimates, but below some of the
extremes observed. We compare the production efficiency with observable
properties, and find a weak negative correlation with the UV-continuum slope,
and a positive correlation with the OIII equivalent width. We also consider the
dust-attenuated production efficiency (i.e. intrinsic ionising emissivity per
unit dust-attenuated far-UV luminosity), and find a median of
. Within our sample of
galaxies, it is the stellar populations in low
mass galaxies that contribute the most to the total ionising emissivity. Active
galactic nuclei (AGN) emission accounts for % of the total emissivity
at a given redshift, and extends the LyC luminosity function by dex.Comment: 18 pages, 17 figures, submitted to MNRA
First Light And Reionisation Epoch Simulations (FLARES) XI: [OIII] emitting galaxies at
JWST has now made it possible to probe the rest-frame optical line emission
of high-redshift galaxies extending to z~9, and potentially beyond. To aid in
the interpretation of these emerging constraints, in this work we explore
predictions for [OIII] emission in high-redshift galaxies using the First Light
and Reionisation Epoch Simulations (FLARES). We produce predictions for the
[OIII] luminosity function, its correlation with the UV luminosity, and the
distribution of equivalent widths (EWs). We also explore how the [OIII] EW
correlates with physical properties including specific star formation rate,
metallicity, and dust attenuation. Our predictions are largely consistent with
recent observational constraints on the luminosity function, average equivalent
widths, and line ratios. However, they fail to reproduce the observed tail of
high-EW sources and the number density of extreme line emitters. Possibilities
to explain these discrepancies include an additional source of ionising photons
and/or greater stochasticity in star formation in the model or photometric
scatter and/or bias in the observations. With JWST now rapidly building larger
samples and a wider range of emission lines the answer to this remaining
discrepancy should be available imminently.Comment: 15 pages, accepted for publication in MNRAS, minor changes from
original versio
Cosmic Evolution Early Release Science (CEERS) survey: The colour evolution of galaxies in the distant Universe
The wavelength-coverage and sensitivity of JWST now enables us to probe the
rest-frame UV - optical spectral energy distributions (SEDs) of galaxies at
high-redshift (). From these SEDs it is, in principle, through SED fitting
possible to infer key physical properties, including stellar masses, star
formation rates, and dust attenuation. These in turn can be compared with the
predictions of galaxy formation simulations allowing us to validate and refine
the incorporated physics. However, the inference of physical properties,
particularly from photometry alone, can lead to large uncertainties and
potential biases. Instead, it is now possible, and common, for simulations to
be \emph{forward-modelled} to yield synthetic observations that can be compared
directly to real observations. In this work, we measure the JWST broadband
fluxes and colours of a robust sample of galaxies using the Cosmic
Evolution Early Release Science (CEERS) Survey. We then analyse predictions
from a variety of models using the same methodology and compare the
NIRCam/F277W magnitude distribution and NIRCam colours with observations. We
find that the predicted and observed magnitude distributions are similar, at
least at the distributions differ somewhat, though our
observed sample size is small and thus susceptible to statistical fluctuations.
Likewise, the predicted and observed colour evolution show broad agreement, at
least at . There is however some disagreement between the observed and
modelled strength of the strong line contribution. In particular all the models
fails to reproduce the F410M-F444W colour at , though, again, the sample
size is small here.Comment: 11 pages, 10 figures, submitted to MNRA
A Framework for the Development, Design and Implementation of a Sustained Arctic Ocean Observing System
Rapid Arctic warming drives profound change in the marine environment that have significant socio-economic impacts within the Arctic and beyond, including climate and weather hazards, food security, transportation, infrastructure planning and resource extraction. These concerns drive efforts to understand and predict Arctic environmental change and motivate development of an Arctic Region Component of the Global Ocean Observing System (ARCGOOS) capable of collecting the broad, sustained observations needed to support these endeavors. This paper provides a roadmap for establishing the ARCGOOS. ARCGOOS development must be underpinned by a broadly-endorsed framework grounded in high-level policy drivers and the scientific and operational objectives that stem from them. This should be guided by a transparent, internationally accepted governance structure with recognized authority and organizational relationships with the national agencies that ultimately execute network plans. A governance model for ARCGOOS must guide selection of objectives, assess performance and fitness-to-purpose, and advocate for resources. A requirements-based framework for an ARCGOOS begins with the Societal Benefit Areas (SBAs) that underpin the system. SBAs motivate investments and define the system's science and operational objectives. Objectives can then be used to identify key observables and their scope. The domains of planning/policy, strategy, and tactics define scope ranging from decades and basins to focused observing with near real time data delivery. Patterns emerge when this analysis is integrated across an appropriate set of SBAs and science/operational objectives, identifying impactful variables and the scope of the measurements. When weighted for technological readiness and logistical feasibility, this can be used to select Essential ARCGOOS Variables, analogous to Essential Ocean Variables of the Global Ocean Observing System. The Arctic presents distinct needs and challenges, demanding novel observing strategies. Cost, traceability and ability to integrate region-specific knowledge have to be balanced, in an approach that builds on existing and new observing infrastructure. ARCGOOS should benefit from established data infrastructures following the Findable, Accessible, Interoperable, Reuseable Principles to ensure preservation and sharing of data and derived products. Linking to the Sustaining Arctic Observing Networks (SAON) process and involving Arctic stakeholders, for example through liaison with the International Arctic Science Committee (IASC), can help ensure success