437 research outputs found
A tale of two sites -- II: Inferring the properties of minihalo-hosted galaxies with upcoming 21-cm interferometers
The first generation of galaxies is expected to form in minihalos, accreting
gas through cooling, and possessing unique properties. Although
unlikely to be directly detected in UV/infrared surveys, the radiation from
these molecular-cooling galaxies (MCGs) could leave an imprint in the 21-cm
signal from the Cosmic Dawn. Here we quantify their detectability with upcoming
radio interferometers. We generate mock 21-cm power spectra using a model for
both MCGs as well as more massive, atomic-cooling galaxies (AGCs), allowing
both populations to have different properties and scaling relations. The galaxy
parameters are chosen so as to be consistent with: (i) high-redshift UV
luminosity functions; (ii) the upper limit on the neutral fraction from QSO
spectra; (iii) the Thomson scattering optical depth to the CMB; and (iv) the
timing of the recent putative EDGES detection. The latter implies a significant
contribution of MCGs to the Cosmic Dawn, if confirmed to be cosmological. We
then perform Bayesian inference on two models including and ignoring MCG
contributions. Comparing their Bayesian evidences, we find a strong preference
for the model including MCGs, despite the fact that it has more free
parameters. This suggests that if MCGs indeed play a significant role in the
Cosmic Dawn, it should be possible to infer their properties from upcoming
21-cm power spectra. Our study illustrates how these observations can
discriminate among uncertain galaxy formation models with varying complexities,
by maximizing the Bayesian evidence.Comment: 12 pages, 3 figures, submitted to MNRAS, comments are welcom
Inferring reionization and galaxy properties from the patchy kinetic Sunyaev-Zel'dovich signal
The patchy kinetic Sunyaev-Zel'dovich (kSZ) signal is an integral probe of
the timing and morphology of the epoch of reionization (EoR). Recent
observations have claimed a low signal-to-noise (S/N) measurement, with a
dramatic increase in S/N expected in the near future. In this work, we quantify
what we can learn about the EoR from the kSZ signal. We perform Bayesian
inference by sampling galaxy properties and using forward-models of the kSZ as
well as other EoR and galaxy observations in the likelihood. Including the
recent kSZ measurement obtained by the South Pole Telescope
(K) shifts the
posterior distribution in favor of faster and later reionization models,
resulting in lower values of the optical depth to the CMB: with a 68 confidence interval (C.I.). The combined
EoR and UV luminosity function observations also imply a typical ionizing
escape fraction of (95 C.I.), without a strong
dependence on halo mass. We show how the patchy kSZ power from our posterior
depends on the commonly-used parameters of reionization. For a given midpoint
and duration, the EoR morphology only has a few percent impact on the patchy
kSZ power in our posterior. However, a physical model is needed to obtain tight
constraints from the current low S/N patchy kSZ measurement, as it allows us to
take advantage of complimentary high- observations. Future high S/N
detections of the patchy kSZ should decrease the current uncertainties on the
timing of the EoR by factors of 2 - 3.Comment: 14 pages, 6 figures, submitted to MNRA
Implications of JWST galaxies for galaxy formation at high redshift
Using a semi-analytic galaxy-formation model, we study analogues of 8
recently discovered JWST galaxies at . We select analogues from a
cosmological simulation with a volume and an effective
particle number of enabling resolution of every atomic-cooling galaxy
at . We vary model parameters to reproduce the observed UV luminosity
function of , aiming for a statistically representative
high-redshift galaxy mock catalogue. Using the forward-modelled JWST
photometry, we identify analogues from this catalogue and study their
properties as well as possible evolutionary paths and local environments. We
find faint JWST galaxies () remain consistent with
standard galaxy-formation model and that our fiducial catalogue includes large
samples of their analogues. The properties of these analogues broadly agree
with conventional SED fitting results, except for having systematically lower
redshifts due to the evolving UV luminosity function, and for having higher
specific star formation rates as a result of burstier histories in our model.
On the other hand, only a handful of bright galaxy analogues can be identified
for observed galaxies. Moreover, in order to reproduce
JWST galaxy candidates, boosted star-forming efficiencies and reduced feedback
regulation are necessary relative to models of lower-redshift populations. This
suggests star formation in the first galaxies could differ significantly from
their lower-redshift counterparts. We also find that these candidates are
subject to low-redshift contamination, which is present in our fiducial results
as both the dusty or quiescent galaxies at .Comment: 10 pages, 11 figures, submitted to MNRAS, comments welcome
Dark-Ages Reionisation & Galaxy Formation Simulation XVI: The Thermal Memory of Reionisation
Intergalactic medium temperature is a powerful probe of the epoch of
reionisation, as information is retained long after reionisation itself.
However, mean temperatures are highly degenerate with the timing of
reionisation, with the amount heat injected during the epoch, and with the
subsequent cooling rates. We post-process a suite of semi-analytic galaxy
formation models to characterise how different thermal statistics of the
intergalactic medium can be used to constrain reionisation. Temperature is
highly correlated with redshift of reionisation for a period of time after the
gas is heated. However as the gas cools, thermal memory of reionisation is
lost, and a power-law temperature-density relation is formed, with . Constraining our model
against observations of electron optical depth and temperature at mean density,
we find that reionisation likely finished at with a soft spectral slope of . By
restricting spectral slope to the range motivated by population II
synthesis models, reionisation timing is further constrained to . We find that, in the future, the degeneracies between
reionisation timing and background spectrum can be broken using the scatter in
temperatures and integrated thermal history.Comment: 17 pages, 17 figures, Accepted for publication in MNRA
21cm signal sensitivity to dark matter decay
The redshifted 21cm signal from the Cosmic Dawn is expected to provide
unprecedented insights into early Universe astrophysics and cosmology. Here we
explore how dark matter can heat the intergalactic medium before the first
galaxies, leaving a distinctive imprint in the 21cm power spectrum. We provide
the first dedicated Fisher matrix forecasts on the sensitivity of the Hydrogen
Epoch of Reionization Array (HERA) telescope to dark matter decays. We show
that with 1000 hours of observation, HERA has the potential to improve current
cosmological constraints on the dark matter decay lifetime by up to three
orders of magnitude. Even in extreme scenarios with strong X-ray emission from
early-forming, metal-free galaxies, the bounds on the decay lifetime would be
improved by up to two orders of magnitude. Overall, HERA shall improve on
existing limits for dark matter masses below GeV for decays into
and below few MeV for decays into photons.Comment: 33 pages, 12 figure
Expanding CRISPR/Cas9 Genome Editing Capacity in Zebrafish Using SaCas9.
The type II CRISPR/Cas9 system has been used widely for genome editing in zebrafish. However, the requirement for the 5'-NGG-3' protospacer-adjacent motif (PAM) of Cas9 from Streptococcus pyogenes (SpCas9) limits its targeting sequences. Here, we report that a Cas9 ortholog from Staphylococcus aureus (SaCas9), and its KKH variant, successfully induced targeted mutagenesis with high frequency in zebrafish. Confirming previous findings, the SpCas9 variant, VQR, can also induce targeted mutations in zebrafish. Bioinformatics analysis of these new Cas targets suggests that the number of available target sites in the zebrafish genome can be greatly expanded. Collectively, the expanded target repertoire of Cas9 in zebrafish should further facilitate the utility of this organism for genetic studies of vertebrate biology
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