290 research outputs found
Clustering-based redshift estimation : application to VIPERS/CFHTLS
We explore the accuracy of the clustering-based redshift estimation proposed by Ménard et al. when applied to VIMOS Public Extragalactic Redshift Survey (VIPERS) and Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) real data. This method enables us to reconstruct redshift distributions from measurement of the angular clustering of objects using a set of secure spectroscopic redshifts. We use state-of-the-art spectroscopic measurements with iAB 0.5 which allows us to test the accuracy of the clustering-based redshift distributions. We show that this method enables us to reproduce the true mean colour–redshift relation when both populations have the same magnitude limit. We also show that this technique allows the inference of redshift distributions for a population fainter than the reference and we give an estimate of the colour–redshift mapping in this case. This last point is of great interest for future large-redshift surveys which require a complete faint spectroscopic sample.Publisher PDFPeer reviewe
Euclid: Discovering pair-instability supernovae with the Deep Survey
Pair-instability supernovae are theorized supernovae that have not yet been
observationally confirmed. They are predicted to exist in low-metallicity
environments. Because overall metallicity becomes lower at higher redshifts,
deep near-infrared transient surveys probing high-redshift supernovae are
suitable to discover pair-instability supernovae. The Euclid satellite, which
is planned to be launched in 2023, has a near-infrared wide-field instrument
that is suitable for a high-redshift supernova survey. Although no dedicated
supernova survey is currently planned during the Euclid's 6 year primary
mission, the Euclid Deep Survey is planned to make regular observations of
three Euclid Deep Fields (40 deg2 in total) spanning six years. While the
observations of the Euclid Deep Fields are not frequent, we show that the
predicted long duration of pair-instability supernovae would allow us to search
for high-redshift pair-instability supernovae with the Euclid Deep Survey.
Based on the current observational plan of the Euclid mission, we conduct
survey simulations in order to estimate the expected numbers of
pair-instability supernova discoveries. We find that up to several hundred
pair-instability supernovae at z < ~ 3.5 can be discovered by the Euclid Deep
Survey. We also show that pair-instability supernova candidates can be
efficiently identified by their duration and color that can be determined with
the current Euclid Deep Survey plan. We conclude that the Euclid mission can
lead to the first confident discovery of pair-instability supernovae if their
event rates are as high as those predicted by recent theoretical studies. We
also update the expected numbers of superluminous supernova discoveries in the
Euclid Deep Survey based on the latest observational plan.Comment: 12 pages, 13 figures, 2 tables, submitted to Astronomy & Astrophysic
Euclid: Modelling massive neutrinos in cosmology -- a code comparison
The measurement of the absolute neutrino mass scale from cosmological
large-scale clustering data is one of the key science goals of the Euclid
mission. Such a measurement relies on precise modelling of the impact of
neutrinos on structure formation, which can be studied with -body
simulations. Here we present the results from a major code comparison effort to
establish the maturity and reliability of numerical methods for treating
massive neutrinos. The comparison includes eleven full -body implementations
(not all of them independent), two -body schemes with approximate time
integration, and four additional codes that directly predict or emulate the
matter power spectrum. Using a common set of initial data we quantify the
relative agreement on the nonlinear power spectrum of cold dark matter and
baryons and, for the -body codes, also the relative agreement on the
bispectrum, halo mass function, and halo bias. We find that the different
numerical implementations produce fully consistent results. We can therefore be
confident that we can model the impact of massive neutrinos at the sub-percent
level in the most common summary statistics. We also provide a code validation
pipeline for future reference.Comment: 43 pages, 17 figures, 2 tables; published on behalf of the Euclid
Consortium; data available at https://doi.org/10.5281/zenodo.729797
The PAU Survey & Euclid: Improving broad-band photometric redshifts with multi-task learning
Current and future imaging surveys require photometric redshifts (photo-z) to
be estimated for millions of galaxies. Improving the photo-z quality is a major
challenge to advance our understanding of cosmology. In this paper, we explore
how the synergies between narrow-band photometric data and large imaging
surveys can be exploited to improve broad-band photometric redshifts. We use a
multi-task learning (MTL) network to improve broad-band photo-z estimates by
simultaneously predicting the broad-band photo-z and the narrow-band photometry
from the broad-band photometry. The narrow-band photometry is only required in
the training field, which enables better photo-z predictions also for the
galaxies without narrow-band photometry in the wide field. This technique is
tested with data from the Physics of the Accelerating Universe Survey (PAUS) in
the COSMOS field. We find that the method predicts photo-z that are 14% more
precise down to magnitude i_AB<23, while reducing the outlier rate by 40% with
respect to the baseline network mapping broad-band colours to only photo-zs.
Furthermore, MTL significantly reduces the photo-z bias for high-redshift
galaxies, improving the redshift distributions for tomographic bins with z>1.
Applying this technique to deeper samples is crucial for future surveys like
\Euclid or LSST. For simulated data, training on a sample with i_AB <23, the
method reduces the photo-z scatter by 15% for all galaxies with 24<i_AB<25. We
also study the effects of extending the training sample with photometric
galaxies using PAUS high-precision photo-zs, which further reduces the photo-z
scatter.Comment: 20 pages, 16 figure
Euclid preparation. XXIV. Calibration of the halo mass function in CDM cosmologies
Euclid's photometric galaxy cluster survey has the potential to be a very
competitive cosmological probe. The main cosmological probe with observations
of clusters is their number count, within which the halo mass function (HMF) is
a key theoretical quantity. We present a new calibration of the analytic HMF,
at the level of accuracy and precision required for the uncertainty in this
quantity to be subdominant with respect to other sources of uncertainty in
recovering cosmological parameters from Euclid cluster counts. Our model is
calibrated against a suite of N-body simulations using a Bayesian approach
taking into account systematic errors arising from numerical effects in the
simulation. First, we test the convergence of HMF predictions from different
N-body codes, by using initial conditions generated with different orders of
Lagrangian Perturbation theory, and adopting different simulation box sizes and
mass resolution. Then, we quantify the effect of using different halo-finder
algorithms, and how the resulting differences propagate to the cosmological
constraints. In order to trace the violation of universality in the HMF, we
also analyse simulations based on initial conditions characterised by
scale-free power spectra with different spectral indexes, assuming both
Einstein--de Sitter and standard CDM expansion histories. Based on
these results, we construct a fitting function for the HMF that we demonstrate
to be sub-percent accurate in reproducing results from 9 different variants of
the CDM model including massive neutrinos cosmologies. The calibration
systematic uncertainty is largely sub-dominant with respect to the expected
precision of future mass-observation relations; with the only notable exception
of the effect due to the halo finder, that could lead to biased cosmological
inference.Comment: 24 pages, 21 figures, 5 tables, 3 appendixes
Euclid preparation - VII. Forecast validation for Euclid cosmological probes
Aims. The Euclid space telescope will measure the shapes and redshifts of galaxies to reconstruct the expansion history of the Universe and the growth of cosmic structures. The estimation of the expected performance of the experiment, in terms of predicted constraints on cosmological parameters, has so far relied on various individual methodologies and numerical implementations, which were developed for different observational probes and for the combination thereof. In this paper we present validated forecasts, which combine both theoretical and observational ingredients for different cosmological probes. This work is presented to provide the community with reliable numerical codes and methods for Euclid cosmological forecasts.
Methods. We describe in detail the methods adopted for Fisher matrix forecasts, which were applied to galaxy clustering, weak lensing, and the combination thereof. We estimated the required accuracy for Euclid forecasts and outline a methodology for their development. We then compare and improve different numerical implementations, reaching uncertainties on the errors of cosmological parameters that are less than the required precision in all cases. Furthermore, we provide details on the validated implementations, some of which are made publicly available, in different programming languages, together with a reference training-set of input and output matrices for a set of specific models. These can be used by the reader to validate their own implementations if required.
Results. We present new cosmological forecasts for Euclid. We find that results depend on the specific cosmological model and remaining freedom in each setting, for example flat or non-flat spatial cosmologies, or different cuts at non-linear scales. The numerical implementations are now reliable for these settings. We present the results for an optimistic and a pessimistic choice for these types of settings. We demonstrate that the impact of cross-correlations is particularly relevant for models beyond a cosmological constant and may allow us to increase the dark energy figure of merit by at least a factor of three
Euclid preparation. TBD. The effect of linear redshift-space distortions in photometric galaxy clustering and its cross-correlation with cosmic shear
Cosmological surveys planned for the current decade will provide us with
unparalleled observations of the distribution of galaxies on cosmic scales, by
means of which we can probe the underlying large-scale structure (LSS) of the
Universe. This will allow us to test the concordance cosmological model and its
extensions. However, precision pushes us to high levels of accuracy in the
theoretical modelling of the LSS observables, in order not to introduce biases
in the estimation of cosmological parameters. In particular, effects such as
redshift-space distortions (RSD) can become relevant in the computation of
harmonic-space power spectra even for the clustering of the photometrically
selected galaxies, as it has been previously shown in literature studies. In
this work, we investigate the contribution of linear RSD, as formulated in the
Limber approximation by arXiv:1902.07226, in forecast cosmological analyses
with the photometric galaxy sample of the Euclid survey, in order to assess
their impact and quantify the bias on the measurement of cosmological
parameters that neglecting such an effect would cause. We perform this task by
producing mock power spectra for photometric galaxy clustering and weak
lensing, as expected to be obtained from the Euclid survey. We then use a
Markov chain Monte Carlo approach to obtain the posterior distributions of
cosmological parameters from such simulated observations. We find that
neglecting the linear RSD leads to significant biases both when using galaxy
correlations alone and when these are combined with cosmic shear, in the
so-called 32pt approach. Such biases can be as large as
-equivalent when assuming an underlying CDM cosmology. When
extending the cosmological model to include the equation-of-state parameters of
dark energy, we find that the extension parameters can be shifted by more than
.Comment: 15 pages, 5 figures. To be submitted in A&
Euclid preparation: VII. Forecast validation for Euclid cosmological probes
Aims. The Euclid space telescope will measure the shapes and redshifts of galaxies to reconstruct the expansion history of the Universe and the growth of cosmic structures. The estimation of the expected performance of the experiment, in terms of predicted constraints on cosmological parameters, has so far relied on various individual methodologies and numerical implementations, which were developed for different observational probes and for the combination thereof. In this paper we present validated forecasts, which combine both theoretical and observational ingredients for different cosmological probes. This work is presented to provide the community with reliable numerical codes and methods for Euclid cosmological forecasts. Methods. We describe in detail the methods adopted for Fisher matrix forecasts, which were applied to galaxy clustering, weak lensing, and the combination thereof. We estimated the required accuracy for Euclid forecasts and outline a methodology for their development. We then compare and improve different numerical implementations, reaching uncertainties on the errors of cosmological parameters that are less than the required precision in all cases. Furthermore, we provide details on the validated implementations, some of which are made publicly available, in different programming languages, together with a reference training-set of input and output matrices for a set of specific models. These can be used by the reader to validate their own implementations if required. Results. We present new cosmological forecasts for Euclid. We find that results depend on the specific cosmological model and remaining freedom in each setting, for example flat or non-flat spatial cosmologies, or different cuts at non-linear scales. The numerical implementations are now reliable for these settings. We present the results for an optimistic and a pessimistic choice for these types of settings. We demonstrate that the impact of cross-correlations is particularly relevant for models beyond a cosmological constant and may allow us to increase the dark energy figure of merit by at least a factor of three
Euclid preparation: V. Predicted yield of redshift 7<z<9 quasars from the wide survey
We provide predictions of the yield of 7 < z < 9 quasars from the Euclid wide survey, updating the calculation presented in the
Euclid Red Book in several ways. We account for revisions to the Euclid near-infrared filter wavelengths; we adopt steeper rates
of decline of the quasar luminosity function (QLF; Φ) with redshift, Φ ∝ 10k(z−6)
, k = −0.72, and a further steeper rate of decline,
k = −0.92; we use better models of the contaminating populations (MLT dwarfs and compact early-type galaxies); and we make use
of an improved Bayesian selection method, compared to the colour cuts used for the Red Book calculation, allowing the identification
of fainter quasars, down to JAB ∼ 23. Quasars at z > 8 may be selected from Euclid OY JH photometry alone, but selection over
the redshift interval 7 < z < 8 is greatly improved by the addition of z-band data from, e.g., Pan-STARRS and LSST. We calculate
predicted quasar yields for the assumed values of the rate of decline of the QLF beyond z = 6. If the decline of the QLF accelerates
beyond z = 6, with k = −0.92, Euclid should nevertheless find over 100 quasars with 7.0 < z < 7.5, and ∼ 25 quasars beyond the
current record of z = 7.5, including ∼ 8 beyond z = 8.0. The first Euclid quasars at z > 7.5 should be found in the DR1 data release,
expected in 2024. It will be possible to determine the bright-end slope of the QLF, 7 < z < 8, M1450 < −25, using 8 m class telescopes
to confirm candidates, but follow-up with JWST or E-ELT will be required to measure the faint-end slope. Contamination of the
candidate lists is predicted to be modest even at JAB ∼ 23. The precision with which k can be determined over 7 < z < 8 depends on
the value of k, but assuming k = −0.72 it can be measured to a 1σ uncertainty of 0.07
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