362 research outputs found
Euclid: The reduced shear approximation and magnification bias for Stage IV cosmic shear experiments
Context. Stage IV weak lensing experiments will offer more than an order of magnitude leap in precision. We must therefore ensure that our analyses remain accurate in this new era. Accordingly, previously ignored systematic effects must be addressed. Aims. In this work, we evaluate the impact of the reduced shear approximation and magnification bias on information obtained from the angular power spectrum. To first-order, the statistics of reduced shear, a combination of shear and convergence, are taken to be equal to those of shear. However, this approximation can induce a bias in the cosmological parameters that can no longer be neglected. A separate bias arises from the statistics of shear being altered by the preferential selection of galaxies and the dilution of their surface densities in high-magnification regions. Methods. The corrections for these systematic effects take similar forms, allowing them to be treated together. We calculated the impact of neglecting these effects on the cosmological parameters that would be determined from Euclid, using cosmic shear tomography. To do so, we employed the Fisher matrix formalism, and included the impact of the super-sample covariance. We also demonstrate how the reduced shear correction can be calculated using a lognormal field forward modelling approach. Results. These effects cause significant biases in Ωm, Ύ8, ns, ΩDE, w0, and wa of -0:53Ύ, 0:43Ύ, -0:34Ύ, 1:36Ύ, -0:68Ύ, and 1:21Ύ, respectively. We then show that these lensing biases interact with another systematic effect: The intrinsic alignment of galaxies. Accordingly, we have developed the formalism for an intrinsic alignment-enhanced lensing bias correction. Applying this to Euclid, we find that the additional terms introduced by this correction are sub-dominant
Euclid: On the reduced shear approximation and magnification bias for Stage IV cosmic shear experiments
Stage IV weak lensing experiments will offer more than an order of magnitude leap in precision. We must therefore ensure that our analyses remain accurate in this new era. Accordingly, previously ignored systematic effects must be addressed. In this work, we evaluate the impact of the reduced shear approximation and magnification bias, on the information obtained from the angular power spectrum. To first-order, the statistics of reduced shear, a combination of shear and convergence, are taken to be equal to those of shear. However, this approximation can induce a bias in the cosmological parameters that can no longer be neglected. A separate bias arises from the statistics of shear being altered by the preferential selection of galaxies and the dilution of their surface densities, in high-magnification regions. The corrections for these systematic effects take similar forms, allowing them to be treated together. We calculate the impact of neglecting these effects on the cosmological parameters that would be determined from Euclid, using cosmic shear tomography. We also demonstrate how the reduced shear correction can be calculated using a lognormal field forward modelling approach. These effects cause significant biases in Omega_m, n_s, sigma_8, Omega_DE, w_0, and w_a of -0.51 sigma, -0.36 sigma, 0.37 sigma, 1.36 sigma, -0.66 sigma, and 1.21 sigma, respectively. We then show that these lensing biases interact with another systematic: the intrinsic alignment of galaxies. Accordingly, we develop the formalism for an intrinsic alignment-enhanced lensing bias correction. Applying this to Euclid, we find that the additional terms introduced by this correction are sub-dominant
Euclid: The reduced shear approximation and magnification bias for Stage IV cosmic shear experiments
Context: Stage IV weak lensing experiments will offer more than an order of magnitude leap in precision. We must therefore ensure that our analyses remain accurate in this new era. Accordingly, previously ignored systematic effects must be addressed.
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Aims: In this work, we evaluate the impact of the reduced shear approximation and magnification bias on information obtained from the angular power spectrum. To first-order, the statistics of reduced shear, a combination of shear and convergence, are taken to be equal to those of shear. However, this approximation can induce a bias in the cosmological parameters that can no longer be neglected. A separate bias arises from the statistics of shear being altered by the preferential selection of galaxies and the dilution of their surface densities in high-magnification regions.
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Methods: The corrections for these systematic effects take similar forms, allowing them to be treated together. We calculated the impact of neglecting these effects on the cosmological parameters that would be determined from Euclid, using cosmic shear tomography. To do so, we employed the Fisher matrix formalism, and included the impact of the super-sample covariance. We also demonstrate how the reduced shear correction can be calculated using a lognormal field forward modelling approach.
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Results: These effects cause significant biases in Ωm, Ï8, ns, ΩDE, w0, and wa of â0.53Ï, 0.43Ï, â0.34Ï, 1.36Ï, â0.68Ï, and 1.21Ï, respectively. We then show that these lensing biases interact with another systematic effect: the intrinsic alignment of galaxies. Accordingly, we have developed the formalism for an intrinsic alignment-enhanced lensing bias correction. Applying this to Euclid, we find that the additional terms introduced by this correction are sub-dominant
Euclid: the selection of quiescent and star-forming galaxies using observed colours
The Euclid mission will observe well over a billion galaxies out to z ⌠6 and beyond. This will offer an unrivalled opportunity to investigate several key questions for understanding galaxy formation and evolution. The first step for many of these studies will be the selection of a sample of quiescent and star-forming galaxies, as is often done in the literature by using well-known colour techniques such as the âUVJâ diagram. However, given the limited number of filters available for the Euclid telescope, the recovery of such rest-frame colours will be challenging. We therefore investigate the use of observed Euclid colours, on their own and together with ground-based u-band observations, for selecting quiescent and star-forming galaxies. The most efficient colour combination, among the ones tested in this work, consists of the (u â VIS) and (VIS â J) colours. We find that this combination allows users to select a sample of quiescent galaxies complete to above âŒ70 per cent and with less than 15 per cent contamination at redshifts in the range 0.75 65 per cent completeness level and contamination below 20 per cent at 1 < z < 2 for finding quiescent galaxies. In comparison, the sample of quiescent galaxies selected with the traditional UVJ technique is only âŒ20 per cent complete at z < 3, when recovering the rest-frame colours using mock Euclid observations. This shows that our new methodology is the most suitable one when only Euclid bands, along with u-band imaging, are available
Euclid: the selection of quiescent and star-forming galaxies using observed colours
The Euclid mission will observe well over a billion galaxies out to z ⌠6 and beyond. This will offer an unrivalled opportunity to investigate several key questions for understanding galaxy formation and evolution. The first step for many of these studies will be the selection of a sample of quiescent and star-forming galaxies, as is often done in the literature by using well-known colour techniques such as the âUVJâ diagram. However, given the limited number of filters available for the Euclid telescope, the recovery of such rest-frame colours will be challenging. We therefore investigate the use of observed Euclid colours, on their own and together with ground-based u-band observations, for selecting quiescent and star-forming galaxies. The most efficient colour combination, among the ones tested in this work, consists of the (u â VIS) and (VIS â J) colours. We find that this combination allows users to select a sample of quiescent galaxies complete to above âŒ70 per cent and with less than 15 per cent contamination at redshifts in the range 0.75 65 per cent completeness level and contamination below 20 per cent at 1 < z < 2 for finding quiescent galaxies. In comparison, the sample of quiescent galaxies selected with the traditional UVJ technique is only âŒ20 per cent complete at z < 3, when recovering the rest-frame colours using mock Euclid observations. This shows that our new methodology is the most suitable one when only Euclid bands, along with u-band imaging, are available
Euclid: The importance of galaxy clustering and weak lensing cross-correlations within the photometric Euclid survey
Context. The data from the Euclid mission will enable the measurement of the angular positions and weak lensing shapes of over a billion galaxies,
with their photometric redshifts obtained together with ground-based observations. This large dataset, with well-controlled systematic effects, will
allow for cosmological analyses using the angular clustering of galaxies (GCph) and cosmic shear (WL). For Euclid, these two cosmological probes
will not be independent because they will probe the same volume of the Universe. The cross-correlation (XC) between these probes can tighten
constraints and is therefore important to quantify their impact for Euclid.
Aims. In this study, we therefore extend the recently published Euclid forecasts by carefully quantifying the impact of XC not only on the
final parameter constraints for different cosmological models, but also on the nuisance parameters. In particular, we aim to decipher the amount
of additional information that XC can provide for parameters encoding systematic effects, such as galaxy bias, intrinsic alignments (IAs), and
knowledge of the redshift distributions.
Methods. We follow the Fisher matrix formalism and make use of previously validated codes. We also investigate a different galaxy bias model,
which was obtained from the Flagship simulation, and additional photometric-redshift uncertainties; we also elucidate the impact of including the
XC terms on constraining these latter.
Results. Starting with a baseline model, we show that the XC terms reduce the uncertainties on galaxy bias by âŒ17% and the uncertainties on IA
by a factor of about four. The XC terms also help in constraining the Îł parameter for minimal modified gravity models. Concerning galaxy bias,
we observe that the role of the XC terms on the final parameter constraints is qualitatively the same irrespective of the specific galaxy-bias model
used. For IA, we show that the XC terms can help in distinguishing between different models, and that if IA terms are neglected then this can lead
to significant biases on the cosmological parameters. Finally, we show that the XC terms can lead to a better determination of the mean of the
photometric galaxy distributions.
Conclusions. We find that the XC between GCph and WL within the Euclid survey is necessary to extract the full information content from the data
in future analyses. These terms help in better constraining the cosmological model, and also lead to a better understanding of the systematic effects
that contaminate these probes. Furthermore, we find that XC significantly helps in constraining the mean of the photometric-redshift distributions,
but, at the same time, it requires more precise knowledge of this mean with respect to single probes in order not to degrade the final âfigure of
meritâ
Euclid: Covariance of weak lensing pseudo-Cl estimates: Calculation, comparison to simulations, and dependence on survey geometry
An accurate covariance matrix is essential for obtaining reliable cosmological results when using a Gaussian likelihood. In this paper we study the covariance of pseudo-Cestimates of tomographic cosmic shear power spectra. Using two existing publicly available codes in combination, we calculate the full covariance matrix, including mode-coupling contributions arising from both partial sky coverage and non-linear structure growth. For three different sky masks, we compare the theoretical covariance matrix to that estimated from publicly available N-body weak lensing simulations, finding good agreement. We find that as a more extreme sky cut is applied, a corresponding increase in both Gaussian off-diagonal covariance and non-Gaussian super-sample covariance is observed in both theory and simulations, in accordance with expectations. Studying the different contributions to the covariance in detail, we find that the Gaussian covariance dominates along the main diagonal and the closest off-diagonals, but farther away from the main diagonal the super-sample covariance is dominant. Forming mock constraints in parameters that describe matter clustering and dark energy, we find that neglecting non-Gaussian contributions to the covariance can lead to underestimating the true size of confidence regions by up to 70 per cent. The dominant non-Gaussian covariance component is the super-sample covariance, but neglecting the smaller connected non-Gaussian covariance can still lead to the underestimation of uncertainties by 10-20 per cent. A real cosmological analysis will require marginalisation over many nuisance parameters, which will decrease the relative importance of all cosmological contributions to the covariance, so these values should be taken as upper limits on the importance of each component
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: Forecasts from the void-lensing cross-correlation
The Euclid space telescope will survey a large dataset of cosmic voids traced by dense samples of galaxies. In this work we estimate its expected performance when exploiting angular photometric void clustering, galaxy weak lensing, and their cross-correlation. To this aim, we implemented a Fisher matrix approach tailored for voids from the Euclid photometric dataset and we present the first forecasts on cosmological parameters that include the void-lensing correlation. We examined two different probe settings, pessimistic and optimistic, both for void clustering and galaxy lensing. We carried out forecast analyses in four model cosmologies, accounting for a varying total neutrino mass, MÎœ, and a dynamical dark energy (DE) equation of state, w(z), described by the popular Chevallier-Polarski-Linder parametrization. We find that void clustering constraints on h and Ωb are competitive with galaxy lensing alone, while errors on ns decrease thanks to the orthogonality of the two probes in the 2D-projected parameter space. We also note that, as a whole, with respect to assuming the two probes as independent, the inclusion of the void-lensing cross-correlation signal improves parameter constraints by 10â
ââ
15%, and enhances the joint void clustering and galaxy lensing figure of merit (FoM) by 10% and 25%, in the pessimistic and optimistic scenarios, respectively. Finally, when further combining with the spectroscopic galaxy clustering, assumed as an independent probe, we find that, in the most competitive case, the FoM increases by a factor of 4 with respect to the combination of weak lensing and spectroscopic galaxy clustering taken as independent probes. The forecasts presented in this work show that photometric void clustering and its cross-correlation with galaxy lensing deserve to be exploited in the data analysis of the Euclid galaxy survey and promise to improve its constraining power, especially on h, Ωb, the neutrino mass, and the DE evolution
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