UWCScholar :: Browsing by Author "Maartens, Roy"

Browsing by Author "Maartens, Roy"

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Anti-lensing: the bright side of voids
(American Physical Society, 2013) Bolejko, Krzysztof; Clarkson, Chris; Maartens, Roy; Bacon, David; Meures, Nikolai; Beynon, Emma
More than half of the volume of our Universe is occupied by cosmic voids. The lensing magni ca- tion e ect from those under-dense regions is generally thought to give a small dimming contribution: objects on the far side of a void are supposed to be observed as slightly smaller than if the void were not there, which together with conservation of surface brightness implies net reduction in photons received. This is predicted by the usual weak lensing integral of the density contrast along the line of sight. We show that this standard e ect is swamped at low redshifts by a relativistic Doppler term that is typically neglected. Contrary to the usual expectation, objects on the far side of a void are brighter than they would be otherwise. Thus the local dynamics of matter in and near the void is crucial and is only captured by the full relativistic lensing convergence. There are also signi cant nonlinear corrections to the relativistic linear theory, which we show actually under-predicts the e ect. We use exact solutions to estimate that these can be more than 20% for deep voids. This remains an important source of systematic errors for weak lensing density reconstruction in galaxy surveys and for supernovae observations, and may be the cause of the reported extra scatter of eld supernovae located on the edge of voids compared to those in clusters.
Clustering of quintessence on horizon scales and its imprint on HI intensity mapping
(IOP Science, 2013) Duniya, Didam G.A.; Bertacca, Daniele; Maartens, Roy
Quintessence can cluster only on horizon scales. What is the effect on the observed matter distribution? To answer this, we need a relativistic approach that goes beyond the standard Newtonian calculation and deals properly with large scales. Such an approach has recently been developed for the case when dark energy is vacuum energy, which does not cluster at all. We extend this relativistic analysis to deal with dynamical dark energy. Using three quintessence potentials as examples, we compute the angular power spectrum for the case of an HI intensity map survey. Compared to the concordance model with the same small-scale power at z = 0, quintessence boosts the angular power by up to 15% at high redshifts, while power in the two models converges at low redshifts. The difference is mainly due to the background evolution, driven mostly by the normalization of the power spectrum today. The dark energy perturbations make only a small contribution on the largest scales, and a negligible contribution on smaller scales. Ironically, the dark energy perturbations remove the false boost of large-scale power that arises if we impose the (unphysical) assumption that the dark energy is smooth.
Constraining primordial non-Gaussianity by combining next-generation galaxy and 21 cm intensity mapping surveys
(Institute for Ionics, 2023) Sheean, Jolicoeur; Maartens, Roy; Jolicoeur, Sheean; Dlamini, Simthembile
Surveys of the matter distribution contain ‘fossil’ information on possible non-Gaussianity that is generated in the primordial universe. This primordial signal survives only on the largest scales where cosmic variance is strongest. By combining different surveys in a multi-tracer approach, we can suppress the cosmic variance and significantly improve the precision on the level of primordial non-Gaussianity.We consider a combination of an optical galaxy survey, like the recently initiated DESI survey, together with a new and very different type of survey, a 21cm intensity mapping survey, like the upcoming SKAO survey. A Fisher forecast of the precision on the local primordial non-Gaussianity parameter fNL, shows that this multi-tracer combination, together with non-overlap single-tracer information, can deliver precision comparable to that from the CMB. Taking account of the largest systematic, i.e. foreground contamination in intensity mapping, we find that σ( fNL) ∼ 4
Constraining primordial non-gaussianity by combining next-generation galaxy and 21 cm intensity mapping surveys
(SpringerOpen, 2023) Jolicoeur, Sheean; Maartens, Roy; Dlamini, Simthembile
Surveys of the matter distribution contain ‘fossil’ information on possible non-Gaussianity that is generated in the primordialUniverse. This primordial signal survives only on the largest scales where cosmic variance is strongest. By combining different surveys in a multi-tracer approach, we can suppress the cosmic variance and significantly improve the precision on the level of primordial non-Gaussianity.We consider a combination of an optical galaxy survey, like the recently initiated DESI survey, together with a new and very different type of survey, a 21cm intensity mapping survey, like the upcoming SKAO survey.
Constraining the growth rate by combining multiple future surveys
(IOP Publishing, 2020) Viljoen, Jan-Albert; Fonseca, Jos´e; Maartens, Roy
The growth rate of large-scale structure provides a powerful consistency test of the standard cosmological model and a probe of possible deviations from general relativity. We use a Fisher analysis to forecast constraints on the growth rate from a combination of next-generation spectroscopic surveys. In the overlap survey volumes, we use a multi-tracer analysis to significantly reduce the effect of cosmic variance. The non-overlap individual survey volumes are included in the Fisher analysis in order to utilise the entire volume. We use the observed angular power spectrum, which naturally includes all wide-angle and lensing effects and circumvents the need for an Alcock-Paczynski correction. Cross correlations between redshift bins are included by using a novel technique to avoid computation of the sub-dominant contributions. Marginalising over the standard cosmological parameters, as well as the clustering bias in each redshift bin, we find that the precision on γ improves on the best single-tracer precision by up to ∼50%
Constraining the neutrino mass using a multitracer combination of two galaxy surveys and cosmic microwave background lensing
(Oxford University Press, 2022) Ballardini, Mario; Maartens, Roy
Measuring the total neutrino mass is one of the most exciting opportunities available with next-generation cosmological data sets. We study the possibility of detecting the total neutrino mass using large-scale clustering in 21 cm intensity mapping and photometric galaxy surveys, together with cosmic microwave background (CMB) information. We include the scale-dependent halo bias contribution due to the presence of massive neutrinos, and use a multitracer analysis in order to reduce cosmic variance. The multitracer combination of an SKAO-MID 21 cm intensity map with stage 4 CMB dramatically shrinks the uncertainty on total neutrino mass to σ(Mν ) 45 meV, using only linear clustering information (kmax = 0.1 h Mpc−1 ) and without a prior on optical depth. When we add to the multitracer the clustering information expected from Legacy Survey of Space and Time, the forecast is σ(Mν ) 12 meV.
Cosmological constraints from the power spectrum and bispectrum of 21cm intensity maps
(IOP Publishing, 2022) Karagiannis, Dionysios; Maartens, Roy; Randrianjanahary, Liantsoa F.
The 21cm emission of neutral hydrogen is a potential probe of the matter distribution in the Universe after reionisation. Cosmological surveys of this line intensity will be conducted in the coming years by the SKAO and HIRAX experiments, complementary to upcoming galaxy surveys. We present the first forecasts of the cosmological constraints from the combination of the 21cm power spectrum and bispectrum. Fisher forecasts are computed for the constraining power of these surveys on cosmological parameters, the BAO distance functions and the growth function. We also estimate the constraining power on dynamical dark energy and modified gravity. Finally we investigate the constraints on the 21cm clustering bias, up to second order. We take into account the effects on the 21cm correlators of the telescope beam, instrumental noise and foreground avoidance, as well as the Alcock-Paczynski effect and the effects of theoretical errors in the modelling of the correlators.
Cosmological constraints using 2- and 3-point correlations with meerkat, the ska and other surveys
(Universty of the Western Cape, 2024) Randrianjanahary, Liantsoa Finaritra; Maartens, Roy
We explore the information from HI power spectra (tree-level and one-loop) in redshift space and bispectrum tree-level models. 21-cm emission from neutral hydrogen is a promising tool for probing the matter distribution in the universe post-reionization. The HI signals contain signatures of the primordial universe and the growth of large-scale structure in the universe. These signatures are typically analyzed via the 2-point correlation function or power spectrum. However, adding the information from the 3-point correlation function or bispectrum will be crucial to exploiting next-generation intensity mapping experiments. Upcoming surveys by SKAO and HIRAX will undertake intensive line-intensity observations, complementing galaxy surveys. This study provides new forecasts on cosmological constraints derived from the combined analysis of the 21cm power spectrum and bispectrum. We use Fisher predictions to examine how useful these surveys might be for constraining cosmological parameters, BAO distance functions, growth function, and what they mean for dynamical dark energy and modified gravity. We account for telescope beam effects, instrumental noise, foreground avoidance, the Alcock-Paczynski effect, and theoretical modeling errors in the correlators. The investigation also includes assessments of 21-cm clustering bias up to the second order.
Cosmology from HI galaxy surveys with the SKA
(Proceedings of Science, 2014) Maartens, Roy; Abdalla, Filipe B.; Bull, Philip; Camera, Stefano; Benoit-Levy, Aurelien; Joachimi, Benjamin; Kirk, Donnacha; Klöckner, Hans-Rainer; Raccanelli, Alvise; Santos, Mario G.; Zhao, Gong-Bo
The Square Kilometer Array (SKA) has the potential to produce galaxy redshift surveys which will be competitive with other state of the art cosmological experiments in the next decade. In this chapter we summarise what capabilities the first and the second phases of the SKA will be able to achieve in its current state of design. We summarise the different cosmological experiments which are outlined in further detail in other chapters of this Science Book. The SKA will be able to produce competitive Baryonic Oscillation (BAOs) measurements in both its phases. The first phase of the SKA will provide similar measurements in optical and IR experiments with completely different systematic effects whereas the second phase being transformational in terms of its statistical power. The SKA will produce very accurate Redshift Space Distortions (RSD) measurements, being superior to other experiments at lower redshifts, due to the large number of galaxies. Cross correlations of the galaxy redshift data from the SKA with radio continuum surveys and optical surveys will provide extremely good calibration of photometric redshifts as well as extremely good bounds on modifications of gravity. Basing on a Principle Component Analysis (PCA) approach, we find that the SKA will be able to provide competitive constraint on dark energy and modified gravity models. Due to the large area covered the SKA it will be a transformational experiment in measuring physics from the largest scales such as non-Gaussian signals. Finally, the SKA might produce the first real time measurement of the redshift drift. The SKA will be a transformational machine for cosmology as it grows from an early Phase 1 to its full power.
Cosmology on the largest scales with the SKA
(Proceedings of Science, 2014) Camera, Stefano; Raccanelli, Alvise; Bull, Philip; Bertacca, Daniele; Chen, Xuelei; Ferreira, Pedro G.; Kunz, Martin; Maartens, Roy; Mao, Yi; Santos, Mario G.; Shapiro, Paul R.; Viel, Matteo; Xug, Yidong
The study of the Universe on ultra-large scales is one of the major science cases for the Square Kilometre Array (SKA). The SKA will be able to probe a vast volume of the cosmos, thus representing a unique instrument, amongst next-generation cosmological experiments, for scrutinising the Universe’s properties on the largest cosmic scales. Probing cosmic structures on extremely large scales will have many advantages. For instance, the growth of perturbations is well understood for those modes, since it falls fully within the linear régime. Also, such scales are unaffected by the poorly understood feedback of baryonic physics. On ultra-large cosmic scales, two key effects become significant: primordial non-Gaussianity and relativistic corrections to cosmological observables. Moreover, if late-time acceleration is driven not by dark energy but by modifications to general relativity, then such modifications should become apparent near and above the horizon scale. As a result, the SKA is forecast to deliver transformational constraints on non-Gaussianity and to probe gravity on super-horizon scales for the first time.
Cosmology with a SKA HI intensity mapping survey
(Proceedings of Science, 2014) Santos, Mario G.; Bull, Philip; Alonso, David; Camera, Stefano; Ferreira, Pedro G.; Bernardi, Gianni; Maartens, Roy; Viel, Matteo; Villaescusa-Navarro, Francisco; Abdalla, Filipe B.; Jarvis, Matt; Metcalf, R. Benton; Pourtsidou, A.; Wolz, Laura
HI intensity mapping (IM) is a novel technique capable of mapping the large-scale structure of the Universe in three dimensions and delivering exquisite constraints on cosmology, by using HI as a biased tracer of the dark matter density field. This is achieved by measuring the intensity of the redshifted 21cm line over the sky in a range of redshifts without the requirement to resolve individual galaxies. In this chapter, we investigate the potential of SKA1 to deliver HI intensity maps over a broad range of frequencies and a substantial fraction of the sky. By pinning down the baryon acoustic oscillation and redshift space distortion features in the matter power spectrum – thus determining the expansion and growth history of the Universe – these surveys can provide powerful tests of dark energy models and modifications to General Relativity. They can also be used to probe physics on extremely large scales, where precise measurements of spatial curvature and primordial non-Gaussianity can be used to test inflation; on small scales, by measuring the sum of neutrino masses; and at high redshifts where non-standard evolution models can be probed. We discuss the impact of foregrounds as well as various instrumental and survey design parameters on the achievable constraints. In particular we analyse the feasibility of using the SKA1 autocorrelations to probe the large-scale signal.
Detecting the relativistic galaxy bispectrum
(IOP Publishing Ltd, 2020) Maartens, Roy; Jolicoeur, Sheean; Umeh, Obinna
The Fourier galaxy bispectrum is complex, with the imaginary part arising from leading-order relativistic corrections, due to Doppler, gravitational redshift and related lineof-sight effects in redshift space. The detection of the imaginary part of the bispectrum is potentially a smoking gun signal of relativistic contributions. We investigate whether nextgeneration spectroscopic surveys could make such a detection. For a Stage IV spectroscopic Hα survey similar to Euclid, we find that the cumulative signal to noise of this relativistic signature is O(10). Long-mode relativistic effects couple to short-mode Newtonian effects in the galaxy bispectrum, but not in the galaxy power spectrum. This is the basis for detectability of relativistic effects in the bispectrum of a single galaxy survey, whereas the power spectrum requires multiple galaxy surveys to detect the corresponding signal.
Determining the observer’s velocity using radio continuum surveys
(University of the Western Cape, 2019) Randriamiarinarivo, Nandrianina; Maartens, Roy; Bengaly, Carlos
In the standard (‘concordance’) model of Cosmology, there is a fundamental assumption that the Universe is statistically isotropic and homogeneous on large scales, known as the Cosmological Principle. The Cosmological Principle requires that the dipole anisotropy apparent in the CMB should also be observed in galaxy number counts if this signal occurs due to the aberration and Doppler effects from our peculiar motion. This thesis will investigate the accuracy with which the cosmic kinematic dipole can be determined by comparing real data from NRAO VLA Sky Survey (NVSS) catalog with the simulated sky maps following its specifications. The mock maps are generated using FLASK code which assumes a lognormal distribution for the radio count density field from z=0 to z =4 and taking as an entry an angular power spectrum from CAMB which assumed a flat ΛCDM cosmology and a redshift distribution. After analising the kinematic dipole, we turn to the analysis of statistical isotropy in the catalog. We used ANalysis Of Variance (ANOVA) test on patches in the sky of different radii as one of the statistical tools for the analysis. We found that as we go to a higher radius for the patches, we have a better agreement between the theory and the observation as expected. We also saw that the more we are rigorous on the rejection criteria, the smaller is the discrepancy between the observed and simulated number count distribution in the sky. We found an optimum choice of 25◦ as patch size, and if the accepted patches have a maximum of 30% of their pixels masked. Therefore, we find that the NVSS data agrees with the fundamental assumption of statistical isotropy at angular scales > 20◦.
Disentangling non-gaussianity, bias, and general relativistic effects in the galaxy distribution
(American Physical Society, 2012) Bruni, Marco; Crittenden, Robert; Maartens, Roy
Local non-Gaussianity, parametrized by f NL , introduces a scale-dependent bias that is strongest at large scales, precisely where general relativistic (GR) effects also become significant. With future data, it should be possible to constrain f NL = O ( 1 ) with high redshift surveys. GR corrections to the power spectrum and ambiguities in the gauge used to define bias introduce effects similar to f NL = O ( 1 ) , so it is essential to disentangle these effects. For the first time in studies of primordial non-Gaussianity, we include the consistent GR calculation of galaxy power spectra, highlighting the importance of a proper definition of bias. We present observable power spectra with and without GR corrections, showing that an incorrect definition of bias can mimic non-Gaussianity. However, these effects can be distinguished by their different redshift and scale dependence, so as to extract the true primordial non-Gaussianity.
Einstein's legacy in galaxy surveys
(Oxford University Press, 2015) Camera, Stefano; Maartens, Roy; Santos, Mario G.
Non-Gaussianity in the primordial fluctuations that seeded structure formation produces a signal in the galaxy power spectrum on very large scales. This signal contains vital information about the primordial Universe, but it is very challenging to extract, because of cosmic variance and large-scale systematics especially after the Planck experiment has already ruled out a large amplitude for the signal. Whilst cosmic variance and experimental systematics can be alleviated by the multi-tracer method, we here address another systematic—introduced by not using the correct relativistic analysis of the power spectrum on very large scales. In order to reduce the errors we need to include measurements on the largest possible scales. Failure to include the relativistic effects on these scales can introduce significant bias in the best-fit value from future galaxy surveys.
Galaxy Clustering as a Probe for Galaxy Evolution in Simulations
(University of the Western Cape, 2017) Thomas, Nicole; Maartens, Roy
Studying clustering on small scales (<10Mpc) over a large span of red- shifts allows us to connect galaxies to underlying cosmic large-scale structure, and thereby provide constraints on the physical processes that drive galaxy evolution. Relatedly, studying the relative bias of galaxies and their halo occupancy quanti es how the underlying dark matter distribution is traced by baryons in galaxies. Comparing model predictions to current and future multi-wavelength galaxy surveys, en- ables a greater understanding of how galaxy formation processes impact the relationship between galaxies and dark matter
Galaxy correlations and the BAO in a void universe: structure formation as a test of the Copernican Principle
(IOP Science, 2013) February, Sean; Clarkson, Chris; Maartens, Roy
A suggested solution to the dark energy problem is the void model, where accelerated expansion is replaced by Hubble-scale inhomogeneity. In these models, density perturbations grow on a radially inhomogeneous background. This large scale inhomogeneity distorts the spherical Baryon Acoustic Oscillation feature into an ellipsoid which implies that the bump in the galaxy correlation function occurs at different scales in the radial and transverse correlation functions. We compute these for the first time, under the approximation that curvature gradients do not couple the scalar modes to vector and tensor modes. The radial and transverse correlation functions are very different from those of the concordance model, even when the models have the same average BAO scale. This implies that if void models are fine-tuned to satisfy average BAO data, there is enough extra information in the correlation functions to distinguish a void model from the concordance model. We expect these new features to remain when the full perturbation equations are solved, which means that the radial and transverse galaxy correlation functions can be used as a powerful test of the Copernican Principle.
The Hubble constant tension with next-generation galaxy surveys
(IOP Publishing Ltd, 2020) Bengaly, Carlos A.P.; Clarkson, Chris; Maartens, Roy
The rate at which the universe is expanding today is a fundamental parameter in cosmology which governs our understanding of structure formation and dark energy. However, current measurements of the Hubble constant, H0, show a significant tension (∼ 4–6σ) between early- and late-Universe observations. There are ongoing efforts to check the diverse observational results and also to investigate possible theoretical ways to resolve the tension — which could point to radical extensions of the standard model. Here we demonstrate the potential of next-generation spectroscopic galaxy surveys to shed light on the Hubble constant tension. Surveys such as those with Euclid and the Square Kilometre Array (SKA) are expected to reach sub-percent precision on Baryon Acoustic Oscillation (BAO) measurements of the Hubble parameter, with a combined redshift coverage of 0.1 < z < 3. This wide redshift range, together with the high precision and low level of systematics in BAO measurements, mean that these surveys will provide independent and tight constraints on H(z). These H(z) measurements can be extrapolated to z = 0 to provide constraints on H0 using a non-parametric regression.
Hunting down horizon-scale effects with multi-wavelength surveys
(American Astronomical Society, 2015) Fonseca, Jose; Camera, Stefano; Santos, Mario G.; Maartens, Roy
Next-generation cosmological surveys will probe ever larger volumes of the universe, including the largest scales, near and beyond the horizon. On these scales, the galaxy power spectrum carries signatures of local primordial non-Gaussianity (PNG) and horizon-scale general relativistic (GR) effects. However, cosmic variance limits the detection of horizon-scale effects. Combining different surveys via the multi-tracer method allows us to reduce the effect of cosmic variance. This method benefits from large bias differences between two tracers of the underlying dark matter distribution, which suggests a multi-wavelength combination of large volume surveys that are planned on a similar timescale. We show that the combination of two contemporaneous surveys, a large neutral hydrogen intensity mapping survey in SKA Phase 1 and a Euclid-like photometric survey, will provide unprecedented constraints on PNG as well as detection of the GR effects. We forecast that the error on local PNG will break through the cosmic variance limit on cosmic microwave background surveys, depending on assumed priors, bias, and sky coverage. GR effects are more robust to changes in the assumed fiducial model, and we forecast that they can be detected with a signal-to-noise of about 14.
Imprints of Primordial Non-Gaussianity on Large Scale Structure in the Universe
(University of the Western Cape, 2016) Hashim, Mahmoud Yousif Ali Wahba; Maartens, Roy
Large scale structure in the universe is one of the most important probing tools for cosmological modelling. Assuming the hot big bang model of the universe, the expansion history has undergone two phases of acceleration. The primordial phase which had been considered to be responsible for seeding the structure formation and the late phase driven by the mysterious component of the cosmos, Dark Energy. Early inhomogeneity in the structure formation could though leave a signature on the late time universe. We assume the cosmos to have non-Gaussian initial conditions. Gravitational instability is thought to be responsible for late structure evolution. On local scales, non-linear e ects dissipate primordial signal of non-Gaussianity, however on very large scales, the signal is well preserved. Initial non-Gaussianity introduce a scale dependent signature on the galaxy power spectrum on very large scales. This could be very useful to constrain non-Gaussianity parameter via upcoming large scale structure surveys. In this thesis, we show that on very large scales, interacting dark energy perturbations induce a scale-dependent e ect on the galaxy power spectrum on large scales. This could degenerate with primordial non-Gaussianity signal, though a disentanglement between the two signatures are necessary for observational constraints. On small scales, N-body simulations for standard cosmological models are used to investigate the signature of primordial non-Gaussianity on halo mass function. It has a signi cant e ect on very large halos however it is negligible for small mass halos. Interacting Dark Energy is assumed to have a similar e ect on small scales. We prepare the basis for future work that will combine simulations for Interacting Dark Energy models with non-Gaussian initial conditions.

Browsing by Author "Maartens, Roy"

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