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http://hdl.handle.net/2445/19702
Wed, 20 Sep 2017 22:02:05 GMT2017-09-20T22:02:05ZImplications of multiple high-redshift galaxy clusters
http://hdl.handle.net/2445/114892
Title: Implications of multiple high-redshift galaxy clusters
Author: Hoyle, Ben; Jiménez, Raúl (Jiménez Tellado); Verde, Licia
Abstract: To date, 14 high-redshift (z>1.0) galaxy clusters with mass measurements have been observed, spectroscopically confirmed, and are reported in the literature. These objects should be exceedingly rare in the standard Λ cold dark matter (ΛCDM) model. We conservatively approximate the selection functions of these clusters' parent surveys and quantify the tension between the abundances of massive clusters as predicted by the standard ΛCDM model and the observed ones. We alleviate the tension, considering non-Gaussian primordial perturbations of the local type, characterized by the parameter fNL, and derive constraints on fNL arising from the mere existence of these clusters. At the 95% confidence level, fNL>467, with cosmological parameters fixed to their most likely WMAP5 values, or fNL≳123 (at 95% confidence) if we marginalize over prior WMAP5 parameters. In combination with fNL constraints from cosmic microwave background and halo bias, this determination implies a scale dependence of fNL at ≃3σ. Given the assumptions made in the analysis, we expect any future improvements to the modeling of the non-Gaussian mass function, survey volumes, or selection functions to increase the significance of fNL>0 found here. In order to reconcile these massive, high-z clusters with fNL=0, their masses would need to be systematically lowered by 1.5σ, or the σ8 parameter should be ∼3σ higher than cosmic microwave background (and large-scale structure) constraints. The existence of these objects is a puzzle: it either represents a challenge to the ΛCDM paradigm or it is an indication that the mass estimates of clusters are dramatically more uncertain than we think.Fri, 01 Sep 2017 10:07:58 GMThttp://hdl.handle.net/2445/1148922017-09-01T10:07:58ZA halo model with environment dependence: theoretical considerations
http://hdl.handle.net/2445/114886
Title: A halo model with environment dependence: theoretical considerations
Author: Gil Marín, Héctor; Jiménez, Raúl (Jiménez Tellado); Verde, Licia
Abstract: We present a modification of the standard halo model with the goal of providing an improved description of galaxy clustering. Recent surveys, like the Sloan Digital Sky Survey (SDSS) and the Anglo-Australian two-degree survey (2dF), have shown that there seems to be a correlation between the clustering of galaxies and their properties such as metallicity and star formation rate, which are believed to be environment-dependent. This environmental dependence is not included in the standard halo model where the host halo mass is the only variable specifying galaxy properties. In our approach, the halo properties, i.e. the concentration, and the halo occupation distribution (HOD) prescription, will not only depend on the halo mass (like in the standard halo model) but also on the halo environment. We examine how different environmental dependence of halo concentration and HOD prescription affects the correlation function. We see that at the level of dark matter, the concentration of haloes moderately affects the dark matter correlation function only at small scales. However, the galaxy correlation function is extremely sensitive to the HOD details, even when only the HOD of a small fraction of haloes is modified.Fri, 01 Sep 2017 09:34:32 GMThttp://hdl.handle.net/2445/1148862017-09-01T09:34:32ZMinimally parametric power spectrum reconstruction from the Lyman-alpha Forest
http://hdl.handle.net/2445/114883
Title: Minimally parametric power spectrum reconstruction from the Lyman-alpha Forest
Author: Bird, Simeon; Peiris, Hiranya V.; Viel, Matteo; Verde, Licia
Abstract: Current results from the Lyman α forest assume that the primordial power spectrum of density perturbations follows a simple power-law form. We present the first analysis of Lyman α data to study the effect of relaxing this strong assumption on primordial and astrophysical constraints. We perform a large suite of numerical simulations, using them to calibrate a minimally parametric framework for describing the power spectrum. Combined with cross-validation, a statistical technique which prevents overfitting of the data, this framework allows us to reconstruct the power spectrum shape without strong prior assumptions. We find no evidence for deviation from scale-invariance; our analysis also shows that current Lyman α data do not have sufficient statistical power to robustly probe the shape of the power spectrum at these scales. In contrast, the ongoing Baryon Oscillation Sky Survey will be able to do so with high precision. Furthermore, this near-future data will be able to break degeneracies between the power spectrum shape and astrophysical parameters.Fri, 01 Sep 2017 09:28:18 GMThttp://hdl.handle.net/2445/1148832017-09-01T09:28:18ZCancelling out systematic uncertainties
http://hdl.handle.net/2445/114881
Title: Cancelling out systematic uncertainties
Author: Noreña, Jorge; Verde, Licia; Jiménez, Raúl (Jiménez Tellado); Pena Garay, Carlos; Gomez, Cesar
Abstract: We present a method to minimize, or even cancel out, the nuisance parameters affecting a measurement. Our approach is general and can be applied to any experiment or observation where systematic errors are a concern e.g. are larger than statistical errors. We compare it with the Bayesian technique used to deal with nuisance parameters: marginalization, and show how the method compares and improves by avoiding biases. We illustrate the method with several examples taken from the astrophysics and cosmology world: baryonic acoustic oscillations (BAOs), cosmic clocks, Type Ia supernova (SNIa) luminosity distance, neutrino oscillations and dark matter detection. By applying the method we not only recover some known results but also find some interesting new ones. For BAO experiments we show how to combine radial and angular BAO measurements in order to completely eliminate the dependence on the sound horizon at radiation drag. In the case of exploiting SNIa as standard candles we show how the uncertainty in the luminosity distance by a second parameter modelled as a metallicity dependence can be eliminated or greatly reduced. When using cosmic clocks to measure the expansion rate of the universe, we demonstrate how a particular combination of observables nearly removes the metallicity dependence of the galaxy on determining differential ages, thus removing the age-metallicity degeneracy in stellar populations. We hope that these findings will be useful in future surveys to obtain robust constraints on the dark energy equation of state.Fri, 01 Sep 2017 09:17:53 GMThttp://hdl.handle.net/2445/1148812017-09-01T09:17:53ZDoes stellar mass assembly history vary with environment?
http://hdl.handle.net/2445/114876
Title: Does stellar mass assembly history vary with environment?
Author: Hoyle, Ben; Jiménez, Raúl (Jiménez Tellado); Verde, Licia
Abstract: Using the publicly available vespa data base of SDSS Data Release 7 spectra, we calculate the stellar mass weighted age (hereafter MWA) as a function of local galaxy density and dark matter halo mass. We compare our results with semi-analytic models from the public Millennium Simulation. We find that the stellar MWA has a large scatter which is inherent in the data and consistent with that seen in semi-analytic models. The stellar MWA is consistent with being independent (to first order) with local galaxy density, which is also seen in semi-analytic models. By splitting the sample into bins of total stellar mass, we find a strong dependence, with stellar MWA increasing for more massive galaxies. As a function of increasing dark matter halo mass (using the SDSS New York Value Added Group catalogues), we find that the average stellar MWA for member galaxies increases, which is again found in semi-analytic models. We again split the sample into bins of total stellar mass, and still find a strong dependence on stellar MWA for increasing mass galaxies, but additionally a second order trend of increasing stellar MWA with increasing dark matter mass of the host halo. Furthermore we use public dark matter mass accretion history (MAH) code calibrated on simulations, to calculate the dark matter MWA as a function of dark matter halo mass. In agreement with earlier analyses, we find that the stellar MWA and the dark matter MWA are anticorrelated for large mass haloes, i.e, dark matter accretion does not seem to be the primary factor in determining when stellar mass was assembled. This effect can be described by downsizing.Fri, 01 Sep 2017 08:46:58 GMThttp://hdl.handle.net/2445/1148762017-09-01T08:46:58ZNon-Gaussianity from large-scale structure surveys
http://hdl.handle.net/2445/114874
Title: Non-Gaussianity from large-scale structure surveys
Author: Verde, Licia
Abstract: With the advent of galaxy surveys which provide large samples of galaxies or galaxy clusters over a volume comparable to the horizon size (SDSS-III, HETDEX, Euclid, JDEM, LSST, Pan-STARRS, CIP, etc.) or mass-selected large cluster samples over a large fraction of the extra-galactic sky (Planck, SPT, ACT, CMBPol, B-Pol), it is timely to investigate what constraints these surveys can impose on primordial non-Gaussianity. I illustrate here three different approaches: higher-order correlations of the three dimensional galaxy distribution, abundance of rare objects (extrema of the density distribution), and the large-scale clustering of halos (peaks of the density distribution). Each of these avenues has its own advantages, but, more importantly, these approaches are highly complementary under many respects.Fri, 01 Sep 2017 08:37:05 GMThttp://hdl.handle.net/2445/1148742017-09-01T08:37:05ZEnhancing the cosmic shear power spectrum
http://hdl.handle.net/2445/110930
Title: Enhancing the cosmic shear power spectrum
Author: Simpson, Fergus; Harnois-Deraps, Joachim; Heymans, Catherine; Jiménez, Raúl (Jiménez Tellado); Joachimi, Benjamin; Verde, Licia
Abstract: Applying a transformation to a non-Gaussian field can enhance the information content of the resulting power spectrum, by reducing the correlations between Fourier modes. In the context of weak gravitational lensing, it has been shown that this gain in information content is significantly compromised by the presence of shape noise. We apply clipping to mock convergence fields, a technique which is known to be robust in the presence of noise and has been successfully applied to galaxy number density fields. When analysed in isolation the resulting convergence power spectrum returns degraded constraints on cosmological parameters. However, substantial gains can be achieved by performing a combined analysis of the power spectra derived from both the original and transformed fields. Even in the presence of realistic levels of shape noise, we demonstrate that this approach is capable of reducing the area of likelihood contours within the Omega(m) - sigma(8) plane by more than a factor of 3.Fri, 12 May 2017 11:23:35 GMThttp://hdl.handle.net/2445/1109302017-05-12T11:23:35ZOn post-inflation validity of perturbation theory in Horndeski scalar-tensor models
http://hdl.handle.net/2445/110183
Title: On post-inflation validity of perturbation theory in Horndeski scalar-tensor models
Author: Germani, Cristiano; Kudryashova, Nina; Watanabe, Yuki
Abstract: By using the newtonian gauge, we re-confirm that, as in the minimal case, the re-scaled Mukhanov-Sasaki variable is conserved leading to a constraint equation for the Newtonian potential. However, conversely to the minimal case, in Horndeski theories, the super-horizon Newtonian potential can potentially grow to very large values after inflation exit. If that happens, inflationary predictability is lost during the oscillating period. When this does not happen, the perturbations generated during inflation can be standardly related to the CMB, if the theory chosen is minimal at low energies. As a concrete example, we analytically and numerically discuss the new Higgs inflationary case. There, the Inflaton is the Higgs boson that is non-minimally kinetically coupled to gravity. During the high-energy part of the post-inflationary oscillations, the system is anisotropic and the Newtonian potential is largely amplified. Thanks to the smallness of today's amplitude of curvature perturbations, however, the system stays in the linear regime, so that inflationary predictions are not lost. At low energies, when the system relaxes to the minimal case, the anisotropies disappear and the Newtonian potential converges to a constant value. We show that the constant value to which the Newtonian potential converges is related to the frozen part of curvature perturbations during inflation, precisely like in the minimal case.Thu, 27 Apr 2017 10:02:33 GMThttp://hdl.handle.net/2445/1101832017-04-27T10:02:33Z(Lack of) Cosmological evidence for dark radiation after Planck
http://hdl.handle.net/2445/110169
Title: (Lack of) Cosmological evidence for dark radiation after Planck
Author: Verde, Licia; Feeney, Stephen M.; Mortlock, D. J.; Peiris, Hiranya V.
Abstract: We use Bayesian model comparison to determine whether extensions to Standard-Model neutrino physics primarily additional effective numbers of neutrinos and/or massive neutrinos are merited by the latest cosmological data. Given the significant advances in cosmic microwave background (CMB) observations represented by the Planck data, we examine whether Planck temperature and CMB lensing data, in combination with lower redshift data, have strengthened (or weakened) the previous findings. We conclude that the state-of-the-art cosmological data do not show evidence for deviations from the standard (ΛCDM) cosmological model (which has three massless neutrino families). This does not mean that the model is necessarily correct in fact we know it is incomplete as neutrinos are not massless but it does imply that deviations from the standard model (e.g., non-zero neutrino mass) are too small compared to the current experimental uncertainties to be inferred from cosmological data alone.Wed, 26 Apr 2017 14:31:17 GMThttp://hdl.handle.net/2445/1101692017-04-26T14:31:17ZIs there evidence for additional neutrino species from cosmology?
http://hdl.handle.net/2445/110167
Title: Is there evidence for additional neutrino species from cosmology?
Author: Feeney, Stephen M.; Peiris, Hiranya V.; Verde, Licia
Abstract: It has been suggested that recent cosmological and flavor-oscillation data favor the existence of additional neutrino species beyond the three predicted by the Standard Model of particle physics. We apply Bayesian model selection to determine whether there is indeed any evidence from current cosmological datasets for the standard cosmological model to be extended to include additional neutrino flavors. The datasets employed include cosmic microwave background temperature, polarization and lensing power spectra, and measurements of the baryon acoustic oscillation scale and the Hubble constant. We also consider other extensions to the standard neutrino model, such as massive neutrinos, and possible degeneracies with other cosmological parameters. The Bayesian evidence indicates that current cosmological data do not require any non-standard neutrino properties.Wed, 26 Apr 2017 14:13:36 GMThttp://hdl.handle.net/2445/1101672017-04-26T14:13:36Z