Interpolating Masked Weak Lensing Signal with Karhunen-Loeve Analysis

We explore the utility of Karhunen Loeve (KL) analysis in solving practical problems in the analysis of gravitational shear surveys. Shear catalogs from large-field weak lensing surveys will be subject to many systematic limitations, notably incomplete coverage and pixel-level masking due to foreground sources. We develop a method to use two dimensional KL eigenmodes of shear to interpolate noisy shear measurements across masked regions. We explore the results of this method with simulated shear catalogs, using statistics of high-convergence regions in the resulting map. We find that the KL procedure not only minimizes the bias due to masked regions in the field, it also reduces spurious peak counts from shape noise by a factor of ~ 3 in the cosmologically sensitive regime. This indicates that KL reconstructions of masked shear are not only useful for creating robust convergence maps from masked shear catalogs, but also offer promise of improved parameter constraints within studies of shear peak statistics.Comment: 13 pages, 9 figures; submitted to Ap

The Effect of Corner Modes in the Initial Conditions of Cosmological Simulations

In view of future high-precision large-scale structure surveys, it is important to quantify the percent and subpercent level effects in cosmological N-body simulations from which theoretical predictions are drawn. One such effect involves deciding whether to zero all modes above the one-dimensional Nyquist frequency, the so-called “corner” modes, in the initial conditions. We investigate this effect by comparing power spectra, density distribution functions, halo mass functions, and halo profiles in simulations with and without these modes. For a simulation with a mass resolution of mp ~ 1011 -h M 1 , we find that at z > 6, the difference in the matter power spectrum is large at wavenumbers above ∼80% of kNy, reducing to below 2% at all scales by z ~ 3. Including corner modes results in a better match between low- and high-resolution simulations at wavenumbers around the Nyquist frequency of the low-resolution simulation, but the effect of the corner modes is smaller than the effect of particle discreteness. The differences in mass functions are 3% for the smallest halos at z = 6 for the mp ~ 1011 -h M 1 simulation, but we find no significant difference in the stacked profiles of well-resolved halos at z 6. Thus removing power at ∣k∣ > kNy in the initial conditions of cosmological simulations has a small effect on small scales and high redshifts, typically below a few percent

Robust, data-driven inference in non-linear cosmostatistics

We discuss two projects in non-linear cosmostatistics applicable to very large surveys of galaxies. The first is a Bayesian reconstruction of galaxy redshifts and their number density distribution from approximate, photometric redshift data. The second focuses on cosmic voids and uses them to construct cosmic spheres that allow reconstructing the expansion history of the Universe using the Alcock-Paczynski test. In both cases we find that non-linearities enable the methods or enhance the results: non-linear gravitational evolution creates voids and our photo-z reconstruction works best in the highest density (and hence most non-linear) portions of our simulations.Comment: 14 pages, 10 figures. Talk given at "Statistical Challenges in Modern Astronomy V," held at Penn Stat

Probing dark energy with cluster counts and cosmic shear power spectra: including the full covariance

(Abridged) Combining cosmic shear power spectra and cluster counts is powerful to improve cosmological parameter constraints and/or test inherent systematics. However they probe the same cosmic mass density field, if the two are drawn from the same survey region, and therefore the combination may be less powerful than first thought. We investigate the cross-covariance between the cosmic shear power spectra and the cluster counts based on the halo model approach, where the cross-covariance arises from the three-point correlations of the underlying mass density field. Fully taking into account the cross-covariance as well as non-Gaussian errors on the lensing power spectrum covariance, we find a significant cross-correlation between the lensing power spectrum signals at multipoles l~10^3 and the cluster counts containing halos with masses M>10^{14}Msun. Including the cross-covariance for the combined measurement degrades and in some cases improves the total signal-to-noise ratios up to plus or minus 20% relative to when the two are independent. For cosmological parameter determination, the cross-covariance has a smaller effect as a result of working in a multi-dimensional parameter space, implying that the two observables can be considered independent to a good approximation. We also discuss that cluster count experiments using lensing-selected mass peaks could be more complementary to cosmic shear tomography than mass-selected cluster counts of the corresponding mass threshold. Using lensing selected clusters with a realistic usable detection threshold (S/N~6 for a ground-based survey), the uncertainty on each dark energy parameter may be roughly halved by the combined experiments, relative to using the power spectra alone.Comment: 32 pages, 15 figures. Revised version, invited original contribution to gravitational lensing focus issue, New Journal of Physic

Forecasts of non-Gaussian parameter spaces using Box-Cox transformations

Forecasts of statistical constraints on model parameters using the Fisher matrix abound in many fields of astrophysics. The Fisher matrix formalism involves the assumption of Gaussianity in parameter space and hence fails to predict complex features of posterior probability distributions. Combining the standard Fisher matrix with Box-Cox transformations, we propose a novel method that accurately predicts arbitrary posterior shapes. The Box-Cox transformations are applied to parameter space to render it approximately multivariate Gaussian, performing the Fisher matrix calculation on the transformed parameters. We demonstrate that, after the Box-Cox parameters have been determined from an initial likelihood evaluation, the method correctly predicts changes in the posterior when varying various parameters of the experimental setup and the data analysis, with marginally higher computational cost than a standard Fisher matrix calculation. We apply the Box-Cox-Fisher formalism to forecast cosmological parameter constraints by future weak gravitational lensing surveys. The characteristic non-linear degeneracy between matter density parameter and normalisation of matter density fluctuations is reproduced for several cases, and the capabilities of breaking this degeneracy by weak lensing three-point statistics is investigated. Possible applications of Box-Cox transformations of posterior distributions are discussed, including the prospects for performing statistical data analysis steps in the transformed Gaussianised parameter space.Comment: 14 pages, 7 figures; minor changes to match version published in MNRA

Looking the void in the eyes - the kSZ effect in LTB models

As an alternative explanation of the dimming of distant supernovae it has recently been advocated that we live in a special place in the Universe near the centre of a large void described by a Lemaitre-Tolman-Bondi (LTB) metric. The Universe is no longer homogeneous and isotropic and the apparent late time acceleration is actually a consequence of spatial gradients in the metric. If we did not live close to the centre of the void, we would have observed a Cosmic Microwave Background (CMB) dipole much larger than that allowed by observations. Hence, until now it has been argued, for the model to be consistent with observations, that by coincidence we happen to live very close to the centre of the void or we are moving towards it. However, even if we are at the centre of the void, we can observe distant galaxy clusters, which are off-centre. In their frame of reference there should be a large CMB dipole, which manifests itself observationally for us as a kinematic Sunyaev-Zeldovich (kSZ) effect. kSZ observations give far stronger constraints on the LTB model compared to other observational probes such as Type Ia Supernovae, the CMB, and baryon acoustic oscillations. We show that current observations of only 9 clusters with large error bars already rule out LTB models with void sizes greater than approximately 1.5 Gpc and a significant underdensity, and that near future kSZ surveys like the Atacama Cosmology Telescope, South Pole Telescope, APEX telescope, or the Planck satellite will be able to strongly rule out or confirm LTB models with giga parsec sized voids. On the other hand, if the LTB model is confirmed by observations, a kSZ survey gives a unique possibility of directly reconstructing the expansion rate and underdensity profile of the void.Comment: 20 pages, 9 figures, submitted to JCA

Particle size determines the anti-inflammatory effect of wheat bran in a model of fructose over-consumption : implication of the gut microbiota

We investigated the impact of the particle size of wheat bran on gut dysbiosis and inflammation induced by a fructose overload. Mice received drinking water with or without fructose (30%) and a standard diet supplemented with or without 5% of wheat bran fractions characterized by different average particle sizes (1690 pm versus 150 um) for 8 weeks. Fructose increased Enterobacteriaceae associated with higher expression of key inflammatory genes in the liver. The two wheat bran fractions differently affected specific gut bacteria known to be involved in the regulation of the gut barrier function and/or inflammatory processes. Moreover, wheat bran with small particle size was the sole fibre that reduced hepatic and systemic inflammatory markers upon high fructose intake. The anti-inflammatory effects of wheat bran may be dependent on their particle size and could be related to the changes in caecal Enterobacteriaceae

The human somatostatin receptor type 2 as an imaging and suicide reporter gene for pluripotent stem cell-derived therapy of myocardial infarction

Rationale: Pluripotent stem cells (PSCs) are being investigated as a cell source for regenerative medicine since they provide an infinitive pool of cells that are able to differentiate towards every cell type of the body. One possible therapeutic application involves the use of these cells to treat myocardial infarction (MI), a condition where billions of cardiomyocytes (CMs) are lost. Although several protocols have been developed to differentiate PSCs towards CMs, none of these provide a completely pure population, thereby still posing a risk for neoplastic teratoma formation. Therefore, we developed a strategy to (i) monitor cell behavior noninvasively via site-specific integration of firefly luciferase (Fluc) and the human positron emission tomography (PET) imaging reporter genes, sodium iodide symporter (hNIS) and somatostatin receptor type 2 (hSSTr2), and (ii) perform hSSTr2-mediated suicide gene therapy via the clinically used radiopharmacon 177Lu-DOTATATE. Methods: Human embryonic stem cells (ESCs) were gene-edited via zinc finger nucleases to express Fluc and either hNIS or hSSTr2 in the safe harbor locus, adeno-associated virus integration site 1. Firstly, these cells were exposed to 4.8 MBq 177Lu-DOTATATE in vitro and cell survival was monitored via bioluminescence imaging (BLI). Afterwards, hNIS+ and hSSTr2+ ESCs were transplanted subcutaneously and teratomas were allowed to form. At day 59, baseline 124I and 68Ga-DOTATATE PET and BLI scans were performed. The day after, animals received either saline or 55 MBq 177Lu-DOTATATE. Weekly BLI scans were performed, accompanied by 124I and 68Ga-DOTATATE PET scans at days 87 and 88, respectively. Finally, hSSTr2+ ESCs were differentiated towards CMs and transplanted intramyocardially in the border zone of an infarct that was induced by left anterior descending coronary artery ligation. After transplantation, the animals were monitored via BLI and PET, while global cardiac function was evaluated using cardiac magnetic resonance imaging. Results: Teratoma growth of both hNIS+ and hSSTr2+ ESCs could be followed noninvasively over time by both PET and BLI. After 177Lu-DOTATATE administration, successful cell killing of the hSSTr2+ ESCs was achieved both in vitro and in vivo, indicated by reductions in total tracer lesion uptake, BLI signal and teratoma volume. As undifferentiated hSSTr2+ ESCs are not therapeutically relevant, they were differentiated towards CMs and injected in immune-deficient mice with a MI. Long-term cell survival could be monitored without uncontrolled cell proliferation. However, no improvement in the left ventricular ejection fraction was observed.Conclusion: We developed isogenic hSSTr2-expressing ESCs that allow noninvasive cell monitoring in the context of PSC-derived regenerative therapy. Furthermore, we are the first to use the hSSTr2 not only as an imaging reporter gene, but also as a suicide mechanism for radionuclide therapy in the setting of PSC-derived cell treatment

Mass assembly of galaxies: Smooth accretion versus mergers

Galaxies accrete their mass by means of both smooth accretion from the cosmic web, and the mergers of smaller entities. We wish to quantify the respective role of these two modes of accretion, which could determine the morphological types of galaxies observed today. Multi-zoom cosmological simulations are used to estimate as a function of time the evolution of mass in bound systems, for dark matter as well as baryons. The baryonic contents of dark matter haloes are studied. Merger histories are followed as a function of external density, and the different ways in which mass is assembled in galaxies and the stellar component accumulated are quantified. We find that most galaxies assemble their mass through smooth accretion, and only the most massive galaxies also grow significantly through mergers. The mean fraction of mass assembled by accretion is 77 %, and by mergers 23 %. We present typical accretion histories of hundreds of galaxies: masses of the most massive galaxies increase monotonically in time, mainly through accretion, many intermediate-mass objects also experience mass-loss events such as tidal stripping and evaporation. However, our simulations suffer from the overcooling of massive galaxies caused by the neglect of active galaxy nuclei (AGN) feedback. The time by which half of the galay mass has assembled, both in dark matter and baryons, is a decreasing function of mass, which is compatible with the observations of a so-called downsizing. At every epoch in the universe, there are low-mass galaxies actively forming stars, while more massive galaxies form their stars over a shorter period of time within half the age of the universe.Comment: A&A Accepted, 19 pages, 17 figure