Day 1203

Thursday.

1612.06891
Theoretical challenges in galaxy formation
Naab, Ostriker

In this review, focus on one major challenge for galaxy formation theory: to understand the underlying physical processes that regulate the structure of the interstellar medium, star formation and the driving of galactic outflows.  This requires accurate physical models and numerical sims, which can precisely describe the multi-phase structure of the interstellar medium on the currently unresolved few hundred parsecs scales of large scale cosmo sims.  Such models ultimately require the full accounting for the dominant cooling and heating processes, the radiation and winds from massive stars and accreting BHs, an accurate treatment of SNe explosions as well as the non-thermal components of the ISM like B fields and cosmic rays.

Day 1202

Wednesday.

1612.06535
Weak gravitational lensing
Bartelmann, Maturi

According to the theory of GR, masses deflect light in a way similar to convex glass lenses.  This gravitational lensing effect is astigmatic, giving rise to image distortions.  These distortions allow to quantify cosmic structures statistically on a broad range of scales, and to map the spatial distribution of dark and visible matter.  Summarise the theory of WL and review applications to galaxies, galaxy clusters and large-scale structures in the Universe.

Day 1201

Monday.  Tuesday.

1612.05637
CMB lens sample covariance and consistency relations
Motloch, Hu, Benoit-Lévy

GL information from the 2 and higher point statistics of the CMB temperature and polarization fields are intrinsically correlated because they are lensed by the same realization of structure between last scattering and observation.  Using an analytic model for lens sample covariance, show that there is one mode, separately measurable in the lensed CMB PS and lensing reconstruction, that carries most of this correlation.  Once these measurements become lens sample variance dominated, this mode should provide a useful consistency check between the observable that is largely free of sampling and cosmo parameter errors.  Violations of consistency could indicate systematic errors in the data and lens reconstruction or new physics at last scattering, any of which could bias cosmo inferences and delensing for gravitational waves.  A second mode provides a weaker consistency check for a spatially flat universe.  The analysis isolates the additional information supplied by lensing in a model independent manner but is also useful for understanding and forecasting CMB cosmo parameter errors in the extended LCDM parameter space of DE, curvature and massive neutrinos.  Introduce and test a simple but accurate forecasting technique for this purpose that neither double counts lensing information nor neglects lensing in the observables.


1612.05647
The VIMOS public extragalactic redshift survey (VIPERS).  Gravity test from the combination of redshift-space distortions and galaxy-galaxy lensing at $0.5<z<1.2$
de la Torre, Jullo, Giocoli, et al

Carry out a joint analysis of z-space distortions and gg lensing, with the aim of measuring the growth rate of structure; this is a key quantity for understanding the nature of gravity on cosmo scales and late-time cosmic acceleration.  Make use of the final VIPERS z survey dataset, which maps a portion of the Universe at a z of z~0.8, and the lensing data from the CFHTLenS survey over the same area of the sky.  Build a consistent theoretical model that combines non-linear galaxy biasing and z-space distortion models, and confront it with observations.  The two probes are combined in a Bayesian maximum likelihood analysis to determine the growth rate of structure at 2 redshifts z-0.6 and 0.86.  Obtain measurement of f sigma8(0.6)=0.48±0.12 and f sigma8(0.886)=0.48±0.10.  The additional gg lensing constraint alleviates galaxy bias and sigma8 degeneracies, providing direct measurements of [f,sigma8](0.6) = [0.93±0.22, 0.52±0.06] and [f,sigma8](0.86) = [0.99±0.19, 0.48±0.04].  These measurements are statistically consistent with a Universe where the gravitational interactions can be described by GR, although they are not yet accurate enough to rule out some commonly considered alternatives.  Finally, as a complementary test, measure the gravitational slip parameter, E_G, for the first time at z>0.6.  Find values of E_G(0.6)=0.16±0.09 and E_G(0.86)=0.09±).07, when E_G is averaged over scales above 3 h^-1 Mpc.  Find that the E_G measurements exhibit slightly lower values than expected for standard relativistic gravity in a LCDM background, although the results are consistent with 1-2 sigma.

Day 1200

Friday.

1612.04825
Galaxy-galaxy lensing in EAGLE: comparison with data from 180 square degrees of the KiDS and GAMA surveys
Velliscig, Cacciato, Hoekstra, et al

Present predictions for the gg lensing profile from the EAGLE hydro cosmo sim at z=0.18, in the spatial range 0.02 < R/(Mpc/h) < 2, and for 5 log qui-spaced stellar mass bins in the range 10.3<log10(Mstar/Msun)<11.8.  Compare these excess surface density profiles to the observed signal from BG galaxies imaged by KiDS and spectroscopically confirmed FG galaxies from GAMA.  Exploiting the GAMA galaxy group catalogue, the profiles of central and satellite galaxies are computed separately for groups with at least 5 members to minimize contamination.  EAGLE predictions are in broad agreement with the observed profiles for both central and satellite galaxies, although the signal is underestimated at R~0.5-2 Mpc/h for the highest stellar mass bins.  When central and satellite galaxies are considered simultaneously, agreement is found only when the selection function of lens galaxies is taken into account in detail.  Specifically, in the case of GAMA galaxies, it is crucial to account for the variation of the fraction of satellite galaxies in bins of stellar mass induced by the flux-limited nature of the survey.  Report the inferred stellar-to-halo mass relation and find good agreement with recent published results.  Note how the precision of the gg lensing profiles in the sims holds the potential to constrain fine-grained aspects of the galaxy-dark matter connection.

Day 1199

Thursday.

1612.04664
Flat-sky Pseudo-Cls analysis for Weak gravitational lensing
Asgari, Taylor, Joachimi, Kitching

Investigate the use of estimators of WL power spectra based on a flat-sky implementation of the Pseudo-Cl (PCl) technique, where the masked shear field is transformed without regard for masked regions of sky.  This masking mixes power, and E-covergence and B-modes.  To study the accuracy of forward-modeling and full-sky power spectrum recovery, consider both large-area survey geometries, and small-scale masking due to stars and a checkerboard model for field-of-view gaps.  The power spectrum for the large-area survey geometry is sparsely-sampled and highly oscillatory, which makes modelling problematic.  Instead, derive an overall calibration for large-are mask bias using simulated fields.  The effects of small-area star masks can be accurately corrected for, while the checkerboard mask has oscillatory and spiky behavior which leads to percent biases.  Apodisation of the masked fields leads to increased biases and a loss of information.  Find that construction of an unbiased forward-modded of the raw PCls is possible, and recover the full-sky convergence power to within a few percent accuracy for both Gaussian and lognormal-distributed shear fields.  Propagating this through to cosmo parameters using a Fisher-Matrix formalism, find possible to make unbiased estimates of parameters for surveys up to 1200 deg2 with 30 galaxies per arcmin2, beyond which the percent biases become larger than the statistical accuracy.  This implies a flat-sky PCl analysis is accurate for current surveys but a Euclid-like survey will require higher accuracy.

Day 1198

Wednesday.  Thursday.

1612.04041
Cosmology with weak-lensing peak counts
Lin

WL causes distortions of galaxy images and probes massive structures on large scales, allowing to understand the late-time evolution of the Universe.  One way to extract the cosmo info from WL is to use peak statistics.  Peaks are tracers of massive haloes and therefore probe the mass function.  They retain non-Gaussian information and have already been shown as a promising tool to constrain cosmology.  In this work, develop a new model to predict WL peak counts.  The model generates fast sims based on halo sampling and selects peaks from the derived lensing maps.  This approach has 3 main advantages.  First, the model is very fast: only several seconds are required to perform a realization.  Second, including realistic conditions is straightforward.  Third, the model provides the full distribution information because of its stochasticity.  Show that the model agrees well with N-body sims.  Then, study the impacts of the cosmo-dependent covariance on constraints and explore different parameter inference methods.  A special focus is put on approximate Bayesian computation (ABC), an accept-reject sampler without the need to estimate the likelihood.  Show that ABC is able to yield robust constraints with much reduced time costs.  Several filtering techniques are studied to improve the extraction of multi scale information.  Finally, the new model is applied to the CFHTLenS, KiDS DR1/2, and DES SV data sets.  The preliminary results agree with the Planck constraints assuming LCDM.  Overall, this thesis forges an innovative tool for future WL surveys.  The manuscript provides a brief review on WL peak counts.


1612.04247
Impact of baryons and super-cluster environments on weak lensing measurements
Peters, Brown, Kay, Barnes

Use a combination of full hydrodynamic and DM only sims to investigate the effect that super-cluster environments and baryonic physics have on the matter power spectrum.  This is done by re-simulating a sample of super-cluster sub-volumes, identified in a large cosmologically representative DM only sim, along with a random control sample.  On large scales, find that the matter PS measured from the super-cluster sample has at least 2x as much power as that measured from the random sample, while on small scales the super-cluster sample has less power than the random sample.  The investigation of the effect of baryons physics on the matter PS is found to be in agreement with previous studies.  However, find that the effect of environment on the matter power spectrum is dominant over the effect of baryons.  In addition, investigate the effect of targeting a cosmologically non-representative, super-cluster region of the sky in the WL shear PS.  Do this by generating shear and convergence maps using a LoS integration technique, which intercepts the random and supercluster sub-volumes.  Find the convergence power spectrum measured from the super-cluster sample has a larger amplitude than that measured from the random sample at all scales, and by more than a factor of 2 for ell<1e3.  Frame the results within the context of the Super-CLusterAssisted Shear Survey (Super-CLASS), which aims to measure the cosmic shear signal in the radio band by targeting a region of the sky that contains 5 Abell clusters.  Assuming the Super-CLASS survey will have a source density of 1.5 galaxies/arcmin2, forecast a detection significance of 2.7±1.5, which indicates that the Super-CLASS project will likely make a cosmic shear detection with radio data alone.


1612.04360
Large-scale assembly bias of dark matter haloes
Lazeyras, Musso, Schmidt

Present precise measurements of the assembly bias of DM haloes, i.e. the dependent of halo bias on other properties than the mass, using curved "separate universe" N-body sims which effectively incorporate an infinite-wavelength matter overdnesity into the BG density.  This method measure the LIMD bias parameters b_n in the large-scale limit.  Focus on the dependence of the first two Eulerian biases b1 and b2 on 4 halo properties: the concentration, spin, mass accretion rate, and ellipticity.  Quantitatively compare the results with previous works in which assembly bias was measured on fairly small scales.  Despite this difference, the findings are in good agreement with previous results.  Also look at the joint dependence of bias on 2 halo properties in addition to the mass.  Finally, using the excursion set peaks model, attempt to shed new insights on how assembly bias arises in this analytical model. 

Day 1197

Friday.  Monday.  Tuesday.

1612.03034
First test of Verlinde's theory of emergent gravity using weak gravitational lensing measurements
Brouwer, et al

Verlinde (2016) proposed that the observed excess gravity in galaxies and clusters is the consequence of Emergent Gravity (EG).  In this theory the standard gravitational laws are modified on galactic and larger scales due to the displacement of dark energy by baryonic matter.  EG gives an estimate of the excess gravity (described as an apparent DM density) in terms of the baryonic mass distribution and the Hubble parameter.  In this work, present the first test of EG using WL, within the regime of validity of the current model.  Although there is no direct description of lensing and cosmology in EG yet, can make a reasonable estimate of the expected lensing signal of low redshift galaxies by assuming a BG LCDM cosmology.  Measure the (apparent) average surface mass density profiles of 33,613 isolated central galaxies, and compare them to those predicted by EG based on the galaxies' baryonic masses.  To this end, employ the ~180 sq.deg. overlap of KiDS with the spectroscopic GAMA survey.  Find that the prediction from EG, despite requiring no free parameters, is in good agreement with the observed gglensing profiles in 4 different stellar mass bins.  Although this performance is remarkable, this study is only a first step.  Further advancements on both the theoretical framework and observational tests of EG are needed before it can be considered a fully developed and solidly tested theory.


1612.03121
Integrated cosmological probes: extended analysis
Nicola, Refregier, Amara

Recent progress in cosmology has relied on combining different cosmo probes.  In earlier work, implemented an integrated approach to cosmology where the probes are combined into a common framework at the map level.  This has the advantage of taking full account of the correlations between the different probes, to provide a stringent test of systematics and the validity of the cosmo model.  Extend this analysis to include not only CMB temperature, galaxy clustering, WL from SDSS but also CMB lensing, WL from DES SV, Type Ia SNe and H0 measurements.  This yields 12 auto and cross power spectra as well as BG probes.  Furthermore, extend the treatment of systematic uncertainties.  For LCDM, find results that are consistent with earlier work.  Given the enlarged data set and systematics treatment, this confirms the robustness of the analysis and results.  Furthermore, find that the best-fit cosmo model gives a good fit to the data considered with no signs of tensions within the analysis.  Also find the constraints to be consistent with this found by WMAP9, SPT and ACT and the KiDS WL survey.  Comparing with the Planck Collaboration results, see a broad agreement, but there are indications of a tension from the marginalized constraints in most pairs of cosmological parameters.  Since the analysis includes CMB temperature Planck data at 10<ell<610, the tension appears to arise between the Planck high-ell and the other measurements.  Furthermore, find the constraints on the probe calibration parameters to be in agreement with expectations, showing that the datasets are mutually consistent.  In particular, this yields a confirmation of the amplitude calibration of the WL measurements from SDSS, DES SV and Planck CMB lensing from the integrated analysis.

Day 1196

Thursday.

1612.02173
A cooperative approach among methods for photometric redshifts estimation: an application to KiDS data
Cavuoti, et al

Using a KiDS subset of ~25,000 galaxies with measured spec-z's, derive photo-z's using i) 3 different empirical methods based on supervised machine learning, ii) the BPZ model and iii) classical SED template fitting procedure (Le Phare).  Confirm that, in the regions of photometric parameter space properly sampled by the spectroscopic templates, machine learning methods provide better redshift estimates, with a lower scatter and a smaller fraction of outliers.  SED fitting techniques, however, provide useful information on the galaxy spectral type which can be effectively used to constrain systematic errors and to better characterize potential catastrophic outliers.  Such classification is then used to specialize the training of regression machine learning models, by demonstrating that a hybrid approach, involving SED fitting and machine learning in a single collaborative framework, can be effectively used to improve the accuracy of photo-z estimates. 


1612.02264
Cosmological constraints with weak lensing peak counts and second-order statistics in a large-field survey
Peel, et al

Peak statistics in weak lensing maps access the non-Gaussian information contained in the LS distribution of matter in the Universe.  They are therefore a promising complement to 2pt and higher-order statistics to constrain the cosmological models.  To prepare for the high-precision data of next-generation surveys, assess the constraining power of peak counts in a simulated Euclid-like survey on the cosmo parameters Omega_m, sigma_8, and w_0.  In particular, study how the Camelus model -- a fast stochastic algorithm for predicting peaks -- can be applied to such large surveys.  Measure the peak count abundance in a mock shear catalogue of ~5k sq. deg. using a multi scale mass map filtering technique.  Then constrain the parameters of the mock survey using Camelus combined with approximate Bayesian computation (ABC).  Find that peak statistic yield a tight but significantly biased constraint in the sigma_8-Omega_m plane, indicating the need to better understand and control the model's systematics.  Calibrate the model to remove the bias and compare results to those from the 2PCF measured on the same field.  In this case, find the derived parameter Sigma_8=sigma_8(Omega_m/0.27)^alpha = 0.76±0.03 with alpha=0.65 for peaks, while for 2PCF the values is SIgma_8=0.76±0.02 with alpha=0.70.  Therefore see comparable constraining power between the 2 probes, and the offset of their sigma_8-Omega_m degeneracy directions suggests that a combined analysis would yield tighter constraints than either measure alone.  As expected, w_0 cannot be well constrained without a tomographic analysis, but its degeneracy directions with the other two varied parameters are still clear for both peaks and 2PCF.

Day 1195

Wednesday.

1612.01533
Estimating the weak-lensing rotation signal in radio cosmic shear surveys
Thomas, Whittaker, Camera, Brown

The WL distortion tensor contains two other effects in addition to the two components of shear: the convergence and rotation.  The rotation mode is not measurable using the standard cosmic shear estimators based on galaxy shapes, as there is no information on the original shapes of the images before they were lensed.  Due to this, no estimator has been proposed for the rotation mode in cosmo WL surveys, and the rotation mode has never been constrained.  Here, derive an estimator for his quantity, which is based on the use of radio polarization measurements of the intrinsic position angles of galaxies.  The rotation mode can be sourced by a physics beyond LCDM, and also offers the chance to perform consistency checks of LCDM and of WL surveys themselves.  Present simulations of this estimator and show that, for the pedagogical example of cosmic string spectra, this estimator could detect a signal that is consistent with the constraints from Planck.  Examine the connection between the rotation mode and the shear B-modes and thus how this estimator could help control systematics in future radio WL surveys.

Day 1194

Friday.  Monday.  Tuesday.

1612.00752
Non-linear shrinkage estimation of large-scale structure covariance
Joachimi

In many astrophysical settings covariance matrices of large datasets have to be determined empirically from a finite number of mock realizations.  The resulting noise degrades inference and precludes it completely if there are fewer realizations than data points.  This work applies a recently proposed non-linear shrinkage estimator of covariance to a realistic example from large-scale structure cosmology.  After optimizing its performance for the usage in likelihood expressions, the shrinkage estimator yields subdominant bias and variance comparable to that of the standard estimator with a factor ~50 less realizations.  This is achieved without any prior information on the properties of the data or the structure of the covariance matrix, at negligible computational cost.


1512.00770
Unequal-time correlates for cosmology
Kitching, Heavens

Measurements of the power spectrum from large-scale structure surveys have to date assumed an equal-time approximation, where the full cross-correlation power spectrum of the matter density field evaluated at different times (or distances) has been approximated either by the power spectrum at fixed time, or in an improved fashion, by a geometric mean P(k; r1, r2) = [P(k;r1)P(k;r2)]^1/2.  In this paper, investigate the expected impact of the geometric mean ansatz, and present an application in assessing the impact on weak gravitational lensing cosmological parameter inference, using an perturbative unequal-time correlation.  As one might expect, find that the impact of this assumption is greatest at large separations in redshift Delta z > 0.3 where the change in the amplitude of the matter power spectrum can be as much as 10 percent for k>5h/Mpc.  However, of more concern is that the corrections for small separations, where the clustering is not close to zero, may not be negligibly small.  In particular, find that for a Euclid- or LSST-like weak lensing experiment the assumption of dual-time correlators may result in biased predictions of the cosmic shear power spectrum, and that the impact is strongly dependent on the amplitude of the intrinsic alignment signal.  To compute uneuqal-time correlations to sufficient accuracy will require advances in either perturbation theory to high k-modes, or extensive use of simulations.


1612.00839
The 2-degree field lensing survey: photometric redshifts from a large new training sample to r<19.5
Wolf, et al

Present a new training set for estimating empirical photometric redshifts of galaxies, which was created as part of the 2dFLenS project.  This training set is located in a 700 sq deg area of the KiDS South field and is randomly selected and nearly complete at r<19.5.  Investigate the photometric z performance obtained with ugriz photometry from VST-ATLAS and W1/W2 from WISE, based on several empirical and template methods.  The best redshift errors are obtained with kernel-density estimation, as are the lowest biases, which are consistent with zero within statistical noise.  The 68th percentiles of the redshift scatter for magnitude-limited samples at r<(15.5, 17.5, 19.5) are (0.014, 0.017, 0.028).  In this magnitude range, there are no known ambiguities in the color-redshift map, consistent with a small rate of redshift outliers.  In the fainter regime, the KDE method produces p(z) estimates per galaxy that represent unbiased and accurate redshift frequency expectations.  The p(z) sum over any subsample is consistent with the true redshift frequency plus Poisson noise.  Further improvements in redshift precision at r<20 would mostly be expected from filter sets with narrower passbands to increase the sensitivity of course to small changes in redshift.


1612.00847
Data-driven, interpretable photometric redshifts trained on heterogeneous and unrepresentative data
Leistedt, Hogg

Present a new method for inferring photo-z in deep galaxy and quasar surveys, based on a data driven model of latent SEDs and a physical model of photometric fluxes as a function of redshift.  This conceptually novel approach combines the advantages of both machine-learning and template-fitting methods by building template SEDs directly from the training data.  This is made computationally tractable with gaussian Processes operating in flux-z space, encoding the physics of redshift and the projection of galaxy SEDs onto photometric band passes.  This method alleviates the need of acquiring representative training data or constructing detailed galaxy SED models; it requires only that the photometric band passes and calibrations be known or have parameterized unknowns.  The training data can consist of a combination of spectroscopic and deep many-band photometric data, which do not need to entirely spatially overlap with the target survey of interest or even involve the same photometric bands.  Showase the method on the i-magnitude-selected, spectroscopically-confirmed galaxies in the COSMOS field.  The model is trained on the deepest bands (from SUBARU and HST) and photo-zs are derived using the shallower SDSS optical bands only.  Demonstrate that accurate z point estimates and probability distributions are obtained despite the training and target sets having very different z distributions, noise properties, and even photometric bands.  The model can also be used to predict missing photometric fluxes, or to simulated populations of galaxies with realistic fluxes and z, for example.  This method opens a new era in which photo-z for large photometric surveys are derived using a flexible yet physical model of the data trained on all available surveys (spectroscopic and photometric).


1612.00852
On the validity of the Born approximation for beyond-Gaussian weak lensing observables
Petri, Haiman, May

Accurate forward modeling of WL observables from cosmo parameters is necessary for upcoming galaxy surveys.  Because WL probes structures in the non-linear regime, analytical forward modeling is very challenging, if not impossible.  Numerical sims of WL features rely on ray-tracing through the outputs of N-body sims, which requires knowledge of the gravitational potential and accurate solvers for light ray trajectories.  A less accurate procedure, based on the Born approximation, only requires knowledge of the density field, and can be implemented more efficiently and at a lower computational cost.  In this work, use sims to show that deviations of the Born-approximated convergence power spectrum, skewness and kurtosis from their fully ray-traced counterparts are consistent with the smallest non-trivial post-Born corrections (so-called geodesic and lens-lens terms).  Find, however, that the perturbative approach for the geodesic correction breaks down at higher orders.  Also find that cosmo parameter biases induced by the Born approximation are negligible even for an LSST-like analyses.  Using the LensTools software suite, show that the Born approximation saves a factor of 4 in computing time with respect to the full ray-tracing in reconstructing the convergence.

Day 1193

Thursday.

1611.10326
Weak lensing magnification in the Dark Energy Survey Science Verification Data
Garcia-Fernandez, et al

In this paper the effect of WL magnification on galaxy number counts is studied by cross-correlating the positions of 2 galaxy samples, separated by redshift, using data from the DES SV data set.  The analysis is carried out for 2 photometrically-selected galaxy samples, with mean photometric redshifts in the 0.2<z<0.4 and 0.7<z<1.0 ranges, in the riz bands.  A signal is detected with a 3.5 sigma significance level in each of the bands tested, and is compatible with the magnification predicted by the LCDM model.  After an extensive analysis, it cannot be attributed to any known systematic effect.  The detection of the magnification signal is robust to estimated uncertainties in the outlier rate of the photometric redshifts, but this will be an important issue for use of photometric redshifts in magnification measurements from larger samples.  In addition to the detection of the magnification signal, a method to select the sample with the maximum signal-to-noise is proposed and validated with data.