Day 1519

Monday.

1812.09266
Relativistic bias in neutrino cosmologies
Fidler, Sujata, Archidiacono

Halos and galaxies are tracers of the underlying DM structures.  While their bias is well understood in the case of a simple Universe composed dominantly of DM, the relation becomes more complex in the presence of massive neutrinos.  Indeed massive neutrinos introduce rich dynamics in the process of structure formation leading to scale-dependent bias.  Study this process from the perspective of GR employing a simple spherical collapse model.  Find a characteristic signature at the neutrino free-streaming scale in addition to a large-scale feature from GR.  The scale-dependent halo bias opposes the suppression in the matter distribution due to neutrino free-streaming and leads to corrections of a few percent in the halo power spectrum.  It is not only sensitive to the sum of the neutrino-masses, but respond to the individual masses.  Accurate models for the neutrino bias are a crucial ingredient for the future data analysis and play an important role in constraining the neutrino masses.

Day 1518

Friday.

1812.08169
Testing dark matter and modifications to gravity using local Milky Way Observables
Lisanti, et al

Galactic rotation curve are often considered the first robust evidence for the existence of dark matter.  However, even in the presence of a dark matter halo, other galactic scale observations, such as the Baryonic Tully-Fisher relation and the radial acceleration relation, remain challenging to explain.  This has motivated long-distance, IR modifications to gravity as an alternative to the DM hypothesis.  Present a framework to test a general classification of IR gravity modifications using local Milky Way observables, including the vertical acceleration field, the rotation curve, the baryonic surface density, and the stellar disk profile.  Focus on models that predict scalar amplifications of gravity, i.e., models that increase the magnitude but do not change the direction of the gravitational acceleration.  Modified Newtonian Dynamics (MOND) is one such example.  Find that an IR modification to gravity of this type is in tension with observations of the MW scale radius and bulge mass and that DM provides a better fit to the data.  Conclude that models like MOND struggle to simultaneously explain both the rotational velocity and vertical motion of nearby stars in the MW.


1812.08206
Constraining neutrino mass with weak lensing Minkowski Functionals
Marques, et al

The presence of massive neutrinos affects structure formation, leaving imprints on large-scale structure observables such as the weak lensing field.  The common lensing analysis with 2pt statistics are insensitive to the large amount of non-Gaussian information in the density field.  Investigate non-Gaussian tools, in particular the Minkowski Functionals (MFs)---morphological descriptors including area, perimeter, and genus---in an attempt to recover the higher-order information.  Use convergence maps from the Cosmological Massive Neutrino Simulations (MassiveNus) and assume galaxy noise, density and z distribution for an LSST-like survey.  Show that MFs are sensitive to the neutrino mass sum, and the sensitivity is z dependent and is non-Gaussian.  Find that redshift tomography significantly improves the constraints on neutrino mass for MFs, compared to the improvements for the PS.  Attribute this to the stronger z dependence of neutrino effects on small scales.  Then build an emulator to model the PS and MFs, and study the constraints on M_nu, Omega_m, A_s from the PS, MFs, and their cmbination.  Show that MFs significantly outperform the PS in constraining neutrino mass, by more than a factor of four.  However, a thorough study of the impact from systematics such as baryon physics and galaxy shape and redshift biases will be important to realize the full potential of MFs.

Day 1517

Thursday.

1812.06981
Observable tests of self-interacting dark matter in galaxy clusters: BCG wobbles in a constant density core
Harvey, et al

Models of CDM always predict a cusp, centrally concentrated distribution of DM in galaxy clusters.  Constant density cores would be strong evidence for beyond-CDM physics, such as self-interacting dark matter (SIDM).  An observable consequence would be oscillations of the BCG in otherwise relaxed galaxy clusters.  Offset BCGs have indeed been observed -- but only interpreted via a simplified, analytic model of oscillations.  Compare these observations to the BAHAMAS-SIDM suite of cosmo sims, which include SIDM and a full hydrodynamical treatment of SF and feedback.  Predict that the median offset of BCGs increases with the SIDM cross-section and cluster mass, while CDM exhibits no trend in mass.  Interpolating between the simulated cross-sections, find that the observations (of 10 clusters) have a 38% probability of being consistent with CDM, and prefer cross-section sigma/m<0.22 cm^2/g at 95 % CL.  This is on the verge of discriminating between DM models that would explain discrepancies in the behavior of dwarf galaxies, and will be improved by larger surveys by Euclid or SuperBIT.

Day 1516

Wednesday.



1812.07437

Information content of the weak lensing bispectrum for the next generation of galaxy surveys
Rizzato, et al

Present a full analysis of the information content in the joint convergence WL PS-BS accounting for the complexity of modern WL LSS surveys.  Developed a high performance code that allows highly parallelized prediction of the binned tomographic observables and their joint non-Gaussian covariance matrix accounting for terms up to the 6pt correlation function and super sample effects.  This performance allows several interesting scientific questions to be addressed.  Find that the bispectrum provides an improvement in terms of S/N of about 45% on top of the PS, main it a powerful source of information for future surveys.  Interestingly, the super sample covariance has a negligible impact on this joint analysis.  Furthermore capable to test the impact of theoretical uncertainties in the halo model used to build the observables; with presently allowed variations, conclude that the impact is negligible on the S/N.  Finally, consider data compression possibilities to optimize future analyses of the WL bispectrum.  Find that, ignoring systematics, 5 equi-populated z bins are enough to recover the information content of a Euclid-like survey, with negligible improvement when increasing to 10 bins.  Also explore principal component analysis and dependence on the triangle shapes as ways to reduce the numerical complexity of the problem.

Day 1515

Tuesday.

1812.06191
Why chromatic imaging matters
Sanchez-Bermudez, et al

During the last two decades, the fist generation of beam combiners at the VLT Interferometer has proved the importance of optical interferometry for high-angular resolution astrophysical studies in the near- and mid-infrared.  With the advent of 4-beam combiners at the VLTI, the u-v coverage per pointing increases significantly, providing an opportunity to use reconstructed images as powerful scientific tools.  Therefore, interferometric imaging is already a key feature of the new generation of VLTI instruments, as well as for other interferometric facilities like CHARA and JWST.  It is thus imperative to account for the current image reconstruction capabilities and their expected evolutions in the coming years.  Here, present a general overview of the current situation of optical interferometric image reconstruction with a focus on new wavelength-dependent information, highlighting its main advantages and limitations.  As an Appendix, include several cookbooks describing the usage and installation of several state-of-the art image reconstruction packages.  To illustrate the current capabilities of the software available to the community, recover chromatic images, from simulated MATISE data, using the MCMC software SQUEEZE.  With these images, aim at showing the importance of selecting good regularization functions and their impact on the reconstruction.


1812.06618
Ultrahigh-energy cosmic rays
Mariazzi

UHECRs arrive at Earth from the most energetic astrophysical accelerators in the universe.  They collide with atoms in the upper atmosphere with energies about 10 times higher than any man-made accelerator, and produce gigantic cascades of secondary particles, called extensive air showers (EAS).  EASs can be detected spreading particle detectors over a large area to record the interactions of secondary particles.  The Pierre Auger Observatory has been designed to investigate the origin and nature of UHECRs using the combination of information from a surface array, measuring the lateral distributions of secondary particles at the ground, and fluorescence telescopes, observing the longitudinal profile of the EM component of EAS, providing an enhanced reconstruction capability.  In this contribution, the status and prospects of understanding the physics of UHECRs will be reviewed, focusing on the progress made thanks to the measurements of the Pierre Auger Observatory.  Physics results form the UHECR data collected with the PAO opened new perspectives and motivated an upgrade of the Observatory, AugerPrime, whose main characteristics are also presented.


1812.06918
Environmental dependence of ellipticity correlation functions of intrinsic alignments
Reischke, Schäfer

Investigate the environmental dependence of the IA in cosmic shear surveys.  Use the quadratic and linear alignment model to describe the contributions by spiral and elliptical galaxies, respectively.  The density field is in both cases described by a Gaussian random field and ellipticity correlation functions that are conditional on the environment of the galaxies are constructed by sampling random values for the tidal tensor and inertial tensor.  The covariance of the Gaussian random process from which the tensor entries are drawn is decomposed by means of a spherical Fourier-Bessel transformation of the density field.  The dependence on environment is modeled by the number of positive eigenvalues of the tidal tensor, which allows a differentiation between voids, sheets, filaments and superclusters.  Find that elliptical galaxies align strongest in elongated structures such as sheets and filaments with an amplitude almost an order of magnitude higher compared to the alignment in clusters or voids.  In contrast to this, spiral galaxies align equally strong in all environments.  Cross-alignments between different environments are smaller than the respective auto-correlations subject to the Cauchy-Schwartz inequality which is an effective bound on their amplitude.  Furthermore, find misalignment between inertial and tidal tensor to be stronger in anisotropic regions compared to clusters or voids.  While the imprint of WL on galaxy ellipticities is agnostic about the environment, using environment information can help to distinguish between lensing and the IA signal.


1812.06922
Influence of the local Universe on weak gravitational lensing surveys
Reischke, et al

Observations of the LSS implicitly assume an ideal FLRW observer with the ambient structure having no influence on the observer.  However, due to correlations in the LSS, cosmological observables are dependent on the position of an observer.  Investigate this influence in full generality for a weakly non-Gaussian random field, for which expressions are derived for angular spectra of large-scale structure observables conditional on a property of the LSS that is typical for the observer's location.  As an application, apply to the formalism to angular spectra of the WL effect and provide numerical estimates for the resulting change on the spectra using linear structure formation.  For angular WL spectra, find the effect to be of order of a few percent, for instance estimate for an overdensity of delta=0.5 and multipoles up to ell=100 the change in the WL spectra to be approximately 4%.  Show that without accounting for correlation between the density at observer's location and the WL spectra, the values of the parameters Omega_m and sigma_8 are underestimated by a few %.  Thus, this effect will be important when analyzing data from future surveys such as Euclid, which aim at the %-level precision.  The effect is difficult to capture in simulations, as estimates of the number of numerical simulations necessary to quantify the effect are high.

Day 1514

Friday.  Monday.

1812.05105
Searching for oscillations in the primordial power spectrum with CMB and LSS Data
Zeng, et al

Different inflationary models predict oscillatory features in the primordial power spectrum.  These can leave imprint on both the CMB and LSS of our Universe, that can be searched for the current data.  Inspired by the axion-monodromy model of inflation, search for primordial oscillations that are logarithmic in wavenumber, using both CMB data from the Planck satellite and LSS data from the WiggleZ galaxy survey.  Find that, within the search range for the new oscillation parameters (amplitude, frequency and phase), both CMB-only and CMB+LSS data yield the same best-fit oscillation frequency of log_10 omega = 1.5, improving the fit over LCDM by Delta chi^2 = -9 and Delta chi^2 = -13 (roughly corresponding to 2 sigma and 2.8 sigma significance), respectively.  Bayesian evidence for the log-oscillation model versus LCDM indicates a very slight preference for the latter.  Future CMB and LSS data will further probe this scenario.


1812.05113
Explicit Bayesian treatment of unknown foreground contaminations in galaxy surveysPorqueres, et al

The treatment of unknown foreground contaminations will be one of the major challenges for galaxy clustering analyses of coming decadal surveys.  These data contaminations introduce erroneous large-scale effects in recovered power spectra and inferred DM density fields.  In this work, present an effective solution to this problem in terms of a robust likelihood designed to account for effects due to unknown foreground and target contaminations.  Conceptually, this robust likelihood marginalizes over the unknown large-scale contamination amplitudes.  Showcase the effectiveness of this novel likelihood via an application to a mock SDSS-III data set subject to dust extinction contamination.  In order to illustrate the performance of the proposed likelihood, infer the underlying DM density field and reconstruct the matter power spectrum while being maximally agnostic about the foregrounds.  These results are contrasted to an analysis with a standard Poisson likelihood, as typically used in modern large-scale structure analyses.  While the standard Poissonian analyses yields excessive power for large-scale modes and introduces an overall bias in the power spectrum, their likelihood provides unbiased estimates of the matter power spectrum over the entire range of Fourier modes considered in this work.  Further demonstrate that the approach accurately accounts for and corrects effects of unknown foreground contaminations when inferring three-dimensional density fields.  Robust likelihood approaches, as presented in this work, will be crucial to control unknown systematics and maximize the outcome of the decadal surveys.


1812.05116
Dark energy survey year 1 results: validation of weak lensing cluster member contamination estimates from P(z) decomposition
Varga, et al

WL source galaxy catalogs used in estimating the masses of galaxy clusters can be heavily contaminated by cluster members, prohibiting accurate mass calibration.  In this study, test the performance of an estimator for the extent of cluster member contamination based on decomposing the photometric redshift P(z) of source galaxies into contaminating and background components.  Perform a full survey mock analysis on a simulated sky survey approximately mirroring the true number profile of contaminating cluster member galaxies in the simulation and the estimated one.  Further apply the method to estimate the cluster member contamination for the DES Y1 redMaPPer cluster mass calibration analysis, and compare the results to an alternative approach based on the angular correlation of WL source galaxies.  Find indications that correlation based estimates are biased by the selection of the WL sources in the cluster vicinity, which does not strongly impact the P(z) decomposition method.  Collectively, these benchmarks demonstrate the strength of the P(z) decomposition method in alleviating membership contamination and enabling highly accurate cluster WL studies without broad exclusion of source galaxies, thereby improving the total constraining power of cluster mass calibration via weak lensing.


1812.05594
On the road to per-cent accuracy: nonlinear reaction of the matter power spectrum to dark energy and modified gravity
Cataneo, et al

Present a general method to compute the nonlinear matter power spectrum for DE and modified gravity scenarios with % level accuracy.  By adopting the halo model and nonlinear perturbation theory, predict the reaction of a LCDM matter power spectrum to the physics of an extended cosmo parameter space.  By comparing the predictions to N-body sims, demonstrate that with no-free parameters, can recover the nonlinear matter power spectrum for a wide range of different w0-wa DE models to better than 1% accuracy out to k~1 h Mpc^{-1}.  Obtain a similar performance for both DGP and f(R) gravity, with the nonlinear matter power spectrum predicted to better than 3% accuracy over the same range of scales.  When including direct measurements of the halo mass function from the simulations, this accuracy improves to 1%.  With a single suite of standard LCDM N-body sims, the methodology provides a direct route to constrain a wide range of non-standard extensions to the concordance cosmology in the high S/N NL regime.


1812.05608
An older, more quiescent universe from Panchromatic SED fitting of the 3D-HST survey
Leja, et al

Galaxy observations are influenced by many physical parameters: stellar masses, star formation fates (SFRs), SFHs, metallicities, dust ,BH activity, and more.  As a result, inferring accurate physical parameters requires high-dimensional models which capture or marginalize over this complexity.  Here, re-assess inferences of galaxy stellar masses and SFRs using the 14-paramter physical model Prospector-Alpha build in the Prospector Bayesian inference framework.  Fit the photometry of 58,461 galaxies from the 3D-HST catalogs at 0.5<z<2.5.  The resulting stellar masses are ~0.1-0.3 dex larger than the fiducial masses while remaining consistent with dynamical constraints.  This change is primarily due to the systematically older SFHs inferred with Prospector.  The SFRs are ~0.1-1+ dex lower than UV+IR SFRs, with the largest offsets caused by emission from "old" (t>100 Myr) stars.  These new inferences lower the observed cosmic star formation rate density by ~0.2 dex and increase the observed stellar mass growth by ~0.1 dex, finally bringing these two quantities into agreement and implying an older, more quiescent Universe than found by previous studies at these redshifts.  Corroborate these results by showing that the Prospector-Alpha SFHs are both more physically realistic and are much better predictors of the evolution of the stellar mass function.  Finally, highlight examples of observational data which can break degeneracies in the current model; these observations can be incorporated into prior's in future models to produce new & more accurate physical parameters.


1812.05613
A conclusive test for star formation prescriptions in cosmological hydrodynamical simulations
Buck, Dutton, Maccio

State-of-the-art cosmo hydro sims of galaxy formation have reached the point at which their outcomes result in galaxies with ever more realism.  Still, the employed sub-grid models include several free parameters such as the density threshold, n, to localize the SF gals.  In this work, investigate the possibilities to utilize the observed clustered nature of SF in order to refine SF prescriptions and constrain the density threshold parameter.  To this end, measure the clustering strength, correlation length and power-law index of the 2pt correlation function of young (tau<50 Myr) stellar particles and compare the results to observations from the HST Legacy Extragalactic UV survey (LEGUS).  Simulations reveal a clear trend of larger clustering signal and power-law index and lower correlation length as the SF threshold increases with only mild dependence on galaxy properties such as stellar mass or specific SFR.  In conclusion, find that the observed clustering of SF is inconsistent with a low threshold for SF (n<1 cm^{-3}) and strongly favors a high density threshold for SF (n>10 cm^{-3}) which in cosmological hydrodynamical sims (evolved to z=0) is currently only employed by the NIHAO and FIRE simulations.


1812.05733
Constraining scatter in the stellar mss-halo mass relation for haloes less massive than the Milky Way
Allen, Behroozi, Ma

Most galaxies are hosted by massive, invisible DM haloes, yet little is known about the scatter in the stellar mass--hallo mass relation for galaxies with host halo masses M_h <= 1e11 Msun.  Using mock catalogues based on DM simulations, find that two observable signatures are sensitive to scatter in the stellar mass--halo mass relation even at these mass scales; i.e., conditional stellar mass functions and velocity distribution functions for neighboring galaxies.  Compute these observables for 179,373 galaxies in SDSS with stellar masses M*>1e9 Msun and 0.01<z<0.307.  Then compare to mock observations generated from the Bolshoi-Planck DM sims for stellar mass-halo mass scatters ranging from 0 to 0.6 dex.  The observed results are consistent with simulated results for low values of scatter (~0.2 dex), but SDSS statistics are insufficient to provide firm constraints.  This method could provide much tighter constraints on stellar mass--halo mass scatter in the future if applied to larger data sets, especially the anticipated DE spectroscopic instrument bright galaxy survey, and constraining the scatter could have important implications for galaxy formation and evolution.


1812.05777
Numerical convergence of simulations of galaxy formation: the abundance and internal structure of cold dark matter haloes
Ludlow, Schaye, Bower

Study the impact of numerical parameters on the properties of CDM haloes formed in collisionless cosmological simulations.  Quantify convergence in the median spherically-averaged circular velocity profiles for haloes of widely varying particle number, as well as in the statistics of their structural scaling relations and mass functions.  In agreement with prior work focused on single haloes, the results suggest that cosmological simulations yield robust halo properties for a wide range of softening parameters, epsilon, provided: 1) epsilon is not larger than a "convergence radius", r_conv, which is dictated by 2-body relaxation and determined by particle number, and 2) sufficient number of time steps are taken to accurately resolve particle orbits with short dynamical times.  Provided these conditions are met, median circular velocity profiles converge to within approx 10% for radii beyond which the local 2-body relaxation timescale exceeds the Hubble time by a factor kappa == t_relax/t_H>0.177, with better convergence attained for higher kappa.  Provide analytic estimates of r_conv that build on previous attempts in two ways: first, by highlighting its explicit (but weak) softening-dependence and, second, by providing a simple criterion in which r_conv is determined entirely by the mean inter particle spacing, ell; for example, <10% convergence in circular velocity for r>0.05 ell.  Show how these analytic criteria can be used to assess convergence in structural scaling relations for dark matter haloes as a function of their mass or maximum circular speed, V_max.  The convergence radius is smaller than the virial radius, r_200, of all haloes resolved with >=32 particles, a result that is verified explicitly using the suite of sims.


1812.05781
Denoising weak lensing mass maps with deep learning
Shirasaki, et al

WL is a powerful probe of the large-scale cosmic matter distribution.  Wide-field galaxy surveys allow us to generate the so-called WL maps, but actual observations suffer from noise due to imperfect measurement of galaxy shape distortions and to the limited number density of the source galaxies.  In this paper, explore a deep-learning approach to reduce the noise.  Develop an image-to-image translation method with conditional adversarial networks (CANs), which learn efficient mapping from ain input noise WL map to the underlying noise field.  Train the CANs using 30000 image pairs obtained from 1000 ray-tracing sims of WL.  Show that the trained CANs reproduce the true 1pt probability distribution function of the noiseless lensing map with a bias less than 1 sigma on average, where sigma is the statistical error.  Since a number of model parameters are used in the CANs, the method has additional error budgets when reconstructing the summary statistics of WL maps.  The typical amplitude of such reconstruction error is found to be of 1-2 sigma level.  Interestingly, pixel-by-pixel denoising for under-dense regions is less biased than denoising over-dense regions.  The deep-learning approach is complementary to existing analysis methods which focus on clustering properties and peak statistics of WL maps.


1812.05995
Core cosmology library: precision cosmological predictions for LSST
Chisari, et al

The Core Cosmology Library (CCL) provides routines to compute basic cosmological observables to a high degree of accuracy, which have been verified with an extensive suite of validation tests.  Predictions are provided for many cosmological quantities, including distances, angular power spectra, correlation functions, halo bias and the halo mass function through state-of-the-art modeling prescriptions available in the literature.  Fiducial specifications for the expected galaxy distributions for LSST are also included, together with the capability of computing redshift distributions for a user-defined photometric redshift model.  A rigorous validation procedure, based on comparisons between CCL and independent software packages, allows establishment of a well-defined numerical accuracy for each predicted quantity.  As a result, predictions for correlation functions of galaxy clustering, gg lensing and cosmic shear are demonstrated to be within a fraction of the expected statistical uncertainty of the observables for the models and in the range of scales of interest to LSST.  CCL is an open source software package written in C, with a python interface and publicly available at GitHub.com/LSSTDESC/CCL.


1812.06076
KiDS+VIKING-450: Cosmic shear tomography with optical+infrared data
Hildebrandt, et al

Present a tomographic cosmic shear analysis of KiDS combined with the VISTA Kilo-Degree Infrared Galaxy Survey (VIKING).  This is the first time that a full optical to near-infrared data set has been used for a wide-field cosmo WL experiment.  This unprecedented data, spanning 450-deg^2, allows significant improvement of the estimation of photo-z, such that robustly higher-z sources can be included for the lensing measurement, and most importantly, solidify the knowledge of the z distributions of the sources.  Based on a flat LCDM model, find S8==sigma8 sqrt(Omega_m/0.3)=0.737-0.036+0.040 in a blind analysis from cosmic shear alone.  The tension between KiDS cosmic shear and the Planck Legacy CMB measurements remains in this systematically more robust analysis, with S8 differing by 2.3 sigma.  This result is insensitive to changes in the priors on nuisance parameters for IA, baryon feedback, and neutrino mass.  KiDS shear measurements are calibrated with a new, more realistic set of image simulations and no significant B-modes are detected in the survey, indicating that systematic errors are under control  When calibrating the redshift distributions by assuming the 30-band COSMOS-2015 photo-z are correct (following DES and HSC), find the tension with Planck is alleviated.  The COSMOS-2015-calibrated KiDS z distributions are however discrepant with the results from the extensive spectroscopic calibration sample and the distributions recovered using angular clustering measurements, which is deemed more reliable.  The robust determination of source z distributions remains one of the most challenging aspects for future cosmic shear surveys.


1812.06077
KiDS_VIKING-450: A new combined optical & near-IR dataset for cosmology and astrophysics
Wright, et al

Present the curation and verification of a new combined optical and NIR dataset for cosmo and astrophysics, derived from the combination of ugri-band imaging from KiDS and ZYJHKs-band imaging from VIKING.  This dataset is unrivaled in cosmological imaging surveys due to tis combination of area 458 deg^2 before masking), depth (r<=25), and wavelength coverage (ugriZYJHKs).  The combination of survey depth, area and (most importantly) wavelength coverage allows significant reductions in systematic uncertainties (i.e. reductions of between 10 and 60% in bias, outlier rate, and scatter) in photometric-to-spectroscopic z comparisons, compared to the optical-only case at photo-z above 0.7.  The complementarily between the optical and NIR surveys means that over 80% of the sources, across all photo-z, have significant detection (i.e. not upper limits) in the 8 reddest bands.  Derive photometry, photo-z, and stellar masses for all sources in the survey, and verify these data products against existing spectroscopic galaxy sample.  Demonstrate the fidelity of the higher-level data products by constructing the survey stellar mass functions in 8 volume-complete z bins.  Find that these photometrically derived mass functions provide excellent agreement with previous mass evolution studies derived using spectroscopic surveys.  The primary data products presented in this paper are publicly available at kids.strw.leidenuniv.nl.

Day 1513

Thursday.

1812.04897
LSST Cadence optimization white paper in support of observations of unresolved tidal stellar streams in galaxies beyond the Local Group
Laine, et al

Deep observations of faint surface brightness stellar tidal streams in external galaxies with LSST are addressed in this Whilte Paper contribution.  Propose using the Wide-Fast-Deep survey that contains several nearby galaxies (at distances where the stars themselves are not resolved, i.e., beyond 20 Mpc).  In the context of hierarchical galaxy formation, it is necessary to understand the prevalence and properties of tidal substructure around external galaxies based on integrated (i.e., unresolved) diffuse light.  This requires collecting observations on much larger samples of galaxies thant the MW and M31.  Compare the observed structures to the predictions of cosmological models of galactic halo formation that inform us about the number and properties of streams around MW-like galaxies.  The insight gained from these comparisons will allow us to infer the properties of stream progenitors (masses, dynamics, metallicities, stellar populations).  The changes in the host galaxies caused by the interactions with the dissolving companion galaxies will be another focus of these studies.    Conclude by discussing synergies with WFIRST and Euclid, and also provide concrete suggestions for how the effects of scattered light could be minimized in LSST images to optimize the search for low surface brightness features, such as faint unresolved stellar tidal streams.

Day 1512

Wednesday.

1812.04014
Sparse Bayesian mass-mapping with uncertainties: hypothesis testing of structure
Price, et al

A crucial aspect of mass-mapping, via WL, is quantification of the uncertainty introduced during the reconstruction process.  Properly accounting for these errors has been largely ignored to date.  Present results from a new method that reconstructs maximum a posteriori (MAP) convergence maps by formulating an unconstrained Bayesian inference problem with Laplace-type ell_1-norm sparsity-promoting priors, which is solved via convex optimization.  Approaching mass-mapping in this manner allows exploitation of recent developments in probability concentration theory to infer theoretically conservative uncertainties for the MAP reconstructions, without relying on assumptions of Gaussianity. For the first time, these methods allow performing hypothesis testing of structure, from which it is possible to distinguish between physical objects and artifacts of the reconstruction.  Present this new formalism, demonstrate the method on illustrative examples, before applying the developed formalism to two observational datasets o f the Abel-520 cluster.  In the Bayesian framework it is found that neither Abel-520 dataset can conclusively determine the physicality of individual local massive substructure at significant confidence.  However, in both cases the recovered MAP estimators are consistent with both sets of data.


1812.04017
Sparse Bayesian mass-mapping with uncertainties: local credible intervals

Price et al.

Until recently mass-mapping techniques for WL convergence reconstruction have lacked a principled statistical framework upon which to quantify reconstruction uncertainties, without making strong assumptions of Gaussianity.  In previous work, presented a sparse hierarchical Bayesian formalism for convergence reconstruction that addresses this shortcoming.  Here, draw on the concept of local credible intervals (cf. Bayesian error bars) as an extension of the uncertainty quantification techniques previously detailed.  These uncertainty quantification techniques are benchmarked against those recovered via Px-MALA - a state of the art proximal MCMC algorithm.  Find that typically the recovered uncertainties are everywhere conservative, of similar magnitude and highly correlated (Pearson correlation coefficient >=0.85) with those recovered via Px-MALA.  Moreover, demonstrate an increase in computational efficiency of O(1e6) when using the sparse Bayesian approach over MCMC techniques.  This computational saving is critical for the application of Bayesian uncertainty quantification to large-scale stage IV surveys such as LSST and Euclid.


1812.04018
Sparse Bayesian mass-mapping with uncertainties: peak statistics and feature locations
Price, et al

WL convergence maps - upon which higher order statistics can be calculated - can be recovered from observations of the shear field by solving the lensing inverse problem.  For typical surveys this inverse problem is ill-posed (often seriously) leading to substantial uncertainty on the recovered convergence maps.  In this paper, propose novel methods for quantifying the Bayesian uncertainty in the location of recovered features and the uncertainty in the cumulative peak statistic - the peak count as a function of SNR.  Adopt the sparse hierarchical Bayesian mass-mapping framework developed in previous work, which provides robust reconstructions and principled statistical interpretation of reconstructed convergence maps without the need to assume or impose Gaussianity.  Demonstrate the uncertainty quantification techniques on both Bolshoi N-body (cluster scale) and Buzzard V-1.5 (large scale structure) N-body simulations.  For the first time, this methodology allows one to recover approximate Bayesian upper and lower limits on the cumulative peak statistic at well defined confidence levels.

Day 1511

Tuesday.

1812.02749
Be it therefore resolved: Cosmological simulations of dwarf galaxies with extreme resolution
Wheeler, Hopkins, et al

Study a suite of extremely high-resolution cosmological FIRE simulations of dwarf galaxies (M_halo <~1e10 Msun), run to z=0 with 30 Msun resolution, sufficient (for the first time) to resolve the internal structure of individual supernovae remnants within the cooling radius.  Every halo with M_halo >~1e8.6 Msun is populated by a resolved stellar galaxy, suggesting very low-mass dwarfs may be ubiquitous in the field.  The ultra-faint dwarfs (UFDs; M*<1e5 Msun) have their star formation truncated early (z>~2), likely by deionization, while classical dwarfs (M*>1d5 Msun) continue forming stars to z<0.5.  The systems have bursty SF histories, forming most of their stars in periods of elevated SF strongly clustered in both space and time.  This allows the dwarf with M*/Mhalo>1e-4 to form a dark matter core >200 pc, while lower-mass UFDs exhibit cusps down to <~100pc, as expected from energetic arguments.  The dwarfs with M*>1e4 Msun have half-mass radii (R_1/2) in agreement with Local Group (LG) dwarfs; dynamical mass vs R_1/2 and the degree of rotational support also resemble observations.  The lowest-mass UFDs are below surface brightness limits of current surveys but are potentially visible in next-generation surveys (LSST).  The stellar metallicities are lower than in LG dwarfs; this may reflect pre-enrichment of the LG by the massive hosts or Pop-III stars.  Consistency with lower resolution studies implies that the simulations are numerically robust (for a given physical model).


1812.03167
Transverse velocities with the moving lens effect
Hotinli, et al

Gravitational potentials with change in time induce fluctuations in the observed CMB temperature.  Cosmological structure moving transverse to the line of sight provides a specific example known as the moving lens effect.  Here, explore how the observed CMB temperature fluctuations combined with the observed matter over-density can be used to infer the transverse velocity of cosmological structure on large scales.  Show that near-future CMB surveys and galaxy surveys will have the statistical power to make a first detection of the moving lens effect.  Discuss applications for the reconstructed transverse velocity.


1812.03248
An overview of the LSST image processing pipelines
Bosch, et al

LSST is an ambitious astronomical survey with a similarly ambitious Data Management component.  Data Management for LSST includes processing on both nightly and yearly cadences to generate transient alerts, deep catalogs of the static sky, and forced photometry light-curves for billions of objects at hundreds of epoch, spanning at least a decade.  The algorithms running in these pipelines are individually sophisticated and interact in subtle ways.  This paper provides an overview of these pipelines, focusing more on those interactions than the details of any individual algorithm.


1812.03983
Towards emulating cosmic shear data: revisiting the calibration f the shear measurements for the Kilo-Degree Survey
Kannawadi, Hoekstra, et al

Exploiting the full statistical power of future cosmic shear surveys will necessitate improvements to the accuracy with which the gravitational lensing signal is measured.  Present a framework for calibrating shear and image simulations that demonstrates the importance of including realistic correlations between galaxy morphology, size and more importantly, photometric redshifts.  This realism is essential so that selection and shape measurement biases can be calibrated accurately for a tomographic cosmic shear analysis.  Emulate KiDS observations of the COSMIS field using morphological information from HST imaging, faithfully reproducing the measured galaxy properties from KiDS observations of the same field.  Calibrate the shear measurements from lensfit, and find through a range of sensitivity test that lensfit is robust and unbiased within the allowed 2% tolerance of the study.  Results show that the calibration has to be performed by selecting the tomographic samples in the simulations, consistent with the actual cosmic shear analysis, because the joint distributions of galaxy properties are found to vary with redshift.  Ignoring this redshift variations could result in misestimating the shear bias by an amout that exceeds the allowed tolerance.  To improve the calibration for future cosmic shear analyses, it will be essential to also correctly account for the measurement of photometric redshifts, which requires simulating multi-band observations.

Day 1510

Monday.

1812.02950
Origin of the first cosmic rays
Ohira, Murase

Non-thermal phenomena are ubiquitous in the Universe, and CRs play various roles in different environments.  When, where and how CRs are first generated shine the Big Bang? Argue that blast waves from the first cosmic explosions at z~20 lead to Weibel mediated non relativistic shocks and CRs can be generated by the diffusive shock acceleration mechanism.  Show that protons are accelerated at least up to sub-GeV energies, and the fast velocity component of SN ejecta is likely to allow CRs to achieve a few GeV in energy.  Discuss other possible accelerators of the first CRs, including accretion shocks due to the cosmological structure formation.  These CRs can play various roles such as the magnetic field amplification in the early universe.

Day 1509

Wednesday.

1812.01031
A $\gamma$-ray determination of the Universe's star-formation history
The Fermi-LAT Collaboration, et al

The light emitted by all galaxies over the history of the Universe produces the extragalactic background light (EBL) at UV, optical, and IR wavelengths.  The EBL is a source of opacity for gamma rays via photon-photon interactions, leaving an imprint in the spectra of distant gamma-ray sources.  Measure this attenuation using 739 active galaxies and one gamma-ray burst detected by Fermi LAT.  This allows reconstruction of the evolution of the EBL and determine the SFH of the Universe over 90% of cosmic time.  The SFH is consistent with independent measurements from galaxy surveys, peaking at z~2.  Upper limits of the EBL at the epoch of re-ionization suggest a turnover in the abundance of faint galaxies at z~6.


1812.07962
A unifying theory of dark energy and dark matter: negative masses and matter creation within a modified $\Lambda$ CDM framework
Farnes

DE and DM constitute 95% of the observable Universe.  Yet the physical nature of these 2 phenomena remains a mystery.  Einstein suggested a long-forgotten solution: gravitationally repulsive negative masses, which drive cosmic expansion and cannot coalesce into light-emitting structures.  However, contemporary cosmological results are derived upon the reasonable assumption that the Universe only contains positive masses.  By reconsidering this assumption, construct a toy model which suggests that both dark phenomena can be unified into a single negative mass fluid.  The model is a modified LCDM cosmology, and indicates that continuously created negative masses can resemble the cosmological constant and can flatten the rotation curves of galaxies.  The model leads to a cyclic universe with a time-variable Hubble parameter, potentially providing compatibility with the current tension that is emerging in cosmological measurements.  In the first 3-d N-body sims of negative mass matter in the scientific literature, this exotic material naturally forms haloes around galaxies that extend to several galactic radii.  These haloes are not cusp.  The proposed cosmological model is therefore able to predict the observed distribution of DM in galaxies from first principles.  The model makes several testable predictions and seems to have the potential to be consistent with observational evidence from distant SNe, the CMB, and galaxy clusters.  These findings may imply that negative masses are a real and physical aspect of our Universe, or alternatively may imply the existence of a superseding theory that in some limit can be modeled by effective negative masses.  Both cases lead to the surprising conclusion that the compelling puzzle of the dark Universe may have been due to a simple sign error.


1812. 1812.01679
Cluster cosmology constraints from the 2500 deg$^2$ SPT-SZ Survey: inclusion of weak gravitational lensing data from Magellan and the Hubble Space Telescope
Bocquet, Dietrich, Schrabback, et al

Derive cosmo constraints using a galaxy cluster sample selected from the 2500 deg2 SPT-SZ survey.  The sample spans 0.25<z<1.75 and consists of 377 cluster candidates with SZ detection significance xi>5.  The sample is supplemented with optical weak gravitational lensing measurements of 32 clusters in the range 0.29<z<1.13 (using Magelland and HST) and X_ray measurements of 89 cluster in the range 0.25<z<1.75 (Chandra).  Rely on minimal modeling assumptions: i) WL provides and accurate means of measuring halo masses ii) the mean SZ and X-ray observables are related to the true halo mass through power-law relations in mass and dimensionless Hubble parameter E(z) with a-priori unknown parameters, iii) there is (correlated, lognormal) intrinsic scatter and scatter due to measurement uncertainties relating these observables to their mean relations.  Assuming a flat nuLCDM model, in which the sum of neutrino masses is a free parameter, measure Omega_m=0.276±0.047, sigma8=0.781±0.037, and the parameter combination sigma8(Omega_m/0.3)^0.2=0.766±0.025.  The redshift evolution of the X-ray Y_X--mass and Y_X-- mass relation shows a 2.3 sigma deviation from self-similarity.  The mass-slope of the M_gas--mass relation is steeper than self-similarity at the 2.5 sigma level.  In a nu wCDM cosmology, measure the DE equation of state parameter w=-1.55±0.41 from the cluster data.  Perform a measurement of the growth of structure since z~1.7 and find no evidence for tension with the prediction from GR.


1812.02125
The behavior of galactic cosmic ray intensity during solar activity cycle 24
Ross, Chaplin

Studied long-term variations of galactic cosmic ray (GCR) intensity in relation to the sunspot number (SSN) during the most recent solar cycles.  This study analyses the time-lag between the GCR intensity and SSN, and hysteresis plots of the GCR count range against SSN for solar activity cycles 20-23 to validate a methodology against previous results in the literature, before applying the method to provide a timely update on the behavior of cycle 24.  Cross-plots of SSN vs GCR show a clear difference between the odd-numbered and even-numbered cycles.  Linear and elliptical models have been fit to the data with the linear fit and elliptical model proving the more suitable model for even-numbered and odd-numbered solar activity cycles respectively, in agreement with previous literature.  Through the application of these methods for the 24th solar activity cycle, it has been show that cycle 24 experienced a lag of 2-4 months and follows the trend of the preceding activity cycles albeit with a slightly longer lag than previous even-numbered cycles.  It has been shown through the hysteresis analysis that the linear fit is a better representative model for cycle 24, as the ellipse model doesn't show a significant improvement, which is also in agreement with previous even-numbered cycles.


1812.02148
Dipole distortions in the intergalactic medium
Inman, Pen, Villaescusa-Navarro

Baryonic feedback can significantly modify the spatial distribution of matter on small scales and create a bulk relative velocity between the dominant CDM and the hot gas.  Study the consequences of such bulk motions using two high resolution hydro sims, one with no feedback and one with very strong feedback.  Find that relative velocities of order 100 km/s are produced in the strong feedback sims whereas it is much smaller when there is no feedback.  Such relative motions induce dipole distortions to the gas, which is quantified by computing the dipole correlation function.  Find halo coordinates and velocities are systematically changed in the direction of the relative velocity.  Finally, discuss potential to observe the relative velocity via large scale structure, SZ and line emission measurements.  Given the nonlinear nature of this effect, it should next be studied in simulations with different feedback implementations/strengths to determine the available model space.


1812.02285
How may hydrated NEOs are there?
Rivkin, DeMeo

Hydrated minerals are tracers of early solar system history, and have been proposed as a possible focus for economic activity in space.  NEOs are important to both of these, especially the most accessible members of that community.  Because there are very few identified hydrated NEOs, use the Ch spectral class of asteroids as a proxy for hydrated asteroids, and use published work about NEO delivery, main-belt taxonomic distributions, NEO taxonomic distributions, and observed orbital distributions to estimate the number of hydrated asteroids with different threshold sizes and at different levels of accessibility.  Expect 53±27 Ch asteroids to be present in the known population of NEOs >1 km diameter, and using two different approaches to estimate accessibility, expect 17±9 of them to be more accessible on a round trip than the surface of the Moon.  If there is no need to define minimum size, expect 700±350 hydrated objects that meet that accessibility criterion.  While there are few unknown NEOs larger than 1 km, the population of smaller NEOs yet to be discovered could also be expected to contain proportionally-many hydrated objects.  Finally, estimate that hydrated NEOs are unlikely to bring enough water to account for the ice found at the lunar poles, though it is possible that asteroid-delivered hydrated minerals could be found near their impact sites across the lunar surface.


1812.02333
Null test for interactions in the dark sector
von Martins, et al

Since there is no known symmetry in Nature that prevents a non-animal coupling between the DE and CDM components, such a possibility constitutes an alternative to standard cosmology, with its theoretical and observational consequences being of great interest.  In this paper, propose a new null test on the standard evolution of the dark sector based on the time dependence of the ratio between the CDM and DE energy densities which, in the standard LCDM scenario, scales necessarily as a^{-3}.  Use the latest measurements of SN Ia, cosmic chronometers and angular BAOs to reconstruct the expansion history using model-independent Machine Learning techniques, namely, the Linear Model formalism and Gaussian Processes.  Find that while the standard evolution is consistent with the data at 3 sigma level, some deviations from the LCDM model are found at low redshifts, which may be associated with the current tension between local and global determinations of H0.

Day 1508

Tuesday.

1811.12940

Binary black hole population properties inferred from the first and second observing runs of Advanced LIGO and Advanced Virgo

The LIGO Scientific Collaboration, The Virgo Collaboration

Present results on the mass, spin, and redshift distributions of the ten binary black hole mergers detected in Advanced LIGO's and Advanced Virgo's first and second observing runs.  Constrain properties of the binary black hole (BBH) mass spectrum using models with a range of parameterizations of the BBH mass and spin distributions.  Find that the mass distribution of the more massive black hole in each binary is well approximated by models with almost no BHs larger than 45 Msun, and a power law index of alpha=....  Also show that BBHs are unlikely to be composed of BHs with large spins aligned to the orbital angular momentum.  Modeling the evolution of the BBH merger rate with redshift, show that it is increasing with redshift with credibility ....  Marginalizing over uncertainties in the BBH population, find robust estimates of the BBH merger rate density of R=...  As the BBH catalog grows in future observing runs, expect that uncertainties in the population model parameters will shrink, potentially providing insights into the formation of black holes via supernovae, binary interactions of massive stars, stellar cluster dynamics, and the formation history of BHs across cosmic time.

1812.00346

Influence of gravity waves on the climatology of high-altitude Martian carbon dioxide ice clouds

Yigit, et al

CO2 ice clouds have been routinely observed in the middle atmosphere of Mars.  However, there are still uncertainties concerning physical mechanisms that control their altitude, geographical, and seasonal distributions.  Using the Max Planck Institute Martian General Circulaion Model (MPI-MGCM), incorporating a state-of-the-art whole atmosphere subgrid-scale gravity wave parameterization, demonstrate that internal gravity waves generated by lower atmospheric weather processes have wide reaching impact on the Martian climate.  Globally, gas cool the upper atmosphere of Mars by ~10% and facilitate high-altitude CO2 ice cloud formation.  CO2 ice cloud seasonal variations in the mesosphere and the mesopause region appreciably coincide with the spatio-temporal variations of GW effects, providing insight into the observed distribution of clouds.  The results suggest that GW propagation and dissipation constitute a necessary physical mechanism for CO2 ice cloud formation in the Martian upper atmosphere during all seasons.

1812.00514

LSST observing strategy white paper: LSST Observations of WFIRST Deep Fields

Foley, Koekeloer, Spergel, et al

WFIRST is expected to launch i the mid-2020s.  With its wide-field near-IR camera, it will survey the sky to unprecedented detail.  As part of normal operations and as the result of multiple expected dedicated surveys, WFIRST will produce several relatively wide-field (tens of square degrees) deep (limiting magnitude of 28 or fainter) fields.  In particular, a planned SN survey is expected to image 3 deep fields in the LSST footprint roughly every 5 days over 2 years.  Stacking all data, this river will produce, over all WFIRST SN fields in the LSST footprint, ~12-25 deg2 and ~5-15 deg^2 regions to depths of 28 mag and 29 mag, respectively.  Suggest LSST undertake mini-surveys that will match the WFIRST cadence and simultaneously observe the SN survey fields during the 2yr WFIRST SN survey, achieving a stacked depth similar to that of the WFIRST data.  Also suggest additional observations of these same regions throughout the LSST survey to get deep images earlier, have long-term monitoring in the fields, and produce deeper images overall.  These fields will provide a legacy for cosmology, extragalactic, and transient/variable science.


1812.00607
Simultaneous LSST nd Euclid observations - advantages for Solar System Objects
Snodrass, et al

The ESA Euclid mission is a space telescope that will survey ~15000 sq deg of the sky, primarily to study the distant universe (constraining cosmological parameters through the lensing of galaxies).  It is also expected to observe ~150,000 Solar System Objects (SSOs), primarily in poorly understood high inclination populations, as it will mostly avoid ±15 degrees from the ecliptic plane.  With a launch data of 2022 and a 6 year survey, Euclid and LSST will operate at the same time, and have complementary capabilities.  Propose a LSST mini-survey to coordinate quasi-simultaneous observations between these two powerful observatories, when possible, with the primary aim of greatly improving the orbits of SSOs discovered by these facilities.  As Euclid will operate from a halo orbit around the Sun-Earth L2 Lagrangian point, there will be significant parallax between observations from Earth and Euclid (0.01 AU).  This means that simultaneous observations will give an independent distance measurement to SSOs, giving additional constraints on orbits compared to single Euclid visits.


1812.00638
Neutrino properties and the cosmological tensions in the $\Lambda$LCDM model
Gariazzo

Review the current status of the constraints on the neutrino properties from cosmological measurements, with a particular focus on their mass and effective number.  Also discuss the existing tensions within the context of the LCDM model, including the discrepancies on the Hubble parameter and on the matter fluctuations at small scales, and how neutrinos could help to alleviate the aforementioned problems.


1812.00861
Accurately computing weak lensing convergence
Koksbang, Clarkson

WL will play an important role in future cosmo surveys, including Euclid and SKA.  Sufficiently accurate theoretical predictions are important for correctly interpreting these surveys and hence for extracting correct cosmological parameter estimations.  Quantify for the first time in a relativistic setting how many post-Born and lens-lens coupling correction are required for sub-percent accuracy of the theoretical WL convergence and distance-z relation for z<2 (the primary WL range for Euclid and SKA).  Do this by randomly ray-tracing through a fully relativistic exact solution of the Einstein Field Equations which consists of randomly picked mass-compensated under-densities of realistic amplitudes.  Find that one needs to include lens-lens coupling terms and post-Born corrections at least up to second and 3rd order respectively for sub-percent accuracy of the convergence and angular diameter distance d_A.  Find that, out of the random lines of sight studied, post-Born corrections can be as large as 70% of the total correction to the area distance.  Also provide a simplified operator formalism for calculating the leading corrections to these quantities to arbitrary order.