Day 1292

Thursday.  Friday.  Monday.  Tuesday.

1707.08153
Parameter constraints from weak lensing tomography of galaxy shapes and cosmic microwave background fluctuations
Merkel, Schaefer

It has recently been shown that cross-correlating CMB lensing and 3D cosmic shear allows to considerably tighten cosmological parameter constraints.  Investigate whether similar improvement can be achieved in a conventional tomographic setup.  Present Fisher parameter forecasts for a Euclid-like galaxy survey in combination with different ongoing and forthcoming CMB experiments.  In constrast to a fully three-dimensional analysis, find only marginal improvement.  Assuming Planck-like CMB data, show that including the full covariance of the combined CMB and cosmic shear data improves the DE figure of merit by only 3%.  The marginalized error on the sum of neutrinos asses is reduced at the same level.  For a next generation CMB satellite mission such as Prism, the predicted improvement of the DE FoM amounts to approximately 25%.  Furthermore, show that the small improvement is contrasted by a increased bias in the dark energy parameters when the intrinsic alignment of galaxies is not correctly accounted for in the full covariance matrix.


1707.08256
Cross-correlation redshift calibration without spectroscopic calibration samples in DES Science Verification Data
Davis, Rozo, et al

Galaxy cross-correlations with high-fidelity z samples hold the potential to precisely calibrate systematic photometric z uncertainties arising from the unavailability of complete and representative training and validation samples of galaxies.  However, application of this technique in the DES is hampered by the relatively low number density, small area, and modest z overlap between photometric and spectroscopic samples.  Propose instead using photometric catalogs with reliable photo-z for photo-z calibration via cross-correlations.  Verify the viability of the proposal using redMaPPer clusters from the SDSS to successfully recover the redshift distribution of SDSS spectroscopic galaxies.  Demonstrate how to combine photo-z with X-correlation data to calibrate photo-z biases while marginalizing over possible clustering bias evolution in either the calibration or unknown photometric samples.  Apply the method to DES SV data in order to constrain the photo-z distribution of a galaxy sample selected for WL studies, constraining the mean of the tomographic z distributions to a statistical uncertainty of Delta z ~ ±0.01.  Forecast that the proposal can in principle control photo-z uncertainties in DES WL experiments at a level near the intrinsic statistical noise of the experiment over the range of z where redMaPPer clusters are available.  The realists provide strong motivation to launch a program to fully characterize the systematic errors from bias evolution and photo-z shapes in the calibration procedure.


1707.09369
Cluster richness-mass calibration with cosmic microwave background lensing
Geach, Peacock

Identifying galaxy clusters through overdenisties of galaxies in photometric surveys is the oldest and arguably the most economic and mass-sensitive detect method, compared to X-ray and SZ effect surveys that detect the hot ICM.  However, a perennial problem has been the mapping of optical 'richness' measurements on to total cluster mass.  Emitted at a conformal distance of 14 Gpc, the CMB acts as a backlight to all intervening mass in the Universe, and therefore has been gravitationally lensed.  Here, present a calibration of cluster optical richness at the 10% level by measuring the average CMB lensing convergence measured by Planck towards the positions of large numbers of optically-selected cluster, detecting the deflection of photons by haloes of total mass of the order 1e14 Msun.  Although mainly aimed at the study of large-scale structures, the Planck lensing reconstruction can yield nearly unbiased results for stacked cluster on arc minute scales.  The lensing convergence only depends on the redshift integral of the fractional overdensity of matter, so this approach offers a clean measure of cluster mass over most of cosmic history, largely independent of baryon physics.

Day 1291

Monday.  Tuesday.  Wednesday. 

1707.06755

Reanalysis of the BICEP2, Keck and Planck Data: no evidence for gravitational radiation

Gott, Colley

A joint analysis of data collected by the Planck and BICEP2+Keck teams has previously given r=0.09±0.05 for BICEP2 and r=0.02±0.03 for Keck.  Analyzing BICEP2 using its published noise estimate, Colley+Gott(2015) found r=0.09±0.04, agreeing with the final joint results for BICEP2.  With the Keck data now available, they have done something the joint analysis did not: a correlation study of the BICEP2 vs. Keck B-mode maps.  Knowing the correlation coefficient between the two and their amplitudes allows us to determine the noise in each map (which is checked using the E-modes).  Find the noise power in the BICEP2 map to be twice the original BICEP2 published estimate, explaining the anomalously high r value obtained by BICEP2.  Now find r=0.004±0.04 for BICEP2 and r=-0.01±0.04 for Keck.  Since r>=0 by definition, this implies a maximum likelihood value of r=0, or no evidence for gravitational waves.  Starobinsky Inflation (r=0.0036) is not ruled out, however.  Krauss+Wilzcek (2014) have already argued that "measurement of polarization of the CMB due to a long-wavelength stochastic background of gravitational waves from Inflation in the early Universe would firmly establish the quantization of gravity," and, therefore, the existence of gravitons.  Argue it would also constitute a detection of gravitational Hawking radiation (explicitly from the causal horizons due to Inflation).

1707.07003

Witnessing galaxy assembly in an extended z~3 structure

Fumagalli, et al

Present new observations acquired with the Multi Unit Spectroscopic Explorer instrument on the VLT in a quasar field that hosts a high column-density damped Lya absorber (DLA) at z~3.25. Detect Lya emission from a nebula at the redshift of the DLA with line luminosity (27±1)e41 erg/s, which extends over 37±1 kpc above a surface brightness limit of 6e-19 erg/s/cm2/arcsec2 at a projected distance of 30.5±0.5 kpc from the quasar sightline.  Two clumps lie inside this nebula, both with Lya rest-frame equivalent width >50A and with relative line-of-sight velocities aligned with two main absorption components seen in the DLA spectrum.  In addition, identify a compact galaxy at a projected distance of 19.1±0.05 kpc from the quasar sightline.  The galaxy spectrum is noisy but consistent with that of a star-forming galaxy at the DLA redshift.  Argue that the Lya nebula is ionized by radiation from SF inside the two clumps, or by radiation from the compact galaxy.  In either case, these data imply the presence of a structure with size >>50 kpc inside which galaxies are assembling, a picture consistent with galaxy formation in groups and filaments as predicted by cosmological simulations such as the EAGLE simulations.

1707.07535

Probing superfoods with weak lensing

Higuchi, Inoue

CMB has non-Gaussian features in the temperature fluctuations.  An anomalous cold spot surrounded with a hot ring, called the Cold Spot, is one such feature.  If a large underdense region (super void) resides towards the Cold Spot, a systematic shape distortion in the images of BG source galaxies via WL should be detected.  In order to estimate the detectability of such signals, use N-body sims to simulate full-sky ray-tracing of source galaxies.  Search for a most prominent underdense region using the simulated convergence maps smoothed at a scale of 20 degree and obtained tangential shears around it.  The lensing signal expected in a concordant LCDM model can be detected at a signal-to-noiseratio S/N~3.  If a super void with a radius of ~200 Mpc/h and a density contrast delta0~-0.3 at the centre resides at a redshift z~0.2, on-going and near-future WL surveys would detect a lensing signal with S/N~5 without resorting to stacking.


1707.07693
What sets the central structure of dark matter haloes?
Ogiya, Hahn

DM haloes forming near the thermal cut-off scale of the density perturbations are unique, since they are the smallest objects and form through monolithic gravitational collapse, while larger haloes contrastingly have experienced mergers.  While standard CDM sims readily produce haloes that follow the universal NFW density profile with an inner slope, rho~r^-alpha with alpha=1, recent simulations have found that when the free-streaming cut-off is resolved, the resulting haloes follow nearly power-law density profiles of alpha~1.5.  In this paper, study the formation of density cusps in haloes using idealized N-body sims of the collapse of proto-haloes.  When the proto-halo profile is initially cored due to particle free-streaming at high z, universally find ~r^-1.5 profiles irrespective of the proto-halo profile slope outside the core and large-scale non-spherical perturbations.  Quite in contrast, when the proto-halo has a power-law profile, then obtain profiles compatible with the NFW shape when the density slope of the porto-halo patch is shallower than a critical value, alpha_ini~0.3, while the final slope can be steeper for alpha_ini>~0.3.  Further demonstrate that the r^-1.5 profiles are sensitive to small scale noise, which gradually drives them towards an inner slope of -1, where they become resilient to such perturbations.  Demonstrate that the r^-1.5 solutions are in hydrostatic equilibrium, largely consistent with a simple analytic model, and provide arguments that angular momentum appears to determine the inner slope.

Day 1290

Thursday.  Friday.  

1707.06233

Cosmic shear calibration with forward modeling

Bruderer, Nicola, Amara, Refregier, Herbel, Kacprzak

WL is a powerful probe of the dark sector of the Universe.  One of the main challenges for this technique is the treatment of systematics in the measurement of cosmic shear from galaxy shapes.  In an earlier work, Refregier+Amara (2014) have proposed the Monte Carlo control loops (MCCL) to overcome these effects using a forward modeling approach.  Focus here on one of the control loops in this method, the task of which is the calibration of the shear measurement.  For this purpose, first consider the requirements on the shear systematics for a given survey and propagate them to different systematic terms.  Use two 1-pt statistics to calibrate the shear measurement and six further 1-pt statistics as diagnostics.  Also propagate the systematics levels that is estimated form the 1pt functions to the 2pt functions for the different systematic error sources.  This allows assessment of the consistency between the systematics levels measured in different ways.  To test the method, construct synthetic sky surveys with an area of 1700 deg^2.  With some simplifying assumptions, able to meet the requirements on the shear calibration for this survey configurations.  Furthermore, account for the total residual shear systematics in terms of the contributing sources.  Discuss how this MCCL framework can be applied to current and future WL surveys.

1707.06312

ICE-COLA: fast simulations for weak lensing observables

Izard, Fosalba, Crocce

Approximate methods to full N-body sims provide a fast and accurate solution to the development of mock catalogues for the modeling of galaxy clustering observables.  In this paper, extend ICE-COLA (Izard+2016), based on an optimized implementation of the approximate COLA method, to produce WL maps and halo catalogues in the light cone using an integrated and self consistent approach.  Show that despite the approximate dynamics, the catalogues thus produced enable an accurate modeling of WL observables one decade beyond the characteristic scale where the growth becomes non-linear.  In particular, compare ICE-COLA to the MICE-GC N-body simulation for some fiducial cases representative of upcoming surveys and find that, for sources at z=1, their convergence power spectra agree to within one percent up to high multipoles (i.e., of order 1000).  The corresponding shear two point functions, xi+ and xi-, yield similar accuracy down to 2 and 20 arcmin respectively, while tangential shear around a z=0.5 lens sample is accurate down to 4 arcmin.  Show that such accuracy is stable against an increased angular resolution of the weak lensing maps.  Hence, this opens the possibility of using approximate methods for the joint modeling of galaxy clustering and weak lensing observables and their covariance in ongoing and future galaxy surveys.

1707.06529

Massive data compression for parameter-dependent covariance matrices

Heavens, et al

Show how the massive data compression algorithm MPED can be used to reduce, by orders of magnitude, the number of simulated datasets that are required to estimate the covariance matrix required for the analysis of gaussian-distributed data.  This is relevant when the covariance matrix cannot be calculated directly.  The compression is especially valuable when the covariance matrix varies with the model parameters.  In this case, it may be prohibitively expensive to run enough simulations to estimate the full covariance matrix throughout the parameter space.  This compression may be particularly valuable for the next-generation of weak lensing surveys, such as proposed for Euclid and LSST, for which the number of summary data (such as band power or shear correlation estimates) is very large, ~1e4, due to the large number of tomographic redshift bins that the data will be divided into.  In the pessimistic case where the covariance matrix is estimated separately for all points in an MCMC analysis, This may require an unfeasible 1e9 simulations.  Show here that MOPED can reduce this number by a factor of 1000, or a factor of ~1e6 if some regularity in the covariance matrix is assumed, reducing the number of simulations required to a manageable 1e3, making an otherwise intractable analysis feasible.

1707.06559

The mass dependence of dark matter halo alignments with large-scale structure

Piras, Joachimi, et al

Tidal gravitational forces can modify the shape of galaxies and clusters of galaxies, thus correlating their orientation with the surrounding matter density field.  Study the dependence of this phenomenon, known as IA, on the mass of the DM haloes that host these bright structures, analyzing the Millennium and MIllennium-XXL N-body sims.  Closely follow the observational approach, measuring the halo position-halo shape alignment and subsequently dividing out the dependence on halo bias.  Derive a theoretical scaling of the IA amplitude with mass in a DM universe, and predict a power-law with slope beta_M in the range 1/3 to 1/2, depending on mass scale.  Find that the sim data agree with each other and with the theoretical prediction remarkably well over three orders of magnitude in mass, with the joint analysis yielding an estimate of beta_M=0.36±0.01.  This result does not depend on z or on the details of the halo shape measurements.  The analysis is repeated on observational data, obtaining a significantly higher value, eta_M=0.56±0.05.  There are also small but significant deviations from the simple model in the sim signals at both the high- and low-mass end.  Discuss possible reasons for these discrepancies, and argue that they can be attributed to physical processes not captured in the model or in the DM-only simulations.

1707.06627

KiDS-450 + 2dFLenS: Cosmological parameter constraints from weak gravitational lensing tomography and overlapping redshift-space galaxy clustering

Joudaki, Blake, et al

Perform a combined analysis of cosmic shear tomography, gg lensing tomography, and redshift-space multiple power spectra (monopole and quadrupole) using 450 deg^2 of imaging data by KiDS overlapping with 2 spectroscopic surveys: 2dFLenS and BOSS.  Restrict the gg lensing and multipole power spectrum measurements to the overlapping regions with KiDS, and self-consistently compute the full covariance between the different observables using a large suite of N-body sims.  Methodically analyze different combinations of the observables, finding that gg lensing measurements are particularly useful in improving the constraint on the intrinsic alignment amplitude (by 30%, positive at 3.5 sigma in the fiducial data analysis), while the multipole power spectra are useful in tightening the constraints along the lensing degeneracy direction (e.g. factor of 2 stronger matter density constraint in the fiducial analysis).  The fully combined constraint on S8=sigma8 sqrt(Omega_m/0.3) = 0.742±0.035, which is an improvement by 20% compared to KiDS alone, corresponds to a 2.6 sigma discordance with Planck, and is not significantly affected by fitting to a more conservative set of scales. The tightening of the parameter space disables resolving the discordance with an extended cosmology that is simultaneously favored in a model selection sense, including the sum of neutrino masses, curvature, evolving DE, and modified gravity.  The complementarity of the observables allow for constraints on modified gravity degrees of freedom that are not simultaneously bounded with either probe alone, and up to a factor of 3 improvement in the S8 constraint in the extended cosmology compared to KiDS alone.

Day 1289

Wednesday.


1707.05327
The size evolution of star-firing and quenched galaxies in the IllustrisTNG simulation
Genel, et al

Analyze scaling relations and evolution histories of galaxy sizes in the TNG100, part of the Illustris TNG simulations suite.  Observational qualitative trends of size with stellar mass, SFR and z are reproduced, and a quantitative comparison of projected r-band sizes at 0~<z<~2 shows agreement to better than 0.25 dex.  Follow populations of z=0 galaxies with a range of masses backwards in time along their main progenitor branches, separately for MS and quenched galaxies.  The main findings are as follows.  (i) At M*,z=0>1e9.5 Msun, the main progenitors evolve in different ways, with quenched galaxies hardly growing in median size before quenching, whereas MS  galaxies grow their median size continuously, thus opening a gap from the progenitors of quenched galaxies.  This is partly because the MS high-z progenitors of quenched z=0 galaxies are drawn from the lower end of the size distribution of the overall populations of MS high-z galaxies.  (ii)  Quenched galaxies with M*,z=0>1e9.5 Msun experience a steep size growth on the size-mass plane after their quenching time, but the size growth rate as a function of time is similar to that of MS galaxies.  Hence, the size gap is not closed by z=0.  (iii) At all masses but M*,z=0>1e11 Msun, most of the size (and mass) growth of quenched galaxies occurs while they are still on the MS, and the size variation among quenched galaxies is driven by different degrees of growth on the MS rather than after quenching.

Day 1288

Monday.  Tuesday.


1707.04253
The resilience of life to astrophysical events
Sloan, Batista, Loeb

Much attention has been given in the literature to the effects of astrophysical events on human and land-based life.  However, little has been discussed on the resilience of life itself.  Instead explore the statistics of events that completely sterilize an Earth-like planet with planet radii in the range 0.5-1.5 R_Earth and temperatures of ~300K, eradicating all forms of life.  Consider the relative likelihood of complete global sterilization events from three astrophysical sources -- SNe, gamma-ray bursts, large asteroid impacts, and passing-by stars.  To assess such probabilities consider what cataclysmic event could lead to the annihilation of not just human life, but also extremophiles, through the boiling of all water in Earth's oceans.  Surprisingly find that the although human life is somewhat fragile to nearby events, the resilience of Ecdysozoa such as Milnesium tardigradum renders global sterilization an unlikely event.


1707.04256
Small-scale challenges to the $\Lambda$CDM Paradigm
Bullock, Boylan-Kolchin

The DE plus cold dark matter (LCDM) cosmological model has been a demonstrably successful framework for predicting and explains the large-scale structure of Universe and its evolution with time.  Yet on length scales smaller than ~1 Mpc and mass scales smaller than ~1e11 Msun, the theory faces a number of challenges.  For example, the observed cores of many DM dominated galaxies are both less dense and less cuspy than naively predicted in LCDM.  The number of small galaxies and dwarf satellites in the Local Group is also far below the predicted count of low-mass DM haloes and subheads within similar volumes.  These issues underlie the most well-documented problems with LCDM: Cusp/Core, Missing Satellites, and Too-Big-to-Fail.  The key questions is whether a better understanding of baryon physics, DM physics, or both will be required to meet these challenges.  Other anomalies, including the observed planar and orbital configurations of Local Group satellites and the tight baryonic/dark matter scaling relations obeyed by the galaxy population, have been less thoroughly explored in the context of LCDM theory.  Future surveys to discover faint, distant dwarf galaxies and to precisely measure their masses and density structure hold promising avenues for testing possible solutions to the small-scale challenges going forward.  Observational programs to constrain or discover and characterize the number of truly dark low-mass halos are among the most important, and achievable, goals in this field over the next decade.  These efforts will either further verify the LCDM paradigm or demand a substantial revision in the understanding of the nature of dark matter.


1707.04267
Predicting structures in the zone of avoidance
Source, et al

The Zone of Avoidance (ZOA), whose emptiness is an artifact of our Galaxy dust, has been challenging observers as well as theoretisch for many years.  Multiple attempts have been made on the observational side to maps this region in order to better understand the local flows.  On the theoretical side, however, this region is often simply statistically populated with structures but no real attempt has been made to confront theoretical and observed matter distributions.  This paper takes a step forward using constrained realizations of the local Universe shown to be perfect substitutes of local Universe-like simulations for smooth high density peak studies.  Far from generating completely 'random' structures in the ZOA, the reconstruction technique arranges matter according to the surrounding environment of this region.  More precisely, the mean distributions of structures in a series of constrained and random realizations differ: while densities annihilate each other when averaging over 200 random realizations, structures persist when summing 200 constrained realizations.  The probability distribution function of ZOA grid cells to be highly overdense is a Gaussian with a 15% mean in the random case, while that of the constrained case exhibits large tails.  This implies that areas with the largest probabilities host most likely a structure.  Comparisons between these predictions and observations, like this of the Puppis 3 cluster, show a remarkable agreement and allow us to assert the presence of the recently highlighted by observations, Vela supercluster at about 180 Mpc/h, right behind the thickest dust layers of our Galaxy.


1707.04334
Impications of a wavelength dependent PSF for weak lensing measurements
Eriksen, Hoekstra

The convolution of galaxy images by PSF is the dominant source of bias for WL studies, and an accurate estimate of the PSF is required to obtain unbiased shape measurements.  The PSF estimate for a galaxy depends on its SED, because the instrumental PSF is generally a function of the wavelength.  In this paper, explore various approaches to determine the resulting 'effective' PSF using broad-band data.  Considering the Euclid mission as a reference, find that standard SED template fitting methods result in biases that depend on source redshift, although this may be remedied if the algorithms can be optimized for this purpose.  Using a machine-learning algorithm, show that, at least in principle, the required accuracy can be achieved with the current survey parameters.  It is also possible to account for the correlations between photometric redshift and PSF estimates that arise from the use of the same photometry.  Explore the impact of errors in photometric calibrations, errors in the assumed wavelength dependence of the PSF model and limitations of the adopted template libraries.  The results indicate that the required accuracy for Euclid can be achieved using the data that are planed to determine photometric redshifts.


1707.04488
On the insufficiency of arbitrarily precise covariance matrices
Sellentin, Heavens

Investigate whether a Gaussian likelihood, as routinely assumed in the analysis of cosmological data, is supported by simulated survey data.  Define test statistics, based on a novel method that first destroys Gaussian correlations in a dataset, and then measures the non-Gaussian correlations that remain.  This procedure flags pairs of datapoints which depend on each other in a non-Gaussian fashion, and thereby identifies where the assumption of a Gaussian likelihood breaks down.  Using this diagnostic, find that non-Gaussian correlations in the CHFTLenS cosmic shear correlation functions are significant.  With a simple exclusion of the most contaminated datapoints, the posterior for s8 is shifted without broadening, but find no significant reduction in the tension with s8 derived from Planck CMB data.  However, also show that the one-point distributions of the correlation statistic are noticeably skewed, such that sound WL data sets are intrinsically likely to lead to a systematically low lensing amplitude being inferred.  The detected non-Gaussianities get larger with increasing angular scale such that for future wide-angle surveys such as Euclid or LSST, with their very small statistical errors, the large-scale modes are expected to be increasingly affected.  The shifts in posteriors may then not be negligible and recommend that these diagnostic tests by run as part of future analyses.


1707.04590
On the power spectrum of dark matter substructure in strong gravitational lenses
Rivero, Cyr-Racine, Dvorkin

Studying the smallest self-bound dark matter structure n the Universe can yield important clues about the fundamental particle nature of dark matter.  Galaxy-sacle strong gravitational lensing provides a unique way to detect and characterize DM substructures at cosmological distances from the MW.  Within the CDM paradigm, the number of low-mass sub haloes within lens galaxies is expected to be large, implying that their contribution to the lensing convergence field is approximately Gaussian and could thus be described by their power spectrum.  Develop here a general formalism to compute from first principles the subscturture convergence power spectrum for different populations of DM sub halos.  As an example, apply the framework to 2 distinct sub halo populations: a truncated NFW sub halo population motivated by standard CDM, and a truncated cored sub halo population motivated by self-interacting dark matter (SIDM).  Study in detail how the subhead abundance, mass function, internal density profile, and concentration affect the amplitude and shape of substructure power spectrum.  Determine that the power spectrum is mostly sensitive to a specific combination of the sub halo abundance and moments of the mass function, as well as to the average tidal truncation scale of the largest sub halos included in the analysis.  Interestingly, show that the asymptotic slope of the subscturture power spectrum at large wavenumber reflects the internal density profile of the sub halos.  In particular, the SIDM power spectrum exhibits a characteristic steepening at large wavenumber absent in the CDM power spectrum, opening the possibility of using this observable, if at all measurable, to discern between these 2 scenarios.


1707.04594
Implications of tides for life on exoplanets
Lingam, Loeb

As evident from the nearby examples of Proxima Centauri and TRAPPIST-1, Earth-sized planets in the habitable zone of low-mass stars are common.  Here, focus on such planetary systems and argue that their (oceanic) tides could be more prominent due to stronger tidal forces.  Identify the conditions under which tides may exert a significant positive influence on biotic processes - abiogenesis, biological rhythms and stimulating photosynthesis.  Conclude the analysis by identifying large-scale algal blooms as potential temporal biosignatures in reflectance light curves that can arise indirectly as a consequence of strong tidal forces.


1707.04606
The discovery of a gravitationally lensed supernova Ia at redshift 2.22
Rubin, et al

Present the discovery and measurements of a gravitationally lensed supernova (SN) behind the galaxy cluster MOO J1014+0038.  Based on multi-band HST and VLT photometry and spectroscopy, find a 99% probability that the SN is a SN Ia, and a 1% chance of a CC SN.  The typing algorithm combines the shape and color of the light curve with the expected rates of each SN type in the host galaxy.  With a redshift of 2.2216, this is the highest redshift SN Ia discovered with a spectroscopic host-galaxy redshift.  A further distinguishing feature is that the lensing cluster, at z=1.23, is the most distant to date to have an amplified SN.  The SN lies in the middle of the color and light-curve shape distributions found at lower z, disfavoring strong evolution to z=2.22.  Estimate an amplification of 2.8+0.6-0.5 (1.10±0.23 mag) --- compatible with the value estimated from WL-derived mass and the mass-concentration relation from LCDM simulations --- making it the most amplified SN Ia discovered behind a galaxy cluster.


1707.04924
The dependence of halo mass on galaxy size at fixed stellar mass using weak lensing
Charlton, et al

Stellar mass has been show to correlate with halo mass, with non-negligible scatter.  The stellar mass-size and luminosity-size relationships of galaxies also show significant scatter in galaxy size at fixed stellar mass.  It is possible that, at fixed stellar mass and galaxy color, the halo mass is correlated with galaxy size.  Galaxy-galaxy lensing allows us to measure the mean masses of dark matter haloes for stacked samples of galaxies.  Extend the analysis of the galaxies in the CFHTLenS catalogue by fitting single Sersic surface brightness profiles to the lens galaxies in order to recover half-light radius values, allowing determination of halo masses for lenses according to their size.  Comparing the halo masses and sizes to baselines for that stellar mass yields a differential measurement of the halo mass-galaxy size relationship at fixed stellar mass, defined as Mh(M*)~r_eff^eta(M*).  Find that on average, the lens galaxies have an eta=0.42±0.12, i.e. larger galaxies live in more massive DM haloes.  The eta is strongest for high mass LRGs.  Investigation of this relationship in hydro sims suggests that, at a fixed M*, satellite galaxies have a larger eta and greater scatter in the Mh and r_eff relationship compared to central galaxies.

Day 1287

Friday.


1707.04105
KiDS-i-800: comparing weak gravitational lensing measurements in same-sky surveys
Amon, et al

Present a weak gravitational lensing analysis of 815 deg2 of i-band imaging from KiDS-i-800.  In contrast to the deep r-band observations, which take priority during excellent seeing conditions and form the primary KiDS dataset (KiDS-r-450), the complementary yet shallower KiDS-i-800 spans a wide range of observing conditions.  The overlapping KiDS-i-800 and KiDS-r-450 imaging therefore provides a unique opportunity to assess the robustness of weak lensing measurements.  In the analysis, introduce two new 'null' tests.  The 'nulled' 2pt shear correlation function uses a matched catalogue to show that KiDS-i-800 and KiDS-r-450 shear calibration agree at the level of 1±4%.  Use 5 galaxy lens samples to determine a 'nulled' gg-lensing signal from the full KiDS-i-800 and KiDS-r-450 surveys and find that the measurements agree to 7±5% when the KiDS-i-800 source redshift distribution is calibrated using 30-band photometric redshifts from the COSMOS survey.  With an average effective source density of 3.8 galaxies/arcmin^2, a median redshift of z_med~0.5 and complete spectroscopic overlap, the wide area KiDS-i-band imaging is ideal for large-area cross correlation studies.

Day 1286

Monday.  Tuesday.  Wednesday.  Thursday.


1707.01904
Individual stellar halos of massive galaxies measured to 100 kpc at $0.3<z<0.5$ using Hyper Suprime-Cam
Huang, Leauthaud, et al

Massive galaxies display extended light profiles that can reach several hundreds of kilo parsecs.  These stellar halos provide a fossil record of galaxy assembly histories.  Using data that is both wide (~100 sq deg) and deep (i>28.5 mag/arcsec^1 in i-band), present a systematic study of stellar haloes of a sample of more than 3000 galaxies at 0.3<z<0.5 with log M*/Msun>11.4.  The study is based on high-quality (0.6 arcsec seeing) imaging data from HSC SSP, which enables us to individually estimate surface mass density profiles to 100 kpc without stacking.  As in previous work, find that more massive galaxies exhibit more extended outer profiles.  When this expended light is not properly accounted for as a result of shallow imaging or inadequate profile modeling, the derived stellar mass function can be significantly underestimated at the highest masses.  Across the sample, the ellipticity of outer light profiles increases substantially as larger radii is probed.  Show for the first time that these ellipticity gradients steepen dramatically as a function of galaxy mass, but detect no mass-dependence in outer color gradients.  The results support the two-phase formation scenario for massive galaxies in which outer envelopes are built up at late times from a series of merging events.  Provide surface mass density profiles in a convenient tabulated format to facilitate comparisons with predictions from numerical simulations of galaxy formation.


1707.01907
Constraints on the mass-richness relation from the abundance and weak lensing of SDSS clusters
Murata, et al

Develop a method for constraining the scaling relation of optical richness (lambda) with halo masses (M) for a sample of galaxy clusters based on a forward modeling approach for the Planck cosmology, where the probability distribution of optical richness for a given mass is modeled: P(ln lambda | M).  To model the abundance and the stacked lensing profiles, employ the halo emulator that outputs the halo mass function and the stacked lensing profile for an arbitrary set of halo mass and redshift, calibrated based on a suite of high-resolution N-body simulations.  By applying the method to 8,312 SDSS redMaPPer clusters with 20<=lambda<=100 and 0.10<=z_lambda<=0.33, show that the log-normal distribution model for P(ln lambda | M), with four free parameters, well reproduces the measured abundances and lensing profiles simultaneously.  The constraints are characterized by the mean relation, <ln lambda>(M)=A+Bln(M/Mpivot), with A=3.21 and B=1.00 for the pivot mass scale Mpivot=3e14 Msun/h, and the scatter sigma_{ln_lambda|M} = sigma_0 + q ln(M/Mpivot) with sigma_0=0.45 and q=-0.17.  However, find that a large scatter for the low richness bins, especially 20<=lambda<~30, is required in order for the model to reproduce the measurements by the contributions from low-mass haloes for the Planck cosmology.  Without such a large scatter, the model prediction for the lensing profiles tends to overestimate the measured amplitudes.  This might imply a possible contamination for low-richness clusters due to the projection effects. Such a low-mass halo contribution is significantly reduced when applying the method to the sample of 30<=lambda<=100.


1707.01908
Microlensing makes lensed quasar time delays significantly time variable
Tie, Kochanek

The time delays of gravitationally lensed quasars are generally believed to be unique numbers whose measurement is limited only by the quality of the light curves and the models for the contaminating contribution of gravitational microlensing to the light curves. This belief is incorrect -- gravitational microlensing also produces changes in the actual time delays on the ~day(s) light-crossing time scale of the emission region.  This is due to a combination of the inclination of the disk relative to the line of sight and the differential magnification of the temperature fluctuations producing the variability.  Demonstrate this both mathematically and with direct calculations using microlensing magnification patterns.  Measuring these delay fluctuations can provide a physical scale for microlensing observations, removing the need for priors on either the microlens masses or the component velocities.  That time delays in lensed quasars are themselves time variable likely explains why repeated delay measurements of individual lensed quasars appear to vary by more than their estimated uncertainties.  This effect is also an important new systematic problem for attempts to use time delays in lensed quasars for cosmology or to detect substructures (satellites) in lens galaxies.


1707.02160
TOPCAT: Desktop exploration of tabular data for astronomy and beyond
Taylor

TOPCAT, the Tool for OPerations on Catalogues And Tables, is an interactive desktop application for retrieval, analysis and manipulation of tabular data, offering a powerful and flexible range of interactive visualization options amongst other features.  Its visualization capabilities focus on enabling interactive exploration of large static local tables - millions of rows and hundreds of columns can easily be handled on a standard desktop or laptop machine, and various options are provided for meaningful graphical representation of such large datasets.  TOPCAT has been developed in the context of astronomy, but many of its features are equally applicable to other domains.  The software, which is free and open source, is written in Java, and the underlying high-performance visualization library is suitable for re-use in other applications.


1707.02259
Exploring cosmic origins with CORE: gravitational lensing of the CMB
Challinor, et al

Lensing of the CMB is now a well-developed probe of LS clustering over a broad range of redshifts.  By exploiting the non-Gaussian imprints of lensing in the polarization of the CMB, the CORE mission can produce a clean map of the lensing deflections over nearly the full-sky.  The number of high-S/N modes in this map will exceed current CMB lensing maps by a factor of 40, and the measurement will be sample-variance limited on all scales where linear theory is valid.  Here, summarize this mission product and discuss the science that it will enable.  For example, the summed mass of neutrinos will be determined to an accuracy of 17 meV combining CORE lensing and CMB two-point information with contemporaneous BAO measurements, 3 times smaller than the minimum total mass allowed by neutrino oscillations.  In the search for B-mode polarization from primordial gravitational waves with CORE, lens-induced B-modes will dominate over instrument noise, limiting constraints on the gravitational wave power spectrum amplitude.  With lensing reconstructed by CORE, one can "delens" the observed polarization internally, reducing the lensing B-mode power by 60%.  This improves to 70% by combing lensing and CIB measurements from CORE, reducing the error on the gravitational wave amplitude by 2.5 compared to no delensing (in the null hypothesis).  Lensing measurements from CORE will allow calibration of the halos masses of the 40,000 galaxy clusters that it will find, with constraints dominated by the clean polarization-based estimators.  CORE can accurately remove Galactic emission from CMB maps with its 19 frequency channels.  Present initial findings that show that residual Galactic foreground contamination will not be a significant source of bias for lensing power spectrum measurements with CORE.


1707.02863
The impact of redshift on galaxy morphometric classification: case studies for SDSS, DES, LSST and HST with Morfometryka
de Albernaz Ferreira, Ferrari

Carried a detailed analysis on the impact ofcosmo redshift in the non-parametric approach to automated galaxy morphology classification.  Artifically redshifted each galaxy from the EFIGI 4458 sample (re-centered at z~0) simulating SDSS, DES, LSST, and HST instruments setups over the range 0<z<1.5.  Then traced how the morphometry is degraded in each z using Morfometryka.  In the process, re-sampled all catalog to several resolutions and to a diverse SNR range, allowing us to understand the impact of image sampling and noise on the measurements separately.  Summarize by exploring the impact of these effects on the capacity to perform automated galaxy supervised morphological classification by investigating the degradation of the classifier's metrics as a function of redshift for each instrument.  The overall conclusion is that a reliable classification can be made for z<0.2 with SDSS, z<0.5 with DES, z<0.8 for LSST and for at least z<1.5 with HST.


1707.03169
Morpho-z: improving photometric redshifts with galaxy morphology
Soo, Moraes, Joachimi, Hartley, Lahav, et al

Conduct a comprehensive study of the effects of incorporating galaxy morphology information in photometric redshift estimation.  Using machine learning methods, assess the changes in the scatter and catastrophic outlier fraction of photometric redshifts when galaxy size, ellipticity, Service index and surface brightness are included in training on galaxy samples from the SDSS and the CFHT Stripe-82 survey (CS82).  Show that by adding galaxy morphological parameters to full ugriz photometry, only mild improvements are obtained, while the gains are substantial in cases where fewer passbands are available.  For instance, the combination of grz photometry and morphological parameters almost fully recovers the metrics of 5-band photo-zs.  Demonstrate that with morphology, it is possible to determine useful redshift distribution N(z) of galaxy samples without any color information.  Also find that the inclusion of quasar redshifts and associated object sizes in training improves the quality of photometric redshift catalogues, compensating for the lack of a good star-galaxy separator.  Further show that morphological information can mitigate biases and scatter due to bad photometry.  As an application, derive both point estimates and posterior distributions of redshifts for the official CS82 catalogue, training on morphology and SDSS Stripe-82 ugriz bands when available.  The redshifts yield a 68th percentile error of 0.058(1+z), and a catastrophic outlier fraction of 5.2 per cent.  Further include a deep extension trained on morphology and single i-band CS82 photometry.


1707.03358
Small-scale structure and the Lyman-$\alpha$ forest baryon acoustic oscillation feature
Hirata

The BAO feature in the Ly-a forest is one of the key probes of the cosmic expansion rate at z~2.5, well before DE is believed to have become dynamically significant.  A key advantage of the BAO as a standard ruler is that it is a sharp feature and hence is more robust against broadband systematic effects than other cosmo probes.  However, if the Ly-a forest transmission is sensitive to the initial streaming velocity of the baryons relative to the dark matter, then the BAO peak position can be shifted.  Investigate this sensitivity using a suite of hydro sims of small regions of the IGM with a range of box sizes and physics assumptions; each sim starts from initial conditions at the kinematic decoupling era (z~1059), undergoes a discrete change from neutral gas to ionized gas thermal evolution at reionization (z~8), and is finally processed into a Ly-a forest transmitted flux cube.  Streaming velocities suppress small-scale structure, leading to less violent relaxation after reionization.  The changes in the gas distribution and temperature-density relation at low z are more subtle, due to the convergent temperature evolution in the ionized phase.  The change in the BAO scale is estimated to be of the order of 0.12% at z=2.5; some of the major uncertainties and avenues for future improvement are discussed.  The predicted streaming velocity shift would be a subdominant but not negligible effect (of order 0.26 sigma) for the upcoming DESI Ly-a forest survey, and exceeds the cosmic variance floor.  It is hoped that this study will motivate additional theoretical work on the magnitude of the BAO shift, both in the Ly-a forest and in other tracers of LSS.

Day 1285

Thursday.  Friday.


1707.01108
ZOMG III: the effect of halo assembly on the satellite population
Gerald, Romano-Díaz, Borzyszkowski, Porciani

Use zoom hydro sims to investigate the properties of satellites within galaxy-sized DM haloes with different assembly histories.  Consider two classes of haloes at redshift z=0: 'stalled' haloes that assembled at z>1 and 'accreting' ones that are still forming nowadays.  Have previously shown that the stalled haloes are embedded within thick filaments of the cosmic web while the accreting ones lie where multiple thin filaments converge.  Find that satellites in the two classes have both similar and different properties.  Their mass spectra, radial count profiles, baryonic and stellar content, and the amount of material they shed are indistinguishable.  However, the mass fraction locked in satellites is substantially larger for the accreting haloes as they experience more mergers at late times.  The largest difference is found in the satellite kinematics.  Substructures fall towards the accreting haloes along quasi-radial trajectories whereas an important tangential velocity component is developed, before accretion, while orbiting the filament that surrounds the stalled haloes.  Thus, the velocity anisotropy parameter of the satellites (beta) is positive for the accreting heroes and negative for the stalled ones.  This signature enables us to tentatively categorize the Milky Way halo as stalled based on a recent measurement of beta.  Half of the haloes contain clusters of satellites with aligned orbital angular momenta corresponding to flattened structures in space.  These features are not driven by baryonic physics and are only found in haloes hosting grad-design spiral galaxies, independently of their assembly history.


1707.01285
Shear measurement bias: dependencies on methods, simulation parameters and measured parameters
Pujol, et al

Present a study of the dependencies of shear and ellipticity bias on simulation (input) and measured (output) parameters, noise, PSF anisotropy, pixel size and the model bias coming from two different independent shape estimators.  Use simulated images from Galsim based on the GREAT3 control-space-constant branch and measure ellipticity and shear bias from a model-firing method (gFIT) and a moment-based method (KSB).  Show the bias dependencies found on input and output parameters for both methods and identify the main dependencies and causes.  Find consistent results between the two methods (given the precision of the analysis) and important dependencies on orientation and morphology properties such as flux, size and ellipticity.  Show cases where shear bias and elliptical bias behave very different for the two methods due to the different nature of these measurements.  Also show that noise and pixelization play an important role on the bias dependencies on the output properties.  Find a large model bias for galaxies consisting of a bulge and a disk with different ellipticities or orientations.  Also see an important coupling between several properties on the bias dependencies.  Because of this, need to study several properties simultaneously in order to properly understand the nature of shear bias.

Day 1284

Wednesday.


1707.01020
Astrometric accuracy during the past 2000 years
Høg

The great development of astrometry accuracy since the observations by Hipparchus about 150 BC was documented in 2008 in the first version of the present report.  This report is updated, e.g. with recent information on the catalogues before 1800 AD.  The development has often been displayed in diagrams showing the accuracy versus time.  A new such diagram is provided in a figure and in a .png file (section 2) and this information will presumably be the main interest for most readers.  For the specialist reader, a detailed documentation is provided in order to give confidence in the diagram and to show how the knowledge about astrometric accuracy has improved in the recent 20 years.  The history of these diagrams is illustrated in the appendix.


1707.01072
Effects of self-calibration of intrinsic alignment on cosmological parameter constraints from future cosmic shear surveys
Yao, Ischak, Lin, Troxel

IA of galaxies have been recognized as one of the most serious contaminates to WL.  These systematics need to be isolated and mitigated in order for ongoing and future lensing surveys to tech their full potential.  The IA self-calibration (SC) method was shown in previous studies to be able to reduce the GI contamination by up to a factor of 10 for the 2pt and 3pt correlations.  The SC method does not require to assume an IA model in its working and can extract the GI signal from the sample photo-z survey offering the possibility to test and understand structure formation scenarios and their relationship to IA models.  In this paper, study the effects of the IA SC mitigation method on the precision and accuracy of cosmo parameter constraints from future cosmic shear surveys LSST, WFIRST and Euclid.  Perform analytical and numerical calculations to estimate the loss of precision and the residual bias in the best fit cosmo parameters after the self-calibration is performed.  Take into account uncertainties from photometric z and the galaxy bias.  Find that the confidence contours are slightly inflated from applying the SC method itself while a significant increase is due to the inclusion of the photo-z uncertainties.  The bias of cosmological parameters is reduced from several-sigma, when IA is not corrected for, to below 1-sigma after SC is applied.  These numbers are comparable to those resulting from applying the method of marginalizing over IA model parameters despite the fact that the two methods operate very differently.  Conclude that implementing the SC for these future cosmic-shear surveys will not only allow one to efficiently mitigate the GI contaminant but also help to understand their modeling and link to structure formation.

Day 1283

Tuesday.


1707.00483
Problems with KiDS
Efstathiou, Lemos

KiDS has been used in several recent papers to infer constraints on the amplitude of the matter power spectrum and matter density at low redshift.  Some of these analyses have claimed tension with the Planck LCDM cosmology at the ~2-3 sigma level, perhaps indicative of new physics.  However, Planck is consistent with other low redshift probes of the matter power spectrum such as z-space distortions and the combined galaxy-mass and galaxy-galaxy power spectra.  Perform consistency tests of the KIDS data, finding internal tensions for various cuts of the data at >3 sigma significance. Until these internal tensions are understood, argue that it is premature to claim evidence for new physics from KiDS.

Day 1282

Monday.


1706.09899
The EAGLE simulations of galaxy formation: public release of particle data
The EAGLE team

This manual accompanies the release of the particle data for 24 simulations of the EAGLE suite of cosmo hydro sims of galaxy formation by the virgo consortium.  It describes how to download these snapshots and how to extract datasets from them, emphasizes the meaning of variables, and their units.  Provide examples for extracting the particle data in python.  This data release complements the earlier release of numerous integrated properties of the galaxies in EAGLE through an SQL relational database.  This database has been updated to include the additional simulations that are part of the present data release.  Scientists wanting to use EAGLE may find it useful to first investigate whether their analysis can be performed using the database, before accessing the particle data.  The particles in the snapshot files are indexed by a peano-hilbert key.  This allows for an eased extraction of simply connected spatial volumes, without needing to read the entire snapshot.  This makes it possible to analyse many aspects of galaxies using modest computing resources, even when using EAGLE sims with large numbers of particles.  A reading routine is provided to simplify this process.


1706.09906
Halo assembly bias and the tidal anisotropy of the local halo environment
Paranjape, Hahn, Sheth

Study the role of the local tidal environment in determining the assembly bias of DM haloes.  Previous results suggest that the anisotropy of a halo's environment (i.e., whether it lies in a filament orin a more isotropic region) can play a significant role in determining the eventual mass and the age of the halo.  Statistically isolate this effect using correlations between the large-scale and small-scale environments of simulated haloes at z=0 with masses between 1e11.6 < (m/(Msun/h)) < 1e14.9.  Probe the large scale environment using a novel alo-by-halo estimator of linear bias.  For the small-scale environment, identify a variable alpha_R that captures the tidal anisotropy in a region of radius R=4R_200b around the halo and correlates strongly with halo bias at fixed mass.  Segregating haloes by alpha_R reveals two distinct populations.  Haloes in highly isotropic local environments (alpha_R<~0.2) behave as expected form the simplest, spherically averaged analytical models of structure formation, showing a negative correlation between their concentration and large-scale bias at all masses.  In contrast, halos in anisotropic, filament-like environments (alpha_R>0.5) tend to show a positive correlation between bias and concentration at any mass.  The multi-scale analysis cleanly demonstrates how the overall assembly bias trend across halo mass emerges as an average over these different halo populations, and provides valuable insights towards building analytical models that correctly incorporate assembly bias.  Also discuss potential implications for the nature and detectability of galaxy assembly bias.


1706.09928
Instrumental response model and detrending for the Dark Energy Camera
Bernstein, et al

Describe the model for the mapping from sky brightness to the digital output of the DECam, and describe the algorithms adopted by the DES for inverting this model to obtain photometric measures of celestial objects from the raw camera output.  The calibration aims for fluxes that are uniform across the camera field of view and across the full angular and temporal span of the DES observations, approaching the accuracy limits set by shot noise for the full dynamic range of DES observations.  The DES pipeline incorporates several substantive advances over standard detrending techniques, including: principal-components-based sky and fringe subtraction; correction of the "brighter-fatter" nonlinearity; use of internal consistency in on-sky observations to disentangle the influences of quantum efficiency, pixel-size variations, and scattered light in the dome flats; and pixel-by-pixel characterization of instrument spectral response, through combination of internal-consistency constraints with auxiliary calibration data.  This article provides conceptual derivations of the detrending/calibration steps, and the procedures for obtaining the necessary calibration data.  Other publications will describe the implementation of these concepts for the DES operational pipeline, the detailed methods, and the validation that the techniques can bring DECam photometry and astrometry within ~2mmag and ~3 mas, respectively, of fundamental atmospheric and statistical limits.  The DES techniques should be broadly applicable to wide-field imagers.


1706.10281
Dark matter under the microscope: Constraining compact dark matter with caustic crossing events
Diego, Kaiser, Broadhurst, et al

A galaxy cluster acts as a cosmic telescope over BG galaxies but also as a cosmic microscope of the lens imperfections.  The diverging magnification of lensing caustics enhances the microlensing effect of substructure present within the lensing mass.  Fine-scale structure can be accessed as a moving background source brightens and disappears when crossing these caustics.  The recent recognition of a distant lensed star near the Einstein radius of the galaxy cluster MACSJ1149.5+2223 (Kelly+2017) allows the rare opportunity to reach sub solar mass microlensing through a super-critical column of cluster matter.  Here, compare these observations with high-resolution ray-tracing simulations that include stellar microlensing set by the observed intracluster starlight and also primordial BHs that may be responsible for the recently observed LIGO events.  explore different scenarios with microlenses from the intracluster medium and BHs, including primordial ones, and examine strategies to exploit these unique alignments.  Find that the best constraints on the fraction of compact DM in the small-mass regime can be obtained in regions of the cluster where the ICM plays a negligible role.  This new lensing phenomenon should be widespread and can be detected within modest-redshift lensed galaxies so that the luminosity distance is not prohibitive for detecting individual magnified stars.  Continuous HST monitoring of several such optimal arcs will be rewarded by an unprecedented mass spectrum of compact objects that can contribute to uncovering the nature of dark matter.


1706.10286
A comparison of cosmological parameters determined from CMB temperature power spectra form the South Pole Telescope and the Planck satellite
Aylor, Hou, Knox, Sstory, et al

The Planck CMB temperature data are best fit with a LCDM model that is in mine tension with constraints from other cosmological probes.  The SPT 2540 deg^2 SPT-SZ survey offers measurements on sub-degree angular scales (multipoles 650<ell<2500) with sufficient precision to use as an independent check of the Planck data.  Here, build on the recent joint analysis of the SPT-SZ and Planck data in Hou+2017 by comparing LCDM parameter estimates using the temperature power spectrum from both data sets in the SPT-SZ survey region.  Also restrict the multipole range used in parameter fitting to focus on modes measured well by both SPT and Planck, thereby greatly reducing sample variance as a driver of parameter differences and creating a stringent test for systematic errors.  Find no evidence of systematic errors from such tests.  When expanding the maximum multipole of SPT data used, see low-significance shifts in the angular scale of the sound horizon and the physical baryon and CDM densities, with a resulting trend to higher Hubble constant.  When SPT and Planck data are compared on the SPT-SZ sky patch to Planck full-sky data but keep the multipole range restricted, find differences in the parameters n_s and A_s e^-2tau.  Perform further checks, investigating instrumental effects and modeling assumptions, and find no evidence that the effects investigated are responsible for any of the parameter shifts.  Taken together, these tests reveal no evidence for systematic errors in SPT or Planck data in the overlapping sky coverage and multiple range and, at most, weak evidence for a breakdown of LCDM or systematic errors influencing either the Planck data outside the SPT-SZ survey area or the SPT data at ell>2000.