Day 1236

Wednesday.  Thursday.  Friday.  Monday.  Tuesday.

1703.08205
Nonlinearity and pixel shifting effects in HXRG infrared detectors
Plazas, Shapiro, Smith, Rhodes, Huff

Study the NL in the conversion from charge to voltage in infrared detectors (HXRG) for use in precision astronomy.  Present laboratory measurements of the NL function of a H2RG detector and discuss the accuracy to which it would need to be calibrated in future space missions to perform cosmological measurements through the weak gravitational lensing technique.  In addition, present an analysis of archival data from the infrared H1RG detector of WFC3 in HST that provides evidence consistent with the existence of a sensor effect analogous to the brighter-fatter effect found in CCDs.  Propose a model in which this effect could be understood as shifts in the effective pixel boundaries, and discuss prospects of laboratory measurement to fully characterize this effect.


1703.08550
The fate of the gaseous disks of galaxies that fall into clusters
Ruggiero, Neto

Galaxy clusters are known to induce gas loss in infallible galaxies due to the ram pressure exerted by the intracluster medium over their gals content.  In this paper, investigate this process through a set of simulations of MW-like galaxies falling inside idealized clusters of 1e14 Msun and 1e15 Msun, containing a cool-core or not, using the adaptive mesh refinement code RAMSES.  Use these sims to constrain how much of the initial mass contained in the gaseous disk of the galaxy will be converted into stars and how much of it will be lost, after a single crossing of the entire cluster.  Find that, if the galaxy reaches the central region of a cool-core cluster, it is expected to lose all its gas, independently of its entry conditions and of the cluster's mass.  On the other hand, it is expected to never lose all its gas after crossing a cluster with a cool core just once.  Before reaching the center of the cluster, the SFR of the galaxy is always enhanced, by a factor of 1.5 to 3.  If the galaxy crosses the cluster without being completely stripped, its final amount of gas is on average two times smaller after crossing the 1e15 Msun cluster, relative to the 1e14 Msun cluster.  This is reflected in the final SFR of the galaxy, which is also 2x smaller in the former, ranging from 0.5-1 Msun / yr, compared to 1-2 Msun/year for the latter.


1703.08809
There is no kinematic backreaction
Kaiser

In the conventional framework for cosmological dynamics the scale factor a(t) is assumed to obey the 'background' Friedmann equation for a perfectly homogeneous universe while particles move according to equations of motions driven by the gravity sourced by the density fluctuations.  It has been suggested that the emergence of structure modifies the evolution of a(t) via 'kinematic' backreaction and that this may avoid the need for dark energy.  Show that the conventional equation are exact in Newtonian gravity -- which should accurately describe the low-z universe -- and there is no approximation in the use of the homogeneous universe equation for a(t).  Conclude the there is no back reaction of structure on a(t) and that the need for dark energy cannot be avoided in this way.

Day 1235

Monday.  Tuesday.

1703.05823
Measurements and simulations of the brighter-fatter effect in CCD sensors
Lage, Bradshaw, Tyson

Reduction of images and science analysis from ground-based telescopes such as the LSST requires detailed knowledge of the PSF of the image, which includes components attributable to the instrument as well as components attributable to the atmosphere.  Because the atmospheric component is constantly changing, the PSF is typically extracted from each image by measuring the size and shape of the star images across the CCD, then building a fitting function over the focal plane which is used to model the PSF for analysis of extended sources such as galaxies.  Since the stars in each CCD field have a range of brightnesses, accurate knowledge of the PSF for point sources of varying brightness is essential.  It has been found that in thick, fully-depleted CCDs, the electrostatic repulsion of charge stored in the collecting wells gives rise to a larger and slightly more elliptical PSF for brighter stars.  This "brighter-fatter" effect has been reported in some detail in the literature.  In this work, report direct and indirect measurements of this effect in prototype LSST sensors, and describe a detailed physics-based model of the electrostatics and charge transport within the CCD.


1703.06657
A KiDS weak lensing analysis of assembly bias in GAMA galaxy groups
Dvornik, et al

Investigate possible signatures of halo assembly bias for spectroscopically selected galaxy groups from the GAMA survey using weak lensing measurements from the spatially overlapping regions of the deeper, high-imaging-quality photometric KiDS survey.  Use GAMA groups with a apparent richness larger than 4 to identify samples with comparable mean host masses but with a different radial distribution of satellite galaxies, which is a proxy for the formation time of the haloes.  Measure the weak lensing signal for groups with a steeper than average and with a shallower than average satellite distribution and find no sign of halo assembly bias, with the bias ratio of 0.85±0.3, which is consistent with the LCDM precision.  The galaxy groups have typical masses of 1e13 Msun/h, naturally complementing previous studies of halo assembly bias on galaxy cluster scales.

Day 1234

Friday.

1703.05326
A cross-correlation-based estimate of the galaxy luminosity function
van Daalen, White

Extend existing methods for using cross-correlations to derive redshift distributions for photometric galaxies, without using photometric redshifts.  The model presented in this paper simultaneously yields highly accurate and unbiased redshift distributions and, for the first time, redshift-dependent luminosity functions, using only clustering information and the apparent magnitudes of the galaxies as input.  In contrast to many existing techniques for recovering unbiased redshift distributions, the output of the method is not degenerate with the galaxy bias b(z), which is achieved by modeling the shape of the luminosity bias.  Successfully apply the method to a mock galaxy survey and discuss the potential application to the model to real data.


1703.05575
Yet another introduction to relativistic astrophysics
Foschini

Late Winter Lecture Notes, Short Course (10 hrs) of Relativistic Astrophysics held at the Department of Physics and Astronomy of the University of Padova, March 13-17, 2017.

Day 1233

Tuesday.  (Wednesday.)  Thursday.

1703.05142
Redshift drift of gravitational lensing
Piattella, Giani

Investigate the effect of the redshift drift in strong gravitational lensing.  The z drift produces a time variation of i) the apparent position of a lensed source and ii) the time delay among incoming signals from different images.  Dub these effects as angular drift and time delay drift, respectively, and analyze their relevance in cosmology.

Day 1232

Monday.

1703.03407
LIGER: mock relativistic light-cones from Newtonian simulations
Borzyszkowski, Bertacca, Porciani

A new method to create mock galaxy catalogues in z space including GR to linear order in cosmo perturbations.  LIGER (light cones with general relativity) takes a N-body or hydro Newtonian sim as an input and outputs the distribution of galaxies in comoving redshift space. This result is achieved making use of a coordinate transformation and simultaneously accounting for lensing magnification.  The calculation includes both local corrections and terms that have been integrated along the line of sight.  The fast implementation allows the production of many realizations that can be used to forecast the performance of forthcoming wide-angle surveys and to estimate the covariance matrix of the observables.  To facilitate this use, also present a variant of LIGER designed for large-volume sims with low mass resolution.  In this case, the galaxy distribution on large scales is obtained by biasing the matter-density field.  Finally, present two sample applications of LIGER.  First, discuss the impact of weak gravitational lensing onto the angular clustering of galaxies in a Euclid-like survey.  In agreement with previous analytical studies, find that magnification bias can be measured with high confidence.  Second, focus on two generally neglected Doppler-induced effects: magnification and the change of number counts with redshift.  Show that the corresponding z-space distortions can be detected at 5.5 sigma significance with the completed SKA.

Day 1231

Friday.

1703.02991
The third data release of the Kilo-Degree Survey and associated data products
de Jong, et al

KiDS is an ongoing optical wide-fields making survey with the OmegaCAM camera at the VLT Survey Telescope.  It aims to image 1500 square degrees in four filters (ugri).  The core science driver is mapping the large-scale matter distribution in the Universe, using WL shear and photometric redshift measurements.  Further science cases include galaxy evolution, Milky Way structure, detection of high-redhisft clusters, and finding rare sources such as strong lenses and quasars.  Present DR3 and several associated data products, adding further area, homogenized photometric calibration, photometric redshifts and WL shear measurements to the first 2 releases.  A dedicated pipeline embedded in the Astro-WISE information system is used for the production of the main release.  Modifications with respect to earlier releases are described in detail.  Photometric redshifts have been derived using both Bayesian template fitting, and machine-learning techniques.  For the WL measurements, optimized procedures based on the THELI data reduction and lensfit shear measurement packages are used.  In DR3 stacked ugri images, weight maps, masks, and source lists for 292 new survey tiles (~300 sq. deg) are made available.  The multi-band catalogue, including homogenized photometry and photometric z, covers the combined DR1, DR2 and DR3 footprint of 440 survey tiles (447 sq.deg).  Limiting magnitudes are typically 24.3, 25.1, 24.9, 23.8 (5 sigma in a 2" aperture) in ugri, respectively, and the typical r-band PSF size is less than 0.7".  The photometric homogenization scheme ensures accurate colors and an absolute calibration stable to ~2% for gri's and ~3% in u.  Separately released are WL shear catalogue and photometric redshifts based on 2 different machine-linearing techniques.


1703.03383
KiDS-450: Tomographic cross-correlation of galaxy shear with {/it Planck} Lensing
Harnois-Dëraps, et al

Present the tomographic cross-correlation between galaxy lensing measured in KiDS-450 with overlapping lensing measurements with CMB, as detected by Planck 2015.  Compare joint probe measurement to the theoretical expectation for a flat LCDM cosmology, assuming the best-fitting cosmological parameters from the KiDS-450 cosmic shear and Planck CMB analyses.  Find that the results are consistent within 1 sigma with the KiDS-450 cosmology, with an amplitude re-scaling parameter A_KiDS=0.86±0.19.  Adopting a Planck cosmology, find the results are consistent within 2 sigma, with A_Planck =0.68±0.15.  Show that the agreement is improved in both cases when the contamination to the signal by intrinsic galaxy alignments is accounted for, increasing A by ~0.1.  This is the first topographic analysis of the galaxy  lensing -- CMB lensing crosscorrelation signal, and is based on 5 photometric redshift bins.  Use this measurement as an independent validation of the multiplicative shear calibration and of the calibrated source redshift distribution at high z.  Find that constraints on these 2 quantities are strongly correlated when obtained from this technique, which should therefore not be considered as a stand-alone competitive calibration tool.

Day 1230

Thursday.

1703.02642
CMU DeepLens: Deep learning for automatic image-based galaxy-galaxy strong lens finding
Lanusse, et al

Train and validate the model on a set of 20k LSST-like mock observations including a range of lensed systems of various sizes and S/N.  Find on the simulated data set that for a rejection rate of non-lenses of 99%, a completeness of 90% can be achieved for lenses with Einstein radii larger than 1.4" and S/N larger than 20 on individual g-band LSST exposures.  Finally, emphasize the importance of realistically complex simulations for training such machine learning methods by demonstrating that the performance of models of significantly different complexities cannot be distinguished on simpler simulations.  Code publicly available at GitHub.com/McWilliamsCenter/CMUDeepLens.

Day 1229

Wednesday.

1703.02070
Unbiased clustering estimation in the presence of missing observations
Bianchi, Percival

In order to be efficient, spectroscopic galaxy redshift surveys do not obtain redshifts for all galaxies in the population targeted.  The missing galaxies are often clustered, commonly leading to a lower proportion of successful observations in dense regions.  One example is the close-pair issue for SDSS spectroscopic galaxy surveys, which have a deficit of pairs of observed galaxies with angular separation closer than the hardware limit on placing neighboring fibers.  Spatially clustered missing observations will exist in the next generations of surveys.  Various schemes have previously been suggested to mitigate these effects, but none works for all situations.  Argue that the solution is to link the missing galaxies to those observed with statistically equivalent clustering properties, and that the best way to do this is to rerun the targeting algorithm, varying the angular position of the observations.  Provided that every pair has a non-zero probability of being observed in one realization of the algorithm, then a pair-unweighting scheme linking targets to successful observations, can correct these issues.  Present such a scheme, and demonstrate its validity using realizations of an idealized simple survey strategy.


1703.02071
Using angular pair unweighting to improve 3D clustering measurements
Percival, Bianchi

Analysis of mocks suggests that, if an angular clustering measurement is available over twice the area covered spectroscopically, weighting gives a ~10-20% reduction of the variance of the monopole correction function on the BAO scale.

Day 1228

Friday.  Monday.  Tuesday.

1703.01575
Weak lensing power spectrum reconstruction by counting galaxies. -- I: the ABS method
Yang, et al

Propose and analytical method of blind separation (ABS) of cosmic magnification from the intrinsic fluctuations of galaxy number density in the observed (lensed) galaxy number density distribution.  The ABS method utilizes the different dependencies of the signal (cosmic magnification) and contamination (galaxy intrinsic clustering) in galaxy flux, to separate the two.  It works directly on the measured cross galaxy angular power spectra between different flux bins. It determines/reconstructs the lensing power spectrum analytically, without assumptions of galaxy intrinsic clustering and cosmology.  It is unbiased in the limit of infinite number of galaxies.  In reality the lensing reconstruction accuracy depends on survey configurations, galaxy biases, and other complexities, due to finite number of galaxies and the resulting shot noise in the cross galaxy power spectra.  Estimate its performance (systematic and statistical errors) in various cases.  Find that state IV DE surveys such as SKA and LSST are capable of reconstructing the lensing power spectrum at z~1 and ell<Z5000 accurately.  This lensing reconstruction only requires counting galaxies, and is therefore highly complementary to the cosmic shear measurement by the same surveys.


1703.01679
Astrometric calibration and performance of the Dark Energy Camera
Bernstein et al

Characterize the ability of DECam to perform relative astrometry across its 500Mpix, 3 deg2 science FoV, and across 4 years of operation.  This is done using internal comparisons of ~4e7 measurements of high-S/N stellar images obtained in repeat visits to fields of moderate stellar density, with the telescope dithered to move the sources around the array.  An empirical astrometric model includes terms for: optical distortions; stray electric fields in the CCD detectors; chromatic terms in the instrumental and atmospheric optics; shifts in CCD relative positions of up to ~10 um when the DECam temperature cycles; and lower-order distortions to each exposure from changes in atmospheric refraction and telescope alignment.  Errors in this astrometric model are dominated by stochastic variations with typical amplitudes of 10-30mas (in a 30s exposures) and 5-10 arcmin coherence length, plausibly attributed to Kolmogorov-spectrum atmospheric turbulence.  The size of these atmospheric distortions is not closely related to the seeing.  Given an astrometric reference catalog at density ~0.7 arcmin^-2, e.g. from Gaia, the typical atmospheric distortions can be interpolated to 7 mac RMS accuracy (for 30s exposures) with 1 arcmin coherence length for residual errors.  Remaining detectable error contributors are 2-4 has RMS from unmodelled stray E_fields in the devices, and another 2-4 was RMS from focal plane shifts between camera thermal cycles.  Thus the astrometric solution for a single DECam exposures is accurate to 3-6 has (0.02 pixels, or 300 nm) on the focal plane, plus the stochastic atmospheric distortion.


1703.01791
Multipolar moments of weak lensing signal around clusters.  Weighing filaments in harmonic space
Gouin, et al

Aim: to understand the connectivity of the cosmic web with unbiased mass tracers like WL is of prime importance to prob the underlying cosmology, seek dynamical signatures of DM, and quantify environmental effects on galaxy formation.  Methods: Mock catalogues of galaxy clusters are extracted from the N-body PLUS simulation.  For each cluster, the aperture multipolar moments of the convergence are calculated in two annuli (inside and outside the virial radius).  By stacking their modulus, a statistical estimator is built to characterize the angular mass distribution around clusters.  The moments are compared to predictions from perturbation theory and spherical collapse.  Results: The main weakly chromatic excess of multipolar power on large scales is undetstood as arising from the contraction of the primordial cosmic web driven by the growing potential well of the cluster.  In the inner region, the initial quadrupole prevails, while centering suppresses odd multipoles, especially m=1.  Predictions for the signal amplitude as a function of the cluster-centric distance, mass and redshift are presented.  The prospects of measuring this signal are estimated for current and future lensing data sets.  Inside the virial radius, multipoles up to m=8-12 can be measured at >10 sigma with 10k clusters at z=0.3.  In the outer regions, around 4 Rvir, detection is possible up to m=8 but the noise from intervening large-scale structure dominates.  Conclusions: the Euclid mission should provide all the necessary information to study the comics evolution of the connectivity of the cosmic web around lensing clusters using multipolar moments.

Day 1227

Thursday.

1703.00010
Offsets between member galaxies and dark matter in clusters: a test with the Illustris simulation
Ng, et al

DM with a non-zero self-interacting cross section (sigma_SIDM) has been positive as a solution to a number of outstanding astrophysical mysteries.  Many studies of merging galaxy clusters have given constraints on sigma_SIDM based on the spatial offset between the member galaxy population and the DM distribution.  Assuming sigma_SIDM=0, how likely is it to see the galaxy-DM offset values observed in merging clusters of galaxies?  To answer this question, formulate a hypothesis test using data from Illustris, a LCDM cosmo sim.  Select 43 Illustris clusters and their galaxy members at z~0 and examine the accuracy of commonly used galaxy summary statistics, including kernel-density-estimation (KDE) luminosity peak, KDE number density peak, shrinking aperture, centroid and the location of the BCG.  Use the DM particles to reproduce commonly adopted methods to identify DM peaks based on gravitational lensing cluster maps.  By analyzing each cluster in 768 projection, determine the optimistic noise floor in the measurements of the galaxy-DM offsets.  Find that the choice of the galaxy summary statistics affects the inferred offset values substantially, with the BCG and the luminosity peak giving the tightest 68-th percentile offset levels, <~4 kpc and <~32 kpc, respectively.  Shrinking aperture, number density and centroid give a large offset scatter of about 50-100 kpc at the 68th percentile level, even for clusters with only one dominant mass component.  Out of the 15 reported offsets from observed merging clusters examined, 13 of them are consistent with Illustris unrelaxed cluster offsets at the 2-sigma (95-th percentile) level, i.e. consistent with the hypothesis that LCDM is the true underlying physical model.

Day 1226

Tuesday.  Wednesday.

1702.08449
First data release of the Hyper Suprime-Cam Subaru Strategic Program
Aihira, et al

The HSC-SSP is a 3-layered imaging survey aimed at addressing some of the most outstanding questions in astronomy today, including the nature of dark matter and dark energy.  The survey has been awarded 300 nights of observing time at Subaru.  The survey started in March 2014.  This paper presents the first public data release of HSC-SSP.  This release includes data taken in the first 1.7 years of observations (61.5 nights) and each of the Wide, Deep, and UltraDeep layers covers about 108, 26, and 4 square degrees down to depths of i~26.4, ~26.5, and ~27.2 mag, respectively (5 sigma for point sources).  All the layers are observed in 5 broad-bands (grizy) and the Deep and UltraDeep layers are observed in narrow-bands as well.  Achieve an impressive image quality of 0.6" in the i-band in the Wide layer.  Show that 1-2% PSF photometry (rms) both internally and externally (against Pan-STARRS1) is achieved, and ~10mas and ~40mas internal and external astrometric accuracy, respectively.  Both the calibrated images and catalogs are made available to the community through dedicated user interfaces and database servers.  In addition to the pipeline products, also provide value-added products such as photometric redshifts and a collection of public spectroscopic redshifts.  Detailed descriptions of all the data can be found online.  The data release website is hsc-release.mtk.nao.ac.jp.


1702.08485
The weak lensing masses of filaments between luminous red galaxies
Epps, Hudson

In the standard model of non-linear structure formation, a cosmic web of dark-matter dominated filaments connects dark matter also.  In this paper, stack the weak lensing signal of an ensemble of filaments between groups and clusters of galaxies.  Specifically, detect the weak lensing signal, using CFHTLenS galaxy ellipticities, from stacked filaments between SDSS-III/BOSS luminous red galaxies (LRGs).  As a control, compare the physical LRG pairs with projected LRG pairs that are more widely separated in redshift space.  Detect the excess filament mass density in the projected pairs at the 5 sigma level, finding a mass of (1.6±0.3)e13 Msun for a stacked filament region 7.1 Mpc/h long and 2.5 Mpc/h wide.  This filament signal is compared with a model based on the 3-pt galaxy-galaxyconvergence correlation function, as developed in Clampitt, Jain & Takada (2014), yielding reasonable agreement.


1702.08614
Testing redMaPPer centering probabilities using galaxy clustering and galaxy-galaxy lensing
Hikage, Mandelbaum, Leauthaud, Rozo, Rykoff

Galaxy cluster centering is one of the key issues for precision cosmology studies using galaxy surveys.  The redMaPPer estimates the centering probability of member galaxies from photometric information; however, the centering algorithm has not previously been well-tested.  Test the centering probabilities of redMaPPer cluster catalog using the projected cross correlation between redMaPPer clusters with photometric red galaxies and galaxy-galaxy lensing.  Focus on the subsample of redMaPPer clusters in which the redMaPPer central galaxies (RMCGs) are not the brightest member galaxies (BMEM) and both of them have spectroscopic redshift.  This subsample represents nearly 10% of the whole cluster sample.  Also make a "High Pcen" sample where the central probability of RMCGs is larger than 99% to be used as a reference sample of central galaxies.  Find a clear difference in the cross-correlation measurements between RMCGs and BMEMs, and the estimated centering probability is 74±10% for RMCGs and 13±4% for BMEMs in the sample.  These values are in agreement with the central probability values reported by redMaPPer (75% for RMCG and 10% for BMEMs) within 1 sigma.  The analysis provides a strong consistency test of the redMaPPer centering probabilities.  The results suggest that redMaPPer centering probabilities are reliably estimated, and that the brightest galaxy in the cluster is not always the central galaxy.