Day 1787

Monday, Tuesday, Wednesday, Thursday, Friday.

2012.09175

Shape noise and dispersion in precision weak lensing

Gurri, et al

We analyse the first measurements from precision weak lensing (PWL): a new methodology for measuring individual galaxy-galaxy weak lensing through velocity information. Our goal is to understand the observed shear distribution from PWL, which is broader than can be explained by the statistical measurement errors. We identify two possible sources of scatter to explain the observed distribution: a shape noise term associated with the underlying assumption of circular stable rotation, and an astrophysical signal consistent with a log-normal dispersion around the stellar-to-halo mass relation (SHMR). We have modelled the observed distribution as the combination of those two factors and quantified their most likely values given our data. For the current sample, we measure an effective shape noise of σγ=0.024±0.007, highlighting the low noise impact of the method and positioning PWL as ∼10 times more precise than conventional weak lensing. We also measure an average dispersion in shears of ξγ=0.53+0.26−0.28\,dex over the range of 8.5<logM⋆<11. With the most basic assumption of γ∼Mh, our dispersion measurements suggest a higher than expected dispersion in the SHMR at constant stellar mass.

2012.09196

The parallax of Omega Cenetauri measured from Gaia EDR3 and a direct, geometric calibration of the Tip of the Red Giant Branch and the Hubble constant

Soltis, Casertano, Riess

We use data from the ESA Gaia mission Early Data Release 3 (EDR3) to measure the trigonometric parallax of ω Cen, the first high precision parallax measurement for the most massive globular cluster in the Milky Way. We use a combination of positional and high quality proper motion data from EDR3 to identify over 100,000 cluster members, of which 67,000 are in the magnitude and color range where EDR3 parallaxes are best calibrated. We find the estimated parallax to be robust, demonstrating good control of systematics within the color-magnitude diagram of the cluster. We find a parallax for the cluster of 0.191±0.001 (statistical) ±0.004 (systematic) mas (2.2\% total uncertainty) corresponding to a distance of 5.24±0.11kpc. The parallax of ω Cen provides a unique opportunity to directly and geometrically calibrate the luminosity of the Tip of the Red Giant Branch (TRGB) because it is the only cluster with sufficient mass to provide enough red giant stars, more than 100 one magnitude below the tip, for a precise, model-free measurement of the tip. Combined with the pre-existing and most widely-used measurements of the tip and foreground Milky Way extinction, we find MI,TRGB=−3.97±0.06 mag for the I-band luminosity of the blue edge. Using the TRGB luminosity calibrated from the Gaia EDR3 parallax of ω Cen to calibrate the luminosity of SNIa results in a value for the Hubble constant of H0=72.1±2.0 km s−1 Mpc−1. We make the data for the stars in ω Cen available electronically and encourage independent analyses of the results presented here.

2012.09204

The proper motion of Andromeda from Gaia eDR3: confirming a nearly radial orbit

Salomon, et al

We present an analysis of the proper motion of the Andromeda galaxy (M31), based on the Early Third Data Release of the {\it Gaia} mission. We use the {\it Gaia} photometry to select young blue main sequence stars, and apply several quality cuts to obtain clean samples of these tracers. After correcting the proper motion measurements for the internal rotation of the M31 disk motion, we derive an apparent motion of 53.6±7.7μas/yr with respect to the {\it Gaia} reference frame, or 62.0±9.6μas/yr after applying a zero-point correction determined from quasars within 20deg from M31. Accounting for the Solar reflex motion we deduce a relative velocity between Andromeda and the Milky way (in a non-rotating frame at the current location of the Sun) of 46.7±40.8km.s−1, (along right ascension) and −64.7±31.7km.s−1 (along declination), with a total transverse velocity of Vtrans=79.8±38.3km.s−1. These values are consistent with (but more accurate than) earlier Hubble Space Telescope measurements that predict future merger between the two galaxies. We also note a surprisingly large difference in the derived proper motion between the blue stars in M31 and samples of red stars that appear to lie in that galaxy. We suspect that this is due to contamination from a foreground stellar stream.

2012.09218

Neutron stars as probes of dark matter

Pérez-García, Silk

Neutron Stars (NSs) are compact stellar objects that are stable solutions in General Relativity. Their internal structure is usually described using an equation of state that involves the presence of ordinary matter and its interactions. However there is now a large consensus that an elusive sector of matter in the Universe, described as dark matter, remains as yet undiscovered. In such a case, NSs should contain both, baryonic and dark matter. We argue that depending on the nature of the dark matter and in certain circumstances, the two matter components would form a mixture inside NSs that could trigger further changes, some of them observable. The very existence of NSs constrains the nature and interactions of dark matter in the Universe

2012.09554

Assessing tension metrics with Dark Energy Survey and Planck data

Lemos, et al

Quantifying tensions -- inconsistencies amongst measurements of cosmological parameters by different experiments -- has emerged as a crucial part of modern cosmological data analysis. Statistically-significant tensions between two experiments or cosmological probes may indicate new physics extending beyond the standard cosmological model and need to be promptly identified. We apply several tension estimators proposed in the literature to the Dark Energy Survey (DES) large-scale structure measurement and Planck cosmic microwave background data. We first evaluate the responsiveness of these metrics to an input tension artificially introduced between the two, using synthetic DES data. We then apply the metrics to the comparison of Planck and actual DES Year 1 data. We find that the parameter differences, Eigentension, and Suspiciousness metrics all yield similar results on both simulated and real data, while the Bayes ratio is inconsistent with the rest due to its dependence on the prior volume. Using these metrics, we calculate the tension between DES Year 1 3×2pt and Planck, finding the surveys to be in ∼2.3σ tension under the ΛCDM paradigm. This suite of metrics provides a toolset for robustly testing tensions in the DES Year 3 data and beyond.

2012.09614

Impact of baryons in cosmic shear analyses with tomographic aperture mass statistics

Martinet, et al

Non-Gaussian cosmic shear statistics based on weak-lensing aperture mass (Map) maps can outperform the classical shear two-point correlation function (γ-2PCF) in terms of cosmological constraining power. Reaching the full potential of these new estimators however requires an accurate modeling of the physics of baryons as the extra non-Gaussian information mostly reside at small scales. We present one such modeling based on the Magneticum hydrodynamical simulation for the KiDS-450, DES-Y1, and a Euclid-like surveys. We compute the bias due to baryons on the lensing PDF and the distribution of peaks and voids in Map maps and propagate it to the cosmological forecasts on the structure growth parameter S8, the matter density parameter Ωm and the dark energy equation of state w0, using the SLICS and cosmo-SLICS sets of dark matter only simulations. We report a negative bias of a few percents on S8 and Ωm and also measure a positive bias of the same level on w0 when including a tomographic decomposition. These biases are increased to the order of ∼5% when combining Map statistics with the γ-2PCF as these estimators show similar dependency on the AGN feedback. We verify that these biases constitute less than a 1σ shift on the probed cosmological parameters for current cosmic shear surveys. Baryons, however, need to be accounted for at the percent level for future Stage IV surveys and we propose to include uncertainty on the AGN feedback amplitude by marginalizing over this parameter using multiple simulations such as those presented in this paper. Finally, we explore the possibility of mitigating the impact of baryons by filtering the Map map but find that this process would require to suppress the small-scale information to a point where the constraints would no longer be competitive.

2012.07707

Self-calibration and robust propagation of photometric redshift distribution uncertainties in weak gravitational lensing

Stölzner, Joachimi, Korn, Hildebrandt, Wright

We present a method that accurately propagates residual uncertainties in photometric redshift distributions into the cosmological inference from weak lensing measurements. The redshift distributions of tomographic redshift bins are parameterised using a flexible modified Gaussian mixture model. We fit this model to pre-calibrated redshift distributions and implement an analytic marginalisation over the potentially several hundred redshift nuisance parameters in the weak lensing likelihood, which is demonstrated to accurately recover the cosmological posterior. By iteratively fitting cosmological and nuisance parameters arising from the redshift distribution model, we perform a self-calibration of the redshift distributions via the tomographic cosmic shear measurements. Our method is applied to the third data release of the Kilo-Degree Survey combined with the VISTA Kilo-Degree Infrared Galaxy Survey (KV450). We find constraints on cosmological parameters that are in very good agreement with the fiducial KV450 cosmic shear analysis and investigate the effects of the more flexible model on the self-calibrated redshift distributions. We observe posterior shifts of the medians of the five tomographic redshift distributions of up to Δz≈0.02, which are however degenerate with an observed decrease of the amplitude of intrinsic galaxy alignments by about 10%.

2012.07266

MADLens, a python package for fast and differentiable non-Gaussian lensing simulations

Böhm, Feng, Lee, Dai

We present MADLens a python package for producing non-Gaussian lensing convergence maps at arbitrary source redshifts with unprecedented precision. MADLens is designed to achieve high accuracy while keeping computational costs as low as possible. A MADLens simulation with only 2563 particles produces convergence maps whose power agree with theoretical lensing power spectra up to L=10000 within the accuracy limits of HaloFit. This is made possible by a combination of a highly parallelizable particle-mesh algorithm, a sub-evolution scheme in the lensing projection, and a machine-learning inspired sharpening step. Further, MADLens is fully differentiable with respect to the initial conditions of the underlying particle-mesh simulations and a number of cosmological parameters. These properties allow MADLens to be used as a forward model in Bayesian inference algorithms that require optimization or derivative-aided sampling. Another use case for MADLens is the production of large, high resolution simulation sets as they are required for training novel deep-learning-based lensing analysis tools. We make the MADLens package publicly available under a Creative Commons License (this https URL).

2012.07071

The role of dark matter halo in the evolution of the non-stationary disk of spiral galaxies

Mirtadjieva, Mannapova

In this paper, we consider the problem of the evolution of the disk subsystem of galaxies in view of the halo. To this end, we have studied the dependence of the evolution of a non-linearly non-radially disk oscillating in its plane depending on the basic parameters of the dark matter halo numerically. The dark matter halo stabilizes the instabilities in the plane of the disk, but destabilizes its vertical oscillations. The global disk structure is dependent strongly on the mass and shape of the of dark matter halo. The evolutionary dependence of the oscillation process of a self-gravitating disk versus the indicated parameters of the dark matter halo are constructed.

2012.06611

A stringent upper limit on dark matter self-interaction cross section from cluster strong lensing

Andrade, et al

We analyze strongly lensed images in 8 galaxy clusters to measure their dark matter density profiles in the radial region between 10 kpc and 100 kpc, and use this to constrain the self-interaction cross section of dark matter (DM) particles. We infer the mass profiles of the central DM halos, bright central galaxies, key member galaxies, and DM subhalos for the member galaxies for all 8 clusters using the QLens code. The inferred DM halo surface densities are fit to a self-interacting dark matter (SIDM) model, which allows us to constrain the self-interaction cross section. When our full method is applied to mock data generated from two clusters in the Illustris-TNG simulation, we find results consistent with no dark matter self-interactions as expected. For the eight observed clusters with maximum circular velocities in the range of 1400 to 2000 km/s, we find that the upper limit for the self-interaction cross section per unit mass of dark matter is 0.065 cm2/gat the 95% confidence level.

2012.08467

Organized randoms: learning and correcting for systematic galaxy clustering patterns in KiDS using self-organizing maps

Johnston, et al

We present a new method for the mitigation of observational systematic effects in angular galaxy clustering via corrective random galaxy catalogues. Real and synthetic galaxy data, from the Kilo Degree Survey's (KiDS) 4th Data Release (KiDS-1000) and the Full-sky Lognormal Astro-fields Simulation Kit (FLASK) package respectively, are used to train self-organising maps (SOMs) to learn the multivariate relationships between observed galaxy number density and up to six systematic-tracer variables, including seeing, Galactic dust extinction, and Galactic stellar density. We then create `organised' randoms, i.e. random galaxy catalogues with spatially variable number densities, mimicking the learnt systematic density modes in the data. Using realistically biased mock data, we show that these organised randoms consistently subtract spurious density modes from the two-point angular correlation function w(ϑ), correcting biases of up to 12σ in the mean clustering amplitude to as low as 0.1σ, over a high signal-to-noise angular range of 7-100 arcmin. Their performance is also validated for angular clustering cross-correlations in a bright, flux-limited subset of KiDS-1000, comparing against an analogous sample constructed from highly-complete spectroscopic redshift data. Each organised random catalogue object is a `clone' carrying the properties of a real galaxy, and is distributed throughout the survey footprint according to the parent galaxy's position in systematics-space. Thus, sub-sample randoms are readily derived from a single master random catalogue via the same selection as applied to the real galaxies. Our method is expected to improve in performance with increased survey area, galaxy number density, and systematic contamination, making organised randoms extremely promising for current and future clustering analyses of faint samples.

2012.08423

Estimating low-order aberrations through a Lyot coronagraph with a Zernike wavefront sensor for exoplanet imaging

Pourcelot, et al

Imaging exo-Earths is an exciting but challenging task because of the 10^-10 contrast ratio between these planets and their host star at separations narrower than 100 mas. Large segmented aperture space telescopes enable the sensitivity needed to observe a large number of planets. Combined with coronagraphs with wavefront control, they present a promising avenue to generate a high-contrast region in the image of an observed star. 
Another key aspect is the required stability in telescope pointing, focusing, and co-phasing of the segments of the telescope primary mirror for long-exposure observations of rocky planets for several hours to a few days. These wavefront errors should be stable down to a few tens of picometers RMS, requiring a permanent active correction of these errors during the observing sequence. To calibrate these pointing errors and other critical low-order aberrations, we propose a wavefront sensing path based on Zernike phase-contrast methods to analyze the starlight that is filtered out by the coronagraph at the telescope focus. In this work we present the analytical retrieval of the incoming low order aberrations in the starlight beam that is filtered out by an Apodized Pupil Lyot Coronagraph, one of the leading coronagraph types for starlight suppression. We implement this approach numerically for the active control of these aberrations and present an application with our first experimental results on the High-contrast imager for Complex Aperture Telescopes (HiCAT) testbed, the STScI testbed for Earth-twin observations with future large space observatories, such as LUVOIR and HabEx, two NASA flagship mission concepts.

2012.08292

Does the observational data favor a local void?

Cai, et al

The increasing tension between the different local direct measurements of the Hubble expansion rate and that inferred from the Cosmic Microwave Background observation by Λ-Cold-Dark-Matter model could be a smoking gun of new physics, if not caused by either observational systematics or local bias. We complete previous investigation on the local bias from a local void by globally fitting the Pantheon sample over all parameters in the radial profile function of a local void described by an inhomogeneous but isotropic Lemaître-Tolman-Bondi metric with a cosmological constant. Our conclusion strengths the previous studies that the current tension on Hubble constant cannot be saved by a local void alone.

2012.08267

Analytical model-based analysis of long-exposure images from ground-based telescopes

Leboulleux, et al

The search for Earth-like exoplanets requires high-contrast and high-angular resolution instruments, which designs can be very complex: they need an adaptive optics system to compensate for the effect of the atmospheric turbulence on image quality and a coronagraph to reduce the starlight and enable the companion imaging. During the instrument design phase and the error budget process, studies of performance as a function of optical errors are needed and require multiple end-to-end numerical simulations of wavefront errors through the optical system. 
In particular, the detailed analysis of long-exposure images enables to evaluate the image quality (photon noise level, impact of optical aberrations and of adaptive optics residuals, etc.). Nowadays simulating one long but finite exposure image means drawing several thousands of random frozen phase screens, simulating the image associated with each of them after propagation through the imaging instrument, and averaging all the images. Such a process is time consuming, demands a great deal of computer resources, and limits the number of parametric optimization. 
We propose an alternative and innovative method to directly express the statistics of ground-based images for long but finite exposure times. It is based on an analytical model, which only requires the statistical properties of the atmospheric turbulence. Such a method can be applied to optimize the design of future instruments such as SPHERE+ (VLT) or the planetary camera and spectrograph (PCS - ELT) or any ground-based instrument.

2012.08082

Anomaly detection in astronomical images with generative adversarial networks

Storey-Fisher, et al

We present an anomaly detection method using Wasserstein generative adversarial networks (WGANs) on optical galaxy images from the wide-field survey conducted with the Hyper Suprime-Cam (HSC) on the Subaru Telescope in Hawai'i. The WGAN is trained on the entire sample, and learns to generate realistic HSC-like images that follow the distribution of the training data. We identify images which are less well-represented in the generator's latent space, and which the discriminator flags as less realistic; these are thus anomalous with respect to the rest of the data. We propose a new approach to characterize these anomalies based on a convolutional autoencoder (CAE) to reduce the dimensionality of the residual differences between the real and WGAN-reconstructed images. We construct a subsample of ~9,000 highly anomalous images from our nearly million object sample, and further identify interesting anomalies within these; these include galaxy mergers, tidal features, and extreme star-forming galaxies. The proposed approach could boost unsupervised discovery in the era of big data astrophysics.

2012.07960

Observations of the Lyman-a universe

Ouchi, ,et al

Hydrogen Lyman-α (Lyα) emission has been one of the major observational probes for the high redshift universe, since the first discoveries of high-z Lyα emitting galaxies in the late 1990s. Due to the strong Lyα emission originated by resonant scattering and recombination of the most-abundant element, Lyα observations witness not only HII regions of star formation and AGN but also diffuse HI gas in the circum-galactic medium (CGM) and the inter-galactic medium (IGM). Here we review Lyα sources, and present theoretical interpretations reached to date. We conclude that: 1) A typical Lyα emitter (LAE) at z≳2 with a L∗ Lyα luminosity is a high-z counterpart of a local dwarf galaxy, a compact metal-poor star-forming galaxy (SFG) with an approximate stellar (halo) mass and star-formation rate of 108−9M⊙ (1010−11M⊙) and 1−10M⊙ yr−1, respectively; 2) High-z SFGs ubiquitously have a diffuse Lyα emitting halo in the CGM extending to the halo virial radius and beyond; 3) Remaining neutral hydrogen at the epoch of reionization makes a strong dimming of Lyα emission for galaxies at z>6 that suggest the late reionization history. The next generation large telescope projects will combine Lyαemission data with HI Lyα absorptions and 21cm radio data that map out the majority of hydrogen (HI+HII) gas, uncovering the exchanges of i) matter by outflow/inflow and ii) radiation, relevant to cosmic reionization, between galaxies and the CGM/IGM.

2012.08567

DES Y3  results: blending shear and redshift biases in image simulations

MacCrann, et al

As the statistical power of galaxy weak lensing reaches percent level precision, large, realistic and robust simulations are required to calibrate observational systematics, especially given the increased importance of object blending as survey depths increase. To capture the coupled effects of blending in both shear and photometric redshift calibration, we define the effective redshift distribution for lensing, nγ(z), and describe how to estimate it using image simulations. We use an extensive suite of tailored image simulations to characterize the performance of the shear estimation pipeline applied to the Dark Energy Survey (DES) Year 3 dataset. We describe the multi-band, multi-epoch simulations, and demonstrate their high level of realism through comparisons to the real DES data. We isolate the effects that generate shear calibration biases by running variations on our fiducial simulation, and find that blending-related effects are the dominant contribution to the mean multiplicative bias of approximately −2%. By generating simulations with input shear signals that vary with redshift, we calibrate biases in our estimation of the effective redshfit distribution, and demonstrate the importance of this approach when blending is present. We provide corrected effective redshift distributions that incorporate statistical and systematic uncertainties, ready for use in DES Year 3 weak lensing analyses.

2012.08566

Dark Energy Survey Year 3 results: redshift calibration of the weak lensing source galaxies

Myles, et al

Determining the distribution of redshifts of galaxies observed by wide-field photometric experiments like the Dark Energy Survey is an essential component to mapping the matter density field with gravitational lensing. In this work we describe the methods used to assign individual weak lensing source galaxies from the Dark Energy Survey Year 3 Weak Lensing Source Catalogue to four tomographic bins and to estimate the redshift distributions in these bins. As the first application of these methods to data, we validate that the assumptions made apply to the DES Y3 weak lensing source galaxies and develop a full treatment of systematic uncertainties. Our method consists of combining information from three independent likelihood functions: Self-Organizing Map p(z)(SOMPZ), a method for constraining redshifts from galaxy photometry; clustering redshifts (WZ), constraints on redshifts from cross-correlations of galaxy density functions; and shear ratios (SR), which provide constraints on redshifts from the ratios of the galaxy-shear correlation functions at small scales. Finally, we describe how these independent probes are combined to yield an ensemble of redshift distributions encapsulating our full uncertainty. We calibrate redshifts with combined effective uncertainties of σ⟨z⟩∼0.01 on the mean redshift in each tomographic bin.

2012.08534

Cosmic distances calibrated to 1% precision with Gaia EDR3 parallaxes and Hubble Space Telescope photometry of 75 Milky Way Cepheids confirm tension with LambdaCDM

Riess, et al

We present an expanded sample of 75 Milky Way Cepheids with Hubble Space Telescope (HST) photometry and Gaia EDR3 parallaxes which we use to recalibrate the extragalactic distance ladder and refine the determination of the Hubble constant. All HST observations were obtained with the same instrument (WFC3) and filters (F555W, F814W, F160W) used for imaging of extragalactic Cepheids in Type Ia supernova (SN Ia) hosts. The HST observations used the WFC3 spatial scanning mode to mitigate saturation and reduce pixel-to-pixel calibration errors, reaching a mean photometric error of 5 millimags per observation. We use new Gaia EDR3 parallaxes, vastly improved since DR2, and the Period-Luminosity (PL) relation of these Cepheids to simultaneously calibrate the extragalactic distance ladder and to refine the determination of the Gaia EDR3 parallax offset. The resulting geometric calibration of Cepheid luminosities has 1.0% precision, better than any alternative geometric anchor. Applied to the calibration of SNe~Ia, it results in a measurement of the Hubble constant of 73.0 +/- 1.4 km/sec/Mpc, in good agreement with conclusions based on earlier Gaia data releases. We also find the slope of the Cepheid PL relation in the Milky Way, and the metallicity dependence of its zeropoint, to be in good agreement with the mean values derived from other galaxies. In combination with the best complementary sources of Cepheid calibration, we reach 1.8% precision and find H_0=73.2 +/- 1.3 km/sec/Mpc, a 4.2 sigma difference with the prediction from Planck CMB observations under LambdaCDM. We expect to reach ~1.3% precision in the near term from an expanded sample of ~40 SNe Ia in Cepheid hosts.

2012.09620

Analytical solution to the zonal harmonics problem using Koopman Operator Theory

Arnas, Linares

This work introduces the use of the Koopman Operator Theory to generate analytical solutions for the zonal harmonics problem of a satellite orbiting a non spherical celestial body. Particularly, the solution proposed directly provides the osculating evolution of the system and can be automated to generate any approximation order to the solution. Moreover, this manuscript defines a modified set of orbital elements that can be applied to any kind of orbit and that allows the Koopman Operator to generate stable and accurate solutions. In that regard, several examples of application are included, showing that the proposed methodology can be used in any kind of orbit, including circular, elliptic, parabolic and hyperbolic orbits.

2012.09255

Gravitational waves from density perturbations in an early matter domination era

Dalianis, Kouvaris

We calculate the gravitational wave background produced from density perturbations in an early matter domination era where primordial black holes form. The formation of black holes requires perturbations out of the linear regime. Space with such perturbations reach a maximum expansion before it collapses asymmetrically forming a Zel'dovich pancake which depending on the parameters can either lead to a black hole or a virialized halo. In both cases and due to the asymmetry of the collapsing matter, a quadrupole moment generates gravitational waves which leave an imprint in the form of a stochastic background that can be detectable by near future gravitational interferometers.

2012.09240

Space occupancy in low-earth orbit

Bombardelli, et al

With the upcoming launch of large constellations of satellites in the low-Earth orbit (LEO) region it will become important to organize the physical space occupied by the different operating satellites in order to minimize critical conjunctions and avoid collisions. Here, we introduce the definition of space occupancy as the domain occupied by an individual satellite as it moves along its nominal orbit under the effects of environmental perturbations throughout a given interval of time. After showing that space occupancy for the zonal problem is intimately linked to the concept of frozen orbits and proper eccentricity, we provide frozen-orbit initial conditions in osculating element space and obtain the frozen-orbit polar equation to describe the space occupancy region in closed analytical form. We then analyze the problem of minimizing space occupancy in a realistic model including tesseral harmonics, third-body perturbations, solar radiation pressure, and drag. The corresponding initial conditions, leading to what we call minimum space occupancy (MiSO) orbits, are obtained numerically for a set of representative configurations in LEO. The implications for the use of MiSO orbits to optimize the design of mega-constellations are discussed.