Location: Guildhall Studio

H5 - Wednesday 14:00-15:40 (Hendrik Hildebrandt)

New observation for MeV gamma spectra and distributions of both Galactic Center and Cosmic Background MeV gammas be SMILE2+ balloon-borne experiment


Toru Tanimori (Physics division, Graduate School of Science, Kyoto University)

Recently, it has been pointed out the lack of the precise data and the enough sensitive observation opportunity for astronomical MeV gamma rays from lots of fields such as GRB, Supernovae, Cosmic-ray, Nucleosynthesis, evolution of galaxies and AGN, JET, solar physics, and Dark matter indirect search etc. For example, only COMPTEL provided two spectra of Galactic Diffuse MeV gammas (GDMG) and Cosmic Background MeV gammas (CBMG), which are very important for the evolution of galaxies and AGN and indirect search of light DMs. In particular, recently the MeV gammas of GDMG is pointed out to be more sensitive for DM than Galactic Diffuse GeV gammas due to its simple astronomical gamma sources. However, those two spectra included large statistical and systematic errors in spite of 9years observation, since all instruments for MeV gammas suffered from severe radiation background generated with the interaction of cosmic-rays and satellite in space. Thus, experimentally those detections are very difficult even at present.
In 2018 April, we (SMILE-project in Comic-ray Group of Kyoto University) have observed MeV gamma rays for southern hemisphere by Electron Tracking Compton Camera (ETCC) using JAXA one-day balloon at Australia (SMILE2+ Project). By measuring all parameters of Compton scattering in each gamma, ETCC has achieved for the first time to obtain the complete directions of all MeV gammas same as optical telescopes, and to distinguish signal gammas completely from huge background gammas in space. In this observation, ETCC with a large Field of View (FoV) of 3sr observed MeV gammas from 3/5 of all sky including Galactic Center, crab, and the most of CBMG. By reconstructing the Compton process, we successfully obtained pure comic gammas by reducing background by more 2 orders, which is clearly certificated by the obvious enhancement of detected gamma flux with ~30% during Galactic Center passing through the FoV. It is certainly consistent with the ratio of CBMG and GDMG observed so far in both sub-MeV (0.2-1MeV) and MeV (1-7MeV) regions. 511keV line gamma and GDMG in sub-MeV are detected with ~5 and >10 sigma, respectively. Also we have preliminarily obtained the CDMG in MeV with >10sigma and ~10^5 events of CBMG in which contains only a few 10% background for getting its spectrum and distribution Thus, we obtained good data with high statistics and very low systematics even one day observation. Here we will present fluxes and distributions of CBMG and GDMG from sub=MeV to MeV region, which will be a first reliable data for discussing above issues. In addition, we present the reliable way to reach ~3 order better sensitivity than present ones for exploring “so-called” MeV Gap (0.1-50MeV).

Dark Energy Survey Year 3 cosmic shear


Alexandra Amon (Kavli Institute for Particle and Cosmology, Stanford University )

I will present the current status of the weak lensing analysis from the Dark Energy Survey (DES) Year 3 data. This analysis spans the full 5000 sq. deg. of sky, in riz photometric bands, with over one hundred million galaxies. The dataset includes 8-band photometry in 4 deep fields from a combination of DES and Vista, key to the new approach for the estimation calibration of the redshift distribution of the sample. I will detail the status of the redshift analysis and shear catalog validation in the pursuit of unprecedented measurements of the two-point cosmic shear correlation function. The derived cosmological constraints will be the the most precise from weak-lensing cosmic shear to date and will allow us to test consistency with those from the cosmic microwave background (CMB) and the standard cosmological model, LCDM. I will focus on the steps we take to ensure the robustness of the analysis. Finally, I will report on the outlook for future cosmic shear analyses from DES Year 5 and LSST and discuss challenges in achieving a control of systematics that allows us to take full advantage of the available statistical power of our shear catalogs.

Constraining Decaying Dark Matter in the Dark Energy Survey


Angela Chen (Physics, University of Michigan)

Recent cosmological observations have revealed a discrepancy in Hubble
constant at 4σ level between early and late universe probes. We study a class
of decaying dark matter models as a possible solution to the much-discussed
observed tensions between early- and late- universe probes. We test the model
against present-day data, focusing on are DES 3x2pt correlation function data,
and Planck TT, TE, and EE power spectra. We pay particular attention on the
treatment of non-linearities and massive neutrinos. The goal of this ongoing
study, performed within the DES analysis framework, is to provide a stringent
test of the decaying dark matter models against cutting-edge data.

Spectroscopic galaxy surveys: near and far.


Michael Wilson (Physics Division, Lawrence Berkeley National Lab. )

DESI has seen first light in late 2019, with survey validation and first science data to be taken in early 2020.
With the resulting redshift-space distortions signal, we will reshape our understanding of Dark Energy and the
Early Universe. I’ll report on the planning for early science and lead into what might happen after DESI. Specifically,
on the motivation and potential for a high-redshift survey of 2 < z < 5 Lyman-break galaxies. This, in synergy with
CMB lensing, looks a highly promising measure of primordial non-Gaussianity.

H6 - Wednesday 16:10-17:50 (Hendrik Hildebrandt)

The impact of super – sample covariance on Fisher matrix forecasts for the neutrino mass


Vincenzo Fabrizio Cardone (I.N.A.F. – Osservatorio Astronomico di Roma)

We revisit the constraints that future surveys will put on the mass of neutrinos including the impact of the super – sample covariance. We perform Fisher matrix forecasts using as observables cosmic shear tomography, photometric and spectroscopic galaxy clustering, and the cross – correlation among them. We compare the results without and with the inclusion of the super – sample covariance term quantifying the degradation of the constraints.

The signature of primordial black holes in the dark matter halos of galaxies


Michael Hawkins (Institute for Astronomy, University of Edinburgh)

This talk investigates the claim that stars in the lensing galaxy of a gravitationally lensed quasar system can always account for the observed microlensing of the individual quasar images. A small sample of gravitationally lensed quasar systems was chosen where the quasar images appear to lie on the fringe of the stellar distribution of the lensing galaxy. As with most quasar systems, all the individual quasar images were observed to be microlensed. The surface brightness of the lensing galaxy at the positions of the quasar images was measured from HST frames, and converted to stellar surface mass density. The surface density of smoothly distributed dark matter at the image positions was obtained from lensing models of the quasar systems and applied to the stellar surface mass density to give the optical depth to microlensing. This was then used to assess the probability that the stars in the lensing galaxy could be responsible for the observed microlensing. The results were supported by microlensing simulations of the star fields around the quasar images combined with values of convergence and shear from the lensing models. Taken together, the probability that all the observed microlensing is due to stars was found to be 3X10^-4. Errors resulting from surface brightness measurement, mass-to-light ratio and the contribution of the dark matter halo do not significantly affect this result. It is argued that the most plausible candidates for the microlenses are primordial black holes, either in the dark matter halos of the lensing galaxies, or more generally distributed along the lines of sight to the quasars.

A Geometric Probe of Cosmology: Gravitational Lensing Time Delays and Quasar Reverberation Mapping


Angela Ng (Physics, The University of Sydney)

We present a novel, purely geometric test of cosmology based on measurements of differential time delays between images of strongly lensed quasars due to finite source effects. Our approach is solely dependent on cosmology via a ratio of angular diameter distances, the image separation, and the source size. It thereby entirely avoids the challenges of lens modelling that conventionally limit time delay cosmography, and instead entails the lensed reverberation mapping of the quasar Broad Line Region. We demonstrate that differential time delays are measurable with short cadence spectroscopic monitoring of lensed quasars, through the timing of kinematically identified features within the broad emission lines. This provides a geometric determination of an angular diameter distance ratio complementary to standard probes, and as a result is a powerful new method of constraining cosmology.

Cross-correlating the astrophysical gravitational wave background with galaxy catalogues


Omar Contigiani (Lorentz Institute / Leiden Observatory, Leiden University)

We investigate the correlation between the distribution of galaxies and the predicted gravitational wave background of astrophysical origin. We prove that the average contribution to the background as a function of cosmic time can be easily constrained by cross-correlating with galaxy catalogues at different redshifts. Furthermore, the interpretation of this signal allows us to explain and address the discrepant predictions for the autocorrelation signal available in the literature. Because we show that the impact of shot noise is negligible, our results suggest that gravitational wave background is a powerful probe for merger physics when combined with galaxy surveys.

H7 - Thursday 14:00-15:40 (Hendrik Hildebrandt)

Hybrid Map Inference from Large-Scale Galaxy Clustering


Mike Shengbo Wang (Institute of Cosmology and Gravitation, University of Portsmouth)

Upcoming galaxy redshift surveys such as DESI and Euclid will cover a wider and deeper volume of the cosmos, bringing hope to constraining cosmological parameters sensitive to measurements of large-scale fluctuations with unprecedented precision. However, current analysis techniques are designed for smaller surveys, employing various geometrical approximations, such as the plane-parallel limit, that may degrade these constraints. In this talk, we propose a hybrid map approach: the largest fluctuations distorted by radial observational effects are more faithfully captured by a spherical Fourier–Bessel map, and smaller fluctuations are computationally efficiently distilled into a compressed Cartesian map. This approach will be applied to detecting primordial non-Gaussianity through the scale-dependent tracer bias.

Consistent Cosmic Shear Analysis with KiDS and DES


Marika Asgari (Astronomy, University of Edinburgh)

Cosmological constraints from weak lensing surveys are in mild tension with CMB analysis of the Planck data, a result which has sparked both skepticism and excitement within the community. In this talk, I present cosmic shear analyses of KV450 and DES-Y1 data, comparing the cosmological constraints from different two point statistics, exploring their sensitivity to a range of systematic errors.

KiDS + GAMA: constraints on dark energy and modified gravity from combined large-scale structure probes


Alessio Spurio Mancini (Department of Physics and Astronomy, University College London)

The main goal of current and future surveys is to use different cosmological probes to investigate the true nature of cosmic acceleration. In this talk I will present cosmological constraints obtained from a combined analysis of weak gravitational lensing, galaxy-galaxy lensing and galaxy clustering from the Kilo-Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey. With this analysis we set constraints on parameters that describe the Horndeski class of dark energy and modified gravity models, which includes the majority of extensions to ΛCDM that could explain cosmic acceleration. Analysing the KiDS and GAMA datasets in Horndeski gravity rather than in ΛCDM significantly reduces the long-standing tension between the cosmological model favoured by large-scale structure surveys and the best-fitting parameters from Planck measurements of the Cosmic Microwave Background. I will conclude my talk with a look at how these constraints can be improved with future data from Stage IV cosmological surveys such as Euclid.

The cosmology of the low-redshift Universe: Constraining ΛCDM with BOSS and KiDS


Tilman Troester (Institute for Astronomy, University of Edinburgh)

We reanalyse the anisotropic galaxy clustering measurement from the Baryon Oscillation Spectroscopic Survey (BOSS), demonstrating that using the full shape information provides cosmological constraints that are comparable to other low-redshift probes. We find Ωm = 0.317+0.015-0.019, σ8 = 0.710±0.049, and h = 0.704±0.024 for flat ΛCDM cosmologies. We quantify the agreement between the Planck 2018 constraints from the cosmic microwave background and BOSS, finding the two data sets to be consistent within a flat ΛCDM cosmology using the Bayes factor as well as the prior-insensitive suspiciousness statistic.
Combining two low-redshift probes, we jointly analyse the clustering of BOSS galaxies with weak lensing measurements from the Kilo-Degree Survey (KV450). The combination of BOSS and KV450 improves the measurement by up to 45%, constraining σ8 = 0.702±0.029 and S8 = 0.728±0.026, in 3.6σ and 3.4σ sigma tension with Planck, respectively. Over the full 5D parameter space, the odds in favour of single cosmology describing galaxy clustering, lensing, and the cosmic microwave background are 7±2. The suspiciousness statistic signals a 2.1±0.3σ tension between the combined low-redshift probes and measurements from the cosmic microwave background.

H8 - Thursday 16:10-17:50 (Hendrik Hildebrandt)

Euclid Surveys


Roberto Scaramella (INAF – ROme Astronomical Observatory )

We will give a summary of the current status of surveys planned for the Euclid mission. Both the wide and the deep survey will give a wealth of information for Cosmology, Large Scale Structure and galaxy evolution.

The significance of the peculiar motions of the objects in the gravitational lensing time delay calculations


Gihan Weerasekara (Department of Physics, University of Colombo)

A light ray coming from a faraway source can produce multiple images due to the gravitational lensing effects of a nearby object such as a galaxy. There is a difference in light arriving times in these multiple images which is known as gravitational lensing time delay. Objects involved in this scenario, that is the source, the lens and the observer are having random peculiar motions irrespective of the cosmological expansion due to the dark energy. In the present context when the gravitational lensing time delays are calculated the peculiar motion of the objects are neglected. In this research we have calculated more realistic time delays taking into account the peculiar speeds of the objects concerned. In that we have identified the peculiar motion of the lens is having a notable effect in the gravitational lensing time delay. The change in time delay difference due to the peculiar motions is in the order of 5-10 % of the time delay calculated without the peculiar motions. Therefore, this value is significant and cannot be neglected in calculating gravitational lensing time delays.

Weak Lensing with the Lyman Alpha Forest


Sam Youles (ICG, University of Portsmouth)

The Lyman alpha forest in the spectrum of a quasar is displaced by a small angle when the apparent position of the quasar is affected by weak gravitational lensing. These displacements can be seen as localised variations in the 2-point correlation function. We have developed a method to detect this effect, which will enable the reconstruction of the lensing power spectrum. Weak lensing of Lyman-alpha, particularly in cross correlation with CMB lensing, has the potential to place cosmological constraints on the growth of structure.

Strongly Lensed Supernovae as a probe of Cosmology and Astrophysics


Max Foxley-Marrable (Institute of Cosmology and Gravitation, University of Portsmouth)

Strongly gravitationally lensed supernovae (gLSNe) will enable us to probe cosmology and astrophysics in unique ways. Type Ia gLSNe can be used to measure the Hubble Constant (H0) independently of the cosmological distance ladder through time delay cosmography. Additionally, the standardisable nature of Type Ia supernovae (SNe) will afford tight constraints on the mass-sheet degeneracy, arguably the largest source of systematics in lens modelling. I will outline how microlensing can impact the measurement of H0. I will then show that by being selective with our gLSNe sample in LSST, we can potentially obtain an independent measurement of H0 with the mass-sheet degeneracy suppressed at the 0.5% level.

gLSNe could also provide insight into the astrophysics of supernovae. By detecting a gLSNe before the appearance of later multiple images, we could in principle obtain day zero spectra and photometry of the supernova, provided we accurately predict the time delay of the trailing images. I will present forecasts for the annual rates of candidate gLSNe using LSST and ZTF, and forecast peak magnitude distributions for early phase Type Ia (single-degenerate) and Type IIP SNe found in the trailing lensed images.