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We extend the evolution–mapping approach, introduced in the first paper of this series to describe non-linear matter density fluctuations, to statistics of the cosmic velocity field. This framework classifies cosmological parameters into shape parameters, which determine the shape of the linear matter power spectrum, |$P_{\rm L}(k, z)$|⁠ , and evolution parameters, which control its amplitude at any redshift. Evolution–mapping leverages the fact that density fluctuations in cosmologies with identical shape parameters but different evolution parameters exhibit similar non-linear evolutions when expressed as a function of clustering amplitude. We analyse a suite of N-body simulations sharing identical shape parameters but spanning a wide range of evolution parameters. Using a method for estimating the volume-weighted velocity field based on the Voronoi tessellation of simulation particles, we study the non-linear evolution of the velocity divergence power spectrum, |$P_{\theta \theta }(k)$|⁠ , and its cross-power spectrum with the density field, |$P_{\delta \theta }(k)$|⁠. We demonstrate that the evolution–mapping relation applies accurately to |$P_{\theta \theta }(k)$| and |$P_{\delta \theta }(k)$|⁠. While this breaks down in the strongly non-linear regime, deviations can be modelled in terms of differences in the suppression factor, |$g(a) = D(a)/a$|⁠ , similar to those for the density field. Such modelling describes the differences in |$P_{\theta \theta }(k)$| between models with the same linear clustering amplitude to better than 1 per cent accuracy at all scales and redshifts considered. Evolution–mapping simplifies the description of the cosmological dependence of non-linear density and velocity statistics, streamlining the sampling of large cosmological parameter spaces for cosmological analysis. [ABSTRACT FROM AUTHOR]

Approximate N -body methods, such as fastpm and cola , have been successful in modelling halo and galaxy clustering statistics, but their low resolution on small scales is a limitation for applications that require high precision. Full N -body simulations can provide better accuracy but are too computationally expensive for a quick exploration of cosmological parameters. This paper presents a method for correcting distinct haloes identified in fast N -body simulations, so that various halo statistics improve to a percent level accuracy. The scheme seeks to find empirical corrections to halo properties such that the virial mass is the same as that of a corresponding halo in a full N -body simulation. The modified outer density contour of the corrected halo is determined on the basis of the fastpm settings and the number of particles inside the halo. This method only changes some parameters of the halo finder, and does not require any extra CPU-cost. We demonstrate that the adjusted halo catalogues of fastpm simulations significantly improve the precision of halo mass-based statistics from redshifts |$z=0.0$| to 1.0, and that our calibration can be applied to different cosmologies without needing to be recalibrated. [ABSTRACT FROM AUTHOR]

We study how future Type Ia supernovae (SNIa) standard candles detected by the Vera C. Rubin Observatory (LSST) can constrain some cosmological models. We use a realistic 3-yr SNIa simulated data set generated by the LSST Dark Energy Science Collaboration time domain pipeline, which includes a mix of spectroscopic and photometrically identified candidates. We combine these data with cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) measurements to estimate the dark energy model parameters for two models – the baseline Lambda cold dark matter (ΛCDM) and Chevallier–Polarski–Linder (CPL) dark energy parametrization. We compare them with the current constraints obtained from the joint analysis of the latest real data from the Pantheon SNIa compilation, CMB from Planck 2018 and BAO. Our analysis finds tighter constraints on the model parameters along with a significant reduction of correlation between H 0 and σ8,0. We find that LSST is expected to significantly improve upon the existing SNIa data in the critical analysis of cosmological models. [ABSTRACT FROM AUTHOR]

Strong gravitational lensing and microlensing of supernovae (SNe) are emerging as a new probe of cosmology and astrophysics in recent years. We provide an overview of this nascent research field, starting with a summary of the first discoveries of strongly lensed SNe. We describe the use of the time delays between multiple SN images as a way to measure cosmological distances and thus constrain cosmological parameters, particularly the Hubble constant, whose value is currently under heated debates. New methods for measuring the time delays in lensed SNe have been developed, and the sample of lensed SNe from the upcoming Rubin Observatory Legacy Survey of Space and Time (LSST) is expected to provide competitive cosmological constraints. Lensed SNe are also powerful astrophysical probes. We review the usage of lensed SNe to constrain SN progenitors, acquire high-z SN spectra through lensing magnifications, infer SN sizes via microlensing, and measure properties of dust in galaxies. The current challenge in the field is the rarity and difficulty in finding lensed SNe. We describe various methods and ongoing efforts to find these spectacular explosions, forecast the properties of the expected sample of lensed SNe from upcoming surveys particularly the LSST, and summarize the observational follow-up requirements to enable the various scientific studies. We anticipate the upcoming years to be exciting with a boom in lensed SN discoveries. [ABSTRACT FROM AUTHOR]

Hubble constant H 0 and weighted amplitude of matter fluctuations S 8 determinations are biased to higher and lower values, respectively, in the late universe with respect to early universe values inferred by the Planck collaboration within flat ΛCDM cosmology. If these anomalies are physical, that is, not due to systematics, they naively suggest that H 0 decreases and S 8 increases with effective redshift. Here, subjecting matter density today Ω m to a prior, corresponding to a combination of Planck CMB and BAO data, we perform a consistency test of the Planck -ΛCDM cosmology and show that S 8 determinations from f σ8 (z) constraints increase with effective redshift. Due to the redshift evolution, a ∼3σ tension in the S 8 parameter with Planck at lower redshifts remarkably becomes consistent with Planck within 1σ at high redshifts. This provides corroborating support for an S 8 discrepancy that is physical in origin. We further confirm that the flat ΛCDM model is preferred over a theoretically ad hoc model with a jump in S 8 at a given redshift. In the absence of the CMB+BAO Ω m prior, we find that >3σ tensions with Planck in low-redshift data are ameliorated by shifts in the parameters in high-redshift data. Results here and elsewhere suggest that the ΛCDM cosmological parameters are redshift dependent. Fitting parameters that evolve with redshift is a recognizable hallmark of model breakdown. [ABSTRACT FROM AUTHOR]

Unimodular gravity is an alternative theory of gravity to general relativity. The gravitational field equations are given by the trace-free version of Einstein's field equations. Due to the structure of the theory, unimodular gravity admits a diffusion term that characterizes a possible non-conservation of the canonical energy–momentum tensor locally. Employing this feature of unimodular gravity, in this work, we explicitly show how to construct an inflationary phase that can be contrasted with current observations. In particular, we focus on three different inflationary scenarios of physical interest. An important element in these scenarios is that the accelerated expansion is driven by the diffusion term exclusively, i.e. there is no inflaton. Furthermore, the primordial spectrum during inflation is generated by considering inhomogeneous perturbations associated to standard hydrodynamical matter (modelled as a single ultra-relativistic fluid). For each of the scenarios, we obtain the prediction for the primordial spectrum and contrast it with recent observational bounds using Planck 2018 + Bicep2/KECK Array data. [ABSTRACT FROM AUTHOR]

We present an estimate of the bulk flow in a volume of radii 150−200 h−1 Mpc using the minimum variance method with data from the CosmicFlows-4 (CF4) catalogue. The addition of new data in the CF4 has resulted in an increase in the estimate of the bulk flow in a sphere of radius 150 h−1 Mpc relative to the CosmicFlows-3 (CF3). This bulk flow has an |$\sim 0.015~{{\ \rm per\ cent}}$| chance of occurring in the standard cosmological model with cosmic microwave background derived parameters. Given that the CF4 is deeper than the CF3, we were able to use the CF4 to accurately estimate the bulk flow on scales of 200 h−1 Mpc (equivalent to 266 Mpc for Hubble constant H 0 = 75 km s−1 Mpc−1) for the first time. This bulk flow is in even greater tension with the standard model, having |$\sim 1.5\times 10^{-4}\ \%$| probability of occurring. To estimate the bulk flow accurately, we introduce a novel method to calculate distances and velocities from distance moduli that is unbiased and accurate at all distances. Our results are completely independent of the value of H 0. [ABSTRACT FROM AUTHOR]

Type Ia supernovae (SNe Ia), standardizable candles that allow tracing the expansion history of the Universe, are instrumental in constraining cosmological parameters, particularly dark energy. State-of-the-art likelihood-based analyses scale poorly to future large data sets, are limited to simplified probabilistic descriptions, and must explicitly sample a high-dimensional latent posterior to infer the few parameters of interest, which makes them inefficient. Marginal likelihood-free inference, on the other hand, is based on forward simulations of data, and thus can fully account for complicated redshift uncertainties, contamination from non-SN Ia sources, selection effects, and a realistic instrumental model. All latent parameters, including instrumental and survey-related ones, per object and population-level properties, are implicitly marginalized, while the cosmological parameters of interest are inferred directly. As a proof of concept, we apply truncated marginal neural ratio estimation (TMNRE), a form of marginal likelihood-free inference, to bahamas , a Bayesian hierarchical model for salt parameters. We verify that TMNRE produces unbiased and precise posteriors for cosmological parameters from up to 100 000 SNe Ia. With minimal additional effort, we train a network to infer simultaneously the |${\sim}100\, 000$| latent parameters of the supernovae (e.g. absolute brightnesses). In addition, we describe and apply a procedure that utilizes local amortization of the inference to convert the approximate Bayesian posteriors into frequentist confidence regions with exact coverage. Finally, we discuss the planned improvements to the model that are enabled by using a likelihood-free inference framework, like selection effects and non-Ia contamination. [ABSTRACT FROM AUTHOR]

In this paper, we present COMET , a Gaussian process emulator of the galaxy power spectrum multipoles in redshift space. The model predictions are based on one-loop perturbation theory and we consider two alternative descriptions of redshift-space distortions: one that performs a full expansion of the real- to redshift-space mapping, as in recent effective field theory models, and another that preserves the non-perturbative impact of small-scale velocities by means of an effective damping function. The outputs of COMET can be obtained at arbitrary redshifts, for arbitrary fiducial background cosmologies, and for a large parameter space that covers the shape parameters ω c , ω b , and ns , as well as the evolution parameters h ,  As , Ω K , w 0, and wa. This flexibility does not impair COMET 's accuracy, since we exploit an exact degeneracy between the evolution parameters that allows us to train the emulator on a significantly reduced parameter space. While the predictions are sped up by two orders of magnitude, validation tests reveal an accuracy of |$0.1\, {{\ \rm per\ cent}}$| for the monopole and quadrupole (⁠|$0.3\, {{\ \rm per\ cent}}$| for the hexadecapole), or alternatively, better than |$0.25\, \sigma$| for all three multipoles in comparison to statistical uncertainties expected for the Euclid survey with a tenfold increase in volume. We show that these differences translate into shifts in mean posterior values that are at most of the same size, meaning that COMET can be used with the same confidence as the exact underlying models. COMET is a publicly available python package that also provides the tree-level bispectrum multipoles and Gaussian covariance matrices. [ABSTRACT FROM AUTHOR]

We propose a new method to calibrate gamma-ray burst (GRB) correlations employing intermediate redshift data sets, instead of limiting to z ≃ 0 catalogues, and applied it to the well-consolidated Amati correlation. This model-independent calibration technique is based on the Bézier polynomial interpolation of the most updated observational Hubble data and baryonic acoustic oscillations (BAO) and alleviates de facto the well-known circularity problem affecting GRB correlations. In doing so, we also investigate the influence of the BAO scales r s, got from Planck results, and |$r_{\rm s}^{\rm fid}$|⁠ , got from the considered fiducial cosmology, by considering the cases |$(r_{\rm s}/r_{\rm s}^{\rm fid})=1$| and |$(r_{\rm s}/r_{\rm s}^{\rm fid})\ne 1$|⁠. We get constraints on the cosmic parameters, using Markov chain–Monte Carlo simulations, first fixing and then leaving free the spatial curvature density parameter Ωk. Compared to previous literature, we obtain tighter constraints on the mass density parameter Ωm. In particular, our findings turn out to be highly more compatible with those got from standard candle indicators within the Lambda cold dark matter paradigm. Finally, we critically re-examine the recent H 0 tension in view of our outcomes. [ABSTRACT FROM AUTHOR]

We set out to rederive the 8 Hubble parameter values obtained from estimated relative galaxy ages by Simon et al. We find that to obtain the level of precision claimed in H (⁠|$\mathit{ z}$|⁠), unrealistically small galaxy age uncertainties have to be assumed. Also, some parameter values will be correlated. In our analysis we find that the uncertainties in the Hubble parameter values are significantly larger when 8 independent H (⁠|$\mathit{ z}$|⁠) are obtained using Monte Carlo sampling. Smaller uncertainties can be obtained using Gaussian processes, but at the cost of strongly correlated results. We do not obtain any useful constraints on the Hubble parameter from the galaxy data employed. [ABSTRACT FROM AUTHOR]

Recent works have shown that weak lensing magnification must be included in upcoming large-scale structure analyses, such as for the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST), to avoid biasing the cosmological results. In this work, we investigate whether including magnification has a positive impact on the precision of the cosmological constraints, as well as being necessary to avoid bias. We forecast this using an LSST mock catalogue and a halo model to calculate the galaxy power spectra. We find that including magnification has little effect on the precision of the cosmological parameter constraints for an LSST galaxy clustering analysis, where the halo model parameters are additionally constrained by the galaxy luminosity function. In particular, we find that for the LSST gold sample (i < 25.3) including weak lensing magnification only improves the galaxy clustering constraint on Ωm by a factor of 1.03, and when using a very deep LSST mock sample (i < 26.5) by a factor of 1.3. Since magnification predominantly contributes to the clustering measurement and provides similar information to that of cosmic shear, this improvement would be reduced for a combined galaxy clustering and shear analysis. We also confirm that not modelling weak lensing magnification will catastrophically bias the cosmological results from LSST. Magnification must therefore be included in LSST large-scale structure analyses even though it does not significantly enhance the precision of the cosmological constraints. [ABSTRACT FROM AUTHOR]

Galaxy clusters are biased tracers of the underlying matter density field. At very large radii beyond about 10 Mpc  h −1, the shear profile shows evidence of a second-halo term. This is related to the correlated matter distribution around galaxy clusters and proportional to the so-called halo bias. We present an observational analysis of the halo bias–mass relation based on the AMICO galaxy cluster catalogue, comprising around 7000 candidates detected in the third release of the KiDS survey. We split the cluster sample into 14 redshift-richness bins and derive the halo bias and the virial mass in each bin by means of a stacked weak lensing analysis. The observed halo bias–mass relation and the theoretical predictions based on the Lambda cold dark matter standard cosmological model show an agreement within 2σ. The mean measurements of bias and mass over the full catalogue give |$M_{200c} = (4.9 \pm 0.3) \times 10^{13}\, {\rm M}_{\odot }/{\it h}$| and |$b_h \sigma _8^2 = 1.2 \pm 0.1$|⁠. With the additional prior of a bias–mass relation from numerical simulations, we constrain the normalization of the power spectrum with a fixed matter density Ωm = 0.3, finding σ8 = 0.63 ± 0.10. [ABSTRACT FROM AUTHOR]

We perform a joint BAO and RSD analysis using the eBOSS DR16 LRG and ELG samples in the redshift range of z ∈ [0.6, 1.1], and detect an RSD signal from the cross-power spectrum at a ∼4σ confidence level, i.e. f σ8 = 0.317 ± 0.080 at z eff = 0.77. Based on the chained power spectrum, which is a new development in this work to mitigate the angular systematics, we measure the BAO distances and growth rate simultaneously at two effective redshifts, namely, D M/ r d (z = 0.70) = 17.96 ± 0.51,  D H/ r d (z = 0.70) = 21.22 ± 1.20,  f σ8 (z = 0.70) = 0.43 ± 0.05, and D M/ r d (z = 0.845) = 18.90 ± 0.78,  D H/ r d (z = 0.845) = 20.91 ± 2.86,  f σ8 (z = 0.845) = 0.30 ± 0.08. Combined with BAO measurements including those from the eBOSS DR16 QSO and Lyman-α sample, our measurement has raised the significance level of a non-zero ΩΛ to ∼11σ. The data product of this work is publicly available at https://github.com/icosmology/eBOSS%5fDR16%5fLRGxELG and https://www.sdss.org/science/final-bao-and-rsd-measurements/. [ABSTRACT FROM AUTHOR]

This paper outlines the science case for line-intensity mapping with a space-borne instrument targeting the sub-millimeter (microwaves) to the far-infrared (FIR) wavelength range. Our goal is to observe and characterize the large-scale structure in the Universe from present times to the high redshift Epoch of Reionization. This is essential to constrain the cosmology of our Universe and form a better understanding of various mechanisms that drive galaxy formation and evolution. The proposed frequency range would make it possible to probe important metal cooling lines such as [CII] up to very high redshift as well as a large number of rotational lines of the CO molecule. These can be used to trace molecular gas and dust evolution and constrain the buildup in both the cosmic star formation rate density and the cosmic infrared background (CIB). Moreover, surveys at the highest frequencies will detect FIR lines which are used as diagnostics of galaxies and AGN. Tomography of these lines over a wide redshift range will enable invaluable measurements of the cosmic expansion history at epochs inaccessible to other methods, competitive constraints on the parameters of the standard model of cosmology, and numerous tests of dark matter, dark energy, modified gravity and inflation. To reach these goals, large-scale structure must be mapped over a wide range in frequency to trace its time evolution and the surveyed area needs to be very large to beat cosmic variance. Only a space-borne mission can properly meet these requirements. [ABSTRACT FROM AUTHOR]

Astrocombs are ideal spectrograph calibrators whose limiting precision can be derived using a second, independent, astrocomb system. We therefore analyse data from two astrocombs (one 18 GHz and one 25 GHz) used simultaneously on the HARPS (High Accuracy Radial velocity Planet Searcher) spectrograph at the European Southern Observatory. The first aim of this paper is to quantify the wavelength repeatability achieved by a particular astrocomb. The second aim is to measure wavelength calibration consistency between independent astrocombs, that is to place limits or measure any possible zero-point offsets. We present three main findings, each with important implications for exoplanet detection, varying fundamental constant and redshift drift measurements. First, wavelength calibration procedures are important: using multiple segmented polynomials within one echelle order results in significantly better wavelength calibration compared to using a single higher order polynomial. Segmented polynomials should be used in all applications aimed at precise spectral line position measurements. Secondly, we found that changing astrocombs causes significant zero-point offsets (⁠|${\approx}60\, {\rm cm\, s}^{-1}$| in our raw data) which were removed. Thirdly, astrocombs achieve a precision of |${\lesssim }4\, {\rm cm\, s}^{-1}$| in a single exposure (⁠|${\approx }10{{\,\rm per\,cent}}$| above the measured photon-limited precision) and 1 cm s−1 when time-averaged over a few hours, confirming previous results. Astrocombs therefore provide the technological requirements necessary for detecting Earth–Sun analogues, measuring variations of fundamental constants and the redshift drift. [ABSTRACT FROM AUTHOR]

We develop a cosmological parameter estimation code for (tomographic) angular power spectra analyses of galaxy number counts, for which we include, for the first time, redshift-space distortions (RSDs) in the Limber approximation. This allows for a speed-up in computation time, and we emphasize that only angular scales where the Limber approximation is valid are included in our analysis. Our main result shows that a correct modelling of RSD is crucial not to bias cosmological parameter estimation. This happens not only for spectroscopy-detected galaxies, but even in the case of galaxy surveys with photometric redshift estimates. Moreover, a correct implementation of RSD is especially valuable in alleviating the degeneracy between the amplitude of the underlying matter power spectrum and the galaxy bias. We argue that our findings are particularly relevant for present and planned observational campaigns, such as the Euclid satellite or the Square Kilometre Array, which aim at studying the cosmic large-scale structure and trace its growth over a wide range of redshifts and scales. [ABSTRACT FROM AUTHOR]

The angular power spectrum C ℓ(⁠|$z$| i , |$z$| j ) is a gauge-independent observable that is in principle the natural tool for analysing galaxy number counts. In practice, the problem is that the computational requirements for next-generation spectroscopic surveys such as Euclid and the Square Kilometre Array are currently unfeasible. We propose a new method to save computational time for spectroscopic angular power spectra. This hybrid method is modelled on the Fourier power spectrum approach of treating relatively thick redshift bins (Δ |$z$|  ∼ 0.1) as separate surveys. In the hybrid method, each thick bin is further subdivided into thin bins (δ |$z$|  ∼ 0.01); all the correlations within each thick bin are computed, whilst cross-bin correlations beyond the thick bins are neglected. Constraints on cosmological parameters from the hybrid method are comparable to those from the standard galaxy |$P_{\rm g}({\boldsymbol k},z)$| analysis – but they have the advantage that cosmic evolution, wide-angle, and lensing effects are naturally included, whilst no Alcock–Paczynski correction is needed. The hybrid method delivers much tighter constraints than a 2D tomographic approach that is typical for photometric surveys, which considers only thick bins and the correlations between them. Furthermore, for standard cosmological parameters our method is not biased by neglecting the effects of lensing on number counts, whilst the tomographic method is strongly biased. [ABSTRACT FROM AUTHOR]

We use all available baryon acoustic oscillation distance measurements and Hubble parameter data to constrain the cosmological constant Λ, dynamical dark energy, and spatial curvature in simple cosmological models. We find that the consensus spatially flat ΛCDM (Λ cold dark matter) model provides a reasonable fit to the data, but depending on the Hubble constant prior and cosmological model, it can be a little more than 1σ away from the best-fitting model, which can favour mild dark energy dynamics or non-flat spatial hypersurfaces. [ABSTRACT FROM AUTHOR]

Future Baryon Acoustic Oscillation surveys aim at observing galaxy clustering over a wide range of redshift and galaxy populations at great precision, reaching tenths of a percent, in order to detect any deviation of dark energy from the lambda cold dark matter ($$\rm {\Lambda CDM}$$) model. We utilize a set of paired quasi- N -body FastPM simulations that were designed to mitigate the sample variance effect on the BAO feature and evaluated the BAO systematics as precisely as ∼0.01 per cent. We report anisotropic BAO scale shifts before and after density field reconstruction in the presence of redshift-space distortions over a wide range of redshift, galaxy/halo biases, and shot noise levels. We test different reconstruction schemes and different smoothing filter scales, and introduce physically motivated BAO fitting models. For the first time, we derive a Galilean-invariant infrared resummed model for halos in real and redshift space. We test these models from the perspective of robust BAO measurements and non-BAO information such as growth rate and non-linear bias. We find that pre-reconstruction BAO scale has moderate fitting-model dependence at the level of 0.1–0.2 per cent for matter while the dependence is substantially reduced to less than 0.07 per cent for halos. We find that post-reconstruction BAO shifts are generally reduced to below 0.1 per cent in the presence of galaxy/halo bias and show much smaller fitting model dependence. Different reconstruction conventions can potentially make a much larger difference on the line-of-sight BAO scale, upto 0.3 per cent. Meanwhile, the precision (error) of the BAO measurements is quite consistent regardless of the choice of the fitting model or reconstruction convention. [ABSTRACT FROM AUTHOR]

Motivated by the prospect of the wealth of data arising from the inauguration of the era of gravitational wave detection by ground-based interferometers the DES collaboration, in partnership with members of the LIGO collaboration and members of the astronomical community at large, have established a research program to search for their optical counterparts and to explore their use as cosmological probes. In this talk we present the status of our program and discuss prospects for establishing this new probe as part of the portfolio of the Dark Energy research program in the future, in particular for the next generation survey, LSST. [ABSTRACT FROM AUTHOR]

On August 17, 2017 LIGO/Virgo detected a binary neutron star via gravitational waves. We observed 70 sq-degrees in the LIGO/Virgo spatial localization with the DECam on the 4m Blanco telescope covering 80% of the final map. Our group independently discovered an optical counterpart in NGC 4993. We searched our entire imaged region: the object in NGC 4993 was the only viable candidate. Our observations of NGC4993 show complicated morphology but simple star formation history. Our x-ray and radio observations indicate an off-axis jet as afterglow. Our high-cadence optical and infrared spectra show a source that must be described by at least two components, one of which is dominated by the r-process nucleosynthesis elements characteristic of a kilonova. Our modeling of the light curve demonstrates such a model in which 0.05 M⊙ of material is ejected from the system. Finally, we discuss the first standard siren measurement of H0. [ABSTRACT FROM AUTHOR]

Motivated by the prospect of the wealth of data arising from the inauguration of the era of gravitational wave detection by ground-based interferometers the DES collaboration, in partnership with members of the LIGO collaboration and members of the astronomical community at large, have established a research program to search for their optical counterparts and to explore their use as cosmological probes. In this talk we present the status of our program and discuss prospects for establishing this new probe as part of the portfolio of the Dark Energy research program in the future, in particular for the next generation survey, LSST. [ABSTRACT FROM AUTHOR]

On August 17, 2017 LIGO/Virgo detected a binary neutron star via gravitational waves. We observed 70 sq-degrees in the LIGO/Virgo spatial localization with the DECam on the 4m Blanco telescope covering 80% of the final map. Our group independently discovered an optical counterpart in NGC 4993. We searched our entire imaged region: the object in NGC 4993 was the only viable candidate. Our observations of NGC4993 show complicated morphology but simple star formation history. Our x-ray and radio observations indicate an off-axis jet as afterglow. Our high-cadence optical and infrared spectra show a source that must be described by at least two components, one of which is dominated by the r-process nucleosynthesis elements characteristic of a kilonova. Our modeling of the light curve demonstrates such a model in which 0.05 M⊙ of material is ejected from the system. Finally, we discuss the first standard siren measurement of H0. [ABSTRACT FROM AUTHOR]

The Hubble constant is a key cosmological parameter that sets the present-day expansion rate as well as the age, size, and critical density of the Universe. Intriguingly, there is currently a tension in the measurements of its value in the standard flat ΛCDM model – observations of the Cosmic Microwave Background with the Planck satellite lead to a value of the Hubble constant that is lower than the measurements from the local Cepheids-supernovae distance ladder and strong gravitational lensing. Precise and accurate Hubble constant measurements from independent probes, including water masers, are necessary to assess the significance of this tension and the possible need of new physics beyond the current standard cosmological model. We present the progress toward an accurate Hubble constant determination. [ABSTRACT FROM AUTHOR]

We consider a sample of dwarf galaxies with accurate distances and velocities around 14 massive groups in the Local Volume. We combine all the data into a single synthetic group, and then determine its radius of the zero-velocity surface, separating it against the global cosmic expansion. Our estimation is derived from fitting the the spherical infall model (including effects of the cosmological constant) to the observational data. We found the optimal value of the radius to be 0.93 ± 0.02 Mpc. Assuming the Planck model parameters, it corresponds to the total mass of the synthetic group (1.6 ± 0.2) × 1012 M ⊙. Thus, we obtain the paradoxical result that the total mass of the synthetic group estimated on the scale of 3–4 its virial radius is only 60% of the virial mass estimate. Anyway, we conclude that wide outskirts of the nearby groups do not contain a large amount of hidden mass outside their virial radii. [ABSTRACT FROM AUTHOR]

Two new high-precision measurements of the deuterium abundance from absorbers along the line of sight to the quasar PKS1937–1009 were presented. The absorbers have lower neutral hydrogen column densities (N(HI) ≈ 18 cm − 2 ) than for previous high-precision measurements, boding well for further extensions of the sample due to the plenitude of low column density absorbers. The total high-precision sample now consists of 12 measurements with a weighted average deuterium abundance of D/H = 2 . 55 ± 0 . 02 × 10 − 5 . The sample does not favour a dipole similar to the one detected for the fine structure constant. The increased precision also calls for improved nucleosynthesis predictions. For that purpose we have updated the public AlterBBN code including new reactions, updated nuclear reaction rates, and the possibility of adding new physics such as dark matter. The standard Big Bang Nucleosynthesis prediction of D/H = 2 . 456 ± 0 . 057 × 10 − 5 is consistent with the observed value within 1.7 standard deviations.

Models for galaxy clusters abundance and their spatial distribution are sensitive to cosmological parameters. Present and future surveys will provide high-redshift sample of clusters, such as Dark Energy Survey (z ⩽ 1.3), making cluster number counts one of the most promising cosmological probes. In the literature, some cosmological analyses are carried out using small cluster catalogs (tens to hundreds), like in Sunyaev-Zel'dovich (SZ) surveys. However, it is not guaranteed that maximum likelihood estimators of cosmological parameters are unbiased in this scenario. In this work we study different estimators of the cold dark matter density parameter Ωc, σ8 and the dark energy equation of state parameter w0 obtained from cluster abundance. Using an unbinned likelihood for cluster number counts and the Monte Carlo approach, we determine the presence of bias and how it varies with the size of the sample. Our fiducial models are based on the South Pole Telescope (SPT). We show that the biases from SZ estimators do not go away with increasing sample sizes and they may become the dominant source of error for an all sky survey at the SPT sensitivity. [ABSTRACT FROM PUBLISHER]

The Arecibo Legacy Fast ALFA (ALFALFA) survey is a second generation blind extragalactic HI survey currently in progess which is exploiting Arecibo's superior sensitivity, angular resolution and digital technology to derive a census of the local HI universe over a cosmologically significant volume. As of the time of this meeting, some 4500 good quality extragalactic HI line sources have been identified in about 15% of the final survey area. ALFALFA is detecting HI masses as low as 106M⊙ and as large as 1010.8M⊙ with positional accuracies typically better than 20″, allowing immediate identification of the most probable optical counterparts. Only 3% of all extragalactic HI sources and less than 1% of detections with MH I > 109.5M⊙ cannot be identified with a stellar component. Because ALFALFA is far from complete, the discussion here focuses on limitations of past surveys that ALFALFA will overcome because of its greater volume, sensitivity and reduced susceptibility to source confusion and on a sampling of illustrative preliminary results. First ALFALFA results already suggest, in agreement with previous studies, that there does not appear to be a cosmologically significant population of optically dark but HI rich galaxies. ALFALFA promises a wealthy dataset for the exploration of many issues in near-field cosmology and galaxy evolution studies, setting the stage for their extension to higher redshifts in the future with the Square Kilometer Array (SKA). [ABSTRACT FROM PUBLISHER]

• We suggest the current assignments of spacetime geometries to the Friedmann-Lemaitre-Robertson-Walker (FLRW) model are probably incorrect and suggest more useful descriptions. • This new assignment is consistent with our Universe exhibiting sparse matter density and quasi-Euclidean geometry and the calculated matter density agrees with Big Bang nucleosynthesis calculations. • Assigning a value of 1 for flat spacetime geometry to Friedmann's normalised K is useful for estimating H 0 and will help resolve the "tension" surrounding current estimates by different investigators. • We extend the FLRW model towards the Big Bang and discover a simple explanation of how matter creation developed into the currently geometrically flat Universe with sparse, homogeneous, isotropic matter and energy distributions. The description of spacetime is an fundamental problem of cosmology. We explain why the current assignments of spacetime geometries for Ω k of the Friedmann-Lemaître-Robertson-Walker (FLRW) model are probably incorrect and suggest more useful descriptions. We show that Ω k represents not only curvature but the influence of matter density on the extent of spacetime between massive objects. Recent analyses of supernovae type Ia (SNe Ia) and HII/GEHR data with the FLRW model present the best fits with a small value for Ω m and a large Ω k. These results are consistent with our Universe exhibiting sparse matter density and quasi-Euclidean geometry and the small Ω m value agrees with Big Bang nucleosynthesis calculations. We suggest the geometry of our current Universe is better described by a value for Ω k ≈ 1 rather than 0. As an example we extend the FLRW model towards the Big Bang and discover a simple explanation of how matter creation developed into the currently geometrically flat Universe with sparse, homogeneous, isotropic matter and energy distributions. Assigning Ω k ≈ 1 to describe quasi-Euclidean spacetime geometry is also useful for estimating H 0 and should help resolve the "tension" surrounding current estimates by different investigators. [ABSTRACT FROM AUTHOR]

A new non-parametric method based on Gaussian Processes (GP) was proposed recently to measure the Hubble constant H0. The freedom in this approach comes in the chosen covariance function, which determines how smooth the process is and how nearby points are correlated. We perform coverage tests with a thousand mock samples within the ΛCDM model in order to determine what covariance function provides the least biased results. The function Matérn(5/2) is the best with sligthly higher errors than other covariance functions, although much more stable when compared to standard parametric analyses. [ABSTRACT FROM PUBLISHER]

The location of two nearby galaxy groups within ~20 Mpc in the Leo region allows for a detailed study of low-mass galaxies. A catalog of HI line detections in Leo (9h36m < α < 11h36m, +8° < δ < +16°) has been made from the blind HI survey ALFALFA. More sensitive single-pixel Arecibo observations targeted Leo dwarf candidates noted optically by Karachentsev et al. 2004 (K04) to determine group members and allow for a comparison of HI and optically-selected samples. This presentation highlights the differences between the two samples and the significant contribution blind HI surveys can make to the missing satellites problem. [ABSTRACT FROM PUBLISHER]