Astrophysics

Aims: To study the dependence of the dynamical properties of dark matter halos on their environment in a whole-sky Λ CDM light-cone simulation extending to z∼0.65 . The properties of interest are halo shape (parametrized by its principal axes), spin and virialisation status, the alignment of halo spin and shape, as well as the shape-shape and spin-spin alignments among halo neighbours. Methods: We define the halo environment using the notion of halo isolation status determined by the distance to its nearest neighbor. This defines a maximum spherical region around each halo devoid of other halos, above the catalog threshold mass. We consider as 'close halo pairs', the pairs that are separated by a distance lower than a specific threshold. In order to decontaminate our results from the known dependence of halo dynamical properties on mass, we use a random sampling procedure in order to compare properties of similar halo abundance distributions. Results: (a) We find a strong dependence of halo properties on their environment, confirming that isolated halos are more aspherical and more prolate with lower spin values. (b) Correlations between halo properties exist and are mostly independent of halo environment. (c) Halo spins are aligned with the minor axis, regardless of halo shape. (d) Close halo neighbors have their major axes statistically aligned, while they show a slight but statistically significant preference for anti-parallel spin directions. The latter result is enhanced for the case of close halo pairs in low-density environments. Furthermore, we find a preference of the spin vectors to be oriented perpendicular to the line connecting such close halo pairs.

We develop a machine learning model to detect dark substructure (subhalos) within simulated images of strongly lensed galaxies. Using the technique of image segmentation, we turn the task of identifying subhalos into a classification problem where we label each pixel in an image as coming from the main lens, a subhalo within a binned mass range, or neither. Our network is only trained on images with a single smooth lens and either zero or one subhalo near the Einstein ring. On a test set of noiseless simulated images with a single subhalo, the network is able to locate subhalos with a mass of 10 8 M ⊙ and place them in the correct or adjacent mass bin, effectively detecting them 97% of the time. For this test set, the network detects subhalos down to masses of 10 6 M ⊙ at 61% accuracy. However, noise limits the sensitivity to light subhalo masses. With 1% noise (with this level of noise, the distribution of signal-to-noise in the image pixels approximates that of images from the Hubble Space Telescope for sources with magnitude <20 ), a subhalo with mass 10 8.5 M ⊙ is detected 86% of the time, while subhalos with masses of 10 8 M ⊙ are only detected 38% of the time. Furthermore, the model is able to generalize to new contexts it has not been trained on, such as locating multiple subhalos with varying masses, subhalos far from the Einstein ring, or more than one large smooth lens.

We quantify the information content of the non-linear matter power spectrum, the halo mass function, and the void size function, using the Quijote N-body simulations. We find that these three statistics exhibit very different degeneracies amongst the cosmological parameters, and thus the combination of all three probes enables the breaking of degeneracies, in turn yielding remarkably tight constraints. We perform a Fisher analysis using the full covariance matrix, including all auto- and cross-correlations, finding that this increases the information content for neutrino mass compared to a correlation-free analysis. The multiplicative improvement of the constraints on the cosmological parameters obtained by combining all three probes compared to using the power spectrum alone are: 137, 5, 8, 20, 10, and 43, for Ω m , Ω b , h , n s , ? 8 , and M ν , respectively. The marginalized error on the sum of the neutrino masses is ?( M ν )=0.018eV for a cosmological volume of 1( h ?? Gpc ) 3 , using k max =0.5h Mpc ?? , and without CMB priors. We note that this error is an underestimate insomuch as we do not consider super-sample covariance, baryonic effects, and realistic survey noises and systematics. On the other hand, it is an overestimate insomuch as our cuts and binning are suboptimal due to restrictions imposed by the simulation resolution. Given upcoming galaxy surveys will observe volumes spanning ??00( h ?? Gpc ) 3 , this presents a promising new avenue to measure neutrino mass without being restricted by the need for accurate knowledge of the optical depth, which is required for CMB-based measurements. Furthermore, the improved constraints on other cosmological parameters, notably Ω m , may also be competitive with CMB-based measurements.

We investigate the detectability of leading-order relativistic effects in the bispectrum of future 21cm intensity mapping surveys. The relativistic signal arises from Doppler and other line-of-sight effects in redshift space. In the power spectrum of a single tracer, these effects are suppressed by a factor $\cH^2/k^2$. By contrast, in the bispectrum the relativistic signal couples to short-scale modes, leading to an imaginary contribution that scales as $\cH/k$, thus increasing the possibility of detection. Previous work has shown that this relativistic signal is detectable in a Stage IV H α galaxy survey. {We show that the signal is also detectable by next-generation 21cm intensity maps, but typically with a lower signal-to-noise, due to foreground and telescope beam effects.

In this paper, we apply the multi-tracer technique to harmonic-space (i.e.\ angular) power spectra with a likelihood-based approach. This goes beyond the usual Fisher matrix formalism hitherto implemented in forecasts with angular statistics, opening up a window for future developments and direct application to available data sets. We also release a fully-operational modified version of the publicly available code CosmoSIS, where we consistently include all the add-ons presented in the previous papers of this series. The result is a modular cosmological parameter estimation suite for angular power spectra of galaxy number counts, allowing for single and multiple tracers, and including density fluctuations, redshift-space distortions, and weak lensing magnification. We demonstrate the improvement on parameter constraints enabled by the use of multiple tracers on a multi-tracing analysis of luminous red galaxies and emission line galaxies. We obtain an enhancement of 44% on the 2σ upper bound on the sum of neutrino masses. Our code is publicly available at this https URL.

We show that the recent NANOGrav result can be interpreted as a stochastic gravitational wave signal associated to formation of primordial black holes from high-amplitude curvature perturbations. The indicated amplitude and power of the gravitational wave spectrum agrees well with formation of primordial seeds for supermassive black holes.

A cosmological model with an energy transfer between the dark matter (DM) and dark energy (DE) can give rise to comparable energy densities at the present epoch. The present work deals with the perturbation analysis, parameter estimation and Bayesian evidence calculation of interacting models with dynamical coupling parameter that determines the strength of the interaction. We have considered two cases, where the interaction is a more recent phenomenon and where the interaction is a phenomenon in the distant past. Moreover, we have considered the quintessence DE equation of state with Chevallier-Polarski-Linder (CPL) parametrisation and energy flow from DM to DE. Using the current observational datasets like the cosmic microwave background (CMB), baryon acoustic oscillation (BAO), Type Ia Supernovae (SNe Ia) and redshift-space distortions (RSD), we have estimated the mean values of the parameters. Using the perturbation analysis and Bayesian evidence calculation, we have shown that interaction present as a brief early phenomenon is preferred over a recent interaction.

Diffuse filaments connect galaxy clusters to form the cosmic web. Detecting these filaments could yield information on the magnetic field strength, cosmic ray population and temperature of intercluster gas, yet, the faint and large-scale nature of these bridges makes direct detections very challenging. Using multiple independent all-sky radio and X-ray maps we stack pairs of luminous red galaxies as tracers for cluster pairs. For the first time, we detect an average surface brightness between the clusters from synchrotron (radio) and thermal (X-ray) emission with ??? significance, on physical scales larger than observed to date ( ?? Mpc). We obtain a synchrotron spectral index of ��?1.0 and estimates of the average magnetic field strength of 30?�B??0 nG, derived from both equipartition and Inverse Compton arguments, implying a 5 to 15 per cent degree of field regularity when compared with Faraday rotation measure estimates. While the X-ray detection is inline with predictions, the average radio signal comes out higher than predicted by cosmological simulations and dark matter annihilation and decay models. This discovery demonstrates that there are connective structures between mass concentrations that are significantly magnetised, and the presence of sufficient cosmic rays to produce detectable synchrotron radiation.

We investigate the possibility to induce double peaks of gravitational wave(GW) spectrum from primordial scalar perturbations in inflationary models with three inflection points.Where the inflection points can be generated from a polynomial potential or generated from Higgs like ? 4 potential with the running of quartic this http URL such models, the inflection point at large scales predicts the scalar spectral index and tensor-to-scalar ratio consistent with current CMB constraints, and the other two inflection points generate two large peaks in the scalar power spectrum at small scales, which can induce GWs with double peaks energy spectrum. We find that for some choices parameters the double peaks spectrum can be detected by future GW detectors, and one of the peaks around f??10 ?? ??10 ?? Hz can also explain the recent NANOGrav signal. Moreover, the peaks of power spectrum allow for the generation of primordial black holes, which account for a significant fraction of dark matter.

In this article we compare a variety of well known dynamical dark energy models using the cosmic microwave background measurements from the 2018 Planck legacy and 2015 Planck data releases, the baryon acoustic oscillations measurements and the local measurements of H 0 obtained by the SH0ES (Supernovae, H 0 , for the Equation of State of Dark energy) collaboration analysing the Hubble Space Telescope data. We discuss the alleviation of H 0 tension, that is obtained at the price of a phantom-like dark energy equation of state. We perform a Bayesian evidence analysis to quantify the improvement of the fit, finding that all the dark energy models considered in this work are preferred against the ? CDM scenario. Finally, among all the possibilities analyzed, the CPL model is the best one in fitting the data and solving the H 0 tension at the same time. However, unfortunately, this dynamical dark energy solution is not supported by the baryon acoustic oscillations (BAO) data, and the tension is restored when BAO data are included for all the models.