The morphology of galaxy clusters is for the first time approached on synthetic maps of thermal Sunyaev-Zel'dovich effect applying several morphological parameters. Five parameters have been already largely applied on X-ray maps of clusters, while two are introduced in this work to be used specifically for cluster observations in the microwave region. We also introduce a general parameter, which properly combines the single ones, segregating more efficiently relaxed and disturbed clusters, as defined by common theoretical 3D indicators. Our analysis is applied on a sample of 258 massive clusters (M$>5\times10^{14}h^{-1}$M$_\odot$ at $z=0$) extracted from the MUSIC hydrodynamical simulations at four redshifts from 0.43 to 0.82, including radiative processes of cooling and star formation (CSF), as well as non-radiative physics (NR). The stability of each parameter is tested on maps obtained from different lines of sight for a couple of clusters classified as relaxed and disturbed. A correlation between the parameters estimated on a subsample of our catalogue on X-ray maps and SZ maps is evaluated and found to be strong only for the concentration parameter. Furthermore, we investigate the correlation between the general morphological parameter and the hydrostatic mass bias, finding it to be low. Finally we compute the 2D projected shift between the SZ centroid and the centre of mass of the cluster finding it to be strongly correlated with the morphology of the cluster and possibly resulting as good observational dynamical state indicator, assuming the latter to represent the position of the BCG.
We present the first weak lensing calibration of $\mu_{\star}$, a new galaxy cluster mass proxy corresponding to the total stellar mass of red and blue members, in two cluster samples selected from the SDSS Stripe 82 data: 230 redMaPPer clusters at redshift $0.1\leq z<0.33$ and 136 Voronoi Tessellation (VT) clusters at $0.1 \leq z < 0.6$. We use the CS82 shear catalog and stack the clusters in $\mu_{\star}$ bins to measure a mass-observable power law relation. For redMaPPer clusters we obtain $M_0 = (1.77 \pm 0.36) \times 10^{14}h^{-1} M_{\odot}$, $\alpha = 1.74 \pm 0.62$. For VT clusters, we find $M_0 = (4.31 \pm 0.89) \times 10^{14}h^{-1} M_{\odot}$, $\alpha = 0.59 \pm 0.54$ and $M_0 = (3.67 \pm 0.56) \times 10^{14}h^{-1} M_{\odot}$, $\alpha = 0.68 \pm 0.49$ for a low and a high redshift bin, respectively. Our results are consistent, internally and with the literature, indicating that our method can be applied to any cluster finding algorithm. In particular, we recommend that $\mu_{\star}$ be used as the mass proxy for VT clusters. Catalogs including $\mu_{\star}$ measurements will enable its use in studies of galaxy evolution in clusters and cluster cosmology.
Galaxy systems with large magnitude gaps - defined as the difference in magnitude between the central galaxy and the brightest satellite in the central region - have been claimed to have earlier formation histories. In this study we measure the mass concentration, as an indicator of early formation, of ensembles of galaxy systems divided by redshift and magnitude gaps in the $r$ band. We use cross-correlation weak lensing measurements with NFW parametric mass profiles to measure masses and concentrations of these ensembles from a catalogue of systems built from the SDSS Coadd by the redMaPPer algorithm. The lensing shear data come from the CFHT Stripe 82 (CS82) survey, and consists of $i$-band images of the SDSS Stripe 82 region. We find that the stack made up of systems with larger magnitude gaps has a high probability of being more concentrated on average, in the lowest redshift slice ($0.2<z<0.4$), both when dividing in quartiles ($P=0.98$) and terciles ($P=0.85$). These results lend credibility to the claim that the magnitude gap is an indicator of earlier formed systems.
Cluster mergers leave distinct signatures in the ICM in the form of shocks and diffuse cluster radio sources that provide evidence for the acceleration of relativistic particles. However, the physics of particle acceleration in the ICM is still not fully understood. Here we present new 1-4 GHz Jansky Very Large Array (VLA) and archival Chandra observations of the HST Frontier Fields Cluster Abell 2744. In our new VLA images, we detect the previously known $\sim2.1$ Mpc radio halo and $\sim1.5$ Mpc radio relic. We carry out a radio spectral analysis from which we determine the relic's injection spectral index to be $\alpha_{\rm{inj}} = -1.12 \pm 0.19$. This corresponds to a shock Mach number of $\mathcal{M}$ = 2.05$^{+0.31}_{-0.19}$ under the assumption of diffusive shock acceleration. We also find evidence for spectral steepening in the post-shock region. We do not find evidence for a significant correlation between the radio halo's spectral index and ICM temperature. In addition, we observe three new polarized diffuse sources and determine two of these to be newly discovered giant radio relics. These two relics are located in the southeastern and northwestern outskirts of the cluster. The corresponding integrated spectral indices measure $-1.81 \pm 0.26$ and $-0.63 \pm 0.21$ for the SE and NW relics, respectively. From an X-ray surface brightness profile we also detect a possible density jump of $R=1.39^{+0.34}_{-0.22}$ co-located with the newly discovered SE relic. This density jump would correspond to a shock front Mach number of $\mathcal{M}=1.26^{+0.25}_{-0.15}$.
The cosmological consequences of a slow rolling scalar field with constant kinetic term in analogy to the vertical movement of a skydiver after reaching terminal velocity are investigated. It is shown that the terminal scalar field hypothesis is quite realistic. In this approach, the scalar field potential is given by a quadratic function of the field. This model provides solutions in which the Universe was dominated in the past by a mixture of baryons and dark matter, is currently accelerating (as indicated by type Ia supernovae data), but will be followed by a contraction phase. The theoretical predictions of this model are consistent with current observations, therefore, a terminal scalar field is a viable candidate to dark energy.
We study preheating in models where a scalar inflaton is directly coupled to a non-Abelian $SU(2)$ gauge field. In particular, we examine $m^2 \phi^2$ inflation with a conformal, dilaton-like coupling to the non-Abelian sector. We describe a numerical scheme that combines lattice gauge theory with standard finite difference methods applied to the scalar field. We show that a significant tachyonic instability allows for efficient preheating, which is parametrically suppressed by increasing the non-Abelian self-coupling. Additionally, we comment on the technical implementation of the evolution scheme and setting initial conditions.
Supermassive blackholes with masses of a billion solar masses or more are known to exist up to $z=7$. However, the present-day environments of the descendants of first quasars is not well understood and it is not known if they live in massive galaxy clusters or more isolated galaxies at $z=0$. We use a dark matter-only realization (BTMassTracer) of the BlueTides cosmological hydrodynamic simulation to study the halo properties of the descendants of the most massive black holes at $z=8$. We find that the descendants of the quasars with most massive black holes are not amongst the most massive halos. They reside in halos of with group-like ($\sim 10^{14}M_{\odot}$) masses, while the most massive halos in the simulations are rich clusters with masses $\sim 10^{15} M_{\odot}$. The distribution of halo masses at low redshift is similar to that of the descendants of least massive black holes, for a similar range of halo masses at $z=8$, which indicates that they are likely to exist in similar environments. By tracing back to the $z = 8$ progenitors of the most massive (cluster sized) halos at $z=0$; we find that their most likely black hole mass is less than $10^7 M_{\odot}$; they are clearly not amongst the most massive black holes. We also provide estimates for the likelihood of finding a high redshift quasar hosting a black hole with masses above $10^{7} M_{\odot}$ for a given halo mass at $z=0$. For halos above $10^{15} M_{\odot}$, there is only $20 \%$ probability that their $z=8$ progenitors hosted a black hole with mass above $10^{7} M_{\odot}$.
We present a newly discovered correlation between the wind outflow velocity and the X-ray luminosity in the luminous ($L_{\rm bol}\sim10^{47}\,\rm erg\,s^{-1}$) nearby ($z=0.184$) quasar PDS\,456. All the contemporary \textit{XMM-Newton}, \textit{NuSTAR} and \textit{Suzaku} observations from 2001--2014 were revisited and we find that the centroid energy of the blueshifted Fe\,K absorption profile increases with luminosity. This translates into a correlation between the wind outflow velocity and the hard X-ray luminosity (between 7--30\,keV) where we find that $v_{\rm w}/c \propto L_{7-30}^{\gamma}$ where $\gamma=0.22\pm0.04$. We also show that this is consistent with a wind that is predominately radiatively driven, possibly resulting from the high Eddington ratio of PDS\,456.
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Dark matter subhalos are the remnants of (incomplete) halo mergers. Identifying them and establishing their evolutionary links in the form of merger trees is one of the most important applications of cosmological simulations. The Hierachical Bound-Tracing (HBT) code identifies halos as they form and tracks their evolution as they merge, simultaneously detecting subhalos and building their merger trees. Here we present a new implementation of this approach, HBT+, that is much faster, more user friendly, and more physically complete than the original code. Applying HBT+ to cosmological simulations we show that both the subhalo mass function and the peak-mass function are well fit by similar double-Schechter functions.The ratio between the two is highest at the high mass end, reflecting the resilience of massive subhalos that experience substantial dynamical friction but limited tidal stripping. The radial distribution of the most massive subhalos is more concentrated than the universal radial distribution of lower mass subhalos. Subhalo finders that work in configuration space tend to underestimate the masses of massive subhalos, an effect that is stronger in the host centre. This may explain, at least in part, the excess of massive subhalos in galaxy cluster centres inferred from recent lensing observations. We demonstrate that the peak-mass function is a powerful diagnostic of merger tree defects, and the merger trees constructed using HBT+ do not suffer from the missing or switched links that tend to afflict merger trees constructed from more conventional halo finders. We make the HBT+ code publicly available.
The local velocity distribution of dark matter plays an integral role in interpreting the results from direct detection experiments. We previously showed that metal-poor halo stars serve as excellent tracers of the virialized dark matter velocity distribution using a high-resolution hydrodynamic simulation of a Milky Way--like halo. In this paper, we take advantage of the first \textit{Gaia} data release, coupled with spectroscopic measurements from the RAdial Velocity Experiment (RAVE), to study the kinematics of stars belonging to the metal-poor halo within an average distance of $\sim 5$ kpc of the Sun. We study stars with iron abundances [Fe/H]$ < -1.5$ and $-1.8$ that are located more than $1.5$ kpc from the Galactic plane. Using a Gaussian mixture model analysis, we identify the stars that belong to the halo population, as well as some kinematic outliers. We find that both metallicity samples have similar velocity distributions for the halo component, within uncertainties. Assuming that the stellar halo velocities adequately trace the virialized dark matter, we study the implications for direct detection experiments. The Standard Halo Model, which is typically assumed for dark matter, is discrepant with the empirical distribution by $\sim6\sigma$ and predicts fewer high-speed particles. As a result, the Standard Halo Model overpredicts the nuclear scattering rate for dark matter masses below $\sim 10$ GeV. The kinematic outliers that we identify may potentially be correlated with dark matter substructure, though further study is needed to establish this correspondence.
MAGIC is a system of two Cherenkov telescopes designed to perform observations of gamma rays with energies from about 50 GeV to tens of TeV. A low energy threshold and an excellent low energy performance make it a powerful instrument for studies of high energy processes in Active Galactic Nuclei (AGN). The MAGIC Collaboration dedicates about 40% of the telescopes' time to such observations, both monitoring of known emitters, and Target of Opportunity observations of flaring events. In this presentation we will discuss the recent highlights of the MAGIC AGN program. In particular, multi year monitoring of radio galaxies, such as M87, and strong peculiar blazars, such as PG 1553+113, will be presented together with new discoveries based on the Target Of Opportunity program.
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We use the Aurora radiation-hydrodynamical simulations to study the mean free path (MFP) for hydrogen ionizing photons during the epoch of reionization. We directly measure the MFP by averaging the distance 1 Ry photons travel before reaching an optical depth of unity along random lines-of-sight. During reionization the free paths tend to end in neutral gas with densities near the cosmic mean, while after reionizaton the end points tend to be overdense but highly ionized. Despite the increasing importance of discrete, over-dense systems, the cumulative contribution of systems with $N_{\rm{HI}} \lesssim 10^{16.5}~{\rm cm^{-2}}$ suffices to drive the MFP at $z \approx 6$, while at earlier times higher column densities are more important. After reionization the typical size of HI systems is close to the local Jeans length, but during reionization it is much larger. The mean free path for photons originating close to galaxies, $\rm{MFP_{gal}}$, is much smaller than the cosmic MFP. After reionization this enhancement can remain significant up to starting distances of $\sim 1$ comoving Mpc. During reionization, however, $\rm{MFP_{gal}}$ for distances $\sim 10^2 - 10^3$ comoving kpc typically exceeds the cosmic MFP. These findings have important consequences for models that interpret the intergalactic MFP as the distance escaped ionizing photons can travel from galaxies before being absorbed and may cause them to under-estimate the required escape fraction from galaxies, and/or the required emissivity of ionizing photons after reionization.
We present integral field spectroscopy of galaxy cluster Abell 3827, using ALMA and VLT/MUSE. It reveals an unusual configuration of strong gravitational lensing in the cluster core, with at least seven lensed images of a single background spiral galaxy. Lens modelling based on HST imaging had suggested that the dark matter associated with one of the cluster's central galaxies may be offset. The new spectroscopic data enable better subtraction of foreground light, and better identification of multiple background images. The inferred distribution of dark matter is consistent with being centered on the galaxies, as expected by LCDM. Each galaxy's dark matter also appears to be symmetric. Whilst we do not find an offset between mass and light (suggestive of self-interacting dark matter) as previously reported, the numerical simulations that have been performed to calibrate Abell 3827 indicate that offsets and asymmetry are still worth looking for in collisions with particular geometries. Meanwhile, ALMA proves exceptionally useful for strong lens image identifications.
We present a visibility based estimator namely, the Tapered Gridded Estimator (TGE) to estimate the power spectrum of the diffuse sky signal. The TGE has three novel features. First, the estimator uses gridded visibilities to estimate the power spectrum which is computationally much faster than individually correlating the visibilities. Second, a positive noise bias is removed by subtracting the auto-correlation of the visibilities which is responsible for the noise bias. Third, the estimator allows us to taper the field of view so as to suppress the contribution from the sources in the outer regions and the sidelobes of the telescope's primary beam. We first consider the two dimensional (2D) TGE to estimate the angular power spectrum $C_{\ell}$. We have also extended the TGE to estimate the three dimensional (3D) power spectrum $P({\bf k})$ of the cosmological 21-cm signal. Analytic formulas are presented for predicting the variance of the binned power spectrum. Both the estimators and their variance predictions are validated using simulations of $150 \, {\rm MHz}$ GMRT observations. We have applied the 2D TGE to estimate $C_{\ell}$ using visibility data for two of the fields observed by TIFR GMRT Sky Survey (TGSS). We find that the sky signal, after subtracting the point sources, is likely dominated by the diffuse Galactic synchrotron radiation across the angular multipole range $240 \le \ell \lesssim 500$.
The WIMPzilla hypothesis is that the dark matter is a super-weakly-interacting and super-heavy particle. Conventionally, the WIMPzilla abundance is set by gravitational particle production during or at the end of inflation. In this study we allow the WIMPzilla to interact directly with Standard Model fields through the Higgs portal, and we calculate the thermal production (freeze-in) of WIMPzilla dark matter from the annihilation of Higgs boson pairs in the plasma. The two particle-physics model parameters are the WIMPzilla mass and the Higgs-WIMPzilla coupling. The two cosmological parameters are the reheating temperature and the expansion rate of the universe at the end of inflation. We delineate the regions of parameters space where either gravitational or thermal production is dominant, and within those regions we identify the parameters that predict the observed dark matter relic abundance. Allowing for thermal production opens up the parameter space, even for Planck-suppressed Higgs-WIMPzilla interactions.
With recent Lyman-alpha forest data from BOSS and XQ-100, some studies suggested that the lower mass limit on the fuzzy dark matter (FDM) particles is lifted up to $10^{-21}$ eV. However, such a limit was obtained by $\Lambda$CDM simulations with the FDM initial condition and the quantum pressure (QP) was not taken into account which could have generated non-trivial effects in large scales structures. We investigate the QP effects in cosmological simulations systematically, and find that QP leads to further suppression of the matter power spectrum at small scales. Furthermore, we estimate the flux power spectrum of Lyman-alpha forest, and compare it with data from BOSS and XQ-100 to set the lower bound on the FDM particle mass to $10^{-23}$ eV. We carefully estimate the uncertainty in the calculation of one-dimensional flux power spectrum due to the temperature of the hydrogen gas, and conclude that unless the effect of QP and the uncertainties of the temperature of the hydrogen gas are properly taken into account, one cannot exclude the FDM of mass larger than $10^{-22}$ eV at statistically significant levels.
When Peccei-Quinn (PQ) symmetry breaking happens after inflation, the axion field takes random values in causally disconnected regions. This leads to fluctuations of order one in the axion energy density around the QCD epoch. These over-densities eventually decouple from the Hubble expansion and form so-called miniclusters. We present a semi-analytical method to calculate the average axion energy density, as well as the power spectrum, from the re-alignment mechanism in this scenario. Furthermore, we develop a modified Press & Schechter approach, suitable to describe the collapse of non-linear density fluctuations during radiation domination, which is relevant for the formation of axion miniclusters. It allows us to calculate the double differential distribution of gravitationally collapsed miniclusters as a function of their mass and size. For instance, assuming a PQ scale of $10^{11}$ GeV, minicluster masses range from about $5 \times 10^{-16}$ to $3 \times 10^{-13}$ solar masses and have sizes from about $4\times 10^4$ to $7\times 10^5$ km at the time they start to collapse.
We present results for the first three years of OzDES, a six-year programme to obtain redshifts for objects in the Dark Energy Survey (DES) supernova fields using the 2dF fibre positioner and AAOmega spectrograph on the Anglo-Australian Telescope. OzDES is a multi-object spectroscopic survey targeting multiple types of targets at multiple epochs over a multi-year baseline, and is one of the first multi-object spectroscopic surveys to dynamically include transients into the target list soon after their discovery. At the end of three years, OzDES has spectroscopically confirmed almost 100 supernovae, and has measured redshifts for 17,000 objects, including the redshifts of 2,566 supernova hosts. We examine how our ability to measure redshifts for targets of various types depends on signal-to-noise, magnitude, and exposure time, finding that our redshift success rate increases significantly at a signal-to-noise of 2 to 3 per 1-Angstrom bin. We also find that the change in signal-to-noise with exposure time closely matches the Poisson limit for stacked exposures as long as 10 hours. We use these results to predict the redshift yield of the full OzDES survey, as well as the potential yields of future surveys on other facilities such as the 4m Multi-Object Spectroscopic Telescope (4MOST), the Subaru Prime Focus Spectrograph (PFS), and the Maunakea Spectroscopic Explorer (MSE). This work marks the first OzDES data release, comprising 14,693 redshifts. OzDES is on target to obtain over a yield of approximately 5,700 supernova host-galaxy redshifts.
In quantum gravity perturbation theory in Newton's constant G is known to be badly divergent, and as a result not very useful. Nevertheless some of the most interesting phenomena in physics are often associated with non-analytic behavior in the coupling constant and the existence of nontrivial quantum condensates. It is therefore possible that pathologies encountered in the case of gravity are more likely the result of inadequate analytical treatment, and not necessarily a reflection of some intrinsic insurmountable problem. The nonperturbative treatment of quantum gravity via the Regge-Wheeler lattice path integral formulation reveals the existence of a new phase involving a nontrivial gravitational vacuum condensate, and a new set of scaling exponents characterizing both the running of G and the long-distance behavior of invariant correlation functions. The appearance of such a gravitational condensate is viewed as analogous to the (equally nonperturbative) gluon and chiral condensates known to describe the physical vacuum of QCD. The resulting quantum theory of gravity is highly constrained, and its physical predictions are found to depend only on one adjustable parameter, a genuinely nonperturbative scale xi in many ways analogous to the scaling violation parameter Lambda MSbar of QCD. Recent results point to significant deviations from classical gravity on distance scales approaching the effective infrared cutoff set by the observed cosmological constant. Such subtle quantum effects are expected to be initially small on current cosmological scales, but could become detectable in future high precision satellite experiments.
We investigate the Hamiltonian structure of a class of gravitational theories whose actions are linear in the lapse function. We derive the necessary and sufficient condition for a theory in this class to have two or less local physical degrees of freedom. As an application we then find several concrete examples of modified gravity theories in which the total number of local physical degrees of freedom in the gravity sector is two.
In this paper, we re-examine the light deflection in the Schwarzschild and the Schwarzschild--de Sitter spacetime. First, supposing a static and spherically symmetric spacetime, we propose the definition of the total deflection angle $\alpha$ of the light ray by constructing a quadrangle $\Sigma^4$ on the optical reference geometry ${\cal M}^{\rm opt}$ determined by the optical metric $\bar{g}_{ij}$. On the basis of the definition of the total deflection angle $\alpha$ and the Gauss--Bonnet theorem, we derive two formulas to calculate the total deflection angle $\alpha$; (1) the angular formula that uses four angles determined on the optical reference geometry ${\cal M}^{\rm opt}$ or the curved $(r, \phi)$ subspace ${\cal M}^{\rm sub}$ being a slice of constant time $t$ and (2) the integral formula on the optical reference geometry ${\cal M}^{\rm opt}$ which is the areal integral of the Gaussian curvature $K$ in the area of a quadrangle $\Sigma^4$ and the line integral of the geodesic curvature $\kappa_g$ along the curve $C_{\Gamma}$. The curve $C_{\Gamma}$ is the unperturbed reference straight line that is the geodesic $\Gamma$ on the background spacetime such as the Minkowski or the de Sitter spacetime, and therefore $C_{\Gamma}$ is a straight line in the Euclidean sense. We demonstrate that the two formulas give the same total deflection angle $\alpha$ for the Schwarzschild and the Schwarzschild--de Sitter spacetime. In particular, in the Schwarzschild case, the result coincides with Epstein--Shapiro's formula when the source $S$ and the receiver $R$ of the light ray are located at infinity. In addition, in the Schwarzschild--de Sitter case, there appear order ${\cal O}(\Lambda m)$ terms in addition to the Schwarzschild-like part, while order ${\cal O}(\Lambda)$ terms disappear.
The Large Synoptic Survey Telescope is designed to provide an unprecedented optical imaging dataset that will support investigations of our Solar System, Galaxy and Universe, across half the sky and over ten years of repeated observation. However, exactly how the LSST observations will be taken (the observing strategy or "cadence") is not yet finalized. In this dynamically-evolving community white paper, we explore how the detailed performance of the anticipated science investigations is expected to depend on small changes to the LSST observing strategy. Using realistic simulations of the LSST schedule and observation properties, we design and compute diagnostic metrics and Figures of Merit that provide quantitative evaluations of different observing strategies, analyzing their impact on a wide range of proposed science projects. This is work in progress: we are using this white paper to communicate to each other the relative merits of the observing strategy choices that could be made, in an effort to maximize the scientific value of the survey. The investigation of some science cases leads to suggestions for new strategies that could be simulated and potentially adopted. Notably, we find motivation for exploring departures from a spatially uniform annual tiling of the sky: focusing instead on different parts of the survey area in different years in a "rolling cadence" is likely to have significant benefits for a number of time domain and moving object astronomy projects. The communal assembly of a suite of quantified and homogeneously coded metrics is the vital first step towards an automated, systematic, science-based assessment of any given cadence simulation, that will enable the scheduling of the LSST to be as well-informed as possible.
We show that the coherent oscillations of a spin-2 field from bimetric theory can easily account for the observed dark matter abundance. We obtain the equation of motion for the field in a cosmological setting and discuss in detail the phenomenology of the model. The framework is testable in precision measurements of oscillating electric charge in atomic clocks, using atomic spectroscopy and in dedicated resonant mass detectors as well as in axion-like-particles experiments, which therefore provide a new window to probe and test gravity itself. We also comment on possible multimetric extensions of the framework that straightforwardly implement the clockwork mechanism for gravity.
A class of methods for measuring time delays between astronomical time series is introduced in the context of quasar reverberation mapping, which is based on measures of randomness or complexity of the data. Several distinct statistical estimators are considered that do not rely on polynomial interpolations of the light curves nor on their stochastic modeling, and do not require binning in correlation space. Methods based on von Neumann's mean-square successive-difference estimator are found to be superior to those using other estimators. An optimized von Neumann scheme is formulated, which better handles sparsely sampled data and outperforms current implementations of discrete correlation function methods. This scheme is applied to existing reverberation data of varying quality, and consistency with previously reported time delays is found. In particular, the size-luminosity relation of the broad-line region in quasars is recovered with a scatter comparable to that obtained by other works, yet with fewer assumptions made concerning the process underlying the variability. The proposed method for time-lag determination is particularly relevant for irregularly sampled time series, and in cases where the process underlying the variability cannot be adequately modeled.
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We introduce a new family of primordial cosmological perturbations that are not described by traditional power spectra. At the linear level, these perturbations live in the kernel of the spatial Laplacian operator, and thus we call them cosmological zero modes. We compute the cosmic microwave background (CMB) temperature and polarization anisotropy induced by these modes, and forecast their detection sensitivity using a cosmic-variance limited experiment. In particular, we consider two configurations for the zero modes: The first configuration consists of stochastic metric perturbations described by white noise on a "holographic screen" located at our cosmological horizon. The amplitude of the power spectrum of this white noise can be constrained to be $\lesssim 9 \times 10^{-14}$. The second configuration is a primordial monopole beyond our cosmological horizon. We show that such a monopole, with "charge" $Q$, can be detected in the CMB sky up to a distance of $11.6 ~ Q^{1/4}\times$ horizon radius (or $160~ Q^{1/4}$ Gpc). More generally, observational probes of cosmological zero modes can shed light on non-perturbative phenomena in the primordial universe, beyond our observable horizon.
We consider the dynamics in and near galaxy clusters. Gas, dark matter and galaxies are presently falling into the clusters between approximately 1 and 5 virial radii. At very large distances, beyond 10 virial radii, all matter is following the Hubble flow, and inside the virial radius the matter particles have on average zero radial velocity. The cosmological parameters are imprinted on the infall profile of the gas, however, no method exists, which allows a measurement of it. We consider the results of two cosmological simulations (using the numerical codes RAMSES and Gadget) and find that the gas and dark matter radial velocities are very similar. We derive the relevant dynamical equations, in particular the generalized hydrostatic equilibrium equation, including both the expansion of the Universe and the cosmological background. This generalized gas equation is the main new contribution of this paper. We combine these generalized equations with the results of the numerical simulations to estimate the contribution to the measured cluster masses from the radial velocity: inside the virial radius it is negligible, and inside two virial radii the effect is below 40%, in agreement the earlier analyses for DM. We point out how the infall velocity in principle may be observable, by measuring the gas properties to distance of about two virial radii, however, this is practically not possible today.
We propose the disappearance of "the hyperon puzzle" in neutron star (NS) by invoking two new-physics prescriptions: modified gravity theory and braneworld scenario. By assuming that NS lives on a $3$-brane within a $5d$ empty AdS bulk, gravitationally governed by Eddington-inspired Born-Infeld (EiBI) theory, the field equations can be effectively cast into the usual Einstein's with "apparent" anisotropic energy-momentum tensor. Solving the corresponding brane-TOV equations numerically, we study its mass-radius relation. It is known that the appearance of finite brane tension $\lambda$ reduces the compactness of the star. The compatibility of the braneworld results with observational constraints of NS mass and radius can be restored in our model by varying the EiBI's coupling constant, $\kappa$. We found that within the astrophysically-accepted range of parameters ($0<\kappa<6\times10^6\text{m}^2$ and $\lambda\gg1~ \text{MeV}^4$) the NS can have mass $\sim2.1~ \text{M}_\odot$ and radius $\sim10$ km.
Interpreting the small-scale clustering of galaxies with halo models can elucidate the connection between galaxies and dark matter halos. Unfortunately, the modelling is typically not sufficiently accurate for ruling out models in a statistical sense. It is thus difficult to use the information encoded in small scales to test cosmological models or probe subtle features of the galaxy-halo connection. In this paper, we attempt to push halo modelling into the "accurate" regime with a fully numerical mock-based methodology and careful treatment of statistical and systematic errors. An advantage of this approach is that it can easily incorporate clustering statistics beyond the traditional two-point statistics. We use this modelling methodology to test the standard $\Lambda\mathrm{CDM}$ + halo model against the clustering of SDSS DR7 galaxies. Specifically, we use the projected correlation function, group multiplicity function and galaxy number density as constraints. We find that while the model provides a good match to each statistic separately, it struggles to fit them jointly. Adding group statistics leads to a more stringent test of the model and significantly tighter constraints on model parameters. We explore the impact of varying the adopted halo definition and cosmological model and find that changing the cosmology makes a significant difference. The most successful model we tried (Planck cosmology with Mvir halos) matches the clustering of low luminosity galaxies, but exhibits a $2.3 \sigma$ tension with the clustering of luminous galaxies, thus providing evidence that the "standard" halo model needs to be extended. This work represents the most accurate modelling of small-scale clustering to-date and opens the door to adding interesting freedom to the halo model and including additional clustering statistics as constraints.
We show that the reheating temperature of a matter-domination era in the early universe can be pushed down close to $1 \mathinner{\mathrm{MeV}}$ if the reheating takes place through non-hadronic decays of the dominant matter and neutrino-antineutrino asymmetries are still large enough, $|L| \gtrsim \mathcal{O}(10^{-2}-1)$ (depending on the neutrino flavor) at the end of reheating.
We constrain the history of reionization using the data from Planck 2015 Cosmic Microwave Background (CMB) temperature and polarization anisotropy observations. We also use prior constraints on the reionization history at redshifts $\sim7-8$ obtained from Lyman-$\alpha$ emission observations. Using the free electron fractions at different redshifts as free parameters, we construct the complete reionization history using polynomials. Our construction provides an extremely flexible framework to search for the history of reionization as a function of redshifts. We present a conservative and an optimistic constraint on reionization that are categorized by the flexibilities of the models and datasets used to constrain them, and we report that CMB data marginally favors extended reionization histories. In both the cases, we find the mean values of optical depth to be larger ($\approx0.09$ and $0.1$) than what we find in standard steplike reionization histories ($0.079\pm0.017$). At the same time we also find that the maximum free electron fraction allowed by the data for redshifts more than 15 is $\sim0.25$ at 95.4\% confidence limit in the case of optimistic constraint.
Weakly interacting massive particles are a widely well-probed dark matter candidate by the dark matter direct detection experiments. Theoretically, there are a large number of ultraviolet completed models that consist of a weakly interacting massive particle dark matter. The variety of models make the comparison with the direct detection data complicated and often non-trivial. To overcome this, in the non-relativistic limit, the effective theory was developed in the literature which works very well to significantly reduce the complexity of dark matter-nucleon interactions and to better study the nuclear response functions. In the effective theory framework for a spin-1/2 dark matter, we combine three independent likelihood functions from the latest PandaX, LUX, and XENON1T data, and give a joint limit on each effective coupling. The astrophysical uncertainties of the dark matter distribution are also included in the likelihood. We further discuss the isospin violating cases of the interactions. Finally, for both dimension-five and dimension-six effective theories above the electroweak scale, we give updated limits of the new physics mass scales.
In the framework of polynomial Palatini cosmology, we investigate a simple cosmological homogeneous and isotropic model with matter in the Einstein frame. We show that in this model during cosmic evolution, it appears the early inflation and the accelerating phase of the expansion for the late times. In this frame we obtain the Friedmann equation with matter and dark energy in the form of a scalar field with the potential whose form is determined in a covariant way by the Ricci scalar of the FRW metric. The energy density of matter and dark energy are also parametrized through the Ricci scalar. The early inflation is obtained only for an infinitesimally small fraction of energy density of matter. Between the matter and dark energy, there exists interaction because the dark energy is decaying. For characterization of inflation we calculate the slow roll parameters and the constant roll parameter in terms of the Ricci scalar. We have found a characteristic behaviour of the time dependence of density of dark energy on the cosmic time following the logistic-like curve which interpolates two almost constant value phases. From the required numbers of $N$-folds we have found a bound on model parameter.
The damping process of a homogeneous oscillating scalar field that indirectly interacts with a thermal bath through a mediator field is investigated over a wide range of model parameters. We consider two types of mediator fields, those that can decay to the thermal bath and those that are individually stable but pair annihilate. The former case has been extensively studied in the literature by treating the damping as a local effect after integrating out the assumed close-to-equilibrium mediator field. The same approach does not apply if the mediator field is stable and freezes out of equilibrium. To account for the latter case, we adopt a non-local description of damping that is only meaningful when we consider full half-oscillations of the field being damped. The damping rates of the oscillating scalar field and the corresponding heating rate of the thermal bath in all bulk parameter regions are calculated in both cases, corroborating previous results in the direct decay case. Using the obtained results, the time it takes for the amplitude of the scalar field to be substantially damped is estimated.
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As wide-field surveys yield ever more precise measurements, cosmology has entered a phase of high precision requiring highly accurate and fast theoretical predictions. At the heart of most cosmological model predictions is a numerical solution of the Einstein-Boltzmann equations governing the evolution of linear perturbations in the Universe. We present PyCosmo, a new Python-based framework to solve this set of equations using a special pur- pose solver based on symbolic manipulations, automatic generation of C++ code and sparsity optimisation. The code uses a consistency relation of the field equations to adapt the time step and does not rely on physical approximations for speed-up. After reviewing the system of first-order linear homogeneous differential equations to be solved, we describe the numerical scheme implemented in PyCosmo. We then compare the predictions and performance of the code for the computation of the transfer functions of cosmological perturbations and compare it to existing cosmological Boltzmann codes. We find that we achieve comparable execution times for comparable accuracies. While PyCosmo does not yet have all the features of other codes, our approach is complementary to existing cosmological Boltzmann solvers and can be used as an independent test of their numerical solutions. The symbolic representation of the Einstein-Boltzmann equation system in PyCosmo provides a convenient interface for implementing extended cosmological models. We also discuss how the PyCosmo framework can also be used as a general framework to compute cosmological quantities as well as observables for both interactive and high-performance batch jobs applications. Information about the PyCosmo package and future code releases are available at this http URL
The eROSITA mission will provide the largest sample of galaxy clusters detected in X-ray to date (one hundred thousand expected). This sample will be used to constrain cosmological models by measuring cluster masses. An important mass proxy is the electron temperature of the hot plasma detected in X-rays. We want to understand the detection properties and possible bias in temperatures due to unresolved substructures in the cluster halos. We simulated a large number of galaxy cluster spectra with known temperature substructures and compared the results from analysing eROSITA simulated observations to earlier results from Chandra. We were able to constrain a bias in cluster temperatures and its impact on cluster masses as well as cosmological parameters derived from the survey. We found temperatures in the eROSITA survey to be biased low by about five per cent due to unresolved temperature substructures (compared to emission-weighted average temperatures from the Chandra maps). This bias would have a significant impact on the eROSITA cosmology constraints if not accounted for in the calibration. We isolated the bias effect that substructures in galaxy clusters have on temperature measurements and their impact on derived cosmological parameters in the eROSITA cluster survey.
In order to best improve constraints on cosmological parameters and on models of modified gravity using current and future galaxy surveys it is necessary maximally exploit the available data. As redshift-space distortions mean statistical translation invariance is broken for galaxy observations, this will require measurement of the monopole, quadrupole and hexadecapole of not just the galaxy power spectrum, but also the galaxy bispectrum. A recent (2015) paper by Scoccimarro demonstrated how the standard bispectrum estimator may be expressed in terms of Fast Fourier Transforms (FFTs) to afford an extremely efficient algorithm, allowing the bispectrum multipoles on all scales and triangle shapes to be measured in comparable time to those of the power spectrum. In this paper we present a suite of alternative proxies to measure the three-point correlation multipoles. In particular, we describe a modal (or plane wave) decomposition to capture the information in each multipole in a series of basis coefficients, and also describe three compressed estimators formed using the skew-spectrum, the line correlation function and the integrated bispectrum, respectively. As well as each of the estimators offering a different measurement channel, and thereby a robustness check, it is expected that some (especially the modal estimator) will offer a vast data compression, and so a much reduced covariance matrix. This compression may be vital to reduce the computational load involved in extracting the available three-point information.
The models of cyclic universes and cyclic multiverses based on the alternative gravity theories of varying constants are considered.
Context: The gravitational lensing time delay method provides a one-step
determination of the Hubble constant (H0) with an uncertainty level on par with
the cosmic distance ladder method. However, to further investigate the nature
of the dark energy, a H0 estimate down to 1% level is greatly needed. This
requires dozens of strongly lensed quasars that are yet to be delivered by
ongoing and forthcoming all-sky surveys.
Aims: In this work we aim to determine the spectroscopic redshift of
PSOJ0147, the first strongly lensed quasar candidate found in the Pan-STARRS
survey. The main goal of our work is to derive an accurate redshift estimate of
the background quasar for cosmography.
Methods: To obtain timely spectroscopically follow-up, we took advantage of
the fast-track service programme that is carried out by the Nordic Optical
Telescope. Using a grism covering 3200 - 9600 A, we identified prominent
emission line features, such as Ly-alpha, N V, O I, C II, Si IV, C IV, and [C
III] in the spectra of the background quasar of the PSOJ0147 lens system. This
enables us to determine accurately the redshift of the background quasar.
Results: The spectrum of the background quasar exhibits prominent absorption
features bluewards of the strong emission lines, such as Ly-alpha, N V, and C
IV. These blue absorption lines indicate that the background source is a broad
absorption line (BAL) quasar. Unfortunately, the BAL features hamper an
accurate determination of redshift using the above-mentioned strong emission
lines. Nevertheless, we are able to determine a redshift of 2.341+/-0.001 from
three of the four lensed quasar images with the clean forbidden line [C III].
In addition, we also derive a maximum outflow velocity of ~ 9800 km/s with the
broad absorption features bluewards of the C IV emission line. This value of
maximum outflow velocity is in good agreement with other BAL quasars.
We investigate the particle production from thermal gravitational annihilation in the very early universe, which is an important contribution for particles that might not be in thermal equilibrium or/and only have gravitational interaction, such as dark matter (DM). For particles with spin 0, 1/2 and 1 we calculate the relevant cross sections through gravitational annihilation and give the analytic formulas with full mass-dependent terms. We find that DM with mass between TeV and $10^{16}$GeV could have the relic abundance that fits the observation, with small dependence on its spin. We also discuss the effects of gravitational annihilation from inflatons. Interestingly, contributions from inflatons could be dominant and have the same power dependence on Hubble parameter of inflation as that from vacuum fluctuation. Also, fermion production from inflatons, in comparison to boson, is suppressed by its mass due to helicity selection.
The ubiquity of Lyman alpha (Ly$\alpha$) emission in a sample of four bright [O III]-strong star-forming galaxies with redshifts above 7 has led to the suggestion that such luminous sources represent a distinct population compared to their fainter, more numerous, counterparts. The presence of Ly$\alpha$ emission within the reionization era could indicate that these sources created early ionized bubbles due to their unusually strong radiation, possibly due to the presence of active galactic nuclei. To test this hypothesis we have secured long integration spectra with XSHOOTER on the VLT for three $z\simeq$7 sources selected to have similar luminosities and prominent excess fluxes in the IRAC 3.6 or 4.5$\mu$m band, usually attributed to strong [O III] emission. We secured additional spectroscopy for one of these galaxies at $z$=7.15 using MOSFIRE at the Keck telescope. For this, the most well-studied source in our sample with the strongest IRAC excess, we detect prominent nebular emission from He II and NV indicative of a non-thermal source. For the other two sources at $z$=6.81 and $z$=6.85, for which no previous optical/near infrared spectroscopy was initially available, Ly$\alpha$ is seen in one and CIII] emission in the other. Although a modest sample, our results further support the hypothesis that the phenomenon of intense [O III] emission is associated preferentially with sources lying in early ionized bubbles. However, even though one of our sources at $z$=7.15 clearly indicates the presence of non-thermal radiation, such ionized bubbles may not uniquely arise in this manner. We discuss the unique advantages of extending such challenging diagnostic studies with JWST.
We investigated the regular multi-horizon black holes in the Einstein gravity, $F(R)$ gravity and the 5 dimensional Gauss-Bonnet gravity, all of them coupled with non-linear electrodynamics. We presented several explicit examples of the actions which admit the solutions describing regular black hole space-time with multi-horizons. Thermodynamics of the obtained black hole solutions is studied. The explicit expressions of the temperature, the entropy, the thermodynamical energy and the free energy are obtained. Although the temperature vanishes in the extremal limit where the radii of the two horizons coincide with each other as in the standard multi-horizon black hole like the Reissner-Nordstr\" om black hole or the Kerr black hole, the larger temperature corresponds to the larger horizon radius. This is different from the standard black holes, where the larger temperature corresponds to the smaller horizon radius. We also found that the specific heat becomes positive for the large temperature, which is also different from the standard black holes, where the specific heat is negative. It should be also noted that the thermodynamical energy is not identical with the ADM mass. Furthermore in case of the Gauss-Bonnet gravity,it is demonstrated that the entropy can become negative.
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