A steepening feature in the outer density profiles of dark matter halos - the splashback radius - has drawn much attention recently. A possible observational detection has even been made for galaxy clusters. Theoretically, Adhikari et al. have estimated the location of the splashback radius by computing the secondary infall trajectory of a dark matter shell through a growing dark matter halo with an NFW profile. However, since they imposed a shape of the halo profile rather than computing it consistently from the trajectories of the dark matter shells, they could not provide the full shape of the dark matter profile around the splashback radius. We improve on this by extending the self-similar spherical collapse model of Fillmore & Goldreich to a $\Lambda$CDM universe. This allows us to compute the dark matter halo profile and the trajectories simultaneously from the mass accretion history. Our results on the splashback location agree qualitatively with Adhikari et al. but with small quantitative differences at large mass accretion rates. We present new fitting formulae for the splashback radius $R_{\rm sp}$ in various forms, including the ratios of $R_{\rm sp} / R_{\rm 200c}$ and $R_{\rm sp} / R_{\rm 200m}$. Numerical simulations have made the puzzling discovery that the splashback radius scales well with $R_{\rm 200m}$ but not with $R_{\rm 200c}$. We trace the origin of this to be the correlated increase of $\Omega_{\rm m}$ and the average halo mass accretion rate with an increasing redshift.
In the past several decades, the standard cosmological model has been established and its parameters have been measured to a high precision, while there are still many of the fundamental questions in cosmology; such as the physics in the very early Universe, the origin of the cosmic acceleration and the nature of the dark matter. The future world's largest radio telescope, Square Kilometre Array (SKA), will be able to open the new frontier of cosmology and will be one of the most powerful tools for cosmology in the next decade. The cosmological surveys conducted by the SKA would have the potential not only to answer these fundamental questions but also deliver the precision cosmology. In this article we briefly review the role of the SKA from the view point of the modern cosmology. The cosmology science led by the SKA-Japan Consortium (SKA-JP) Cosmology Science Working Group is also discussed.
Cosmic reionization is known to be a major phase transition of the gas in the Universe. Since astronomical objects formed in the early Universe, such as the first stars, galaxies and black holes, are expected to have caused cosmic reionization, the formation history and properties of such objects are closely related to the reionization process. In spite of the importance of exploring reionization, our understandings regarding reionization is not sufficient yet. Square Kilometre Array (SKA) is a next-generation large telescope that will be operated in the next decade. Although several programs of next-generation telescopes are currently scheduled, the SKA will be the unique telescope with a potential to directly observe neutral hydrogen up to z~30, and provide us with valuable information on the Cosmic Dawn (CD) and the Epoch of Reionization (EoR). The early science with the SKA will start in a few years; it is thus the time for us to elaborate a strategy for CD/EoR Science with the SKA. The purpose of this document is to introduce Japanese scientific interests in the SKA project and to report results of our investigation.
We investigate the prospect of constraining scalar field dark energy models using HI 21-cm intensity mapping surveys. We consider a wide class of coupled scalar field dark energy models whose predictions about the background cosmological evolution are different from the $\Lambda$CDM predictions by a few percent. We find that these models can be statistically distinguished from $\Lambda$CDM through their imprint on the 21-cm angular power spectrum. At the fiducial $z= 1.5$, corresponding to a radio interferometric observation of the post-reionization HI 21 cm observation at frequency $568 \rm MHz$, these models can infact be distinguished from the $\Lambda$CDM model at $ {\rm SNR }> 3 \sigma$ level using a 10,000 hr radio observation distributed over 40 pointings of a SKA1-mid like radio-telescope. We also show that tracker models are more likely to be ruled out in comparison with $\Lambda$CDM than the thawer models. Future radio observations can be instrumental in obtaining tighter constraints on the parameter space of dark energy models and supplement the bounds obtained from background studies.
Dark energy equation of state $w(z)$ parametrizations with two parameters and given monotonicity are generically either convex or concave functions. This makes them suitable for fitting either freezing or thawing quintessence models but not both simultaneously. Fitting a dataset based on a freezing model with an unsuitable (concave when increasing) $w(z)$ parametrization (like CPL) can lead to significant misleading features like crossing of the phantom divide line, incorrect $w(z=0)$, incorrect slope \etc that are not present in the underlying cosmological model. To demonstrate this fact we generate scattered cosmological data both at the level of $w(z)$ and the luminosity distance $D_L(z)$ based on either thawing or freezing quintessence models and fit them using parametrizations of convex and of concave type. We then compare statistically significant features of the best fit $w(z)$ with actual features of the underlying model. We thus verify that the use of unsuitable parametrizations can lead to misleading conclusions. In order to avoid these problems it is important to either use both convex and concave parametrizations and select the one with the best Akaike Information Criterion (AIC) or use principal component analysis thus splitting the redshift range into independent bins. In the latter case however, significant information about the slope of $w(z)$ at high redshifts is lost. Finally, we propose a new family of parametrizations (nCPL) $w(z)=w_0+w_a (\frac{z}{1+z})^n$ which generalizes the CPL and interpolates between thawing and freezing parametrizations as the parameter $n$ increases to values larger than 1.
We study the degree to which the cosmic microwave background (CMB) can be used to constrain primordial non-Gaussianity involving one tensor and two scalar fluctuations, focusing on the correlation of one $B$-mode polarization fluctuation with two temperature fluctuations. In the simplest models of inflation, the tensor-scalar-scalar primordial bispectrum is non-vanishing and is of the same order in slow-roll parameters as the scalar-scalar-scalar bispectrum. We calculate the $\langle BTT\rangle$ correlation arising from a primordial tensor-scalar-scalar bispectrum, and show that constraints from an experiment like CMB-Stage IV using this observable are more than an order of magnitude better than those on the same primordial coupling obtained from temperature measurements alone. We argue that $B$-mode non-Gaussianity opens up an as-yet-unexplored window into the early Universe, demonstrating that significant information on primordial physics remains to be harvested from CMB anisotropies.
The halo shape plays a central role in determining important observational properties of the halos such as mass, concentration and lensing cross sections. The triaxiality of lensing galaxy clusters has a substantial impact on the distribution of the largest Einstein radii, while weak lensing techniques are sensitive to the intrinsic halo ellipticity. In this work, we provide scaling relations for the shapes of dark matter halos as a function of mass (peak height) and redshift over more than four orders of magnitude in halo masses, namely from $10^{11.5} h^{-1}$M$_\odot$ to $10^{15.8}h^{-1}$M$_\odot$. We have analysed four dark matter only simulations from the MultiDark cosmological simulation suite with more than 56 billion particles within boxes of 4.0, 2.5, 1.0 and 0.4 $h^{-1}$Gpc size assuming Planck cosmology. The dark matter halos have been identified in the simulations using the RockStar halo finder, which also determines the axis ratios in terms of the diagonalisation of the inertia tensor. The minor-to-major and intermediate-to-major axis ratios are well described by simple functional forms. We provide the corresponding fitting functions in order to infer the axis ratios for an hypothetical halo of a given mass at a given redshift.
The equivalence between theories depending on the derivatives of $R$, i.e. $f\left( R,\nabla R,...,\nabla^{n}R\right) $, and scalar-tensorial theories is verified. The analysis is done in both metric and Palatini formalisms. It is shown that $f\left( R,\nabla R,...,\nabla^{n}R\right) $ theories are equivalents to Brans-Dicke theories with kinetic terms $\omega_{0}=0$ and $\omega_{0}= - \frac{3}{2}$ for metric and Palatini formalisms respectively. This result is analogous to what happens for $f(R)$ theories. Furthermore, sufficient conditions are established for $f\left( R,\nabla R,...,\nabla^{n}R\right) $ theories to be written as scalar-tensorial theories. Finally, some examples are studied and the comparison of $f\left( R,\nabla R,...,\nabla^{n}R\right) $ theories to $f\left( R,\Box R,...\Box^{n}R\right) $ theories are performed.
We present evidence from cosmological hydrodynamical simulations for a co-evolution of the slope of the total (dark and stellar) mass density profiles, gamma_tot, and the dark matter fractions within the half-mass radius, f_DM, in early-type galaxies. The relation can be described as gamma_tot = A f_DM + B and holds for all systems at all redshifts. We test different feedback models and find that the general trend is independent of the assumed feedback processes and is set by the decreasing importance of dissipative processes towards lower redshifts and for more massive systems. Early-type galaxies are smaller, more concentrated, have lower dark matter fractions and steeper total density slopes at high redshifts and at lower masses for a given redshift. The values for A and B change distinctively with the assumed feedback model, and thus this relation can be used as a test for feedback models. A similar correlation exists between gamma_tot and the stellar mass surface density Sigma_*. The model with weak stellar feedback and, in particular, feedback from black holes is in better agreement with observations. All simulations, independent of the assumed feedback model, predict steeper total density slopes and lower dark matter fractions at higher redshifts. While the latter is in agreement with the observed trends, the former is in conflict with currently available lensing observations, which indicate constant or decreasing density slopes. This discrepancy cannot be overcome by any of the feedback models included in this study.
In the magnetosphere of a rotating black hole, an inner Alfven critical surface (IACS) must be crossed by inflowing plasma. Inside the IACS, Alfven waves are inward directed toward the black hole. The majority of the proper volume of the active region of spacetime (the ergosphere) is inside of the IACS. The charge and the totally transverse momentum flux (the momentum flux transverse to both the wave normal and the unperturbed magnetic field) are both determined exclusively by the Alfven polarization. However, numerical simulations of black hole magnetospheres are often based on 1-D HLL Riemann solvers that readily dissipate Alfven waves. Elements of the dissipated wave emerge in adjacent cells regardless of the IACS, there is no mechanism to prevent Alfvenic information from crossing outward. Thus, it is unclear how simulated magnetospheres attain the substantial Goldreich-Julian charge density associated with the rotating magnetic field. The HLL Riemann solver is also notorious for producing large recurring transients (i.e., it prevents a "well-balanced" numerical scheme), potentially masking the causal physical transients required to achieve a steady state. To overcome these shortcomings, we have formulated a one-dimensional Riemann solver, called HLLI, which incorporates the Alfven discontinuity and the contact discontinuity. We have also formulated a multidimensional Riemann solver, called MuSIC, that enables low dissipation propagation of Alfven waves in multiple dimensions. Such Riemann solvers also enable simulations that are well-balanced at least up to second order. The importance of higher order schemes in lowering the numerical dissipation of Alfven waves is also catalogued.
To understand the role of the environment in galaxy formation, evolution, and present-day properties, it is essential to study the multi-frequency behavior of different galaxy populations under various environmental conditions. We crossmatch the SDSS DR10 group catalog with GAMA Data Release 2 and Wide-field Survey Explorer (WISE) data to construct a catalog of 1651 groups and 11436 galaxies containing photometric information in 15 different wavebands ranging from ultraviolet (0.152 {\mu}m) to mid-infrared (22 {\mu}m). We perform the spectral energy distribution (SED) fitting of galaxies using the MAGPHYS code and estimate the rest frame luminosities and stellar masses. We use the 1/Vmax method to estimate the galaxy stellar mass and luminosity functions, and the luminosity density field of galaxies to define the large scale environment of galaxies. The stellar mass functions of both central and satellite galaxies in groups are different in low and high density large scale environments. Satellite galaxies in high density environments have a steeper low mass end slope compared to low density environments, independently of the galaxy morphology. Central galaxies in low density environments have a steeper low mass end slope but the difference disappears for fixed galaxy morphology. The characteristic stellar mass of satellite galaxies is higher in high density environments and the difference exists only for galaxies with elliptical morphologies. Galaxy formation in groups is more efficient in high density large scale environments. Groups in high density environments have higher abundances of satellite galaxies, irrespective of the satellite galaxy morphology. The elliptical satellite galaxies are generally more massive in high density environments. The stellar masses of spiral satellite galaxies show no dependence on the large scale environment.
It has been shown in a companion paper that the late time acceleration of the universe can be accounted for by an extension of the QCD color to a $SU(3)$ invisible sector (IQCD). In this work we discuss a unified framework such the scale of dark chiral-breaking dictates both the accelerated expansion of the universe, and the origin of dark matter. We find that the strong and gravitational dynamics of dark quarks and gluons evolve to eventually form exotic dark stars. We discuss the dynamical complexity of these dark compact objects in light of dark big bang nucleosynthesis. We argue how IQCD favors a halo composed of very compact dark neutron stars, strange/quark stars and black holes, with masses $M_{MACHO}< 10^{-7}M_{\odot}$. This avoids limit from MACHO and EROS collaborations as well as limit from clusters. We also discuss possible phenomenological implications in dark matter searches. We argue that dark supernovae and dark binaries can emit very peculiar gravitational waves signal testable by the LIGO/VIRGO collaboration and future projects dedicated to these aspects.
We perform neutrino radiation-hydrodynamics simulations for the merger of asymmetric binary neutron stars in numerical relativity. Neutron stars are modeled by soft and moderately stiff finite-temperature equations of state (EOS). We find that the properties of the dynamical ejecta such as the total mass, neutron richness profile, and specific entropy profile depend on the mass ratio of the binary systems for a given EOS in a unique manner. For the soft EOS (SFHo), the total ejecta mass depends weakly on the mass ratio, but the average of electron number per baryon ($Y_e$) and specific entropy ($s$) of the ejecta decreases significantly with the increase of the degree of mass asymmetry. For the stiff EOS (DD2), with the increase of the mass asymmetry degree, the total ejecta mass significantly increases while the average of $Y_e$ and $s$ moderately decreases. We find again that only for the soft EOS (SFHo), the total ejecta mass exceeds $0.01M_\odot$ irrespective of the mass ratio chosen in this paper. The ejecta have a variety of electron number per baryon with its average approximately between $Y_e \sim 0.2$ and $\sim 0.3$ irrespective of the EOS employed, which is well-suited for the production of the r-process heavy elements (second and third peaks), although its averaged value decreases with the increase of the degree of mass asymmetry.
We propose a qualitative scenario to interpret the argued association between the recent direct measurement of the gravitational wave event GW150914 by LIGO-Virgo collaborations and the hard $X$-ray transient detected by Fermi-GBM $0.4$ sec after. In a binary system of two gravitationally collapsing objects with a non-vanishing electric charge, the compenetration of the two magnetospheres occurring during the coalescence, through turbulent magnetic reconnection, produces a highly collimated relativistic outflow that becomes optically thin and shines in the GBM field of view. We propose that this process should be expected as a commonplace in the future joint gravitational/electromagnetic detections.
The Square Kilometre Array will revolutionize pulsar studies with its wide field-of-view, wide-band observation and high sensitivity, increasing the number of observable pulsars by more than an order of magnitude. Pulsars are of interest not only for the study of neutron stars themselves but for their usage as tools for probing fundamental physics such as general relativity, gravitational waves and nuclear interaction. In this article, we summarize the activity and interests of SKA-Japan Pulsar Science Working Group, focusing on an investigation of modified gravity theory with the supermassive black hole in the Galactic Centre, gravitational-wave detection from cosmic strings and binary supermassive black holes, a study of the physical state of plasma close to pulsars using giant radio pulses and determination of magnetic field structure of Galaxy with pulsar pairs.
We present the outline and first results of a project using the synergies of the long term blazar radiomillimetre monitoring program F-GAMMA, the continued scanning of the millimetre-submillimetre sky by the Planck satellite, together with several dedicated observing programs at the Effelsberg 100m telescope, to obtain a data sample unprecedented in both time resolution and frequency span.
The QCD axion couplings of various invisible axion models are presented. In particular, the exact global symmetry U(1)$_{\rm PQ}$ in the superpotential is possible for the anomalous U(1) from string compactification, broken only by the gauge anomalies at one loop level, and is shown to have the resultant invisible axion coupling to photon, $c_{a\gamma\gamma}\ge \frac83-c_{a\gamma\gamma}^{\rm ch\,br}$ where $c_{a\gamma\gamma}^{\rm ch\,br}\simeq 2$. However, this bound is not applicable in approximate U(1)$_{\rm PQ}$ models with sufficiently suppressed U(1)$_{\rm PQ}$-breaking superpotential terms. We also present a simple method to obtain $c_{a\gamma\gamma}^0$ which is the value obtained above the electroweak scale.
In this work we study the partially constrained vielbein formulation of the new quasidilaton theory of massive gravity which couples to both physical and fiducial metrics simultaneously via a composite effective metric. This formalism improves the new quasidilaton model since the Boulware-Deser ghost is removed fully non-linearly at all scales. This also yields crucial implications in the cosmological applications. We derive the governing cosmological background evolution and study the stability of the attractor solution.
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(abridged) The large-scale distribution of galaxies is generally analyzed using the two-point correlation function. However, this statistic does not capture the topology of the distribution, and it is necessary to resort to higher order correlations to break degeneracies. We demonstrate that an alternate approach using network analysis can discriminate between topologically different distributions that have similar two-point correlations. We investigate two galaxy point distributions, one produced by a cosmological simulation and the other by a L\'evy walk. For the cosmological simulation, we adopt the redshift $z = 0.58$ slice from Illustris (Vogelsberger et al. 2014A) and select galaxies with stellar masses greater than $10^8$$M_\odot$. The two point correlation function of these simulated galaxies follows a single power-law, $\xi(r) \sim r^{-1.5}$. Then, we generate L\'evy walks matching the correlation function and abundance with the simulated galaxies. We find that, while the two simulated galaxy point distributions have the same abundance and two point correlation function, their spatial distributions are very different; most prominently, \emph{filamentary structures}, absent in L\'evy fractals. To quantify these missing topologies, we adopt network analysis tools and measure diameter, giant component, and transitivity from networks built by a conventional friends-of-friends recipe with various linking lengths. Unlike the abundance and two point correlation function, these network quantities reveal a clear separation between the two simulated distributions; therefore, the galaxy distribution simulated by Illustris is not a L\'evy fractal quantitatively. We find that the described network quantities offer an efficient tool for discriminating topologies and for comparing observed and theoretical distributions.
Whitbourn & Shanks (2014) have reported evidence for a local void underdense by ~15% extending to 150-300h-1Mpc around our position in the Southern Galactic Cap (SGC). Assuming a local luminosity function they modelled K- and r-limited number counts and redshift distributions in the 6dFGS/2MASS and SDSS redshift surveys and derived normalised n(z) ratios relative to the standard homogeneous cosmological model. Here we test further these results using maximum likelihood techniques that solve for the galaxy density distributions and the galaxy luminosity function simultaneously. We confirm the results from the previous analysis in terms of the number density distributions, indicating that our detection of the 'Local Hole' in the SGC is robust to the assumption of either our previous, or newly estimated, luminosity functions. However, there are discrepancies with previously published K and r band luminosity functions. In particular the r-band luminosity function has a steeper faint end slope than the r0.1 results of Blanton et al. (2003) but is consistent with the r0.1 results of Montero-Dorta & Prada (2009); Loveday et al. (2012).
Gravitational waves from inspiraling compact binaries are known to be an excellent absolute distance indicator, yet it is unclear whether electromagnetic counterparts of these events are securely identified for measuring their redshifts, especially in the case of black hole-black hole mergers such as the one recently observed with the Advanced LIGO. We propose to use the cross-correlation between spatial distributions of gravitational wave sources and galaxies with known redshifts as an alternative means of constraining the distance-redshift relation from gravitational waves. In our analysis, we explicitly include the modulation of the distribution of gravitational wave sources due to weak gravitational lensing. We show that the cross-correlation analysis in next-generation observations will be able to tightly constrain the relation between the absolute distance and the redshift, and therefore constrain the Hubble constant as well as dark energy parameters.
The cosmic distance can be precisely determined using a `standard ruler' imprinted by primordial baryon acoustic oscillation (hereafter BAO) in the early Universe. The BAO at the targeted epoch is observed by analysing galaxy clustering in redshift space (hereafter RSD) for which a theoretical formulation is not yet fully understood, and thus makes this methodology unsatisfactory. The BAO analysis following a full RSD modelling is contaminated by systematic uncertainties due to a non-linear smearing effects such as non-linear corrections and by random viral velocity of galaxies. However, the BAO can be probed independently of RSD contamination using the BAO peak positions located in the 2D anisotropic correlation function. A new methodology is presented to measure peak positions, to test whether it is also contaminated by the same systematics in RSD, and to provide the radial and transverse cosmic distances determined by the 2D BAO peak positions. We find that in our model independent anisotropic clustering analysis we can obtain about $2\%$ and $5\%$ constraints on $D_A$ and $H^{-1}$ respectively with current BOSS data, which is competitive with other analysis.
Ever refined cosmological measurements have established the $\Lambda$CDM concordance model, with the key cosmological parameters being determined to percent-level precision today. This allows us to make explicit predictions for the spectral distortions of the cosmic microwave background (CMB) created by various processes occurring in the early Universe. Here, we summarize all guaranteed CMB distortions and assess their total uncertainty within $\Lambda$CDM. We also compare simple methods for approximating them, highlighting some of the subtle aspects when it comes to interpreting future distortion measurements. Under simplified assumptions, we briefly study how well a PIXIE-like experiment may measure the main distortion parameters (i.e., $\mu$ and $y$). Next generation CMB spectrometers are expected to detect the distortion caused by reionization and structure formation at extremely high significance. They will also be able to constrain the small-scale power spectrum through the associated $\mu$-distortion, improving limits on running of the spectral index. Distortions from the recombination era, adiabatic cooling of matter relative to the CMB and dark matter annihilation require a higher sensitivity than PIXIE in its current design. The crucial next step is an improved modeling of foregrounds and instrumental aspects, as we briefly discuss here.
It is important to correctly subtract point sources from radio-interferometric data in order to measure the power spectrum of diffuse radiation like the Galactic synchrotron or the Epoch of Reionization 21-cm signal. It is computationally very expensive and challenging to image a very large area and accurately subtract all the point sources from the image. The problem is particularly severe at the sidelobes and the outer parts of the main lobe where the antenna response is highly frequency dependent and the calibration also differs from that of the phase center. Here we show that it is possible to overcome this problem by tapering the sky response. Using simulated 150 MHz observations, we demonstrate that it is possible to suppress the contribution due to point sources from the outer parts by using the Tapered Gridded Estimator to measure the angular power spectrum C_l of the sky signal. We also show from the simulation that this method can self-consistently compute the noise bias and accurately subtract it to provide an unbiased estimation of C_l.
We show that the Planck 2015 and BICEP2/KECK measurements of the Cosmic Microwave Background (CMB) anisotropies provide together an information gain of 0.82 +- 0.13 bits on the reheating history over all slow-roll single-field models of inflation. This corresponds to a 40% improvement compared to the Planck 2013 constraints on the reheating. Our method relies on an exhaustive CMB data analysis performed over nearly 200 models of inflation to derive the Kullback-Leibler entropy between the prior and the fully marginalized posterior of the reheating parameter. This number is a weighted average by the Bayesian evidence of each model to explain the data thereby ensuring its fairness and robustness.
The aberration and Doppler coupling effects of the Cosmic Microwave Background (CMB) were recently measured by the Planck satellite. The most straightforward interpretation leads to a direct detection of our peculiar velocity $\beta$, consistent with the measurement of the well-known dipole. In this paper we discuss the assumptions behind such interpretation. We show that the Doppler couplings are a sum of two effects: our peculiar velocity and a second order large-scale effect due to the dipolar part of the gravitational potential. We find that the two effects are exactly degenerate but {\it only} if we assume second-order initial conditions from single-field Inflation. Thus, detecting a discrepancy in the value of $\beta$ from the dipole and the Doppler couplings implies the presence of non-Gaussianity. We also analyze the aberration signal and we show that it is a sum of two independent effects: our peculiar velocity and lensing due to a first order large-scale dipolar gravitational potential, independently on Gaussianity of the initial conditions. In general such effects are not degenerate and so a discrepancy between the measured $\beta$ from the dipole and aberration could be accounted for by a dipolar gravitational potential. Only through a fine-tuning of the radial profile of the potential it is possible to have a complete degeneracy with a boost effect. Finally we discuss that we also expect other signatures due to integrated second order terms, which may be further used to disentangle this scenario from a simple boost.
Homogeneous and isotropic, nonsingular, bouncing world models are designed to evade the initial singularity at the beginning of the cosmic expansion. Here, we study the thermodynamics of the subset of these models governed by general relativity. Considering the entropy of matter, radiation and that the entropy of the apparent horizon is proportional to its area, we argue that these models do not respect the generalised second law of thermodynamics, also away from the bounce.
How can effective barotropic matter emerge from the interaction of cosmological fluids in an isotropic and homogeneous cosmological model? The dynamics of homogeneous and isotropic Friedmann-Lema\^itre-Robertson-Walker universes is a natural special case of generalized Lotka-Volterra systems where each of the universe's fluid components can be seen as a competitive species in a predator-prey model. (Jungle universe : arXiv:1306.1037) In addition to numerical simulations illustrating this behaviour among the barotropic fluids filling the universe, we analytically pinpoint that effective time-dependent barotropic indices can arise from a physical coupling between those fluids whose dynamics could then look like that of another type of cosmic fluid, such as a cosmological constant. Since the nature of dark energy is still unknown, this dynamical approach could help understanding some of the properties of dark matter and dark energy at large cosmological scales.
Radio relics are Mpc-scale diffuse radio sources at the peripheries of galaxy clusters which are thought to trace outgoing merger shocks. We present XMM-Newton and Suzaku observations of the galaxy cluster Abell 2744 (z=0.306), which reveal the presence of a shock front 1.5 Mpc East of the cluster core. The surface-brightness jump coincides with the position of a known radio relic. Although the surface-brightness jump indicates a weak shock with a Mach number $\mathcal{M}=1.7_{-0.3}^{+0.5}$, the plasma in the post-shock region has been heated to a very high temperature ($\sim13$ keV) by the passage of the shock wave. The low acceleration efficiency expected from such a weak shock suggests that mildly relativistic electrons have been re-accelerated by the passage of the shock front.
The far-infrared fine-structure line [CII] at 1900.5GHz is known to be one of the brightest cooling lines in local galaxies, and therefore it has been suggested to be an efficient tracer for star-formation in very high-redshift galaxies. However, recent results for galaxies at $z>6$ have yielded numerous non-detections in star-forming galaxies, except for quasars and submillimeter galaxies. We report the results of ALMA observations of two lensed, star-forming galaxies at $z = 6.029$ and $z=6.703$. The galaxy A383-5.1 (star formation rate [SFR] of 3.2 M$_\odot$yr$^{-1}$ and magnification of $\mu = 11.4$) shows a line detection with $L_{\rm [CII]} = 8.3\times10^{6}$ L$_\odot$, making it the so far lowest $L_{\rm [CII]}$ ever detected at $z>6$. For MS0451-H (SFR = 0.4M$_\odot$yr$^{-1}$ and $\mu = 100\pm20$) we provide an upper limit of $L_{\rm [CII]} < 3\times10^{5}$ L$_\odot$, which is 1\,dex below the local SFR-$L_{\rm [CII]}$ relations. The results are consistent with predictions for low-metallicity galaxies at $z>6$, however, other effects could also play a role in terms of decreasing $L_{\rm [CII]}$. The detection of A383-5.1 is encouraging and suggests that detections are possible, but much fainter than initially predicted.
We report the discovery of 15 quasars and bright galaxies at $5.7 < z < 6.9$. This is the initial result from the Subaru High-$z$ Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the exquisite multi-band imaging data produced by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. The candidate selection is performed by combining several photometric approaches including a Bayesian probabilistic algorithm to reject stars and dwarfs. The spectroscopic identification was carried out with the Gran Telescopio Canarias and the Subaru Telescope for the first 80 deg$^2$ of the survey footprint. The success rate of our photometric selection is quite high, approaching 100 % at the brighter magnitudes ($z_{\rm AB} < 23.5$ mag). Our selection also recovered all the known high-$z$ quasars on the HSC images. Among the 15 discovered objects, six are likely quasars, while the other six with interstellar absorption lines and in some cases narrow emission lines are likely bright Lyman-break galaxies. The remaining three objects have weak continua and very strong and narrow Ly $\alpha$ lines, which may be excited by ultraviolet light from both young stars and quasars. These results indicate that we are starting to see the steep rise of the luminosity function of $z \ge 6$ galaxies, compared to that of quasars, at magnitudes fainter than $M_{\rm 1450} \sim -22$ mag or $z_{\rm AB} \sim 24$ mag. Follow-up studies of the discovered objects as well as further survey observations are ongoing.
The gravitational baryogensis may not generate a sufficient baryon asymmetry in the standard thermal history of the Universe when we take into account the gravitino problem. Hence it has been suggested that anisotropy of the Universe can enhance the generation of the baryon asymmetry through the increase of the time change of the Ricci scalar curvature. We study the gravitational baryogenesis in the presence of anisotropy, which is produced at the end of an anisotropic inflation. Although we confirm that the generated baryon asymmetry is enhanced compared with the original isotropic cosmological model, taking into account the constraint on the anisotropy by the recent CMB observations, we find that it is still difficult to obtain the observed baryon asymmetry only through the gravitational baryogenesis without suffering from the gravitino problem.
Current searches for gravitational waves from compact-object binaries with the LIGO and Virgo observatories employ waveform models with spins aligned (or anti-aligned) with the orbital angular momentum. Here, we derive a new statistic to search for compact objects carrying generic (precessing) spins. Applying this statistic, we construct banks of both aligned- and generic-spin templates for binary black holes and neutron-star--black-hole binaries, and compare the effectualness of these banks towards simulated populations of generic-spin systems. We then use these banks in a pipeline analysis of Gaussian noise to measure the increase in background incurred by using generic- instead of aligned-spin banks. Although the generic-spin banks have a factor of ten to twenty more templates than the aligned-spin banks, we find an overall improvement in signal recovery at fixed false-alarm rate for systems with high-mass ratio and highly precessing spins ---up to 60\% for neutron-star--black-hole mergers. This gain in sensitivity comes at a small loss of sensitivity ($\lesssim$4\%) for systems that are already well-covered by aligned-spin templates. Since the observation of even a single binary merger with misalinged spins could provide unique astrophysical insights into the formation of these sources, we recommend that the method described here be developed further to mount a viable search for generic-spin binary mergers in LIGO/Virgo data.
Minimal chaotic models of D-term inflation predicts too large primordial tensor perturbations. Although it can be made consistent with observation utilizing higher order terms in the K\"ahler potential, expansion is not controlled in the absence of symmetries. We comprehensively study the conditions of K\"ahler potential for D-term plateau-type potentials and discuss its symmetry. They include the alpha-attractor model with a massive vector supermultiplet and its generalization leading to pole inflation of arbitrary order. We extend the models so that it can describe Coulomb phase, gauge anomaly is cancelled, and fields other than inflaton are stabilized during inflation. We also point out a generic issue for large-field D-term inflation that the masses of the non-inflaton fields tend to exceed the Planck scale.
We investigate the geodesics of a Schwarzschild spacetime embedded in an isotropic expanding cosmological background (McVittie metric). We focus on bound particle geodesics in a background including matter and phantom dark energy with constant dark energy equation of state parameter $w<-1$ involving a future Big Rip singularity at a time $t_{\ast}$. Such geodesics have been previously studied in the Newtonian approximation and found to lead to dissociation of bound systems at a time $t_{rip}<t_{\ast}$ which for fixed background $w$, depends on a single dimensionless parameter $\bar{\omega}_0$ related to the angular momentum and depending on the mass and the size of the bound system. We extend this analysis to large massive bound systems where the Newtonian approximation is not appropriate and we compare the derived dissociation time with the corresponding time in the context of the Newtonian approximation. By identifying the time when the effective potential minimum disappears due to the repulsive force of dark energy we find that the dissociation time of bound systems occurs earlier than the prediction of the Newtonian approximation. However, the effect is negligible for all existing cosmological bound systems and it would become important only in hypothetical bound extremely massive ($10^{20} M_\odot$) and large ($100Mpc$) bound systems. We verify this result by explicit solution of the geodesic equations. This result is due to an interplay between the repulsive phantom dark energy effects and the existence of the well known innermost stable orbits of Schwarzschild spacetimes.
We consider reheating in a class of asymptotically safe quantum field theories recently studied in \cite{Litim:2014uca, Litim:2015iea}. These theories allow for an inflationary phase in the very early universe. Inflation ends with a period of reheating. Since the models contain many scalar fields which are intrinsically coupled to the inflaton there is the possibility of parametric resonance instability in the production of these fields, and the danger that the induced curvature fluctuations will become too large. Here we show that the parametric instability indeed arises, and that hence the energy transfer from the inflaton condensate to fluctuating fields is rapid. Demanding that the curvature fluctuations induced by the parametrically amplified entropy modes do not exceed the upper observational bounds puts a lower bound on the number of fields which the model of Ref.~\cite{Litim:2014uca, Litim:2015iea} must contain. This bound also depends on the total number of e-foldings of the inflationary phase.
It has been shown that gravitational waves propagate through ideal fluids without experiencing any dispersion or dissipation. However, if the medium has a non-zero shear viscosity $\eta$ , gravitational waves will be dissipated at a rate proportional to $G \eta$. We test dark matter and dark energy models with non-zero shear viscosity by calculating the dissipation of GW150914 which propagates over a distance of 410 Mpc through the dissipative fluid and testing the data with the theoretical prediction. We put an upper bound on the shear viscosity of the cosmological fluid as $\eta < 1.9 \times 10^{9} {\rm Pa \,\, sec}$ which is close to the critical viscosity of fluids at which the viscous pressure becomes significant for the dynamics of the universe. The upper bound on $\eta$ is lower than the estimated shear viscosity of self-interacting dark matter in galaxy cluster Abel 3827. Future observations of gravitational waves at LIGO have the potential of detecting the viscosity of dark matter and dark energy.
We present early results from Radio Galaxy Zoo, a web-based citizen science project for visual inspection and classification of images from all-sky radio surveys. The goals of the project are to classify individual radio sources (particularly galaxies with multiple lobes and/or complex morphologies) as well as matching the continuum radio emission to the host galaxy. Radio images come from the FIRST and ATLAS surveys, while matches to potential hosts are performed with infrared imaging from WISE and SWIRE. The first twelve months of classification yielded more than 1 million classifications of more than 60,000 sources. For images with at least 75% consensus by the volunteer classifiers, the accuracy is comparable to visual inspection by the expert science team. Based on mid-infrared colors, the hosts associated with radio emission are primarily a mixture of elliptical galaxies, QSOs, and LIRGs, which are in good agreement with previous studies. The full catalog of radio lobes and their host galaxies will measure the relative populations of host types as a function of radio morphology and power. Radio Galaxy Zoo has also been an effective method for detecting extremely rare objects, such as HyMORs and giant radio galaxies. Results from the project are being used to train automatic algorithms for host matching for use in future large continuum surveys such as EMU, as well as establishing roles for citizen science in projects such as the SKA.
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Near-field cosmology - using detailed observations of the Local Group and its environs to study wide-ranging questions in galaxy formation and dark matter physics - has become a mature and rich field over the past decade. There are lingering concerns, however, that the relatively small size of the present-day Local Group ($\sim$ 2 Mpc diameter) imposes insurmountable sample-variance uncertainties, limiting its broader utility. We consider the evolution of the Local Group with time and show that it reaches $3' \approx 7$ co-moving Mpc in linear size (a volume of $\approx 350\,{\rm Mpc}^3$) at $z=7$. The Local Group is a representative portion of the Universe at early cosmic epochs according to multiple metrics. In a sense, the Local Group is therefore the ultimate deep field: its stellar fossil record traces the cosmic evolution for galaxies with $10^{3} < M_{\star}(z=0) / M_{\odot} < 10^{9}$ (reaching $m_{1500} > 38$ at $z\sim7$) over a region that, in terms of size, is comparable to or larger than the Hubble Ultra-Deep Field (HUDF) for the entire history of the Universe. It is highly complementary to the HUDF, as it probes \textit{much} fainter galaxies but does not contain the intrinsically rarer, brighter sources that are detectable in the HUDF. Archaeological studies in the Local Group also provide the ability to trace the evolution of individual galaxies across time as opposed to evaluating statistical connections between temporally distinct populations. In the JWST era, resolved stellar populations will probe regions larger than the HUDF and any deep JWST fields, further enhancing the value of near-field cosmology.
The evolution of the large-scale distribution of matter is sensitive to a variety of fundamental parameters that characterise the dark matter, dark energy, and other aspects of our cosmological framework. Since the majority of the mass density is in the form of dark matter that cannot be directly observed, to do cosmology with large-scale structure one must use observable (baryonic) quantities that trace the underlying matter distribution in a (hopefully) predictable way. However, recent numerical studies have demonstrated that the mapping between observable and total mass, as well as the total mass itself, are sensitive to unresolved feedback processes associated with galaxy formation, motivating explicit calibration of the feedback efficiencies. Here we construct a new suite of large-volume cosmological hydrodynamical simulations (called BAHAMAS, for BAryons and HAloes of MAssive Systems) where subgrid models of stellar and Active Galactic Nucleus (AGN) feedback have been calibrated to reproduce the present-day galaxy stellar mass function and the hot gas mass fractions of groups and clusters in order to ensure the effects of feedback on the overall matter distribution are broadly correct. We show that the calibrated simulations reproduce an unprecedentedly wide range of properties of massive systems, including the various observed mappings between galaxies, hot gas, total mass, and black holes, and represent a significant advance in our ability to mitigate the primary systematic uncertainty in most present large-scale structure tests.
Cosmic Microwave Background (CMB) experiments, such as WMAP and Planck, measure intensity anisotropies and build maps using a \emph{linearized} formula for relating them to the temperature blackbody fluctuations. However such a procedure also generates a signal in the maps in the form of y-type distortions, and thus degenerate with the thermal SZ (tSZ) effect. These are small effects that arise at second-order in the temperature fluctuations not from primordial physics but from such a limitation of the map-making procedure. They constitute a contaminant for measurements of: our peculiar velocity, the tSZ and of primordial y-distortions, but they can nevertheless be well-modelled and accounted for. We show that the largest distortions arises at high ell from a leakage of the CMB dipole into the y-channel which couples to all multipoles, but mostly affects the range ell <~ 400. This should be visible in Planck's y-maps with an estimated signal-to-noise ratio of about 9. We note however that such frequency-dependent terms carry no new information on the nature of the CMB dipole. This implies that the real significance of Planck's Doppler coupling measurements is actually lower than quoted. Finally, we quantify the relevance of the removal of such effects in order improve future measurements of tSZ and of primordial y-type distortions.
We focus on the evidence of a past minor merger discovered in the halo of the Andromeda galaxy (M31). Previous N-body studies have moderately succeeded to reproduce observed giant stellar stream (GSS) and stellar shells in the halo of M31. The observed distribution of red giant branch stars in the halo of M31 shows an asymmetric surface brightness profile across the GSS; however, most of the theoretical studies have not paid much attention to the internal structure of the GSS. We notice that numerical experiments so far have not examined the morphology of the progenitor galaxy in detail. To investigate the physical connection between the characteristic surface brightness in the GSS and the morphology of the progenitor dwarf galaxy, we perform systematic surveys of N-body simulations varying the thickness, rotation velocity, and initial inclination of the disc dwarf galaxy. Our result suggests that the key to the formation of the observed structures is the progenitor's rotation. Not only we reproduce observed GSS and two shells in detail, but also we predict additional structures for further observations. We predict the detectability of the progenitor's stellar core in phase-space density distribution, azimuthal metallicity gradient of the western shell-like structure, and an additional extended shell at the north-western direction that will limit the properties of the progenitor galaxy.
Galactic magnetic fields in the local Universe are strong and omnipresent. Now evidence accumulates that galaxies were magnetized already in the early Universe. Theoretical scenarios including the turbulent small-scale dynamo predict magnetic energy densities comparable to the one of turbulence. Based on the assumption of this energy equipartition, we determine the galactic synchrotron flux as a function of redshift. The conditions in the early Universe are different from the present day, in particular the galaxies have more intense star formation. To cover a large range of conditions we consider models based on two different types of galaxies: one model galaxy comparable to the Milky Way and one typical high-z starburst galaxy. We include a model of the steady state cosmic ray spectrum and find that synchrotron emission can be detected up to cosmological redshifts with current and future radio telescopes. Turbulent dynamo theory is in agreement with the origin of the observed correlation between the far-infrared (FIR) luminosity L_FIR and the radio luminosity L_radio. Our model reproduces this correlation well at z=0. We extrapolate the FIR-radio correlation to higher redshift and predict a time evolution with a significant deviation from its present-day appearance already at z~2. In particular, we predict a decrease of the radio luminosity with redshift which is caused by the increase of cosmic ray energy losses at high z. The result is an increase of the ratio between L_FIR and L_radio. Simultaneously, we predict that the slope of the FIR-radio correlation becomes shallower with redshift. This behavior of the correlation could be observed in the near future with ultra-deep radio surveys.
Cosmological hysteresis is a purely thermodynamical phenomenon caused by the gradient in pressure, hence the characteristic equation of state during the expansion and contraction phases of the universe are different, provided that the universe bounces and recollapses. During hysteresis pressure asymmetry is created due to the presence of a single scalar field in the dynamical process. Also such an interesting scenario has vivid implications in cosmology when applied to variants of modified gravity models described within the framework of membrane paradigm. Cyclic universe along with scalar field leads to the increase in the amplitude of the cosmological scale factor at each consecutive cycles of the universe. Detailed analysis shows that the conditions which creates a universe with an ever increasing expansion, depend on the signature of the hysteresis loop integral $\oint pdV$ and on membrane model parameters.
We consider dynamics of a flat anisotropic Universe filled by a perfect fluid near a cosmological singularity in quadratic gravity. Two possible regimes are described -- the Kasner anisotropic solution and an isotropic "vacuum radiation" solution which has three sub cases depending on whether the equation of state parameter $w$ is bigger, smaller or equals to $1/3$. Initial conditions for numerical integrations have been chosen near General Relativity anisotropic solution with matter (Jacobs solution). We have found that for such initial conditions there is a range of values of coupling constants so that the resulting cosmological singularity is isotropic.
In this paper, we describe 220Rn calibration source that was developed for liquid noble gas detectors. The key advantage of this source is that it can provide 212Bi-212Po consecutive events, which enables us to evaluate the vertex resolution of a detector at low energy by comparing low-energy events of 212Bi and corresponding higher-energy alpha-rays from 212Po. Since 220Rn is a noble gas, a hot metal getter can be used when introduced using xenon as the carrier gas. In addition, no long-life radioactive isotopes are left behind in the detector after the calibration is complete; this has clear advantage over the use of 222Rn which leaves long- life radioactivity, i.e., 210Pb. Using a small liquid xenon test chamber, we developed a system to introduce 220Rn via the xenon carrier gas; we demonstrated the successful introduction of 6 times 10^2 220Rn atoms in our test environment.
We study the effective field theory that describes the low-energy physics of self-gravitating media. The field content consists of four derivatively coupled scalar fields that can be identified with the internal comoving coordinates of the medium. Imposing SO(3) internal spatial invariance, the theory describes supersolids. Stronger symmetry requirements lead to superfluids, solids and perfect fluids, at lowest order in derivatives. In the unitary gauge, massive gravity emerges, being thus the result of a continuous medium propagating in spacetime. Our results can be used to explore systematically the effects and signatures of modifying gravity consistently at large distances. The dark sector is then described as a self-gravitating medium with dynamical and thermodynamic properties dictated by internal symmetries. These results indicate that the divide between dark energy and modified gravity, at large distance scales, is simply a gauge choice.
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We present the results of an X-ray spectral analysis of 153 galaxy clusters observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These clusters, which span 0 < z < 1.5, were drawn from a larger, mass-selected sample of galaxy clusters discovered in the 2500 square degree South Pole Telescope Sunyaev Zel'dovich (SPT-SZ) survey. With a total combined exposure time of 9.1 Ms, these data yield the strongest constraints to date on the evolution of the metal content of the intracluster medium (ICM). We find no evidence for strong evolution in the global (r<R500) ICM metallicity (dZ/dz = -0.06 +/- 0.04 Zsun), with a mean value at z=0.6 of <Z> = 0.23 +/- 0.01 Zsun and a scatter of 0.08 +/- 0.01 Zsun. These results imply that >60% of the metals in the ICM were already in place at z=1 (at 95% confidence), consistent with the picture of an early (z>1) enrichment. We find, in agreement with previous works, a significantly higher mean value for the metallicity in the centers of cool core clusters versus non-cool core clusters. We find weak evidence for evolution in the central metallicity of cool core clusters (dZ/dz = -0.21 +/- 0.11 Zsun), which is sufficient to account for this enhanced central metallicity over the past ~10 Gyr. We find no evidence for metallicity evolution outside of the core (dZ/dz = -0.03 +/- 0.06 Zsun), and no significant difference in the core-excised metallicity between cool core and non-cool core clusters. This suggests that strong radio-mode AGN feedback does not significantly alter the distribution of metals at r>0.15R500. Given the limitations of current-generation X-ray telescopes in constraining the ICM metallicity at z>1, significant improvements on this work will likely require next-generation X-ray missions.
Alternative theories of gravity typically invoke an environment-dependent "screening mechanism" to allow phenomenologically interesting deviations from general relativity (GR) to manifest on larger scales, while reducing to GR on small scales. The observation of the transition from screened to unscreened behavior would be compelling evidence for beyond-GR physics. In this paper, we show that pairwise peculiar velocity statistics -- in particular the relative radial velocity dispersion, $\sigma_\parallel$ -- can be used to observe this transition when they are binned by some measure of halo environment. We establish this by measuring the radial velocity dispersion between pairs of halos in N-body simulations for 3 $f(R)$ gravity and 4 Symmetron models. We develop an estimator involving only line-of-sight velocities to show that this quantity is observable, and bin the results in halo mass, ambient density, and the "isolatedness" of halos. Ambient density is found to be the most relevant measure of environment; it is distinct from isolatedness, and correlates well with theoretical expectations for the Symmetron model. Binning $\sigma_\parallel$ in ambient density, we find a strong environment-dependent signature for the Symmetron models, with the velocities showing a clear transition from GR to non-GR behavior. No such transition is observed for $f(R)$, as the relevant scales are deep in the unscreened regime. Observations of the relative radial velocity dispersion in forthcoming peculiar velocity surveys, if binned appropriately by environment, therefore offer a valuable way of detecting the screening signature of modified gravity.
The Planck collaboration has measured the temperature and polarization of the cosmic microwave background well enough to determine the locations of eight peaks in the temperature (TT) power spectrum, five peaks in the polarization (EE) power spectrum and twelve extrema in the cross (TE) power spectrum. The relative locations of these extrema give a striking, and beautiful, demonstration of what we expect from acoustic oscillations in the plasma; e.g., that EE peaks fall half way between TT peaks. We expect this because the temperature map is predominantly sourced by temperature variations in the last scattering surface, while the polarization map is predominantly sourced by gradients in the velocity field, and the harmonic oscillations have temperature and velocity 90 degrees out of phase. However, there are large differences in expectations for extrema locations from simple analytic models vs. numerical calculations. Here we quantitatively explore the origin of these differences in gravitational potential transients, neutrino free-streaming, the breakdown of tight coupling, the shape of the primordial power spectrum, details of the geometric projection from three to two dimensions, and the thickness of the last scattering surface. We also compare the peak locations determined from Planck measurements to expectations under the $\Lambda$CDM model. Taking into account how the peak locations were determined, we find them to be in agreement.
We explore effects of the screening due to the relativistic electron-positron plasma and presence of resonances in the secondary reactions leading to A=7 nuclei during the Big Bang Nucleosynthesis. In particular, we investigate and examine possible low-lying resonances in the 7Be(3He, g)10C reaction and examine the resultant destruction of 7Be for various resonance locations and strengths. While a resonance in the 10C compound nucleus is thought to have negligible effects we explore the possibility of an enhancement from plasma screening that may adjust the final 7Be abundance. We find the effects of relativistic screening and possible low-lying resonances to be relatively small in the standard Early Universe models.
We propose a new method to test modified gravity theories, taking advantage of the available data on extrasolar planets. We computed the deviations from the Kepler third law and use that to constrain gravity theories beyond General Relativity. We investigate gravity models which incorporate three screening mechanisms: the Chameleon, the Symmetron and the Vainshtein. We find that data from exoplanets orbits put strong constraints in the parameter space for the Chameleon and Symmetron models, complementary to other methods, like interferometers for example. In opposition, the constraints on the $f(R)$ models are weaker with respect to the cosmological ones. With the constraints on Vainshtein we are able to work beyond the hypothesis that the crossover scale is of the same order of magnitude than the Hubble radius $r_c \sim c^{-1}H_0$, which makes the screening work automatically.
We study the compatibility of large quasar groups with the concordance cosmological model. Large Quasar Groups are very large spatial associations of quasars in the cosmic web, with sizes of 50-250h^-1 Mpc. In particular, the largest large quasar group known, named Huge-LQG, has a longest axis of ~860h^-1 Mpc, larger than the scale of homogeneity (~260 Mpc), which has been pointed as a possible violation of the cosmological principle. Using mock catalogues constructed from the Horizon Run 2 cosmological simulation, we found that large quasar groups size, quasar member number and mean overdensity distributions in the mocks agree with observations. The Huge-LQG is found to be a rare group with a probability of 0.3 per cent of finding a group as large or larger than the observed, but an extreme value analysis shows that it is an expected maximum in the sample volume with a probability of 19 per cent of observing a largest quasar group as large or larger than Huge-LQG. The Huge-LQG is expected to be the largest structure in a volume at least 5.3 +- 1 times larger than the one currently studied.
We use the EAGLE galaxy formation simulation to study the effects of baryons on the power spectrum of the total matter and dark matter distributions and on the velocity fields of dark matter and galaxies. On scales $k\geq \sim4{h\,{\rm Mpc}^{-1}}$ the effect of baryons on the amplitude of the total-matter power spectrum is greater than $1\%$. The back-reaction of baryons affects the density field of the dark matter at the level of $\sim3\%$ on scales of $1\leq k/({h\,{\rm Mpc}^{-1}})\leq 5$. The dark matter velocity divergence power spectrum at $k\leq \sim0.5{h\,{\rm Mpc}^{-1}}$ is changed by less than $1\%$. The 2D redshift-space power spectrum is affected at the level of $\sim6\%$ at $k_\perp\geq \sim1{h\,{\rm Mpc}^{-1}}$, but for $k_\perp\leq 0.4{h\,{\rm Mpc}^{-1}}$ the amplitude differs by less than $1\%$. We report vanishingly small baryonic velocity bias for haloes: the peculiar velocities of haloes with with $M_{200}>3\times10^{11}{{\rm M}_{\odot}}$ (hosting galaxies with $M_{*}>10^9{{\rm M}_{\odot}}$) are affected at the level of at most $1~$km/s, which is negligible for $1\%$-precision cosmology. We caution that since EAGLE overestimates cluster gas fractions it may also underestimate the impact of baryons, particularly for the total matter power spectrum. Nevertheless, our findings suggest that for theoretical modelling of redshift space distortions and galaxy velocity-based statistics, baryons and their back-reaction can be safely ignored at the current level of observational accuracy. However, we confirm that the modelling of the total matter power spectrum in weak lensing studies needs to include realistic galaxy formation physics in order to achieve the accuracy required in the precision cosmology era.
The recently published analytic probability density function for the mildly non-linear cosmic density field within spherical cells is used to build a simple but accurate maximum likelihood estimate for the redshift evolution of the variance of the density, which, as expected, is shown to have smaller relative error than the sample variance. This estimator provides a competitive probe for the equation of state of dark energy, reaching a few percent accuracy on wp and wa for a Euclid-like survey. The corresponding likelihood function can take into account the configuration of the cells via their relative separations. A code to compute one-cell density probability density functions for arbitrary initial power spectrum, top-hat smoothing and various spherical collapse dynamics is made available online so as to provide straightforward means of testing the effect of alternative dark energy models and initial power-spectra on the low-redshift matter distribution.
Using the recent observation of gravitational waves (GW) produced by a black-hole merger, we place a lower bound on the energy above which a multifractal spacetime would manifest an anomalous geometry and, in particular, violations of Lorentz invariance. In the so-called multifractional theory with $q$-derivatives, we show that the deformation of dispersion relations is much stronger than in generic quantum-gravity approaches (including loop quantum gravity) and, contrary to the latter, present observations on GWs can place very strong bounds on the characteristic scales at which spacetime deviates from standard Minkowski. The energy at which multifractal effects should become apparent is $E_*>10^{14}\,\text{GeV}$ (thus improving previous bounds by 12 orders of magnitude) when the exponents in the measure are fixed to their central value $1/2$. We also estimate, for the first time, the effect of logarithmic oscillations in the measure (corresponding to a discrete spacetime structure) and find that they do not change much the bounds obtained in their absence, unless the amplitude of the oscillations is fine tuned. This feature or, in alternative, a presentation effect, both unavailable in known quantum-gravity scenarios, are crucial to avoid the theory to be ruled out by gamma-ray burst (GRB) observations, for which $E_*\gg 10^{17}\,\text{GeV}$.
We present an Integral Field Unit survey of 73 galaxy clusters and groups with the VIsible Multi Object Spectrograph (VIMOS) on VLT. We exploit the data to determine the H$\alpha$ gas dynamics on kpc-scales to study the feedback processes occurring within the dense cluster cores. We determine the kinematic state of the ionised gas and show that the majority of systems ($\sim$ 2/3) have relatively ordered velocity fields on kpc scales that are similar to the kinematics of rotating discs and are decoupled from the stellar kinematics of the Brightest Cluster Galaxy. The majority of the H$\alpha$ flux ($>$ 50%) is typically associated with these ordered kinematics and most systems show relatively simple morphologies suggesting they have not been disturbed by a recent merger or interaction. Approximately 20% of the sample (13/73) have disturbed morphologies which can typically be attributed to AGN activity disrupting the gas. Only one system shows any evidence of an interaction with another cluster member. A spectral analysis of the gas suggests that the ionisation of the gas within cluster cores is dominated by non stellar processes, possibly originating from the intracluster medium itself.
We explore the evolutionary behaviors of compact objects in a modified gravitational theory with the help of structure scalars. Particularly, we consider the spherical geometry coupled with heat and radiation emitting shearing viscous matter configurations. We construct structure scalars by splitting the Riemann tensor orthogonally in $f(R,T)$ gravity with and without constant $R$ and $T$ constraints, where $R$ is the Ricci scalar and $T$ is the trace of the energy-momentum tensor. We investigate the influence of modification of gravity on the physical meaning of scalar functions for radiating spherical matter configurations. It is explicitly demonstrated that even in modified gravity, the evolutionary phases of relativistic stellar systems can be analyzed through the set of modified scalar functions.
The gravitationally-lensed galaxy A1689-zD1 is one of the most distant spectroscopically confirmed sources ($z=7.5$). It is the earliest known galaxy where the interstellar medium (ISM) has been detected; dust emission was detected with the Atacama Large Millimetre Array (ALMA). A1689-zD1 is also unusual among high-redshift dust emitters as it is a sub-L* galaxy and is therefore a good prospect for the detection of gaseous ISM in a more typical galaxy at this redshift. We observed A1689-zD1 with ALMA in bands 6 and 7 and with the Green Bank Telescope (GBT) in band Q. We map the mm thermal dust emission, confirming the large dust emission found before, and finding two spatial components with sizes about 0.4-1.7 kpc (lensing-corrected). The rough spatial morphology is similar to what is observed in the near-infrared with HST and points to a perturbed dynamical state, perhaps indicative of a major merger or a disc in early formation. The ALMA photometry is used to constrain the far-infrared spectral energy distribution, yielding a moderate dust temperature ($T_{\rm dust} \sim 35$ K for $\beta = 1.65$). We do not detect the CO(3-2) line in the GBT data with a 95% upper limit of 0.3mJy observed. We find a slight excess emission in ALMA band 6 at 220.9 GHz. If this excess is real, it is likely due to emission from the [CII] 158.8 $\mu$m line at $z_{\rm [CII]} = 7.603$. The stringent upper limits on the [CII] and CO(3-2) line luminosities suggest a high ISM gas density in A1689-zD1.
X-ray extragalactic surveys are ideal laboratories for the study of the evolution and clustering of active galactic nuclei (AGN). The XXL Survey spans two fields of a combined 50 $deg^2$ observed for more than 6Ms with XMM-Newton, occupying the parameter space between deep surveys and very wide area surveys; at the same time it benefits from a wealth of ancillary data. This paper marks the first release of the XXL point source catalogue selected in the 2-10 keV energy band with limiting flux $F_{2-10keV}=4.8\cdot10^{-14}\rm{erg\,s^{-1}\,cm^{-2}}$. We use both public and proprietary data sets to identify the counterparts of the X-ray point-like sources and improved upon the photometric redshift determination for AGN by applying a Random Forest classification trained to identify for each object the optimal photometric redshift model library. We also assign a probability to each source to be a star or an outlier. We model with Bayesian analysis the X-ray spectra assuming a power-law model with the presence of an absorbing medium. We find an average unabsorbed photon index of $\Gamma=1.85$ and average hydrogen column density $\log{N_{H}}=21.07 cm^{-2}$. We find no trend of $\Gamma$ or $N_H$ with redshift and a fraction of 26% absorbed sources ($\log N_{H}>22$). We show that the XXL-1000-AGN number counts extended the number counts of the COSMOS survey to higher fluxes and are fully consistent with the Euclidean expectation. We constrain the intrinsic luminosity function of AGN in the 2-10 keV energy band where the unabsorbed X-ray flux is estimated from the X-ray spectral fit up to z=3. Finally, we demonstrate the presence of a supercluster size structure at redshift 0.14, identified by means of percolation analysis of the XXL-1000-AGN sample. The XXL survey, reaching a medium flux limit and covering a wide area is a stepping stone between current deep fields and planned wide area surveys.
We explore the space of scalar-tensor theories containing two disformally related metrics, and find a discontinuity pointing to a special "critical" cosmological solution. This solution has a simple geometrical interpretation based on the action of a probe 3-brane embedded in an $EAdS_2\times E_3$ geometry. Due to the different maximal speeds of propagation for matter and gravity, the cosmological fluctuations start off inside the horizon even without inflation, and will more naturally have a thermal origin (since there is never vacuum domination). The critical model makes an unambiguous, non-tuned prediction for the spectral index of the scalar fluctuations left outside the horizon: $n_s= 0.96478(64)$. Adding to this that no gravitational waves are produced, we have unveiled the most predictive model on offer.
We present models of low- and high-ionization metal-line absorbers (O I, C II, C IV and Mg II) during the end of the reionization epoch, at z ~ 6. Using four cosmological hydrodynamical simulations with different feedback schemes (including the Illustris and Sherwood simulations) and two different choices of hydro-solver, we investigate how the overall incidence rate and equivalent width distribution of metal-line absorbers varies with the galactic wind prescription. We find that the O I and C II absorbers are reasonably insensitive to the feedback scheme. All models, however, struggle to reproduce the observations of C IV and Mg II, which are probing down to lower overdensities than O I and C II at z ~ 6, suggesting that the metals in the simulations are not being transported out into the IGM efficiently enough. The situation is improved but not resolved if we choose a harder (but still reasonable) and/or (locally) increased UV background at z ~ 6.
Self-accelerating backgrounds in massive gravity provide an arena to explore the Cauchy problem for derivatively coupled fields that obey complex constraints which reduce the phase space degrees of freedom. We present here an algorithm based on the Kronecker form of a matrix pencil that finds all hidden constraints, for example those associated with derivatives of the equations of motion, and characteristic curves for any 1+1 dimensional system of linear partial differential equations. With the Regge-Wheeler-Zerilli decomposition of metric perturbations into angular momentum and parity states, this technique applies to fully 3+1 dimensional perturbations of massive gravity around any isotropic self-accelerating background. Five spin modes of the massive graviton propagate once the constraints are imposed: two spin-2 modes with luminal characteristics present in the massless theory as well as two spin-1 modes and one spin-0 mode. Although the new modes all possess the same - typically spacelike - characteristic curves, the spin-1 modes are parabolic while the spin-0 modes are hyperbolic. The joint system, which remains coupled by non-derivative terms, cannot be solved as a simple Cauchy problem from a single non-characteristic surface. We also illustrate the generality of the algorithm with other cases where derivative constraints reduce the number of propagating degrees of freedom or order of the equations.
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