Dark matter numerical simulations and the N-body method are essential for understanding how structure forms and evolves in the Universe. However, the discrete nature of N-body simulations can affect its accuracy when modelling collisionless systems. We introduce a new approach to simulate the gravitational evolution of cold collisionless fluids by solving the Vlasov-Poisson equations in terms of adaptively refineable "Lagrangian phase space elements". These geometrical elements are piecewise smooth maps between three-dimensional Lagrangian space and six-dimensional Eulerian phase space and approximate the continuum structure of the distribution function. They allow for dynamical adaptive splitting to follow the evolution even in regions of very strong mixing. We discuss various test problems which demonstrate the correctness and performance of our method. We show that it has several advantages compared to standard N-body algorithms by i) explicitly tracking the fine-grained distribution function, ii) naturally representing caustics, iii) providing an arbitrarily regular density field defined everywhere in space, iv) giving a smooth and regular gravitational potential field, thus eliminating the need for any type of ad-hoc force softening. Finally, we illustrate the feasibility of using our method for cosmological studies by simulating structure formation in a warm dark matter cosmology. We show that spurious collisionality and discreteness noise of N-body methods are both strongly suppressed, which eliminates artificial fragmentation of filaments while providing access to the full deterministic evolution of the fluid in phase space. Therefore, we argue that our new approach improves on the N-body method when simulating self-gravitating cold and collisionless fluids, and is the first method that allows to explicitly follow the fine-grained evolution in six-dimensional phase space.
Proto-galaxies forming in low-mass dark matter haloes are thought to provide the majority of ionising photons needed to reionise the Universe, due to their high escape fractions of ionising photons. We study how the escape fraction in high-redshift galaxies relates to the physical properties of the halo in which the galaxies form by computing escape fractions for 75801 haloes between redshifts 27 and 6 that were extracted from the FiBY project, high-resolution cosmological hydrodynamics simulations of galaxy formation. We find that the main constraint on the escape fraction is the presence of dense gas within 10 pc of the young sources that emit the majority of the ionising photons produced over the lifetime of the stellar population. This results in a strong mass dependence of the escape fraction. The lower potential well in haloes with virial mass below 10^8 solar mass results in lower column densities close to the sources that can be penetrated by the radiation from young, massive stars. In general only a single stellar population forms in these haloes, so supernova feedback sets in too late to strongly affect the escape fraction. In haloes with higher virial mass supernova feedback plays an important role, but only 30% of the haloes in this mass range has an escape fraction higher than 1%. We find a large range of escape fractions in haloes with similar properties, caused by different distributions of the dense gas in the halo. On average the escape fraction of HeI-ionising photons is higher than HI-ionising photons, but almost no HeII-ionising photons escape. Due to the inhomogeneous distribution of the dense gas the escape fraction is highly anisotropic. The strong mass dependence, the large spread and the large anisotropy of the escape fraction may strongly affect the topology of reionisation and is something current models of reionisation should strive to take into account.
We investigate the impact of sinks of ionizing radiation on the reionization-era 21-cm signal, focusing on 1-point statistics. We consider sinks in both the intergalactic medium and inside galaxies. At a fixed filling factor of HII regions, sinks will have two main effects on the 21-cm morphology: (i) as inhomogeneous absorbers of ionizing photons they result in smaller and more widespread cosmic HII patches; and (ii) as reservoirs of neutral gas they contribute a non-zero 21-cm signal in otherwise ionized regions. Both effects damp the contrast between neutral and ionized patches during reionization, making detection of the epoch of reionization with 21-cm interferometry more challenging. Here we systematically investigate these effects using the latest semi-numerical simulations. We find that sinks dramatically suppress the peak in the redshift evolution of the variance, corresponding to the midpoint of reionization. As previously predicted, skewness changes sign at midpoint, but the fluctuations in the residual HI suppress a late-time rise. Furthermore, large levels of residual HI dramatically alter the evolution of the variance, skewness and power spectrum from that seen at lower levels. In general, the evolution of the large-scale modes provides a better, cleaner, higher signal-to-noise probe of reionization.
We explore the possibility of measuring the mass accretion rate of galaxy clusters by using dense galaxy redshift surveys of their outer regions. By approximating the accretion with the infall of a spherical shell, the mass accretion rate only depends on the mass profile of the cluster in a thin shell at radii larger than $R_{200}$. This approximation is rather crude in hierarchical clustering scenarios, where both smooth accretion and aggregation of smaller dark matter haloes contribute to the mass accretion of clusters. Nevertheless, in the redshift range $z=[0,1]$, our prescription returns an average mass accretion rate within $20 \%$ of the average rate derived with the more realistic merger trees of dark matter haloes extracted from $N$-body simulations. The mass accretion rate of galaxy clusters has been the topic of numerous detailed numerical and theoretical investigations, but so far it has remained inaccessible to measurements in the real Universe. Our result suggests that measuring the mass accretion rate of galaxy clusters is actually feasible, thus providing a potential new observational test of the cosmological and structure formation models.
We present a suite of cosmological radiation-hydrodynamical simulations of the assembly of galaxies driving the reionization of the intergalactic medium (IGM) at z >~ 6. The simulations account for the hydrodynamical feedback from photoionization heating and the explosion of massive stars as supernovae (SNe). Our reference simulation, which was carried out in a box of size 25 comoving Mpc/h using 2 x 512^3 particles, produces a reasonable reionization history and matches the observed UV luminosity function of galaxies. Simulations with different box sizes and resolutions are used to investigate numerical convergence, and simulations in which either SNe or photoionization heating or both are turned off, are used to investigate the role of feedback from star formation. Ionizing radiation is treated using accurate radiative transfer at the high spatially adaptive resolution at which the hydrodynamics is carried out. SN feedback strongly reduces the star formation rates (SFRs) over nearly the full mass range of simulated galaxies and is required to yield SFRs in agreement with observations. Photoheating helps to suppress star formation in low-mass galaxies, but its impact on the cosmic SFR is small. Because the effect of photoheating is masked by the strong SN feedback, it does not imprint a signature on the UV galaxy luminosity function. Photoheating does provide a strong positive feedback on reionization because it smooths density fluctuations in the IGM, which lowers the IGM recombination rate substantially. Our simulations demonstrate a tight non-linear coupling of galaxy formation and reionization, motivating the need for the accurate and simultaneous inclusion of photoheating and SN feedback in models of the early Universe.
We study the impact of baryonic physics on cosmological parameter estimation with weak lensing surveys. We run a set of cosmological hydrodynamics simulations with different galaxy formation models. We then perform ray-tracing simulations through the total matter density field to generate 100 independent convergence maps of 25 deg$^2$ field-of-view, and use them to examine the ability of the following three lensing statistics as cosmological probes; power spectrum, peak counts, and Minkowski Functionals. For the upcoming wide-field observations such as Subaru Hyper Suprime-Cam (HSC) survey with a sky coverage of 1400 deg$^2$, the higher-order statistics provide tight constraints on the matter density, density fluctuation amplitude, and dark energy equation of state, but appreciable parameter bias is induced by the baryonic processes such as gas cooling and stellar feedback. When we use power spectrum, peak counts, and Minkowski Functionals, the relative bias in the dark energy equation of state parameter $w$ is at a level of, respectively, $\sim0.06\sigma$, $0.5-0.6\sigma$, and $0.01-0.1\sigma$ where $\sigma$ is the overall error derived from Fisher analysis. We find the bias is induced in different directions in the parameter space depending on the statistics employed. While the two-point statistics, i.e. power spectrum, yield robust results against baryonic effects, the overall constraining power is weak compared with the other higher-order statistics. On the other hand, using higher-order statistics alone results in significantly biased parameter estimate. We suggest to use an optimized combination of, for example, power spectrum and higher-order statistics so that the baryonic effects on parameter estimation are mitigated. Such `calibrated' combination can place stringent and robust constraints on cosmological parameters.
Measurement of Cosmic Microwave Background (CMB) anisotropies has been playing a lead role in precision cosmology by providing some of the tightest constrains on cosmological models and parameters. However, precision can only be meaningful when all major systematic effects are taken into account. Non-circular beams in CMB experiments can cause large systematic deviation in the angular power spectrum, not only by modifying the measurement at a given multipole, but also introducing coupling between different multipoles through a deterministic bias matrix. Here we add a mechanism for emulating the effect of a full bias matrix to the Planck likelihood code through the parameter estimation code SCoPE. We show that if the angular power spectrum was measured with a non-circular beam, the assumption of circular Gaussian beam or considering only the diagonal part of the bias matrix can lead to huge error in parameter estimation. We demonstrate that, at least for elliptical Gaussian beams, use of scalar beam window functions obtained via Monte Carlo simulations starting from a fiducial spectrum, as implemented in Planck analyses for example, leads to em only few percent of sigma deviation of the best-fit parameters. However, we notice more significant differences in the posterior distributions for some of the parameters, which would in turn lead to incorrect errorbars. These differences can be reduced, so that the errorbars match within few percent, by adding an iterative reanalysis step, where the beam window function would be recomputed using the best-fit spectrum estimated in the first step.
Inspired on the well known dynamical dichotomy predicted in voids, where some underdense regions expand whereas others collapse due to overdense surrounding regions, we explored the interplay between the void inner dynamics and its large scale environment. The environment is classified depending on its density as in previous works. We analyse the dynamical properties of void-centered spherical shells at different void-centric distances depending on this classification. The above dynamical properties are given by the angular distribution of the radial velocity field, its smoothness, the field dependence on the tracer density and shape, and the field departures from linear theory. We found that the velocity field in expanding voids follows more closely the linear prediction, with a more smooth velocity field. However when using velocity tracers with large densities such deviations increase. Voids with sizes around $18\,h^{-1}\,Mpc$ are in a transition regime between regions with expansion overpredicted and underpredicted from linear theory. We also found that velocity smoothness increases as the void radius, indicating the laminar flow dominates the expansion of larger voids (more than $18\,h^{-1}\,Mpc$). The correlations observed suggest that nonlinear dynamics of the inner regions of voids could be dependent on the evolution of the surrounding structures. These also indicate possible scale couplings between the void inner expansion and the large scale regions where voids are embedded. These results shed some light to the origin of nonlinearities in voids, going beyond the fact that voids just quickly becomes nonlinear as they become emptier.
We study the Integrated Sachs-Wolfe (ISW) effect in ghost-free, massive bigravity, where only one metric couples to matter. We focus on the infinite-branch bigravity (IBB) model which exhibits viable cosmic expansion histories and stable linear perturbations, while the cosmological constant is set to zero and the late-time accelerated expansion of the Universe is due solely to the gravitational interaction terms. The ISW contribution to the CMB auto-correlation power spectrum is predicted, as well as the cross-correlation between the CMB temperature anisotropies and the large-scale structure. We use ISW amplitudes as observed in the WMAP 9-year temperature data together with galaxy and AGN data provided by the WISE mission, in order to compare the theoretical predictions to the observations. The ISW amplitudes in IBB are found to be larger than the corresponding ones in the standard LCDM model by roughly a factor of 1.5, but are still consistent with the observations.
We discuss the potential of a next generation space-borne CMB experiment for studies of extragalactic sources with reference to COrE+, a project submitted to ESA in response to the M4 call. We consider three possible options for the telescope size: 1m, 1.5m and 2m (although the last option is probably impractical, given the M4 boundary conditions). The proposed instrument will be far more sensitive than Planck and will have a diffraction-limited angular resolution. These properties imply that even the 1m telescope option will perform substantially better than Planck for studies of extragalactic sources. The source detection limits as a function of frequency have been estimated by means of realistic simulations. The most significant improvements over Planck results are presented for each option. COrE+ will provide much larger samples of truly local star-forming galaxies, making possible analyses of the properties of galaxies (luminosity functions, dust mass functions, star formation rate functions, dust temperature distributions, etc.) across the Hubble sequence. Even more interestingly, COrE+ will detect, at |b|> 30 deg, thousands of strongly gravitationally lensed galaxies. Such large samples are of extraordinary astrophysical and cosmological value in many fields. Moreover, COrE+ high frequency maps will be optimally suited to pick up proto-clusters of dusty galaxies, i.e. to investigate the evolution of large scale structure at larger redshifts than can be reached by other means. Thanks to its high sensitivity COrE+ will also yield a spectacular advance in the blind detection of extragalactic sources in polarization. This will open a new window for studies of radio source polarization and of the global properties of magnetic fields in star forming galaxies and of their relationships with SFRs.
We present a general expression for the values of the average kinetic energy and of the temperature of kinetic decoupling of a WIMP, valid for any cosmological model. We show an example of the usage of our solution when the Hubble rate has a power-law dependence on temperature, and we show results for the specific cases of kination cosmology and low- temperature reheating cosmology.
The "green valley" is a wide region separating the blue and the red peaks in the ultraviolet-optical color magnitude diagram, first revealed using GALEX UV photometry. The term was coined by Christopher Martin in 2005. Green valley highlights the discriminating power of UV to very low relative levels of ongoing star formation, to which the optical colors, including u-r, are insensitive. It corresponds to massive galaxies below the star-forming "main" sequence, and therefore represents a critical tool for the study of the quenching of star formation and its possible resurgence in otherwise quiescent galaxies. This article reviews the results pertaining to morphology, structure, environment, dust content and gas properties of green valley galaxies in the local universe. Their relationship to AGN is also discussed. Attention is given to biases emerging from defining the "green valley" using optical colors. We review various evolutionary scenarios and we present evidence for a new, quasi-static view of the green valley, in which the majority of galaxies currently in the green valley were only partially quenched in the distant past and now participate in a slow cosmic decline of star formation, which also drives down the activity on the main sequence, presumably as a result of the dwindling accretion/cooling onto galaxy disks.
In the Local Group, almost all satellite dwarf galaxies that are within the virial radius of the Milky Way (MW) and M31 exhibit strong environmental influence. The orbital histories of these satellites provide the key to understanding the role of the MW/M31 halo, lower-mass groups, and cosmic reionization on the evolution of dwarf galaxies. We examine the virial-infall histories of satellites with M_star = 10 ^ {3 - 9} M_sun using the ELVIS suite of cosmological zoom-in dissipationless simulations of 48 MW/M31-like halos. Satellites at z = 0 fell into the MW/M31 halos typically 5 - 8 Gyr ago at z = 0.5 - 1. However, they first fell into any host halo typically 7 - 10 Gyr ago at z = 0.7 - 1.5. This difference arises because many satellites experienced "group preprocessing" in another host halo, typically of M_vir ~ 10 ^ {10 - 12} M_sun, before falling into the MW/M31 halos. Satellites with lower-mass and/or those closer to the MW/M31 fell in earlier and are more likely to have experienced group preprocessing; half of all satellites with M_star < 10 ^ 6 M_sun were preprocessed in a group. Infalling groups also drive most satellite-satellite mergers within the MW/M31 halos. Finally, none of the surviving satellites at z = 0 were within the virial radius of their MW/M31 halo during reionization (z > 6), and only < 4% were satellites of any other host halo during reionization. Thus, effects of cosmic reionization versus host-halo environment on the formation histories of surviving dwarf galaxies in the Local Group occurred at distinct epochs and are separable in time.
We review results from cosmic X-ray surveys of active galactic nuclei (AGNs) over the past ~ 15 yr that have dramatically improved our understanding of growing supermassive black holes (SMBHs) in the distant universe. First, we discuss the utility of such surveys for AGN investigations and the capabilities of the missions making these surveys, emphasizing Chandra, XMM-Newton, and NuSTAR. Second, we briefly describe the main cosmic X-ray surveys, the essential roles of complementary multiwavelength data, and how AGNs are selected from these surveys. We then review key results from these surveys on the AGN population and its evolution ("demographics"), the physical processes operating in AGNs ("physics"), and the interactions between AGNs and their environments ("ecology"). We conclude by describing some significant unresolved questions and prospects for advancing the field.
Light degrees of freedom that modify gravity on cosmological scales must be "screened" on solar system scales in order to be compatible with data. The Vainshtein mechanism achieves this through a breakdown of classical perturbation theory, as large interactions involving new degrees of freedom become important below the so-called Vainshtein radius. We begin to develop an extension of the Parameterized Post-Newtonian (PPN) formalism that is able to handle Vainshteinian corrections. We argue that theories with a unique Vainshtein scale must be expanded using two small parameters. In this Parameterized Post-Newtonian-Vainshteinian (PPNV) expansion, the primary expansion parameter that controls the PPN order is, as usual, the velocity $v$. The secondary expansion parameter, $\alpha$, controls the strength of the Vainshteinian correction and is a theory-specific combination of the Schwarzschild radius and the Vainshtein radius of the source that is independent of its mass. We present the general framework and apply it to Cubic Galileon theory both inside and outside the Vainshtein radius. The PPNV framework can be used to determine the compatibility of such theories with solar system and other strong-field data.
This is continuation of our programme to search for the elusive radio-quiet BL Lacs, by carrying out a systematic search for intranight optical variability (INOV) in a subset of `weak-line quasars' which are already designated as `high-confidence BL Lac candidate' and are also known to be radio-quiet. For 6 such radio-quiet weak-line quasars (RQWLQs), we present here new INOV observations taken in 11 sessions of duration >3 hours each. Combining these data with our previously published INOV monitoring of RQWLQs in 19 sessions yields INOV observations for a set of 15 RQWLQs monitored in 30 sessions, each lasting more than 3 hours. The 30 differential light curves, thus obtained for the 15 RQWLQs, were subjected to a statistical analysis using the F-test, and the deduced INOV characteristics of the RQWLQs then compared with those published recently for several prominent AGN classes, also applying the F-test. From our existing INOV observations, there is a hint that RQWLQs in our sample show a significantly higher INOV duty cycle than radio-quiet quasars and radio lobe-dominated quasars. Two sessions when we have detected strong (blazar-like) INOV for RQWLQs are pointed out, and these two RQWLQs are therefore the best known candidates for radio-quiet BL Lacs, deserving to be pursued. For a proper comparison with the INOV properties already established for (brighter) members of several prominent classes of AGN, a factor of 2-3 improvement in the INOV detection threshold for the RQWLQs is needed and it would be very interesting to check if that would yield a significantly higher estimate for INOV duty cycle than is found here.
Detection of supernovae (SNe) and, more generally, of transient events in large surveys can provide numerous false detections. In the case of a deferred processing of survey images, this implies reconstructing complete light curves for all detections, requiring sizable processing time and resources. Optimizing the detection of transient events is thus an important issue for both present and future surveys. We present here the optimization done in the SuperNova Legacy Survey (SNLS) for the 5-year data differed photometric analysis. In this analysis, detections are derived from stacks of subtracted images with one stack per lunation. The 3-year analysis provided 300,000 detections dominated by signals of bright objects that were not perfectly subtracted. We developed a subtracted image stack treatment to reduce the number of non SN-like events using morphological component analysis. This technique exploits the morphological diversity of objects to be detected to extract the signal of interest. At the level of our subtraction stacks, SN-like events are rather circular objects while most spurious detections exhibit different shapes. A two-step procedure was necessary to have a proper evaluation of the noise in the subtracted image stacks and thus a reliable signal extraction. We also set up a new detection strategy to obtain coordinates with good resolution for the extracted signal. SNIa Monte-Carlo (MC) generated images were used to study detection efficiency and coordinate resolution. When tested on SNLS 3-year data this procedure decreases the number of detections by two, losing only 5% of SN-like events, all faint ones. MC results show that SNIa detection efficiency is equivalent to that of the original method for bright events, while the coordinate resolution is improved.
We investigate the cosmological evolution of mimetic matter model with arbitrary scalar potential. The cosmological reconstruction is explicitly done for different choices of potential. The cases that mimetic matter model shows the evolution as Cold Dark Matter(CDM), wCDM model, dark matter and dark energy with dynamical $Om(z)$ or phantom dark energy with phantom-non-phantom crossing are presented in detail. The cosmological perturbations for such evolution are studied in mimetic matter model. For instance, the evolution behavior of the matter density contrast which is different from usual one, i.e. $\ddot \delta + 2 H \dot \delta - \kappa ^2 \rho \delta /2 = 0$ is investigated. The possibility of peculiar evolution of $\delta$ in the model under consideration is shown. Special attention is paid to the behavior of matter density contrast near to future singularity where decay of perturbations may occur much earlier the singularity.
We present a pilot study on the origin and assembly history of the ICL for four galaxy clusters at 0.44<z<0.57 observed with the Hubble Space Telescope from the Cluster Lensing and Supernova Survey with Hubble (CLASH) sample. Using this sample of clusters we set an empirical limit on the amount of scatter in ICL surface brightness profiles of such clusters at z=0.5 and constrain the progenitor population and formation mechanism of the ICL by measuring the ICL surface brightness profile, the ICL color and color gradient, and the total ICL luminosity within 10<r<110 kpc. The observed scatter is physical, which we associate with differences in ICL assembly process, formation epoch, and/or ICL content. Using stellar population synthesis models we transform the observed colors to metallicity. For three of the four clusters we find clear negative gradients that, on average, decrease from super solar in the central regions of the BCG to sub-solar in the ICL. Such negative color/metallicity gradients can arise from tidal stripping of L* galaxies and/or the disruption of dwarf galaxies, but not major mergers with the BCG. We also find that the ICL at 110 kpc has a color comparable to m*+2 red sequence galaxies and a total luminosity between 10<r<110 kpc of 4-8 L*. This suggests that the ICL is dominated by stars liberated from galaxies with L>0.2 L* and that neither dwarf disruption nor major mergers with the BCG alone can explain the observed level of luminosity and remain consistent with either the observed evolution in the faint end slope of the luminosity function or predictions for the number of BCG major mergers since z=1. Taken together, the results of this pilot study are suggestive of a formation history for these clusters in which the ICL is built-up by the stripping of >0.2 L* galaxies, and disfavor significant contribution to the ICL by dwarf disruption or major mergers with the BCG.
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We investigate the possibility of detecting the 3D cross correlation power spectrum of the Ly-$\alpha$ forest and HI 21 cm signal from the post reionization epoch. Other than the direct dependence on the dark matter power spectrum, the cross-correlation signal is found to be sensitive to the respective bias parameters which dictates the strength of anisotropy in redshift space. We find that the cross-correlation power spectrum can be detected using $400 ~ \, \rm hrs$ observation with SKA-mid (phase 1) and a futuristic BOSS like experiment with a quasar density of $30 ~ \rm deg^{-2}$ at a peak SNR of $15$ for a single field experiment at redshift $z = 2.5$. We model the clustering of HI distribution for the Ly-$\alpha$ forest and 21 cm signal on large scales using the linear bias model. We probe the possibility of independently constraining these parameters using the cross power spectrum. We find that with the same experiments $1 \sigma$ marginalized errors on the 21-cm linear redshift space distortion parameter $\beta_T$ and $\beta_F$ corresponding to the Ly-$\alpha $ forest are $\sim 2.7 \%$ and $\sim 1.4 \%$ respectively for $10$ independent pointings of the SKA. This prediction indicates a significant improvement over existing measurements. We claim that the cross correlation of the Ly-$\alpha$ and 21 cm observation in 3D not only ascertains the cosmological origin of the signal in presence of astrophysical foregrounds but also provides stringent constraints on large scale HI bias. This provides an independent probe towards understanding cosmological structure formation.
Dark Stars (DS) are stellar objects made (almost entirely) of ordinary atomic material but powered by the heat from Dark Matter (DM) annihilation (rather than by fusion). Weakly Interacting Massive Particles (WIMPs), among the best candidates for DM, can be their own antimatter and can accumulate inside the star, with their annihilation products thermalizing with and heating the DS. The resulting DSs are in hydrostatic and thermal equilibrium. The first phase of stellar evolution in the history of the Universe may have been dark stars. Though DM constituted only $<0.1\%$ of the mass of the star, this amount was sufficient to power the star for millions to billions of years. Depending on their DM environment, early DSs can become very massive ($>10^6 M_\odot$), very bright ($>10^9 L_\odot$), and potentially detectable with the James Webb Space Telescope (JWST). Once the DM runs out and the dark star dies, it may collapse to a black hole; thus DSs can provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses DSs existing today but focuses on the early generation of dark stars.
The remarkable progress in cosmic microwave background (CMB) studies over past decade has led to the era of precision cosmology in striking agreement with the $\Lambda$CDM model. However, the lack of power in the CMB temperature anisotropies at large angular scales (low-$\ell$), as has been confirmed by the recent Planck data also (up to $\ell=40$), is still an open problem. One can avoid to seek an explanation for this problem by attributing the lack of power to cosmic variance or can look for explanations i.e., different inflationary potentials or initial conditions for inflation to begin with, non-trivial topology, ISW effect etc. Features in the primordial power spectrum (PPS) motivated by the early universe physics has been the most common solution to address this problem. In the present work we also follow this approach and consider a set of PPS which have features and constrain the parameters of those using WMAP 9 year and Planck data employing Markov-Chain Monte Carlo (MCMC) analysis. The prominent feature of all the models of PPS that we consider is an infra-red cut off which leads to suppression of power at large angular scales. We consider models of PPS with maximum three extra parameters and use Akaike information criterion ($AIC$) of model selection to compare the models. We find that inflationary models with cut off features lead to a better fit of the observed data compared to simple power law model. For most models we find good constraints for the cut off scale $k_c$, however, for other parameters our constraints are not that good. We find that model with sharp cut off in PPS best-fit the WMAP 9 year data and Starabinsky models is the preferred model for the joint WMAP 9 year + Planck data set, which is also able to produce CMB power suppression up to $\ell\leq30$ to some extent.
In this work we model the quintessence potential in a Taylor series expansion, up to second order, around the present-day value of the scalar field. The field is evolved in a thawing regime assuming zero initial velocity. We use the latest data from the Planck satellite, baryonic acoustic oscillations observations from the Sloan Digital Sky Survey, and Supernovae luminosity distance information from Union$2.1$ to constrain our models parameters, and also include perturbation growth data from WiggleZ. We show explicitly that the growth data does not perform as well as the other datasets in constraining the dark energy parameters we introduce. We also show that the constraints we obtain for our model parameters, when compared to previous works of nearly a decade ago, have not improved significantly. This is indicative of how little dark energy constraints, overall, have improved in the last decade, even when we add new growth of structure data to previous existent types of data.
In this paper the next attempt is made to clarify the nature of the Euclidean behavior of the boundary in the angular size-redshift cosmological test. It is shown experimentally that this can be explained by the selection determined by anisotropic morphology and anisotropic radiation of extended radio sources. A catalogue of extended radio sources with minimal flux densities of about 0.01 Jy at 1.4 GHz was compiled for conducting the test. Without the assumption of their size evolution, the agreement between the experiment and calculation was obtained both in the Lambda CDM model (Omega_m=0.27 , Omega_v=0.73.) and the Friedman model (Omega = 0.1 ).
The minimal sub-Planckian axion inflation model accounts for a large scalar-to-tensor ratio via a spiralling trajectory in the field space of a complex field $\Phi$. Here we consider how the predictions of the model are modified by Planck scale-suppressed corrections. In the absence of Planck corrections the model is equivalent to a $\phi^{4/3}$ chaotic inflation model. Planck corrections become important when the dimensionless coupling $\xi$ of $|\Phi|^{2}$ to the topological charge of the strongly-coupled gauge sector $F \tilde{F}$ satisfies $\xi \sim 1$. For values of $|\Phi|$ which allow the Planck corrections to be understood via an expansion in powers of $|\Phi|^{2}/M_{Pl}^{2}$, we show that their effect is produce a significant modification of the tensor-to-scalar ratio from its $\phi^{4/3}$ chaotic inflation value without strongly modifying the spectral index. In addition, to leading order in $|\Phi|^2/M_{Pl}^{2}$, the Planck modifications of $n_{s}$ and $r$ satisfy a consistency relation, $\Delta n_{s} = - \Delta r/16$. Observation of these shifts and their correlation would allow the model to be distinguished from a simple $\phi^{4/3}$ chaotic inflation model and would also provide a signature for the influence of leading-order Planck corrections.
Using a framework based on the 1+3 formalism we carry out a study on axially and reflection symmetric perfect and geodesic fluids, looking for possible models of sources radiating gravitational waves. Therefore, the fluid should be necessarily shearing, for otherwise the magnetic part of the Weyl tensor vanishes, leading to a vanishing of the super-Poynting vector. However, for the family of perfect, geodesic fluids considered here, it appears that all possible cases reduce to conformally flat, shear--free, vorticity-free, fluids, i.e Friedmann-Roberston-Walker. The super-Poynting vector vanishes and therefore no gravitational radiation is expected to be produced. The physical meaning of the obtained result is discussed.
We propose an extension of natural inflation, where the inflaton potential is a general periodic function. Specifically, we study elliptic inflation where the inflaton potential is given by Jacobi elliptic functions or Jacobi theta functions, which appear in gauge and Yukawa couplings in the string theories compactified on toroidal backgrounds. We show that the predicted values of the spectral index and the tensor-to-scalar ratio interpolate from natural inflation to exponential inflation such as $R^2$- and Higgs inflation or brane inflation, where the spectral index asymptotes to $n_s = 1-2/N \simeq 0.967$ for the e-folding number $N = 60$. Such elliptic inflation can be thought of as a specific realization of multi-natural inflation, where the inflaton potential consists of multiple sinusoidal functions. We also discuss examples in string theory where the Jacobi theta function appears in the inflaton potential.
We report the discovery of the merging cluster, RXCJ2359.3-6042, from the REFLEX II cluster survey and present our results from all three detectors combined in the imaging and spectral analysis of the XMM-Newton data. Also known as Abell 4067, this is a unique system, where a compact bullet penetrates an extended, low density cluster at redshift z=0.099 clearly seen from our follow-up XMM-Newton observation. The bullet goes right through the central region of the cluster without being disrupted and we can clearly watch the process how the bullet component is stripped of its layers outside the core. There is an indication of a shock heated region in the East of the cluster with a higher temperature. The bulk temperature of the cluster is about 3.12 keV implying a lower mass system. Spearheading the bullet is a cool core centred by a massive early type galaxy. The temperatures and metallicities of a few regions in the cluster derived from the spectral analysis supports our conjecture based on the surface brightness image that a much colder compact component at 1.55 keV with large metallicity (0.75 Zsol) penetrates the main cluster, where the core of the infalling component survived the merger leaving stripped gas behind at the centre of the main cluster. We also give an estimate of the total mass within r500, which is about 2e14Msol from the deprojected spherical-beta modelling of the cluster in good agreement with other mass estimates from the M--Tx and M-sigma_v relations.
The lore paradigm for solving so-called horizon and flatness problems in cosmology is the primordial inflation. Plethora of inflationary models have been built in last decades and first experimental probes seem to appear in favor of the inflationary paradigm. We will focus here on one of them, the Higgs inflation, and show the combined constraint required for such a model at cosmological as well as gravitational scales, i.e. for compact objects. We will show that Higgs inflation model gives rise to particlelike solutions around compact objects, dubbed Higgs monopoles, characterized by the nonminimal coupling parameter as well as the mass and the compactness of the object. For large values of the nonminimal coupling constant and specific compactness, the amplitude of the Higgs field inside the matter distribution can be arbitrarily large.
The galilean genesis scenario is an alternative to inflation in which the universe starts expanding from Minkowski in the asymptotic past by violating the null energy condition stably. Several concrete models of galilean genesis have been constructed so far within the context of galileon-type scalar-field theories. We give a generic, unified description of the galilean genesis scenario in terms of the Horndeski theory, i.e., the most general scalar-tensor theory with second-order field equations. In doing so we generalize the previous models to have a new parameter (denoted by {\alpha}) which results in controlling the evolution of the Hubble rate. The background dynamics is investigated to show that the generalized galilean genesis solution is an attractor, similarly to the original model. We also study the nature of primordial perturbations in the generalized galilean genesis scenario. In all the models described by our generalized genesis Lagrangian, amplification of tensor perturbations does not occur as opposed to what happens in quasi-de Sitter inflation. We show that the spectral index of curvature perturbations is determined solely from the parameter {\alpha} and does not depend on the other details of the model. In contrast to the original model, a nearly scale-invariant spectrum of curvature perturbations is obtained for a specific choice of {\alpha}.
We present the structural and star formation properties of 59 void galaxies as part of the Void Galaxy Survey (VGS). Our aim is to study in detail the physical properties of these void galaxies and study the effect of the void environment on galaxy properties. We use Spitzer 3.6 $\rm{\mu m}$ and B-band imaging to study the morphology and color of the VGS galaxies. For their star formation properties, we use Halpha and GALEX near-UV imaging. We compare our results to a range of galaxies of different morphologies in higher density environments. We find that the VGS galaxies are in general disk dominated and star forming galaxies. Their star formation rates are, however, often less than 1 $\rm{M_{\odot}}$ $\rm{yr^{-1}}$. There are two early-type galaxies in our sample as well. In $\rm{r_{e}}$ versus $\rm{M_{B}}$ parameter space, VGS galaxies occupy the same space as dwarf irregulars and spirals.
We introduce Coronal-Line Forest Active Galactic Nuclei (CLiF AGN), AGN which have a rich spectrum of forbidden high-ionization lines (FHILs, e.g. [FeVII], [FeX] and [NeV]), as well as relatively strong narrow ($\sim$300 km s$^{-1}$) H$\alpha$ emission when compared to the other Balmer transition lines. We find that the kinematics of the CLiF emitting region are similar to those of the forbidden low-ionization emission-line (FLIL) region. We compare emission line strengths of both FHILs and FLILs to CLOUDY photoionization results and find that the CLiF emitting region has higher densities (10$^{4.5}$ $<$ n$_H$ $<$ 10$^{7.5}$ cm$^{-3}$) when compared to the FLIL emitting region (10$^{3.0}$ $<$ n$_H$ $<$ 10$^{4.5}$ cm$^{-3}$). We use the photoionization results to calculate the CLiF regions radial distances (0.04 $<$ R$_{CLiF}$ $<$ 32.5 pc) and find that they are comparable to the dust grain sublimation distances (0.10 $<$ R$_{SUB}$ $<$ 4.3 pc). As a result we suggest that the inner torus wall is the most likely location of the CLiF region, and the unusual strength of the FHILs is due to a specific viewing angle giving a maximal view of the far wall of the torus without the continuum being revealed.
We perform a blind search for the variability of the gamma-ray sky in the energy range E>1 GeV using 308 weeks of the Fermi-LAT data. We use the technique based on the comparison of the weekly photon counts and exposures in sky pixels by means of the Kolmogorov-Smirnov test. We consider the flux variations in the region significant if statistical probability of uniformity is less than $4\times10^{-6}$, which corresponds to 0.05 false detections in the whole set of 12288 pixels. Close inspection of the detected variable regions result in identification of 8 sources without previous known variability. Two of them are included in the second Fermi LAT source catalogue (FBQS J122424.1+243623 and GB6 J0043+3426) and one (3EG J1424+3734) was reported by EGRET and also was included in the First Fermi LAT source catalogue (1FGL), but is missing in the 2FGL. Possible identifications of five other sources are obtained using NED and SIMBAD databases (1RXS J161939.9+765515, PMN J2320-6447, PKS 0226-559, PKS J0030-0211, PMN J0225-2603). These new variable gamma-ray sources demonstrate recurring flaring activity with time scale ~weeks and have hard spectra. Their spectral energy distributions deviate significantly from a simple power-law shape and often peak around ~GeV. These properties of activity are typical for flaring blazars.
We study the cosmology of bimetric theory with a composite matter coupling. We find two possible branches of background evolution. We investigate the question of stability of cosmological perturbations. For the tensor and vector perturbations, we derive conditions on the absence of ghost and gradient instabilities. For the scalar modes, we obtain conditions for avoiding ghost degrees. In the first branch, we find that one of the scalar modes becomes a ghost at the late stages of the evolution. Conversely, this problem can be avoided in the second branch. However, we also find that the constraint for the second branch prevents the doubly coupled matter fields from being the standard ingredients of cosmology. We thus conclude that a realistic and stable cosmological model requires additional minimally coupled matter fields.
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The redshift-space distortion (RSD) of galaxies surrounding massive clusters is emerging as a promising testbed for theories of modified gravity. Conventional applications of this method rely upon the assumption that the velocity field in the cluster environment is uniquely determined by the cluster mass profile. Yet, real dark matter halos in N-body simulations are known to violate the assumption that virial mass determines the configuration space distribution, an effect known as assembly bias. In this Letter, I show that assembly bias in simulated dark matter halos also manifests in velocity space. In the 1-10 Mpc environment surrounding a cluster, high-concentration "tracer" halos exhibit a 10-20% larger pairwise-velocity dispersion profile relative to low-concentration tracer halos of the same mass. This difference is comparable to the size of the RSD signal predicted by f(R) models designed to account for the cosmic acceleration. I use the age matching technique to study how color-selection effects may influence the cluster RSD signal, finding a ~10% effect due to redder satellites preferentially occupying higher mass halos, and a ~5% effect due to assembly-biased colors of centrals. In order to use cluster RSD measurements to robustly constrain modified gravity, we likely will need to develop empirical galaxy formation models more sophisticated than any in the current literature.
We compare model results from our semi-analytic merger tree based framework for high-redshift ($z \simeq 5-20$) galaxy formation against reionization indicators including the Planck electron scattering optical depth ($\tau_{es}$) and the ionizing photon emissivity ($\dot n_{ion}$) to constrain the particle mass of Warm Dark Matter (WDM). Our framework traces the Dark Matter (DM) and baryonic assembly of galaxies in 4 DM cosmologies: Cold Dark Matter (CDM) and WDM with a particle mass of $m_x = 2.25,3$ and 5 keV. It includes all the key processes of star formation, supernova feedback, the merger/accretion/ejection driven evolution of gas and stellar mass, and the effect of the ultra-violet background (UVB) created during reionization in photo-evaporating the gas content of galaxies in halos with $M_h \leq 10^9 M_\odot$. We show that current Planck $\tau_{es}$ values rule out $m_x \leq 2.5$ keV WDM, even in the physically unlikely scenario that all ionizing photons produced by these galaxies escape and contribute to reionization (i.e. $f_{esc}=1$). With the largest number of UVB-suppressed galaxies, CDM faces a "stalling" of the reionization process with this effect decreasing with the disappearance of small-scale structure with decreasing $m_x$. Finally, we find the bulk of the reionization photons come from galaxies with a halo mass $M_h \leq 10^9M_\odot$, stellar mass $M_* \leq 10^7M_\odot$ and UV magnitude $ -18 \leq M_{UV} \leq -13$ in CDM. The progressive suppression of low-mass halos with decreasing $m_x$ leads to a shift in the "reionization" population to larger (halo and stellar) masses of $M_h \geq 10^9M_\odot$ and $M_* \geq 10^7M_\odot$ for $m_x \geq 3$ keV WDM, although the UV limits effectively remain unchanged.
The use of Type~Ia SNe has thus far produced the most reliable measurement of the expansion history of the Universe, suggesting that $\Lambda$CDM offers the best explanation for the redshift--luminosity distribution observed in these events. But the analysis of other kinds of source, such as cosmic chronometers, gamma ray bursts, and high-$z$ quasars, conflicts with this conclusion, indicating instead that the constant expansion rate implied by the $R_{\rm h}=ct$ Universe is a better fit to the data. The central difficulty with the use of Type~Ia SNe as standard candles is that one must optimize three or four nuisance parameters characterizing supernova luminosities simultaneously with the parameters of an expansion model. Hence in comparing competing models, one must reduce the data independently for each. We carry~out such a comparison of $\Lambda$CDM and the $R_{\rm h}=ct$ Universe, using the Supernova Legacy Survey (SNLS) sample of 252 SN~events, and show that each model fits its individually reduced data very well. But since $R_{\rm h}=ct$ has only one free parameter (the Hubble constant), it follows from a standard model selection technique that it is to be preferred over $\Lambda$CDM, the minimalist version of which has three (the Hubble constant, the scaled matter density and either the spatial curvature constant or the dark-energy equation-of-state parameter). We estimate by the Bayes Information Criterion that in a pairwise comparison, the likelihood of $R_{\rm h}=ct$ is $\sim 90\%$, compared with only $\sim 10\%$ for a minimalist form of $\Lambda$CDM, in which dark energy is simply a cosmological constant. Compared to $R_{\rm h}=ct$, versions of the standard model with more elaborate parametrizations of dark energy are judged to be even less likely.
We investigate whether the large scale structure environment of galaxy clusters imprints a selection bias on Sunyaev Zel'dovich (SZ) catalogs. Such a selection effect might be caused by line of sight (LoS) structures that add to the SZ signal or contain point sources that disturb the signal extraction in the SZ survey. We use the Planck PSZ1 union catalog (Planck Collab- oration et al. 2013a) in the SDSS region as our sample of SZ selected clusters. We calculate the angular two-point correlation function (2pcf) for physically correlated, foreground and background structure in the RedMaPPer SDSS DR8 catalog with respect to each cluster. We compare our results with an optically selected comparison cluster sample and with theoretical predictions. In contrast to the hypothesis of no environment-based selection, we find a mean 2pcf for background structures of -0.049 on scales of $\lesssim 40'$, significantly non-zero at $\sim 4 \sigma$, which means that Planck clusters are more likely to be detected in regions of low background density. We hypothesize this effect arises either from background estimation in the SZ survey or from radio sources in the background. We estimate the defect in SZ signal caused by this effect to be negligibly small, of the order of $\sim 10^{-4}$ of the signal of a typical Planck detection. Analogously, there are no implications on X-ray mass measurements. However, the environ- mental dependence has important consequences for weak lensing follow up of Planck galaxy clusters: we predict that projection effects account for half of the mass contained within a 15' radius of Planck galaxy clusters. We did not detect a background underdensity of CMASS LRGs, which also leaves a spatially varying redshift dependence of the Planck SZ selection function as a possible cause for our findings.
We represent a method to reconstruct the equation of state for dark energy directly from observational Hubble parameter data in a nonparametric way. We use principal component analysis (PCA) to extract the signal from data with noise. In addition, we modify Akaike information criteria (AIC) to guarantee the quality of reconstruction and avoid over-fitting simultaneously. The results show that our method is robust in reconstruction of dark energy equation of state. Although current observational Hubble parameter data alone can not give a strong constraint yet, future observations with more accurate data can help to improve the quality of reconstruction significantly, which is consistent with the results of H.-R. Yu et al.
Galaxy intrinsic alignment can be a severe source of error in weak-lensing studies. The problem has been widely studied by numerical simulations and with heuristic models, but without a clear theoretical justification of its origin and amplitude. In particular, it is still unclear whether intrinsic alignment of galaxies is dominated by formation and accretion processes or by the effects of the instantaneous tidal field acting upon them. We investigate this question by developing a simple model of intrinsic alignment for elliptical galaxies, based on the instantaneous tidal field. Making use of the galaxy stellar distribution function, we estimate the intrinsic alignment signal and find that although it has the expected dependence on the tidal field, it is too weak to account for the observed signal. This is an indirect validation of the standard view that intrinsic alignment is caused by formation and/or accretion processes.
Context. Galaxy clusters can be used as cosmological probes, but to this end, they need to be thoroughly understood. Combining all cluster observables in a consistent way will help us to understand their global properties and their internal structure. Aims. We provide proof of the concept that the projected gravitational potential of galaxy clusters can directly be reconstructed from X-ray observations. We also show that this joint analysis can be used to locally test the validity of the equilibrium assumptions in galaxy clusters. Methods. We used a newly developed reconstruction method, based on Richardson-Lucy deprojection, that allows reconstructing projected gravitational potentials of galaxy clusters directly from X-ray observations. We applied this algorithm to the well-studied cluster Abell 1689 and compared the gravitational potential reconstructed from X-ray observables to the potential obtained from gravitational lensing measurements. [...] Results. Assuming spherical symmetry and hydrostatic equilibrium, the potentials recovered from gravitational lensing and from X-ray emission agree very well beyond 500 kpc. Owing to the fact that the Richardson-Lucy deprojection algorithm allows deprojecting each line of sight independently, this result may indicate that non-gravitational effects and/or asphericity are strong in the central regions of the clusters. Conclusions. We demonstrate the robustness of the potential reconstruction method based on the Richardson-Lucy deprojection algorithm and show that gravitational lensing and X-ray emission lead to consistent gravitational potentials. Our results illustrate the power of combining galaxy-cluster observables in a single, non-parametric, joint reconstruction of consistent cluster potentials that can be used to locally constrain the physical state of the gas.
The extremely high sensitivity and resolution of the Square Kilometre Array (SKA) will be useful for addressing a wide set of themes relevant for cosmology, in synergy with current and future cosmic microwave background (CMB) projects. Many of these themes also have a link with future optical-IR and X-ray observations. We discuss the scientific perspectives for these goals, the instrumental requirements and the observational and data analysis approaches, and identify several topics that are important for cosmology and astrophysics at different cosmic epochs.
We present constraints on testing general relativity (GR) at cosmological scales using recent data sets and the impact of galaxy intrinsic alignment (IA) in the CFHTLenS lensing data on those constraints. We consider CMB temperature data from Planck, the galaxy power spectrum from WiggleZ, weak lensing tomography from the CFHTLenS, ISW-galaxy cross correlations, and BAO data from 6dF, SDSS DR7, and BOSS DR9. We use a parameterization of the modified gravity (MG) that is binned in redshift and scale, a parameterization that evolves monotonically in scale but is binned in redshift, and a functional parameterization that evolves only in redshift. We present the results in terms of the MG parameters $Q$ and $\Sigma$. We employ an IA model with an amplitude $A_{CFHTLenS}$ that is included in the parameter analysis. We find an improvement in the constraints on the MG parameters corresponding to $40-53\%$ increase on the figure of merit compared to previous studies, and GR is found consistent with the data at the $95\%$ CL. The bounds found on $A_{CFHTLenS}$ are sensitive to whether the MG parameterization is scale dependent, and the correlations between $A_{CFHTLenS}$ and MG parameters are found weak to moderate. $A_{CFHTLenS}$ is found consistent with zero for the 3 MG parameterizations and when the whole lensing sample is used. A significantly non-zero $A_{CFHTLenS}$ for GR and the scale-independent MG parameterization is found when we use the optimized early-type galaxy sample of (Heymans et al. 2013). We find that the tensions observed in previous studies persist, and there is an indication that CMB data and lensing data prefer different values for MG parameters, particularly for the parameter $\Sigma$. The analysis of the confidence contours and probability distributions suggest that the bimodality found follows that of the known tension in the $\sigma_8$ parameter. (Abridged)
We review most dynamical constraints on the gravitational field of spiral galaxies in general, and of the Milky Way in particular. Such constraints are of prime importance for determining the characteristics of the putative dark matter haloes of galaxies. For the Milky Way, we review observational constraints in the inner parts (cored or cusped dark matter distribution, maximum disk or not), in the solar neighbourhood (local dark matter density) and in the outer parts (virial mass and triaxial shape of the dark matter halo). We also point out various caveats, systematic effects, and large current uncertainties. Many fundamental parameters such as the local circular velocity are poorly known, evidence for triaxiality of the dark halo is shaky, and different estimates of the virial mass as well as of the local dark matter density vary by at least a factor of two. We however argue that the current best-fit value for the local dark matter density, which should be used as a benchmark for direct dark matter detection searches, is of the order of 0.5 GeV/cm3. We also explain why alternatives to particle dark matter on galactic scales should still be very seriously considered.
The mass and structural evolution of massive galaxies is one of the hottest topics in galaxy formation. This is because it may reveal invaluable insights into the still debated evolutionary processes governing the growth and assembly of spheroids. However, direct comparison between models and observations is usually prevented by the so-called "progenitor bias", i.e., new galaxies entering the observational selection at later epochs, thus eluding a precise study of how pre-existing galaxies actually evolve in size. To limit this effect, we here gather data on high-redshift brightest group and cluster galaxies, evolve their (mean) host halo masses down to z=0 along their main progenitors, and assign as their "descendants" local SDSS central galaxies matched in host halo mass. At face value, the comparison between high redshift and local data suggests a noticeable increase in stellar mass of a factor of >2 since z~1, and of >2.5 in mean effective radius. We then compare the inferred stellar mass and size growth with those predicted by hierarchical models for central galaxies, selected at high redshifts to closely match the halo and stellar mass bins as in the data. Only hierarchical models characterized by very limited satellite stellar stripping and parabolic orbits are capable of broadly reproducing the stellar mass and size increase of a factor ~2-4 observed in cluster galaxies since z ~1. The predicted, average (major) merger rate since z~1 is in good agreement with the latest observational estimates.
Interaction of charges in CCDs with the already accumulated charge distribution causes both a flux dependence of the point-spread function (an increase of observed size with flux, also known as the brighter/fatter effect) and pixel-to-pixel correlations of the noise in flat fields. We describe these effects in the Dark Energy Camera (DECam) with charge dependent shifts of effective pixel borders, i.e. the Antilogus et al. (2014) model, which we fit to measurements of flat-field noise correlations. The latter fall off approximately as a power-law r^-2.5 with pixel separation r, are isotropic except for an asymmetry in the direct neighbors along rows and columns, are stable in time, and are weakly dependent on wavelength. They show variations from chip to chip at the 20% level that correlate with the silicon resistivity. The charge shifts predicted by the model cause biased shape measurements, primarily due to their effect on bright stars, at levels exceeding weak lensing science requirements. We measure the flux dependence of star images and show that the effect can be mitigated by applying the reverse charge shifts at the pixel level during image processing. Differences in stellar size, however, remain significant due to residuals at larger distance from the centroid.
Higgs G-inflation takes advantage of a Galileon-like ghost-free derivative coupling. It is a nonrenormalizable operator and is strongly coupled at high energy scales. Perturbative analysis has no longer predictive power there. In general, when the Lagrangian is expanded around the vacuum, the strong coupling scale is identified as the mass scale that appears in nonrenormalizable operators. In inflationary models, however, the identification of the strong coupling scale is subtle, since the structures of the kinetic term as well as the interaction itself are modified by the background inflationary dynamics. As a result, the strong coupling scale is back ground field dependent. In this letter, we evaluate the strong coupling scale of the fluctuations around the inflationary background including the Nambu Goldstone mode associated with the symmetry breaking in the Higgs G-inflation. We find that the system is weakly coupled when the scales which we now observe exit the horizon during inflation, and the observational predictions with the semiclassical treatment are valid. However, we also find that the inflaton field value where the strong coupling scale and the Hubble scale meet is less than the Planck scale. Therefore, we cannot describe the model from the Planck scale, or the chaotic initial condition.
We present the first extensive study of the coronal line variability in an active galaxy. Our data set for the nearby source NGC 4151 consists of six epochs of quasi-simultaneous optical and near-infrared spectroscopy spanning a period of about eight years and five epochs of X-ray spectroscopy overlapping in time with it. None of the coronal lines showed the variability behaviour observed for the broad emission lines and hot dust emission. In general, the coronal lines varied only weakly, if at all. Using the optical [Fe VII] and X-ray O VII emission lines we estimate that the coronal line gas has a relatively low density of n~10^3 cm^-3 and a relatively high ionisation parameter of log U~1. The resultant distance of the coronal line gas from the ionising source is about two light years, which puts this region well beyond the hot inner face of the obscuring dusty torus. The high ionisation parameter implies that the coronal line region is an independent entity rather than part of a continuous gas distribution connecting the broad and narrow emission line regions. We present tentative evidence for the X-ray heated wind scenario of Pier & Voit. We find that the increased ionising radiation that heats the dusty torus also increases the cooling efficiency of the coronal line gas, most likely due to a stronger adiabatic expansion.
We consider the evolution of electromagnetic fields coupled to conduction currents during the reheating era, under the assumption that the currents may be described by second order casual hydrodynamics. The resulting theory is not conformally invariant. The expansion of the Universe produces temperature gradients which couple to the current and generally oppose Ohmic dissipation. Although the effect is not strong, it suggests that the unfolding of hydrodynamic instabilities in these models may follow a different pattern than in first order theories, and even than in second order theories on non expanding backgrounds.
Interactions between dark matter and dark energy, allowing both conformal and and disformal couplings, are studied in detail. We discuss the background evolution, anisotropies in the cosmic microwave background and large scale structures. One of our main findings is that a large conformal coupling is not necessarily disallowed in the presence of a general disformal term. On the other hand, we find that negative disformal couplings very often lead to instabilities in the scalar field. Studying the background evolution and linear perturbations only, our results show that it is observationally challenging to disentangle disformal from purely conformal couplings.
Measurements of the neutral hydrogen gas content of a sample of 93 post-merger galaxies are presented, from a combination of matches to the ALFALFA.40 data release and new Arecibo observations. By imposing completeness thresholds identical to that of the ALFALFA survey, and by compiling a mass-, redshift- and environment-matched control sample from the public ALFALFA.40 data release, we calculate gas fraction offsets (Delta f_gas) for the post-mergers, relative to the control sample. We find that the post-mergers have HI gas fractions that are consistent with undisturbed galaxies. However, due to the relative gas richness of the ALFALFA.40 sample, from which we draw our control sample, our measurements of gas fraction enhancements are likely to be conservative lower limits. Combined with comparable gas fraction measurements by Fertig et al. in a sample of galaxy pairs, who also determine gas fraction offsets consistent with zero, we conclude that there is no evidence for significant neutral gas consumption throughout the merger sequence. From a suite of 75 binary merger simulations we confirm that star formation is expected to decrease the post-merger gas fraction by only 0.06 dex, even several Gyr after the merger. Moreover, in addition to the lack of evidence for gas consumption from gas fraction offsets, the observed HI detection fraction in the complete sample of post-mergers is twice as high as the controls, which suggests that the post-merger gas fractions may actually be enhanced. We demonstrate that a gas fraction enhancement in post-mergers, relative to a stellar mass-matched control sample, would indeed be the natural result of merging randomly drawn pairs from a parent population which exhibits a declining gas fraction with increasing stellar mass.
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We discuss the question of gauge choice when analysing second-order relativistic perturbations and when defining the galaxy bias at second order. Some misconceptions in the recent literature on the comoving-synchronous gauge are addressed and we show that this gauge is appropriate at second order to describe the matter overdensity and to define local Lagrangian bias.
We make use of two suites of ultra-high resolution N-body simulations of individual dark matter haloes, the Phoenix and the Aquarius Projects, to investigate the systematics of subhalo assembly histories in host haloes differing by a factor of 1000 in mass. We find that the progenitors of the present day subhalo population are relatively more abundant in high mass haloes, in contrast to previous studies claiming a universal abundance independent of the mass of the host halo. This is mainly because these studies count progenitors that pass through the halo and are later re-accreted more than once. The fraction of these 'wavering' progenitors is larger in less massive haloes. The typical accretion time for all progenitors varies strongly with host halo mass: $z \sim 5$ for the Galactic-scale Aquarius haloes and $z \sim 2.5$ for the cluster-scale Phoenix haloes. Once progenitors start to orbit their parent haloes, they rapidly lose their original mass, but nevertheless more than 80 (70) percent of them survive to present day in the Phoenix (Aquarius) haloes. At given redshift, the fraction of subhaloes that survive is independent of the host halo mass, whilst the fraction of mass lost by subhaloes is larger in higher mass haloes. These systematics explain many similarities and differences between subhalo populations in haloes of different masses at the present day.
Constraining the properties of Population III (Pop III) stars will be very challenging because they reside in small galaxies at high redshift which will be difficult to detect even with future instruments such as the James Webb Space Telescope (JWST). In this paper, we suggest that intensity mapping may be a promising method to study Pop III stars. Intensity mapping is a technique proposed to measure large-scale fluctuations of galaxy line emission in three dimensions without resolving individual sources. This technique is well suited for observing many faint galaxies because it can measure their cumulative emission even if they cannot be directly detected. We focus on intensity mapping of He II recombination lines, and in particular He II 1640 \AA{}. These lines are much stronger in Pop III stars than Pop II stars because the harder spectra of Pop III stars are expected to produce many He II ionizing photons. Measuring the He II 1640 \AA{} intensity mapping signal, along with the signals from other lines such as Ly$\alpha$, H$\alpha$, and metal lines, could give constraints on the initial mass function (IMF) and star formation rate density (SFRD) of Pop III stars as a function of redshift. To demonstrate the feasibility of these observations, we estimate the strength of the Pop III He II 1640 \AA{} intensity mapping signal from $z=10-20$. We show that at $z\approx10$, the signal could be measured accurately by two different hypothetical future instruments, one which cross-correlates He II 1640 \AA{} with CO(1-0) line emission from galaxies and the other with 21 cm emission from the intergalactic medium (IGM).
We analyze publicly available void catalogs of the Baryon Oscillation Spectroscopic Survey Data Release 10 at redshifts $0.4<z<0.7$. The first goal of this paper is to extend the Cosmic Microwave Background stacking analysis of previous spectroscopic void samples at $z<0.4$. In addition, the DR10 void catalog provides the first chance to spectroscopically probe the volume of the Granett et al. (2008) supervoid catalog that constitutes the only set of voids which has shown a significant detection of a cross-correlation signal between void locations and average CMB chill. We found that the positions of voids identified in the spectroscopic DR10 CMASS galaxy catalog typically do not coincide with the locations of the Granett et al. (2008) supervoids in the overlapping volume, in spite of the presence of large underdense regions of high void-density in DR10. The stacking of filtered CMB temperatures at these different void locations shows a $\Delta T = - 6.2 \pm 3.4 ~\mu K$ signal for the 120 largest voids, otherwise the correlation is washed out by statistical uncertainties. This correlation is, however, significantly lower than the $\Delta T = - 11.5 \pm 3.7 ~\mu K$ we found by stacking 35 of the 50 Granett et al. (2008) supervoids available in the DR10 volume. This failure to reproduce the signal with a different void catalog may be due to systematic differences in the detection of voids in photometric and spectroscopic samples.
We address how to construct an infinitely cyclic universe model. A major consideration is to make the entropy cyclic which requires the entropy to be reset to zero in each cycle expansion to turnaround, to contraction, to bounce, etc. Here we reset entropy at the turnaround by selecting the visible universe from the multiverse which is generated by the accelerated expansion. In the model, the observed homogeneity is explained by the low entropy at the bounce, The observed flatness arises from the contraction together with the reduction in size between the expanding and contracting universe. The present flatness is predicted to be very precise.
We investigate a simplified model of dark matter where a Majorana fermion $\chi$ coannihilates with a colored scalar top partner $\tilde{t}$. We explore the cosmological history, with particular emphasis on the most relevant low-energy parameters: the mass splitting between the dark matter and the coannihilator, and the Yukawa coupling $y_\chi$ that connects these fields to the Standard Model top quarks. We also allow a free quartic coupling $\lambda_h$ between a pair of Higgs bosons and $\tilde{t}$ pairs. We pay special attention to the case where the values take on those expected where $\tilde{t}$ corresponds to the superpartner of the right-handed top, and $\chi$ is a bino. Direct detection, indirect detection, and colliders are complementary probes of this simple model.
We investigate the direct detection phenomenology of a class of dark matter (DM) models in which DM does not directly interact with nuclei, {but rather} the products of its annihilation do. When these annihilation products are very light compared to the DM mass, the scattering in direct detection experiments is controlled by relativistic kinematics. This results in a distinctive recoil spectrum, a non-standard and or even {\it absent} annual modulation, and the ability to probe DM masses as low as a $\sim$10 MeV. We use current LUX data to show that experimental sensitivity to thermal relic annihilation cross sections has already been reached in a class of models. Moreover, the compatibility of dark matter direct detection experiments can be compared directly in $E_{min}$ space without making assumptions about DM astrophysics. Lastly, when DM has direct couplings to nuclei, the limit from annihilation to relativistic particles in the Sun can be stronger than that of conventional non-relativistic direct detection by more than three orders of magnitude for masses in a 2-8 GeV window.
The origin of ultra-compact dwarfs (UCDs)--objects larger and more massive than typical globular clusters (GCs), but more compact than typical dwarf galaxies--has been hotly debated in the 15 years since their discovery. Even whether UCDs should be considered galactic in origin, or simply the most extreme GCs, is not yet settled. We present the dynamical properties of 97 spectroscopically confirmed UCDs (rh >~10 pc) and 911 GCs associated with central cD galaxy of the Virgo cluster, M87. Our UCDs, of which 89% have M_star > ~2X10^6 M_sun and 92% are as blue as the classic blue GCs, nearly triple the sample of previous confirmed Virgo UCDs, providing by far the best opportunity for studying the global dynamics of a UCD system. We found that (1) UCDs have a surface number density profile that is shallower than that of the blue GCs in the inner ~ 70 kpc and as steep as that of the red GCs at larger radii; (2) UCDs exhibit a significantly stronger rotation than the GCs, and the blue GCs seem to have a velocity field that is more consistent with that of the surrounding dwarf ellipticals than with that of UCDs; (3) UCDs have a radially increasing orbital anisotropy profile, and are tangentially-biased at radii < ~ 40 kpc and radially-biased further out. In contrast, the blue GCs become more tangentially-biased at larger radii beyond ~ 40 kpc; (4) GCs with M_star > 2X10^6 M_sun have rotational properties indistinguishable from the less massive ones, suggesting that it is the size, instead of mass, that differentiates UCDs from GCs as kinematically distinct populations. We conclude that most UCDs in M87 are not consistent with being merely the most luminous and extended examples of otherwise normal GCs. The radially-biased orbital structure of UCDs at large radii is in general agreement with the "tidally threshed dwarf galaxy" scenario.
We simulate the formation of a low metallicity (0.01 Zsun) stellar cluster in a dwarf galaxy at redshift z~14. Beginning with cosmological initial conditions, the simulation utilizes adaptive mesh refinement and sink particles to follow the collapse and evolution of gas past the opacity limit for fragmentation, thus resolving the formation of individual protostellar cores. A time- and location-dependent protostellar radiation field, which heats the gas by absorption on dust, is computed by integration of protostellar evolutionary tracks with the MESA code. The simulation also includes a robust non-equilibrium chemical network that self-consistently treats gas thermodynamics and dust-gas coupling. The system is evolved for 18 kyr after the first protostellar source has formed. In this time span, 30 sink particles representing protostellar cores form with a total mass of 81 Msun. Their masses range from ~0.1 Msun to 14.4 Msun with a median mass ~0.5-1 Msun. Massive protostars grow by competitive accretion while lower-mass protostars are stunted in growth by close encounters and many-body ejections. In the regime explored here, the characteristic mass scale is determined by the temperature floor set by the cosmic microwave background and by the onset of efficient dust-gas coupling. It seems unlikely that host galaxies of the first bursts of metal-enriched star formation will be detectable with the James Webb Space Telescope or other next-generation infrared observatories. Instead, the most promising access route to the dawn of cosmic star formation may lie in the scrutiny of metal-poor, ancient stellar populations in the Galactic neighborhood. The observable targets that correspond to the system simulated here are ultra-faint dwarf satellite galaxies such as Bootes II, Segue I and II, and Willman I.
Motivated by the mathematic theory of split-complex numbers (or hyperbolic numbers, also perplex numbers) and the split-quaternion numbers (or coquaternion numbers), we define the notion of split-complex scalar field and the split-quaternion scalar field. Then we explore the cosmic evolution of these scalar fields in the background of spatially flat Friedmann-Robertson-Walker Universe. We find that both the quintessence field and the phantom field could naturally emerge in these scalar fields. Introducing the metric of field space, these theories fall into a subclass of the multi-field theories which have been extensively studied in inflationary cosmology. Using the brane world model, the split-complex Dirac-Born-Infeld Lagrangian is constructed and analyzed.
Among the prominent low-mass dark matter candidates is the QCD axion but also other light and weakly interacting particles beyond the Standard Model. We review briefly the case for such dark matter and give an overview on most recent experimental efforts within laboratory searches, where we focus on experiments exploiting a potential electromagnetic coupling of such particles.
We study a sample of 11 Type II supernovae (SNe) discovered by the OGLE-IV survey. All objects have well sampled I-band light curves, and at least one spectrum. We find that 3 or 4 of the 11 SNe have a declining light curve, making them SNe II-L, while the rest have plateaus that can be as short as 70d, unlike the 100d typically found in nearby galaxies. These SNe are also brighter than found in the local Universe, and show that magnitude limited surveys find SNe that are different than found in nearby galaxies. We discuss this sample in the context of understanding Type II SNe as a class and their suggested use as standard candles.
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The XENON100 experiment is the second phase of the XENON program for the direct detection of the dark matter in the universe. The XENON100 detector is a two-phase Time Projection Chamber filled with 161 kg of ultra pure liquid xenon. The results from 224.6 live days of dark matter search with XENON100 are presented. No evidence for dark matter in the form of WIMPs is found, excluding spin-independent WIMP-nucleon scattering cross sections above 2 $\times$ 10$^{-45}$ cm$^2$ for a 55 GeV/c$^2$ WIMP at 90% confidence level (C.L.). The most stringent limit is established on the spin-dependent WIMP-neutron interaction for WIMP masses above 6 GeV/c$^2$, with a minimum cross section of 3.5 $\times$ 10$^{-40}$ cm$^2$ (90% C.L.) for a 45 GeV/c$^2$ WIMP. The same dataset is used to search for axions and axion-like-particles. The best limits to date are set on the axion-electron coupling constant for solar axions, $g_{Ae}$ < 7.7 $\times$ 10$^{-12}$ (90% C.L.), and for axion-like-particles, $g_{Ae}$ < 1 $\times$ 10$^{-12}$ (90% C.L.) for masses between 5 and 10 keV/c$^2$.
By considering linear-order departures from general relativity, we compute a novel expression for the weak lensing convergence power spectrum under alternative theories of gravity. This comprises an integral over a 'kernel' of general relativistic quantities multiplied by a theory-dependent 'source' term. The clear separation between theory-independent and -dependent terms allows for an explicit understanding of each physical effect introduced by altering the theory of gravity. We take advantage of this to explore the degeneracies between gravitational parameters in weak lensing observations.
Ever since WMAP announced its first results, different analyses have shown that there is weak evidence for several large-scale anomalies in the CMB data. While the evidence for each anomaly appears to be weak, the fact that there are multiple seemingly unrelated anomalies makes it difficult to account for them via a single statistical fluke. So, one is led to considering a combination of these anomalies. But, if we "hand-pick" the anomalies (test statistics) to consider, we are making an \textit{a posteriori} choice. In this article, we propose two statistics that do not suffer from this problem. The statistics are linear and quadratic combinations of the $a_{\ell m}$'s with random co-efficients, and they test the null hypothesis that the $a_{\ell m}$'s are independent, normally-distributed, zero-mean random variables with an $m$-independent variance. The motivation for such statistics is generality; equivalently, it is a non \textit{a posteriori} choice. But, a very useful by-product of considering such statistics is this: Because most physical models that lead to large-scale anomalies result in coupling multiple $\ell$ and $m$ modes, the "coherence" of this coupling should get enhanced if a combination of different modes is considered. Using fiducial data, we demonstrate that the method works and discuss how it can be used with actual CMB data to make quite general statements about how incompatible the data are with the null hypothesis.
We study a nonsingular bounce inflation model, which can drive the early universe from a contracting phase, bounce into an ordinary inflationary phase, followed by the reheating process. Besides the bounce that avoided the Big-Bang singularity which appears in the standard cosmological scenario, we make use of the Horndesky theory and design the kinetic and potential forms of the lagrangian, so that neither of the two big problems in bouncing cosmology, namely the ghost and the anisotropy problems, will appear. The cosmological perturbations can be generated either in the contracting phase or in the inflationary phase, where in the latter the power spectrum will be scale-invariant and fit the observational data, while in the former the perturbations will have nontrivial features that will be tested by the large scale structure experiments. We also fit our model to the CMB TT power spectrum.
In the context of count-in-cells statistics, the joint probability distribution of the density in two concentric spherical shells is predicted from first first principle for sigmas of the order of one. The agreement with simulation is found to be excellent. This statistics allows us to deduce the conditional one dimensional probability distribution function of the slope within under dense (resp. overdense) regions, or of the density for positive or negative slopes. The former conditional distribution is likely to be more robust in constraining the cosmological parameters as the underlying dynamics is less evolved in such regions. A fiducial dark energy experiment is implemented on such counts derived from Lambda-CDM simulations.
We investigate the dynamics of the FLRW flat cosmological models in which the vacuum energy varies with redshift. A particularly well motivated model of this type is the so-called quantum field vacuum, in which both kind of terms $H^{2}$ and constant appear in the effective dark energy density affecting the evolution of the main cosmological functions at the background and perturbation levels. Specifically, it turns out that the functional form of the quantum vacuum endows the vacuum energy of a mild dynamical evolution which could be observed nowadays and appears as dynamical dark energy. Interestingly, the low-energy behaviour is very close to the usual $\Lambda$CDM model, but it is by no means identical. Finally, within the framework of the quantum field vacuum we generalize the large scale structure properties, namely growth of matter perturbations, cluster number counts and spherical collapse model.
In this paper we investigate the limits imposed by thermodynamics to a dark energy fluid. We obtain the heat capacities and the compressibilities for a dark energy fluid. These thermodynamical variables are easily accessible experimentally for any terrestrial fluid. The thermal and mechanical stabilities require these quantities to be positive. We show that such requirements forbid the existence of a cosmic fluid with negative constant EoS parameter which excludes vacuum energy as a candidate to explain the cosmic acceleration. We also show that the current observational data from SN Ia, BAO and $H(z)$ are in conflict with the physical constraints that a general dark energy fluid with a time-dependent EoS parameter must obey which can be interpreted as an evidence against the dark energy hypothesis. Although our result excludes the vacuum energy, a geometrical cosmological term as originally introduced by Einstein in the field equations remains untouched.
Ultra-deep observations of ECDF-S with Chandra and XMM-Newton enable a search for extended X-ray emission down to an unprecedented flux of $2\times10^{-16}$ ergs s$^{-1}$ cm$^{-2}$. We present the search for the extended emission on spatial scales of 32$^{\prime\prime}$ in both Chandra and XMM data, covering 0.3 square degrees and model the extended emission on scales of arcminutes. We present a catalog of 46 spectroscopically identified groups, reaching a redshift of 1.6. We show that the statistical properties of ECDF-S, such as logN-logS and X-ray luminosity function are broadly consistent with LCDM, with the exception that dn/dz/d$\Omega$ test reveals that a redshift range of $0.2<z<0.5$ in ECDF-S is sparsely populated. The lack of nearby structure, however, makes studies of high-redshift groups particularly easier both in X-rays and lensing, due to a lower level of clustered foreground. We present one and two point statistics of the galaxy groups as well as weak-lensing analysis to show that the detected low-luminosity systems are indeed low-mass systems. We verify the applicability of the scaling relations between the X-ray luminosity and the total mass of the group, derived for the COSMOS survey to lower masses and higher redshifts probed by ECDF-S by means of stacked weak lensing and clustering analysis, constraining any possible departures to be within 30\% in mass. Abridged.
During inflation, the geometry of spacetime is described by a (quasi-)de Sitter phase. Inflationary observables are determined by the underlying (softly broken) de Sitter isometry group SO(1, 4) which acts like a conformal group on R^3: when the fluctuations are on super-Hubble scales, the correlators of the scalar fields are constrained by conformal invariance. Heavy fields with mass m larger than the Hubble rate H correspond to operators with imaginary dimensions in the dual Euclidean three-dimensional conformal field theory. By making use of the dS/CFT correspondence we show that, besides the Boltzmann suppression expected from the thermal properties of de Sitter space, the generic effect of heavy fields in the inflationary correlators of the light fields is to introduce power-law suppressed corrections of the form O(H^2/m^2). This can be seen, for instance, at the level of the four-point correlator for which we provide the correction due to a massive scalar field exchange.
We employ a suite of 75 simulations of galaxies in idealised major mergers (stellar mass ratio ~2.5:1), with a wide range of orbital parameters, to investigate the spatial extent of interaction-induced star formation. Although the total star formation in galaxy encounters is generally elevated relative to isolated galaxies, we find that this elevation is a combination of intense enhancements within the central kpc and moderately suppressed activity at large galacto-centric radii. The radial dependence of the star formation enhancement is stronger in the less massive galaxy than in the primary, and is also more pronounced in mergers of more closely aligned disc spin orientations. Conversely, these trends are almost entirely independent of the encounter's impact parameter and orbital eccentricity. Our predictions of the radial dependence of triggered star formation, and specifically the suppression of star formation beyond kph-scales, will be testable with the next generation of integral-field spectroscopic surveys.
In the cold dark matter (CDM) paradigm, bulges easily form through galaxy mergers, either major or minor, or through clumpy disks in the early universe, where clumps are driven to the center by dynamical friction. Also pseudo-bulges, with a more disky morphology and kinematics, can form more slowly through secular evolution of a bar, where resonant stars are elevated out of the plane, in a peanut/box shape. As a result, in CDM cosmological simulations, it is very difficult to find a bulgeless galaxy, while they are observed very frequently in the local universe. A different picture emerges in alternative models of the missing mass problem. In MOND (MOdified Newtonian Dynamics), galaxy mergers are much less frequent, since the absence of dark matter halos reduces the dynamical friction between two galaxies. Also, while clumpy galaxies lead to rapid classical bulge formation in CDM, the inefficient dynamical friction with MOND in the early-universe galaxies prevents the clumps to coalesce together in the center to form spheroids. This leads to less frequent and less massive classical bulges. Bars in MOND are more frequent and stronger, and have a more constant pattern speed, which modifies significantly the pseudo-bulge morphology. The fraction of pseudo-bulges is expected to be dominant in MOND.
We study the impacts of reheating temperature on the inflationary predictions of the spectral index and tensor-to-scalar ratio. Assuming that reheating process is very fast, the reheating temperature can be constrained for sinusoidal oscillation within a factor of 10 - 100 or even better with the prospect of future observations. Beyond this, we find that the predictions can also be insensitive to the reheating temperature in certain models, including the Higgs inflation.
A recent revision of black hole scaling relations (Kormendy & Ho 2013), indicates that the local mass density in black holes should be increased by up to a factor of five with respect to previously determined values. The local black hole mass density is connected to the mean radiative efficiency of accretion through the time integral of the AGN volume density and a significant increase of the local black holes mass density would have interesting consequences on AGN accretion properties and demography. One possibility to explain a large black hole mass density is that most of the Black Hole growth is via radiatively inefficient channels such as super Eddington accretion, however, given the intrinsic degeneracies in the Soltan argument, this solution is not unique. Here we show how it is possible to accommodate a larger fraction of heavily buried, Compton thick AGN, without violating the limit imposed by the hard X-ray and mid-infrared backgrounds spectral energy density.
In the effective theory of isoscalar and isovector dark matter-nucleon interactions mediated by a heavy spin-1 or spin-0 particle, 8 isotope-dependent nuclear response functions can be generated in the dark matter scattering by nuclei. We compute the 8 nuclear response functions for the 16 most abundant elements in the Sun, i.e. H, $^{3}$He, $^{4}$He, $^{12}$C, $^{14}$N, $^{16}$O, $^{20}$Ne, $^{23}$Na, $^{24}$Mg, $^{27}$Al, $^{28}$Si, $^{32}$S, $^{40}$Ar, $^{40}$Ca, $^{56}$Fe, and $^{59}$Ni, through detailed numerical shell model calculations. We use our response functions to compute the rate of dark matter capture by the Sun for all isoscalar and isovector dark matter-nucleon effective interactions, including several operators previously considered for dark matter direct detection only. We study in detail the dependence of the capture rate on specific dark matter-nucleon interaction operators, and on the different elements in the Sun. We find that a so far neglected momentum dependent dark matter coupling to the nuclear vector charge gives a larger contribution to the capture rate than the constant spin-dependent interaction commonly included in experimental searches. Our investigation lays the foundations for model independent analyses of dark matter induced neutrino signals from the Sun. The nuclear response functions obtained in this study are listed in analytic form in an appendix, ready to be used in other projects.
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