We analyzed available observational data of a sample of dark matter (DM)
dominated galaxies and clusters of galaxies and we have found correlations
between the virial mass, $M_{vir}$, of halos and basic parameters of their
cores, namely, the mean DM density, pressure and entropy. These correlations
are a natural consequence of similar evolution of all such objects. It is
driven mainly by gravitational interactions what implies a high degree of self
similarity of both the process of halos formation and their internal structure.
We confirmed the CDM--like shape of both the small and large scale power
spectrum. However, our reconstruction of the evolutionary history of observed
objects requires either a multicomponent composition of DM or a more complex
primordial power spectrum of density perturbations with significant excess of
power at scales of clusters of galaxies and larger. We demonstrated that a
model with suitable combination of the heavy DM particles (CDM) and DM
particles with large damping scale (HDM) could provide a successful description
of the observational data in a wide range of masses.
In this work we will test an alternative model of gravity belonging to the large family of galileon models. It is characterized by an intrinsic breaking of the Vainshtein mechanism inside large astrophysical objects, thus having possibly detectable observational signatures. We will compare theoretical predictions from this model with the observed total mass profile for a sample of clusters of galaxies. The profiles are derived using two complementary tools: X-ray hot intra-cluster gas dynamics, and strong and weak gravitational lensing. We find that a dependence with the dynamical internal status of each cluster is possible; for those clusters which are very close to be relaxed, and thus less perturbed by possible astrophysical local processes, the galileon model gives a quite good fit to both X-ray and lensing observations. Both masses and concentrations for the dark matter halos are consistent with earlier results found in numerical simulations and in the literature, and no compelling statistical evidence for a deviation from general relativity is detectable from the present observational state. Actually, the characteristic galileon parameter $\Upsilon$ is always consistent with zero, and only an upper limit ($\lesssim0.086$ at $1\sigma$, $\lesssim0.16$ at $2\sigma$, and $\lesssim0.23$ at $3\sigma$) can be established. Some interesting distinctive deviations might be operative, but the statistical validity of the results is far from strong, and better data would be needed in order to either confirm or reject a potential tension with general relativity.
The cumulative number count $N$, of sources above a threshold is known to approximately follow a power law behaviour $N\propto S^{-x}$. We study the variation of spectral index $x$ across the sky in order to look for possible signals of violation of isotropy. We develop a rigorous algorithm of likelihood maximisation to accurately fit for the spectral index. We divide the sky into upper and lower hemispheres for a particular choice of $z$-axis and determine the difference $\Delta x$ between the best fit values of the spectral indices between the two hemispheres. The maximum value of this difference obtained by varying over the $z$-axis provides us with a measure of departure from isotropy. We find that the data support isotropy of the spectral index. The maximum difference is found to be 1.3\% of the full sky best fit value of $x$. The deviation is found to be significant only at 2$\sigma$ level which indicates a weak departure from isotropy. We also perform a dipole fit to the spectral index as a function of the angular coordinates. The result is found to be consistent with isotropy.
We investigate how the hydrostatic suppression of baryonic accretion affects the growth rate of dark matter halos during the Epoch of Reionization. By comparing halo properties in a simplistic hydrodynamic simulation in which gas only cools adiabatically, with its collisionless equivalent, we find that halo growth is slowed as hydrostatic forces prevent gas from collapsing. In our simulations, at the high redshifts relevant for reionization (between ${\sim}6$ and ${\sim}11$), halos that host dwarf galaxies ($\lesssim 10^{9} \mathrm{M_\odot}$) can be reduced by up to a factor of 2 in mass due to the hydrostatic pressure of baryons. Consequently, the inclusion of baryonic effects reduces the amplitude of the low mass tail of the halo mass function by factors of 2 to 4. In addition, we find that the fraction of baryons in dark matter halos hosting dwarf galaxies at high redshift never exceeds ${\sim}90\%$ of the cosmic baryon fraction. When implementing baryonic processes, including cooling, star formation, supernova feedback and reionization, the suppression effects become more significant with further reductions of ${\sim}30\%$ to 60\%. Although convergence tests suggest that the suppression may become weaker in higher resolution simulations, this suppressed growth will be important for semi-analytic models of galaxy formation, in which the halo mass inherited from an underlying N-body simulation directly determines galaxy properties. Based on the adiabatic simulation, we provide tables to account for these effects in N-body simulations, and present a modification of the halo mass function along with explanatory analytic calculations.
The statistical distribution of galaxies is a powerful probe to constrain cosmological models and gravity. In particular the matter power spectrum $P(k)$ brings information about the cosmological distance evolution and the galaxy clustering together. However the building of $P(k)$ from galaxy catalogues needs a cosmological model to convert angles on the sky and redshifts into distances, which leads to difficulties when comparing data with predicted $P(k)$ from other cosmological models, and for photometric surveys like LSST. The angular power spectrum $C_\ell(z_1,z_2)$ between two bins located at redshift $z_1$ and $z_2$ contains the same information than the matter power spectrum, is free from any cosmological assumption, but the prediction of $C_\ell(z_1,z_2)$ from $P(k)$ is a costly computation when performed exactly. The Angpow software aims at computing quickly and accurately the auto ($z_1=z_2$) and cross ($z_1 \neq z_2$) angular power spectra between redshift bins. We describe the developed algorithm, based on developments on the Chebyshev polynomial basis and on the Clenshaw-Curtis quadrature method. We validate the results with other codes, and benchmark the performance. Angpow is flexible and can handle any user defined power spectra, transfer functions, and redshift selection windows. The code is fast enough to be embedded inside programs exploring large cosmological parameter spaces through the $C_\ell(z_1,z_2)$ comparison with data. We emphasize that the Limber's approximation, often used to fasten the computation, gives wrong $C_\ell$ values for cross-correlations.
Reliable extraction of cosmological information from clustering measurements of galaxy surveys requires estimation of the error covariance matrices of observables. The accuracy of covariance matrices is limited by our ability to generate sufficiently large number of independent mock catalogs that can describe the physics of galaxy clustering across a wide range of scales. Furthermore, galaxy mock catalogs are required to study systematics in galaxy surveys and to test analysis tools. In this investigation, we present a fast and accurate approach for generation of mock catalogs for the upcoming galaxy surveys. Our method relies on low-resolution approximate gravity solvers to simulate the large scale dark matter field, which we then populate with halos according to a flexible nonlinear and stochastic bias model. In particular, we extend the \textsc{patchy} code with an efficient particle mesh algorithm to simulate the dark matter field (the \textsc{FastPM} code), and with an efficient and robust MCMC method relying on the \textsc{emcee} code for constraining the parameters of the bias model. Using the halos in the BigMultiDark high-resolution $N$-body simulation as a reference catalog, we demonstrate that our technique can model the bivariate probability distribution function, power spectrum, and bispectrum of halos in the reference catalog. Specifically, we show that the new ingredients permit us to reach percentage accuracy in the power spectrum up to $k\sim 0.4\; h\mathrm{Mpc}^{-1}$ (within 5$\%$ up to $k\sim 0.6\; h\mathrm{Mpc}^{-1}$) with accurate bispectra improving previous results based on Lagrangian perturbation theory.
We quantify the number density of compact massive (M > 5x10^10 M_sun) galaxies at intermediate redshifts (0.2<z<0.6) in the equatorial SDSS Stripe 82 region (~250 sq. degrees). This is the largest volume probed up to date allowing to decrease the effect of cosmic variance. Structural parameters are obtained in the i-band using the CFHT Stripe 82 (CS82) survey with an exquisite median seeing of ~0.6". We explore a variety of definitions of compactness present in the literature. We find that the absolute number of compact galaxies is very dependent on the adopted definition, and can change up to a factor of >10. However, we systematically measure a factor of ~5 more compacts at the same redshift than what was previously reported on smaller fields with HST imaging, more affected by cosmic variance. This means that the decrease in number density from z~1.5 to z~0.2 might be only of a factor of ~2-5, significantly smaller than what previously reported: this supports progenitor bias as the main contributor to the size evolution. This decrease is roughly compatible with the predictions from recent numerical simulations. Only extreme compact galaxies (Reff < 1.5x(M/10^11 M_sun)^0.75 and M > 10^10.7 M_sun) seem to drop in number by a factor of ~20 and therefore probably experience a noticeable size evolution.
The fine details of the large-scale structure in the local universe provide important empirical benchmarks for testing cosmological models of structure formation. Dwarf galaxies are key object for such studies. Enlarge the sample of known dwarf galaxies in the local universe. We performed a search for faint, unresolved low-surface brightness dwarf galaxies in the M101 group complex, including the region around the major spiral galaxies M101, M51, and M63 lying at a distance 7.0, 8.6, and 9.0 Mpc, respectively. The new dwarf galaxy sample can be used in a first step to test for significant substructure in the 2D-distribution and in a second step to study the spatial distribution of the galaxy complex. Using filtering algorithms we surveyed 330 square degrees of imaging data obtained from the Sloan Digital Sky Survey. The images were visually inspected. The spatial distribution of known galaxies and candidates was analyzed transforming the system into a M101 eigenframe, using the special geometrical alignment of the group. We discovered 15 new dwarf galaxies and carried out surface photometry in the g and r bands. The similarity of the photometric properties of these dwarfs to those of Local Group dwarfs suggest membership to the M101 group complex. The sky distribution of the candidates follows the thin planar structure outlined by the known members of the three subgroups. The ~3Mpc long filamentary structure has a rms thickness of 72 kpc. The planar structure of the embedded M101 subgroup is even thinner, with rms=49 kpc. The formation of this structure might be due to the expansion of the Local Void to which it borders. Other implications are discussed as well. We show the viability of SDSS data to extend the sample of dwarfs in the local universe and test cosmological models on small scales.
Spectral absorption features can be used to constrain the stellar initial mass function (IMF) in the integrated light of galaxies. Spectral indices used at low redshift are in the far red, and therefore increasingly hard to detect at higher and higher redshifts as they pass out of atmospheric transmission and CCD detector wavelength windows. We employ IMF-sensitive indices at bluer wavelengths. We stack spectra of red, quiescent galaxies around $z=0.4$, from the DEEP2 Galaxy Redshift Survey. The $z=0.4$ red galaxies have 2 Gyr average ages so that they cannot be passively evolving precursors of nearby galaxies. They are slightly enhanced in C and Na, and slightly depressed in Ti. Split by luminosity, the fainter half appears to be older, a result that should be checked with larger samples in the future. We uncover no evidence for IMF evolution between $z=0.4$ and now, but we highlight the importance of sample selection, finding that an SDSS sample culled to select archetypal elliptical galaxies at z$\sim$0 is offset toward a more bottom heavy IMF. Other samples, including our DEEP2 sample, show an offset toward a more spiral galaxy-like IMF. All samples confirm that the reddest galaxies look bottom heavy compared with bluer ones. Sample selection also influences age-color trends: red, luminous galaxies always look old and metal-rich, but the bluer ones can be more metal-poor, the same abundance, or more metal-rich, depending on how they are selected.
We present the detection of four far-infrared fine-structure oxygen lines, as well as strong upper limits for the CO(2-1) and [N II] 205 um lines, in 3C 368, a well-studied radio-loud galaxy at z = 1.131. These new oxygen lines, taken in conjunction with previously observed neon and carbon fine-structure lines, suggest a powerful active galactic nucleus (AGN), accompanied by vigorous and extended star formation. A starburst dominated by O8 stars, with an age of ~6.5 Myr, provides a good fit to the fine-structure line data. This estimated age of the starburst makes it nearly concurrent with the latest episode of AGN activity, suggesting a link between the growth of the supermassive black hole and stellar population in this source. We do not detect the CO(2-1) line, down to a level twelve times lower than the expected value for star forming galaxies. This lack of CO line emission is consistent with recent star formation activity if the star-forming molecular gas has low metallicity, is highly fractionated (such that CO is photodissociated through much of the clouds), or is chemically very young (such that CO has not yet had time to form). It is also possible, though we argue unlikely, that the ensemble of fine structure lines are emitted from the region heated by the AGN.
Links to: arXiv, form interface, find, astro-ph, recent, 1701, contact, help (Access key information)
We present a low-frequency view of the Perseus cluster with new observations from the Karl G. Jansky Very Large Array (JVLA) at 230-470 MHz. The data reveal a multitude of new structures associated with the mini-halo. The mini-halo seems to be influenced both by the AGN activity as well as by the sloshing motion of the cool core cluster's gas. In addition, it has a filamentary structure similar to that seen in radio relics found in merging clusters. We present a detailed description of the data reduction and imaging process of the dataset. The depth and resolution of the observations allow us to conduct for the first time a detailed comparison of the mini-halo structure with the X-ray structure as seen in the Chandra X-ray images. The resulting image shows very clearly that the mini-halo emission is mostly contained behind the cold fronts, similar to that predicted by simulations of gas sloshing in galaxy clusters. However, due to the proximity of the Perseus cluster, as well as the quality of the data at low radio frequencies and at X-ray wavelengths, we also find evidence of fine structure. This structure includes several radial radio filaments extending in different directions, a concave radio structure associated with the southern X-ray bay and sharp edges that correlate with X-ray edges. Mini-halos are therefore not simply diffuse, uniform radio sources, but are rather filled with a rich variety of complex structures. These results illustrate the high-quality images that can be obtained with the new JVLA at low radio-frequencies, as well as the necessity to obtain deeper, higher-fidelity radio images of mini-halos and halos in clusters to further understand their origin.
The high quality data provided by helioseismology, solar neutrino flux measurements, spectral determination of solar abundances, nuclear reactions rates coefficients among other experimental data, leads to the highly accurate prediction of the internal structure of the present Sun - the standard solar model. In this talk, I have discussed how the standard solar model, the best representation of the real Sun, can be used to study the properties of dark matter, for which two complementary approaches have been developed: - to limit the number of theoretical candidates proposed as the dark matter particles, this analysis complements the experimental search of dark matter, and - as a template for the study of the impact of dark matter in the evolution of stars, which possibly occurs for stellar populations formed in regions of high density of dark matter, such as stars formed in the centre of galaxies and the first generations of stars.
This paper derives an upper limit on the density $\rho_{\scriptstyle\Lambda}$ of dark energy based on the requirement that cosmological structure forms before being frozen out by the eventual acceleration of the universe. By allowing for variations in both the cosmological parameters and the strength of gravity, the resulting constraint is a generalization of previous limits. The specific parameters under consideration include the amplitude $Q$ of the primordial density fluctuations, the Planck mass $M_{\rm pl}$, the baryon-to-photon ratio $\eta$, and the density ratio $\Omega_M/\Omega_b$. In addition to structure formation, we use considerations from stellar structure and Big Bang Nucleosynthesis (BBN) to constrain these quantities. The resulting upper limit on the dimensionless density of dark energy becomes $\rho_{\scriptstyle\Lambda}/M_{\rm pl}^4<10^{-90}$, which is $\sim30$ orders of magnitude larger than the value in our universe $\rho_{\scriptstyle\Lambda}/M_{\rm pl}^4\sim10^{-120}$. This new limit is much less restrictive than previous constraints because additional parameters are allowed to vary. With these generalizations, a much wider range of universes can develop cosmic structure and support observers. To constrain the constituent parameters, new BBN calculations are carried out in the regime where $\eta$ and $G=M_{\rm pl}^{-2}$ are much larger than in our universe. If the BBN epoch were to process all of the protons into heavier elements, no hydrogen would be left behind to make water, and the universe would not be viable. However, our results show that some hydrogen is always left over, even under conditions of extremely large $\eta$ and $G$, so that a wide range of alternate universes are potentially habitable.
The hypothesis is made that, at large scales where General Relativity may be
applied, the empty space is scale invariant. This establishes a relation
between the cosmological constant and the scale factor of the scale invariant
framework. This relation brings major simplifications in the scale invariant
equations for cosmology, which now contain a new term, depending on the
derivative of the scale factor, that opposes to gravity and produces an
accelerated expansion. The displacements due to the acceleration term make a
high contribution Omega_l to the energy-density of the Universe, satisfying an
equation of the form Omega_m+\Omega_k+Omega_l = 1. The models do not demand the
existence of unknown particles. There is a family of flat models with different
density parameters Omega_m < 1.
Numerical integrations of the cosmological equations for different values of
the curvature and density parameter k and Omega_m are performed. The presence
of even tiny amounts of matter in the Universe tends to kill scale invariance.
The point is that for Omega_m = 0.3 the effect is not yet completely killed.
The models with non-zero density start explosively with first a braking phase
followed by a continuously accelerating expansion. Several observational
properties are examined, in particular the distances, the m--z diagram, the
Omega_m vs. lambda plot. Comparisons with observations are also performed for
the Hubble constant H_0 vs. Omega_m, for the expansion history in the plot
H(z)/(z+1) vs. redshift z and for the transition redshift from braking to
acceleration. These first dynamical tests are satisfied by the scale invariant
models, which thus deserve further studies.
Consistency relations of large-scale structures provide exact nonperturbative results for cross-correlations of cosmic fields in the squeezed limit. They only depend on the equivalence principle and the assumption of Gaussian initial conditions, and remain nonzero at equal times for cross-correlations of density fields with velocity or momentum fields, or with the time derivative of density fields. We show how to apply these relations to observational probes that involve the integrated Sachs-Wolfe effect or the kinematic Sunyaev-Zeldovich effect. In the squeezed limit, this allows us to express the three-point cross-correlations, or bispectra, of two galaxy or matter density fields, or weak lensing convergence fields, with the secondary CMB distortion in terms of products of a linear and a nonlinear power spectrum. In particular, we find that cross-correlations with the integrated Sachs-Wolfe effect show a specific angular dependence. These results could be used to test the equivalence principle and the primordial Gaussianity, or to check the modeling of large-scale structures.
To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandra observations of the HST Frontier Fields cluster MACS J0717.5+3745. The Chandra image shows a complex merger event, with at least four components belonging to different merging subclusters. NW of the cluster, $\sim 0.7$ Mpc from the center, there is a ram-pressure-stripped core that appears to have traversed the densest parts of the cluster after entering the ICM from the direction of a galaxy filament to the SE. We detect a density discontinuity NNE of this core which we speculate is associated with a cold front. Our radio images reveal new details for the complex radio relic and radio halo in this cluster. In addition, we discover several new filamentary radio sources with sizes of 100-300 kpc. A few of these seem to be connected to the main radio relic, while others are either embedded within the radio halo or projected onto it. A narrow-angled-tailed (NAT) radio galaxy, a cluster member, is located at the center of the radio relic. The steep spectrum tails of this AGN leads into the large radio relic where the radio spectrum flattens again. This morphological connection between the NAT radio galaxy and relic provides evidence for re-acceleration (revival) of fossil electrons. The presence of hot $\gtrsim 20$ keV ICM gas detected by Chandra near the relic location provides additional support for this re-acceleration scenario.
Big Bang nucleosynthesis (BBN) theory predicts the abundances of the light elements D, $^3$He, $^4$He and $^7$Li produced in the early universe. The primordial abundances of D and $^4$He inferred from observational data are in good agreement with predictions, however, the BBN theory overestimates the primordial $^7$Li abundance by about a factor of three. This is the so-called "cosmological lithium problem". Solutions to this problem using conventional astrophysics and nuclear physics have not been successful over the past few decades, probably indicating the presence of new physics during the era of BBN. We have investigated the impact on BBN predictions of adopting a generalized distribution to describe the velocities of nucleons in the framework of Tsallis non-extensive statistics. This generalized velocity distribution is characterized by a parameter $q$, and reduces to the usually assumed Maxwell-Boltzmann distribution for $q$ = 1. We find excellent agreement between predicted and observed primordial abundances of D, $^4$He and $^7$Li for $1.069\leq q \leq 1.082$, suggesting a possible new solution to the cosmological lithium problem.
A revolution in galaxy cluster science is only a few years away. The survey machines eROSITA and Euclid will provide cluster samples of never-before-seen statistical quality. XMM-Newton will be the key instrument to exploit these rich datasets in terms of detailed follow-up of the cluster hot gas content, systematically characterizing sub-samples as well as exotic new objects.
To explain the unusual richness and compactness of the Abell 2744, we propose a hypothesis that it may be a rich supercluster aligned along the sightline, and present a supporting evidence obtained numerically from the MultiDark Planck 2 simulations with a linear box size of $1\,h^{-1}$Gpc. Applying the friends-of-friends (FoF) algorithm with a linkage length of $0.33$ to a sample of the cluster-size halos from the simulations, we identify the superclusters and investigate how many superclusters have filamentary branches that would appear to be similar to the Abell 2744 if the filamentary axis is aligned with the sightline. Generating randomly a unit vector as a sightline at the position of the core member of each supercluster and projecting the positions of the members onto the plane perpendicular to the direction of the sightline, we measure two dimensional distances ($R_{2d}$) of the member halos from the core for each supercluster. Defining a Abell 2744-like spuercluster as the one having a filamentary branch composed of eight or more members with $R_{2d}\le 1\,$Mpc and masses comparable to those of the observed Abell 2744 substructures, we find one Abell 2744-like supercluster at $z=0.3$ and two at $z=0$. Repeating the same analysis but with the data from the Big MultiDark Planck simulations performed on a larger box of linear size of $2.5\,h^{-1}$Mpc, we find that the number of the Abell 2744-like superclusters at $z=0$ increases up to eighteen, among which three are found more massive than $5\times 10^{15}\,M_{\odot}$.
We argue that $isotropic$ scalar fluctuations in solid inflation are adiabatic in the super-horizon limit. During the solid phase this adiabatic mode has peculiar features: constant energy-density slices and comoving slices do not coincide, and their curvatures, parameterized respectively by $\zeta$ and $\mathcal R$, both evolve in time. The existence of this adiabatic mode implies that Maldacena's squeezed limit consistency relation holds after angular average over the long mode. The correlation functions of a long-wavelength spherical scalar mode with several short scalar or tensor modes is fixed by the scaling behavior of the correlators of short modes, independently of the solid inflation action or dynamics of reheating.
We present a demonstration of delensing the observed cosmic microwave background (CMB) B-mode polarization anisotropy. This process of reducing the gravitational-lensing generated B-mode component will become increasingly important for improving searches for the B modes produced by primordial gravitational waves. In this work, we delens B-mode maps constructed from multi-frequency SPTpol observations of a 90 deg$^2$ patch of sky by subtracting a B-mode template constructed from two inputs: SPTpol E-mode maps and a lensing potential map estimated from the $\textit{Herschel}$ $500\,\mu m$ map of the CIB. We find that our delensing procedure reduces the measured B-mode power spectrum by 28% in the multipole range $300 < \ell < 2300$; this is shown to be consistent with expectations from theory and simulations and to be robust against systematics. The null hypothesis of no delensing is rejected at $6.9 \sigma$. Furthermore, we build and use a suite of realistic simulations to study the general properties of the delensing process and find that the delensing efficiency achieved in this work is limited primarily by the noise in the lensing potential map. We demonstrate the importance of including realistic experimental non-idealities in the delensing forecasts used to inform instrument and survey-strategy planning of upcoming lower-noise experiments, such as CMB-S4.
So far, direct detection searches have come empty handed in their quest for Dark Matter (DM). Meanwhile, asteroseismology arises as a complementary tool to study DM, as its accumulation in a star can enhance energy transport, by providing a conduction mechanism, producing significant changes in the stellar structure during the course of the star's evolution. The stellar core, particularly affected by the presence of DM, can be investigated through precise asteroseismic diagnostics. We modelled three stars including DM energy transport: the Sun, a slightly less massive and much older star, KIC 7871531 ($0.85 \, M_{\odot}$, $9.41 \, \text{Gyr}$), and a more massive and younger one, KIC 8379927 ($1.12 \, M_{\odot}$, $1.82 \, \text{Gyr}$). We considered both the case of Weakly Interactive Massive Particles, albeit with a low annihilation, and the case of Asymmetric DM for which the number of trapped particles in the star can be much greater. By analysing these models with asteroseismic separation ratios weighted towards the core, we found indications limiting the effective spin-dependent DM-proton coupling for masses of a few GeV. This independent result is very close to the most recent and most stringent direct detection DM constraints.
We present the combined Chandra and Swift-BAT spectral analysis of seven Seyfert 2 galaxies selected from the Swift-BAT 100-month catalog. We selected nearby (z<=0.03) sources lacking of a ROSAT counterpart and never previously observed with Chandra in the 0.3-10 keV energy range, and targeted these objects with 10 ks Chandra ACIS-S observations. The X-ray spectral fitting over the 0.3-150 keV energy range allows us to determine that all the objects are significantly obscured, having NH>=1E23 cm^(-2) at a >99% confidence level. Moreover, one to three sources are candidate Compton thick Active Galactic Nuclei (CT-AGN), i.e., have NH>=1E24 cm^(-2). We also test the recent "spectral curvature" method developed by Koss et al. (2016) to find candidate CT-AGN, finding a good agreement between our results and their predictions. Since the selection criteria we adopted have been effective in detecting highly obscured AGN, further observations of these and other Seyfert 2 galaxies selected from the Swift-BAT 100-month catalog will allow us to create a statistically significant sample of highly obscured AGN, therefore better understanding the physics of the obscuration processes.
We develop a general framework for the open dynamics of an ensemble of quantum particles subject to spacetime fluctuations about the flat background. An arbitrary number of interacting bosonic and fermionic particles are considered. A systematic approach to the generation of gravitational waves in the quantum domain is presented that recovers known classical limits in terms of the quadrupole radiation formula and back-reaction dissipation. Classical gravitational emission and absorption relations are quantized into their quantum field theoretical counterparts in terms of the corresponding operators and quantum ensemble averages. Certain arising consistency issues related to factor ordering have been addressed and resolved. Using the theoretical formulation established here with numerical simulations in the quantum regime, we demonstrate new predictions including decoherence through the spontaneous emission of gravitons and collectively amplified "superradiance" of gravitational waves by a highly coherent state of identical particles.
The recently proposed coupled scalar tachyon bounce (CSTB) model is a bounce universe model based on Type IIB string theory. We investigate the dynamics of fluctuations across the bounce point and check whether the scale invariance of the spectrum of the primordial density perturbations generated during the phase of matter-dominated contraction is preserved by the bounce. To this end we utilize the AdS/CFT correspondence: we map the fluctuations onto the boundary before the onset of the strongly coupled gravitational interactions in the bulk. We endow time dependence to the bulk spacetime metric and find an exact solution to the dilaton equation in Type IIB string in an $AdS_5 \times S^5$ background. The time-dependent dilaton determines dynamics of the gauge fields on the boundary. We can thus map the density fluctuations to the boundary and observe their evolution on the boundary even when the bulk gravity becomes strongly coupled near the bounce point. Allowing sufficient time after the bounce point as the bulk returns to weakly coupled state, we map the boundary fluctuations back and compare the post-bounce spectrum with the pre-bounce one. The scale invariance as well as the stability of the spectrum of the primordial density perturbations obtained in the contraction phase of the CST bounce universe model is proven to be unaffected by the bounce.
Based on the Effective Field Theory (EFT) of cosmological perturbations, we revisit the nonsingular cosmologices, without using the integral inequality. We clarify the pathology in nonsingular cubic Galileon models and show how to cure it in EFT with new insights into this issue. With a new application of $R^{(3)}\delta g^{00}$ operator, we build a model with a Genesis phase followed by slow-roll inflation. The spectrum of primordial perturbation may be simulated numerically, which shows itself a large-scale cutoff, as hinted by the CMB large scale anomalies.
A fourth-order theory of gravity is considered which in terms of dynamics has the same degrees of freedom and number of constraints as those of scalar-tensor theories. In addition it admits a canonical point-like Lagrangian description. We study the critical points of the theory and we show that it can describe the matter epoch of the universe and that two accelerated phases can be recovered one of which describes a de Sitter universe. Finally for some models exact solutions are presented.
Links to: arXiv, form interface, find, astro-ph, recent, 1701, contact, help (Access key information)
We present here predictions for the spatial distribution of 21 cm brightness temperature fluctuations from high-dynamic-range simulations for AGN-dominated reionization histories that have been tested against available Lyman-alpha and CMB data. We model AGN by extrapolating the observed M-sigma relation to high redshifts and assign them ionizing emissivities consistent with recent UV luminosity function measurements. We assess the observability of the predicted spatial 21 cm fluctuations by ongoing and upcoming experiments in the late stages of reionization in the limit in which the hydrogen 21 cm spin temperature is significantly larger than the CMB temperature. Our AGN-dominated reionization histories increase the variance of the 21 cm emission by a factor of up to ten compared to similar reionization histories dominated by faint galaxies, to values close to 100 mK^2 at scales accessible to experiments (k < 1 h/cMpc). This is lower than the sensitivity claimed to have been already reached by ongoing experiments by only a factor of about two or less. When reionization is dominated by AGN, the 21 cm power spectrum is enhanced on all scales due to the enhanced bias of the clustering of the more massive haloes and the peak in the large scale 21 cm power is strongly enhanced and moved to larger scales due to bigger characteristic bubble sizes. AGN dominated reionization should be easily detectable by LOFAR (and later HERA and SKA1) at their design sensitivity, assuming successful foreground subtraction and instrument calibration. Conversely, these could become the first non-trivial reionization scenarios to be ruled out by 21 cm experiments, thereby constraining the contribution of AGN to reionization.
Simulations of self-interacting dark matter (SIDM) predict that dark matter should lag behind galaxies during a collision. If the interaction is mediated by a high-mass force carrier, the distribution of dark matter can also develop asymmetric dark matter tails. To search for this asymmetry, we compute the gravitational lensing properties of a mass distribution with a free skewness parameter. We apply this to the dark matter around the four central galaxies in cluster Abell 3827. In the galaxy whose dark matter peak has previously been found to be offset, we measure skewness $s=0.23^{+0.05}_{-0.22}$ in the same direction as the peak offset. Our method may be useful in future gravitational lensing analyses of colliding galaxy clusters and merging galaxies.
The forecasted accuracy of upcoming surveys of large-scale structure cannot be achieved without a proper quantification of the error induced by foreground removal (or other systematics like 0-point photometry offset). Because these errors are highly correlated on the sky, their influence is expected to be especially important at very large scales. In this work we quantify how the uncertainty in the visibility mask of a survey influences the measured power spectrum of a sample of tracers of the density field and its covariance matrix. We start from a very large set of 10,000 catalogs of dark matter halos in periodic cosmological boxes, produced with the PINOCCHIO approximate method. To make an analytic approach feasible, we assume luminosity-independent halo bias and an idealized geometry for the visibility mask. We find that the power spectrum of these biased tracers can be expressed as the sum of a cosmological term, a mask term and a term involving their convolution. The mask and convolution terms scale like $P\propto l^2\sigma_A^2$, where $\sigma_A^2$ is the variance of the uncertainty on the visibility mask. With $l=30-100$ Mpc$/h$ and $\sigma_A=5-20$\%, the mask term can be significant at $k\sim0.01-0.1\ h/$Mpc, and the convolution term can amount to $\sim 1-10$\% of the total. For the power spectrum covariance, the coupling of the convolution term with the other two gives rise to several mixed terms, that we quantify by difference using the mock catalogs. These are found to be of the same order of the mask covariance, and to introduce non-diagonal terms at large scales. Then, the power spectrum covariance matrix cannot be expressed as the sum of a cosmological and of a mask term. Our results lie down the theoretical bases to quantify the impact that uncertainties in the mask calibration have on the derivation of cosmological constraints from large spectroscopic surveys. [Abridged]
We use the Horizon Run 4 cosmological N -body simulation to study the effects of distant and close interactions on the alignments of the shapes, spins, and orbits of targets haloes with their neighbours, and their dependence on the local density environment and neighbour separation. Interacting targets have a significantly lower spin and higher sphericity and oblateness than all targets. Interacting pairs initially have anti-parallel spins, but the spins develop parallel alignment as time goes on. Neighbours tend to evolve in the plane of rotation of the target, and in the direction of the major axis of prolate haloes. Moreover, interactions are preferentially radial, while pairs with non-radial orbits are preferentially prograde. The alignment signals are stronger at high-mass and for close separations, and independent on the large-scale density. Positive alignment signals are found at redshifts up to 4, and increase with decreasing redshifts. Moreover, the orbits tend to become prograde at low redshift, while no alignment is found at high redshift (z = 4).
We introduce CRASH-AMR, a new version of the cosmological Radiative Transfer (RT) code CRASH, enabled to use refined grids. This new feature allows us to attain higher resolution in our RT simulations and thus to describe more accurately ionisation and temperature patterns in high density regions. We have tested CRASH-AMR by simulating the evolution of an ionised region produced by a single source embedded in gas at constant density, as well as by a more realistic configuration of multiple sources in an inhomogeneous density field. While we find an excellent agreement with the previous version of CRASH when the AMR feature is disabled, showing that no numerical artifact has been introduced in CRASH-AMR, when additional refinement levels are used the code can simulate more accurately the physics of ionised gas in high density regions. This result has been attained at no computational loss, as RT simulations on AMR grids with maximum resolution equivalent to that of a uniform cartesian grid can be run with a gain of up to 60% in computational time.
We present an analysis of the pairwise velocity statistics from a suite of cosmological N-body simulations describing the "Running Friedmann-Lema\^itre-Robertson-Walker" (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends {\Lambda}CDM with a time-evolving vacuum energy density. To enforce local conservation of matter a time-evolving gravitational coupling is also included. Our results constitute the first study of velocities in the R-FLRW cosmology, and we also compare with other dark energy simulations suites, repeating the same analysis. We find a strong degeneracy between the pairwise velocity and {\sigma}_8 at z=0 for almost all scenarios considered, which remains even when we look back to epochs as early as z=2. We also investigate various Coupled Dark Energy models, some of which show minimal degeneracy, and reveal interesting deviations from {\Lambda}CDM which could be readily exploited by future cosmological observations to test and further constrain our understanding of dark energy.
Motivated by tension between the predictions of ordinary cold dark matter (CDM) and observations at galactic scales, ultralight axionlike particles (ULALPs) with mass of the order $10^{-22}~{\rm eV}$ have been proposed as an alternative CDM candidate. We consider cold and collisionless ULALPs produced in the early universe by the vacuum realignment mechanism and constituting most of CDM. The ULALP fluid is commonly described by classical field equations. However, we show that, like QCD axions, the ULALPs thermalize by gravitational self-interactions and form a Bose-Einstein condensate (BEC), a quantum phenomenon. ULALPs, like QCD axions, explain the observational evidence for caustic rings of dark matter because they thermalize and go to the lowest energy state available to them. This is one of rigid rotation on the turnaround sphere. By studying the heating effect of infalling ULALPs on galactic disk stars and the thickness of the nearby caustic ring as observed from a triangular feature in the IRAS map of our galactic disk, we obtain lower mass bounds on the ULALP mass of order $10^{-23}~{\rm eV}$ and $10^{-20}~{\rm eV}$ respectively.
The phase transition responsible for axion dark matter production can create large amplitude isocurvature perturbations which collapse into dense objects known as axion miniclusters. We use microlensing data from the EROS survey, and from recent observations with the Subaru Hyper Suprime Cam to place constraints on the minicluster scenario. We compute the microlensing event rate for miniclusters treating them as spatially extended objects with an extended mass function. Using the published bounds on the number of microlensing events we bound the fraction of DM collapsed into miniclusters, $f_{\rm MC}$. For an axion with temperature dependent mass consistent with the QCD axion we find $f_{\rm MC}<0.22(m_a/100\,\mu\text{eV})^{-0.57}$, which represents the first observational constraint on the minicluster fraction. We forecast that a high-efficiency observation of ten nights with Subaru would be sufficient to constrain $f_{\rm MC}\lesssim 0.1$ over the entire QCD axion mass range. We make various approximations to derive these constraints and dedicated analyses by the observing teams of EROS and Subaru are necessary to confirm our results. If accurate theoretical predictions for $f_{\rm MC}$ can be made in future then microlensing can be used to exclude, or discover, the QCD axion. Further details of our computations are presented in a companion paper.
We consider gauge invariant cosmological perturbations in UV-modified, z=3 Horava gravity with one scalar matter field, which has been proposed as a renormalizable gravity theory without the ghost problem in four dimensions. In order to exhibit its dynamical degrees of freedom, we consider the Hamiltonian reduction method and find that, by solving "all" the constraint equations, the degrees of freedom are the same as those of Einstein gravity: One scalar and two tensor (graviton) modes when a scalar matter field presents. However, we confirm that there is no extra graviton modes and general relativity is recovered in IR, which achieves the consistency of the model. From the UV-modification terms which break the detailed balance condition in UV, we obtain scale-invariant power spectrums for "non"-inflationary backgrounds, like the power-law expansions, without knowing the details of early expansion history of Universe. This could provide a new framework for the Big Bang cosmology. Moreover, we find that "tensor and scalar fluctuations travel differently in UV, generally". We present also some clarifying remarks about confusing points in the literatures.
We explore for the first time the effect of self-interacting dark matter (SIDM) on the dark matter (DM) and baryonic distribution in massive galaxies formed in hydrodynamical cosmological simulations, including explicit baryonic physics treatment. A novel implementation of Super-Massive Black Hole (SMBH) formation and evolution is used, as in Tremmel et al.(2015, 2016), allowing to explicitly follow SMBH dynamics at the center of galaxies. A high SIDM constant cross-section is chosen, $\sigma$=10 $\rm cm^2/gr$, to amplify differences from CDM models. Milky Way-like galaxies form a shallower DM density profile in SIDM than they do in CDM, with differences already at 20 kpc scales. This demonstrates that even for the most massive spirals the effect of SIDM dominates over the adiabatic contraction due to baryons. Strikingly, the dynamics of SMBHs differs in the SIDM and reference CDM case. SMBHs in massive spirals have sunk to the centre of their host galaxy in both the SIDM and CDM run, while in less massive galaxies about 80$\%$ of the SMBH population is off-centered in the SIDM case, as opposed to the CDM case in which $\sim$90$\%$ of SMBHs have reached their host's centre. SMBHs are found as far as $\sim$9 kpc away from the centre of their host SIDM galaxy. This difference is due to the increased dynamical friction timescale caused by the lower DM density in SIDM galaxies compared to CDM, resulting in 'core stalling'. This pilot work highlights the importance of simulating in a full hydrodynamical context different DM models combined to SMBH physics to study their influence on galaxy formation.
Subject of this article is the relationship between modern cosmology and fundamental physics, in particular general relativity as a theory of gravity on one side, together with its unique application in cosmology, and the formation of structures and their statistics on the other. It summarises arguments for the formulation for a metric theory of gravity and the uniqueness of the construction of general relativity. It discusses symmetry arguments in the construction of Friedmann-Lema\^itre cosmologies as well as assumptions in relation to the presence of dark matter, when adopting general relativity as the gravitational theory. A large section is dedicated to $\Lambda$CDM as the standard model for structure formation and the arguments that led to its construction, and to the of role statistics and to the problem of scientific inference in cosmology as an empirical science. The article concludes with an outlook on current and future developments in cosmology.
Broad emission-line outflows of active galactic nuclei (AGNs) have been proposed for many years but are very difficult to quantitatively study because of the coexistence of the gravitationally-bound and outflow emission. We present detailed analysis of a heavily reddened quasar, SDSS J000610.67+121501.2, whose normal ultraviolet (UV) broad emission lines (BELs) are heavily suppressed by the Dusty Torus as a natural "Coronagraph", thus the blueshifted BELs (BBELs) can be reliably measured. The physical properties of the emission-line outflows are derived as follows: ionization parameter $U \sim 10^{-0.5}$, column density $N_{\rm H}\sim 10^{22.0}$ cm$^{-2}$, covering fraction of $\sim 0.1$ and upper limit density of $n_{\rm H}\sim 10^{5.8}$ cm$^{-3}$. The outflow gases are located at least 41 pc away from the central engine, which suggests that they have expanded to the scale of the dust torus or beyond. Besides, Lya shows a narrow symmetric component, to our surprise, which is undetected in any other lines. After inspecting the narrow emission-line region and the starforming region as the origin of the Lya narrow line, we propose the end-result of outflows, diffusing gases in the larger region, acts as the screen of Lya photons. Future high spatial resolution spectrometry and/or spectropolarimetric observation are needed to make a final clarification.
With the first two detections in late 2015, astrophysics has officially entered into the new era of gravitational wave observations. Since then, much has been going on in the field with a lot of work focussing on the observations and implications for astrophysics and tests of general relativity in the strong regime. However much less is understood about how gravitational detectors really work at their fundamental level. For decades, the response to incoming signals has been customarily calculated using the very same physical principle, which has proved so successful in the first detections. In this paper we review the physical principle that is behind such a detection at the very fundamental level, and we try to highlight the peculiar subtleties that make it so hard in practice. We will then mention how detectors are built starting from this fundamental measurement element.
Links to: arXiv, form interface, find, astro-ph, recent, 1701, contact, help (Access key information)
The possible slowing down of cosmic acceleration was widely studied. However, the imposition of dark energy parametrization brought some tensions. In our recent paper, we test this possibility using a model-independent method, Gaussian processes. However, the reason of generating these tensions is still closed. In the present paper, we analyse the derivative of deceleration parameter to solve the problems. The reconstruction of the derivative again suggests that no slowing down of acceleration is presented within 95\% C.L. from current observational data. We then deduce its constraint on dark energy. The corresponding constraint clearly reveals the reason of tension between different models in previous work. We also study the essential reason of why current data cannot convincingly measure the slowing down of acceleration. The constraints indicate that most of current data are not in the allowed region.
We study formation of stellar mass binary black holes (BBHs) originating from Population III (PopIII) stars, performing stellar evolution simulations for PopIII binaries with MESA. We find that a significant fraction of PopIII binaries form massive BBHs through stable mass transfer between two stars in a binary, without experiencing common envelope phases. We investigate necessary conditions required for PopIII binaries to form BBHs coalescing within the Hubble time with a semi-analytical model calibrated by the stellar evolution simulations. The formation efficiency of coalescing PopIII BBHs is estimated for two different initial conditions for PopIII binaries with large and small separations, respectively. Consequently, in both models, $\sim 10\%$ of the total PopIII binaries form BBHs only through stable mass transfer and $\sim 10\%$ of these BBHs merge due to gravitational wave emission within the Hubble time. Furthermore, the chirp mass of merging BBHs has a flat distribution over $15\lesssim M_{\rm chirp}/M_\odot \lesssim 35$. This formation pathway of PopIII BBHs is presumably robust because stable mass transfer is less uncertain than common envelope evolution, which is the main formation channel for Population II BBHs. We also test the hypothesis that the BBH mergers detected by LIGO originate from PopIII stars using our result and the total number of PopIII stars formed in the early universe as inferred from the optical depth measured by Planck. We conclude that the PopIII BBH formation scenario can explain the mass-weighted merger rate of the LIGO's O1 events with the maximal PopIII formation efficiency inferred from the Planck measurement, even without BBHs formed by unstable mass transfer or common envelope phases.
We propose a simple analytic model to understand when star formation is time-steady versus bursty on short (<~10 Myr) time scales in galaxies. Recent models explain the observed Kennicutt-Schmidt relation between star formation rate and gas surface densities in galaxies as resulting from a balance between stellar feedback and gravity. We argue that bursty star formation occurs when such an equilibrium cannot be stably sustained, and identify two regimes in which galaxy-scale star formation should be bursty: i) at high redshift (z>~1) for galaxies of all masses, and ii) at low masses (depending on gas fraction) for galaxies at any redshift. At high redshift, characteristic galactic dynamical time scales become too short for supernova feedback to effectively respond to gravitational collapse in galactic discs (an effect recently identified for galactic nuclei), whereas in dwarf galaxies star formation occurs in too few bright star-forming regions to effectively average out. Burstiness is also enhanced at high redshift owing to elevated gas fractions in the early Universe. Our model can thus explain the bursty star formation histories observationally-inferred in both local dwarf and high-redshift galaxies, as well as the bursty star formation rates predicted in these regimes by recent high-resolution galaxy formation simulations. In our model, bursty star formation is associated with particularly strong spatio-temporal clustering of supernovae. Such clustering can promote the formation of galactic winds and our model may thus also explain the much higher wind mass loading factors inferred in high-redshift massive galaxies relative to their z~0 counterparts.
Mergers of galaxies are thought to cause significant gas inflows to the inner parsecs, which can activate rapid accretion onto supermassive black holes (SMBHs), giving rise to Active Galactic Nuclei (AGN). During a significant fraction of this process, SMBHs are predicted to be enshrouded by gas and dust. Studying 52 galactic nuclei in infrared-selected local Luminous and Ultra-luminous infrared galaxies in different merger stages in the hard X-ray band, where radiation is less affected by absorption, we find that the amount of material around SMBHs increases during the last phases of the merger. We find that the fraction of Compton-thick (CT, $N_{\rm\,H}\geq 10^{24}\rm\,cm^{-2}$) AGN in late merger galaxies is higher ($f_{\rm\,CT}=65^{+12}_{-13}\%$) than in local hard X-ray selected AGN ($f_{\rm\,CT}=27\pm 4\%$), and that obscuration reaches its maximum when the nuclei of the two merging galaxies are at a projected distance of $D_{12}\simeq0.4-10.8$ kiloparsecs ($f_{\rm\,CT}=77_{-17}^{+13}\%$). We also find that all AGN of our sample in late merger galaxies have $N_{\rm\,H}> 10^{23}\rm\,cm^{-2}$, which implies that the obscuring material covers $95^{+4}_{-8}\%$ of the X-ray source. These observations show that the material is most effectively funnelled from the galactic scale to the inner tens of parsecs during the late stages of galaxy mergers, and that the close environment of SMBHs in advanced mergers is richer in gas and dust with respect to that of SMBHs in isolated galaxies, and cannot be explained by the classical AGN unification model in which the torus is responsible for the obscuration.
We present the discovery and spectroscopic confirmation with the ESO NTT and Gemini South telescopes of eight new 6.0 < z < 6.5 quasars with z$_{AB}$ < 21.0. These quasars were photometrically selected without any star-galaxy morphological criteria from 1533 deg$^{2}$ using SED model fitting to photometric data from the Dark Energy Survey (g, r, i, z, Y), the VISTA Hemisphere Survey (J, H, K) and the Wide-Field Infrared Survey Explorer (W1, W2). The photometric data was fitted with a grid of quasar model SEDs with redshift dependent Lyman-{\alpha} forest absorption and a range of intrinsic reddening as well as a series of low mass cool star models. Candidates were ranked using on a SED-model based $\chi^{2}$-statistic, which is extendable to other future imaging surveys (e.g. LSST, Euclid). Our spectral confirmation success rate is 100% without the need for follow-up photometric observations as used in other studies of this type. Combined with automatic removal of the main types of non-astrophysical contaminants the method allows large data sets to be processed without human intervention and without being over run by spurious false candidates. We also present a robust parametric redshift estimating technique that gives comparable accuracy to MgII and CO based redshift estimators. We find two z $\sim$ 6.2 quasars with HII near zone sizes < 3 proper Mpc which could indicate that these quasars may be young with ages < 10$^6$ - 10$^7$ years or lie in over dense regions of the IGM. The z = 6.5 quasar VDESJ0224-4711 has J$_{AB}$ = 19.75 is the second most luminous quasar known with z > 6.5.
Optical and near-infrared photometry, optical spectroscopy, and soft X-ray and UV monitoring of the changing look active galactic nucleus NGC 2617 show that it continues to have the appearance of a type-1 Seyfert galaxy. An optical light curve for 2010--2016 indicates that the change of type probably occurred between October 2010 and February 2012 and was not related to the brightening in 2013. In 2016 NGC 2617 brightened again to a level of activity close to that of April 2013. We find variations in all passbands and in both the intensities and profiles of the broad Balmer lines. A new displaced emission peak has appeared in H$\beta$. X-ray variations are well correlated with UV--optical variability and possibly lead by $\sim$ 2--3 days. The $K$ band lags the $J$ band by about 21.5 $\pm$ 2.5 days and lags the combined $B+J$ filters by $\sim$ 25 days. $J$ lags $B$ by about 3 days. This could be because $J$-band variability arises from the outer part of the accretion disc while $K$-band variability comes from thermal re-emission by dust. We propose that spectral type changes are a result of increasing central luminosity causing sublimation of the innermost dust in the hollow bi-conical outflow. We briefly discuss various other possible reasons which might explain the dramatic changes NGC 2617.
Links to: arXiv, form interface, find, astro-ph, recent, 1701, contact, help (Access key information)
Strong gravitational lensing provides a powerful test of Cold Dark Matter (CDM) as it enables the detection and mass measurement of low mass haloes even if they do not contain baryons. Compact lensed sources such as Active Galactic Nuclei (AGN) are particularly sensitive to perturbing subhalos, but their use as a test of CDM has been limited by the small number of systems which have significant radio emission. Radio emission is extended enough avoid significant lensing by stars in the plane of the lens galaxy, and red enough to be minimally affected by differential dust extinction. Narrow-line emission is a promising alternative as it is also extended and, unlike radio, detectable in virtually all optically selected AGN lenses. We present first results from a WFC3 grism narrow-line survey of lensed quasars, for the quadruply lensed AGN HE0435-1223. Using a forward modelling pipeline which enables us to robustly account for blending between nearby images and the main lens galaxy, we measure the [OIII] 5007 \AA$~$ flux ratios of the four lensed quasar images. We find that the lensed [OIII] fluxes and positions are well fit by a simple smooth mass model for the main lens. Our data rule out a $>10^{8} (10^{7.2}) M_{600}/M_\odot$ NFW perturber within $\sim$1."0 (0."1) arcseconds of the lensed images, where $M_{600}$ is the perturber mass within its central 600 pc. The non-detection is broadly consistent with the expectations of $\Lambda$CDM for a single system. The sensitivity achieved demonstrates that powerful limits on the nature of dark matter can be obtained with the analysis of the entire sample of narrow-line lenses.
We present the results of a systematic search for Lyman-alpha emitters (LAEs) at $6 \lesssim z \lesssim 7.6$ using the HST WFC3 Infrared Spectroscopic Parallel (WISP) Survey. Our total volume over this redshift range is $\sim 8 \times10^5$ Mpc$^3$, comparable to many of the narrowband surveys despite their larger area coverage. We find two LAEs at $z=6.38$ and $6.44$ with line luminosities of L$_{\mathrm{Ly}\alpha} \sim 4.7 \times 10^{43}$ erg s$^{-1}$, putting them among the brightest LAEs discovered at these redshifts. Taking advantage of the broad spectral coverage of WISP, we are able to rule out almost all lower-redshift contaminants. The WISP LAEs have a high number density of $7.7\times10^{-6}$ Mpc$^{-3}$. We argue that the LAEs reside in Mpc-scale ionized bubbles that allow the Lyman-alpha photons to redshift out of resonance before encountering the neutral IGM. We discuss possible ionizing sources and conclude that the observed LAEs alone are not sufficient to ionize the bubbles.
The effect of baryons on the matter power spectrum is likely to have an observable effect for future galaxy surveys, like Euclid or LSST. As a first step towards a fully predictive theory, we investigate the effect of non-radiative hydrodynamics on the structure of galaxy groups sized halos, which contribute the most to the weak lensing power spectrum. We perform high resolution (more than one million particles per halo and one kilo-parsec resolution) non-radiative hydrodynamical zoom-in simulations of a sample of 16 halos, comparing the profiles to popular analytical models. We find that the total mass profile is well fitted by a Navarro, Frenk & White model, with parameters slightly modified from the dark matter only simulation. We also find that the Komatsu & Seljak hydrostatic solution provides a good fit to the gas profiles, with however significant deviations, arising from strong turbulent mixing in the core and from non-thermal, turbulent pressure support in the outskirts. The turbulent energy follows a shallow, rising linear profile with radius, and correlates with the halo formation time. Using only three main structural halo parameters as variables (total mass, concentration parameter and central gas density), we can predict with an accuracy better than 20% the individual gas density and temperature profiles. For the average total mass profile, which is relevant for power spectrum calculations, we even reach an accuracy of 1%. The robustness of these predictions has been tested against resolution effects, different types of initial conditions and hydrodynamical schemes.
We study the expected variance of measurements of the Hubble constant, $H_0$, as calculated in either linear perturbation theory or using non-linear velocity power spectra derived from $N$-body simulations. We compare the variance with that obtained by carrying out mock observations in the N-body simulations, and show that the estimator typically used for the local Hubble constant in studies based on perturbation theory is different from the one used in studies based on N-body simulations. The latter gives larger weight to distant sources, which explains why studies based on N-body simulations tend to obtain a smaller variance than that found from studies based on the power spectrum. Although both approaches result in a variance too small to explain the discrepancy between the value of $H_0$ from CMB measurements and the value measured in the local universe, these considerations are important in light of the percent determination of the Hubble constant in the local universe.
Although the cusp-core controversy for dwarf galaxies is seen as a problem, I argue that the cored central profiles can be explained by flattened cusps because they suffer from conflicting measurements and poor statistics and because there is a large number of conventional processes that could have flattened them since their creation, none of which requires new physics. Other problems, such as "too big to fail", are not discussed.
A brief review of supersymmetric models and their candidates for dark matter is carried out. The neutralino is a WIMP candidate in the MSSM where $R$-parity is conserved, but this model has the $\mu$ problem. There are natural solutions to this problem that necessarily introduce new structure beyond the MSSM, including new candidates for dark matter. In particular, in an extension of the NMSSM, the right-handed sneutrino can be used for this job. In $R$-parity violating models such as the $\mu\nu$SSM, the gravitino can be the dark matter, and could be detected by its decay products in gamma-ray experiments.
We report the $4 \, \sigma$ detection of a faint object with a flux of ~ 0.3 mJy, in the vicinity of the quadruply lensed QSO MG0414+0534 using the Atacama Large Millimeter/submillimeter array (ALMA) Band 7. The object is most probably a dusty dark dwarf galaxy, which has not been detected in either the optical, near-infrared (NIR) or radio (cm) bands. An anomaly in the flux ratio of the lensed images observed in Band 7 and the mid-infrared (MIR) band and the reddening of the QSO light color can be simultaneously explained if we consider the object as a lensing substructure with an ellipticity ~ 0.7 at a redshift of $0.5 \lesssim z \lesssim 1$. Using the best-fit lens models with three lenses, we find that the dark matter plus baryon mass associated with the object is $\sim 10^9\, M_{\odot}$, the dust mass is $\sim 10^7\,M_{\odot}$ and the linear size is $\gtrsim 5\,$kpc. Thus our findings suggest that the object is a dusty dark dwarf galaxy. A substantial portion of faint submillimeter galaxies (SMGs) in the universe may be attributed to such dark objects.
According to the dS/CFT correspondence, correlators of fields generated during a primordial de Sitter phase are constrained by three-dimensional conformal invariance. Using the properties of radially quantized conformal field theories and the operator-state correspondence, we glean information on some points. The Higuchi bound on the masses of spin-s states in de Sitter is a direct consequence of reflection positivity in radially quantized CFT$_3$ and the fact that scaling dimensions of operators are energies of states. The partial massless states appearing in de Sitter correspond from the boundary CFT$_3$ perspective to boundary states with highest weight for the conformal group. We discuss inflationary consistency relations and the role of asymptotic symmetries which transform asymptotic vacua to new physically inequivalent vacua by generating long perturbation modes. We show that on the CFT$_3$ side, asymptotic symmetries have a nice quantum mechanics interpretation. For instance, acting with the asymptotic dilation symmetry corresponds to evolving states forward (or backward) in "time" and the charge generating the asymptotic symmetry transformation is the Hamiltonian itself. Finally, we investigate the symmetries of anisotropic inflation and show that correlators of four-dimensional free scalar fields can be reproduced in the dual picture by considering an isotropic three-dimensional boundary enjoying dilation symmetry, but with a nonvanishing vacuum expectation value of the boundary stress-energy momentum tensor.
We study the role of field redefinitions in general scalar-tensor theories. In particular, we first focus on the class of field redefinitions linear in the spin-2 field and involving derivatives of the spin-0 mode, generically known as disformal transformations. We start by defining the action of a disformal transformation in the tangent space. Then, we take advantage of the great economy of means of the language of differential forms to compute the full transformation of Horndeski's theory under general disformal transformations. We obtain that Horndeski's action maps onto itself modulo a reduced set of non-Horndeski Lagrangians. These new Lagrangians are found to be invariant under disformal transformation that depend only in the first derivatives of the scalar. Moreover, these combinations of Lagrangians precisely appear when expressing in our basis the constraints of the recently proposed Extended Scalar-Tensor (EST) theories. These results allow us to classify the different orbits of scalar-tensor theories invariant under particular disformal transformations, namely the special disformal, kinetic disformal and disformal Horndeski orbits. In addition, we consider generalizations of this framework. We find that there are possible well-defined extended disformal transformations that have not been considered in the literature. However, they generically cannot link Horndeski theory with EST theories. Finally, we study further generalizations in which extra fields with different spin are included. These field redefinitions can be used to connect different gravity theories such as multi-scalar-tensor theories, generalized Proca theories and bi-gravity. We discuss how the formalism of differential forms could be useful for future developments in these lines.
Links to: arXiv, form interface, find, astro-ph, recent, 1701, contact, help (Access key information)