Pulsar Timing Arrays (PTAs) use high accuracy timing of a collection of low timing noise pulsars to search for gravitational waves in the microhertz to nanohertz frequency band. The sensitivity of such a PTA depends on how the available observing time is allocated among the pulsars in the array. Here, we report on a preliminary analysis of observing strategies for the current North American Nanohertz Observatory for Gravitational Waves (NANOGrav) PTA. We also investigate the affects of an additional pulsar on the array sensitivity, with the goal of suggesting where PTA pulsar searches might be best directed. We demonstrate that there exists a slight advantage to finding a new pulsar near where the array is already most sensitive. Further, the study suggests that more observing time should be dedicated to the already low noise pulsars in order to have the greatest positive effect on the PTA sensitivity. We have made a web-based sensitivity mapping tool available at this http URL
We use high-resolution three-dimensional adaptive mesh refinement simulations to investigate the interaction of high-redshift galaxy outflows with low-mass virialized clouds of primordial composition. While atomic cooling allows star formation in objects with virial temperatures above $10^4$ K, "minihaloes" below this threshold are generally unable to form stars by themselves. However, these objects are highly susceptible to triggered star formation, induced by outflows from neighboring high-redshift starburst galaxies. Here we conduct a study of these interactions, focusing on cooling through non-equilibrium molecular hydrogen (H$_2$) and hydrogen deuteride (HD) formation. Tracking the non-equilibrium chemistry and cooling of 14 species and including the presence of a dissociating background, we show that shock interactions can transform minihaloes into extremely compact clusters of coeval stars. Furthermore, these clusters are all less than $\approx 10^6 M_\odot,$ and they are ejected from their parent dark matter halos: properties that are remarkably similar to those of the old population of globular clusters.
We present deep, high-quality K-band images of complete subsamples of powerful radio and sub-mm galaxies at z=2. The data were obtained in the best available seeing at UKIRT and Gemini North, with integration times scaled to ensure that comparable rest-frame surface brightness levels are reached for all galaxies. We fit two-dimensional axi-symmetric galaxy models to determine galaxy morphologies at rest-frame optical wavelengths > 4000A, varying luminosity, axial ratio, half-light radius, and Sersic index. We find that, while some images show evidence of galaxy interactions, >95% of the rest-frame optical light in all galaxies is well-described by these simple models. We also find a clear difference in morphology between these two classes of galaxy; fits to the individual images and image stacks reveal that the radio galaxies are moderately large (<r{1/2}>=8.4+-1.1kpc; median r{1/2}=7.8), de Vaucouleurs spheroids (<n> = 4.07+-0.27; median n=3.87), while the sub-mm galaxies appear to be moderately compact (<r{1/2}>=3.4+-0.3kpc; median r{1/2}=3.1kpc) exponential discs (<n>=1.44+-0.16; median n=1.08). We show that the z=2 radio galaxies display a well-defined Kormendy relation but that, while larger than other recently-studied high-z massive galaxy populations, they are still ~1.5 times smaller than their local counterparts. The scalelengths of the starlight in the sub-mm galaxies are comparable to those reported for the molecular gas. Their sizes are also similar to those of comparably massive quiescent galaxies at z>1.5. In terms of stellar mass surface density, the majority of the radio galaxies lie within the locus defined by local ellipticals. In contrast, while best modelled as discs, most of the sub-mm galaxies have higher stellar mass densities than local galaxies, and appear destined to evolve into present-day massive ellipticals.
We perform an extensive analysis of the Civ line in three large spectroscopic
surveys of quasars. Differing approaches for fitting the Civ line can be found
in the literature, and we compare the most common methods to highlight the
relative systematics associated with each. We develop a line fitting procedure
and apply it to the Civ line in spectra from the SDSS, 2QZ and 2SLAQ surveys.
Our results are compared with a previous study of the Mgii line in the same
sample. Civ tends to be broader than the Mgii line in spectra that have both,
and the average ratio between the lines is consistent with a simplistic model
for a photoionised, virialised and stratified broad-line region. There is a
statistically significant correlation between the widths of the Civ and Mgii
lines. However, the correlation is weak, and the scatter around a best fit is
only marginally less than the full dynamic range of line widths.
Motivated by previous work, we examine the dispersion in the distribution of
Civ line widths. We find that the dispersion in Civ line widths is essentially
independent of both redshift and luminosity. This is in stark contrast to the
Mgii line, which shows a strong luminosity dependence.
Finally we consider our results in terms of their implications for virial
black hole mass estimation. The inconsistency between Mgii and Civ line widths
in single spectra, combined with the differing behaviour of the Mgii and Civ
line width distributions, indicates that there must be an inconsistency between
Mgii and Civ virial mass estimators. Furthermore, the level of intrinsic
dispersion in Mgii and Civ line widths contributes less dynamic range to virial
mass estimates than the error associated with the estimates. The indication is
that the line width term in these UV virial mass estimators may be essentially
irrelevant with respect to the typical uncertainty on a mass estimate.
First order phase transitions in the early universe can give rise to a stochastic background of gravitational waves. A hypothetical first order electroweak phase transition is particularly interesting in this respect, since the signal is in the good frequency range to be detectable by the space interferometer LISA. Three main processes lead to the production of the gravitational wave signal: the collision of the broken phase bubbles, the magnetohydrodynamical turbulence in the plasma stirred by the bubble collisions, and the magnetic fields amplified by the magnetohydrodynamical turbulence. The main features of the gravitational wave spectrum, such as the peak frequency, the amplitude, and the slopes both at low and high wave-number can be predicted by general arguments based on the characteristics of the source: in particular, the structure of its space and time correlation. We find that the gravitational wave signal from a first order phase transition occurring at electroweak symmetry breaking falls into the LISA sensitivity range if the phase transition lasts for about one hundredth of the Hubble time and the energy density of the turbulent motions is about twenty percent of the total energy density in the universe at the phase transition time.
Malin 1 is a unique, extraordinarily large low surface brightness galaxy. The structure and the origins of the galaxy are poorly understood. The reason for such a situation is an absence of detailed observational data, especially, of high-resolution kinematics. In this Letter we study the stellar kinematics of the inner part (r < 15 kpc) of Malin 1. We present spectroscopic arguments in favour of a small galaxy - Malin 1B - being a companion probably interacting with the main galaxy - Malin 1. This object is clearly seen in many published images of Malin 1 but is not mentioned in any astronomical databases. Malin 1B is located at the projected distance of 14 kpc from the Malin 1's nucleus and has small - 65$\pm$16 km/s - relative velocity, which we determined for the first time. We suggest that ongoing interaction with Malin 1B can explain main morphological features of the Malin 1's central region - two-armed spiral structure, a bar, and an external one-armed spiral pattern. We also investigated the large scale environment of Malin 1 and postulate that the galaxy SDSS J123708.91+142253.2 might be responsible for the formation of extended low-surface brightness envelope by means of head-on collision with Malin 1 (in the framework of collision scenario proposed by Mapelli et al. 2008). To test the collisional origins of Malin 1 global structure, more observational data and new numerical models are needed.
We study the generation of helical magnetic fields during inflation induced by an axial coupling of the electromagnetic field to the inflaton. During slow roll inflation, we find that such a coupling always leads to a blue spectrum with $B^2 \propto k$. We also show that a short deviation from slow roll does not result in strong modifications to the shape of the spectrum. The magnetic energy density at the end of inflation is too small to back-react on the background dynamics of the inflaton. We calculate the evolution of the correlation length and the field amplitude during the inverse cascade and viscous damping of the helical magnetic field in the radiation era after inflation. The final magnetic fields turn out to be far too weak to provide the seeds for the observed fields in galaxies and clusters.
We propose that gravity be intrinsically quantum-mechanical, so that in the absence of quantum mechanics the geometry of the universe would be Minkowski. We show that in such a situation gravity does not require any independent quantization of its own, with it being quantized simply by virtue of its being coupled to the quantized matter fields that serve as its source. We show that when the gravitational and matter fields possess an underlying conformal symmetry, the gravitational field and fermionic matter-field zero-point fluctuations cancel each other identically. Then, when the fermions acquire mass by a dynamical symmetry breaking procedure that induces a cosmological constant in such conformal theories, the zero-point fluctuations readjust so as to cancel the induced cosmological constant identically. The zero-point vacuum problem and the cosmological constant vacuum problems thus mutually solve each other. We illustrate our ideas in a completely solvable conformal-invariant model, namely two-dimensional quantum Einstein gravity coupled to a Nambu-Jona-Lasinio self-consistent fermion.
We reconsider non-minimal \lambda \phi^4 chaotic inflation which includes the gravitational coupling term \xi \mathcal{R} \phi^2, where \phi denotes a gauge singlet inflaton field and \mathcal{R} is the Ricci scalar. For \xi >> 1 we require, following recent discussions, that the energy scale \lambda^{1/4} m_P / \sqrt{\xi} for inflation should not exceed the effective UV cut-off scale m_P / \xi, where m_P denotes the reduced Planck scale. The predictions for the tensor to scalar ratio r and the scalar spectral index n_s are found to lie within the WMAP 1-\sigma bounds for 10^{-12} < \lambda < 10^{-4} and 10^{-3} < \xi < 10^2. In contrast, the corresponding predictions of minimal \lambda \phi^4 chaotic inflation lie outside the WMAP 2-\sigma bounds. We also find that r > 0.002, provided the scalar spectral index n_s > 0.96. In estimating the lower bound on r we take into account possible modifications due to quantum corrections of the tree level inflationary potential.
Massive evolved stars can produce large amounts of dust, and far-infrared (IR) data are essential for determining the contribution of cold dust to the total dust mass. Using Herschel, we search for cold dust in three very dusty massive evolved stars in the Large Magellanic Cloud: R71 is a Luminous Blue Variable, HD36402 is a Wolf-Rayet triple system, and IRAS05280-6910 is a red supergiant. We model the spectral energy distributions using radiative transfer codes and find that these three stars have mass-loss rates up to 10^-3 solar masses/year, suggesting that high-mass stars are important contributors to the life-cycle of dust. We found far-IR excesses in two objects, but these excesses appear to be associated with ISM and star-forming regions. Cold dust (T < 100 K) may thus not be an important contributor to the dust masses of evolved stars.
To assess how future progress in gravitational microlensing computation at high optical depth will rely on both hardware and software solutions, we compare a direct inverse ray-shooting code implemented on a graphics processing unit (GPU) with both a widely-used hierarchical tree code on a single-core CPU, and a recent implementation of a parallel tree code suitable for a CPU-based cluster supercomputer. We examine the accuracy of the tree codes through comparison with a direct code over a much wider range of parameter space than has been feasible before. We demonstrate that all three codes present comparable accuracy, and choice of approach depends on considerations relating to the scale and nature of the microlensing problem under investigation. On current hardware, there is little difference in the processing speed of the single-core CPU tree code and the GPU direct code, however the recent plateau in single-core CPU speeds means the existing tree code is no longer able to take advantage of Moore's law-like increases in processing speed. Instead, we anticipate a rapid increase in GPU capabilities in the next few years, which is advantageous to the direct code. We suggest that progress in other areas of astrophysical computation may benefit from a transition to GPUs through the use of "brute force" algorithms, rather than attempting to port the current best solution directly to a GPU language -- for certain classes of problems, the simple implementation on GPUs may already be no worse than an optimised single-core CPU version.
We investigate thermodynamics of the apparent horizon in $f(R)$ gravity in the Palatini formalism with non-equilibrium and equilibrium descriptions. We demonstrate that it is more transparent to understand the horizon entropy in the equilibrium framework than that in the non-equilibrium one. Furthermore, we show that the second law of thermodynamics can be explicitly verified in both phantom and non-phantom phases for the same temperature of the universe outside and inside the apparent horizon.
We present a novel radiation hydrodynamics code, START, which is a smoothed particle hydrodynamics (SPH) scheme coupled with accelerated radiative transfer. The basic idea for the acceleration of radiative transfer is parallel to the tree algorithm that is hitherto used to speed up the gravitational force calculation in an N-body system. It is demonstrated that the radiative transfer calculations can be dramatically accelerated, where the computational time is scaled as Np log Ns for Np SPH particles and Ns radiation sources. Such acceleration allows us to readily include not only numerous sources but also scattering photons, even if the total number of radiation sources is comparable to that of SPH particles. Here, a test simulation is presented for a multiple source problem, where the results with START are compared to those with a radiation SPH code without tree-based acceleration. We find that the results agree well with each other if we set the tolerance parameter as < 1.0, and then it demonstrates that START can solve radiative transfer faster without reducing the accuracy. One of important applications with START is to solve the transfer of diffuse ionizing photons, where each SPH particle is regarded as an emitter. To illustrate the competence of START, we simulate the shadowing effect by dense clumps around an ionizing source. As a result, it is found that the erosion of shadows by diffuse recombination photons can be solved. Such an effect is of great significance to reveal the cosmic reionization process.
Despite being very successful in explaining the wide range of precision experimental results obtained so far, the Standard Model (SM) of elementary particles fails to address the two greatest discoveries of the recent decades: dark matter (DM) and tiny but nonzero neutrino masses. Typically the new models beyond the SM explain only one of these observations. Instead, in the present article, we take the view that they both point towards the same new extension of the Standard Model. The new particles introduced are responsible simultaneously for neutrino masses and for the dark matter of the Universe. The stability of dark matter and the smallness of neutrino masses are guaranteed by a U(1) global symmetry, broken to a remnant Z_2. The canonical seesaw mechanism is forbidden and neutrino masses emerge at the loop level being further suppressed by the small explicit breaking of the U(1) symmetry. The new particles and interactions are invoked at the electroweak scale and lead to a rich phenomenology in colliders, in lepton flavour violating rare decays and in direct and indirect dark matter searches, making the model testable in the coming future.
We establish the evolution equations of the set of independent variables characterizing the 2PN rigorous conservative dynamics of a spinning compact binary, with the inclusion of the leading order spin-orbit, spin-spin and mass quadrupole - mass monopole effects, for generic (noncircular, nonspherical) orbits. More specifically, we give a closed system of first order ordinary differential equations for the orbital elements of the osculating ellipse and for the angles characterizing the spin orientations with respect to the osculating orbit. We also prove that (i) the relative angle of the spins stays constant for equal mass black holes, irrespective of their orientation, and (ii) the special configuration of equal mass black holes with equal, but anti-aligned spins, both laying in the plane of motion (leading to the largest recoil so far) is preserved during the inspiral at 2PN level of accuracy, with leading order spin-orbit, spin-spin and mass quadrupolar contributions included.
The multiplicity distributions produced by the variation of time-dependent gravitational fields in a conformally flat background geometry are computed with particular attention to the dynamical symmetries stemming from the simultaneous conservation of the charge and of the comoving three-momentum. From the analysis of the scaling properties for large average multiplicities it is argued that the obtained gravitational distributions belong to the same class of infinitely divisible distributions found, for fixed centre of mass energies and symmetric (pseudo)rapidity intervals, in charged multiplicities produced in proton-proton, proton-antiproton and in heavy ion collisions. Different classes of multiplicity distributions can be unified in a common expression by using the (positive) discrete representations of the SU(1,1) group. Second-order interference effects are exploited, in full analogy with quantum optics, for interpreting the excess of correlations in comparison with the Poisson case. It is suggested that second-order cross correlations between positively and negatively charged distributions may represent a relevant diagnostic for a closer scrutiny of the multiparticle final state.
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Noticeable deviations from the prediction of the fiducial LCDM cosmology are found in the angular power spectrum of the CMB. Besides large-angle anomalies, the WMAP 1st year data revealed a dip in the power spectrum at l \sim 200, which seemed to disappear in the 3rd year and subsequent angular power spectra. Using the WMAP 1st, 3rd, and 5th year data release, we study the intensity and spatial distribution of this feature in order to unveil its origin and its implications for the cosmological parameters. We show that in all WMAP data releases there is a substantial suppression of the first Doppler peak in a region near the north ecliptic pole.
Much of the progress in our understanding of dynamo mechanisms has been made within the theoretical framework of magnetohydrodynamics (MHD). However, for sufficiently diffuse media, the Hall effect eventually becomes non-negligible. We present results from three dimensional simulations of the Hall-MHD equations subjected to random non-helical forcing. We study the role of the Hall effect in the dynamo efficiency for different values of the Hall parameter, using a pseudospectral code to achieve exponentially fast convergence. We also study energy transfer rates among spatial scales to determine the relative importance of the various nonlinear effects in the dynamo process and in the energy cascade. The Hall effect produces a reduction of the direct energy cascade at scales larger than the Hall scale, and therefore leads to smaller energy dissipation rates. Finally, we present results stemming from simulations at large magnetic Prandtl numbers, which is the relevant regime in hot and diffuse media such a the interstellar medium.
Dwarf and low surface brightness galaxies are ideal objects to test modified Newtonian dynamics (MOND), because in most of these galaxies the accelerations fall below the threshold below where MOND supposedly applies. We have selected from the literature a sample of 27 dwarf and low surface brightness galaxies. MOND is successful in explaining the general shape of the observed rotation curves for roughly three quarters of the galaxies in the sample presented here. However, for the remaining quarter, MOND does not adequately explain the observed rotation curves. Considering the uncertainties in distances and inclinations for the galaxies in our sample, a small fraction of poor MOND predictions is expected and is not necessarily a problem for MOND. We have also made fits taking the MOND acceleration constant, a_0, as a free parameter in order to identify any systematic trends. We find that there appears to be a correlation between central surface brightness and the best-fit value of a_0, in the sense that lower surface brightness galaxies tend to have lower a_0. However, this correlation depends strongly on a small number of galaxies whose rotation curves might be uncertain due to either bars or warps. Without these galaxies, there is less evidence of a trend, but the average value we find for a_0 ~ 0.7*10^-8 cm s^-2 is somewhat lower than derived from previous studies. Such lower fitted values of a_0 could occur if external gravitational fields are important.
By combining Herschel-SPIRE data with archival Spitzer, HI, and CO maps, we investigate the spatial distribution of gas and dust in the two famous grand-design spirals M99 and M100 in the Virgo cluster. Thanks to the unique resolution and sensitivity of the Herschel-SPIRE photometer, we are for the first time able to measure the distribution and extent of cool, submillimetre (submm)-emitting dust inside and beyond the optical radius. We compare this with the radial variation in both the gas mass and the metallicity. Although we adopt a model-independent, phenomenological approach, our analysis provides important insights. We find the dust extending to at least the optical radius of the galaxy and showing breaks in its radial profiles at similar positions as the stellar distribution. The colour indices f350/f500 and f250/f350 decrease radially consistent with the temperature decreasing with radius. We also find evidence of an increasing gas to dust ratio with radius in the outer regions of both galaxies.
The redshift range from 2.2 to 3, is known as the 'redshift desert' of quasars because quasars with redshift in this range have similar optical colors as normal stars and are thus difficult to be found in optical sky surveys. A quasar candidate, SDSS J085543.40-001517.7, which was selected by a recently proposed criterion involving near-IR $Y-K$ and optical $g-z$ colors, was identified spectroscopically as a new quasar with redshift of 2.427 by the LAMOST commissioning observation in December 2009 and confirmed by the observation made with the NAOC/Xinglong 2.16m telescope in March 2010. This quasar was not targeted in the SDSS spectroscopic survey because it locates in the stellar locus of the optical color-color diagrams, while it is clearly separated from stars in the $Y-K$ vs. $g-z$ diagram. Comparing with other SDSS quasars we found this new quasar with $i$ magnitude of 16.44 is apparently the brightest one in the redshift range from 2.3 to 2.7. From the spectral properties we derived its central black hole mass as $(1.4\sim3.9) \times 10^{10} M_\odot$ and the bolometric luminosity as $3.7\times 10^{48}$ \ergs, which indicates that this new quasar is intrinsically very bright and belongs to the most luminous quasars in the universe. Our identification supports that quasars in the redshift desert can be found by the quasar selection criterion involving the near-IR colors. More missing quasars are expected to be recovered by the future LAMOST spectroscopic surveys, which is important to the study of the cosmological evolution of quasars at redshift higher than 2.2.
In this paper, the cosmological dynamics of Brans-Dicke theory in which there are fermions with a coupling to BD scalar field as well as a self-interaction potential is investigated. The conditions that there exists a solution which is stable and represents a late-time accelerated expansion of the universe are found. The variable mass of fermions can not vanish exactly during the evolution of the universe once it exists initially. It is shown that the late-time acceleration depends completely on the self-interaction of the fermionic field if our investigation is restricted to the theory with positive BD parameter $\omega$. Provided a negative $\omega$ is allowed, there will be another two class of stable solutions describing late-time accelerated expansion of the universe.
Comprehensive VLBI and multi-waveband monitoring indicate that a single superluminal knot can cause a number of gamma-ray flares at different locations. However, the often very rapid variability timescale is a challenge to theoretical models when a given flare (perhaps the majority of those observed) is inferred from observations to lie near the 43 GHz core, parsecs from the central engine. We present some relevant observational results, using the BL Lac object AO 0235+164 as an example. We propose a turbulent cell model leading to a frequency-dependent filling factor of the emission region. This feature of the model can provide a solution to the timescale dilemma and other characteristics of blazar emission.
We present skeleton studies of non-Gaussianity in the CMB temperature
anisotropy observed in the WMAP5 data. The local skeleton is traced on the 2D
sphere by cubic spline interpolation which leads to more accurate estimation of
the intersection positions between the skeleton and the secondary pixels than
conventional linear interpolation. We demonstrate that the skeleton-based
estimator of non-Gaussianity of the local type (f_NL) - the departure of the
length distribution from the corresponding Gaussian expectation - yields an
unbiased and sufficiently converged f_NL-likelihood.
We analyse the skeleton statistics in the WMAP5 combined V- and W-band data
outside the Galactic base-mask determined from the KQ75 sky-coverage. The
results are consistent with Gaussian simulations of the the best-fitting
cosmological model, but deviate from the previous results determined using the
WMAP1 data. We show that it is unlikely that the improved skeleton tracing
method, the omission of Q-band data, the modification of the
foreground-template fitting method or the absence of 6 extended regions in the
new mask contribute to such a deviation. However, the application of the Kp0
base-mask in data processing does improve the consistency with the WMAP1
results.
The f_NL-likelihoods of the data are estimated at 9 different smoothing
levels. It is unexpected that the best-fit values show positive correlation
with the smoothing scales. Further investigation argues against a point-source
or goodness-of-fit explanation but finds that about 30% of either Gaussian or
f_NL samples having better goodness-of-fit than the WMAP5 show a similar
correlation. We present the estimate f_NL=47.3+/-34.9 (1sigma error) determined
from the first four smoothing angles and f_NL=76.8+/-43.1 for the combination
of all nine. The former result may be overestimated at the 0.21sigma-level
because of point sources.
We present the second report of our systematic search for strongly lensed quasars from the data of the Sloan Digital Sky Survey (SDSS). From extensive follow-up observations of 136 candidate objects, we find 36 lenses in the full sample of 77,429 spectroscopically confirmed quasars in the SDSS Data Release 5. We then define a complete sample of 19 lenses, including 11 from our previous search in the SDSS Data Release 3, from the sample of 36,287 quasars with i<19.1 in the redshift range 0.6<z<2.2, where we require the lenses to have image separations of 1"<\theta<20" and i-band magnitude differences between the two images smaller than 1.25 mag. Among the 19 lensed quasars, 3 have quadruple-image configurations, while the remaining 16 show double images. This lens sample constrains the cosmological constant to be \Omega_\Lambda=0.84^{+0.06}_{-0.08}(stat.)^{+0.09}_{-0.07}(syst.) assuming a flat universe, which is in good agreement with other cosmological observations. We also report the discoveries of 7 binary quasars with separations ranging from 1.1" to 16.6", which are identified in the course of our lens survey. This study concludes the construction of our statistical lens sample in the full SDSS-I data set.
We investigate the virialization of cosmic structures in the framework of flat FLRW cosmological models, in which the vacuum energy density evolves with time. In particular, our analysis focuses on the study of spherical matter perturbations, as the latter decouple from the background expansion and start to "turn around" and finally collapse. We generalize the spherical collapse model in the case when the vacuum energy is a running quantity of the Hubble rate, $\Lambda=\Lambda(H)$. A particularly well motivated model of this type is the so-called quantum field vacuum, in which $\Lambda(H)$ is a quadratic function, $\Lambda(H)=n_0+n_2\,H^2$, with $n_0\neq 0$. This model has been previously studied by our team using the latest high quality cosmological data to constraint its free parameters, as well as the predicted cluster formation rate. It turns out that the corresponding Hubble expansion history resembles that of the traditional $\Lambda$CDM cosmology. We use this $\Lambda(t)$CDM framework to illustrate the fact that the properties of the spherical collapse model (virial density, collapse factor, etc.) depend on the choice of the considered vacuum energy (homogeneous or clustered). In particular, if the distribution of the vacuum energy is clustered, then, under specific conditions, we can produce more concentrated structures with respect to the homogeneous vacuum energy case.
The fundamental plane of early-type galaxies is a rather tight three-parameter correlation discovered more than twenty years ago. It has resisted a both global and precise physical interpretation despite a consequent number of works, observational, theoretical or using numerical simulations. It appears that its precise properties depend on the population of galaxies in study. Instead of selecting a priori these populations, we propose to objectively construct homologous populations from multivariate analyses. We have undertaken multivariate cluster and cladistic analyses of a sample of 56 low-redshift galaxy clusters containing 699 early-type galaxies, using four parameters: effective radius, velocity dispersion, surface brightness averaged over effective radius, and Mg2 index. All our analyses are consistent with seven groups that define separate regions on the global fundamental plane, not across its thickness. In fact, each group shows its own fundamental plane, which is more loosely defined for less diversified groups. We conclude that the global fundamental plane is not a bent surface, but made of a collection of several groups characterizing several fundamental planes with different thicknesses and orientations in the parameter space. Our diversification scenario probably indicates that the level of diversity is linked to the number and the nature of transforming events and that the fundamental plane is the result of several transforming events. We also show that our classification, not the fundamental planes, is universal within our redshift range (0.007 - 0.053). We find that the three groups with the thinnest fundamental planes presumably formed through dissipative (wet) mergers. In one of them, this(ese) merger(s) must have been quite ancient because of the relatively low metallicity of its galaxies, Two of these groups have subsequently undergone dry mergers to increase their masses. In the k-space, the third one clearly occupies the region where bulges (of lenticular or spiral galaxies) lie and might also have formed through minor mergers and accretions. The two least diversified groups probably did not form by major mergers and must have been strongly affected by interactions, some of the gas in the objects of one of these groups having possibly been swept out. The interpretation, based on specific assembly histories of galaxies of our seven groups, shows that they are truly homologous. They were obtained directly from several observables, thus independently of any a priori classification. The diversification scenario relating these groups does not depend on models or numerical simulations, but is objectively provided by the cladistic analysis. Consequently, our classification is more easily compared to models and numerical simulations, and our work can be readily repeated with additional observables.
We use deep observations taken with the Photodetector Array Camera and Spectrometer (PACS), on board the Herschel satellite as part of the PACS evolutionary probe (PEP) guaranteed project along with submm ground-based observations to measure the dust mass of a sample of high-z submillimeter galaxies (SMGs). We investigate their dust content relative to their stellar and gas masses, and compare them with local star-forming galaxies. High-z SMGs are dust rich, i.e. they have higher dust-to-stellar mass ratios compared to local spiral galaxies (by a factor of 30) and also compared to local ultraluminous infrared galaxies (ULIRGs, by a factor of 6). This indicates that the large masses of gas typically hosted in SMGs have already been highly enriched with metals and dust. Indeed, for those SMGs whose gas mass is measured, we infer dust-to-gas ratios similar or higher than local spirals and ULIRGs. However, similarly to other strongly star-forming galaxies in the local Universe and at high-z, SMGs are characterized by gas metalicities lower (by a factor of a few) than local spirals, as inferred from their optical nebular lines, which are generally ascribed to infall of metal-poor gas. This is in contrast with the large dust content inferred from the far-IR and submm data. In short, the metalicity inferred from the dust mass is much higher (by more than an order of magnitude) than that inferred from the optical nebular lines. We discuss the possible explanations of this discrepancy and the possible implications for the investigation of the metalicity evolution at high-z.
We use a recent sample of 49 galaxies to show that there is a proportionality relation between the black hole mass M_BH and the quantity \mu =M_G*\sigma /c, where M_G is mass of the spheroidal stellar component and \sigma is the stellar velocity dispersion. \mu is called the momentum parameter and the ratio is M_BH/\mu ~3.3. This result is applied to the penetrating-jet feedback model which argues that the correlation that holds is with a momentum-like parameter, although this feedback mechanism is based on energy balance.
We study the effect of dark matter (DM) particles in the Sun, focusing in particular on the possible reduction of the solar neutrinos flux due to the energy carried away by DM particles from the innermost regions of the Sun, and to the consequent reduction of the temperature of the solar core. We find that in the very low-mass range between 4 and 10 GeV, recently advocated to explain the findings of the DAMA and CoGent experiments, the effects on neutrino fluxes are detectable only for DM models with very small, or vanishing, self-annihilation cross section, such as the so-called asymmetric DM models, and we study the combination of DM masses and Spin Dependent cross sections which can be excluded with current solar neutrino data. Finally, we revisit the recent claim that DM models with large self-interacting cross sections can lead to a modification of the position of the convective zone, alleviating or solving the solar composition problem. We show that when the `geometric' upper limit on the capture rate is correctly taken into account, the effects of DM are reduced by orders of magnitude, and the position of the convective zone remains unchanged.
A simple set of diagrammatic rules is formulated for perturbative evaluation of ``in-in" correlators, as is needed in cosmology and other nonequilibrium problems. These rules are both intuitive, and efficient for calculational purposes.
The annihilation cross section of thermal relic dark matter determines both its relic density and indirect detection signals. We determine how large indirect signals may be in scenarios with Sommerfeld-enhanced annihilation, subject to the constraint that the dark matter has the correct relic density. This work refines our previous analysis through detailed treatments of resonant Sommerfeld enhancement and the effect of Sommerfeld enhancement on freeze out. Sommerfeld enhancements raise many interesting issues in the freeze out calculation, and we find that the cutoff of resonant enhancement, force-carrier production and decay rates, the temperature of kinetic decoupling, and the efficiency of self-interactions for preserving thermal velocity distributions all play a role. These effects may have striking consequences; for example, for resonantly-enhanced Sommerfeld annihilation, dark matter freezes out but may then chemically recouple, implying highly suppressed indirect signals, in contrast to naive expectations. In the minimal scenario with standard astrophysical assumptions, and tuning all parameters to maximize the signal, we find that, for force-carrier mass m_\phi = 250 MeV and dark matter masses m_X = 0.1, 0.3, and 1 TeV, the maximal Sommerfeld enhancement factors are S_eff = 7, 30, and 90, respectively. Such boosts are too small to explain both the PAMELA and Fermi excesses. Non-minimal models may require smaller boosts, but the bounds on S_eff could also be more stringent, and dedicated freeze out analyses are required. We consider deviations from standard astrophysical assumptions and non-minimal particle physics models, and we outline the steps required to determine if such considerations may lead to a self-consistent explanation of the PAMELA or Fermi excesses.
The XENON100 and CRESST experiments will directly test the inelastic dark matter explanation for DAMA's 8.9 sigma anomaly. This article discusses how predictions for direct detection experiments depend on uncertainties in quenching factor measurements, the dark matter interaction with the Standard Model and the halo velocity distribution. When these uncertainties are accounted for, an order of magnitude variation is found in the number of expected events at CRESST and XENON100.
We analyze the most salient cosmological features of axions in extensions of the Standard Model with a gauged anomalous extra U(1) symmetry. The model is built by imposing the constraint of gauge invariance in the anomalous effective action, which is extended with Wess-Zumino counterterms. These generate axion-like interactions of the axions to the gauge fields and a gauged shift symmetry. The scalar sector is assumed to acquire a non-perturbative potential after inflation, at the electroweak phase transition, which induces a mixing of the Stuckelberg field of the model with the scalars of the electroweak sector, and at the QCD phase transition. We discuss the possible mechanisms of sequential misalignments which could affect the axions of these models, and generated, in this case, at both transitions. We compute the contribution of these particles to dark matter, quantifying their relic densities as a function of the Stuckelberg mass. We also show that models with a single anomalous U(1) in general do not account for the dark energy, due to the presence of mixed U(1)-SU(3) anomalies.
A new fully quantum method describing penetration of packet from internal well outside with its tunneling through the barrier of arbitrary shape used in problems of quantum cosmology, is presented. The method allows to determine amplitudes of wave function, penetrability $T_{\rm bar}$ and reflection $R_{\rm bar}$ relatively the barrier (accuracy of the method: $|T_{\rm bar}+R_{\rm bar}-1| < 1 \cdot 10^{-15}$), coefficient of penetration (i.e. probability of the packet to penetrate from the internal well outside with its tunneling), coefficient of oscillations (describing oscillating behavior of the packet inside the internal well). Using the method, evolution of universe in the closed Friedmann--Robertson--Walker model with quantization in presence of positive cosmological constant, radiation and component of generalize Chaplygin gas is studied. It is established (for the first time): (1) oscillating dependence of the penetrability on localization of start of the packet; (2) presence of resonant values of energy of radiation $E_{\rm rad}$, at which the coefficient of penetration increases strongly. From analysis of these results it follows: (1) necessity to introduce initial condition into both non-stationary, and stationary quantum models; (2) presence of some definite values for the scale factor $a$, where start of expansion of universe is the most probable; (3) during expansion of universe in the initial stage its radius is changed not continuously, but passes consequently through definite discrete values and tends to continuous spectrum in latter time.
The PICASSO project is using superheated droplets of C$_4$F$_{10}$ for the direct detection of Dark Matter candidates in the {\it spin-dependent} (SD) sector. The total setup includes 32 detectors installed in the SNOLAB underground laboratory in Sudbury (Ontario, Canada). With a concentrated effort in detector purification and with new discrimination tools now available for analysis, Picasso published competitive results in June 2009 \cite{publi2009} and became the leading experiment in the SD sector of direct dark matter searches. The present level of sensitivity is at 0.16 pb on protons at 90% C.L. (M$_W$= 24GeV/c$^2$) following an analysis of two detectors only. The rest of the detectors are now in the process of being analyzed and the experimental search continues in order to further improve the limits or hopefully discover a signal of dark matter. The status of the experiment and the ongoing analysis will be presented.
This short review is addressed to cosmologists.
General relativity predicts that space-time comes to an end and physics comes
to a halt at the big-bang. Recent developments in loop quantum cosmology have
shown that these predictions cannot be trusted. Quantum geometry effects can
resolve singularities, thereby opening new vistas. Examples are: The big bang
is replaced by a quantum bounce; the `horizon problem' disappears; immediately
after the big bounce, there is a super-inflationary phase with its own
phenomenological ramifications; and, in presence of a standard inflaton
potential, initial conditions are naturally set for a long, slow roll inflation
independently of what happens in the pre-big bang branch.
We develop a model of string dynamics with back-reaction from both scaling and non-scaling loops taken into account. The evolution of a string network is described by the distribution functions of coherence segments and kinks. We derive two non-linear equations which govern the evolution of the two distributions and solve them analytically in the limit of late times. We also show that the correlation function is an exponential, and solve the dynamics for the corresponding spectrum of scaling loops.
Using effective field theory (EFT) techniques we calculate the next-to-leading order (NLO) spin-orbit contributions to the gravitational potential of inspiralling compact binaries. We use the covariant spin supplementarity condition (SSC), and explicitly prove the equivalence with previous results by Faye et al. in arXiv:gr-qc/0605139. We also show that the direct application of the Newton-Wigner SSC at the level of the action leads to the correct dynamics using a canonical (Dirac) algebra. This paper then completes the calculation of the necessary spin dynamics within the EFT formalism that will be used in a separate paper to compute the spin contributions to the energy flux and phase evolution to NLO.
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We discuss the merger rate, close galaxy environment, and clustering on scales up to a Mpc of the SWIFT BAT hard X-ray sample of nearby (z<0.05), moderate-luminosity active galactic nuclei (AGN). We find a higher incidence of galaxies with signs of disruption compared to a matched control sample (18% versus 1%) and of close pairs within 30 kpc (24% versus 1%). We also find a larger fraction with companions compared to normal galaxies and optical emission line selected AGN at scales up to 250 kpc. We hypothesize that these merging AGN may not be identified using optical emission line diagnostics because of optical extinction and dilution by star formation. In support of this hypothesis, in merging systems we find a higher hard X-ray to [OIII] flux ratio, as well as emission line diagnostics characteristic of composite or star-forming galaxies, and a larger IRAS 60 um to stellar mass ratio.
We use the semi-analytic model GalICS to predict the Tully-Fisher relation in the B, I and for the first time, in the K band, and its evolution with redshift, up to z \sim 1. We refined the determination of the disk galaxies rotation velocity, with a dynamical recipe for the rotation curve, rather than a simple conversion from the total mass to maximum velocity. The new recipe takes into account the disk shape factor, and the angular momentum transfer occurring during secular evolution leading to the formation of bulges. This produces model rotation velocities that are lower by \sim 40-50 km/s in case of Milky Way-like objects, up to ~50-60 km/s at the high-mass end, and up to ~20-30 km/s for the majority of the spirals, amounting to an average effect of ~20-25 %. We implemented stellar population models with a complete treatment of the TP-AGB branch, which leads to a revision of the mass-to-light ratio in the near-IR. Due to this effect, K band luminosities increase by \sim 0.5 mags at redshift z=0 and by ~1 mags at z=3, while in the I band at the same redshifts the increase amounts to \sim 0.3 and \sim 0.5 mags. With these two new recipes in place, the comparison between the predicted Tully-Fisher relation with a series of datasets in the optical and near-IR, at redshifts between 0 and 1, is used as a diagnostics of the assembly and evolution of spiral galaxies in the model. The new model shows a net improvement over its original version of 2003. However, the z=0 predicted Tully-Fisher is too bright in all bands, although the model is able to reproduce the morphological differentiation observed in the K band. At z>0.4 the match between the model and data improves dramatically. We argue that this behavior is caused by inadequate star formation histories in the model galaxies at low redshifts. The SFR declines too slowly, due to continuous gas infall that is not efficiently suppressed.
We study the role of submillimetre galaxies (SMGs) in the galaxy formation process in the Lambda Cold Dark Matter cosmology. We use the Baugh et al. (2005) semi-analytical model, which matches the observed SMG number counts and redshift distribution by assuming a top-heavy initial mass function (IMF) in bursts triggered by galaxy mergers. We build galaxy merger trees and follow the evolution and properties of SMGs and their descendants. Our primary sample of model SMGs consists of galaxies which had 850 mu fluxes brighter than 5 mJy at some redshift z>1. Our model predicts that the present-day descendants of such SMGs cover a wide range of stellar masses ~ 10^{10} - 10^{12} Msun/h, with a median ~ 10^{11} Msun/h, and that more than 70% of these descendants are bulge-dominated. More than 50% of present day galaxies with stellar masses larger than 7 x 10^{11} Msun/h are predicted to be descendants of such SMGs. We find that although SMGs make an important contribution to the total star formation rate at z~2, the final stellar mass produced in the submillimetre phase contributes only 0.2% of the total present-day stellar mass, and 2% of the stellar mass of SMG descendants, in stark contrast to the popular picture in which the SMG phase marks the production of the bulk of the mass of present day massive ellipticals.
We present a new study of the stellar mass in a sample of ~ 70 submillimeter-selected galaxies (SMGs) with accurate spectroscopic redshifts. We fit combinations of stellar population synthesis models and power laws to the galaxies' observed-frame optical through mid-IR spectral energy distributions to separate stellar emission from non-stellar near-IR continuum. By separating the stellar emission from the non-stellar near-IR continuum, we find that ~ 50% of our sample have non-stellar continuum contributions of less than 10% in rest-frame H-band, but ~ 10% of our sample have non-stellar contributions greater than 50%. We find that the K-band luminosity of the non-stellar continuum emission is correlated with hard X-ray luminosity, indicating an AGN origin of the emission. Upon subtracting this AGN-contributed continuum component from all of the galaxies in our sample, we determine a lower median stellar mass for SMGs than previous studies, ~ 7 x 10^10 M_sun. Our new stellar mass estimates suggest that X-ray detected SMGs fall closer to the local relation between bulge mass and central black hole mass than indicated by previous studies. We combine our new stellar mass estimates with molecular gas mass estimates from observation of CO rotational emission lines to examine the evolutionary status of SMGs, and use constraints of the starburst time-scale from molecular gas studies to estimate the amount of fading our sample would undergo if they passively evolve after the starburst terminates. The results suggest that typical SMGs, while among the most massive galaxies at z ~ 2, are likely to produce descendants of similar mass and luminosity to L* galaxies in the local universe.
The collisionless accretion shock at the outer boundary of a galaxy cluster should primarily heat the ions instead of electrons since they carry most of the kinetic energy of the infalling gas. Near the accretion shock, the density of the intracluster medium is very low and the Coulomb collisional timescale is longer than the accretion timescale. Electrons and ions may not achieve equipartition in these regions. Numerical simulations have shown that the Sunyaev-Zel'dovich observables (e.g., the integrated Comptonization parameter Y) for relaxed clusters can be biased by a few percent. The Y-mass relation can be biased if non-equipartition effects are not properly taken into account. Using a set of hydrodynamical simulations, we have calculated three potential systematic biases in the Y-mass relations introduced by non-equipartition effects during the cross-calibration or self-calibration when using the galaxy cluster abundance technique to constraint cosmological parameters. We then use a semi-analytic technique to estimate the non-equipartition effects on the distribution functions of Y (Y functions) determined from the extended Press-Schechter theory. Depending on the calibration method, we find that non-equipartition effects can induce systematic biases on the Y functions, and the values of the cosmological parameters Omega_8, sigma_8, and the dark energy equation of state parameter w can be biased by a few percent. In particular, non-equipartition effects can introduce an apparent evolution in w of a few percent in all of the systematic cases we considered. Techniques are suggested to take into account the non-equipartition effect empirically when using the cluster abundance technique to study precision cosmology. We conclude that systematic uncertainties in the Y-mass relation of even a few percent can introduce a comparable level of biases in cosmological parameter measurements.
Modified gravity, known as $f(R)$ gravity, has presently been applied to Cosmology as a realistic alternative to dark energy. For this kind of gravity the expansion of the Universe may accelerate while containing only baryonic and cold dark matter. The aim of the present investigation is to place cosmographic constraints on the class of theories of the form $f(R)=R - \alpha/R^n$ within the Palatini approach. Although extensively discussed in recent literature and confronted with several observational data sets, cosmological tests are indeed inconclusive about the true signal of $n$ in this class of theories. This is particularly important to define which kind of corrections (infra-red or high-energy) to general relativity this class of theory indeed represent. We shed some light on this question by examining the evolution of the deceleration parameter $q(z)$ for these theories. We find that for a large range of $\alpha$, models based on $f(R) = R - \alpha/R^{n}$ gravity in the Palatini approach can only have positive values for $n$, placing thus a broad restriction on this class of gravity.
In the last few decades, advances in observational cosmology have given us a standard model of cosmology. We know the content of the universe to within a few percent. With more ambitious experiments on the way, we hope to move beyond the knowledge of what the universe is made of, to why the universe is the way it is. In this review paper we focus on primordial non-Gaussianity as a probe of the physics of the dynamics of the universe at the very earliest moments. We discuss 1) theoretical predictions from inflationary models and their observational consequences in the cosmic microwave background (CMB) anisotropies; 2) CMB--based estimators for constraining primordial non-Gaussianity with an emphasis on bispectrum templates; 3) current constraints on non-Gaussianity and what we can hope to achieve in the near future; and 4) non-primordial sources of non-Gaussianities in the CMB such as bispectrum due to second order effects, three way cross-correlation between primary-lensing-secondary CMB, and possible instrumental effects.
We derive the equations of linear cosmological perturbations for the general Lagrangian density $f (R,\phi, X)/2+L_c$, where $R$ is a Ricci scalar, $\phi$ is a scalar field, and $X=-(\nabla \phi)^2/2$ is a field kinetic energy. We take into account a nonlinear self-interaction term $L_c$ recently studied in the context of "Galileon" cosmology, which keeps the field equations at second order. Taking into account a scalar-field mass explicitly, the equations of matter density perturbations and gravitational potentials are obtained under a quasi-static approximation on sub-horizon scales. We also derive conditions for the avoidance of ghosts and Laplacian instabilities associated with propagation speeds. Our analysis includes most of modified gravity models of dark energy proposed in literature and thus it is convenient to test the viability of such models from both theoretical and observational points of view.
In this paper, we perform a global constraint on the Ricci dark energy model with both the flat case and the non-flat case, using the Markov Chain Monte Carlo (MCMC) method and the combined observational data from the cluster X-ray gas mass fraction, Supernovae of type Ia (397), baryon acoustic oscillations, current Cosmic Microwave Background, and the observational Hubble function. In the flat model, we obtain the best fit values of the parameters in $1\sigma, 2\sigma$ regions: $\Omega_{m0}=0.2927^{+0.0420 +0.0542}_{-0.0323 -0.0388}$, $\alpha=0.3823^{+0.0331 +0.0415}_{-0.0418 -0.0541}$, $Age/Gyr=13.48^{+0.13 +0.17}_{-0.16 -0.21}$, $H_0=69.09^{+2.56 +3.09}_{-2.37 -3.39}$. In the non-flat model, the best fit parameters are found in $1\sigma, 2\sigma$ regions:$\Omega_{m0}=0.3003^{+0.0367 +0.0429}_{-0.0371 -0.0423}$, $\alpha=0.3845^{+0.0386 +0.0521}_{-0.0474 -0.0523}$, $\Omega_k=0.0240^{+0.0109 +0.0133}_{-0.0130 -0.0153}$, $Age/Gyr=12.54^{+0.51 +0.65}_{-0.37 -0.49}$, $H_0=72.89^{+3.31 +3.88}_{-3.05 -3.72}$. Compared to the constraint results in the $\Lambda \textmd{CDM}$ model by using the same datasets, it is shown that the current combined datasets prefer the $\Lambda \textmd{CDM}$ model to the Ricci dark energy model.
The Westerbork Radio Synthesis Telescope, WSRT, has been used to make a deep radio survey of an ~ 1.7 sq degree field coinciding with the AKARI North Ecliptic Pole Deep Field. The observations, data reduction and source count analysis are presented, along with a description of the overall scientific objectives. The survey consisted of 10 pointings, mosaiced with enough overlap to maintain a similar sensitivity across the central region that reached as low as 21 microJy per beam at 1.4 GHz. A catalogue containing 462 sources detected with a resolution of 17"x15" is presented. The differential source counts calculated from the WSRT data have been compared with those from the shallow VLA-NEP survey of Kollgaard et al 1994, and show a pronounced excess for sources fainter than ~ 1 mJy, consistent with the presence of a population of star forming galaxies at sub-mJy flux levels. The AKARI North Ecliptic Pole Deep field is the focus of a major observing campaign conducted across the entire spectral region. The combination of these data sets, along with the deep nature of the radio observations will allow unique studies of a large range of topics including the redshift evolution of the luminosity function of radio sources, the clustering environment of radio galaxies, the nature of obscured radio-loud active galactic nuclei, and the radio/far-infrared correlation for distant galaxies. This catalogue provides the basic data set for a future series of paper dealing with source identifications, morphologies, and the associated properties of the identified radio sources.
We study the growth of the clustering dipole of galaxies from the Two Micron All Sky Survey (2MASS). We find that the dipole does not converge before the completeness limit of the 2MASS Extended Source Catalog, i.e. up to about 300 Mpc/h. We compare the observed growth of the dipole with the theoretically expected, conditional growth for the LambdaCDM power spectrum and cosmological parameters constrained by WMAP. The observed growth turns out to be within 1-sigma confidence level of the theoretical one, once the proper observational window of the 2MASS flux dipole is included. For a contrast, if the adopted window is a top hat, then the predicted dipole grows significantly faster and converges to its final value at a distance of about 200 Mpc/h. We study the difference between the top-hat window and the window for the flux-limited 2MASS survey and we conclude that the growth of the 2MASS dipole at effective distances greater than 200 Mpc/h is only apparent. Eventually, since for the window function of 2MASS the predicted growth is consistent with the observed one, we can compare the two to evaluate beta = (Omega_m)^0.55 / b. The result is beta = 0.38+-0.05, which gives a rough estimate of Omega_m = 0.2+-0.1.
We show that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordial fluctuations. Moreover, our model suggests that inflation lasted for an extremely long period thereby favouring a self-reproducing inflationary model. Dark energy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale.
The detection of ionized bubbles around quasars in redshifted 21-cm maps is possibly one of the most direct future probes of reionization. We consider two models for the growth of spherical ionized bubbles to study the apparent shapes of the bubbles in redshifted 21-cm maps, taking into account the finite light travel time (FLTT) across the bubble. We find that the FLTT, whose effect is particularly pronounced for large bubbles, causes the bubble's image to continue to grow well after it's actual growth is over. There are two distinct FLTT distortions in the bubble's image: (i) its apparent center is shifted along the line of sight (LOS) towards the observer from the quasar; (ii) it's shape is anisotropic along the LOS. The bubble initially appears elongated along the LOS. This is reversed in the later stages of growth where the bubble appears compressed. The FLTT distortions are expected to have an impact on matched filter bubble detection where it is most convenient to use a spherical template for the filter. We find that the best matched spherical filter gives a reasonably good estimate of the size and the shift in the center of the anisotropic image. The mismatch between the spherical filter and the anisotropic image causes a 10 - 20% degradation in the SNR relative to that of a spherical bubble. We conclude that a spherical filter is adequate for bubble detection. The FLTT distortions do not effect the lower limits for bubble detection with 1000 hr of GMRT observations. The smallest spherical filter for which a detection is possible has comoving radii 24 Mpc and 33 Mpc for a 3-sigma and 5-sigma detection respectively, assuming a neutral fraction 0.6 at z \sim 8.
We consider the luminosity and environmental dependence of structural parameters of lenticular galaxies in the near-infrared K band. Using a two-dimensional galaxy image decomposition technique, we extract bulge and disk structural parameters for a sample of 36 lenticular galaxies observed by us in the K band. By combining data from the literature for field and cluster lenticulars with our data, we study correlations between parameters that characterise the bulge and the disk as a function of luminosity and environment. We find that scaling relations such as the Kormendy relation, photometric plane and other correlations involving bulge and disk parameters show a luminosity dependence. This dependence can be explained in terms of galaxy formation models in which faint lenticulars (M_T > -24.5) formed via secular formation processes that likely formed the pseudobulges of late-type disk galaxies, while brighter lenticulars (M_T < -24.5) formed through a different formation mechanism most likely involving major mergers. On probing variations in lenticular properties as a function of environment, we find that faint cluster lenticulars show systematic differences with respect to faint field lenticulars. These differences support the idea that the bulge and disk components fade after the galaxy falls into a cluster, while simultaneously undergoing a transformation from spiral to lenticular morphologies.
Our universe may have formed via bubble nucleation in an eternally-inflating background. Furthermore, the background may have a compact dimension--the modulus of which tunnels out of a metastable minimum during bubble nucleation--which subsequently grows to become one of our three large spatial dimensions. Then the reduced symmetry of the background is equivalent to anisotropic initial conditions in our bubble universe. We compute the inflationary spectrum in such a scenario and, as a first step toward understanding the effects of anisotropy, project it onto spherical harmonics. The resulting spectrum exhibits anomalous multipole correlations, their relative amplitude set by the present curvature parameter, which extend to arbitrarily large multipole moments. This raises the possibility of future detection, if slow-roll inflation does not last too long within our bubble. A full understanding of the observational signal must account for the effects of background anisotropy on photon free streaming, and is left to future work.
In this paper we construct four Kerr-like spacetimes starting from the loop black hole Schwarzschild solutions (LBH) and applying the Newman-Janis transformation. In previous papers the Schwarzschild LBH was obtained replacing the Ashtekar connection with holonomies on a particular graph in a minisuperspace approximation which describes the black hole interior. Starting from this solution, we use a Newman-Janis transformation and we specialize to two different and natural complexifications inspired from the complexifications of the Schwarzschild and Reissner-Nordstrom metrics. We show explicitly that the space-times obtained in this way are singularity free and thus there are no naked singularities. We show that the transformation move, if any, the causality violating regions of the Kerr metric far from r=0. We study the space-time structure with particular attention to the horizons shape. We conclude the paper with a discussion on a regular Reissner-Nordstrom black hole derived from the Schwarzschild LBH and then applying again the Newmann-Janis transformation.
Aims. Recent ATCA, XMM-Newton and MCELS observations of the Magellanic Clouds
(MCs) cover a number of new and known SNRs which are poorly studied, such as
SNR J0528-6714 . This particular SNR exhibits luminous radio-continuum
emission, but is one of the unusual and rare cases without detectable optical
and very faint X-ray emission (initially detected by ROSAT and listed as object
[HP99] 498). We used new multi-frequency radio-continuum surveys and new
optical observations at H{\alpha}, [S ii] and [O iii] wavelengths, in
combination with XMM-Newton X-ray data, to investigate the SNR properties and
to search for a physical explanation for the unusual appearance of this SNR.
Methods. We analysed the X-ray and Radio-Continuum spectra and present
multi-wavelength morphological studies of this SNR.
Results. We present the results of new moderate resolution ATCA observations
of SNR J0528-6714. We found that this object is a typical older SNR with a
radio spectral index of {\alpha}=-0.36 \pm 0.09 and a diameter of D=52.4 \pm
1.0 pc. Regions of moderate and somewhat irregular polarisation were detected
which are also indicative of an older SNR. Using a non-equilibrium ionisation
collisional plasma model to describe the X-ray spectrum, we find temperatures
kT of 0.26 keV for the remnant. The low temperature, low surface brightness,
and large extent of the remnant all indicate a relatively advanced age. The
near circular morphology indicates a Type Ia event.
Conclusions. Our study revealed one of the most unusual cases of SNRs in the
Local Group of galaxies - a luminous radio SNR without optical counterpart and,
at the same time, very faint X-ray emission. While it is not unusual to not
detect an SNR in the optical, the combination of faint X-ray and no optical
detection makes this SNR very unique.
The equivalence between metric and Palatini formalisms in f(R)-gravity can be achieved in the general context of theories with divergence free current. This equivalence is a necessary result of a symmetry which is included in a particular conservation equation of the current. In fact the conservation equation, by an appropriate redefinition of the introduced auxiliary field, may be encoded in a massless scalar field equation.
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Some of the first stars could be cooler and more massive than standard stellar models would suggest, due to the effects of dark matter annihilation in their cores. It has recently been argued that such objects may attain masses in the 10^4--10^7 solar mass range, and that such supermassive dark stars should be within reach of the upcoming James Webb Space Telescope. Notwithstanding theoretical difficulties with this proposal, we argue here that some of these objects should also be readily detectable with both the Hubble Space Telescope and ground-based 8--10 m class telescopes. Existing survey data already place strong constraints 10^7 solar mass dark stars at z~10. We show that such objects must be exceedingly rare or short-lived to have avoided detection.
We show that the black hole-bulge mass scaling relations observed from the local to the high-z Universe can be largely or even entirely explained by a non-causal origin, i.e. they do not imply the need for any physically coupled growth of black hole and bulge mass, for example through feedback by active galactic nuclei (AGN). The creation of the scaling relations can be fully explained by the hierarchical assembly of black hole and stellar mass through galaxy merging, from an initially uncorrelated distribution of BH and stellar masses in the early Universe. We show this with a suite of dark matter halo merger trees for which we make assumptions about (uncorrelated) black hole and stellar mass values at early cosmic times. We then follow the halos in the presence of global star formation and black hole accretion recipes that (i) work without any coupling of the two properties per individual galaxy and (ii) correctly reproduce the observed star formation and black hole accretion rate density in the Universe. With disk-to-bulge conversion in mergers included, our simulations even create the observed slope of ~1.1 for the M_BH-M_bulge-relation at z=0. This also implies that AGN feedback is not a required (though still a possible) ingredient in galaxy evolution. In light of this, other mechanisms that can be invoked to truncate star formation in massive galaxies are equally justified.
We present here the effective theory of inflation `a la Ginsburg-Landau in which the inflaton potential is a polynomial. The slow-roll expansion becomes a systematic 1/N expansion where N ~ 60. The spectral index and the ratio of tensor/scalar fluctuations are n_s - 1 = O(1/N), r = O(1/N) while the running turns to be d n_s/d \ln k = O(1/N^2) and can be neglected. The energy scale of inflation M ~ 0.7 10^{16} GeV is completely determined by the amplitude of the scalar adiabatic fluctuations. A complete analytic study plus the Monte Carlo Markov Chains (MCMC) analysis of the available CMB+LSS data showed: (a) the spontaneous breaking of the phi -> - phi symmetry of the inflaton potential. (b) a lower bound for r: r > 0.023 (95% CL) and r > 0.046 (68% CL). (c) The preferred inflation potential is a double well, even function of the field with a moderate quartic coupling yielding as most probable values: n_s = 0.964, r = 0.051. This value for r is within reach of forthcoming CMB observations. We investigate the DM properties using cosmological theory and the galaxy observations. Our DM analysis is independent of the particle physics model for DM and it is based on the DM phase-space density rho_{DM}/sigma^3_{DM}. We derive explicit formulas for the DM particle mass m and for the number of ultrarelativistic degrees of freedom g_d (hence the temperature) at decoupling. We find that m turns to be at the keV scale. The keV scale DM is non-relativistic during structure formation, reproduces the small and large scale structure but it cannot be responsible of the e^+ and pbar excess in cosmic rays which can be explained by astrophysical mechanisms (Abridged).
We present a simple estimate of the mass 'deficits' in cored spheroids, as a function of galaxy mass and radius within the galaxy. Previous attempts to measure such deficits depended on fitting some functional form to the profile at large radii and extrapolating inwards; this is sensitive to the assumed functional form and does not allow for variation in nuclear profile shapes. We take advantage of larger data sets to directly construct stellar mass profiles of observed systems and measure the stellar mass enclosed in a series of physical radii (M(<R)), for samples of cusp and core spheroids at the same stellar mass. There is a significant bimodality in this distribution at small radii, and we non-parametrically measure the median offset between core and cusp populations (the deficit Delta_M(<R)). We construct the scoured mass profile as a function of radius, without reference to any assumed functional form. The mass deficit rises in power-law fashion (Delta_M(<R) R^{1.3-1.8}) from a significant but small mass at R<10pc, to asymptote to a maximum ~0.5-2 M_BH at ~100pc. At larger radii there is no statistically significant separation between populations; the upper limit to the cumulative scoured mass at ~kpc is ~2-4 M_BH. This does not depend strongly on stellar mass. The dispersion in M(<R) appears larger in the core population, possibly reflecting the fact that scouring increases the scatter in profile shapes. These results are in good agreement with models of scouring from BH binary systems.
Cosmological simulations indicate that cold dark matter (CDM) halos should be triaxial. Verifying observationally this theoretical prediction is, however, less than straightforward because the assembly of galaxies is expected to modify the halo shapes and to render them more axisymmetric. We use a suite of N-body simulations to investigate quantitatively the effect of the growth of a central disk galaxy on the shape of triaxial dark matter halos. As expected, the halo responds to the presence of the disk by becoming more spherical. The net effect depends only weakly on the orientation of the disk relative to the halo principal axes or the timescale of disk assembly, but strongly on the overall gravitational importance of the disk. Our results show that exponential disks whose contribution peaks at less than ~50% of their circular velocity are unable to modify noticeably the shape of the gravitational potential of their surrounding halos. Many dwarf and low surface brightness galaxies are expected to be in this regime, and therefore their detailed kinematics could be used to probe halo triaxiality, one of the basic predictions of the CDM paradigm. We argue that the complex disk kinematics of the dwarf galaxy NGC 2976 might be the reflection of a triaxial halo. Such signatures of halo triaxiality should be common in galaxies where the luminous component is subdominant.
The standard \LambdaCDM cosmological model implies that all celestial bodies are embedded in a perfectly uniform dark energy background, represented by Einstein's cosmological constant, and experience its repulsive antigravity action. Can dark energy have strong dynamical effects on small cosmic scales as well as globally? Continuing our efforts to clarify this question, we focus now on the Virgo Cluster and the flow of expansion around it. We interpret the Hubble diagram, from a new database of velocities and distances of galaxies in the cluster and its environment, using a nonlinear analytical model which incorporates the antigravity force in terms of Newtonian mechanics. The key parameter is the zero-gravity radius, the distance at which gravity and antigravity are in balance. Our conclusions are: 1. The interplay between the gravity of the cluster and the antigravity of the dark energy background determines the kinematical structure of the system and controls its evolution. 2. The gravity dominates the quasi-stationary bound cluster, while the antigravity controls the Virgocentric flow, bringing order and regularity to the flow, which reaches linearity and the global Hubble rate at distances \ga 15 Mpc. 3. The cluster and the flow form a system similar to the Local Group and its outflow. In the velocity-distance diagram, the cluster-flow structure reproduces the group-flow structure with a scaling factor of about 10; the zero-gravity radius for the cluster system is also 10 times larger. The phase and dynamical similarity of the systems on the scales of 1-30 Mpc suggests that a two-component pattern may be universal for groups and clusters: a quasi-stationary bound central component and an expanding outflow around it, due to the nonlinear gravity-antigravity interplay with the dark energy dominating in the flow component.
A diffuse non-thermal component has now been observed in massive merging clusters. To better characterise this component, and to extend analyses done for massive clusters down to a lower mass regime, we are conducting a statistical analysis over a large number of X-ray clusters (from ROSAT based catalogues). By means of their stacked radio and X-ray emissions, we are investigating correlations between the non-thermal and the thermal baryonic components. We will present preliminary results on radio-X scaling relations with which we aim to probe the mechanisms that power diffuse radio emission ; to better constrain whether the non-thermal cluster properties are compatible with a hierarchical framework of structure formation ; and to quantify the non-thermal pressure.
The clustering of galaxies observed in future redshift surveys will provide a wealth of cosmological information. Matching the signal at different redshifts constrains the dark energy driving the acceleration of the expansion of the Universe. In tandem with these geometrical constraints, redshift-space distortions (RSD) depend on the build up of large-scale structure. As pointed out by many authors measurements of these effects are intrinsically coupled. We investigate this link, and argue that it strongly depends on the cosmological assumptions adopted when analysing data. Using representative assumptions for the parameters of the "Euclid" survey in order to provide a baseline future experiment, we show how the derived constraints change due to different model assumptions. We argue that even the assumption of a Friedman-Robertson-Walker (FRW) space-time is sufficient to reduce the importance of the coupling to a significant degree. Taking this idea further, we consider how the data would actually be analysed and argue that we should not expect to be able to simultaneously constrain multiple deviations from the standard $\Lambda$CDM model. We therefore consider different possible ways in which the Universe could deviate from the $\Lambda$CDM model, and show how the coupling between geometrical constraints and structure growth affects the measurement of such deviations.
Applying suitable filters to data is a common way to detect galaxy clusters in blind surveys. Optimal filters are a class of filters that maximise the signal-to-noise ratio from cluster structures. This kind of filtering technique has been applied up to now to weak lensing data. With this work we extend it to cluster search via galaxy overdensities. Our optimal filter for cluster detection in optical surveys uses the information coming from galaxy magnitudes, positions and photometric redshifts. It is based on a model for the spatial and luminosity distribution of galaxies in the clusters and on the observed properties of the field galaxies. The cluster redshift can be estimated even if the galaxy catalogues do not have any redshift information. An analytical estimate of the error on the cluster amplitude is provided, and confirmed through numerical simulations. We apply both the weak lensing and the overdensities optimal filters to the COSMOS field and compare the results with previous cluster detections obtained with different methods. We report a catalogue of 27 galaxy clusters detected with both optimal filtering methods.
We present a new analytical method to calculate the small angle CMB temperature angular power spectrum due to cosmic (super-)string segments. In particular, using our method, we clarify the dependence on the intercommuting probability $P$. We find that the power spectrum is dominated by Poisson-distributed string segments. The power spectrum for a general value of $P$ has a plateau on large angular scales and shows a power-law decrease on small angular scales. The resulting spectrum in the case of conventional cosmic strings is in very good agreement with the numerical result obtained by Fraisse et al.. Then we estimate the upper bound on the dimensionless tension of the string for various values of $P$ by assuming that the fraction of the CMB power spectrum due to cosmic (super-)strings is less than ten percents at various angular scales up to $\ell=2000$. We find that the amplitude of the spectrum increases as the intercommuting probability. As a consequence, strings with smaller intercommuting probabilities are found to be more tightly constrained.
We investigate the impact of massive neutrinos on the distribution of matter in the semi-nonlinear regime (0.1<k<0.6 h Mpc^{-1}). We present a suite of large scale N-body simulations quantifying the scale dependent suppression of the total matter power spectrum, resulting from the free-streaming of massive neutrinos out of high-density regions. Our simulations show a power suppression of 3.5%-90% at k~0.6 h Mpc^{-1} for total neutrino mass, \Sigma m_{\nu}=0.05 eV-1.9 eV respectively. We also discuss the precision levels that future cosmological datasets would have to achieve in order to resolve between the normal and inverted neutrino mass hierarchies.
We present an improved prescription for matter power spectrum in redshift space taking a proper account of both the non-linear gravitational clustering and redshift distortion, which are of particular importance for accurately modeling baryon acoustic oscillations (BAOs). Contrary to the models of redshift distortion phenomenologically introduced but frequently used in the literature, the new model includes the corrections arising from the non-linear coupling between the density and velocity fields associated with two competitive effects of redshift distortion, i.e., Kaiser and Finger-of-God effects. Based on the improved treatment of perturbation theory for gravitational clustering, we compare our model predictions with monopole and quadrupole power spectra of N-body simulations, and an excellent agreement is achieved over the scales of BAOs. Potential impacts on constraining dark energy and modified gravity from the redshift-space power spectrum are also investigated based on the Fisher-matrix formalism. We find that the existing phenomenological models of redshift distortion produce a systematic error on measurements of the angular diameter distance and Hubble parameter by 1~2%, and the growth rate parameter by ~5%, which would become non-negligible for future galaxy surveys. Correctly modeling redshift distortion is thus essential, and the new prescription of redshift-space power spectrum including the non-linear corrections can be used as an accurate theoretical template for anisotropic BAOs.
We have recently identified a new radial migration mechanism resulting from the overlap of spiral and bar resonances in galactic disks. Here we confirm the efficiency of this mechanism in fully self-consistent, Tree-SPH simulations, as well as high-resolution pure N-body simulations. In all barred cases we clearly identify the effect of spiral-bar resonance overlap by a bimodality in the changes of angular momentum in the disk, dL, with maxima near the bar's corotation and outer Lindblad resonance. This is contrasted to the smooth distribution of dL for a simulation with no stable bar present, where strong radial migration is induced by multiple spirals. The presence of a disk gaseous component appears to increase the rate of angular momentum exchange by about 20%. The efficiency of this mechanism is such that galactic stellar disks can extend to over 10 scale-lengths within 1-3 Gyr in both Milky Way size and low-mass galaxies (circular velocity ~100 km/s). We also show that metallicity gradients can flatten in less than 1 Gyr rendering mixing in barred galaxies an order of magnitude more efficient than previously thought.
We present new models for illuminated accretion disks, their structure and reprocessed emission. We consider the effects of incident X-rays on the surface of an accretion disk by solving simultaneously the equations of radiative transfer, energy balance and ionization equilibrium over a large range of column densities. We assume plane-parallel geometry and azimuthal symmetry, such that each calculation corresponds to a ring at a given distance from the central object. Our models include recent and complete atomic data for K-shell processes of the iron and oxygen isonuclear sequences. We examine the effect on the spectrum of fluorescent K$\alpha$ line emission and absorption in the emitted spectrum. We also explore the dependence of the spectrum on the strength of the incident X-rays and other input parameters, and discuss the importance of Comptonization on the emitted spectrum.
We present the discovery of short GRB 080905A, its optical afterglow and host galaxy. Initially discovered by Swift, our deep optical observations enabled the identification of a faint optical afterglow, and subsequently a face-on spiral host galaxy underlying the GRB position, with a chance alignment probability of <1%. There is no supernova component present in the afterglow to deep limits. Spectroscopy of the galaxy provides a redshift of z=0.1218, the lowest redshift yet observed for a short GRB. The GRB lies offset from the host galaxy centre by ~18.5 kpc, in the northern spiral arm which exhibits an older stellar population than the southern arm. No emission lines are visible directly under the burst position, implying little ongoing star formation at the burst location. These properties would naturally be explained were the progenitor of GRB 080905A a compact binary merger.
We present preliminary results of 7 years of Arecibo timing of the pulsar-white dwarf binary PSR J1738+0333. We can measure the proper motion, parallax with excellent precision and have detected the orbital decay. Furthermore, the companion has been detected at optical wavelengths and a mass ratio of 8.1 +/- 0.3 has been measured from the orbital variation of its Doppler shift. Once the companion mass is determined from the optical measurements, this system will provide strong limits for the radiation of dipolar gravitational waves. Assuming that general relativity holds, the fast-improving measurement of the orbital decay, combined with the measurement of the mass ratio, will provide an independent and precise measurement of the component masses.
The $f(T)$ theory, which is an extension of teleparallel, or torsion scalar
$T$, gravity, is recently proposed to explain the present cosmic accelerating
expansion with no need of dark energy. In this paper, we discuss the
constraints on two concrete $f(T)$ models, i.e.,
$f(T)=\alpha (-T)^n$ and $f(T)=-\alpha T(1-e^{pT_0/T})$, proposed by Linder
[arXiv: 1005.3039] from the latest Union2 Type Ia Supernova (Sne Ia) set, the
baryonic acoustic oscillation (BAO) observation, and the Cosmic Microwave
Background (CMB) radiation. Our results show that at the 95% confidence level
$\Omega_{m0}=0.272_{-0.032}^{+0.036}$, $n=0.04_{-0.33}^{+0.22}$ for Model1 and
$\Omega_{m0}=0.272_{-0.034}^{+0.036}$, $p=-0.02_{-0.20}^{+0.31}$ for Model2. A
comparison of these two models with the $\Lambda$CDM by the $\chi^2_{Min}/dof$
(dof: degree of freedom) criterion indicates that $\Lambda$CDM is still favored
slightly by observations. We also study the evolution of the equation of state
for the effective dark energy in the theory and find that Sne Ia favors a
phantom-like dark energy, while Sne Ia + BAO + CMB favors a quintessence-like
one.
We derive the Mg/H ratio in the Orion nebula and in 30 Doradus. We also derive the O/H and the Fe/O ratios in the extremely metal poor galaxy SBS 0335-052. We estimate the dust depletions of Mg, Si, and Fe in Galactic and extragalactic H II regions. Based on these depletions we estimate the fraction of O atoms embedded in dust as a function of the O/H ratio. We find an increasing depletion of O with increasing O/H. The O depletion increases from about 0.08 dex, for the metal poorest H II regions known, to about 0.12 dex, for metal rich H II regions. This depletion has to be considered when comparing nebular with stellar abundances.
Fiber-fed spectrographs dedicated to observing massive portions of the sky are increasingly being more demanded within the astronomical community. For all the fiber-fed instruments, the primordial and common problem is the positioning of the fiber ends, which must match the position of the objects of a target field on the sky. Amongst the different approaches found in the state of the art, actuator arrays are one of the best. Indeed, an actuator array is able to position all the fiber heads simultaneously, thus making the reconfiguration time extremely short and the instrument efficiency high. The SIDE group (see this http URL) at the Instituto de Astrof\'isica de Andaluc\'ia, together with the industrial company AVS and the University of Barcelona, has been developing an actuator suitable for a large and scalable array. A real-scale prototype has been built and tested in order to validate its innovative design concept, as well as to verify the fulfillment of the mechanical requirements. The present article describes both the concept design and the test procedures and conditions. The main results are shown and a full justification of the validity of the proposed concept is provided.
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