We estimated the cross-power spectra of a galaxy sample from the Wide-field Infrared Survey Explorer (WISE) survey with the 7-year Wilkinson Microwave Anisotropy Probe (WMAP) temperature anisotropy maps. A conservatively-selected galaxy sample covers ~13000sq.deg, with a median redshift of z=0.15. Cross-power spectra show correlations between the two data sets with no discernible dependence on the WMAP Q, V and W frequency bands. We interpret these results in terms of the the Integrated Sachs-Wolfe (ISW) effect: for the |b|>20 deg sample at l=6-87, we measure the amplitude (normalized to be 1 for vanilla LambdaCDM expectation) of the signal to be 3.4+-1.1, i.e., 3.1 sigma detection. We discuss other possibilities, but at face value, the detection of the linear ISW effect in a flat universe is caused by large scale decaying potentials, a sign of accelerated expansion driven by Dark Energy.
We place new constraints on the contribution of blazars to the large-scale isotropic gamma-ray background (IGRB) by jointly analyzing the measured source count distribution (log N-log S) of blazars and the measured intensity and anisotropy of the IGRB. We find that these measurements point to a consistent scenario in which unresolved blazars make less than 30% of the IGRB intensity at 1-10 GeV while accounting for the majority of the measured anisotropy in that energy band. These results indicate that the remaining fraction of the IGRB intensity is made by a component with a low level of intrinsic anisotropy.
We examine the cosmic growth of the red sequence in a cosmological hydrodynamic simulation that includes a heuristic prescription for quenching star formation that yields a realistic passive galaxy population today. In this prescription, halos dominated by hot gas are continually heated to prevent their coronae from fueling new star formation. Hot coronae primarily form in halos above ~10^12 Msun, so that galaxies with stellar masses ~10^10.5 Msun are the first to be quenched and move onto the red sequence at z>2. The red sequence is concurrently populated at low masses by satellite galaxies in large halos that are starved of new fuel, resulting in a dip in passive galaxy number densities around 10^10 Msun that agrees qualitatively with observations. Stellar mass growth continues for galaxies even after joining the red sequence, primarily through minor mergers with a typical mass ratio ~20%. For the most massive systems, the size growth implied by the distribution of merger mass ratios is typically ~2 times the corresponding mass growth, consistent with observations. This model reproduces mass-density and colour-density trends in the local universe, with essentially no evolution to z=1, with the hint that such relations may be washed out by z~2. Our simulation produces a high red galaxy fraction at both high galaxy overdensity, independent of stellar mass, and high mass, independent of overdensity, suggesting quenching mechanisms associated with both environment and mass; in our model, both are connected to the presence of surrounding hot gas.
We present a new 400 ks Chandra X-ray observation of the merging galaxy cluster Abell 2146. This deep observation reveals detailed structure associated with the major merger event including the Mach M=2.3+/-0.2 bow shock ahead of the dense, ram pressure stripped subcluster core and the first known example of an upstream shock in the ICM (M=1.6+/-0.1). By measuring the electron temperature profile behind each shock front, we determine the timescale for the electron population to thermally equilibrate with the shock-heated ions. We find that the temperature profile behind the bow shock is consistent with the timescale for Coulomb collisional equilibration and the postshock temperature is lower than expected for instant shock-heating of the electrons. Although like the Bullet cluster the electron temperatures behind the upstream shock front are hotter than expected, favouring the instant heating model, the uncertainty on the temperature values is greater here and there is significant substructure complicating the interpretation. We also measured the width of each shock front and the contact discontinuity on the leading edge of the subcluster core to investigate the suppression of transport processes in the ICM. The upstream shock is ~440 kpc in length but appears remarkably narrow over this distance with a best-fit width of only 6^{+5}_{-3} kpc compared with the mean free path of 23+/-5 kpc. The leading edge of the subcluster core is also narrow with an upper limit on the width of only 2 kpc separating the cool, multiphase gas at 0.5-2 keV from the shock-heated surrounding ICM at ~6 keV. The strong suppression of diffusion and conduction across this edge suggests a magnetic draping layer may have formed around the subcluster core.[abridged]
We present photometry of the nearby galaxy NGC 5128 (Centaurus A) observed with the PACS and SPIRE instruments on board the Herschel Space Observatory, at 70, 160, 250, 350 and 500 {\mu}m, as well as new CO J = 3-2 observations taken with the HARP-B instrument on the JCMT. Using a single component modified blackbody, we model the dust spectral energy distribution within the disk of the galaxy using all five Herschel wavebands, and find dust temperatures of ~30 K towards the centre of the disk and a smoothly decreasing trend to ~20 K with increasing radius. We find a total dust mass of (1.59 \pm 0.05) \times 10^7 M\odot, and a total gas mass of (2.7 \pm 0.2) \times 10^9 M\odot. The average gas-to-dust mass ratio is 103 \pm 8 but we find an interesting increase in this ratio to approximately 275 toward the centre of Cen A. We discuss several possible physical processes that may be causing this effect, including dust sputtering, jet entrainment and systematic variables such as the XCO factor. Dust sputtering by X-rays originating in the AGN or the removal of dust by the jets are our most favoured explanations.
We present the results of a search for the most luminous star-forming galaxies at redshifts z~6 based on CFHT Legacy Survey data. We identify a sample of 40 Lyman break galaxies brighter than magnitude z'=25.3 across an area of almost 4 square degrees. Sensitive spectroscopic observations of seven galaxies provide redshifts for five, of which only two have moderate to strong Lyman alpha emission lines. All five have clear continuum breaks in their spectra. Approximately half of the Lyman break galaxies are spatially resolved in 0.7 arcsec seeing images, indicating larger sizes than lower luminosity galaxies discovered with the Hubble Space Telescope, possibly due to on-going mergers. The stacked optical and infrared photometry is consistent with a galaxy model with stellar mass ~ 10^{10} solar masses. There is strong evidence for substantial dust reddening with a best-fit A_V=0.75 and A_V>0.48 at 2 sigma confidence, in contrast to the typical dust-free galaxies of lower luminosity at this epoch. The spatial extent and spectral energy distribution suggests that the most luminous z~6 galaxies are undergoing merger-induced starbursts. The luminosity function of z=5.9 star-forming galaxies is derived. This agrees well with previous work and shows strong evidence for an exponential decline at the bright end, indicating that the feedback processes which govern the shape of the bright end are occurring effectively at this epoch.
Recent high redshift surveys for 21-cm absorption in damped Lyman-alpha absorption systems (DLAs) take the number of published searches at z > 2 to 25, the same number as at z < 2, although the detection rate at high redshift remains significantly lower (20% cf. 60%). Using the known properties of the DLAs to estimate the unknown profile widths of the 21-cm non-detections and including the limits via a survival analysis, we show that the mean spin temperature/covering factor degeneracy at high redshift is, on average, double that of the low redshift sample. This value is significantly lower than the previous factor of eight for the spin temperatures and is about the same factor as in the angular diameter distance ratios between the low and high redshift samples. That is, without the need for the several pivotal assumptions, which lead to an evolution in the spin temperature, we show that the observed distribution of 21-cm detections in DLAs can be accounted for by the geometry effects of an expanding Universe. That is, as yet there is no evidence of the spin temperature of gas rich galaxies evolving with redshift.
We propose a new scenario for supermassive star (SMS;>10^5Msun) formation in shocked regions of colliding cold accretion flows near the centers of first galaxies. Recent numerical simulations indicate that assembly of a typical first galaxy with virial temperature (~10^4K) proceeds via cold and dense flows penetrating deep to the center, where the supersonic streams collide each other to develop a hot and dense (~10^4K, ~10^3/cc) shocked gas. The post-shock layer first cools by efficient Ly alpha emission and contracts isobarically until 8000K. Whether the layer continues the isobaric contraction depends on the density at this moment: if the density is high enough for collisionally exciting H2 rovibrational levels (>10^4/cc), enhanced H2 collisional dissociation suppresses the gas to cool further. In this case, the layer fragments into massive (>10^5Msun) clouds, which collapse isothermally (~8000K) by the Ly alpha cooling without subsequent fragmentation. As an outcome, SMSs are expected to form and evolve eventually to seeds of supermassive black holes (SMBH). By calculating thermal evolution of the post-shock gas, we delimit the range of post-shock conditions for the SMS formation, which can be expressed as: T>6000K/(n/10^4/cc) for n<10^4/cc and T>5000-6000K for n>10^4/cc, depending somewhat on initial ionization degree. We found that metal enrichment does not affect the above condition for metallicity below 10^-3Zsun if metals are in the gas phase, while condensation of several percent of metals into dust decreases this critical value of metallicity by an order of magnitude. Unlike the previously proposed scenario for SMS formation, which postulates extremely strong ultraviolet radiation to quench H2 cooling, our scenario naturally explains the SMBH seed formation in the assembly process of the first galaxies, even without such a strong radiation.
We present the analysis of a large sample of early-type galaxies (ETGs) at 0<z<3 aimed at tracing the cosmic evolution of their size and compare it with a model of pure dissipationless (dry) merging in the LambdaCDM framework. The effective radius R_e depends on stellar mass M as R_e(M) \propto M}^{alpha} with alpha ~ 0.5 at all redshifts. The redshift evolution of the mass- or SDSS-normalized size can be reproduced as \propto (1+z)^beta with beta ~ -1, with the most massive ETGs possibly showing the fastest evolutionary rate (beta ~ -1.4). This size evolution slows down significantly to beta ~ -0.6 if the ETGs at z>2 are removed from the sample, suggesting an accelerated increase of the typical sizes at z>2, especially for the ETGs with the largest masses. A pure dry merging LambdaCDM model is marginally consistent with the average size evolution at 0<z<1.7, but predicts descendants too compact for z>2 progenitor ETGs. This opens the crucial question on what physical mechanism can explain the accelerated evolution at z>2, or whether an unclear observational bias is partly responsible for that.
We use high angular resolution data, measured from visibility of sources at
the longest baseline of 4500 m of the Australia Telescope Compact Array (ATCA),
for the Australia Telescope 20 GHz (AT20G) survey to obtain angular size
information for > 94% of AT20G sources. We confirm the previous AT20G result
that due to the high survey frequency of 20 GHz, the source population is
strongly dominated by compact sources (79%). At 0.15 arcseconds angular
resolution limit, we show a very strong correlation between the compact and
extended sources with flat and steep-spectrum sources respectively. Thus, we
provide a firm physical basis for the traditional spectral classification into
flat and steep-spectrum sources to separate compact and extended sources. We
find the cut-off of -0.46 to be optimum for spectral indices between 1 and 5
GHz and, hence, recommend the continued use of -0.5 for future studies.
We study the effect of spectral curvature on redshift cut-off of compact AGNs
using recently published redshift data. Using spectral indices at different
frequencies, we correct for the redshift effect and produce restframe frequency
spectra for compact sources for redshift up to ~5. We show that the flat
spectra of most compact sources start to steepen at ~30 GHz. At higher
frequencies, the spectra of both populations are steep so the use of spectral
index does not separate the compact and extended source populations as well as
in lower frequencies. We find that due to the spectral steepening, surveys of
compact sources at higher frequencies (>5 GHz) will have redshift cut-off due
to spectral curvature but at lower frequencies, the surveys are not
significantly affected by spectral curvature, thus, the evidence for a strong
redshift cut-off in AGNs found in lower frequency surveys is a real cut-off and
not a result of K-correction.
The thermal fluctuation level of the Weibel instability is recalculated. It is shown that the divergence of the fluctuations at long wavelengths, i.e. the Weibel infrared catastrophe, never occurs. At large wavelengths the thermal fluctuation level is terminated by the presence of even the smallest available stable thermal anisotropy. Weibel fields penetrate only one skin depth into the plasma. When excited inside, they cause layers of antiparallel fields of skin depth width and vortices which may be subject to reconnection.
A novel modified theory of gravity with the function $F(R) = (1-\sqrt{1-2\lambda R})/\lambda$ is suggested. At small value of the parameter $\lambda$ introduced the action is converted into Einstein-Hilbert action. The theory is consistent with local tests which can give a bound on the value of the parameter $\lambda$. The static Schwarzschild-de Sitter solutions of the model are obtained and analyzed. It was demonstrated that the de Sitter space is unstable but a solution with zero Ricci scalar is stable.
We introduce darkons as fluid particles of a Galilean massless self-gravitating fluid. This fluid exhibits anisotropic scaling with $z=5/3$. The minimal gravitational coupling dynamically generates a gravitational mass density of either sign. Hence such fluid may serve as a model for the dark sector of the Universe. Its cosmological solutions give a deceleration phase for the early Universe and an acceleration phase for the late Universe. Will the steady flow solutions lead to a confining potential and so a possible model for halos?
We present \emph{Chandra} monitoring data for six gravitationally lensed quasars: QJ 0158$-$4325, HE 0435$-$1223, HE 1104$-$1805, SDSS 0924+0219, SDSS 1004+4112, and Q 2237+0305. We detect X-ray microlensing variability in all six lenses with high confidence. We detect energy dependent microlensing in HE 0435$-$1223, SDSS 1004+4112, SDSS 0924+0219 and Q 2237+0305. We present a detailed spectral analysis for each lens, and find that simple power-law models plus Gaussian emission lines give good fits to the spectra. We detect intrinsic spectral variability in two epochs of Q 2237+0305. We detect differential absorption between images in four lenses. We also detect the \feka\ emission line in all six lenses, and the Ni XXVII K$\alpha$ line in two images of Q 2237+0305. The rest frame equivalent widths of the \feka\ lines are measured to be 0.4--1.2 keV, significantly higher than those measured in typical active galactic nuclei of similar X-ray luminosities. This suggests that the \feka\ emission region is more compact or centrally concentrated than the continuum emission region.
(Abridged) This paper presents the first connections made between two local features in velocity-space found in a survey of M giant stars and stellar spatial inhomogeneities on global scales. Comparison to cosmological, chemodynamical stellar halo models confirm that the M giant population is particularly sensitive to rare, recent and massive accretion events. These events can give rise to local observed velocity sequences - a signature of a small fraction of debris from a common progenitor, passing at high velocity through the survey volume, near the pericenters of their eccentric orbits. The majority of the debris is found in much larger structures, whose morphologies are more cloud-like than stream-like and which lie at the orbital apocenters. Adopting this interpretation, the full-space motions represented by the observed velocity features are derived under the assumption that the members within each sequence share a common velocity. Orbit integrations are then used to trace the past and future trajectories of these stars across the sky revealing plausible associations with large, previously-discovered, cloud-like structures. The connections made between nearby velocity structures and these distant clouds represent preliminary steps towards developing coherent maps of such giant debris systems. These maps promise to provide new insights into the origin of debris clouds, new probes of Galactic history and structure, and new constraints on the high-velocity tails of the local dark matter distribution that are essential for interpreting direct detection experiments.
I present the results of the search for an optical precursor to the naked-eye burst - GRB080319B, which reached 5.87m optical peak luminosity in the "Pi of the Sky" data. A burst of such a high brightness could have been preceded by an optical precursor luminous enough to be in detection range of our experiment. The "Pi of the Sky" cameras observed the coordinates of the GRB for about 20 minutes prior to the explosion, thus provided crucial data for the precursor search. No signal within 3 sigma limit was found. A limit of 12m (V-band equivalent) was set based on the data combined from two cameras, the most robust limit to my knowledge for this precursor.
By using the formulation of the reconstruction, we construct models which have an exact solution describing the domain wall. The shape of the domain wall can be flat, de Sitter space-time, or anti-de Sitter space-time. In the constructed domain wall solutions, there often appears ghost with negative kinetic energy. We give, however, an example of the de Sitter domain wall solution without ghost, which could be a toy model of the inflation. We also investigate the localization of the gravity as in the Randall-Sundrum model. It is shown that the four dimensional Newton law could be reproduced even in the de Sitter space-time domain wall solution.
The mathematical structure of the six dimensional physical phase spaces of the non-diagonal Bianchi IX model is analyzed in the neighborhood of the cosmological singularity. Critical points of the Hamiltonian equations appearing at infinities are of the nonhyperbolic type. Specific transformations of the phase space, including projection into finite region, do not change this type of criticality which is difficult for investigation by standard analytical tools. The nonhyperbolicity seems to be a generic feature of considered singular dynamics. The information that can be obtained from the linearized vector field is inconclusive. Making use of the physical Dirac observables as the phase space coordinates lowers substantially the dimensionality of the dynamics arena. Here, using commonly known methods for studying the dynamics may turn out to be quite satisfactory.
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We investigate the formation of the first stars at the end of the cosmic dark ages with a suite of three-dimensional, moving mesh simulations that directly resolve the collapse of the gas beyond the formation of the first protostar at the centre of a dark matter minihalo. The simulations cover more than 25 orders of magnitude in density and have a maximum spatial resolution of 100 km, which extends well below the radius of individual protostars and captures their interaction with the surrounding gas. In analogy to previous studies that employed sink particles, we find that the Keplerian disc around the primary protostar fragments into a number of secondary protostars, which is enabled by H2 collisional dissociation cooling and collision-induced emission. The further evolution of the protostellar system is characterised by strong gravitational torques that transfer angular momentum between the secondary protostars formed in the disc and the surrounding gas. This leads to the migration of about half of the secondary protostars to the centre of the cloud in a free-fall time, where they merge with the primary protostar and facilitate its growth to about five times the mass of the second most massive protostar. By the same token, a fraction of the protostars obtain angular momentum from other protostars via N-body interactions and migrate to higher orbits. On average, only every third protostar survives until the end of the simulation. However, the number of protostars present at any given time increases monotonically, suggesting that the system will continue to grow beyond the limited period of time simulated here.
We investigate the ability of state-of-the-art redshift-space distortions models for the galaxy anisotropic two-point correlation function \xi(r_p, r_\pi), to recover precise and unbiased estimates of the linear growth rate of structure f, when applied to catalogues of galaxies characterised by a realistic bias relation. To this aim, we make use of a set of simulated catalogues at z=0.1 and z=1 with different luminosity thresholds, obtained by populating dark-matter haloes from a large N-body simulation using halo occupation prescriptions. We examine the most recent developments in redshift-space distortions modelling, which account for non-linearities on both small and intermediate scales produced respectively by randomised motions in virialised structures and non-linear coupling between the density and velocity fields. We consider the possibility of including the linear component of galaxy bias as a free parameter and directly estimate the growth rate of structure f. Results are compared to those obtained using the standard dispersion model, over different ranges of scales.We find that the model of Taruya et al. (2010), the most sophisticated one considered in this analysis, provides in general the most unbiased estimates of the growth rate of structure, with systematic errors within 4% over a wide range of galaxy populations spanning luminosities between L > L^* and L > 3L^*. Accounting for the scale-dependence of galaxy bias plays a crucial role in recovering an unbiased estimate of f when fitting quasi non-linear scales. Its impact is found to be more severe for highly-biased tracers such as Luminous Red Galaxies, for which systematic effects in the modelling might be more difficult to mitigate and have to be further investigated. [...]
Following a recent suggestion of axion cooling of photons between the nucleosynthesis and recombination epochs in the Early Universe, we investigate a hybrid model with both axions and relic supersymmetric particles. In this model we demonstrate that the 7Li abundance can be consistent with observations without destroying the important concordance of deuterium abundance.
A quantum expansion parameter, analogous to the Hubble parameter in cosmology, is defined for a free particle quantum wavefunction. By considering the universe as an initial single Gaussian quantum wavepacket whose mass is that of present-day observable universe and whose size is that of the Planck Length at the Planck Time, it is demonstrated that this quantum expansion parameter has a value at the present epoch of the same order as the value of the Hubble constant. The coincidence suggests examining the effect of including this type of quantum wave expansion in traditional general relativistic cosmology and a sample model illustrating this is presented here. Using standard Einstein-de Sitter cosmology ($\Omega$m = 1) it is found that cosmic acceleration (aka dark energy) arises naturally during cosmic history. The time at which the universe switched from deceleration to acceleration (observationally ~7 Gyr before the present epoch) yields a value for the mass of the wavepacket representing the universe at the Planck Time and its present age. This same mass may then be used to obtain a curve for the cosmic expansion rate versus z. This curve is well fit to observational data. The model is used also to obtain an estimate of the inflationary expansion factor.
We apply CMB lensing techniques to large scale structure and solve for the 3-D cosmic tidal field. We use small scale filamentary structures to solve for the large scale tidal shear and gravitational potential. By comparing this to the redshift space density field, one can measure the gravitational growth factor on large scales without cosmic variance. This potentially enables accurate measurements of neutrino masses and reconstruction of radial modes lost in 21 cm intensity mapping, which are essential for CMB and other cross correlations. We relate the tidal fields to the squeezed limit bispectrum, and present initial results from simulations and data from the SDSS.
We have designed a simple multi-scale method that identifies turbulent motions in hydrodynamical grid simulations. The method does not assmume an a-priori coherence scale to distinguish laminar and turbulent flows. Instead, the local mean velocity field around each cell is reconstructed with a multi-scale filtering technique, yielding the maximum scale of turbulent eddies by means of iterations. The method is robust, fast and easily applicable to any grid simulation. We present here the application of this technique to the study of spatial and spectral properties of turbulence in the intra cluster medium, measuring turbulent diffusion and anisotropy of the turbulent velocity field for a variety of driving mechanism: a) accretion of matter in galaxy clusters (simulated with ENZO); b) sloshing motions around cool-cores (simulated with FLASH); c) jet outflows from AGN (simulated with FLASH). The turbulent velocities driven by matter accretion in galaxy clusters are mostly tangential in the inner regions (inside the cluster virial radius) and isotropic in regions close to the virial radius. The same is found for turbulence excited by cool core sloshing, while the jet outflowing from AGN drives mostly radial turbulence motions near its sonic point and beyond. Turbulence leads to a diffusivity in the range =10^29-10^30 cm^2/s in the intra cluster medium. On average, the energetically dominant mechanism of turbulence driving in the intra cluster medium is represented by accretion of matter and major mergers during clusters evolution.
SDSS J120136.02+300305.5 was detected in an XMM-Newton slew from June 2010 with a flux 56 times higher than an upper limit from ROSAT, corresponding to Lx~3x10^44 ergs/s. It has the optical spectrum of a quiescent galaxy (z=0.146). Overall the X-ray flux has evolved consistently with the canonical t^-5/3 model, expected for returning stellar debris from a tidal disruption event, fading by a factor ~300 over 300 days. In detail the source is very variable and became invisible to Swift between 27 and 48 days after discovery, perhaps due to self-absorption. The X-ray spectrum is soft but is not the expected tail of optically thick thermal emission. It may be fit with a Bremsstrahlung or double-power-law model and is seen to soften with time and declining flux. Optical spectra taken 12 days and 11 months after discovery indicate a deficit of material in the broad line and coronal line regions of this galaxy, while a deep radio non-detection implies that a jet was not launched during this event.
[Abridged] In this paper we derive the central stellar mass density within a fixed radius and the effective stellar mass density within the effective radius for a complete sample of 34 ETGs morphologically selected at 0.9<z_{spec}<2 and compare them with those derived for a sample of ~900 local ETGs in the same mass range. We find that the central stellar mass density of high-z ETGs spans just an order of magnitude and it is similar to the one of local ETGs as actually found in previous studies.However, we find that the effective stellar mass density of high-z ETGs spans three orders of magnitude, exactly as the local ETGs and that it is similar to the effective stellar mass density of local ETGs showing that it has not changed since z~1.5, in the last 9-10 Gyr. Thus, the wide spread of the effective stellar mass density observed up to z~1.5 must originate earlier, at z>2. Also, we show that the small scatter of the central mass density of ETGs compared to the large scatter of the effective mass density is simply a peculiar feature of the Sersic profile hence, independent of redshift and of any assembly history experienced by galaxies. Thus, it has no regards with the possible inside-out growth of ETGs. Finally, we find a tight correlation between the central stellar mass density and the total stellar mass of ETGs in the sense that the central mass density increases with mass as M^{~0.6}. This implies that the fraction of the central stellar mass of ETGs decreases with the mass of the galaxy. These correlations are valid for the whole population of ETGs considered independently of their redshift suggesting that they originate in the early-phases of their formation.
We present a statistical analysis of the properties of a large sample of dynamically hot old stellar systems, from globular clusters to giant ellipticals, which was performed in order to investigate the origin of ultra-compact dwarf galaxies. The data were mostly drawn from Forbes et al. (2008). We recalculated some of the effective radii, computed mean surface brightnesses and mass-to-light-ratios, estimated ages and metallicities. We completed the sample with globular clusters of M31. We used a multivariate statistical technique (K-Means clustering), together with a new algorithm (Gap Statistics) for finding the optimum number of homogeneous sub-groups in the sample, using a total of six parameters (absolute magnitude, effective radius, virial mass-to-light ratio, stellar mass-to-light ratio and metallicity). We found six groups. FK1 and FK5 are composed of high- and low-mass elliptical galaxies respectively. FK3 and FK6 are composed of high-metallicity and low-metallicity objects, respectively, and both include globular clusters and ultra-compact dwarf galaxies. Two very small groups, FK2 and FK4, are composed of Local Group dwarf spheroidals. Our groups differ in their mean masses and virial mass-to-light ratios. The relations between these two parameters are also different for the various groups. The probability density distributions of metallicity for the four groups of galaxies is similar to that of the globular clusters and UCDs. The brightest low-metallicity globular clusters and ultra-compact dwarf galaxies tend to follow the mass-metallicity relation like elliptical galaxies. The objects of FK3 are more metal-rich per unit effective luminosity density than high-mass ellipticals.
The 40% Arecibo Legacy Fast ALFA (ALFALFA) survey catalog (\alpha.40) of approximately 10,150 HI-selected galaxies is used to analyze the clustering properties of gas-rich galaxies. By employing the Landy-Szalay estimator and a full covariance analysis for the two-point galaxy-galaxy correlation function, we obtain the real-space correlation function and model it as a power law, \xi(r) = (r/r_0)^(-\gamma), on scales less than 10 h^{-1} Mpc. As the largest sample of blindly HI-selected galaxies to date, \alpha.40 provides detailed understanding of the clustering of this population. We find \gamma = 1.51 +/- 0.09 and r_0 = 3.3 +0.3, -0.2 h^{-1} Mpc, reinforcing the understanding that gas-rich galaxies represent the most weakly clustered galaxy population known; we also observe a departure from a pure power law shape at intermediate scales, as predicted in \Lambda CDM halo occupation distribution models. Furthermore, we measure the bias parameter for the \alpha.40 galaxy sample and find that HI galaxies are severely antibiased on small scales, but only weakly antibiased on large scales. The robust measurement of the correlation function for gas-rich galaxies obtained via the \alpha.40 sample constrains models of the distribution of HI in simulated galaxies, and will be employed to better understand the role of gas in environmentally-dependent galaxy evolution.
We discuss in a critical way the physical foundations of geometric structure of relativistic theories of gravity by the so-called Ehlers-Pirani-Schild formalism. This approach provides a natural interpretation of the observables showing how relate them to General Relativity and to a large class of Extended Theories of Gravity. In particular we show that, in such a formalism, geodesic and causal structures of space-time can be safely disentangled allowing a correct analysis in view of observations and experiment. As specific case, we take into account the case of f(R) gravity.
Light-like galileon solutions have been used to investigate the chronology problem in galileon-like theories, and in some cases may also be considered as solitons, evading a non-existence constraint from a zero-mode argument. Their stabilities have been analyzed via "local" approximation, which appears to suggest that all these light-like solutions are stable. We re-analyze the stability problem by solving the linear perturbation equation \emph{exactly}, and point out that the finite energy condition is essential for the light-like solitons to be stable. We also clarify potential ghost instabilities and why the zero-mode argument can not be naively generalized to include the light-like solitons.
In an unconventional realization of left-right symmetry, the particle corresponding to the left-handed neutrino nu_L (with SU(2)_L interactions) in the right-handed sector, call it n_R (with SU(2)_R interactions), is not its Dirac mass partner, but a different particle which may be a dark-matter candidate. In parallel to leptogenesis in the SU(2)_L sector, asymmetric production of n_R may occur in the SU(2)_R sector. This mechanism is especially suited for n_R mass of order 1 to 10 keV, i.e. warm dark matter, which is a possible new paradigm for explaining the structure of the Universe at all scales.
We analyze the spectrum of axions radiated from collapse of domain walls, which have received less attention in the literature. The evolution of topological defects related to the axion models is investigated by performing field-theoretic lattice simulations. We simulate the whole process of evolution of the defects, including the formation of global strings, the formation of domain walls and the annihilation of the defects due to the tension of walls. The spectrum of radiated axions has a peak at the low frequency, which implies that axions produced by the collapse of domain walls are not highly relativistic. We revisit the relic abundance of cold dark matter axions and find that the contribution from the decay of defects can be comparable with the contribution from strings. This result leads to a severer upper bound on the axion decay constant.
The Vista Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting $K_S$-band time series photometry of the system formed by the two Magellanic Clouds (MC) and the "bridge" that connects them. These data are used to build $K_S$-band light curves of the MC RR Lyrae stars and Classical Cepheids and determine absolute distances and the 3D geometry of the whole system using the $K$-band period luminosity ($PLK_S$), the period - luminosity - color ($PLC$) and the Wesenhiet relations applicable to these types of variables. As an example of the survey potential we present results from the VMC observations of two fields centered respectively on the South Ecliptic Pole and the 30 Doradus star forming region of the Large Magellanic Cloud. The VMC $K_S$-band light curves of the RR Lyrae stars in these two regions have very good photometric quality with typical errors for the individual data points in the range of $\sim$ 0.02 to 0.05 mag. The Cepheids have excellent light curves (typical errors of $\sim$ 0.01 mag). The average $K_S$ magnitudes derived for both types of variables were used to derive $PLK_S$ relations that are in general good agreement within the errors with the literature data, and show a smaller scatter than previous studies.
The notion of an apparent horizon (AH) in a collapsing object can be carried over from the Lema\^{\i}tre -- Tolman (L--T) to the quasi-spherical Szekeres models in three ways: 1. Literally by the definition -- the AH is the envelope of the region, in which every bundle of null geodesics has negative expansion scalar. 2. As the locus, at which null lines that are as nearly radial as possible are turned toward decreasing areal radius $R$. These lines are in general nongeodesic. The name "absolute apparent horizon" (AAH) is proposed for this locus. 3. As the envelope of a region, where null \textit{geodesics} are turned toward decreasing $R$. The name "light collapse region" (LCR) is proposed for this region (which is 3-dimensional in every space of constant $t$); its boundary coincides with the AAH. The AH and AAH coincide in the L--T models. In the quasi-spherical Szekeres models, the AH is different from (but not disjoint with) the AAH. Properties of AAH and LCR are investigated, and the relations between the AAH and the AH are illustrated with diagrams using an explicit example of a Szekeres metric. It turns out that an observer who is already within the AH is, for some time, not yet within the AAH. Nevertheless, no light signal can be sent inside out through the AH. The analogue of AAH for massive particles is also considered.
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A fundamental gap in the current understanding of galaxies concerns the thermodynamical evolution of the ordinary, baryonic matter. On one side, radiative emission drastically decreases the thermal energy content of the interstellar plasma (ISM), inducing a slow cooling flow toward the centre. On the other side, the active galactic nucleus (AGN) struggles to prevent the runaway cooling catastrophe, injecting huge amount of energy in the ISM. The present study intends to deeply investigate the role of mechanical AGN feedback in (isolated or massive) elliptical galaxies, extending and completing the mass range of tested cosmic environments. Our previously successful feedback models, in galaxy clusters and groups, demonstrated that AGN outflows, self-regulated by cold gas accretion, are able to properly quench the cooling flow, without destroying the cool core. Via 3D hydrodynamic simulations (FLASH 3.3), including also stellar evolution, we show that massive mechanical AGN outflows can indeed solve the cooling flow problem for the entire life of the galaxy, at the same time reproducing typical observational features and constraints, such as buoyant underdense bubbles, elliptical shock cocoons, sonic ripples, dredge-up of metals, subsonic turbulence, and extended filamentary or nuclear cold gas. In order to avoid overheating and totally emptying the isolated galaxy, the frequent mechanical AGN feedback should be less powerful and efficient (~1.e-4), compared to the heating required for more massive and bound ellipticals surrounded by the intragroup medium (efficiency ~1.e-3).
We present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey designed to explore the connection between galaxies and intergalactic baryons. The KBSS is optimized for the redshift range z ~ 2-3, combining S/N ~ 100 Keck/HIRES spectra of 15 hyperluminous QSOs with densely sampled galaxy redshift surveys surrounding each QSO sightline. We perform Voigt profile decomposition of all 6000 HI absorbers within the full Lya forest in the QSO spectra. Here we present the distribution, column density, kinematics, and absorber line widths of HI surrounding 886 star-forming galaxies with 2.0 < z < 2.8 and within 3 Mpc of a QSO sightline. We find that N_HI and the multiplicity of HI components increase rapidly near galaxies. The strongest HI absorbers within ~ 100 physical kpc of galaxies have N_HI ~ 3 dex higher than those near random locations in the IGM. The circumgalactic zone of most enhanced HI absorption (CGM) is found within 300 kpc and 300 km/s of galaxies. Nearly half of absorbers with log(N_HI) > 15.5 are found within the CGM of galaxies meeting our photometric selection, while their CGM occupy only 1.5% of the cosmic volume. The spatial covering fraction, multiplicity of absorption components, and characteristic N_HI remain elevated to transverse distances of 2 physical Mpc. Absorbers with log(N_HI) > 14.5 are tightly correlated with the positions of galaxies, while absorbers with lower N_HI are correlated only on Mpc scales. Redshift anisotropies on Mpc scales indicate coherent infall toward galaxies, while on scales of ~100 physical kpc peculiar velocities of 260 km/s are indicated. The median Doppler widths of absorbers within 1-3 virial radii of galaxies are ~50% larger than randomly chosen absorbers of the same N_HI, suggesting higher gas temperatures and/or increased turbulence likely caused by accretion shocks and/or galactic winds.
We present results on the clustering of 282,068 galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS) sample of massive galaxies with redshifts 0.4<z<0.7 which is part of the Sloan Digital Sky Survey III project. Our results cover a large range of scales from ~0.5 to 90 Mpc/h. We compare these estimates with the expectations of a flat LCDM standard cosmological model with parameters compatible with WMAP7 data. We use the MultiDark cosmological simulation, one of the largest N-body runs presently available, together with a simple halo abundance matching technique, to predict galaxy correlation functions, power spectra, abundance of satellites and galaxy biases. We find that the LCDM model gives a reasonable description to the observed correlation functions at z~0.5, which is a remarkably good agreement considering that the model, once matched to the observed abundance of galaxies, does not have any free parameters. However, we find a small (~10%) deviation in the correlation functions for scales ~10-30 Mpc/h. A more realistic abundance matching model and better statistics from upcoming observations are needed to clarify the situation. We also predict that about 7% of the galaxies in the sample are most probably satellites inhabiting central haloes with mass M > ~1e14 M_sun/h. Using the MultiDark simulation we also study the scale-dependent galaxy bias b and find that b~2 for BOSS galaxies at scales > ~10 Mpc/h. The large-scale bias, defined using the extrapolated linear matter power spectrum, depends on the maximum circular velocity of galaxies as b=1+(V_max/(361 km/s))^4/3, or on the galaxy number density as b=0.0377-0.57*log(n_g/(h/Mpc)^3). The damping of the BAO signal produced by non-linear evolution leads to ~2-4% dips in the large-scale bias factor defined in this way. Very accurate fits as a function of abundance and maximum circular velocity of galaxies are provided.
We analyze deep g' and r' band data of 97 galaxy clusters imaged with MegaCam on the Canada-France-Hawaii telescope. We compute the number of luminous (giant) and faint (dwarf) galaxies using criteria based on the definitions of de Lucia et al. (2007). Due to excellent image quality and uniformity of the data and analysis, we probe the giant-to-dwarf ratio (GDR) out to z ~ 0.55. With X-ray temperature (Tx) information for the majority of our clusters, we constrain, for the first time, the Tx-corrected giant and dwarf evolution separately. Our measurements support an evolving GDR over the redshift range 0.05 < z < 0.55. We show that modifying the (g'-r'), m_r' and K-correction used to define dwarf and giant selection do not alter the conclusion regarding the presence of evolution. We parameterize the GDR evolution using a linear function of redshift (GDR = alpha * z + beta) with a best fit slope of alpha = 0.88 +/- 0.15 and normalization beta = 0.44 +/- 0.03. Contrary to claims of a large intrinsic scatter, we find that the GDR data can be fully accounted for using observational errors alone. Consistently, we find no evidence for a correlation between GDR and cluster mass (via Tx or weak lensing). Lastly, the data suggest that the evolution of the GDR at z < 0.2 is driven primarily by dry merging of the massive giant galaxies, which when considered with previous results at higher redshift, suggests a change in the dominant mechanism that mediates the GDR.
The galaxy NGC1313 has attracted the attention of various studies due to the peculiar morphology observed in optical bands, although it is classified as a barred, late-type galaxy with no apparent close-by companions. However, the velocity field suggests an interaction with a satellite companion. Using resolved stellar populations, we study different parts of the galaxy to understand further its morphology. Based on HST/ACS images, we estimated star formation histories by means of the synthetic CMD method in different areas in the galaxy. Incompleteness limits our analysis to ages younger than ~100Myr. Stars in the red and blue He burning phases are used to trace the distribution of recent star formation. Star formation histories suggest a burst in the southern-west region. We support the idea that NGC1313 is experiencing an interaction with a satellite companion, observed as a tidally disrupted satellite galaxy in the south-west of NGC1313. However, we do not observe any indication of a perturbation due to the interaction with the satellite galaxy at other locations across the galaxy, suggesting that only a modest-sized companion that did not trigger a global starburst was involved.
We present a new analysis of the Aquarius simulations done in combination with a semi-analytic galaxy formation model. Our goal is to establish whether the subhalos present in LCDM simulations of Milky Way-like systems could host the dwarf spheroidal (dSph) satellites of our Galaxy. Our analysis shows that, contrary to what has been assumed in most previous work, the mass profiles of subhalos are generally not well fit by NFW models but that Einasto profiles are preferred. We find that for shape parameters alpha = 0.2 - 0.5 and Vmax = 10 - 30 km/s there is very good correspondance with the observational constraints obtained for the nine brightest dSph of the Milky Way. Furthermore, the internal dynamics of these systems, as well as the number of objects of a given circular velocity are also matched if the total mass of the Milky Way is ~8x10^11 Msun, a value that is in agreement with many recent determinations. Our simulations show important scatter in the number of bright satellites, even when the Aquarius Milky Way-like hosts are scaled to a common mass, and we find no evidence for a missing population of massive subhalos in the Galaxy. This conclusion is also supported when we examine the dynamics of the satellites of M31.
We analyse 3D SPH simulations of the evolution of initially quasi-circular massive black hole binaries (BHBs) residing in the central hollow (cavity) of self-gravitating circumbinary discs. We perform a set of simulations adopting different thermodynamics for the gas within the cavity and for the 'numerical size' of the black holes. We study the interplay between gas accretion and gravity torques in changing the binary elements (semi-major axis and eccentricity) and its total angular momentum budget. We pay special attention to the gravity torques, by analysing their physical origin and location. We show that (i) the BHB eccentricity grows due to gravity torques from the inner edge of the disc, independently of the accretion and the adopted thermodynamics; (ii) the semi-major axis decay depends not only on the gravity torques but also on their subtle interplay with the disc-binary angular momentum transfer due to accretion; (iii) the spectral structure of the gravity torques is predominately caused by disc edge overdensities and spiral arms developing in the body of the disc; (iv) the net gravity torque changes sign across the BHB corotation radius: gas inside this radius exerts a net positive torque, while streams located outside this radius (but within the cavity) exert a net negative torque. The relative importance of the two might depend on the thermodynamical properties of the instreaming gas and is crucial in assessing the disc--binary angular momentum transfer; (v) the net torque manifests as a purely kinematic effect as it stems from the low density cavity, where the material flows in and out in highly eccentric orbits. Thus both accretion onto the black holes and the interaction with gas streams inside the cavity must be taken into account to assess the fate of the binary.
A new method for spectroscopic bulge-disc decomposition is presented, in which the spatial light profile in a two-dimensional spectrum is decomposed wavelength-by-wavelength into bulge and disc components, allowing separate one-dimensional spectra for each component to be constructed. This method has been applied to observations of a sample of nine S0s in the Fornax Cluster in order to obtain clean high-quality spectra of their individual bulge and disc components. So far this decomposition has only been fully successful when applied to galaxies with clean light profiles, consequently limiting the number of galaxies that could be separated into bulge and disc components. Lick index stellar population analysis of the component spectra reveals that in those galaxies where the bulge and disc could be distinguished, the bulges have systematically higher metallicities and younger stellar populations than the discs. This correlation is consistent with a picture in which S0 formation comprises the shutting down of star formation in the disc accompanied by a final burst of star formation in the bulge. The variation in spatial-fit parameters with wavelength also allows us to measure approximate colour gradients in the individual components. Such gradients were detected separately in both bulges and discs, in the sense that redder light is systematically more centrally concentrated in all components. However, a search for radial variations in the absorption line strengths determined for the individual components revealed that they are absent from the vast majority of S0 discs and bulges. The absence of gradients in line indices for most galaxies implies that the colour gradient cannot be attributed to age or metallicity variations, and is therefore most likely associated with varying degrees of obscuration by dust.
We examine bounds on adiabatic and isocurvature density fluctuations from $\mu$-type spectral distortions of the cosmic microwave background (CMB). Studies of such distortion are complimentary to CMB measurements of the spectral index and its running, and will help to constrain these parameters on significantly smaller scales. We show that a detection on the order of $\mu \sim 10^{-7}$ would strongly be at odds with the standard cosmological model of a nearly scale-invariant spectrum of adiabatic perturbations. Further, we find that given the current CMB constraints on the isocurvature mode amplitude, a nearly scale-invariant isocurvature mode (common in many curvaton models) cannot produce significant $\mu$-distortion. Finally, we show that future experiments will strongly constrain the amplitude of the isocurvature modes with a highly blue spectrum as predicted by certain axion models.
Recent cosmological data for very large distances challenge the validity of the standard cosmological model. Motivated by the observed spatial flatness the accelerating expansion and the various anisotropies with preferred axes in the universe we examine the consequences of the simple hypothesis that the three-dimensional space has a global R^2 X S^1 topology. We take the radius of the compactification to be the observed cosmological scale beyond which the accelerated expansion starts. We derive the induced corrections to the Newton's gravitational potential and we find that for distances smaller than the S^1-radius the leading 1/r-term is corrected by convergent power series of multipole form in the polar angle making explicit the induced anisotropy by the compactified third dimension. On the other hand, for distances larger than the compactification scale the asymptotic behavior of the potential exhibits a logarithmic dependence with exponentially small corrections. The change of Newton's force from 1/r^2 to 1/r behavior implies a weakening of the deceleration for the expanding universe. Such topologies can also be created locally by standard Newtonian axially symmetric mass distributions with periodicity along the symmetry axis. In such cases we can use our results to obtain measurable modifications of Newtonian orbits for small distances and flat rotation spectra, for large distances at the galactic level.
We present BayeSED, a general purpose tool for doing Bayesian analysis of SEDs by using whatever pre-existing model SED libraries or their linear combinations. The artificial neural networks (ANNs), principal component analysis (PCA) and multimodal nested sampling (MultiNest) techniques are employed to allow a highly efficient sampling of posterior distribution and the calculation of Bayesian evidence. As a demonstration, we apply this tool to a sample of hyperluminous infrared galaxies (HLIRGs). The Bayesian evidences obtained for a pure Starburst, a pure AGN, and a linear combination of Starburst+AGN models show that the Starburst+AGN model have the highest evidence for all galaxies in this sample. The Bayesian evidences for the three models and the estimated contributions of starburst and AGN to infrared luminosity show that HLIRGs can be classified into two groups: one dominated by starburst and the other dominated by AGN. Other parameters and corresponding uncertainties about starburst and AGN are also estimated by using the model with the highest Bayesian evidence. We found that the starburst region of the HLIRGs dominated by starburst tends to be more compact and has a higher fraction of OB star than that of HLIRGs dominated by AGN. Meanwhile, the AGN torus of the HLIRGs dominated by AGN tend to be more dusty than that of HLIRGs dominated by starburst. These results are consistent with previous researches, but need to be tested further with larger samples. Overall, we believe that BayeSED could be a reliable and efficient tool for exploring the nature of complex systems such as dust-obscured starburst-AGN composite systems from decoding their SEDs.
We study star formation (SF) in very active environments, in luminous IR galaxies, which are often interacting. A variety of phenomena are detected, such as central starbursts, circumnuclear SF, obscured SNe tracing the history of recent SF, massive super star clusters, and sites of strong off-nuclear SF. All of these can be ultimately used to define the sequence of triggering and propagation of star-formation and interplay with nuclear activity in the lives of gas rich galaxy interactions and mergers. In this paper we present analysis of high-spatial resolution integral field spectroscopy of central regions of two interacting LIRGs. We detect a nuclear 3.3 um PAH ring around the core of NGC 1614 with thermal-IR IFU observations. The ring's characteristics and relation to the strong star-forming ring detected in recombination lines are presented, as well as a scenario of an outward expanding starburst likely initiated with a (minor) companion detected within a tidal feature. We then present NIR IFU observations of IRAS 19115-2124, aka the Bird, which is an intriguing triple encounter. The third component is a minor one, but, nevertheless, is the source of 3/4 of the SFR of the whole system. Gas inflows and outflows are detected at the locations of the nuclei. Finally, we briefly report on our on-going NIR adaptive optics imaging survey of several dozen LIRGs. We have detected highly obscured core-collapse SNe in the central kpc, and discuss the statistics of "missing SNe" due to dust extinction. We are also determining the characteristics of hundreds of super star clusters in and around the core regions of LIRGs, as a function of host-galaxy properties.
We present a comprehensive study of 250,000 galaxies targeted by the Baryon Oscillation Spectroscopic Survey (BOSS) up to z {\approx} 0.7 with the specific goal of identifying and characterising a population of galaxies that has followed passive evolution (no mergers) as closely as possible. We compute a likelihood that each BOSS galaxy is a progenitor of the Luminous Red Galaxies (LRGs) sample, targeted by SDSS-I/II up z {\approx} 0.5, by using the fossil record of LRGs and their inferred star-formation histories, metallicity histories and dust content. We determine merger rates, luminosity growth rates and the evolution of the large-scale clustering between the two surveys, and we investigate the effect of using different stellar population synthesis models in our conclusions. We demonstrate that our sample is slowly evolving (of the order of 2 {\pm} 1.5% Gyr-1 by merging) by computing the change in weighted luminosity-per-galaxy between the two samples, and that this result is robust to our choice of stellar population models. Our conclusions refer to the bright and massive end of the galaxy population, with Mi0.55 < -22, and M* > 1e11.2M{\odot}, corresponding roughly to 95% and 40% of the LRGs and BOSS galaxy populations, respectively. Our analysis further shows that any possible excess of flux in BOSS galaxies, when compared to LRGs, from potentially unresolved targets at z {\approx} 0.55 must be less than 1% in the r0.55-band (approximately equivalent to the g-band in the rest-frame of galaxies at z = 0.55). We find an evolution of the large-scale clustering that is consistent with dynamical passive evolution, assuming a standard cosmology. We conclude that our likelihoods give a weighted sample that is as clean and as close to passive evolution (in dynamical terms) as possible, and that is optimal for cosmological studies.
In this paper we find new scaling laws for the evolution of $p$-brane networks in $N+1$-dimensional Friedmann-Robertson-Walker universes in the weakly-interacting limit, giving particular emphasis to the case of cosmic superstrings ($p=1$) living in a universe with three spatial dimensions (N=3). In particular, we show that, during the radiation era, the root-mean-square velocity is ${\bar v} =1/{\sqrt 2}$ and the characteristic length of non-interacting cosmic string networks scales as $L \propto a^{3/2}$ ($a$ is the scale factor), thus leading to string domination even when gravitational backreaction is taken into account. We demonstrate, however, that a small non-vanishing constant loop chopping efficiency parameter $\tilde c$ leads to a linear scaling solution with constant $L H \ll 1$ ($H$ is the Hubble parameter) and ${\bar v} \sim 1/{\sqrt 2}$ in the radiation era, which may allow for a cosmologically relevant cosmic string role even in the case of light strings. We also determine the impact that the radiation-matter transition has on the dynamics of weakly interacting cosmic superstring networks.
The Alcubierre warp drive allows a spaceship to travel at an arbitrarily large global velocity by deforming the spacetime in a bubble around the spaceship. Little is known about the interactions between massive particles and the Alcubierre warp drive, or the effects of an accelerating or decelerating warp bubble. We examine geodesics representative of the paths of null and massive particles with a range of initial velocities from -c to c interacting with an Alcubierre warp bubble travelling at a range of globally subluminal and superluminal velocities on both constant and variable velocity paths. The key results for null particles match what would be expected of massive test particles as they approach +/- c. The increase in energy for massive and null particles is calculated in terms of v_s, the global ship velocity, and v_p, the initial velocity of the particle with respect to the rest frame of the origin/destination of the ship. Particles with positive v_p obtain extremely high energy and velocity and become "time locked" for the duration of their time in the bubble, experiencing very little proper time between entering and eventually leaving the bubble. When interacting with an accelerating bubble, any particles within the bubble at the time receive a velocity boost that increases or decreases the magnitude of their velocity if the particle is moving towards the front or rear of the bubble respectively. If the bubble is decelerating, the opposite effect is observed. Thus Eulerian matter is unaffected by bubble accelerations/decelerations. The magnitude of the velocity boosts scales with the magnitude of the bubble acceleration/deceleration.
We study cosmological dynamics of a canonical bulk scalar field in the DGP setup within a superpotential approach. We show that the normal branch of this DGP-inspired model realizes a late-time de Sitter expansion on the brane. We extend this study to the case that the bulk contains a phantom scalar field. Our detailed study in the supergravity-style analysis reveals some yet unexplored aspects of cosmological dynamics of bulk scalar field in the normal DGP setup. Some clarifying examples along with numerical analysis of the model parameter space are presented in each case.
We analyze here the final fate of complete gravitational collapse of a massless scalar field within general relativity. A class of dynamical solutions with initial data close to the Friedmann-Lemaitre-Robertson-Walker (FLRW) collapse model is explicitly given and the Einstein equations are integrated numerically in a neighborhood of the center. We show that the initial data space is evenly divided between the dynamical evolutions that terminate in a black hole final state and those that produce a locally naked singularity. We comment on the genericity aspects of the collapse end-states and the connection to cosmic censorship conjecture is pointed out.
We extend the halo-independent method of Fox, Liu, and Weiner to include energy resolution and efficiency with arbitrary energy dependence, making it more suitable for experiments to use in presenting their results. Then we compare measurements and upper limits on the direct detection of low mass (~10 GeV) weakly interacting massive particles (WIMPs) with spin-independent interactions, including the preliminary upper limit on the annual modulation amplitude from the CDMS collaboration. We find that isospin-symmetric couplings are severely constrained, but isospin-violating couplings are still possible if for example the local Galactic escape speed is small, as found in recent surveys.
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(abridged) Quasar absorption lines provide a precise test of the assumed
constancy of the fundamental constants of physics. We have investigated
potential changes in the fine-structure constant, alpha, and the
proton-to-electron mass ratio, mu.
The many-multiplet method allows one to use optical fine-structure
transitions to constrain (Delta alpha)/alpha at better than the 10^(-5) level.
We present a new analysis of 154 quasar absorbers with 0.2 < z <3.7 in VLT/UVES
spectra. From these absorbers we find 2.2 sigma evidence for angular variations
in alpha under a dipole+monopole model. Combined with previous Keck/HIRES
observations, we find 4.1 sigma evidence for angular (and therefore spatial)
variations in alpha, with maximal increase of alpha occurring in the direction
RA=(17.3 +/- 1.0) hr, dec=(-61 +/- 10) deg. Under a model where the observed
effect is proportional to the lookback-time distance the significance increases
to 4.2 sigma. Dipole models fitted to the VLT and Keck samples and models
fitted to z<1.6 and z>1.6 sub-samples independently yield consistent estimates
of the dipole direction, which suggests that the effect is not caused by
telescope systematics. We consider a number of systematic effects and show that
they are unable to explain the observed dipole effect.
We have used spectra of the quasars Q0405-443, Q0347-383 and Q0528-250 from
VLT/UVES to investigate the absorbers at z=2.595, 3.025 and 2.811 in these
spectra respectively. We find that (Delta mu)/mu=(10.1 +/- 6.6) x 10^(-6), (8.2
+/- 7.5) x 10^(-6) and (-1.4 +/- 3.9) x 10^(-6) in these absorbers
respectively. A second spectrum of Q0528-250 provides an additional constraint
of (Delta mu)/mu=(0.2 +/- 3.2_stat +/- 1.9_sys) x 10^(-6). The weighted mean of
these values yields (Delta mu)/mu=(1.7 +/- 2.4) x 10^(-6), the most precise
constraint on evolution in mu at z>1.
We present a Hubble Space Telescope/Wide Field Planetary Camera 2 weak-lensing study of A520, where a previous analysis of ground-based data suggested the presence of a dark mass concentration. We map the complex mass structure in much greater detail leveraging more than a factor of three increase in the number density of source galaxies available for lensing analysis. The "dark core" that is coincident with the X-ray gas peak, but not with any stellar luminosity peak is now detected with more than 10 sigma significance. The ~1.5 Mpc filamentary structure elongated in the NE-SW direction is also clearly visible. Taken at face value, the comparison among the centroids of dark matter, intracluster medium, and galaxy luminosity is at odds with what has been observed in other merging clusters with a similar geometric configuration. To date, the most remarkable counter-example might be the Bullet Cluster, which shows a distinct bow-shock feature as in A520, but no significant weak-lensing mass concentration around the X-ray gas. With the most up-to-date data, we consider several possible explanations that might lead to the detection of this peculiar feature in A520. However, we conclude that none of these scenarios can be singled out yet as the definite explanation for this puzzle.
Using the photometric redshifts of galaxies from the Sloan Digital Sky Survey III (SDSS-III), we identify 132,684 clusters in the redshift range of 0.05<z<0.8. Monte Carlo simulations show that the false detection rate is less than 6% for the whole sample. The completeness is more than 95% for clusters with a mass of M_{200}>1.0*10^{14} M_{\odot} in the redshift range of 0.05<z<0.42, while clusters of z>0.42 are less complete and have a biased smaller richness than the real one due to incompleteness of member galaxies. We compare our sample with other cluster samples, and find that more than 90% of previously known rich clusters of 0.05<z<0.42 are matched with clusters in our sample. Richer clusters tend to have more luminous brightest cluster galaxies (BCGs). Correlating with X-ray and the Planck data, we show that the cluster richness is closely related to the X-ray luminosity, temperature and Sunyaev-Zel'dovich measurements. Comparison of the BCGs with the SDSS luminous red galaxies (LRGs) sample shows that 25% of LRGs are BCGs of our clusters, and 36% of LRGs are cluster member galaxies. In our cluster sample, 66% of BCGs satisfy the color cuts of the SDSS LRGs selection criteria.
We report CO detections in 17 out of 19 infrared ultraluminous QSO (IR QSO) hosts observed with the IRAM 30m telescope. The cold molecular gas reservoir in these objects is in a range of 0.2--2.1$\times 10^{10}M_\odot$ (adopting a CO-to-${\rm H_2}$ conversion factor $\alpha_{\rm CO}=0.8 M_\odot {\rm (K km s^{-1} pc^2)^{-1}}$). We find that the molecular gas properties of IR QSOs, such as the molecular gas mass, star formation efficiency ($L_{\rm FIR}/L^\prime_{\rm CO}$) and the CO (1-0) line widths, are indistinguishable from those of local ultraluminous infrared galaxies (ULIRGs). A comparison of low- and high-redshift CO detected QSOs reveals a tight correlation between L$_{\rm FIR}$ and $L^\prime_{\rm CO(1-0)}$ for all QSOs. This suggests that, similar to ULIRGs, the far-infrared emissions of all QSOs are mainly from dust heated by star formation rather than by active galactic nuclei (AGNs), confirming similar findings from mid-infrared spectroscopic observations by {\it Spitzer}. A correlation between the AGN-associated bolometric luminosities and the CO line luminosities suggests that star formation and AGNs draw from the same reservoir of gas and there is a link between star formation on $\sim$ kpc scale and the central black hole accretion process on much smaller scales.
In the theory of structure formation, galaxies are biased tracers of the underlying matter density field. The statistical relation between galaxy and matter density field is commonly referred as galaxy bias. In this paper, we test the linear bias model with weak-lensing and galaxy clustering measurements in the 2 square degrees COSMOS field (Scoville et al. 2007). We estimate the bias of galaxies between redshifts z=0.2 and z=1, and over correlation scales between R=0.2 h^-1 Mpc and R=15 h^-1 Mpc. We focus on three galaxy samples, selected in flux (simultaneous cuts I_814W < 26.5 and K_s < 24), and in stellar-mass (10^9 < M_* < 10^10 h^-2 Msun and 10^10 < M^*< 10^11 h^-2 Msun). At scales R > 2 h^-1 Mpc, our measurements support a model of bias increasing with redshift. The Tinker et al. (2010) fitting function provides a good fit to the data. We find the best fit mass of the galaxy halos to be log(M_200 h^-1 Msun) = 11.7^+0.6_-1.3 and log(M_200 h^-1 Msun) = 12.4^+0.2_-2.9 respectively for the low and high stellar-mass samples. In the halo model framework, bias is scale-dependent with a change of slope at the transition scale between the one and the two halo terms. We detect a scale-dependence of bias with a turn-down at scale R=2.3\pm1.5 h^-1 Mpc, in agreement with previous galaxy clustering studies. We find no significant amount of stochasticity, suggesting that a linear bias model is sufficient to describe our data. We use N-body simulations to quantify both the amount of cosmic variance and systematic errors in the measurement.
One of the fundamental problems in extracting the cosmic microwave background signal (CMB) from millimeter/submillimeter observations is the pollution by emission from the Milky Way: synchrotron, free-free, and thermal dust emission. To extract the fundamental cosmological parameters from CMB signal, it is mandatory to minimize this pollution since it will create systematic errors in the CMB power spectra. In previous investigations, it has been demonstrated that the neural network method provide high quality CMB maps from temperature data. Here the analysis is extended to polarization maps. As a concrete example, the WMAP 7-year polarization data, the most reliable determination of the polarization properties of the CMB, has been analysed. The analysis has adopted the frequency maps, noise models, window functions and the foreground models as provided by the WMAP Team, and no auxiliary data is included. Within this framework it is demonstrated that the network can extract the CMB polarization signal with no sign of pollution by the polarized foregrounds. The errors in the derived polarization power spectra are improved compared to the errors derived by the WMAP Team.
Galaxies are not uniformly distributed in space. On large scales the Universe displays coherent structure, with galaxies residing in groups and clusters on scales of ~1-3 Mpc/h, which lie at the intersections of long filaments of galaxies that are >10 Mpc/h in length. Vast regions of relatively empty space, known as voids, contain very few galaxies and span the volume in between these structures. This observed large scale structure depends both on cosmological parameters and on the formation and evolution of galaxies. Using the two-point correlation function, one can trace the dependence of large scale structure on galaxy properties such as luminosity, color, stellar mass, and track its evolution with redshift. Comparison of the observed galaxy clustering signatures with dark matter simulations allows one to model and understand the clustering of galaxies and their formation and evolution within their parent dark matter halos. Clustering measurements can determine the parent dark matter halo mass of a given galaxy population, connect observed galaxy populations at different epochs, and constrain cosmological parameters and galaxy evolution models. This chapter describes the methods used to measure the two-point correlation function in both redshift and real space, presents the current results of how the clustering amplitude depends on various galaxy properties, and discusses quantitative measurements of the structures of voids and filaments. The interpretation of these results with current theoretical models is also presented.
We run N-body smoothed particle hydrodynamics (SPH) simulations of a Milky Way sized galaxy. The code takes into account hydrodynamics, self-gravity, star formation, supernova and stellar wind feedback, radiative cooling and metal enrichment. The simulated galaxy is a barred-spiral galaxy consisting of a stellar and gas disc, enveloped in a static dark matter halo. Similar to what is found in our pure N-body simulation of a non-barred galaxy in Grand et al. (2012), we find that the spiral arms are transient features whose pattern speeds decrease with radius, in such a way that the pattern speed is almost equal to the rotation of star particles. We trace particle motion around the spiral arms at different radii, and demonstrate that there are star particles that are drawn towards and join the arm from behind (in front of) the arm and migrate toward the outer (inner) regions of the disc until the arm disappears as a result of their transient nature. We see this migration over the entire radial range analysed, which is a consequence of the spiral arm co-rotating at all radii. The migration is shown to largely preserve circular orbits (within a few percent). We also demonstrate that there is no significant offset of different star forming tracers across the spiral arm, which is also inconsistent with the prediction of classical density wave theory.
We spectrally fit the GeV gamma-ray flares recently-observed in the Crab Nebula by considering a small blob Lorentz-boosted towards us. We point out that the corresponding inverse-Compton flare at TeV--PeV region is more enhanced than synchrotron by a Lorentz factor square \sim \Gamma^2, which is already excluding \Gamma \gtrsim 200 and will be detected by future TeV - PeV observatories, CTA, Tibet AS + MD and LHAASO for \Gamma \gtrsim 30. We also show that PeV photons emitted from the Crab Nebula are absorbed by Cosmic Microwave Background radiation through electron-positron pair creation.
The decay of a false vacuum of unbroken B-L symmetry is an intriguing and testable mechanism to generate the initial conditions of the hot early universe. If B-L is broken at the grand unification scale, the false vacuum phase yields hybrid inflation, ending in tachyonic preheating. The dynamics of the B-L breaking Higgs field and thermal processes produce an abundance of heavy neutrinos whose decays generate entropy, baryon asymmetry and gravitino dark matter. We study the phase transition for the full supersymmetric Abelian Higgs model. For the subsequent reheating process we give a detailed time-resolved description of all particle abundances. The competition of cosmic expansion and entropy production leads to an intermediate period of constant 'reheating' temperature, during which baryon asymmetry and dark matter are produced. Consistency of hybrid inflation, leptogenesis and gravitino dark matter implies relations between neutrino parameters and superparticle masses, in particular a lower bound on the gravitino mass of 10 GeV.
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We present H\alpha{} fluxes, star formation rates (SFRs) and equivalent widths (EWs) for a sample of 156 nearby galaxies observed in the 12CO J=3-2 line as part of the James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey. These are derived from images and values in the literature and from new H\alpha{} images for 72 galaxies which we publish here. We describe the sample, observations and procedures to extract the H\alpha{} fluxes and related quantities. We discuss the SFR properties of our sample and confirm the well-known correlation with galaxy luminosity, albeit with high dispersion. Our SFRs range from 0.1 to 11 Msun yr-1 with a median SFR value for the complete sample of 0.2 Msun yr-1. This median values is somewhat lower than similar published measurements, which we attribute, in part, to our sample being HI-selected and, thus, not biased towards high SFRs as has frequently been the case in previous studies. Additionally, we calculate internal absorptions for the H\alpha{} line, A(H\alpha{}), which are lower than many of those used in previous studies. Our derived EWs, which range from 1 to 880\AA{} with a median value of 27\AA{}, show little dependence with luminosity but rise by a factor of five from early- to late-type galaxies. This paper is the first in a series aimed at comparing SFRs obtained from H\alpha{} imaging of galaxies with information derived from other tracers of star formation and atomic and molecular gas.
We have discovered a 2.5 Mpc (projected) long filament of infrared-bright galaxies connecting two of the three ~5x10^14 Msun clusters making up the RCS 2319+00 supercluster at z=0.9. The filament is revealed in a deep Herschel Spectral and Photometric Imaging REceiver (SPIRE) map that shows 250-500um emission associated with a spectroscopically identified filament of galaxies spanning two X-ray bright cluster cores. We estimate that the total (8-1000um) infrared luminosity of the filament is Lir~5x10^12 Lsun, which, if due to star formation alone, corresponds to a total SFR 900 Msun/yr. We are witnessing the scene of the build-up of a >10^15 Msun cluster of galaxies, seen prior to the merging of three massive components, each of which already contains a population of red, passive galaxies that formed at z>2. The infrared filament demonstrates that significant stellar mass assembly is taking place in the moderate density, dynamically active circumcluster environments of the most massive clusters at high-redshift, and this activity is concomitant with the hierarchical build-up of large scale structure.
We study satellite galaxy abundances in SDSS by counting photometric galaxies around isolated bright primaries. We present results as a function of the luminosity, stellar mass and colour of the satellites, and of the stellar mass and colour of the primaries. For massive primaries the luminosity and stellar mass functions of satellites are similar in shape to those of field galaxies, but for lower mass primaries they are significantly steeper. The steepening is particularly marked for the stellar mass function. Satellite abundance increases strongly with primary stellar mass, approximately in proportion to expected dark halo mass. Massive red primaries have up to a factor of 2 more satellites than blue ones of the same stellar mass. Satellite galaxies are systematically redder than field galaxies of the same stellar mass. Satellites are also systematically redder around more massive primaries. At fixed primary mass, they are redder around red primaries. We select similarly isolated galaxies from mock catalogues based on the simulations of Guo et al.(2011) and analyze them in parallel with the SDSS data. The simulation reproduces all the above trends qualitatively, except for the steepening of the satellite luminosity and stellar mass functions. Model satellites, however, are systematically redder than in the SDSS, particularly at low mass and around low-mass primaries. Simulated haloes of a given mass have satellite abundances that are independent of central galaxy colour, but red centrals tend to have lower stellar masses, reflecting earlier quenching of their star formation by feedback. This explains the correlation between satellite abundance and primary colour in the simulation. The correlation between satellite colour and primary colour arises because red centrals live in haloes which are more massive, older and more gas-rich, so that satellite quenching is more efficient.
Features in the inflaton potential that are traversed in much less than an e-fold of the expansion can produce observably large non-Gaussianity. In these models first order corrections to the curvature mode function evolution induce effects at second order in the slow roll parameters that are generically greater than ~ 10% and can reach order unity for order unity power spectrum features. From a complete first order expression in generalized slow-roll, we devise a computationally efficient method that is as simple to evaluate as the leading order one and implements consistency relations in a controlled fashion. This expression matches direct numerical computation for step potential models of the dominant bispectrum configurations to better than 1% when features are small and 10% when features are order unity.
We investigate the three-dimensional structure of the nearby edge-on spiral galaxy NGC 891 using 3D Monte Carlo radiative transfer models, with realistic spiral structure and fractally clumped dust. Using the spiral and clumpiness parameters found from recently completed scattered light models we produce lower resolution SED models which reproduce the global UV-to-FIR SED of NGC 891. Our models contain a color gradient across the major axis of the galaxy - similar to what is seen in images of the NGC 891. With minor adjustment our SED models are able to match the majority of M51's SED, a similar galaxy at a near face-on different inclination.
The cosmological distance ladder crucially depends on classical Cepheids (with P=3-80 days), which are primary distance indicators up to 33 Mpc. Within this volume, very few SNe Ia have been calibrated through classical Cepheids, with uncertainty related to the non-linearity and the metallicity dependence of their period-luminosity (PL) relation. Although a general consensus on these effects is still not achieved, classical Cepheids remain the most used primary distance indicators. A possible extension of these standard candles to further distances would be important. In this context, a very promising new tool is represented by the ultra-long period (ULP) Cepheids (P \geq 80 days), recently identified in star-forming galaxies. Only a small number of ULP Cepheids have been discovered so far. Here we present and analyse the properties of an updated sample of 37 ULP Cepheids observed in galaxies within a very large metallicity range of 12+log(O/H) from ~7.2 to 9.2 dex. We find that their location in the colour(V-I)-magnitude diagram as well as their Wesenheit (V-I) index-period (WP) relation suggests that they are the counterparts at high luminosity of the shorter-period (P \leq 80 days) classical Cepheids. However, a complete pulsation and evolutionary theoretical scenario is needed to properly interpret the true nature of these objects. We do not confirm the flattening in the studied WP relation suggested by Bird et al. (2009). Using the whole sample, we find that ULP Cepheids lie around a relation similar to that of the LMC, although with a large spread (~0.4 mag).
It has recently been claimed that the Hubble Sphere represents a previously unknown limit to our view of the universe, with light we detect today coming from a proper distance less than this "Cosmic Horizon" at the present time. By considering the paths of light rays in several cosmologies, we show that this claim is not generally true. In particular, in cosmologies dominated by phantom energy (with an equation of state of \omega < -1) the proper distance to the Hubble Sphere decreases, and light rays can cross it more than once in both directions; such behaviour further diminishes the claim that the Hubble Sphere is a fundamental, but unrecognised, horizon in the universe.
Aims. We study the analogy between local U/LIRGs and high-z massive SFGs by comparing basic H{\alpha} structural characteristics, like size, luminosity and Star Formation Rate (SFR) surface density, in an homogeneous way (i.e. same tracer and size definition, similar physical scales). Methods. We use Integral Field Spectroscopy based H{\alpha} emission maps for a representative sample of 54 local U/LIRGs (66 galaxies). From this initial sample we select 26 objects with H{\alpha} luminosities (L(H{\alpha})) similar to those of massive (i.e. M\ast \sim 10^10 M\odot or larger) SFGs at z \sim 2, and probing similar physical scales. Results. The sizes of the H{\alpha} emitting region in the sample of local U/LIRGs span a large range, with r1/2(H{\alpha}) from 0.2 to 7 kpc. However, about 2/3 of local U/LIRGs with Lir > 10^11.4 L\odot have compact H{\alpha} emission (i.e. r1/2 < 2 kpc). The comparison sample of local U/LIRGs also shows a higher fraction (59%) of objects with compact H{\alpha} emission than the high-z sample (25%). This gives further support to the idea that for this luminosity range the size of the star forming region is a distinctive factor between local and distant galaxies of similar SF rates. However, when using H{\alpha} as a tracer for both local and high-z samples, the differences are smaller than the ones recently reported using a variety of other tracers. Despite of the higher fraction of galaxies with compact H{\alpha} emission, a sizable group (\sim 1/3) of local U/LIRGs are large (i.e. r1/2 > 2 kpc). These are systems showing pre-coalescence merger activity and they are indistinguishable from the massive high-z SFGs galaxies in terms of their H{\alpha} sizes, luminosity and SFR surface densities.
The wide-area imaging surveys with the {\it Herschel} Space Observatory at sub-mm wavelengths have now resulted in catalogs of order one hundred thousand dusty, star-burst galaxies. We make a statistical estimate of $N(z)$ using a clustering analysis of sub-mm galaxies detected at each of 250, 350 and 500 $\mu$m from the Herschel Multi-tiered Extragalactic Survey (HerMES) centered on the Bo\"{o}tes field. We cross-correlate {\it Herschel} galaxies against galaxy samples at optical and near-IR wavelengths from the Sloan Digital Sky Survey (SDSS), the NOAO Deep Wide Field Survey (NDWFS) and the Spitzer Deep Wide Field Survey (SDWFS). We create optical and near-IR galaxy samples based on their photometric or spectroscopic redshift distributions and test the accuracy of those redshift distributions with similar galaxy samples defined with catalogs of the Cosmological Evolution Survey (COSMOS), as the COSMOS field has superior spectroscopy coverage. We model-fit the clustering auto and cross-correlations of {\it Herschel} and optical/IR galaxy samples to estimate $N(z)$ and clustering bias factors. The $S_{350} > 20$ mJy galaxies have a bias factor varying with redshift as $b(z)=1.0^{+1.0}_{-0.5}(1+z)^{1.2^{+0.3}_{-0.7}}$. This bias and the redshift dependence is broadly in agreement with galaxies that occupy dark matter halos of mass in the range of 10$^{12}$ to 10$^{13}$ M$_{\sun}$. We find that the redshift distribution peaks around $z \sim 0.5$ to 1 for galaxies selected at 250 $\mu$m with an average redshift of $< z > = 1.8 \pm 0.2$. For 350 and 500 $\mu$m-selected SPIRE samples the peak shifts to higher redshift, but the average redshift remains the same with a value of $1.9 \pm 0.2$.
Morphological classification of dwarf galaxies into early and late type, though can account for some of their origin and characteristics but does not help to study their formation mechanism. So an objective classification using Principal Component analysis together with K means Cluster Analysis of these dwarf galaxies and their globular clusters is carried out to overcome this problem. It is found that the classification of dwarf galaxies in the Local Volume is irrespective of their morphological indices. The more massive (MV 0 < -13.7) galaxies evolve through self-enrichment and harbor dynamically less evolved younger globular clusters (GCs) whereas fainter galaxies (MV 0 > -13.7) are influenced by their environment in the star formation process.
We investigate the effect of backreaction due to inhomogeneities on the evolution of the present universe by considering a two-scale model within the Buchert framework. Taking the observed present acceleration of the universe as an essential input, we study the effect of inhomogeneities in the future evolution. We find that the backreaction from inhomogeneities causes the acceleration to slow down in the future for a range of initial configurations and model parameters. The present acceleration ensures formation of the cosmic event horizon, and our analysis brings out how the effect of the event horizon could further curtail the global acceleration, and even lead in certain cases to the emergence of a future decelerating epoch.
A key goal of many Cosmic Microwave Background experiments is the detection of gravitational waves, through their B-mode polarization signal at large scales. To extract such a signal requires modelling contamination from the Galaxy. Using the Planck experiment as an example, we investigate the impact of incorrectly modelling foregrounds on estimates of the polarized CMB, quantified by the bias in tensor-to-scalar ratio r, and optical depth tau. We use a Bayesian parameter estimation method to estimate the CMB, synchrotron, and thermal dust components from simulated observations spanning 30-353 GHz, starting from a model that fits the simulated data, returning r<0.03 at 95% confidence for an r=0 model, and r=0.09+-0.03 for an r=0.1 model. We then introduce a set of mismatches between the simulated data and assumed model. Including a curvature of the synchrotron spectral index with frequency, but assuming a power-law model, can bias r high by ~1-sigma (delta r ~ 0.03). A similar bias is seen for thermal dust with a modified black-body frequency dependence, incorrectly modelled as a power-law. If too much freedom is allowed in the model, for example fitting for spectral indices in 3 degree pixels over the sky with physically reasonable priors, we find r can be biased up to ~3-sigma high by effectively setting the indices to the wrong values. Increasing the signal-to-noise ratio by reducing parameters, or adding additional foreground data, reduces the bias. We also find that neglecting a 1% polarized free-free or spinning dust component has a negligible effect on r. These tests highlight the importance of modelling the foregrounds in a way that allows for sufficient complexity, while minimizing the number of free parameters.
The cluster Abell 2163 is a merging system of several subclusters with complex dynamics. It presents exceptional X-rays properties (high temperature and luminosity), suggesting that it is a very massive cluster. Recent 2D analysis of the gas distribution has revealed a complex and multiphase structure. This paper presents a wide-field weak lensing study of the dark matter distribution in the cluster in order to provide an alternative vision of the merging status of the cluster. The 2D mass distribution is built and compared to the galaxies and gas distributions. A Bayesian method, implemented in the Im2shape software, was used to fit the shape parameters of the faint background galaxies and to correct for PSF smearing. A careful color selection on the background galaxies was applied to retrieve the weak lensing signal. Shear signal was measured out to more than 2 Mpc (~12' from the center). The radial shear profile was fit with different parametric mass profiles. The 2D mass map is built from the shear distribution and used to identify the different mass components. The 2D mass map agrees with the galaxy distribution, while the total mass inferred from weak lensing shows a strong discrepancy to the X-ray deduced mass. Regardless of the method used, the virial mass M200 falls in the range 8 to 14 10^14 Msol inside the virial radius (~ 2.0 Mpc), a value that is two times less than the mass deduced from X-rays. The central mass clump appears bimodal in the dark matter distribution, with a mass ratio ~3:1 between the two components. The infalling clump A2163-B is detected in weak lensing as an independent entity. All these results are interpreted in the context of a multiple merger seen less than 1Gyr after the main crossover.
Contrary to the common view voids have very complex internal structure and dynamics. Here we show how the hierarchy of structures in the density field inside voids is reflected by a similar hierarchy of structures in the velocity field. Voids defined by dense filaments and clusters can de described as simple expanding domains with coherent flows everywhere except at their boundaries. At scales smaller that the void radius the velocity field breaks into expanding sub-domains corresponding to sub- voids. These sub-domains break into even smaller sub-sub domains at smaller scales resulting in a nesting hierarchy of locally expanding domains. The ratio between the magnitude of the velocity field responsible for the expansion of the void and the velocity field defining the sub voids is approximately one order of magnitude. The small-scale components of the velocity field play a minor role in the shaping of the voids but they define the local dynamics directly affecting the processes of galaxy formation and evolution. The super-Hubble expansion inside voids makes them cosmic magnifiers by stretching their internal primordial density fluctuations allowing us to probe the small scales in the primordial density field. Voids also act like time machines by "freezing" the development of the medium-scale density fluctuations responsible for the formation of the tenuous web of structures seen connecting proto galaxies in computer simulations. As a result of this freezing haloes in voids can remain "connected" to this tenuous web until the present time. This may have an important effect in the formation and evolution of galaxies in voids by providing an efficient gas accretion mechanism via coherent low-velocity streams that can keep a steady inflow of matter for extended periods of time.
We discuss the implications for cosmic microwave background (CMB) observables, of a class of pre-inflationary dynamics suggested by string models where SUSY is broken due to the presence of D-branes and orientifolds preserving incompatible portions of it. In these models the would-be inflaton is forced to emerge from the initial singularity climbing up a mild exponential potential, until it bounces against a steep exponential potential of "brane SUSY breaking" scenarios, and as a result the ensuing descent gives rise to an inflationary epoch that begins when the system is still well off its eventual attractor. If a pre-inflationary climbing phase of this type had occurred within 6-7 e-folds of the horizon exit for the largest observable wavelengths, displacement off the attractor and initial-state effects would conspire to suppress power in the primordial scalar spectrum, enhancing it in the tensor spectrum and typically superposing oscillations on both. We investigate these imprints on CMB observables over a range of parameters, examine their statistical significance, and provide a semi-analytic rationale for our results. It is tempting to ascribe at least part of the large-angle anomalies in the CMB to pre-inflationary dynamics of this type.
We compute the corrections of thermal photons on the effective potential for the linear sigma model of QCD. Since we are interested in temperatures lower than the confinement temperature, we consider the scalar fields to be out of equilibrium. Two of the scalar field are uncharged while the other two are charged under the U(1) gauge symmetry of electromagnetism. We find that the induced thermal terms in the effective potential can stabilize the embedded pion string, a string configuration which is unstable in the vacuum. Our results are applicable in a more general context and demonstrate that embedded string configurations arising in a wider class of field theories can be stabilized by thermal effects. Another well-known example of an embedded string which can be stabilized by thermal effects is the electroweak Z-string. We discuss the general criteria for thermal stabilization of embedded defects.
In this work we revisit Wald's cosmic no-hair theorem in the context of accelerating Bianchi cosmologies for a generic cosmic fluid with non-vanishing anisotropic stress tensor and when the fluid energy momentum tensor is of the form of a cosmological constant term plus a piece which does not respect strong or dominant energy conditions. Such a fluid is the one appearing in inflationary models. We show that for such a system anisotropy may grow, in contrast to the cosmic no-hair conjecture. In particular, for a generic inflationary model we show that there is an upper bound on the growth of anisotropy. For slow-roll inflationary models our analysis can be refined further and the upper bound is found to be of the order of slow-roll parameters. We examine our general discussions and our extension of Wald's theorem for three classes of slow-roll inflationary models, generic multi-scalar field driven models, anisotropic models involving U(1) gauge fields and the gauge-flation scenario.
Particle production of an Abelian vector boson field with an axial coupling is investigated. The conditions for the generation of scale invariant spectra for the vector field transverse components are obtained. If the vector field contributes to the curvature perturbation in the Universe, scale-invariant particle production enables it to give rise to statistical anisotropy in the spectrum and bispectrum of cosmological perturbations. The axial coupling allows particle production to be parity violating, which in turn can generate parity violating signatures in the bispectrum. The conditions for parity violation are derived and the observational signatures are obtained in the context of the vector curvaton paradigm. Two concrete examples are presented based on realistic particle theory.
In this paper we study the properties of the optical spectra of Type 1 active galactic nuclei (AGNs) by using the unobscured hard X-ray emission as a diagnostic. We develop the `Correlation Spectrum Technique' (CST) and use this to show the strength of correlation between the hard X-ray luminosity and each wavelength of the optical spectrum. This shows that for Broad Line Seyfert 1s all the strong emission lines (broad component of H\alpha and H\beta, [NeIII] \lambda\lambda 3869/3967, [OI] \lambda\lambda 6300/6364, [OII] \lambda\lambda 3726/3729, [OIII] \lambda\lambda 4959/5007) and the optical underlying continuum all strongly correlate with the hard X-ray emission. But the NLS1s appear to be somewhat different. Among the various Balmer line components and the broadband SED components, the best correlation exists between the hard X-ray component and broad component (BC) of the Balmer lines, which supports the view that broad line region (BLR) has the closest link with the AGN's compact X-ray emission. The equivalent widths of Balmer line IC and BC are found to correlate with L$_{2-10keV}$, $\kappa_{2-10keV}^{-1} = L_{bol}/L_{2-10keV}$, Balmer line FWHM and black hole mass. There is a non-linear dependence of the Balmer line IC and BC luminosities with L$_{2-10keV}$ and L$_{5100}$, which suggests that a second-order factor such as the ILR and BLR covering factors affect the Balmer line component luminosities. The Balmer decrement is found to decrease from ~5 in the line core to ~2 in the extended wings, with mean decrements of 2.1 in BLR and 4.8 in ILR. This suggests different physical conditions in these regions. The [OIII] line is composed of a narrow core together with a blue-shifted component with average outflow velocity of $130^{+230}_{-80} km s^{-1}$. The total luminosity of [OIII] \lambda 5007 well correlates with the hard X-ray luminosity.
The spontaneous breaking of B-L symmetry naturally accounts for the small observed neutrino masses via the seesaw mechanism. We have recently shown that the cosmological realization of B-L breaking in a supersymmetric theory can successfully generate the initial conditions of the hot early universe, i.e. entropy, baryon asymmetry and dark matter, if the gravitino is the lightest superparticle (LSP). This implies relations between neutrino and superparticle masses. Here we extend our analysis to the case of very heavy gravitinos which are motivated by hints for the Higgs boson at the LHC. We find that the nonthermal production of 'pure' wino or higgsino LSPs, i.e. weakly interacting particles (WIMPs), in heavy gravitino decays can account for the observed amount of dark matter while simultaneously fulfilling the constraints imposed by primordial nucleosynthesis and leptogenesis within a range of LSP, gravitino and neutrino masses. For instance, a mass of the lightest neutrino of 0.05 eV would require a higgsino mass below 900 GeV and a gravitino mass of at least 20 TeV.
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