We present measurements of the angular correlation function of galaxies selected from the first field of the H-ATLAS survey. Careful removal of the background from galactic cirrus is essential, and currently dominates the uncertainty in our measurements. For our 250 micron-selected sample we detect no significant clustering, consistent with the expectation that the 250 micron-selected sources are mostly normal galaxies at z<~ 1. For our 350 micron and 500 micron-selected samples we detect relatively strong clustering with correlation amplitudes A of 0.2 and 1.2 at 1', but with relatively large uncertainties. For samples which preferentially select high redshift galaxies at z~2-3 we detect significant strong clustering, leading to an estimate of r_0 ~ 7-11 h^{-1} Mpc. The slope of our clustering measurements is very steep, delta~2. The measurements are consistent with the idea that sub-mm sources consist of a low redshift population of normal galaxies and a high redshift population of highly clustered star-bursting galaxies.
To investigate the poorly constrained sub-mm counts and spectral properties of blazars we searched for these in the Herschel-ATLAS (H-ATLAS) science demostration phase (SDP) survey catalog. We cross-matched 500$\mu$m sources brighter than 50 mJy with the FIRST radio catalogue. We found two blazars, both previously known. Our study is among the first blind blazar searches at sub-mm wavelengths, i.e., in the spectral regime where little is still known about the blazar SEDs, but where the synchrotron peak of the most luminous blazars is expected to occur. Our early results are consistent with educated extrapolations of lower frequency counts and question indications of substantial spectral curvature downwards and of spectral upturns at mm wavelengths. One of the two blazars is identified with a Fermi/LAT $\gamma$-ray source and a WMAP source. The physical parameters of the two blazars are briefly discussed.These observations demonstrate that the H-ATLAS survey will provide key information about the physics of blazars and their contribution to sub-mm counts.
We propose a novel method to estimate M_*/M_BH, the ratio of stellar mass (M_*) to black hole mass (M_BH), at various redshifts using two recent observational results: the correlation between the bolometric luminosity of active galactic nuclei (AGN) and the star formation rate (SFR) in their host galaxies, and the correlation between SFR and M_* in star-forming (SF) galaxies. Our analysis is based on M_BH and L_bol measurements in two large samples of type-I AGN at z~1 and z~2, and the measurements of M_*/M_BH in 0.05<z<0.2 red galaxies. We find that M_*/M_BH depends on M_BH at all redshifts. At z~2, M_*/M_BH 280 and ~40 for M_BH=10^8 and M_BH=10^9 M_sol, respectively. M_*/M_BH grows by a factor of ~4-8 from z~2 to z~0 with extreme cases that are as large as 10-20. The evolution is steeper than reported in other studies, probably because we treat only AGN in SF hosts. We caution that estimates of M_*/M_BH evolution which ignore the dependence of this ratio on M_BH can lead to erroneous conclusions.
Aims. The Herschel-ATLAS survey (H-ATLAS) will be the largest area survey to be undertaken by the Herschel Space Observatory. It will cover 550 sq. deg. of extragalactic sky at wavelengths of 100, 160, 250, 350 and 500 microns when completed, reaching flux limits (5 sigma) from 32 to 145mJy. We here present galaxy number counts obtained for SPIRE observations of the first ~14 sq. deg. observed at 250, 350 and 500 microns. Methods. Number counts are a fundamental tool in constraining models of galaxy evolution. We use source catalogs extracted from the H-ATLAS maps as the basis for such an analysis. Correction factors for completeness and flux boosting are derived by applying our extraction method to model catalogs and then applied to the raw observational counts. Results. We find a steep rise in the number counts at flux levels of 100-200mJy in all three SPIRE bands, consistent with results from BLAST. The counts are compared to a range of galaxy evolution models. None of the current models is an ideal fit to the data but all ascribe the steep rise to a population of luminous, rapidly evolving dusty galaxies at moderate to high redshift.
We present a derivation of the star formation rate per comoving volume of quasar host galaxies, derived from stacking analyses of far-infrared to mm-wave photometry of quasars with redshifts 0<z<6 and absolute I-band magnitudes -22>I_AB>-32. We use the science demonstration observations of the first ~16 deg^2 from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) in which there are 240 quasars from the Sloan Digital Sky Survey (SDSS) and a further 171 from the 2dF-SDSS LRG and QSO (2SLAQ) survey. We supplement this data with a compilation of data from IRAS, ISO, Spitzer, SCUBA and MAMBO. H-ATLAS alone statistically detects the quasars in its survey area at >5sigma at 250, 350 and 500um. From the compilation as a whole we find striking evidence of downsizing in quasar host galaxy formation: low-luminosity quasars with absolute magnitudes in the range -22>I_AB>-24 have a comoving star formation rate (derived from 100um rest-frame luminosities) peaking between redshifts of 1 and 2, while high-luminosity quasars with I_AB<-26 have a maximum contribution to the star formation density at z~3. The volume-averaged star formation rate of -22>I_AB>-24 quasars evolves as (1+z)^{2.3 +/- 0.7} at z<2, but the evolution at higher luminosities is much faster reaching (1+z)^{10 +/- 1} at -26>I_AB>-28. We tentatively interpret this as a combination of a declining major merger rate with time and gas consumption reducing fuel for both black hole accretion and star formation.
We have determined the luminosity function of 250um-selected galaxies detected in the ~14 sq.deg science demonstration region of the Herschel-ATLAS project out to a redshift of z=0.5. Our findings very clearly show that the luminosity function evolves steadily out to this redshift. By selecting a sub-group of sources within a fixed luminosity interval where incompleteness effects are minimal, we have measured a smooth increase in the comoving 250um luminosity density out to z=0.2 where it is 3.6+1.4-0.9 times higher than the local value.
We present colour-colour diagrams of detected sources in the Herschel-ATLAS Science Demonstration Field from 100 to 500 microns using both PACS and SPIRE. We fit isothermal modified black bodies to the spectral energy distribution (SED) to extract the dust temperature of sources with counterparts in Galaxy And Mass Assembly (GAMA) or SDSS surveys with either a spectroscopic or a photometric redshift. For a subsample of 330 sources detected in at least three FIR bands with a significance greater than 3 $\sigma$, we find an average dust temperature of $(28 \pm 8)$K. For sources with no known redshift, we populate the colour-colour diagram with a large number of SEDs generated with a broad range of dust temperatures and emissivity parameters, and compare to colours of observed sources to establish the redshift distribution of this sample. For another subsample of 1686 sources with fluxes above 35 mJy at 350 microns and detected at 250 and 500 microns with a significance greater than 3$\sigma$, we find an average redshift of $2.2 \pm 0.6$.
We measure the luminosity and color dependence of galaxy clustering in the SDSS DR7 main galaxy sample, focusing on the projected correlation function w_p(r_p) of volume-limited samples. We interpret our measurements using halo occupation distribution (HOD) modeling assuming a Lambda-CDM cosmology. The amplitude of w_p(r_p) grows slowly with luminosity for L < L_* and increases sharply at higher luminosities, with bias factor b(>L)=1.06+0.23(L/L_*)^{1.12}. At fixed luminosity, redder galaxies have a stronger and steeper w_p(r_p), a trend that runs steadily from the bluest galaxies to the reddest galaxies. The individual luminosity trends for the red and blue galaxy populations are strikingly different. Blue galaxies show a slow but steady increase of w_p(r_p) with luminosity, at all scales. The large-scale clustering of red galaxies shows little luminosity dependence until a sharp increase at L > 4L_*, but the lowest luminosity red galaxies (0.04-0.25 L_*) show very strong clustering on scales r_p < 2 Mpc/h. Most of the observed trends can be naturally understood within the LCDM+HOD framework. The growth of w_p(r_p) with luminosity reflects an overall shift in the halo mass scale, in particular an increase in the minimum host halo mass Mmin. The mass at which a halo has, on average, one satellite galaxy brighter than L is M_1 ~ 17 Mmin(L) over most of the luminosity range. The growth and steepening of w_p(r_p) for redder galaxies reflects the increasing fraction of galaxies that are satellite systems in high mass halos instead of central systems in low mass halos, a trend that is especially marked at low luminosities. Our extensive measurements, provided in tabular form, will allow detailed tests of theoretical models of galaxy formation, a firm grounding of semi-empirical models of the galaxy population, and new cosmological tests.
We use a variant of principal component analysis to investigate the possible temporal evolution of the dark energy equation of state, $w(z)$. We constrain $w(z)$ in multiple redshift bins, utilizing the most recent data from Type Ia supernovae, the cosmic microwave background, baryon acoustic oscillations, the integrated Sachs-Wolfe effect, galaxy clustering, and weak lensing data. Unlike other recent analyses, we find no significant evidence for evolving dark energy; the data remains completely consistent with a cosmological constant. We also study the extent to which the time-evolution of the equation of state would be constrained by a combination of current and future-generation surveys, such as Planck and the Joint Dark Energy Mission.
At the time of recombination, baryons and photons decoupled and the sound speed in the baryonic fluid dropped from relativistic to the thermal velocities of the hydrogen atoms. This is less than the relative velocities of baryons and dark matter computed via linear perturbation theory, so we infer that there are supersonic coherent flows of the baryons relative to the underlying potential wells created by the dark matter. As a result, the advection of small-scale perturbations (near the baryonic Jeans scale) by large-scale velocity flows is important for the formation of the first baryonic structures. This effect involves a quadratic term in the cosmological perturbation theory equations and hence has not been included in studies based on linear perturbation theory. We show that the relative motion suppresses the abundance of the first bound objects, even if one only investigates dark matter haloes, and leads to qualitative changes in their spatial distribution, such as introducing scale-dependent bias and stochasticity. We discuss the possible observable implications for high-redshift galaxy clustering and reionization.
The intergalactic medium (IGM) is the dominant reservoir of baryons at all cosmic epochs. We investigate the evolution of the IGM from z=2-0 in 48 Mpc/h, 110-million particle cosmological hydrodynamic simulations using three prescriptions for galactic outflows. We focus on the evolution of IGM physical properties, and how such properties are traced by Ly-alpha absorption as detectable using HST/COS. Our results broadly confirm the canonical picture that most Ly-alpha absorbers arise from highly ionized gas tracing filamentary large-scale structure. Growth of structure causes gas to move from the diffuse photoionized IGM into other cosmic phases, namely stars, cold and hot gas within galaxy halos, and the unbound and shock-heated warm-hot intergalactic medium (WHIM). By today, baryons are roughly equally divided between bound phases (35%), the diffuse IGM (41%), and the WHIM (24%). Here we (re)define the WHIM as gas with overdensities lower than that in halos and temperatures >10^5 K, in order to more closely align it with "missing baryons". When we tune our photoionizing background to match the observed evolution of the Ly-alpha mean flux decrement, we obtain a line count evolution that broadly agrees with available data. We predict a column density distribution slope of -1.70 for our favored momentum-driven wind model, in agreement with recent observations, and it becomes shallower with redshift. With improved statistics, the frequency of strong lines can be a valuable diagnostic of outflows, and our favored wind model matches existing data best among our models. The relationship between column density and physical density is fairly tight from z=2-0, and evolves as rho N_HI^0.74 10^(-0.37z) for diffuse absorbers. Linewidths only loosely reflect the temperature of the absorbing gas, which will hamper attempts to quantify the WHIM using broad Ly-alpha absorbers. [Abridged]
We study how the universe reheats following an era of chaotic Dirac-Born-Infeld inflation, and compare the rate of particle production with that in models based on canonical kinetic terms. Particle production occurs through non-perturbative resonances whose structure is modified by the nonlinearities of the Dirac-Born-Infeld action. We investigate these modifications and show that the reheating process may be efficient. We estimate the initial temperature of the subsequent hot, radiation-dominated phase.
We discuss the waterfall that ends hybrid inflation. Making some simplifying assumptions, that may be satisfied by GUT inflation models, two issues are addressed. First, the procedure of keeping the quantum fluctuation of the waterfall field only in the regime where it can be regarded as classical. Second, the contribution to the primordial curvature perturbation that is generated during the waterfall. Because the waterfall field is heavy during inflation, the spectrum of this contribution is strongly blue and hence is negligible on cosmological scales.
Probing Gaussianity represents one of the key questions in modern cosmology, because it allows to discriminate between different models of inflation. We test for large-scale non-Gaussianities in the cosmic microwave background (CMB) in a model-independent way. To this end, so-called first and second order surrogates are generated by first shuffling the Fourier phases belonging to the scales not of interest and then shuffling the remaining phases for the length scales under study. Using scaling indices as test statistics we find highly significant signatures for both non-Gaussianities and asymmetries on large scales for the WMAP data of the CMB. We find remarkably similar results when analyzing different ILC-maps based on the WMAP five and seven year data. Such features being independent from the map-making procedure would disfavor the fundamental principle of isotropy as well as canonical single-field slow-roll inflation - unless there is some undiscovered systematic error in the collection or reduction of the CMB data or yet unknown foreground contributions.
The properties of the dust grains (e.g., temperature and mass) can be derived from fitting far-IR SEDs (>100 micron). Only with SPIRE on Herschel has it been possible to get high spatial resolution at 200 to 500 micron that is beyond the peak (~160 micron) of dust emission in most galaxies. We investigate the differences in the fitted dust temperatures and masses determined using only <200 micron data and then also including >200 micron data (new SPIRE observations) to determine how important having >200 micron data is for deriving these dust properties. We fit the 100 to 350 micron observations of the Large Magellanic Cloud (LMC) point-by-point with a model that consists of a single temperature and fixed emissivity law. The data used are existing observations at 100 and 160 micron (from IRAS and Spitzer) and new SPIRE observations of 1/4 of the LMC observed for the HERITAGE Key Project as part of the Herschel Science Demonstration phase. The dust temperatures and masses computed using only 100 and 160 micron data can differ by up to 10% and 36%, respectively, from those that also include the SPIRE 250 & 350 micron data. We find that an emissivity law proportional to lambda^-1.5 minimizes the 100-350 micron fractional residuals. We find that the emission at 500 micron is ~10% higher than expected from extrapolating the fits made at shorter wavelengths. We find the fractional 500 micron excess is weakly anti-correlated with MIPS 24 micron flux and the total gas surface density. This argues against a flux calibration error as the origin of the 500 micron excess. Our results do not allow us to distinguish between a systematic variation in the wavelength dependent emissivity law or a population of very cold dust only detectable at lambda > 500 micron for the origin of the 500 micron excess.
We present some preliminary results from a series of extremely large, high-resolution N-body simulations of the formation of early nonlinear structures. We find that the high-z halo mass function is inconsistent with the Sheth-Tormen mass function, which tends to over-estimate the abundance of rare halos. This discrepancy is in rough agreement with previous results based on smaller simulations. We also show that the number density of minihaloes is correlated with local matter density, albeit with a significant scatter that increases with redshift, as minihaloes become increasingly rare. The average correlation is in rough agreement with a simple analytical extended Press-Schechter model, but can differ by up to factor of 2 in some regimes.
Nuclear Stellar Disks (NSDs), of a few tens to hundreds of parsec across, are a common and yet poorly studied feature of early-type galaxies. Still, such small disks represent a powerful tool to constrain the assembling history of galaxies, since they can be used to trace to the epoch when galaxies experienced their last major merger event. By studying the fraction and stellar age of NSDs it is thus possible to test the predictions for the assembly history of early-type galaxies according the current hierarchical paradigm for galaxy formation. In this paper we have produced the most comprehensive census of NSDs in nearby early-type galaxies by searching for such disks in objects within 100 Mpc and by using archival images from the Hubble Space Telescope. We found that NSDs are present in approximately 20% of early-type galaxies, and that the fraction of galaxies with NSDs does not depend on their Hubble type nor on their galactic environment, whereas the incidence of NSDs appears to decline in the most massive systems. Furthermore, we have separated the light contribution of twelve such disks from that of their surrounding stellar bulge in order to extract their physical properties. This doubles the number of decomposed NSDs and although the derived values for their central surface brightness and scale-length are consistent with previous studies they also give a hint of possible different characteristics due to different formation scenario between nuclear disks and other kinds of large galactic disks.
We determine an expression for the cosmic variance of any "normal" galaxy survey based on examination of M* +/- 1 mag galaxies in the SDSS DR7 data cube. We find that cosmic variance will depend on a number of factors principally: total survey volume, survey aspect ratio, and whether the area surveyed is contiguous or comprised of independent sight-lines. As a rule of thumb cosmic variance falls below 10% once a volume of 10^7h_0.7^-3Mpc^3 is surveyed for a single contiguous region with a 1:1 aspect ratio. Cosmic variance will be lower for higher aspect ratios and/or non-contiguous surveys. Extrapolating outside our test region we infer that cosmic variance in the entire SDSS DR7 main survey region is ~7% to z < 0.1. The equation obtained from the SDSS DR7 region can be generalised to estimate the cosmic variance for any density measurement determined from normal galaxies (e.g., luminosity densities, stellar mass densities and cosmic star-formation rates) within the volume range 10^3 to 10^7 h^-3_0.7Mpc^3. We apply our equation to show that 2 sightlines are required to ensure cosmic variance is <10% in any ASKAP galaxy survey (divided into dz ~0.1 intervals, i.e., ~1 Gyr intervals for z <0.5). Likewise 10 MeerKAT sightlines will be required to meet the same conditions. GAMA, VVDS, and zCOSMOS all suffer less than 10% cosmic variance (~3%-8%) in dz intervals of 0.1, 0.25, and 0.5 respectively. Finally we show that cosmic variance is potentially at the 50-70% level, or greater, in the HST Ultra Deep Field depending on assumptions as to the evolution of clustering. 100 or 10 independent sightlines will be required to reduce cosmic variance to a manageable level (<10%) for HST ACS or HST WFC3 surveys respectively (in dz ~ 1 intervals). Cosmic variance is therefore a significant factor in the z>6 HST studies currently underway.
In gravitational lensing the average colors of the images are not identical to the average color of the source. The highly non-linear mapping of gravitational lensing does not preserve the color balance of the source, and this mapping is different for each image. The color distortion of the images is illustrated using HST images of the lens SL2SJ02140. It is shown that in this lens the color of the images is variable, reflecting the variable color of the source. The average color of the images in SL2SJ02140 are interpreted as a variable amplification of different sources regions with different colors. The variation of the average image colors affects the measurements of the photometric redshift of the images. This is especially true for SL2SJ02140 where the color variations due to the non-linear mapping of the lens simulates pseudo redshifts variations.
Sensitive Herschel far-infrared observations can break degeneracies that were inherent to previous studies of star formation in high-z AGN hosts. Combining PACS 100 and 160um observations of the GOODS-N field with 2Msec Chandra data, we detect ~20% of X-ray AGN individually at >3sig. The host far-infrared luminosity of AGN with L2-10~10^43erg/s increases with redshift by an order of magnitude from z=0 to z~1. In contrast, there is little dependence of far-infrared luminosity on AGN luminosity, for L2-10<~10^44erg/s AGN at z>~1. We do not find a dependence of far-infrared luminosity on X-ray obscuring column, for our sample which is dominated by L2-10<10^44erg/s AGN. In conjunction with properties of local and luminous high-z AGN, we interpret these results as reflecting the interplay between two paths of AGN/host coevolution. A correlation of AGN luminosity and host star formation is traced locally over a wide range of luminosities and also extends to luminous high z AGN. This correlation reflects an evolutionary connection, likely via merging. For lower AGN luminosities, star formation is similar to that in non-active massive galaxies and shows little dependence on AGN luminosity. The level of this secular, non-merger driven star formation increasingly dominates over the correlation at increasing redshift.
Within the framework of the HERM33ES key project, we are studying the star forming interstellar medium in the nearby, metal-poor spiral galaxy M33, exploiting the high resolution and sensitivity of Herschel. We use PACS and SPIRE maps at 100, 160, 250, 350, and 500 micron wavelength, to study the variation of the spectral energy distributions (SEDs) with galacto-centric distance. Detailed SED modeling is performed using azimuthally averaged fluxes in elliptical rings of 2 kpc width, out to 8 kpc galacto-centric distance. Simple isothermal and two-component grey body models, with fixed dust emissivity index, are fitted to the SEDs between 24 and 500 micron using also MIPS/Spitzer data, to derive first estimates of the dust physical conditions. The far-infrared and submillimeter maps reveal the branched, knotted spiral structure of M33. An underlying diffuse disk is seen in all SPIRE maps (250-500 micron). Two component fits to the SEDs agree better than isothermal models with the observed, total and radially averaged flux densities. The two component model, with beta fixed at 1.5, best fits the global and the radial SEDs. The cold dust component clearly dominates; the relative mass of the warm component is less than 0.3% for all the fits. The temperature of the warm component is not well constrained and is found to be about 60K plus/minus 10K. The temperature of the cold component drops significantly from about 24K in the inner 2 kpc radius to 13K beyond 6 kpc radial distance, for the best fitting model. The gas-to-dust ratio for beta=1.5, averaged over the galaxy, is higher than the solar value by a factor of 1.5 and is roughly in agreement with the subsolar metallicity of M33.
Polarized foregrounds are going to be a serious challenge for detecting CMB cosmological B-modes. Both diffuse Galactic emission and extragalactic sources contribute significantly to the power spectrum on large angular scales. At low frequencies, Galactic synchrotron emission will dominate with fractional polarization $\sim 20-40%$ at high latitudes while radio sources can contribute significantly even on large ($\sim 1^{\circ}$) angular scales. Nevertheless, simulations suggest that a detection at the level of $r=0.001$ might be achievable if the foregrounds are not too complex.
We use different particular classes of axially symmetric Szekeres Swiss-cheese models for the study of the apparent dimming of the supernovae of type Ia. We compare the results with those obtained in the corresponding Lemaitre--Tolman Swiss-cheese models. Although the quantitative picture is different the qualitative results are comparable, i.e, one cannot fully explain the dimming of the supernovae using small scale ~50 Mpc inhomogeneities. To fit successfully the data we need structures of at least ~500 Mpc size. However, this result might be an artifact due to the use of axial light rays in axially symmetric models. Anyhow, this work is a first step in trying to use Szekeres Swiss-cheese models in cosmology and it will be followed by the study of more physical models with still less symmetry.
The recently submitted preprint on the first results from the XENON100 dark matter experiment (arxiv:1005.0380) was followed by a criticism by J.I. Collar and D.N. McKinsey (arxiv:1005.0838), focused on our extrapolation of the scintillation efficiency L_eff to the lowest nuclear recoil energies, where no data and no theoretical model exist. Here we add clarifications on our analysis and comment on their criticism.
The mass varying neutrino scenario is a model that successfully explains the origin of dark energy while at the same time solves the coincidence problem. The model is, however, heavily constrained by its stability towards the formation of neutrino bound states when the neutrinos become nonrelativistic. We discuss these constraints and find that natural, adiabatic, stable models with the right amount of dark energy today do not exist. Secondly, we explain why using the lightest neutrino, which is still relativistic, as an explanation for dark energy does not work because of a feedback mechanism from the heavier neutrinos.
In this paper, we investigate the possible theoretical constraint on the parameter $n$ of the agegraphic quintessence model by considering the requirement of the weak gravity conjecture that the variation of the quintessence scalar field $\phi$ should be less than the Planck mass $M_{\rm{p}}$. We obtain the theoretical upper bound $n\lesssim 2.5$ that is inconsistent with the current observational constraint result $2.637<n<2.983$ (95.4% CL). The possible implications of the tension between observational and theoretical constraint results are discussed.
We follow approach of induced matter theory for 5D vacuum BD, introduce induced matter and potential in 4D hypersurfaces, and employ generalized FRW type solution. We confine ourselves to scalar field and scale factors be functions of the time. This makes the induced potential, by its definition, vanishes. When the scale factor of fifth dimension and scalar field are not constants, 5D eqs for any geometry admit a power law relation between scalar field and scale factor of fifth dimension. Hence the procedure exhibits that 5D vacuum FRW like eqs are equivalent, in general, to corresponding 4D vacuum ones with the same spatial scale factor but new scalar field and coupling constant. We show that 5D vacuum FRW like eqs or its equivalent 4D vacuum ones admit accelerated solutions. For constant scalar field, eqs reduce to usual FRW eqs with typical radiation dominated universe. For this situation we obtain dynamics of scale factors for any geometry without any priori assumption. For nonconstant scalar fields and spatially flat geometries, solutions are found to be power law and exponential ones. We also employ weak energy condition for induced matter, that allows negative/positive pressures. All types of solutions fulfill WEC in different ranges. The power law solutions with negative/positive pressures admit both decelerating and accelerating ones. Some solutions accept shrinking extra dimension. By considering nonghost scalar fields and recent observational measurements, solutions are more restricted. We illustrate that accelerating power law solutions, which satisfy WEC and have nonghost fields, are compatible with recent observations in ranges -4/3 < \omega </- -1.3151 and 1.5208 </- n < 1.9583 for dependence of fifth dimension scale factor with usual scale factor. These ranges also fulfill condition nonghost fields in the equivalent 4D vacuum BD eqs.
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We present the discovery of an extremely bright and extended lensed source from the second Red Sequence Cluster Survey (RCS2). RCSGA 032727-132609 is spectroscopically confirmed as a giant arc and counter-image of a background galaxy at $z=1.701$, strongly-lensed by the foreground galaxy cluster RCS2 032727-132623 at $z=0.564$. The giant arc extends over $\sim 38$\,\arcsec and has an integrated $g$-band magnitude of 19.15, making it $\sim 20$ times larger and $\sim 4$ times brighter than the prototypical lensed galaxy MS1512-cB58. This is the brightest distant lensed galaxy in the Universe known to date. Its location in the `redshift desert' provides unique opportunities to connect between the large samples of galaxies known at $z\sim3$ and $z\sim1$. We have collected photometry in 9 bands, ranging from $u$ to $K_s$, which densely sample the rest-frame UV and optical light, including the age-sensitive 4000\AA\ break. A lens model is constructed for the system, and results in a robust total magnification of $2.04 \pm 0.16$ for the counter-image; we estimate an average magnification of $17.2 \pm 1.4$ for the giant arc based on the relative physical scales of the arc and counter-image. Fits of single-component spectral energy distribution (SED) models to the photometry result in a moderately young age, $t = 115 \pm 65$\,Myr, small amounts of dust, $E(B-V) \le 0.035$, and an exponentially declining star formation history with \textit{e}-folding time $\tau = 10-100$\,Myr. After correcting for the lensing magnification, we find a stellar mass of $\log(\mathrm{M}/\mathrm{M}_\odot)=10.0 \pm 0.1$. Allowing for episodic star formation, an underlying old burst could contain up to twice the mass inferred from single-component modeling. This stellar mass estimate is consistent with the average stellar mass of a sample of `BM' galaxies ($1.4 < z < 2.0$) studied by Reddy et al. (2006).
The Extragalactic Background Light (EBL) from the infrared (IR) through the ultraviolet (UV) is dominated by emission from stars, either directly or through absorption and reradiation by dust. It can thus give information on the star formation history of the universe. However, it is difficult to measure directly due to foreground radiation fields from the Galaxy and solar system. Gamma-rays from extragalactic sources at cosmological distances (blazars and gamma-ray bursts) interact with EBL photons creating electron-positron pairs, absorbing the gamma-rays. Given the intrinsic gamma-ray spectrum of a source and its redshift, the EBL can in principle be measured. However, the intrinsic gamma-ray spectra of blazars and GRBs can vary considerably from source to source and the from the same source over short timescales. A maximum intrinsic spectrum can be assumed from theoretical grounds, to give upper limits on the EBL absorption from blazars at low redshift with very high energy (VHE) gamma-ray observations with ground-based Atmospheric Cherenkov telescopes. The Fermi-LAT observations of blazars and GRBs can probe EBL absorption at higher redshifts. The lower energy portion of the LAT spectrum of these sources is unattenuated by the EBL, so that extrapolating this to higher energies can give the maximum intrinsic spectrum for a source. Comparing this to the observed higher energy LAT spectrum will then give upper limits on the EBL absorption. For blazars which have been detected by both the Fermi-LAT and at higher energies by Cherenkov telescopes, combined LAT-VHE observations can put more stringent constraints on the low redshift EBL. These procedures above can also be reversed: for sources with an unknown redshift, a given EBL model and gamma-ray spectrum can lead to an upper limit on the source's redshift.
We present a significant improvement over our previous calculations of the cosmic string contribution to cosmic microwave background (CMB) power spectra, with particular focus on sub-WMAP angular scales. These smaller scales are relevant for the now-operational Planck satellite and additional sub-orbital CMB projects that have even finer resolutions. We employ larger Abelian Higgs string simulations than before and we additionally model and extrapolate the statistical measures from our simulations to smaller length scales. We then use an efficient means of including the extrapolations into our Einstein-Boltzmann calculations in order to yield accurate results over the multipole range 2 < l < 4000. Our results suggest that power-law behaviour cuts in for l > 3000 in the case of the temperature power spectrum, which then allows cautious extrapolation to even smaller scales. We find that a string contribution to the temperature power spectrum making up 10% of power at l=10 would be larger than the Silk-damped primary adiabatic contribution for l > 3500. Astrophysical contributions such as the Sunyaev-Zeldovich effect also become important at these scales and will reduce the sensitivity to strings, but these are potentially distinguishable by their frequency-dependence.
The local universe is the best known part of our universe. Within the CLUES project (this http URL - Constrained Local UniversE Simulations) we perform numerical simulations of the evolution of the local universe. For these simulations we construct initial conditions based on observational data of the galaxy distribution in the local universe. Here we review the technique of these constrained simulations. In the second part we summarize our predictions of a possible Warm Dark Matter cosmology for the observed local distribution of galaxies and the local spectrum of mini-voids as well as a study of the satellite dynamics in a simulated Local Group.
Bose-Einstein condensation of W bosons in the early universe is studied. It is shown that, in the broken phase of the standard electroweak theory, condensed W bosons form a ferromagnetic state with aligned spins. In this case the primeval plasma may be spontaneously magnetized inside macroscopically large domains and form magnetic fields which may be seeds for the observed today galactic and intergalactic fields. However, in a modified theory, e.g. in a theory without quartic self interactions of gauge bosons or for a smaller value of the weak mixing angle, antiferromagnetic condensation is possible. In the latter case W bosons form scalar condensate with macroscopically large electric charge density i.e. with a large average value of the bilinear product of W-vector fields but with microscopically small average value of the field itself.
We point out that if quantum field renormalization is taken into account the predictions of slow-roll inflation for both the scalar and tensorial power spectra change significantly for wavelengths that today are at observable scales
We consider the role of the zero-point energy of a quantum field in cosmology and show that the flow of trans-planckian momenta due to redshift acts as a source for this energy, regularized with a cut-off Lambda in physical momenta. In order to fulfill Bianchi identity, we generalize Einstein equations, and discuss the corresponding Friedmann homogeneous and isotropic models. In case of a de Sitter phase, such as during inflation, the solution shows a logarithmic behaviour of the Hubble parameter, and a primordial spectrum of scalar perturbations characterized by the spectral index ns= 1- Lambda2/(3 pi mP2) with mP the Planck mass. We also discuss possible implications of the scenario on late accelerating stage of the Universe at small redshifts, and the emergence of a fluid characterized by an equation of state w=P/rho= -1+ Lambda2/(9 pi mP2). Primordial perturbation spectrum and dark energy parameter w are thus, predicted to be connected by the simple relation w=-(2+ns)/3.
Turbulence and turbulent mixing in natural fluids begins with big bang turbulence powered by spinning combustible combinations of Planck particles and Planck antiparticles. Particle prograde accretion on a spinning pair releases 42% of the particle rest mass energy to produce more fuel for turbulent combustion. Negative viscosity and negative turbulence stresses work against gravity, creating mass-energy and space-time from the vacuum. Turbulence mixes cooling temperatures until a quark-gluon strong-force SF freeze-out. Gluon-viscosity anti-gravity ({\Lambda}SF) exponentially inflates the fireball to preserve big bang turbulence information at scales larger than ct as the first fossil turbulence. Cosmic microwave background CMB temperature anisotropies show big bang turbulence fossils along with fossils of weak plasma turbulence triggered (10^12 s) as plasma viscous forces permit gravitational fragmentation on supercluster to galaxy mass scales (10^13 s). Turbulent morphologies and viscous-turbulent lengths appear as linear gas-proto-galaxy-clusters GPGCs of the Hubble ultra-deep-field at z~7. GPGCs fragment into PGC Jeans-mass clumps of primordial gas planets at decoupling: the dark matter of galaxies. Planets merge to stars that explode on overfeeding, fertilizing first life, shortly after the plasma to gas transition when most warm primordial soups existed.
We describe the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Early
Release Science (ERS) observations in the Great Observatories Origins Deep
Survey (GOODS) South field. The new WFC3 ERS data provide calibrated, drizzled
mosaics in the mid-UV filters F225W, F275W, and F336W, as well as in the
near-IR filters F098W (\Ys), F125W (J), and F160W (H) in 1-2 HST orbits per
filter. Together with the existing HST Advanced Camera for Surveys (ACS)
GOODS-South mosaics in the BVi'z' filters, these panchromatic 10-band ERS data
cover 40-50 square arcmin from from 0.2-1.7 \mum\ in wavelength at 0\arcspt
07-0\arcspt 15 FWHM resolution and 0\arcspt 090 multidrizzled pixels to depths
of AB\cle 26.0-27.0 mag (5-sigma) for point sources, and AB\cle 25.5-26.5 mag
for compact galaxies.
In this paper, we describe: a) the scientific rationale, and the data taking
plus reduction procedures of the panchromatic 10-band ERS mosaics; b) the
procedure of generating object catalogs across the 10 different ERS filters,
and the specific star-galaxy separation techniques used; and c) the reliability
and completeness of the object catalogs from the WFC3 ERS mosaics. The
excellent 0\arcspt 07-0\arcspt 15 FWHM resolution of HST/WFC3 and ACS makes
star-galaxy separation rather straightforward over a factor of 10 in wavelength
to AB\cle 25-26 mag from the UV to the near-IR, respectively.
We investigate the dust associated with the supernova remnant (SNR) N49 in the Large Magellanic Cloud (LMC) as observed with the Herschel Space Observatory. N49 is unusually bright because of an interaction with a molecular cloud along its eastern edge. We have used PACS and SPIRE to measure the far IR flux densities of the entire SNR and of a bright region on the eastern edge of the SNR where the SNR shock is encountering the molecular cloud. Using these fluxes supplemented with archival data at shorter wavelengths, we estimate the dust mass associated with N49 to be about 10 Msun. The bulk of the dust in our simple two-component model has a temperature of 20-30 K, similar to that of nearby molecular clouds. Unfortunately, as a result of the limited angular resolution of Herschel at the wavelengths sampled with SPIRE, the uncertainties are fairly large. Assuming this estimate of the dust mass associated with the SNR is approximately correct, it is probable that most of the dust in the SNR arises from regions where the shock speed is too low to produce significant X-ray emission. The total amount of warm 50-60 K dust is ~0.1 or 0.4 Msun, depending on whether the dust is modeled in terms of carbonaceous or silicate grains. This provides a firm lower limit to the amount of shock heated dust in N49.
This article deals with the problem of the motion of stars in galaxies. By using the Newton's theory combined with a gravitational time dilatation for the weak gravitational field, it is possible to give a solution without using the dark matter.
We provide a set of numerical N-body simulations for studying the formation of the outer Milky Ways's stellar halo through accretion events. After simulating minor mergers of prograde and retrograde orbiting satellite halo with a Dark Matter main halo, we analyze the signal left by satellite stars in the rotation velocity distribution. The aim is to explore the orbital conditions where a retrograde signal in the outer part of the halo can be obtained, in order to give a possible explanation of the observed rotational properties of the Milky Way stellar halo. Our results show that, for satellites more massive than $\sim 1/40$ of the main halo, the dynamical friction has a fundamental role in assembling the final velocity distributions resulting from different orbits and that retrograde satellites moving on low inclination orbits deposit more stars in the outer halo regions end therefore can produce the counter-rotating behavior observed in the outer Milky Way halo.
The Herschel Space Observatory enables us to accurately measure the bolometric output of starburst galaxies and active galactic nuclei (AGN) by directly sampling the peak of their far-infrared (IR) emission. Here we examine whether the spectral energy distribution (SED) and dust temperature of galaxies have strongly evolved since z~2.5. We use Herschel deep extragalactic surveys from 100 to 500um to compute total IR luminosities in galaxies down to the faintest levels, using PACS and SPIRE in the GOODS-North field (PEP and HerMES key programs). We show that measurements in the SPIRE bands can be used below the statistical confusion limit if information at higher spatial resolution is used to identify isolated galaxies whose flux is not boosted by bright neighbors. Below z~1.5, mid-IR extrapolations are correct for star-forming galaxies with a dispersion of only 40% (0.15dex), therefore similar to z~0 galaxies. This narrow distribution is puzzling when considering the range of physical processes that could have affected the SED of these galaxies. Extrapolations from only one of the 160um, 250um or 350um bands alone tend to overestimate the total IR luminosity. This may be explained by the lack of far-IR constraints around and above ~150um (rest-frame) on local templates. We also note that the dust temperature of luminous IR galaxies around z~1 is mildly colder by 10-15% than their local analogs and up to 20% for ULIRGs at z~1.6. Above z=1.5, distant galaxies are found to exhibit a substantially larger mid- over far-IR ratio, which could either result from stronger broad emission lines or warm dust continuum heated by a hidden AGN. Two thirds of the AGNs identified in the field with a measured redshift exhibit the same behavior as purely star-forming galaxies. Hence a large fraction of AGNs harbor star formation at very high SFR and in conditions similar to purely star-forming galaxies.
We revise and extend the extreme value statistic, introduced in \cite{gup08}, to study directional dependence in the high redshift supernova data; arising either from departures from the cosmological principle or due to direction dependent statistical systematics in e data. We introduce a likelihood function that analytically marginalises over the Hubble constant, and use it to extend our previous statistic. We also introduce a new statistic that is sensitive to direction dependence arising from living off-centre inside a large void, as well as previously mentioned reasons for anisotropy. We show that for large data sets this statistic has a limiting form that can be computed analytically. We apply our statistics to the gold data sets from \cite{rie04} and \cite{rie07}, as in our previous work. Our revision and extension of previous statistic shows that 1) the effect of marginalsing over Hubble constant instead of using its best fit value has only a marginal effect on our results. However, correction of errors in our previous work reduce the level of non-Gaussianity in the 2004 gold data that was found in our earlier work. The revised results for the 2007 gold data show that the data is consistent with isotropy and Gaussianity. Our second statistic confirms these results.
A possible gluon-condensate-induced modified-gravity model with f(R) \propto |R|^{1/2} has been suggested previously. Here, a simplified version is presented using the constant flat-spacetime equilibrium value of the QCD gluon condensate and a single pressureless matter component (cold dark matter). The dynamical equations of a homogeneous spatially-flat Friedmann-Robertson-Walker universe are derived for this simple model. The simple model allows for a careful treatment of the boundary conditions and does not require a further scaling analysis as the original model did. Reliable predictions are obtained for several observable quantities of the homogeneous model universe. In addition, the estimator E_{G}, proposed by Zhang et al. to search for deviations from standard Einstein gravity, is calculated for linear sub-horizon density perturbations.
The stalling radius of a merging massive binary black hole (BBH) is expected to be below 0".1 even in nearby galaxies (Yu 2002), and thus BBHs are not expected to be spatially resolved in the near future. However, as we show below, a BBH may be detectable through the significantly anisotropic stellar velocity distribution it produces on scales 5-10 times larger than the binary separation. We calculate the velocity distribution of stable orbits near a BBH by solving the restricted three body problem for a BBH embedded in a bulge potential. We present high resolution maps of the projected velocity distribution moments, based on snapshots of ~ 10^8 stable orbits. The kinematic signature of a BBH in the average velocity maps is a counter rotating torus of stars outside the BBH Hill spheres. The velocity dispersion maps reveal a dip in the inner region, and an excess of 20-40% further out, compared to a single BH of the same total mass. More pronounced signatures are seen in the third and fourth Gauss-Hermite velocity moments maps. The detection of these signatures may indicate the presence of a BBH currently, or at some earlier time, which depends on the rate of velocity phase space mixing following the BBH merger.
It has been proposed that primordial gas in early dark matter halos, with virial temperatures above 10^4 K, can avoid fragmentation and undergo rapid collapse, possibly resulting in a supermassive black hole (SMBH). This requires the gas to avoid cooling and to remain at temperatures near T=10^4 K. We show that this condition can be satisfied in the presence of a sufficiently strong primordial magnetic field, which heats the collapsing gas via ambipolar diffusion. If the field has a strength above B = 3.6 (comoving) nG, the collapsing gas is kept warm (T=10^4K) until it reaches the critical density n_crit=10^3 cm^{-3} at which the roto-vibrational states of H_2 approach local thermodynamic equilibrium. H_2-cooling then remains inefficient, and the gas temperature stays near 10^4K, even as it continues to collapse to higher densities. The critical magnetic field strength required to permanently suppress H_2-cooling is somewhat higher than upper limit of approx. 2 nG from the cosmic microwave background (CMB). However, it can be realized in the rare (2-3)-sigma regions of the spatially fluctuating B-field; these regions contain a sufficient number of halos to account for the z=6 quasar BHs.
In a series of papers, we propose a theory to explain the formation and properties of rings and spirals in barred galaxies. The building blocks of these structures are orbits guided by the manifolds emanating from the unstable Lagrangian points located near the ends of the bar. In this paper, the last of the series, we present more comparisons of our theoretical results to observations and also give new predictions for further comparisons. Our theory provides the right building blocks for the rectangular-like bar outline and for ansae. We consider how our results can be used to give estimates for the pattern speed values, as well as their effect on abundance gradients in barred galaxies. We present the kinematics along the manifold loci, to allow comparisons with the observed kinematics along the ring and spiral loci. We consider gaseous arms and their relations to stellar ones. We discuss several theoretical aspects and stress that the orbits that constitute the building blocks of the spirals and rings are chaotic. They are, nevertheless, spatially well confined by the manifolds and are thus able to outline the relevant structures. Such chaos can be termed `confined chaos' and can play a very important role in understanding the formation and evolution of galaxy structures and in galactic dynamics in general. This work, in agreement with several others, argues convincingly that galactic dynamic studies should not be limited to the study of regular motions and orbits.
We report VLBA polarimetric observations of the CSS sources 3C119, 3C318, and 3C343 at 5 and 8.4 GHz. The CSS source 3C119 has source rest-frame RM values up to ~10200 rad/m**2 in a region which coincides with a change in the direction of the inner jet. This component is located ~325 pc from the core, which is variable and has a peaked radio spectrum. In the case of 3C318, a rest-frame RM of ~3030 rad/m**2 has been estimated for the brightest component which contributes almost all of the polarised emission. Further, two more extended components have been detected, clearly showing "wiggles" in the jet towards the southern side of the source. The CSS source 3C343 contains two peaks of emission and a curved jet embedded in more diffuse emission. It exhibits complex field directions near the emission peaks, which indicate rest-frame RM values in excess of ~6000 rad/m**2. The locations of the cores in 3C318 and 3C343 are not clear. The available data on mas-scale rest-frame RM estimates for CSS sources show that these have a wide range of values extending up to ~40000 rad/m**2 in the central region of OQ172, and could be located at projected distances from the core of up to ~1600 pc, as in 3C43 where this feature has a rest-frame RM of ~14000 rad/m**2. RM estimates for cores in core-dominated radio sources indicate that in addition to responding to an overall density gradient of the magneto-ionic medium, geometry, orientation and modes of fuelling may also play a significant role. In addition to these effects, the high values of RM in CSS sources are possibly due to dense clouds of gas interacting with the radio jets. The observed distortions in the radio structures of many CSS sources are consistent with this interpretation.
We present VIMOS integral field spectroscopy of the brightest radio-quiet QSO on the southern sky HE 1029-1401 at a redshift of z=0.086. Standard decomposition techniques for broad-band imaging are extended to integral field data in order to deblend the QSO and host emission. We perform a tentative analysis of the stellar continuum finding a young stellar population (<100Myr) or a featureless continuum embedded in an old stellar population (10Gyr) typical for a massive elliptical galaxy. The stellar velocity dispersion of sigma_*=320\pm90 km/s and the estimated black hole mass log(M_BH/M_sun)=8.7\pm0.3 are consistent with the local M_BH-sigma_* relation within the errors. For the first time we map the two-dimensional ionised gas distribution and the gas velocity field around HE 1029-1401. While the stellar host morphology is purely elliptical we find a highly structured distribution of ionised gas out to 16 kpc from the QSO. The gas is highly ionised solely by the QSO radiation and has a significantly lower metallicity than would be expected for the stellar mass of the host, indicating an external origin of the gas most likely due to minor mergers. We find a rotating gas disc around the QSO and a dispersion-dominated non-rotating gas component within the central 3 kpc. At larger distances the velocity field is heavily disturbed, which could be interpreted as another signature of past minor merger events. Alternatively, the arc-like structure seen in the ionised gas might also be indicative of a large-scale expanding bubble, centred on and possibly driven by the active nucleus.
The survival of unbound density substructure against orbital mixing imposes strong constraints on the slope of the underlying gravitational potential and provides a new test on modified gravities. Here we investigate whether the interpretation that the stellar clump in Ursa Minor (UMi) dwarf spheroidal galaxy is a `dynamical fossil' is consistent with Modified Newtonian dynamics (MOND). For UMi mass models inferred by fitting the velocity dispersion profile, the stellar clump around the second peak of UMi is erased very rapidly, within 1.25 Gyr (6.5 orbits), even with the inclusion of self-gravity. We find that the clump can hardly survive for more than 2 Gyr even under more generous conditions. Alternative scenarios which could lead to a kinematically cold clump are discussed but, so far, none of them were found to be fully satisfactory. Our conclusion is that the cold clump in UMi poses a challenge for both LambdaCDM and MOND.
Magnetic fields appear to be a generic feature of the early universe and are a natural source of secondary CMB non-Gaussianity. In recent years the statistical nature of the stresses of a primordial magnetic field has been well studied. In this paper we confirm and extend these studies at one- and two-point level, and present analytical results for a wide range of power-law spectra. We also consider two non-power law cases of interest: a blue spectrum with an extended damping tail on small scales, which could be generated by the non-linear mixing of density and vorticity; and a red spectrum with a damping tail on large scales. We then briefly consider the CMB impacts that result from such fields. While this paper focuses on the one- and two-point moments, the techniques we employ are designed to ease the analysis of the full bispectra induced by primordial magnetic fields.
A possible slowing down of the cosmic expansion is investigated through a kinematic approach. By expanding the luminous distance to fourth order and fitting the SNe Ia data from the most recent compilations (Union, Constitution and Union 2), the marginal likelihood distribution for the deceleration parameter today indicates that there is a considerable probability for $q_0>0$. Also in contrast to the prediction of the $\Lambda$CDM model, the kinematic $q(z)$ reconstruction suggests that the cosmic acceleration could already have peaked and be presently slowing down, what would imply that the recent accelerated expansion of the Universe is a transient phenomenon. The present kinematic results depend neither on the validity of general relativity nor the matter-energy contents of the Universe.
The Szekeres inhomogeneous models can be used to model the true lumpy universe that we observe. This family of exact solutions to Einstein's equations was originally derived with a general metric that has no symmetries. In this work, we perform analytical integrations of the non-radial null geodesics and derive new expressions for the affinely parameterized null tangent vector components, the area (and luminosity) distance and the redshift in these models. This work does not assume spherical or axial symmetry. The general results should be useful for comparisons of the general Szekeres inhomogeneous models to current and future cosmological data.
We present a rest-frame ultraviolet morphological analysis of 78 resolved, high S/N z ~ 3.1 Lyman Alpha Emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S). Using HST/ACS V -band images taken as part of the GEMS, GOODS, and HUDF surveys. For each LAE system identified via our ground-based narrow-band imaging, we have identified those LAE systems with multiple components. We measure the concentration index and present the results of our GALFIT fits for ellipticity, Sersic index, and sizes for each resolved component with S/N > 30 as well as for each LAE system with S/N > 30. The LAEs show a heterogeneous distribution of morphologies while the ma jority tend to be highly concentrated and compact in size. We only measure the morphological properties of resolved LAEs. For systems showing multiple components we also measured the morphology of the individual components. The resolved LAEs are highly concentrated (2 < C < 4) and show a similar distribution to that measured for stars, suggesting that this diagnostic is a poor discriminator near the resolution limit. The measured ellipticities for components show a distribution peaked at {\epsilon} ~ 0.55 which is significantly different from the flat distribution of ellipticities observed for local spiral galaxies and is similar to the distribution found for Lyman-break galaxies at the same redshift. There is a wide range of best-fit Sersic indices (1 < n < 10) with the majority being between 0 < n < 2. The distribution is similar to the distribution of Sersic indices seen locally. A visual inspection of the images suggests a qualitative morphological transition at n ~ 2, with small-n LAEs having extended or multimodal light distributions and relatively little diffuse emission and large-n LAEs have compact central components surrounded by diffuse emission.
We investigate the characteristic radiative efficiency \epsilon, Eddington ratio \lambda, and duty cycle P_0 of high-redshift active galactic nuclei (AGN), drawing on measurements of the AGN luminosity function at z=3-6 and, especially, on recent measurements of quasar clustering at z=3-4.5 from the Sloan Digital Sky Survey. The free parameters of our models are \epsilon, \lambda, and the normalization, scatter, and redshift evolution of the relation between black hole mass \mbh and halo virial velocity V_vir. We compute the luminosity function from the implied growth of the black hole mass function and the quasar correlation length from the bias of the host halos. We test our adopted formulae for the halo mass function and halo bias against measurements from the large N-body simulation developed by the MICE collaboration. The strong clustering of AGNs observed at z=3 and, especially, at z=4 implies that massive black holes reside in rare, massive dark matter halos. Reproducing the observed luminosity function then requires high efficiency \epsilon and/or low Eddington ratio \lambda, with a lower limit (based on 2\sigma agreement with the measured z=4 correlation length) \epsilon> 0.7\lambda/(1+0.7\lambda), implying \epsilon > 0.17 for \lambda > 0.25. Successful models predict high duty cycles, P_0~0.2, 0.5, and 0.9 at z=3.1, 4.5 and 6, respectively, and they require that the fraction of halo baryons locked in the central black hole is much larger than the locally observed value. The rapid drop in the abundance of the massive and rare host halos at z>7 implies a proportionally rapid decline in the number density of luminous quasars, much stronger than simple extrapolations of the z=3-6 luminosity function would predict. (abridged)
We generalize the coset construction of Callan, Coleman, Wess and Zumino to theories in which the Lorentz group is spontaneously broken down to one of its subgroups. This allows us to write down the most general low-energy effective Lagrangian in which Lorentz invariance is non-linearly realized, and to explore the consequences of broken Lorentz symmetry without having to make any assumptions about the mechanism that triggers the breaking. We carry out the construction both in flat space, in which the Lorentz group is a global spacetime symmetry, and in a generally covariant theory, in which the Lorentz group can be treated as a local internal symmetry. As an illustration of this formalism, we construct the most general effective field theory in which the rotation group remains unbroken, and show that the latter is just the Einstein-aether theory.
The Hypervelocity Star survey presents the currently largest sample of radial velocity measurements of halo stars out to 80 kpc. We apply spherical Jeans modeling to these data in order to derive the mass profile of the Galaxy. We restrict the analysis to distances larger than 25 kpc from the Galactic center, where the density profile of halo stars is well approximated by a single power law with logarithmic slope between -3.5 and -4.5. With this restriction, we also avoid the complication of modeling a flattened Galactic disk. In the range 25 < r < 80 kpc, the radial velocity dispersion declines remarkably little; a robust measure of its logarithmic slope is between -0.05 and -0.1. The circular velocity profile also declines remarkably little with radius. The allowed range of V_c(80kpc) lies between 177 and 234 km/s, with the most likely value 197 km/s. Compared with the value at the solar location, the Galactic circular velocity declines by less than 20% over an order of magnitude in radius. Such a flat profile requires a massive and extended dark matter halo. The mass enclosed within 80 kpc is 7e11 solar masses.
We apply our scalar-tensor-vector (STVG) modified gravity theory (MOG) to calculate the infall velocities of the two clusters constituting the Bullet Cluster 1E0657-06. In the absence of an applicable two-body solution to the MOG field equations, we adopt an approximate acceleration formula based on the spherically symmetric, static, vacuum solution of the theory in the presence of a point source. We find that this formula predicts an infall velocity of the two clusters that is consistent with estimates based on hydrodynamic simulations.
We propose to regulate the infinities of eternal inflation by relating a late time cut-off in the bulk to a short distance cut-off on the future boundary. The light-cone time of an event is defined in terms of the volume of its future light-cone on the boundary. We seek an intrinsic definition of boundary volumes that makes no reference to bulk structures. This requires taming the fractal geometry of the future boundary, and lifting the ambiguity of the conformal factor. We propose to work in the conformal frame in which the boundary Ricci scalar is constant. We explore this proposal in the FRW approximation for bubble universes. Remarkably, we find that the future boundary becomes a round three-sphere, with smooth metric on all scales. Our cut-off yields the same relative probabilities as a previous proposal that defined boundary volumes by projection into the bulk along timelike geodesics. Moreover, it is equivalent to an ensemble of causal patches defined without reference to bulk geodesics. It thus yields a holographically motivated and phenomenologically successful measure for eternal inflation.
We present a full high resolution SPIRE FTS spectrum of the nearby ultraluminous infrared galaxy Mrk231. In total 25 lines are detected, including CO J=5-4 through J=13-12, 7 rotational lines of H2O, 3 of OH+ and one line each of H2O+, CH+, and HF. We find that the excitation of the CO rotational levels up to J=8 can be accounted for by UV radiation from star formation. However, the approximately flat luminosity distribution of the CO lines over the rotational ladder above J=8 requires the presence of a separate source of excitation for the highest CO lines. We explore X-ray heating by the accreting supermassive black hole in Mrk231 as a source of excitation for these lines, and find that it can reproduce the observed luminosities. We also consider a model with dense gas in a strong UV radiation field to produce the highest CO lines, but find that this model strongly overpredicts the hot dust mass in Mrk231. Our favoured model consists of a star forming disk of radius 560 pc, containing clumps of dense gas exposed to strong UV radiation, dominating the emission of CO lines up to J=8. X-rays from the accreting supermassive black hole in Mrk231 dominate the excitation and chemistry of the inner disk out to a radius of 160 pc, consistent with the X-ray power of the AGN in Mrk231. The extraordinary luminosity of the OH+ and H2O+ lines reveals the signature of X-ray driven excitation and chemistry in this region.
The characteristic sizes of astrophysical structures, up to the whole observed Universe, can be recovered, in principle, assuming that gravity is the overall interaction assembling systems starting from microscopic scales, whose order of magnitude is ruled by the Planck length and the related Compton wavelength. This result agrees with the absence of screening mechanisms for the gravitational interaction and could be connected to the presence of Yukawa corrections in the Newtonian potential which introduce typical interaction lengths. This result directly comes out from quantization of primordial black holes and then characteristic interaction lengths directly emerge from quantum field theory.
We present NLTE Li abundances for 88 stars in the metallicity range -3.5 < [Fe/H] < -1.0. The effective temperatures are based on the infrared flux method with improved E(B-V) values obtained mostly from interstellar NaI D lines. The Li abundances were derived through MARCS models and high-quality UVES+VLT, HIRES+Keck and FIES+NOT spectra, and complemented with reliable equivalent widths from the literature. The less-depleted stars with [Fe/H] < -2.5 and [Fe/H] > -2.5 fall into two well-defined plateaus of A_{Li} = 2.18 (sigma = 0.04) and A_{Li} = 2.27 (sigma = 0.05), respectively. We show that the two plateaus are flat, unlike previous claims for a steep monotonic decrease in Li abundances with decreasing metallicities. At all metallicities we uncover a fine-structure in the Li abundances of Spite plateau stars, which we trace to Li depletion that depends on both metallicity and mass. Models including atomic diffusion and turbulent mixing seem to reproduce the observed Li depletion assuming a primordial Li abundance A_{Li} = 2.64, which agrees well with current predictions (A_{Li} = 2.72) from standard Big Bang nucleosynthesis. Adopting the Kurucz overshooting model atmospheres increases the Li abundance by +0.08 dex to A_{Li} = 2.72, which perfectly agrees with BBN+WMAP.
Scalar field models of inflation based on a large non-minimal coupling to gravity xi, in particular Higgs Inflation, may violate unitarity at an energy scale Lambda ~ M_p / xi << M_p. In this case the model is incomplete at energy scales relevant to inflation. Here we propose a new unitarity-conserving model of Higgs Inflation. The completion of the theory is achieved via additional interactions which are proportional to products of the derivatives of the Higgs doublet. The resulting model differs from the original version of Higgs Inflation in its prediction for the spectral index, with a classical value n = 0.974. This is expected to be modified by quantum corrections entirely determined by Standard Model couplings, which should allow the model to be tested via CMB and collider experiments.
The present-day Universe appears to be homogeneous on very large scales. Yet when the casual structure of the early Universe is considered, it becomes apparent that the early Universe must have been highly inhomogeneous. The current paradigm attempts to answer this problem by postulating the inflation mechanism However, inflation in order to start requires a homogeneous patch of at least the horizon size. This paper examines if dynamical processes of the early Universe could lead to homogenization. In the past similar studies seem to imply that the set of initial conditions that leads to homogenization is of measure zero. This essay proves contrary: a set of initial conditions for spontaneous homogenization of cosmological models can form a set of non-zero measure.
We demonstrate a new model which uses an ADD type braneworld scenario to produce a multi-state theory of dark matter. Compactification of the extra dimensions onto a sphere leads to the association of a single complex scalar in the bulk with multiple Kaluza-Klein towers in an effective four-dimensional theory. A mutually interacting multi-state theory of dark matter arises naturally within which the dark matter states are identified with the lightest Kaluza-Klein particles of fixed magnetic quantum number. These states are protected from decay by a combination of a global U(1) symmetry and the continuous rotational symmetry about the polar axis of the spherical geometry. We briefly discuss the relic abundance calculation and investigate the spin-independent elastic scattering off nucleons of the lightest and next-to-lightest dark matter states.
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Recent observations of excited CO emission lines from z~2 disc galaxies have shed light on the Kennicutt-Schmidt relation at high-z via observed SFR-CO (J=3-2) relations. Here, we describe a novel methodology for utilising these observations of high-excitation CO to derive the underlying Schmidt (SFR-rho^N) relationship. To do this requires an understanding of the potential effects of differential CO excitation with SFR. If the most heavily star-forming galaxies have a larger fraction of their gas in highly excited CO states than the lower SFR galaxies, then the observed molecular SFR-CO^alpha index, alpha, will be less than the underlying (volumetric) Schmidt index, N. Utilising a combination of SPH models of galaxy evolution and molecular line radiative transfer, we present the first calculations of CO excitation in z~2 disc galaxies with the aim of developing a mapping between various observed SFR-CO relationships and the underlying Schmidt relation. We find that even in relatively luminous z~2 discs, differential excitation does indeed exist, resulting in alpha < N for highly excited CO lines. This means that an observed SFR-CO (J=3-2) relation does not map linearly to SFR-H2 relation. We utilise our model results to provide a mapping from alpha to N for the range of Schmidt indices N=1-2. By comparing to recent observational surveys, we find that the observed (nearly) linear relationship between SFR and CO (J=3-2) emission suggests that an underlying SFR~rho^1.5 relation describes z~2 disc galaxies.
The aim of this paper is to study the astrometric trajectory of microlensing events with an extended lens and/or source. We consider not only a dark lens but also a luminous lens as well. We find that the discontinuous finite-lens trajectories in Takahashi (2003) will become continuous in the finite-source regime. The point lens (source) approximation alone gives an under (over)-estimation of the astrometric signal when the size of the lens and source are not negligible. While the finiteness of the source is revealed when the lens transits the surface of the source, the finite-lens signal is most prominent when the lens is very close to the source. Astrometric microlensing towards the Galactic bulge, SMC, and M31 are discussed, which indicate that the finite-lens effect is beyond the detection limit of current instruments. Nevertheless, it is possible to distinguish between self- and halo lensing through a (non)detection of the astrometric ellipse.We also consider the case where the lens is luminous itself, as has been observed where a lensing event was followed up with the Hubble Space Telescope. We show that the astrometric signal will be reduced in a luminous-lens scenario. The physical properties of the event, such as the lens-source flux ratio, the size of the lens and source nevertheless can be derived by fitting the astrometric trajectory.
We use a high-resolution N-body simulation to study how the influence of large-scale structure in and around clusters causes correlated signals in different physical probes and discuss some implications this has for multi-physics probes of clusters. We pay particular attention to velocity dispersions, matching galaxies to subhalos which are explicitly tracked in the simulation. We find that not only do halos persist as subhalos when they fall into a larger host, groups of subhalos retain their identity for long periods within larger host halos. The highly anisotropic nature of infall into massive clusters, and their triaxiality, translates into an anisotropic velocity ellipsoid: line-of-sight galaxy velocity dispersions for any individual halo show large variance depending on viewing angle. The orientation of the velocity ellipsoid is correlated with the large-scale structure, and thus velocity outliers correlate with outliers caused by projection in other probes. We quantify this orientation uncertainty and give illustrative examples. Such a large variance suggests that velocity dispersion estimators will work better in an ensemble sense than for any individual cluster, which may inform strategies for obtaining redshifts of cluster members. We similarly find that the ability of substructure indicators to find kinematic substructures is highly viewing angle dependent. While groups of subhalos which merge with a larger host halo can retain their identity for many Gyr, they are only sporadically picked up by substructure indicators. (Abridged)
We present the initial imaging and spectroscopic data acquired as part of the VLT VIMOS Lyman-break galaxy Survey. UBR (or UBVI) imaging covers five 36'x36' fields centred on bright z>3 QSOs, allowing ~21,000 2<z<3.5 galaxy candidates to be selected using the Lyman-break technique. We performed spectroscopic follow-up using VIMOS, measuring redshifts for 1020 z>2 LBGs and 10 z>2 QSOs from a total of 19 VIMOS pointings. From the galaxy spectra, we observe a 625+-510 km/s velocity offset between the ISM absorption and Ly-alpha emission line redshifts. Using the photometric and spectroscopic catalogues, we have analysed the galaxy clustering at z~3. In the photometric case, the angular correlation function, w(theta), is well fit by a double power-law with clustering scale-length, r_0 = 3.19+0.32-0.54 Mpc/h for r < 1 Mpc/h and r_0 = 4.59+0.31-0.33 Mpc/h at larger scales. Using the redshift sample we estimate the semi-projected correlation function, w_p(sigma) and find r_0 = 3.67+0.23-0.24 Mpc/h for the VLT sample and r_0 = 3.98+0.14-0.15 Mpc/h for a combined VLT+Keck sample. From the z-space correlation functions and assuming the above xi(r) models, we find that the combined VLT and Keck surveys require a galaxy velocity dispersion, <w_z^2>^1/2 ~ 700 km/s, higher than the ~400 km/s found by previous authors. We also measure a value for the gravitational growth rate parameter of beta(z=3) = 0.48+-0.17, implying a low value for the bias of b = 2.06+1.1-0.5. This value is consistent with the galaxy clustering amplitude which gives b = 2.22+-0.16, assuming the standard cosmology, implying that the evolution of the gravitational growth rate is also consistent with Einstein gravity. We have compared our LBG clustering amplitudes with lower redshift measurements and find that the clustering strength is not inconsistent with that of low-redshift L* spirals for simple 'long-lived' galaxy models.
We propose a class of simple dark energy models which predict a late-time dark radiation component and a distinctive time-dependent equation of state $w(z)$ for redshift $z < 3$. The dark energy field can be coupled strongly enough to Standard Model particles to be detected in colliders, and the model requires only modest additional particle content and little or no fine-tuning other than a new energy scale of order milli-electron volts.
Spacetime curvature plays the primary role in general relativity but Einstein later considered a theory where torsion was the central quantity. Just as the Einstein-Hilbert action in the Ricci curvature scalar R can be generalized to f(R) gravity, we consider extensions of teleparallel, or torsion scalar T, gravity to f(T) theories. The field equations are naturally second order, avoiding pathologies, and can give rise to cosmic acceleration with unique features.
Recent studies have shown that galaxies accrete most of their baryons via the cold mode, from streams with temperatures T~10^4-10^5 K. At these temperatures, the streams should radiate primarily in Lya and have therefore been proposed as a model to power the Lya blobs and other high-redshift Lya sources. We introduce a new Lya radiative transfer code, aRT, and apply it to cosmological hydrodynamical simulations. We address physical and numerical issues that are critical to making accurate predictions for the cooling luminosity, but that have been mostly neglected or treated simplistically so far. We highlight the importance of self-shielding and of properly treating sub-resolution models in simulations. Most existing simulations do not self-consistently incorporate these effects, which can lead to order-of-magnitude errors in the predicted cooling luminosity. Using a combination of post-processing ionizing radiative transfer and re-simulation techniques, we develop an approximation to the consistent evolution of the self-shielded gas. We quantify the dependence of the Lya cooling luminosity on halo mass at z=3 for the simplified problem of pure gas accretion. While cooling in massive halos (without additional energy input from star formation and AGN) is in principle sufficient to produce L_a~10^43-10^44 erg s^-1 blobs, this appears to require including energy released in gas of density sufficient to form stars. Better modeling of the interface between the accretion streams and galactic discs, including feedback processes, is needed to determine whether these high cooling luminosities can be physically realized. Excluding emission from such dense gas yields lower luminosities by up to one to two orders of magnitudes at high masses. Resonant scattering produces diffuse Lya halos, even for centrally concentrated emission, and broad double peaked line profiles. [Abridged]
We present a Chandra monitoring campaign of the highly variable Seyfert galaxy UGC 4203 (the "Phoenix Galaxy") which revealed variations in the X-ray absorbing column density on time scales of two weeks. This is the third, clear case, after NGC 1365 and NGC 7582, of dramatic N_H variability on short time scales observed in a "changing look" source, i.e. an AGN observed in the past in both a reflection-dominated and a Compton-thin state. The inferred limits on the distance of the X-ray absorber from the center suggest that the X-ray "torus" could be one and the same with the broad emission line region. This scenario, first proposed for an "ad-hoc" picture for NGC 1365, may be the common structure of the circumnuclear medium in AGN.
We describe the Herschel Virgo Cluster Survey (HeViCS) and the first data obtained as part of the Science Demonstration Phase (SDP). The data cover a central 4x4 sq deg region of the cluster. We use SPIRE and PACS photometry data to produce 100, 160, 250, 350 and 500 micron luminosity functions (LFs) for optically bright galaxies that are selected at 500 micron and detected in all bands. We compare these LFs with those previously derived using IRAS, BLAST and Herschel-ATLAS data. The Virgo Cluster LFs do not have the large numbers of faint galaxies or examples of very luminous galaxies seen previously in surveys covering less dense environments.
By combining Herschel-SPIRE observations obtained as part of the Herschel Virgo Cluster Survey with 21 cm HI data from the literature, we investigate the role of the cluster environment on the dust content of Virgo spiral galaxies.We show for the first time that the extent of the dust disk is significantly reduced in HI-deficient galaxies, following remarkably well the observed 'truncation' of the HI disk. The ratio of the submillimetre-to- optical diameter correlates with the HI-deficiency, suggesting that the cluster environment is able to strip dust as well as gas. These results provide important insights not only into the evolution of cluster galaxies but also into the metal enrichment of the intra-cluster medium.
Passive early-type galaxies (ETGs) provide an ideal laboratory for studying the interplay between dust formation around evolved stars and its subsequent destruction in a hot gas. Using Spitzer-IRS and Herschel data we compare the dust production rate in the envelopes of evolved AGB stars with a constraint on the total dust mass. Early-type galaxies which appear to be truly passively evolving are not detected by Herschel. We thus derive a distance independent upper limit to the dust grain survival time in the hostile environment of ETGs of < 46 +/- 25 Myr for amorphous silicate grains. This implies that ETGs which are detected at far-infrared wavelengths have acquired a cool dusty medium via interaction. Given likely time-scales for ram-pressure stripping, this also implies that only galaxies with dust in a cool (atomic) medium can release dust into the intra-cluster medium.
We present a resolved dust analysis of three of the largest angular size spiral galaxies, NGC 4501 and NGC 4567/8, in the Herschel Virgo Cluster Survey (HeViCS) Science Demonstration field. Herschel has unprecedented spatial resolution at far-infrared wavelengths and with the PACS and SPIRE instruments samples both sides of the peak in the far infrared spectral energy distribution (SED).We present maps of dust temperature, dust mass, and gas-to-dust ratio, produced by fitting modified black bodies to the SED for each pixel. We find that the distribution of dust temperature in both systems is in the range ~19 - 22 K and peaks away from the centres of the galaxies. The distribution of dust mass in both systems is symmetrical and exhibits a single peak coincident with the galaxy centres. This Letter provides a first insight into the future analysis possible with a large sample of resolved galaxies to be observed by Herschel.
We present the dust properties of a small sample of Virgo cluster dwarf galaxies drawn from the science demonstration phase data set of the Herschel Virgo Cluster Survey. These galaxies have low metallicities (7.8 < 12 + log(O/H) < 8.3) and star-formation rates < 10^{-1} M_{sun}/yr. We measure the spectral energy distribution (SED) from 100 to 500 um and derive dust temperatures and dust masses. The SEDs are fitted by a cool component of temperature T < 20 K, implying dust masses around 10^{5} M_{sun} and dust-to-gas ratios D within the range 10^{-3}-10^{-2}. The completion of the full survey will yield a larger set of galaxies, which will provide more stringent constraints on the dust content of star-forming dwarf galaxies.
The origin of the far-infrared emission from the nearby radio galaxy M87 remains a matter of debate. Some studies find evidence of a far-infrared excess due to thermal dust emission, whereas others propose that the far-infrared emission can be explained by synchrotron emission without the need for an additional dust emission component. We present Herschel PACS and SPIRE observations of M87, taken as part of the science demonstration phase observations of the Herschel Virgo Cluster Survey. We compare these data with a synchrotron model based on mid-infrared, far-infrared, submm and radio data from the literature to investigate the origin of the far-infrared emission. Both the integrated SED and the Herschel surface brightness maps are adequately explained by synchrotron emission. At odds with previous claims, we find no evidence of a diffuse dust component in M87, which is not unexpected in the harsh X-ray environment of this radio galaxy sitting at the core of the Virgo Cluster.
We use the Science Demonstration Phase data of the Herschel Virgo Cluster Survey to search for dust emission of early-type dwarf galaxies in the central regions of the Virgo Cluster as an alternative way of identifying the interstellar medium.We present the first possible far-infrared detection of cluster early-type dwarf galaxies: VCC781 and VCC951 are detected at the 10 sigma level in the SPIRE 250 micron image. Both detected galaxies have dust masses of the order of 10^5 Msun and average dust temperatures ~20K. The detection rate (less than 1%) is quite high compared to the 1.7% detection rate for Hi emission, considering that dwarfs in the central regions are more Hi deficient. We conclude that the removal of interstellar dust from dwarf galaxies resulting from ram pressure stripping, harassment, or tidal effects must be as e?cient as the removal of interstellar gas.
We present grism spectra of emission--line galaxies (ELGs) from 0.6--1.6 microns from the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). These new infrared grism data augment previous optical Advanced Camera for Surveys G800L (0.6--0.95 micron) grism data in GOODS--South, extending the wavelength covereage well past the G800L red cutoff. The ERS grism field was observed at a depth of 2 orbits per grism, yielding spectra of hundreds of faint objects, a subset of which are presented here. ELGs are studied via the \Ha, \OIII, and \OII\ emission lines detected in the redshift ranges 0.2$\cle$z$\cle$1.6, 1.2$\cle$z$\cle$2.4 and 2.0$\cle$z$\cle$3.6 respectively in the G102 (0.8--1.1 microns; R$\sim$210) and G141 (1.1--1.6 microns; R$\sim$130) grisms. The higher spectral resolution afforded by the WFC3 grisms also reveals emission lines not detectable with the G800L grism (e.g., \SII\ and \SIII\ lines). From these relatively shallow observations, line luminosities, star--formation rates, and grism spectroscopic redshifts are determined for a total of 25 ELGs to m$_{AB(F098M)}$$\sim$25 mag. The faintest source in our sample---with a strong but unidentified emission--line---is m$_{AB(F098M)}$$=$26.9 mag. We also detect the expected trend of lower specific star formation rates for the highest mass galaxies in the sample, indicative of downsizing and discovered previously from large surveys. These results demonstrate the remarkable efficiency and capability of the WFC3 NIR grisms for measuring galaxy properties to faint magnitudes.
We present a strong lens analysis of SDSS J1004+4112, a unique quasar lens produced by a massive cluster of galaxies at z=0.68, using a newly developed software for gravitational lensing. We find that our parametric mass model well reproduces all observations including the positions of quasar images as well as those of multiply imaged galaxies with measured spectroscopic redshifts, time delays between quasar images, and the positions of faint central images. The predicted large total magnification of \mu ~ 70 suggests that the lens system is indeed a useful site for studying the fine structure of a distant quasar and its host galaxy. The dark halo component is found to be unimodal centered on the brightest cluster galaxy and the Chandra X-ray surface brightness profile. In addition, the orientation of the halo component is quite consistent with those of the brightest cluster galaxy and member galaxy distribution, implying that the lensing cluster is a relaxed system. The radial profile of the best-fit mass model is in good agreement with a mass profile inferred from the X-ray observation. While the inner radial slope of the dark halo component is consistent with being -1, a clear dependence of the predicted A-D time delay on the slope indicates that an additional time delay measurement will improve constraints on the mass model.
We show that a massive black hole binary might resonantly trap a small third body (e.g. a neutron star) down to a stage when the binary becomes relativistic due to its orbital decay by gravitational radiation. The final fate of the third body would be quite interesting for relativistic astrophysics. For example, the parent binary could expel the third body with a velocity more than 10% of the speed of light. We also discuss the implications of this three-body system for direct gravitational wave observation.
We present clumps of dust emission from Herschel observations of the Large Magellanic Cloud (LMC) and their physical and statistical properties. We catalog cloud features seen in the dust emission from Herschel observations of the LMC, the Magellanic type irregular galaxy closest to the Milky Way, and compare these features with HI catalogs from the ATCA+Parkes HI survey. Using an automated cloud-finding algorithm, we identify clouds and clumps of dust emission and examine the cumulative mass distribution of the detected dust clouds. The mass of cold dust is determined from physical parameters that we derive by performing spectral energy distribution fits to 250, 350, and 500 micronm emission from SPIRE observations using DUSTY and GRASIL radiative transfer calculation with dust grain size distributions for graphite/silicate in low-metallicity extragalactic environments. The dust cloud mass spectrum follows a power law distribution with an exponent of gamma=-1.8 for clumps larger than 400 solar mass and is similar to the HI mass distribution. This is expected from the theory of ISM structure in the vicinity of star formation.
We present the first detailed structure formation and radiative transfer simulations of the reionization history of our cosmic neighbourhood. To this end, we follow the formation of the Local Group of galaxies and nearby clusters by means of constrained simulations, which use the available observational constraints to construct a representation of those structures which reproduces their actual positions and properties at the present time. We find that the reionization history of the Local Group is strongly dependent on the assumed photon production efficiencies of the ionizing sources, which are still poorly constrained. If sources are relatively efficient, i.e. the process is 'photon-rich', the Local Group is primarily ionized externally by the nearby clusters. Alternatively, if the sources are inefficient, i.e. reionization is 'photon-poor' the Local Group evolves largely isolated and reionizes itself. The mode of reionization, external vs. internal, has important implications for the evolution of our neighbourhood, in terms of e.g. its satellite galaxy populations and primordial stellar populations. This therefore provides an important avenue for understanding the young universe by detailed studies of our nearby structures.
Disk-halo decompositions of galaxy rotation curves are generally performed in a parametric way. We construct self-consistent models of nonspherical isothermal halos embedding a zero-thickness disk, by assuming that the halo distribution function is a Maxwellian. The method developed here can be used to study other physically-based choices for the halo distribution function and the case of a disk accompanied by a bulge. In a preliminary investigation we note the existence of a fine tuning between the scalelengths R_{\Omega} and h, respectively characterizing the rise of the rotation curve and the luminosity profile of the disk, which surprisingly applies to both high surface brightness and low surface brightness galaxies. This empirical correlation identifies a much stronger conspiracy than the one required by the smoothness and flatness of the rotation curve (disk-halo conspiracy). The self-consistent models are characterized by smooth and flat rotation curves for very different disk-to-halo mass ratios, hence suggesting that conspiracy is not as dramatic as often imagined. For a typical rotation curve, with asymptotically flat rotation curve at V_{\infty} (the precise value of which can also be treated as a free parameter), and a typical density profile of the disk, self-consistent models are characterized by two dimensionless parameters, which correspond to the dimensional scales (the disk mass-to-light ratio M/L and the halo central density) of standard disk-halo decompositions. We show that if the rotation curve is decomposed by means of our self-consistent models, the disk-halo degeneracy is removed and typical rotation curves are fitted by models that are below the maximum-disk prescription. Similar results are obtained from a study of NGC 3198. Finally, we quantify the flattening of the spheroidal halo, which is significant, especially on the scale of the visible disk.
We investigate the far-infrared-radio correlation (FRC) of stellar-mass-selected galaxies in the Extended Chandra Deep Field South using far-infrared imaging from Spitzer and radio imaging from the Very Large Array and Giant Metre-Wave Radio Telescope. We stack in redshift bins to probe galaxies below the noise and confusion limits. Radio fluxes are K-corrected using observed flux ratios, leading to tentative evidence for an evolution in spectral index. We compare spectral energy distribution (SED) templates of local galaxies for K-correcting FIR fluxes, and show that the data are best fit by a quiescent spiral template (M51) rather than a warm starburst (M82) or ULIRG (Arp220), implying a predominance of cold dust in massive galaxies at high redshift. In contrast we measure total infrared luminosities that are consistent with high star-formation rates. We observe that the FRC index (q) does not evolve significantly over z=0-2 when computed from K-corrected 24 or 160-mum photometry, but that using 70-mum fluxes leads to an apparent decline in q beyond z~1. This suggests some change in the SED at high redshift, either a steepening of the spectrum at rest-frame ~25-35mum or a deficiency at ~70mum leading to a drop in the total infrared/radio ratios. We compare our results to other work in the literature and find synergies with recent findings for high-redshift SEDs.
We defined a sub-sample of twelve GPS sources which have not been observed with the VLBI before, from the Parkes half-Jansky sample, and carried out VLBI observations at 1.6 GHz and 5 GHz with the European VLBI Network (EVN) in 2006 and 2008, respectively, to classify the source structure and to find compact symmetric objects (CSOs). Additionally, we carried out the 4.85 GHz flux density observations for these sources with the Urumqi 25-m telescope between the years 2007 and 2009 to study whether there is any variability in the total flux density of the GPS sources. The results of the 5 GHz VLBI observations and total flux densities of these sources are presented in this paper. From the VLBI morphologies, the spectral indices of components and the total flux variability of the twelve targets, we firmly classify three sources J0210+0419, J1135$-$0021, and J2058+0540 as CSOs, and classify J1057+0012, J1203+0414, and J1600$-$0037 as core-jet sources. The others J0323+0534, J0433$-$0229, J0913+1454, J1109+1043, and J1352+0232 are labelled CSO candidates, and J1352+1107 is a complex feature. Apart from core-jet sources, the total flux densities of the CSOs and candidates are quite stable at 5 GHz both during a long-term of $\sim$20 years relative to the PKS90 data and in a period between 2007 and 2009. The total flux densities are resolved-out by more than 20\% in the 5 GHz VLBI images for 6 sources, probably because of diffuse emission. In addition, we estimated the jet viewing angles $\Theta$ for the confirmed CSOs by using the double-lobe flux ratio of the sources, the result being indicative of relatively large $\Theta$ for the CSOs.
We search for isolated galaxies based on the automatic identification of isolated sources from the Two Micron All-Sky Survey (2MASS) followed by a visual inspection of their surroundings. We use the modified Karachentseva criterion to compile a catalog of 3227 isolated galaxies (2MIG), which contains 6% of 2MASS Extended Sources Catalog (or 2MASX) sources brighter than Ks = 12 mag with angular diameters a_K > 30 arcsec. The catalog covers the entire sky and has an effective depth of z = 0.02. The 2493 very isolated objects of the catalog, which we include into the 2MVIG catalog, can be used as a reference sample to investigate the effects of the environment on the structure and evolution of galaxies located in regions with extremely low density of matter.
In a previous paper we showed that the radio sources selected by combining
large areas radio and optical surveys, present a strong deficit of radio
emission with respect to 3CR radio-galaxies matched in line emission
luminosity. We argued that the prevalence of sources with luminous extended
radio structures in high flux limited samples is due to a selection bias.
Sources with low radio power form the bulk of the radio-loud AGN population but
are still virtually unexplored.
We here analyze their photometric and spectroscopic properties. From the
point of view of their emission lines, the majority of the sample are Low
Excitation Galaxies (LEG), similar to the 3CR objects at the same level of line
luminosity. The hosts of LEG are red, massive Early-Type Galaxies (ETG) with
large black holes masses , statistically indistinguishable from the hosts of
low redshift 3CR/LEG sources. No genuine radio-loud LEG could be found
associated with black holes with a mass substantially lower than 10^8 M(sun) or
with a late type host. The fraction of galaxies with signs of star formation
(5%) is similar to what is found in both the quiescent ETG and 3CR/LEG hosts.
We conclude that the deficit in radio emission cannot be ascribed to
differences in the properties of their hosts. We argue that instead this could
be due to a temporal evolution of the radio luminosity.
A minority (10%) of the sample show rather different properties, being
associated with low black hole masses, with spiral galaxies, or showing a high
excitation spectrum. In general these outliers are the result of the
contamination from Seyfert and from galaxies where the radio emission is
powered by star formation. For the objects with high excitation spectra there
is no a clear discontinuity in either the host or nuclear properties as they
span from radio-quiet and radio-loud AGN.
In an effective field theory model with an ultraviolet momentum cutoff, there is a relation between the effective equation of state of dark energy and the ultraviolet cutoff scale. It implies that a measure of the equation of state of dark energy different from minus one, does not rule out vacuum energy as dark energy. It also indicates an interesting possibility that precise measurements of the infrared properties of dark energy can be used to probe the ultraviolet cutoff scale of effective quantum field theory coupled to gravity. In a toy model with a vacuum energy dominated universe with a Planck scale cutoff, the dark energy effective equation of state is -0.96.
During the month of December, 2009 the blazar 3C 454.3 became the brightest gamma-ray source in the sky, reaching a peak flux F ~2000E-8 ph/cm2/s for E > 100 MeV. Starting in November, 2009 intensive multifrequency campaigns monitored the 3C 454 gamma-ray outburst. Here we report the results of a 2-month campaign involving AGILE, INTEGRAL, Swift/XRT, Swift/BAT, RossiXTE for the high-energy observations, and Swift/UVOT, KANATA, GRT, REM for the near-IR/optical/UV data. The GASP/WEBT provided radio and additional optical data. We detected a long-term active emission phase lasting ~1 month at all wavelengths: in the gamma-ray band, peak emission was reached on December 2-3, 2009. Remarkably, this gamma-ray super-flare was not accompanied by correspondingly intense emission in the optical/UV band that reached a level substantially lower than the previous observations in 2007-2008. The lack of strong simultaneous optical brightening during the super-flare and the determination of the broad-band spectral evolution severely constrain the theoretical modelling. We find that the pre- and post-flare broad-band behavior can be explained by a one-zone model involving SSC plus external Compton emission from an accretion disk and a broad-line region. However, the spectra of the Dec. 2-3, 2009 super-flare and of the secondary peak emission on Dec. 9, 2009 cannot be satisfactorily modelled by a simple one-zone model. An additional particle component is most likely active during these states.
(Abstract abridged) The Abell 222 and 223 clusters are located at an average redshift z ~ 0.21 and are separated by 0.26 deg. Signatures of mergers have been previously found in these clusters, both in X-rays and at opticalwavelengths, thus motivating our study. In X-rays, they are relatively bright, and Abell 223 shows a double structure. A filament has also been detected between the clusters both at optical and X-ray wavelengths. We analyse the optical properties of these two clusters based on deep imaging in two bands, derive their galaxy minosity functions (GLFs) and correlate these properties with X-ray characteristics derived from XMM-Newton data. The GLFs of Abell 222 in the g' and r' bands are well fit by a Schechter function; the GLF is steeper in r' than in g'. For Abell 223, the GLFs in both bands require a second component at bright magnitudes, added to a Schechter function; they are similar in both bands. The Serna & Gerbal method allows to separate well the two clusters. No obvious filamentary structures are detected at very large scales around the clusters, but a third cluster at the same redshift, Abell 209, is located at a projected distance of 19.2 Mpc. X-ray temperature and metallicity maps reveal that the temperature and metallicity of the X-ray gas are quite homogeneous in Abell 222, while they are very perturbed in Abell 223. The Abell 222/Abell 223 system is complex. The two clusters that form this structure present very different dynamical states. Signs of recent interactions are also detected in the optical data where this cluster shows a ``perturbed'' GLF. In summary, the multiwavelength analyses of Abell 222 and Abell 223 are used to investigate the connection between the ICM and the cluster galaxy properties in an interacting system.
In this paper the possibility of generating large scale curvature perturbations induced from the entropic perturbations during the waterfall phase transition of standard hybrid inflation model is studied. We show that whether or not appreciable amounts of large scale curvature perturbations are produced during the waterfall phase transition depend crucially on the competition between the classical and the quantum mechanical back-reactions to terminate inflation. If one considers only the classical evolution of the system we show analytically as well as numerically that the highly blue-tilted entropy perturbations induce highly blue-tilted large scale curvature perturbations during the waterfall phase transition which completely dominate over the original adiabatic curvature perturbations. However, we show that the quantum back-reactions of the waterfall field inhomogeneities produced during the phase transition become important before the classical non-linear back-reactions become relevant. The cumulative quantum back-reactions of very small scales tachyonic modes terminate inflation very efficiently and shut off the curvature perturbations evolution during the waterfall phase transition. This indicates that the standard hybrid inflation model is safe under large scale curvature perturbations during the waterfall phase transition.
Aims: We aim to demonstrate that the Herschel ATLAS (H-ATLAS) is suitable for a blind and unbiased survey for debris disks by identifying candidate debris disks associated with main sequence stars in the initial science demonstration field of the survey. We show that H-ATLAS reveals a population of far-infrared/sub-mm sources that are associated with stars or star-like objects on the SDSS main-sequence locus. We validate our approach by comparing the properties of the most likely candidate disks to those of the known population. Methods: We use a photometric selection technique to identify main sequence stars in the SDSS DR7 catalogue and a Bayesian Likelihood Ratio method to identify H-ATLAS catalogue sources associated with these main sequence stars. Following this photometric selection we apply distance cuts to identify the most likely candidate debris disks and rule out the presence of contaminating galaxies using UKIDSS LAS K-band images. Results: We identify 78 H-ATLAS sources associated with SDSS point sources on the main-sequence locus, of which two are the most likely debris disk candidates: H-ATLAS J090315.8 and H-ATLAS J090240.2. We show that they are plausible candidates by comparing their properties to the known population of debris disks. Our initial results indicate that bright debris disks are rare, with only 2 candidates identified in a search sample of 851 stars. We also show that H-ATLAS can derive useful upper limits for debris disks associated with Hipparcos stars in the field and outline the future prospects for our debris disk search programme.
We perform a detailed and quasi model-independent analysis of direct annihilation of Dark Matter into neutrinos. Considering different cases for scalar and fermionic Dark Matter, we identify several settings in which this annihilation is enhanced, contrary to some statements in the literature. They key point is that several restrictions of, e.g., a supersymmetric framework do not hold in general. The mass generation mechanism of the neutrinos plays an important role, too. We illustrate our considerations by two examples that are not (as usually) suppressed by the smallness of the neutrino mass, for which we also present a numerical analysis. Our results can be easily used as guidelines for model building.
For the description of the early inflation, and acceleration expansion of the Universe, compatible with observational data, the $5D$ noncompact Kaluza--Klein cosmology is investigated. It is proposed that the $5D$ space is filled with a null perfect fluid, resulting a perfect fluid in $4D$ universe, plus one along the fifth dimension. By analyzing the reduced field equations for flat FRW model, we show the early inflationary behavior and current acceleration of the universe.
We explore the kinematical effect of having extra dimensions on the gravity wave emission from cosmic strings. Additional dimensions both round off cusps, and reduce the probability of their formation. We recompute the gravity wave burst, taking into account these two factors, and find a potentially significant damping on the gravity waves of the strings.
We present Suzaku observations of five hard X-ray selected nearby Seyfert 2 galaxies. All the sources were clearly detected with the pin Hard X-ray Detector up to several tens of keV, allowing for a fairly good characterization of the broad-band X-ray continuum. We find that a unique model, even including multiple components, fails to represent the spectra of all the sources. Heavy obscuration manifests itself in different flavours. For two sources there is evidence for a reflection dominated continuum; among the other three, one is "mildly" Compton thick (N_H ~ 10^24 cm-2), while the remaining two are heavily obscured (N_H ~ 10^23.5 cm-2), but Compton thin. Strong, narrow, iron Kalpha lines (EW ~ 1-2 keV) due to neutral or mildly ionized gas, are detected in Compton thick AGN. In all of them the Kalpha line is accompanied by the Kbeta. The intensity and shape of the soft X-ray spectrum are different from object to object. Soft X--rays may originate from a nuclear component scattered off, or leaking through, the X-ray absorber, plus thermal X-rays from the host galaxy. Emission from circumnuclear gas photoionized by the active nucleus, parameterized with a power law plus individual narrow Gaussian lines, also provides an acceptable description of the soft X-ray spectra. The limited Suzaku XIS CCD energy resolution does not allow us to draw firm conclusions on the origin of the soft X--ray emission. We briefly discuss our findings in the light of AGN Unified model and the geometry of the obscuring gas.
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We measure the angular correlation function, w(theta), from 0.5 to 30 arcminutes of detected sources in two wide fields of the Herschel Multi-tiered Extragalactic Survey (HerMES). Our measurements are consistent with the expected clustering shape from a population of sources that trace the dark matter density field, including non-linear clustering at arcminute angular scales arising from multiple sources that occupy the same dark matter halos. By making use of the halo model to connect the spatial clustering of sources to the dark matter halo distribution, we estimate source bias and halo occupation number for dusty sub-mm galaxies at z ~ 2. We find that sub-mm galaxies with 250 micron flux densities above 30 mJy reside in dark matter halos with mass above (5\pm4) x 10^12 M_sun, while (14\pm8)% of such sources appear as satellites in more massive halos.
We present an analytical derivation of the Sachs Wolfe effect sourced by a primordial magnetic field, generated by a causal process, such as a first order phase transition in the early universe. As for the topological defects case, we apply the general relativistic junction conditions to match the perturbation variables before and after the phase transition, in such a way that the total energy momentum tensor is conserved across the transition. We find that the relevant contribution to the magnetic Sachs Wolfe effect comes from the metric perturbations at next-to-leading order in the large scale limit. The leading order term is strongly suppressed due to the presence of free-streaming neutrinos. We derive the neutrino compensation effect and confirm that the magnetic Sachs Wolfe spectrum from a causal magnetic field behaves as l(l+1)C_l^B ~ l^2 as found in the latest numerical analyses.
Interstellar dust grains efficiently absorb and scatter UV and optical radiation in galaxies, and therefore can significantly affect the apparent structure of spiral galaxies. We discuss the effect of dust attenuation on the observed structural properties of bulges and discs. We also present some first results on modelling the dust content of edge-on spiral galaxies using both optical and Herschel far-infrared data. Both of these results demonstrate the complex interplay of dust and star light in spiral galaxies.
We report the result of VLBI observation of the giant radio galaxy J1313+696 (4C +69.15) at 2.3/8.4 GHz, only the core component of the giant radio galaxy was detected in the VLBI observation at the dual frequencies. The result shows a steep spectrum core with $\alpha=-0.82$ ($S \propto \nu^{\alpha}$) between 2.3 GHz and 8.4 GHz. The steep spectrum core may be a sign of renewed activity. Considering also the upper limit flux density of 2.0 mJy at 0.6 GHz from Konar et al. 2004 the core has a GHz-peaked spectrum, implying that the core is compact and absorbed. Further high resolution VLBI observations are needed to identify if the steep spectrum core is consisting of a core and steep spectrum jet.
We report the results of multifrequency-VLBI observations of GHz-Peaked-Spectrum (GPS) radio sources. The VLBI structure and component spectra of some GPS sources are presented. Our VLBI results show that about 80% of the GPS galaxies exhibit a compact double or CSO-like structure, while the GPS quasars tend to show a core-jet. The component spectra of the GPS galaxies are often steep/convex, and the core has a flat spectrum but it is usually hidden or weak. In addition, we studied the variability of GPS sources by comparing new flux density measures, acquired with the Urumqi 25m telescope at 4.85 GHz, with previous 87GB data. The results show that 44% of the GPS quasars varied higher than 10% in passed 20 years, while the fraction is only 12% for the GPS galaxies meaning that the GPS quasars are much more variable than GPS galaxies. In total, 25% of GPS sources show >10% variability at 4.85 GHz in our sample.
We present an analysis of the first space-based far-IR-submm observations of M 33, which measure the emission from the cool dust and resolve the giant molecular cloud complexes. With roughly half-solar abundances, M33 is a first step towards young low-metallicity galaxies where the submm may be able to provide an alternative to CO mapping to measure their H$_2$ content. In this Letter, we measure the dust emission cross-section $\sigma$ using SPIRE and recent CO and \HI\ observations; a variation in $\sigma$ is present from a near-solar neighborhood cross-section to about half-solar with the maximum being south of the nucleus. Calculating the total H column density from the measured dust temperature and cross-section, and then subtracting the \HI\ column, yields a morphology similar to that observed in CO. The H$_2$/\HI\ mass ratio decreases from about unity to well below 10% and is about 15% averaged over the optical disk. The single most important observation to reduce the potentially large systematic errors is to complete the CO mapping of M 33.
We offer a simple parameterization of the rate of star formation in galaxies. In this new approach, we make explicit and decouple the timescales associated (a) with disruptive effects the star formation event itself, from (b) the timescales associated with the cloud assembly and collapse mechanisms leading up to star formation. The star formation law in near-by galaxies, as measured on sub-kiloparsec scales, has recently been shown by Bigiel et al. to be distinctly non-linear in its dependence on total gas density. Our parameterization of the spatially resolved Schmidt-Sanduleak relation naturally accommodates that dependence. The parameterized form of the relation is rho_* ~ epsilon x rho_g/(tau_s + rho_g ^{-n}), where rho_g is the gas density, epsilon is the efficiency of converting gas into stars, and rho_g^{-n} captures the physics of cloud collapse. Accordingly at high gas densities quiescent star formation is predicted to progress as rho_* ~ rho_g, while at low gas densities rho_* ~ rho_g^{1+n}, as is now generally observed. A variable efficiency in locally converting gas into stars as well as the unknown plane thickness variations from galaxy to galaxy, and radially within a given galaxy, can readily account for the empirical scatter in the observed (surface density rather than volume density) relations, and also plausibly account for the noted upturn in the relation at very high apparent projected column densities.
We utilize detailed time-varying models of the coupled evolution of stars and
the HI, H_2, and CO-bright H_2 gas phases in galaxy-sized numerical simulations
to explore the evolution of gas-rich and/or metal-poor systems, expected to be
numerous in the Early Universe. The inclusion of the CO-bright H_2 gas phase,
and the realistic rendering of star formation as an H_2-regulated process (and
the new feedback processes that this entails) allows the most realistic
tracking of strongly evolving galaxies, and much better comparison with
observations. We find that while galaxies eventually settle into states
conforming to Schmidt-Kennicutt (S-K) relations, significant and systematic
deviations of their star formation rates (SFRs) from the latter occur,
especially pronounced and prolonged for ...
...This indicates potentially serious limitations of (S-K)-type relations as
reliable sub-grid elements of star formation physics in simulations of
structure formation in the Early Universe. We anticipate that galaxies with
marked deviations from the S-K relations will be found at high redshifts as
unbiased inventories of total gas mass become possible with ALMA and the EVLA.
Recent studies have shown that the primordial non-Gaussianity affects clustering of dark matter halos through a scale-dependent bias and various constraints on the non-Gaussianity through this scale-dependent bias have been placed. Here we introduce the cross-correlation between the CMB lensing potential and the galaxy angular distribution to effectively extract information about the bias from the galaxy distribution. Then, we estimate the error of non-linear parameter, f_NL, for the on-going CMB experiments and galaxy surveys, such as Planck and Hyper Suprime-Cam (HSC). We found that for the constraint on f_NL with Planck and HSC, the wide field galaxy survey is preferable to the deep one, and the expected error on f_NL can be as small as: {\Delta}f_NL ~ 80 for b_0 = 2 and {\Delta}f_NL ~ 30 for b_0 = 4, where b_0 is the linear bias parameter. It is also found that future wide field galaxy survey could achieve {\Delta}fNL ~ 5 with CMB prior from Planck if one could observe highly biased objects at higher redshift (z ~ 2).
Dwarf irregular galaxies are relatively simple unevolved objects where it is easy to test models of galactic chemical evolution. We aim at deriving the star formation and gas accretion history of IC10, a local dwarf irregular for which abundance, gas and mass determinations are available. We run detailed chemical evolution models to predict the evolution of several chemical elements (He, O, N, S) and compared our predictions with the observational data. We considered also other constraints such as the present time gas fraction and the star formation rate as well as the total estimated mass for IC10. We assumed a dark matter halo for this galaxy and studied the development of a galactic wind. We explored different star formation regimes: bursting and continuous. We also explored different wind situations: i) normal wind, where all the gas is lost at the same rate and ii) metal-enhanced wind, where metals produced by supernovae are preferentially lost. We also explored a case without wind. We varied the star formation efficiency (SFE), the wind efficiency and the time scale for the gas infall, which are the most important parameters in our models. We found that only models with metal-enhanced galactic winds can reproduce the properties of IC10. The star formation must have proceeded in bursts rather than continuously and the bursts must have been no more than ten over the whole galactic lifetime. Finally, IC10 must have formed by a slow process of gas accretion with a timescale of the order of 8 Gyr.
Braneworld models with variable brane tension $\lambda $ introduce a new degree of freedom that allows for evolving gravitational and cosmological constants, the latter being a natural candidate for dark energy. We consider a thermodynamic interpretation of the varying brane tension models, by showing that the field equations with variable $\lambda $ can be interpreted as describing matter creation in a cosmological framework. The particle creation rate is determined by the variation rate of the brane tension, as well as by the brane-bulk energy-matter transfer rate. We investigate the effect of a variable brane tension on the cosmological evolution of the Universe, in the framework of a particular model in which the brane tension is an exponentially dependent function of the scale factor. The resulting cosmology shows the presence of an initial inflationary expansion, followed by a decelerating phase, and by a smooth transition towards a late accelerated de Sitter type expansion. The varying brane tension is also responsible for the generation of the matter in the Universe (reheating period). The physical constraints on the model parameters, resulted from the observational cosmological data, are also investigated.
We describe a simple way of incorporating fluctuations of the Hubble scale during the horizon exit of scalar perturbations into the delta N formalism. The dominant effect comes from the dependence of the Hubble scale on low-frequency modes of the inflaton. This modifies the coefficient of the log-enhanced term appearing in the curvature spectrum at second order in field fluctuations. With this modification, the relevant coefficient turns out to be proportional to the second derivative of the tree-level spectrum with respect to the inflaton phi at horizon exit. A logarithm with precisely the same coefficient appears in a calculation of the log-enhancement of the curvature spectrum based purely on the geometry of the reheating surface. We take this agreement as strong support for the proposed implementation of the delta N formalism. Moreover, our analysis makes it apparent that the log-enhancement of the inflationary power-spectrum is indeed physical if this quantity is defined using a global coordinate system on the reheating surface (or any other post-inflationary surface of constant energy density). However, it can be avoided by defining the spectrum using invariant distances on this surface.
Gravitational parity violation is a possibility motivated by particle physics, string theory and loop quantum gravity. One effect of it is amplitude birefringence of gravitational waves, whereby left and right circularly-polarized waves propagate at the same speed but with different amplitude evolution. Here we propose a test of this effect through coincident observations of gravitational waves and short gamma-ray bursts from binary mergers involving neutron stars. Such gravitational waves are highly left or right circularly-polarized due to the geometry of the merger. Using localization information from the gamma-ray burst, ground-based gravitational wave detectors can measure the distance to the source with reasonable accuracy. An electromagnetic determination of the redshift from an afterglow or host galaxy yields an independent measure of this distance. Gravitational parity violation would manifest itself as a discrepancy between these two distance measurements. We exemplify such a test by considering one specific effective theory that leads to such gravitational parity-violation, Chern-Simons gravity. We show that the advanced LIGO-Virgo network and all-sky gamma-ray telescopes can be sensitive to the propagating sector of Chern-Simons gravitational parity violation to a level roughly two orders of magnitude better than current stationary constraints from the LAGEOS satellites.
We describe the cryostat and supporting electronics for the EBEX experiment. EBEX is a balloon-borne polarimeter designed to measure the B-mode polarization of the cosmic microwave background radiation. The instrument includes a 1.5 meter Gregorian-type telescope and 1432 bolometric transition edge sensor detectors operating at 0.3 K. Electronics for monitoring temperatures and controlling cryostat refrigerators is read out over CANbus. A timing system ensures the data from all subsystems is accurately synchronized. EBEX completed an engineering test flight in June 2009 during which the cryogenics and supporting electronics performed according to predictions. The temperatures of the cryostat were stable, and an analysis of a subset of the data finds no scan synchronous signal in the cryostat temperatures. Preparations are underway for an Antarctic flight.
We use a long (300 ksec), continuous Suzaku X-ray observation of the active nucleus in NGC1365 to investigate the structure of the circumnuclear BLR clouds through their occultation of the X-ray source. The variations of the absorbing column density and of the covering factor indicate that the clouds surrounding the black hole are far from having a spherical geometry (as sometimes assumed), instead they have a strongly elongated and cometary shape, with a dense head (n=10^11 cm^-3) and an expanding, dissolving tail. We infer that the cometary tails must be longer than a few times 10^13 cm and their opening angle must be smaller than a few degrees. We suggest that the cometary shape may be a common feature of BLR clouds in general, but which has been difficult to recognize observationally so far. The cometary shape may originate from shocks and hydrodynamical instabilities generated by the supersonic motion of the BLR clouds into the intracloud medium. As a consequence of the mass loss into their tail, we infer that the BLR clouds probably have a lifetime of only a few months, implying that they must be continuously replenished. We also find a large, puzzling discrepancy (two orders of magnitude) between the mass of the BLR inferred from the properties of the absorbing clouds and the mass of the BLR inferred from photoionization models; we discuss the possible solutions to this discrepancy.
The system of electron beam - degenerate Fermi gas in a magnetic field is investigated. Instabilities of the quantized longitudinal electric waves are studied by a newly derived dispersion equation. Novel branches of longitudinal waves are found, which have no analogies without the Landau quantization. Growth rates of these new modes are obtained. The excitation of the zero sound by an electron beam is discussed and found that the quantization of the energy of electrons imposes a new condition. Furthermore, the excitation of Bogolyubov's type of spectrum by a strong electric field is considered.
The high-redshift gamma-ray bursts (GRBs), GRBs 080913 and 090423, challenge the conventional GRB progenitor models by their short durations, typical for short GRBs, and their high energy releases, typical for long GRBs. Meanwhile, the GRB rate inferred from high-redshift GRBs also remarkably exceeds the prediction of the collapsar model, with an ordinary star formation history. We show that all these contradictions could be eliminated naturally, if we ascribe some high-redshift GRBs to electromagnetic bursts of superconducting cosmic strings. High-redshift GRBs could become a reasonable way to test the superconducting cosmic string model, because the event rate of cosmic string bursts increases rapidly with increasing redshifts, whereas the collapsar rate decreases.
It has recently been shown in high resolution numerical simulations that relativistic collisions of bubbles in the context of a multi-vacua potential may lead to the creation of bubbles in a new vacuum. In this paper, we show that scalar fields with only potential interactions behave like free fields during high-speed collisions; the kick received by them in a collision can be deduced simply by a linear superposition of the bubble wall profiles. This process is equivalent to the scattering of solitons in 1+1 dimensions. We deduce an expression for the field excursion (shortly after a collision), which is related simply to the field difference between the parent and bubble vacua, i.e. contrary to expectations, the excursion cannot be made arbitrarily large by raising the collision energy. There is however a minimum energy threshold for this excursion to be realized. We verify these predictions using a number of 3+1 and 1+1 numerical simulations. A rich phenomenology follows from these collision induced excursions - they provide a new mechanism for scanning the landscape, they might end/begin inflation, and they might constitute our very own big bang, leaving behind a potentially observable anisotropy.
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The central dominant galaxies in galaxy clusters constitute the most massive and luminous galaxies in the Universe. Despite this, the formation of these brightest cluster galaxies (BCGs) and the impact of this on the surrounding cluster environment remain poorly understood. Here we present multi-wavelength observations of the nearby poor X-ray cluster MZ 10451, in which both processes can be studied in unprecedented detail. Chandra observations of the intracluster medium (ICM) in the cluster core, which harbors two optically bright early-type galaxies in the process of merging, show that the system has retained a cool core and a central metal excess. This suggests that any merger-induced ICM heating and mixing remain modest at this stage. Tidally stripped stars seen around either galaxy likely represent an emerging intracluster light component, and the central ICM abundance enhancement may have a prominent contribution from in situ enrichment provided by these stars. The smaller of the merging galaxies shows evidence for having retained a hot gas halo, along with tentative evidence for some obscured star formation, suggesting that not all BCG major mergers at low redshift are completely dissipationless. Both galaxies are slightly offset from the peak of the ICM emission, with all three lying on an axis that roughly coincides with the large-scale elongation of the ICM. Our data are consistent with a picture in which central BCGs are built up by mergers close to the cluster core, by galaxies infalling on radial orbits aligned with the cosmological filaments feeding the cluster.
We present mid-infrared spectra of six FeLoBAL QSOs at 1<z<1.8, taken with the Spitzer space telescope. The spectra span a range of shapes, from hot dust dominated AGN with silicate emission at 9.7 microns, to moderately obscured starbursts with strong Polycyclic Aromatic Hydrocarbon (PAH) emission. The spectrum of one object, SDSS 1214-0001, shows the most prominent PAHs yet seen in any QSO at any redshift, implying that the starburst dominates the mid-IR emission with an associated star formation rate of order 2700 solar masses per year. With the caveats that our sample is small and not robustly selected, we combine our mid-IR spectral diagnostics with previous observations to propose that FeLoBAL QSOs are at least largely comprised of systems in which (a) a merger driven starburst is ending, (b) a luminous AGN is in the last stages of burning through its surrounding dust, and (c) which we may be viewing over a restricted line of sight range.
Massive metal-poor stars might form massive stellar black holes (BHs), with mass 25<=mBH/Msun<=80, via direct collapse. We derive the number of massive BHs (NBH) that are expected to form per galaxy through this mechanism. Such massive BHs might power most of the observed ultra-luminous X-ray sources (ULXs). We select a sample of 64 galaxies with X-ray coverage, measurements of the star formation rate (SFR) and of the metallicity. We find that NBH correlates with the number of observed ULXs per galaxy (NULX) in this sample. We discuss the dependence of our model on the SFR and on the metallicity. The SFR is found to be crucial, consistently with previous studies. The metallicity plays a role in our model, since a lower metallicity enhances the formation of massive BHs. Consistently with our model, the data indicate that there might be an anticorrelation between NULX, normalized to the SFR, and the metallicity. A larger and more homogeneous sample of metallicity measurements is required, in order to confirm our results.
We report the first simultaneous zJHK spectroscopy on the archetypical Seyfert 2 Galaxy NGC 1068 covering the wavelength region 0.9 to 2.4 micron. The slit, aligned in the NS direction and centred in the optical nucleus, maps a region 300 pc in radius at sub-arcsec resolution, with a spectral resolving power of 360 km s^-1. This configuration allow us to study the physical properties of the nuclear gas including that of the north side of the ionization cone, map the strong excess of continuum emission in the K-band and attributed to dust and study the variations, both in flux and profile, in the emission lines. Our results show that (1) Mid- to low-ionization emission lines are splitted into two components, whose relative strengths vary with the position along the slit and seem to be correlated with the jet. (2) The coronal lines are single-peaked and are detected only in the central few hundred of parsecs from the nucleus. (3) The absorption lines indicate the presence of intermediate age stellar population, which might be a significant contributor to the continuum in the NIR spectra. (4) Through some simple photoionization models we find photoionization as the main mechanism powering the emitting gas. (5) Calculations using stellar features point to a mass concentration inside the 100 - 200 pc of about 10^10 solar masses.
We performed stellar population synthesis on the nuclear and extended regions of NGC 1068 by means of near-infrared spectroscopy to disentangle their spectral energy distribution components. This is the first time that such a technique is applied to the whole 0.8 - 2.4 micron wavelength interval in this galaxy. NGC 1068 is one of the nearest and probably the most studied Seyfert 2 galaxy, becoming an excellent laboratory to study the interaction between black holes, the jets that they can produce and the medium in which they propagate. Our main result is that traces of young stellar population are found at ~ 100 south of the nucleus. The contribution of a power-law continuum in the centre is about 25%, which is expected if the light is scattered from a Seyfert 1 nucleus. We find peaks in the contribution of the featureless continuum about 100 - 150 pc from the nucleus on both sides. They might be associated with regions where the jet encounters dense clouds. Further support to this scenario is given by the peaks of hot dust distribution found around these same regions and the H2 emission line profile, leading us to propose that the peaks might be associate to regions where stars are being formed. Hot dust also has an important contribution to the nuclear region, reinforcing the idea of the presence of a dense, circumnuclear torus in this galaxy. Cold dust appears mostly in the south direction, which supports the view that the southwest emission is behind the plane of the galaxy and is extinguished very likely by dust in the plane. Intermediate age stellar population contributes significantly to the continuum, specially in the inner 200 pc.
Because of an old quasar APM 08279 + 5255 at $z=3.91$, some dark energy models face the challenge of the cosmic age problem. It has been shown by Wei and Zhang [Phys. Rev. D {\bf 76}, 063003 (2007)] that the holographic dark energy model is also troubled with such a cosmic age problem. In order to accommodate this old quasar and solve the age problem, we propose in this paper to consider the interacting holographic dark energy in a non-flat universe. We show that the cosmic age problem can be eliminated when the interaction and spatial curvature are both involved in the holographic dark energy model.
We present a multi-wavelength analysis of the merging rich cluster of galaxies Abell 2256. We have observed A2256 at 150 MHz using the Giant Metrewave Radio Telescope and successfully detected the diffuse radio halo and the relic emission over an extent $\sim1.2$ Mpc$^2$. Using this 150 MHz image and the images made using archival observations from the VLA (1369 MHz) and the WSRT (350 MHz), we have produced spectral index images of the diffuse radio emission in A2256. These spectral index images show a distribution of flat spectral index (S$\propto\nu^\alpha$, $\alpha$ in the range -0.7 to -0.9) plasma in the NW of the cluster centre. Regions showing steep spectral indices ($\alpha$ in the range -1.0 to -2.3) are toward the SE of the cluster centre. These spectral indices indicate synchrotron life times for the relativistic plasmas in the range 0.08 - 0.4 Gyr. We interpret this spectral behaviour as resulting from a merger event along the direction SE to NW within the last 0.5 Gyr or so. A shock may be responsible for the NW relic in A2256 and the Mpc scale radio halo towards the SE is likely to be generated by the turbulence injected by mergers. Furthermore, the diffuse radio emission shows spectral steepening toward lower frequencies. This low frequency spectral steepening is consistent with a combination of spectra from two populations of relativistic electrons created at two epochs (two mergers) within the last $\sim$0.5 Gyr. Earlier interpretations of the X-ray and the optical data also suggested that there were two mergers in Abell 2256 in the last 0.5 Gyr, consistent with the current findings. Also highlighted in this study is the futility of correlating the average temperatures of thermal gas and the average spectral indices of diffuse radio emission in respective clusters.
The use of standard rulers, such as the scale of the Baryonic Acoustic oscillations (BAO), has become one of the more powerful techniques employed in cosmology to probe the entity driving the accelerating expansion of the Universe. In this paper, the topology of large scale structure (LSS) is used as one such standard ruler to study this mysterious `dark energy'. By following the redshift evolution of the clustering of luminous red galaxies (LRGs) as measured by their 3D topology (counting structures in the cosmic web), we can chart the expansion rate and extract information about the equation of state of dark energy. Using the technique first introduced in (Park & Kim, 2009), we evaluate the constraints that can be achieved using 3D topology measurements from next-generation LSS surveys such as the Baryonic Oscillation Spectroscopic Survey (BOSS). In conjunction with the information that will be available from the Planck satellite, we find a single topology measurement on 3 different scales is capable of constraining a single dark energy parameter to within 5% and 10% when dynamics are permitted. This offers an alternative use of the data available from redshift surveys and serves as a cross-check for BAO studies.
The Ultra Luminous InfraRed Galaxy Mrk 231 reveals up to seven rotational lines of water (H2O) in emission, including a very high-lying (E_{upper}=640 K) line detected at a 4sigma level, within the Herschel/SPIRE wavelength range, whereas PACS observations show one H2O line at 78 microns in absorption, as found for other H2O lines previously detected by ISO. The absorption/emission dichotomy is caused by the pumping of the rotational levels by far-infrared radiation emitted by dust, and subsequent relaxation through lines at longer wavelengths, which allows us to estimate both the column density of H2O and the general characteristics of the underlying far-infrared continuum source. Radiative transfer models including excitation through both absorption of far-infrared radiation emitted by dust and collisions are used to calculate the equilibrium level populations of H2O and the corresponding line fluxes. The highest-lying H2O lines detected in emission, with levels at 300-640 K above the ground state, indicate that the source of far-infrared radiation responsible for the pumping is compact (radius=110-180 pc) and warm (T_{dust}=85-95 K), accounting for at least 45% of the bolometric luminosity. The high column density, N(H2O)~5x10^{17} cm^{-2}, found in this nuclear component, is most probably the consequence of shocks/cosmic rays, an XDR chemistry, and/or an "undepleted chemistry" where grain mantles are evaporated. A more extended region, presumably the inner region of the 1-kpc disk observed in other molecular species, could contribute to the flux observed in low-lying H2O lines through dense hot cores, and/or shocks. The H2O 78 micron line observed with PACS shows hints of a blue-shifted wing seen in absorption, possibly indicating the occurrence of H2O in the prominent outflow detected in OH (Fischer et al., this volume).
We present radio images of a sample of six Wide-Angle Tail (WAT) radio sources identified in the ATLAS 1.4 GHz radio survey, and new spectroscopic redshifts for four of these sources. These WATs are in the redshift range of 0.1469 - 0.3762, and we find evidence of galaxy overdensities in the vicinity of four of the WATs from either spectroscopic or photometric redshifts. We also present follow-up spectroscopic observations of the area surrounding the largest WAT, S1189, which is at a redshift of ~0.22. The spectroscopic observations, taken using the AAOmega spectrograph on the AAT, show an overdensity of galaxies at this redshift. The galaxies are spread over an unusually large area of ~12 Mpc with a velocity spread of ~4500 km/s. This large-scale structure includes a highly asymmetric FRI radio galaxy and also appears to host a radio relic. It may represent an unrelaxed system with different sub-structures interacting or merging with one another. We discuss the implications of these observations for future large-scale radio surveys.
While Bayesian model selection is a useful tool to discriminate between competing cosmological models, it only gives a relative rather than an absolute measure of how good a model is. Bayesian doubt introduces an unknown benchmark model against which the known models are compared, thereby obtaining an absolute measure of model performance in a Bayesian framework. We apply this new methodology to the problem of the dark energy equation of state, comparing an absolute upper bound on the Bayesian evidence for a presently unknown dark energy model against a collection of known models including a flat LambdaCDM scenario. We find a strong absolute upper bound to the Bayes factor B between the unknown model and LambdaCDM, giving B < 3. The posterior probability for doubt is found to be less than 6% (with a 1% prior doubt) while the probability for LambdaCDM rises from an initial 25% to just over 50% in light of the data. We conclude that LambdaCDM remains a sufficient phenomenological description of currently available observations and that there is little statistical room for model improvement.
The vacuum fluctuations of all quantum fields filling the universe are supposed to leave enormous energy and pressure contributions which are incompatible with observations. It has been recently suggested that, when the effective nature of quantum field theories is properly taken into account, vacuum fluctuations behave as a relativistic gas rather than as a cosmological constant. Accordingly, zero-point energies are tremendously diluted by the universe expansion but provide an extra contribution to radiation energy. Ongoing and future cosmological observations could offer the opportunity to scrutinize this scenario. The presence of such additional contribution to radiation energy can be tested by using primordial nucleosynthesis bounds or measured on Cosmic Background Radiation anisotropy.
The existence of cosmic rays and weak magnetic fields in the intracluster volume has been well proven by deep radio observations of galaxy clusters. However a detailed physical characterization of the non-thermal component of large scale-structures, relevant for high-precision cosmology, is still missing. I will show the importance of combining numerical and theoretical works with cluster observations by a new-generation of radio, Gamma- and X-ray instruments.
Constraints on the expansion history of the universe from measurements of cosmological distances make predictions for large-scale structure growth. Since these predictions depend on assumptions about dark energy evolution and spatial curvature, they can be used to test general classes of dark energy models by comparing predictions for those models with direct measurements of the growth history. I present predictions from current distance measurements for the growth history of dark energy models including a cosmological constant and quintessence. Although a time-dependent dark energy equation of state significantly weakens predictions for growth from measured distances, for quintessence there is a generic limit on the growth evolution that could be used to falsify the whole class of quintessence models. Understanding the allowed range of growth for dark energy models in the context of general relativity is a crucial step for efforts to distinguish dark energy from modified gravity.
Brief response to a Reply [arXiv:1005.2615] on our Comments [arXiv:1005.0838] on XENON100 recent results [arXiv:1005.0380].
We consider the dilaton in the strong string coupling limit and elaborate on the original idea of Damour and Polyakov whereby the dilaton coupling to matter has a minimum with a vanishing value at finite field-value. Combining this type of coupling with an exponential potential, the effective potential of the dilaton becomes matter density dependent. We study the background cosmology, showing that the dilaton can play the role of dark energy. We also analyse the constraints imposed by the absence of violation of the equivalence principle. Imposing these constraints and assuming that the dilaton plays the role of dark energy, we consider the consequences of the dilaton on large scale structures and in particular the behaviour of the slip functions and the growth index at low redshift.
Evidence for an accelerated expansion of the universe as it has been revealed ten years ago by the Hubble diagram of distant type Ia supernovae represents one of the major modern revolutions for fundamental physics and cosmology. It is yet unclear whether the explanation of the fact that gravity becomes repulsive on large scales should be found within general relativity or within a new theory of gravitation. However, existing evidences for this acceleration all come from astrophysical observations. Before accepting a drastic revision of fundamental physics, it is interesting to critically examine the present situation of the astrophysical observations and the possible limitation in their interpretation. In this review, the main various observational probes are presented as well as the framework to interpret them with special attention to the complex astrophysics and theoretical hypotheses that may limit actual evidences for the acceleration of the expansion. Even when scrutinized with sceptical eyes, the evidence for an accelerating universe is robust. Investigation of its very origin appears as the most fascinating challenge of modern physics.
The color-magnitude relation of early-type galaxies differs slightly but significantly from a pure power-law, curving downwards at low and upwards at large luminosities (Mr>-20.5 and Mr<-22.5). This remains true of the color-size relation, and is even more apparent with stellar mass (M* < 3x10^10 M_Sun and M* > 2x10^11 M_Sun). The upwards curvature at the massive end does not appear to be due to stellar population effects. Moreover, it begins on the same stellar mass scale, M* = 2x10^11M_Sun, as that on which the mean axis ratio and color gradients are maximal, and on which the size-luminosity relation curves upwards, and the velocity dispersion-luminosity relation flattens. In contrast, the color-sigma relation, and indeed, most scaling relations with sigma, are well-described by a single power law. Since major dry mergers change neither the colors nor sigma, but they do change masses, sizes, axis ratios and color gradients, the clear features observed in the scaling relations with M*, but not with sigma > 150 km s^-1, suggest that M* > 2x10^11 M_Sun is the scale above which major mergers dominate the assembly history. We discuss three models of the merger histories since z ~ 1 which are compatible with our measurements. In all three models, dry mergers are responsible for the flattening of the color-M* relation at M* > 3x10^10 M_Sun - wet mergers only matter at smaller masses. In one, the merger histories at M* > 2x10^11 M_Sun are dominated by major rather than minor dry mergers, as suggested by the axis ratio and color gradient trends. In another, although both major and minor mergers occur at the high mass end, the minor mergers contribute primarily to the formation of the ICL, rather than to the mass growth of the central massive galaxy. A final model assumes that the reddest objects were assembled by a mix of major and minor dry mergers.
We study the cosmic time evolution of an effective quantum field theory energy-momentum tensor T_{\mu\nu} and show that, as a consequence of the effective nature of the theory, the structure of T_{\mu\nu} is such that the vacuum energy decreases with time. We find that the zero point energy at present time is washed out by the cosmological evolution. The implications of this finding for the cosmological constant problem are investigated.
We provide a holographic dual description of Milgrom's scaling associated with galactic rotation curves. Our argument is based on the recent entropic reinterpretation of Newton's laws of motion. We propose a duality between cold dark matter and modified Newtonian dynamics (MOND). We introduce the concept of MONDian dark matter, and discuss some of its phenomenological implications. At cluster as well as cosmological scales, the MONDian dark matter would behave as cold dark matter, but at the galactic scale, the MONDian dark matter would act as MOND.
Massless interacting scalar fields in de Sitter space have long been known to experience large fluctuations over length scales larger than Hubble distances. A similar situation arises in condensed matter physics in the vicinity of a critical point, and in this better-understood situation such large fluctuations indicate the failure in this regime of mean-field methods. We argue that, for non-Goldstone scalars, these fluctuations similarly should be interpreted as signalling the complete breakdown for de Sitter backgrounds of the semi-classical methods widely used throughout cosmology. By power-counting the infrared properties of Feynman graphs in de Sitter space we find that for a massive scalar interacting through a \lambda \phi ^4 interaction there is no control over the loop approximation for masses smaller than m ~ (\lambda)^(1/2) H/2\pi, where H is the Hubble scale. For small-field inflationary models built with a quartic potential, V = V_0+ 1/2 m^2 \phi ^2 +1/4! \lambda \phi ^4, the use of semiclassical methods implicitly can imply a lower limit, \eta >> \lambda /(12 \pi ^2), to the slow-roll parameters.
A simple inflationary model based on loop quantum cosmology is considered. Within this framework, we show that inflation does not necessarily erase the infor- mation prior to its onset, but that such information may leave its imprint in the energy-spectrum of the gravitational-waves generated at these earliest of times.
The stability properties of the Einstein Static solution of General Relativity are altered when corrective terms arising from modification of the underlying gravitational theory appear in the cosmological equations. In this paper the existence and stability of static solutions are considered in the framework of two recently proposed quantum gravity models. The previously known analysis of the Einstein Static solutions in the semiclassical regime of Loop Quantum Cosmology with modifications to the gravitational sector is extended to open cosmological models where a static neutrally stable solution is found. A similar analysis is also performed in the framework of Horava-Lifshitz gravity under detailed balance and projectability conditions. In the case of open cosmological models the two solutions found can be either unstable or neutrally stable according with the admitted values of the parameters.
The Fermi Gamma-ray Space Telescope recently has detected more than a hundred of blazars. Spectra of the brightest sources cannot be described by a single power-law, but a much better description is obtained with the broken power-law, with the break at a few GeV. We show here that the sharpness and the position of the breaks can be well reproduced by absorption of gamma-rays via photon-photon pair production on He II Lyman recombination continuum and lines. This implies that the blazar zone lies inside the region of highest ionization of the broad-line region within a light-year from a super-massive black hole. The observations of gamma-ray spectral breaks open a way of studying the broad-line region photon field in the extreme-UV/soft X-rays, which are otherwise hidden from our view.
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