Prior to recombination photons, electrons, and atomic nuclei rapidly scattered and behaved, almost, like a single tightly-coupled photon-baryon plasma. We investigate here the accuracy of the tight-coupling approximation commonly used to numerically evolve the baryon and photon perturbation equations at early times. By solving the exact perturbations equations with a stiff solver starting deep in the radiation-dominated epoch we find the level of inaccuracy introduced by resorting to the standard first-order tight-coupling approximation. We develop a new second-order approximation in the inverse Thomson opacity expansion and show that it closely tracks the full solution, at essentially no extra numerical cost. We find the bias on estimates of cosmological parameters introduced by the first-order approximation is, for most parameters, negligible. Finally, we show that our second-order approximation can be used to reduce the time needed to compute cosmic microwave background angular spectra by as much as ~17%.
We report the X-ray detection of two z>1.4 infrared-selected galaxy clusters from the IRAC Shallow Cluster Survey (ISCS). We present new data from the Hubble Space Telescope and the W. M. Keck Observatory that spectroscopically confirm cluster ISCS J1432.4+3250 at z=1.49, the most distant of 18 confirmed z>1 clusters in the ISCS to date. We also present new spectroscopy for ISCS J1438.1+3414, previously reported at z = 1.41, and measure its dynamical mass. Clusters ISCS J1432.4+3250 and ISCS J1438.1+3414 are detected in 36ks and 143ks Chandra exposures at significances of 5.2 sigma and 9.7 sigma, from which we measure total masses of log(M_{200,Lx}/Msun) = 14.4 +/- 0.2 and 14.35^{+0.14}_{-0.11}, respectively. The consistency of the X-ray and dynamical properties of these high redshift clusters further demonstrates that the ISCS is robustly detecting massive clusters to at least z = 1.5.
Using the 32-m Medicina, 45-m Nobeyama, and 100-m Effelsberg telescopes we found a statistically significant velocity offset Delta V = 27 +/- 3 m/s (1sigma) between the inversion transition in NH3(1,1) and low-J rotational transitions in N2H+(1-0) and HC3N(2-1) arising in cold and dense molecular cores in the Milky Way. Systematic shifts of the line centers caused by turbulent motions and velocity gradients, possible non-thermal hyperfine structure populations, pressure and optical depth effects are shown to be lower than or about 1 m/s and thus can be neglected in the total error budget. The reproducibility of Delta V at the same facility (Effelsberg telescope) on a year-to-year basis is found to be very good. Since the frequencies of the inversion and rotational transitions have different sensitivities to variations in mu = m_e/m_p, the revealed non-zero Delta V may imply that mu changes when measured at high (terrestrial) and low (interstellar) matter densities as predicted by chameleon-like scalar field models - candidates to the dark energy carrier. Thus we are testing whether scalar field models have chameleon-type interactions with ordinary matter. The measured velocity offset corresponds to the ratio Delta mu/mu = (mu_space - mu_lab)/mu_lab of (26 +/- 3)x10^{-9} (1sigma).
The amount and characteristics of quantum-mechanically generated relic gravitational waves and primordial density perturbations is a subject of great theoretical and observational importance. Unfortunately, this subject is deeply contaminated by inflationary misunderstandings and incorrect "standard inflationary results". This note presents comments on a particular paper, arXiv:1008.4471v1. However, the comments may have a more general significance and may be of interest to other researchers working in this area of science.
If thick disks are ubiquitous and a natural product of disk galaxy formation and/or evolution processes, all undisturbed galaxies which have evolved during a significant fraction of a Hubble time should have a thick disk. The late-type spiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy without a confirmed thick disk. Using data from the Spitzer Survey of Stellar Structure in Galaxies (S4G) we have identified signs of two disk components in this galaxy. The asymmetries between the light profiles on both sides of the mid-plane of NGC 4244 can be explained by a combination of the galaxy not being perfectly edge-on and a certain degree of opacity of the thin disk. We argue that the subtlety of the thick disk is a consequence of either a limited secular evolution in NGC 4244, a small fraction of stellar material in the fragments which built the galaxy, or a high amount of gaseous accretion after the formation of the galaxy.
The predictions of homogeneous and isotropic cosmological models with ordinary matter and gravity are off by a factor of two in the late universe. One possible explanation is the known breakdown of homogeneity and isotropy due to the formation of non-linear structures. We review how inhomogeneities affect the average expansion rate and can lead to acceleration, and consider a semi-realistic model where the observed timescale of ten billion years emerges from structure formation. We also discuss the relation between the average expansion rate and observed quantities.
We introduce a new, very deep neutral hydrogen (HI) survey being performed with the Westerbork Synthesis Radio Telescope (WSRT). The Westerbork Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) Survey is producing an archive of some of the most sensitive HI observations available, on the angular scales which are most useful for studying faint, diffuse gas in and around nearby galaxies. The survey data are being used to perform careful modeling of the galaxies, characterizing their gas content, morphology, and kinematics, with the primary goal of revealing the global characteristics of cold gas accretion onto spiral galaxies in the local Universe. In this paper, we describe the survey sample selection, the data acquisition, reduction, and analysis, and present the data products obtained during our pilot program, which consists of UGC 2082, NGC 672, NGC 925, and NGC 4565. The observations reveal a first glimpse of the picture that the full HALOGAS project aims to illuminate: the properties of accreting HI in different types of spirals, and across a range of galactic environments. None of the pilot survey galaxies hosts an HI halo of the scale of NGC 891, but all show varying indications of halo gas features. We compare the properties of detected features in the pilot survey galaxies with their global characteristics, and discuss similarities and differences with NGC 891 and NGC 2403.
A thermodynamic motivation for dark energyIt is argued that the discovery of cosmic acceleration could have been anticipated on thermodynamic grounds, namely, the generalized second law and the approach to equilibrium at large scale factor. Therefore, the existence of dark energy -or equivalently, some modified gravity theory- should have been expected. Constraints on cosmological models and modified gravity theories obtained from the said criteria show compatibility with constraints derived from observational data.
We construct a new cosmological model considering the superstring-inspired E_6 unification in the 4-dimensional space at the early stage of the Universe. We develop a concept of parallel existence in Nature of the ordinary and shadow worlds with different cosmological evolutions.
We show that, in a model of modified gravity based on the spectral action functional, there is a nontrivial coupling between cosmic topology and inflation, in the sense that the shape of the possible slow-roll inflation potentials obtained in the model from the nonperturbative form of the spectral action are sensitive not only to the geometry (flat or positively curved) of the universe, but also to the different possible non-simply connected topologies. We show this by explicitly computing the nonperturbative spectral action for some candidate flat cosmic topologies given by Bieberbach manifolds and showing that the resulting inflation potential differs from that of the flat torus by a multiplicative factor, similarly to what happens in the case of the spectral action of the spherical forms in relation to the case of the 3-sphere. We then show that, while the slow-roll parameters differ between the spherical and flat manifolds but do not distinguish different topologies within each class, the power spectra detect the different scalings of the slow-roll potential and therefore distinguish between the various topologies, both in the spherical and in the flat case.
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We report the first direct photon velocity measurements for extragalactic objects. A fiber-optic, photon time-of-flight instrument, optimized for relatively dim sources ($m 12$), is used to measure the velocity of visible photons emanating from galaxies and quasars. Lightspeed is found to be $3.00\pm0.03\times10^{8} \mathrm{m s}^{-1}$, and is invariant, within experimental error, over the range of redshifts measured ($0\leq z\leq1.33$). This measurement provides additional validation of Einstein's theory of General Relativity (GR) and is consistent with the Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) metricl, as well as several alternative cosmological models, notably the hyperbolic anti-de Sitter metric, though not with the pseudo-Euclidean de Sitter metric.
Recently, in a series of works by Liu and Li (L&L), they claimed that there exists a timing asynchrony of $-25.6\,$ms between the spacecraft attitude and radiometer output timestamps in the original raw WMAP time-ordered data (TOD). L&L reprocessed the WMAP data while the aforementioned timing asynchrony has been corrected, and they obtained an improved CMB map in which the quadrupole dropped to nearly zero. In this work, we try to see the implications to dark energy cosmology assuming L&L are right. If the implications make dark energy cosmology more concordant, the plausibility of L&L's findings could be strengthened. On the contrary, if the implications make dark energy cosmology more troublesome, the plausibility of L&L's findings might be weakened. Actually, in this work, we find a good, a bad and a neutral news to L&L, respectively.
Versions of parameterized pseudo-Newtonian gravity theories specially designed for cosmology have been introduced in recent cosmology literature. The modifications demand a zero-pressure fluid in the context of versions of modified Poisson-like equation with two different gravitational potentials. We consider such modifications in the context of relativistic gravity theories where the action is a general algebraic function of the scalar curvature, the scalar field, and the kinetic term of the field. In general it is not possible to isolate the zero-pressure fluid component simultaneously demanding a modification in the Poisson-like equation. Only in the small-scale limit we can realize some special forms of the attempted modifications. We address some loopholes in the possibility of showing non-Einstein gravity nature based on pseudo-Newtonian modifications in the cosmological context. We point out that future observations of gravitational weak lensing together with velocity perturbation can potentially test the validity of Einstein's gravity in cosmology context.
We present J-band long-slit spectroscopic observation of NGC 1068 classified as a Seyfert 2 galaxy. J-band observations with OAO/ISLE provide clear detection of spatially extended [Fe II]1.257um and [P II]1.188um lines. We found that [Fe II]1.257um/[P II]1.188um increases with distance from a central continuum peak. Observed line ratios around the nucleus (continuum peak) are consistent with a typical value expected from photoionization models, while the ratios at 3" - 4" (210-280 pc) east and west of the nucleus are slightly higher than this. In the off nucleus region of NGC 1068 we also found a possible association between [Fe II]1.257um/[P II]1.188um and the radio continuum. This suggests a mild contribution of shock ionization induced by a radio jet outside nucleus while photoionization by the central energy source is dominant near the nucleus.
The nonbaryonic dark matter of the Universe is assumed to consist of new stable particles. A specific case is possible, when new stable particles bear ordinary electric charge and bind in heavy "atoms" by ordinary Coulomb interaction. Such possibility is severely restricted by the constraints on anomalous isotopes of light elements that form positively charged heavy species with ordinary electrons. The trouble is avoided, if stable particles $X^{--}$ with charge -2 are in excess over their antiparticles (with charge +2) and there are no stable particles with charges +1 and -1. Then primordial helium, formed in Big Bang Nucleosynthesis, captures all $X^{--}$ in neutral "atoms" of O-helium (OHe), thus creating a specific Warmer than Cold nuclear-interacting composite dark matter. Slowed down in the terrestrial matter, OHe is elusive for direct methods of underground dark. However OHe-nucleus interaction leads to their binding and in OHe-Na system the energy of such level can be in the interval of energy 2-4 keV. It explains the results of DAMA/NaI and DAMA/LIBRA experiments. The puzzles of direct dark matter searches appear in this solution as a reflection of nontrivial nuclear physics of OHe. (abridged)
We have observed 37 bright, polarized radio sources with the Allen Telescope Array (ATA) to present a novel analysis of their Faraday rotation properties. Each source was observed during the commissioning phase with 2 to 4 100-MHz bands at frequencies ranging from 1 to 2 GHz. These observations demonstrate how the continuous frequency coverage of the ATA's log-periodic receiver can be applied to the study of Faraday rotation measures (RMs). We use RM synthesis to show that wide-bandwidth data can find multiple RM components toward a single source. Roughly a quarter of the sources studied have extra RM components with high confidence (brighter than ~40 mJy), when observing with a RM resolution of roughly 100 rad/m2. These extra components contribute 10%-70% of the total polarized flux. This is the first time multiple RM components have been identified in a large sample of point sources. For our observing configuration, these extra RM components bias the measurement of the peak RM by 10-15 rad/m2 ; more generally, the peak RM cannot be determined more precisely than the RM beam size. Comparing our 1-2 GHz RM spectra to VLBA polarimetric maps shows both techniques can identify complicated Faraday structures in the sources. However, the RM values and fractional polarization are generally smaller at lower frequencies than in the higher-frequency VLBA maps. With a few exceptions, the RMs from this work are consistent with that of earlier, narrow-bandwidth, all-sky surveys. This work also describes the polarimetry calibration procedure and that on-axis ATA observations of linear polarization can be calibrated to an accuracy of 0.2% of Stokes I. Future research directions include studying the time-dependent RM structure in Active Galactic Nuclei (AGNs) and enabling accurate, wide-area RM surveys to test models of Galactic and extragalactic magnetic fields.
An extended XMM-Newton observation of the Seyfert 1 galaxy NGC 4051 has revealed a rich absorption line spectrum indicating the presence of a photoionized outflow with a wide range of velocities and ionization parameter. At low continuum fluxes an emission line spectrum is well defined with both narrow and broad components of several abundant metal ions. The absorption line velocity structure and a broad correlation of velocity and ionization parameter are consistent with an outflow scenario where a highly ionized, high velocity wind, perhaps launched during intermittent super-Eddington accretion, runs into the interstellar medium or previous ejecta, losing much of its kinetic energy in the resultant strong shock. We explore the possibility that a quasi-constant soft X-ray emission component may be evidence of this post-shock cooling. This revised view of AGN outflows is consistent with multiple minor Eddington accretion episodes creating a momentum-driven feedback linking black hole and host galaxy growth.
Cosmological $N$-body simulations have revealed many empirical relationships of dark matter halos, yet the physical origin of these halo properties still remains unclear. On the other hand, the attempts to establish the statistical mechanics for self-gravitating systems have encountered many formal difficulties, and little progress has been made for about fifty years. The aim of this work is to strengthen the validity of the statistical-mechanical approach we have proposed previously to explain the dark matter halo properties. By introducing an effective pressure instead of the radial pressure to construct the specific entropy, we use the entropy principle and proceed in a similar way as that of He & Kang, to obtain an entropy stationary equation. An equation of state for equilibrated dark halos is derived from this entropy stationary equation, by which the dark halo density profiles can be obtained. We also derive the anisotropy parameter and pseudo-phase-space density profile. All these predictions agree well with numerical simulations in the outer regions of dark halos. Our work provides further support to the idea that statistical mechanics for self-gravitating systems is viable.
We present a numerical implementation of radiative transfer based on an explicitly photon-conserving advection scheme, where radiative fluxes over the cell interfaces of a structured or unstructured mesh are calculated with a second-order reconstruction of the intensity field. The approach employs a direct discretisation of the radiative transfer equation in Boltzmann form with adjustable angular resolution that in principle works equally well in the optically thin and optically thick regimes. In our most general formulation of the scheme, the local radiation field is decomposed into a linear sum of directional bins of equal solid-angle, tessellating the unit sphere. Each of these "cone-fields" is transported independently, with constant intensity as a function of direction within the cone. Photons propagate at the speed of light (or optionally using a reduced speed of light approximation to allow larger timesteps), yielding a fully time-dependent solution of the radiative transfer equation that can naturally cope with an arbitrary number of sources, as well as with scattering. The method casts sharp shadows, subject to the limitations induced by the adopted angular resolution. If the number of point sources is small and scattering is unimportant, our implementation can alternatively treat each source exactly in angular space, producing shadows whose sharpness is only limited by the grid resolution. A third hybrid alternative is to treat only a small number of the locally most luminous point sources explicitly, with the rest of the radiation intensity followed in a radiative diffusion approximation. We have implemented the method in the moving-mesh code {\small AREPO}, where it is coupled to the hydrodynamics in an operator splitting approach that subcycles the radiative transfer alternatingly with the hydrodynamical evolution steps.
We carried out extremely sensitive Submillimeter Array (SMA) 340 GHz continuum imaging on two submillimeter galaxies (SMGs): GOODS 850-11 and GOODS 850-13. The observations reach sub-mJy rms sensitivities and, interestingly, resolve both sources into multiple, physically unrelated SMGs. GOODS 850-11 is resolved into two sources at different redshifts. GOODS 850-13 is resolved into three sources, two with different spectroscopic redshifts and one only with a photometric redshift. All the SMA sources have fluxes in the 3-5 mJy range and all are detected at 1.4 GHz. Three of them are detected by Chandra, and one is a previously unknown X-ray SMG. This is the first time that single-dish SMGs are resolved into multiple unrelated sources and also the first time that the SMA has discovered new SMGs. Our results show that identifications of SMGs at any wavelengths other than the submillimeter itself can be misleading, since such identifications usually only pick up one of the real counterparts. Using simulations that mimic our SCUBA and SMA observations, we find that the number of triple systems detected in our SMA survey is much higher than that expected from the current best-determined number counts. We tentatively attribute this to clustering. We also predict that ALMA will find ~1/3 of >5 mJy 850 um SCUBA sources to be multiple systems. Based on our SMA observations and simulations, we suggest that large samples of existing SMGs should be imaged with sensitive interferometric observations, even if the SMGs were previously thought to be securely identified.
We present an all-sky formalism for the CMB bispectrum induced by the primordial non-Gaussianities not only in scalar but also in vector and tensor fluctuations. We find that the bispectrum can be formed in an explicitly rationally invariant way by taking into account the angluar and polarization dependencies of the vector and tensor modes. In order to demonstrate this and present how to use our formalism, we consider a specific example of the correlation between two scalars and a graviton as the source of non-Gaussianity. As a result, we show that the CMB reduced bispectrum of the intensity anisotropies is evaluated as a function of the multipole and the coupling constant between two scalars and a graviton denoted by $g_{tss}$; $|b_{\ell \ell \ell}| \sim \ell^{-4} \times 8 \times 10^{-18} |g_{tss}|$. By estimating the signal-to-noise ratio, we find that the constraint as $|g_{tss}| < 6$ will be expected from PLANCK experiment.
Over cosmic time, galaxies grow through the hierarchical merging of smaller galaxies. However, the bright region of the galaxy luminosity function is incompatible with the simplest version of hierarchical merging, and it is believed that feedback from the central black hole in the host galaxies reduces the number of bright galaxies and regulates the co-evolution of black hole and host galaxy. Numerous simulations of galaxy evolution have attempted to include the physical effects of such feedback with a resolution usually exceeding a kiloparsec. However, interactions between jets and the interstellar medium involve processes occurring on less than kiloparsec scales. In order to further the understanding of processes occurring on such scales, we present a suite of simulations of relativistic jets interacting with a fractal two-phase interstellar medium with a resolution of two parsecs and a largest scale of one kiloparsec. The transfer of energy and momentum to the interstellar medium is considerable, and we find that jets with powers in the range of 10^43-10^46 erg s^-1 can inhibit star formation through the dispersal of dense gas in the galaxy core. We determine the effectiveness of this process as a function of the ratio of the jet power to the Eddington luminosity of the black hole, the pressure of the interstellar medium and the porosity of the dense gas.
The Sunyaev Zel'dovich (SZ) effect is one of the most powerful cosmological tools to investigate the large-scale Universe, in which clusters of galaxies are the most interesting target. The great advantage of the SZ effect of being redshift independent, in contrast with visible and X-ray observations, allows to directly estimate cluster total mass from the integrated comptonization parameter Y, even for faraway clusters. However, the lack of a complete knowledge of the Intra-Cluster gas (ICg) physics can affect the results. Taking into account self-similar temperature and density profiles of the ICg, we study how different ICg morphologies can affect the cluster total mass estimation. Due to the large percentage of cool core (CC) clusters, we analyze this class starting with a limited sample of eight objects, observed by Chandra. We simulate SZ observations of these clusters through X-ray derived information, and re-analyze the mock SZ data with the simplistic assumption for the ICg of an isothermal beta model profile. We estimate the bias on the recovered cluster total mass using different approaches and find it to be significant. Therefore, the lack of knowledge of cluster morphologies, as in the blind SZ effect surveys, like SPT, ACT or Planck, has to be correctly accounted for when employing the Mtot-Y scaling law.
Gravitational-wave astronomy is an area of great promise, yet to be realized. While we are waiting for the first (undisputed!) direct detection of these elusive waves it is useful to take stock and consider the challenges that need to be met if we want this field to reach its full potential. This write-up provides a brief introduction to some of the key ideas and the current state-of-play, and lists a range of modelling questions that need to be considered in the future.
More than 50% of Active Galactic Nuclei (AGNs) are suspected to be red and affected by dust-obscuration. Meanwhile, popular spectral diagnostics of AGNs are based on optical or ultraviolet light, making the dust obscuration as a primary concern for understanding the general nature of AGNs and supermassive black holes residing in them. To provide with a method of investigating properties of the dusty AGNs, we derive new black hole (BH) mass estimators based on velocity widths and luminosities of Near Infrared (NIR) hydrogen emission lines such as P$\alpha$ and P$\beta$, and also investigate the line ratios of these Hydrogen lines. To derive the BH mass ($M_{\rm BH}$) estimators, we used a sample of 37 unobscured Type-1 AGNs with a $M_{\rm BH}$ range of $10^{6.8}$-$10^{9.4} M_{\odot}$, where $M_{\rm BH}$ come from either reverberation mapping method or single-epoch measurement method using Balmer lines. Our work shows that $M_{\rm BH}$ can be estimated from the Paschen line luminosities and the velocity widths to the accuracy of 0.18 - 0.24 dex (rms scatter). We also show that the mean line ratios of the Paschen lines and the Balmer lines are $\mathrm{\frac{H\alpha}{P\alpha}} \simeq 9.00$, $\mathrm{\frac{H\beta}{P\alpha}} \simeq 2.70$, which are consistent with a Case B recombination under a typical AGN broad line region environment. These ratios can be used as reference points when estimating the amount of dust extinction over the broad line region (BLR) for red AGNs. We expect the future application of the new BH mass estimators on red, dusty AGNs to provide a fresh view of obscured AGNs.
We study the stellar populations, star formation histories and star formation
properties for a sample of blue compact dwarf galaxies (BCDs) selected by
cross-correlating the Gil de Paz et al. (2003) sample with the Sloan Digital
Sky Survey Data Release 6 (SDSS DR6). The sample includes 31 BCDs, which span a
large range in galactic parameters. Using a stellar population synthesis
method, we derive the stellar populations and reconstruct the star formation
histories for these BCDs. Our studies confirm that BCDs are not young systems
experiencing their first star formation but old systems undergoing a starburst
activity. The stellar mass-weighted ages can be as old as 10 Gyr while the
luminosity-weighted ages might be up to $\sim 3$ orders of magnitude younger
($\sim 10$ Myr) for most galaxies.
Based on multi-wavelength data, we also study the integrated star formation
properties. The SFR for our sample galaxies spans nearly 3 orders of magnitude,
from a few $10^{-3}$ to $\sim1\,M_\odot$ yr$^{-1}$, with the median value of
$\sim 0.1\, M_\odot$ yr$^{-1}$. We find that about 90% BCDs in our sample have
their birthrate parameter (the ratio of the current SFR to the averaged past
SFR) $b>2-3$. We further discuss correlations of the current SFR with the
integrated galactic stellar mass and explore the connection between SFR and
metallicity.
The oxygen and nitrogen abundance evolutions with redshift of emission-line galaxies in the Sloan Digital Sky Survey are considered for four intervals of galaxy stellar masses, ranging from 10^11.3 M_sun to 10^10.2 M_sun. We have measured their line fluxes and derived the O and N abundances using recent calibrations. The evolution of O and N abundances with redshift clearly shows the galaxy downsizing effect, where enrichment (and hence star formation) ceases in high-mass galaxies at earlier times and shifts to lower-mass galaxies at later epochs. The origin of the scatter in the N/H - O/H diagram has been examined. The most massive galaxies, where O and N enrichment and star formation has already stopped, occupy a narrow band in the N/H -- O/H diagram, defining an upper envelope. The less massive galaxies which are still undergoing star formation at the current epoch are shifted downwards, towards lower N/H values in the N/H - O/H diagram. This downward shift is caused by the time delay between N and O enrichment. This time delay together with the different star formation histories in galaxies is responsible for the large scatter in the N/H -- O/H diagram.
In this contribution we trace the evolution of cool-core clusters out to z~1.3 using high-resolution Chandra data of three representative cluster samples spanning different redshift ranges. Our analysis is based on the measurement of the surface brightness (SB) concentration, c_SB, which strongly anti-correlates with the central cooling time and allows us to characterize the cool-core strength in low S/N data. We confirm a negative evolution in the fraction of cool-core clusters with redshift, in particular for very strong cool-cores. Still, we find evidence for a large population of well formed cool-cores at z ~ 1. This analysis is potentially very effective in constraining the nature and the evolution of the cool-cores, once large samples of high-z clusters will be available. In this respect, we explore the potential of the proposed mission Wide Field X-ray Telescope (WFXT) to address this science case. We conclude that WFXT provides the best trade-off of angular resolution, sensitivity and covered solid angle in order to discover and fully characterize the cool-core cluster population up to z=1.5.
Cosmological runaway solutions may exhibit an exact dilatation symmetry in the asymptotic limit of infinite time. In this limit, the massless dilaton or cosmon could be accompanied by another massless scalar field - the geon. At finite time, small time-dependent masses for both the cosmon and geon are still present due to imperfect dilatation symmetry. For a sufficiently large mass the geon will start oscillating and play the role of dark matter, while the cosmon is responsible for dark energy. The common origin of the mass of both fields leads to an effective interaction between dark matter and dark energy. Realistic cosmologies are possible for a simple form of the effective cosmon-geon-potential. We find an inverse geon mass of a size where it could reduce subgalactic structure formation.
We study, by numerical methods, the time evolution of scalar perturbations in radiation era of Randall-Sundrum braneworld cosmology. Our results confirm an existence of the enhancement of perturbation amplitudes (near horizon crossing), discovered recently. We suggest the approximate solution of equations of the perturbation theory in the high energy regime, which predicts that the enhancement factor is asymptotically constant, as a function of scale. We discuss the application of this result for the problem of primordial black hole production in braneworld cosmology.
We show that the diffuse gamma-ray background (DGRB) observed by the Large Area Telescope (LAT) aboard the Fermi Gamma Ray Space Telescope can be produced entirely by gamma-ray emission from blazars and non-blazar active galactic nuclei. We employ a luminosity-dependent density evolution model of blazars which have a spectral energy distribution sequence related to their luminosity. This model is consistent with and constrained by the spectrum of the DGRB and flux multiplicity function of blazars observed by Fermi-LAT. Our results are consistent with previous work that used EGRET spectral data to forecast the Fermi-LAT DGRB. The model forecasts that > 98% of the flux from blazars will be resolved into point sources by Fermi-LAT with 5 years of observation, with a corresponding reduction of the flux in the DGRB by a factor of 3 to 30 (95% CL). We explore the implications of this reduction of the DGRB flux on the sensitivity of the DGRB observation to dark matter annihilation and decay, and find a corresponding significant enhancement of Fermi-LAT's sensitivity to the dark matter signal's detection or constraint.
In a recent analysis of the 7-year WMAP temperature sky maps, Gurzadyan and Penrose claim to find evidence for violent pre-Big Bang activity in the form of concentric low-variance circles at high statistical significance. In this paper, we perform an independent search for such concentric low-variance circles, employing both chi^2 statistics and matched filters, and compare the results obtained from the 7-year WMAP temperature sky maps with those obtained from LCDM simulations. Our main findings are the following: We do reproduce the claimed ring structures observed in the WMAP data as presented by Gurzadyan and Penrose, thereby verifying their computational procedures. However, the results from our simulations do not agree with those presented by Gurzadyan and Penrose. On the contrary we obtain a substantially larger variance in our simulations, to the extent that the observed WMAP sky maps are fully consistent with the LCDM model as measured by these statistics.
We discuss the diffuse flux of electron neutrinos and antineutrinos from cosmological failed supernovae, stars that collapse directly into a black hole, with no explosion. This flux has a hotter energy spectrum compared to regular, neutron-star forming collapses, and therefore it dominates the total diffuse flux from core collapses above 20-45 MeV of neutrino energy. Reflecting the features of the originally emitted neutrinos, the flux of nu_e and anti-nu_e at Earth is larger for larger survival probability of these species, and for stiffer equations of state of nuclear matter. In the energy window 19-29 MeV, the flux from failed supernovae is susbtantial, ranging from 7% to a dominant fraction of the total flux from all core collapses. It can be as large as phi = 0.38 s^{-1} cm^{-2} for anti-nu_e (phi = 0.28 s^{-1} cm^{-2} for nue), normalized to a local rate of core collapses of R_{cc}(0)=10^{-4} yr^{-1} Mpc^{-3}. In 5 years, a 0.45 Mt water Cherenkov detector should see 5-65 events from failed supernovae, while up to 160 events are expected for the same mass with Gadolinium addition. A 0.1 Mt liquid argon experiment should record 1-11 events. Signatures of neutrinos from failed supernovae are the enhancement of the total rates of events from core collapses (up to a factor of 2) and the appearance of high energy tails in the event spectra.
The possibility of constraining the parameters of scalar field dark energy with barotropic equation of state using different available datasets is discussed. It has been found that the initial value of dark energy equation of state parameter is constrained very weakly by most of the data. We have determined the constraints on this parameter, which come from the combined dataset including supernovae from the full SDSS compilation with the MLCS2k2 fitting of light curves. We discuss also the possibility of distinguishing between different dark energy models with barotropic equation of state using the future data on CMB anisotropies.
Using a cosmological simulation at redshift 5, we find that the baryon-rich cores of intergalactic filaments radiating from galaxies commonly form isothermal gas cylinders. The central gas density is typically about 500 times the cosmic mean total density, and the temperature is typically 1-2 times 10^4 K, just above the Lyman alpha cooling floor. These findings argue that the hydrodynamic properties of the gas are more important than the dark matter in determining the structure. Filaments form a major pipeline for the transport of gas into the centers of galaxies. Since the temperature and ionization state of the gas completely determine the mass per unit length of an isothermal gas cylinder, our findings suggest a constraint upon gas transport into galaxies by this mechanism.
In a recent paper, Gurzadyan & Penrose claim to have found directions on the sky centred on which are circles of anomalously low variance in the cosmic microwave background (CMB). These features are presented as evidence for a particular picture of the very early Universe. We attempted to repeat the analysis of these authors, and we can indeed confirm that such variations do exist in the temperature variance for annuli around points in the data. However, we find that this variation is entirely expected in a sky which contains the usual CMB anisotropies. In other words, properly simulated Gaussian CMB data contain just the sorts of variations claimed. Gurzadyan & Penrose have not found evidence for pre-Big Bang phenomena, but have simply re-discovered that the CMB contains structure.
In the past few years gamma-ray astronomy has entered a golden age. A modern suite of telescopes is now scanning the sky over both hemispheres and over six orders of magnitude in energy. At $\sim$TeV energies, only a handful of sources were known a decade ago, but the current generation of ground-based imaging atmospheric Cherenkov telescopes (H.E.S.S., MAGIC, and VERITAS) has increased this number to nearly one hundred. With a large field of view and duty cycle, the Tibet and Milagro air shower detectors have demonstrated the promise of the direct particle detection technique for TeV gamma rays. At $\sim$GeV energies, the Fermi Gamma-ray Space Telescope has increased the number of known sources by nearly an order of magnitude in its first year of operation. New classes of sources that were previously theorized to be gamma-ray emitters have now been confirmed observationally. Moreover, there have been surprise discoveries of GeV gamma-ray emission from source classes for which no theory predicted it was possible. In addition to elucidating the processes of high-energy astrophysics, gamma-ray telescopes are making essential contributions to fundamental physics topics including quantum gravity, gravitational waves, and dark matter. I summarize the current census of astrophysical gamma-ray sources, highlight some recent discoveries relevant to fundamental physics, and describe the synergetic connections between gamma-ray and neutrino astronomy. This is a brief overview intended in particular for particle physicists and neutrino astronomers, based on a presentation at the Neutrino 2010 conference in Athens, Greece. I focus in particular on results from Fermi (which was launched soon after Neutrino 2008), and conclude with a description of the next generation of instruments, namely HAWC and the Cherenkov Telescope Array.
In Natural Inflation, the Inflaton is a pseudo-Nambu-Goldstone boson which acquires a mass by explicit breaking of a global shift symmetry at scale $f$. In this case, for small field values, the potential is flat and stable under radiative corrections. Nevertheless, slow roll conditions enforce f>>M_p making the validity of the whole scenario questionable. In this letter, we show that a coupling of the Inflaton kinetic term to the Einstein tensor allows f<<M_p by enhancing the gravitational friction acting on the Inflaton during inflation. This new unique interaction, a) keeps the theory perturbative in the whole inflationary trajectory, b) preserves the tree-level shift invariance of the pseudo-Nambu-Goldstone Boson and c) avoids the introduction of any new degrees of freedom with respect the standard Natural Inflation.
Motivated by string/M-theory predictions that scalar field couplings with the Gauss-Bonnet invariant, G, are essential in the appearance of non-singular early time cosmologies, we discuss the viability of an interesting alternative gravitational theory, namely, modified Gauss-Bonnet gravity, and present the viability bounds arising from the energy conditions. In particular, we consider a specific realistic form of f(G) analyzed in the literature that accounts for the late-time cosmic acceleration and that has been found to cure the finite-time future singularities present in the dark energy models, and further examine the respective viability of the specific f(G) model imposed by the weak energy condition.
Active galactic nuclei (AGNs) exhibit variability across the entire electromagnetic spectrum with distinct flaring episodes at different frequencies. The high sensitivity and nearly uniform sky coverage of the Large Area Telescope on board the Fermi satellite make it a powerful tool for monitoring a large number of AGNs over long timescales. This allowed us to detect several flaring AGNs in gamma rays, triggering dedicated multifrequency campaigns on these sources from radio to TeV energies in order to improve our understanding on location, structure and dynamics of the emitting regions, and on particle acceleration mechanisms in AGNs. We discuss the results for two different flaring AGNs: the flat spectrum radio quasar 3C 279 and the radio-loud narrow-line Seyfert 1 PMN J0948+0022.
In the third part of the series presenting the Optical Gravitational Lensing
Experiment (OGLE) microlensing studies of the dark matter halo compact objects
(MACHOs) we describe results of the OGLE-III monitoring of the Large Magellanic
Cloud (LMC). This unprecedented data set contains almost continuous photometric
coverage over 8 years of about 35 million objects spread over 40 square
degrees. We report a detection of two candidate microlensing events found with
the automated pipeline and an additional two, less probable, candidate events
found manually. The optical depth derived for the two main candidates was
calculated following a detailed blending examination and detection efficiency
determination and was found to be tau=(0.16+-0.12)10^-7.
If the microlensing signal we observe originates from MACHOs it means their
masses are around 0.2 M_Sun and they compose only f=3+-2 per cent of the mass
of the Galactic Halo. However, the more likely explanation of our detections
does not involve dark matter compact objects at all and rely on natural effect
of self-lensing of LMC stars by LMC lenses. In such a scenario we can almost
completely rule out MACHOs in the sub-solar mass range with an upper limit at
f<7 per cent reaching its minimum of f<4 per cent at M=0.1 M_Sun. For masses
around M=10 M_Sun the constraints on the MACHOs are more lenient with f ~ 20
per cent. Owing to limitations of the survey there is no reasonable limit found
for heavier masses, leaving only a tiny window of mass spectrum still available
for dark matter compact objects.
Directional detection of non-baryonic Dark Matter is a promising search strategy for discriminating WIMP events from background. However, this strategy requires both a precise measurement of the energy down to a few keV and 3D reconstruction of tracks down to a few mm. To achieve this goal, the MIMAC project has been developed. It is based on a gaseous micro-TPC matrix, filled with 3He, CF4 and/or C4H10. The first results on low energy nuclear recoils (1H and 19F) obtained with a low mono-energetic neutron field are presented. The discovery potential of this search strategy is discussed and illustrated by a realistic case accessible to MIMAC.
The contribution of unresolved sources to the diffuse gamma-ray background could produce anisotropies in this emission on small angular scales. Recent studies have considered the angular power spectrum and other anisotropy metrics as tools for identifying contributions to diffuse emission from unresolved source classes, such as extragalactic and Galactic dark matter as well as various astrophysical gamma-ray source populations. We present preliminary results of an anisotropy analysis of the diffuse emission measured by the Fermi-LAT.
Large-mass bolometers are used in particle physics experiments to search for rare processes. The energy threshold of such detectors plays a critical role in their capability to search for dark matter interactions and rare nuclear decays. We have developed a trigger and a pulse shape algorithm based on the matched filter technique which, when applied to data from test bolometers of the CUORE experiment, lowered the energy threshold from tens of keV to the few keV region. The detection efficiency is in excess of 80%, and nearly all nonphysical pulses are rejected.
We investigate the occurrence of various exotic spacelike singularities in the past and the future evolution of $k = \pm 1$ Friedmann-Robertson-Walker model and loop quantum cosmology using a sufficiently general phenomenological model for the equation of state. We highlight the non-trivial role played by the intrinsic curvature for these singularities and the new physics which emerges at the Planck scale. We show that quantum gravity effects generically resolve all strong curvature singularities including big rip and big freeze singularities. The weak singularities, which include sudden and big brake singularities are ignored by quantum gravity when spatial curvature is negative, as was previously found for the spatially flat model. Interestingly, for the spatially closed model there exist cases where weak singularities may be resolved when they occur in the past evolution. The spatially closed model exhibits another novel feature. For a particular class of equation of state, this model also exhibits an additional physical branch in loop quantum cosmology, a baby universe separated from the parent branch. Our analysis generalizes previous results obtained on the resolution of strong curvature singularities in flat models to isotropic spacetimes with non-zero spatial curvature.
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New Chandra X-ray data and extensive optical spectroscopy, obtained with AAOmega on the 3.9 m Anglo-Australian Telescope, are used to study the complex merger taking place in the galaxy cluster Abell 2744. Combining our spectra with data from the literature provides a catalog of 1237 redshifts for extragalactic objects lying within 15' of the cluster center. From these, we confirm 343 cluster members projected within 3 Mpc of the cluster center. Combining positions and velocities, we identify two major substructures, corresponding to the remnants of two major subclusters. The new data are consistent with a post core passage, major merger taking place along an axis that is tilted well out of the plane of the sky, together with an interloping minor merger. Supporting this interpretation, the new X-ray data reveal enriched, low entropy gas from the core of the approaching, major subcluster, lying ~2' north of the cluster center, and a shock front to the southeast of the previously known bright, compact core associated with the receding subcluster. The X-ray morphology of the compact core is consistent with a Bullet-like cluster viewed from within ~45 degrees of the merger axis. An X-ray peak ~3' northwest of the cluster center, with an associated cold front to the northeast and a trail of low entropy gas to the south, is interpreted as the remnant of an interloping minor merger taking place roughly in the plane of the sky. We infer approximate paths for the three merging components.
We present an analysis of the clustering of galaxies as a function of their stellar mass at 1 < z < 2 using data from the NEWFIRM Medium Band Survey (NMBS). The precise photometric redshifts and stellar masses that the NMBS produces allows us to define a series of mass limited samples of galaxies more massive than 0.7, 1 and 3x10^10 Msun in redshift intervals centered on z = 1.1, 1.5 and 1.9 respectively. In each redshift interval we show that there exists a strong dependence of clustering strength on the stellar mass limit of the sample, with more massive galaxies showing a higher clustering amplitude on all scales. We further interpret our clustering measurements in the LCDM cosmological context using the halo model of galaxy clustering. We show that the typical halo mass of central and satellite galaxies increases with stellar mass, whereas the satellite fraction decreases with stellar mass, qualitatively the same as is seen at z < 1. We see little evidence of any redshift dependence in the stellar mass-to-halo mass relationship over our narrow redshift range. However, when we compare with similar measurements at z~0, we see clear evidence for a change in this relation. If we assume a universal baryon fraction, the ratio of stellar mass to halo mass reveals the fraction of baryons that have been converted to stars. We see that the peak in this star formation efficiency for central galaxies shifts to higher halo masses at higher redshift, moving from ~7x10^11 Msun at z~0 to ~3x10^12 Msun at z~1.5, revealing evidence of `halo downsizing'. Finally we show that for highly biased galaxy populations at z > 1 there may be a discrepancy between the measured space density and clustering and that predicted by the halo model. This could imply that there is a problem with one or more ingredients of the halo model at these redshifts, for instance the halo bias relation or the halo profile.
We present the power spectrum of galaxy clusters measured from the new ROSAT-ESO Flux-Limited X-Ray (REFLEX II) galaxy cluster catalogue. This new sample extends the flux limit of the original REFLEX to $1.8 \times 10^{-12} erg/ s/cm^{2}$, yielding a total of 911 clusters with $\geq 94$ per cent completeness in redshift follow-up. The analysis of the data is improved by creating a set of 100 REFLEX II-like mock galaxy cluster catalogues built from a suite of large volume LCDM N-body simulations (L-BASICC II). The measured power spectrum is in agreement with the predictions from a LCDM cosmological model. The measurements show the expected increase in the amplitude of the power spectrum with increasing X-ray luminosity. On large scales, we show that the shape of the measured power spectrum is compatible with a scale independent bias and provide a model for the amplitude that allows us to connect our measurements with a cosmological model. By implementing a luminosity-dependent power spectrum estimator, we observe that the power spectrum measured from the REFLEX II sample is weakly affected by flux-selection effects. The shape of the measured power spectrum is compatible with a featureless power spectrum on scales $k>0.01\,h/Mpc$ and hence no statistically significant signal of baryonic acoustic oscillations can be detected. We show that the measured REFLEX II power spectrum displays signatures of non-linear evolution.
Tidal interactions between galaxies can trigger star formation, which contributes to the global star formation rate density of the universe and could be a factor in the transformation of blue, star-forming galaxies to red, quiescent galaxies over cosmic time. We investigate tidally-triggered star formation in isolated close galaxy pairs drawn from the Prism Multi-Object Survey (PRIMUS), a low-dispersion prism redshift survey that has measured ~120,000 robust galaxy redshifts over 9.1 deg^2 out to z ~ 1. We select a sample of galaxies in isolated galaxy pairs at redshifts 0.25 < z < 0.75, with no other objects within a projected separation of 300 h^-1 kpc and dz/(1+z) = 0.01, and compare them to a control sample of isolated galaxies to test for systematic differences in their rest-frame FUV-r and NUV-r colors as a proxy for relative specific SFR. We find that galaxies in r_p < 50 h^-1 kpc pairs have bluer dust-corrected UV-r colors on average than the control galaxies by -0.134 +/- 0.045 magnitudes in FUV-r and -0.075 +/- 0.038 magnitudes in NUV-r, corresponding to a ~15-20% increase in SSFR. This indicates an enhancement in SSFR due to tidal interactions. We also find that this relative enhancement is greater for a subset of r_p < 30 h^-1 kpc pair galaxies, for which the average colors offsets are -0.193 +/- 0.065 magnitudes in FUV-r and -0.159 +/- 0.048 magnitudes in NUV-r, corresponding to a ~25-30% increase in SSFR. We test for evolution in the enhancement of tidally-triggered star formation with redshift across our sample redshift range and find marginal evidence for a decrease in SSFR enhancement from 0.25 < z < 0.5 to 0.5 < z < 0.75. This indicates that a change in enhanced star formation triggered by tidal interactions in low density environments is not a contributor to the decline in the global star formation rate density across this redshift range.
We derive a general expression for the large-scale halo bias, in theories with a scale-dependent linear growth, using the excursion set formalism. Such theories include modified gravity models, and models in which the dark energy clustering is non-negligible. A scale dependence is imprinted in both the formation and evolved biases by the scale-dependent growth. Mergers are accounted for in our derivation, which thus extends earlier work which focused on passive evolution. There is a simple analytic form for the bias for those theories in which the nonlinear collapse of perturbations is approximately the same as in general relativity. As an illustration, we apply our results to a simple Yukawa modification of gravity, and use SDSS measurements of the clustering of luminous red galaxies to constrain the theory's parameters.
The properties of blazar variability in the radio band are studied using the unique combination of temporal resolution from single dish monitoring and spatial resolution from VLBA imaging; such measurements, now available in all four Stokes parameters, together with theoretical simulations, identify the origin of radio band variability and probe the characteristics of the radio jet where the broadband blazar emission originates. Outbursts in total flux density and linear polarization in the optical-to-radio bands are attributed to shocks propagating within the jet spine, in part based on limited modeling invoking transverse shocks; new radiative transfer simulations allowing for shocks at arbitrary angle to the flow direction confirm this picture by reproducing the observed centimeter-band variations observed more generally, and are of current interest since these shocks may play a role in the gamma-ray flaring detected by Fermi. Recent UMRAO multifrequency Stokes V studies of bright blazars identify the spectral variability properties of circular polarization for the first time and demonstrate that polarity flips are relatively common. All-Stokes data are consistent with the production of circular polarization by linear-to-circular mode conversion in a region that is at least partially self-absorbed. Detailed analysis of single-epoch, multifrequency, all-Stokes VLBA observations of 3C 279 support this physical picture and are best explained by emission from an electron-proton plasma.
Using data from our Parkes & ATCA HI survey of six groups analogous to the Local Group, we find that the HI mass function and velocity distribution function for loose groups are the same as those for the Local Group. Both mass functions confirm that the "missing satellite" problem exists in other galaxy groups.
We numerically compute features in the power-spectrum that originate from the decay of fields during inflation. Using a simple, phenomenological, multi-field setup, we increase the number of fields from a few to thousands. Whenever a field decays, its associated potential energy is transferred into radiation, causing a jump in the equation of state parameter and mode mixing at the perturbed level. We observe discrete steps in the power-spectrum if the number of fields is low, in agreement with analytic arguments in the literature. These features become increasingly smeared out once many fields decay within a given Hubble time. In this regime we confirm the validity of the analytic approach to staggered inflation, which is based on a coarse-graining procedure. Our numerical approach bridges the aforementioned analytic treatments, and can be used in more complicated scenarios.
We present ground-based and HST optical observations of the optical transients (OTs) of long-duration Gamma Ray Bursts (GRBs) 060729 and 090618, both at a redshift of z = 0.54. For GRB 060729, bumps are seen in the optical light curves (LCs), and the late-time broadband spectral energy distributions (SEDs) of the OT resemble those of local type Ic supernovae (SNe). For GRB 090618, the dense sampling of our optical observations has allowed us to detect well-defined bumps in the optical LCs, as well as a change in colour, that are indicative of light coming from a core-collapse SN. The accompanying SNe for both events are individually compared with SN1998bw, a known GRB-supernova, and SN1994I, a typical type Ic supernova without a known GRB counterpart, and in both cases the brightness and temporal evolution more closely resemble SN1998bw. We also exploit our extensive optical and radio data for GRB 090618, as well as the publicly-available SWIFT -XRT data, and discuss the properties of the afterglow at early times. In the context of a simple jet-like model, the afterglow of GRB 090618 is best explained by the presence of a jet-break at t-to > 0.5 days. We then compare the rest-frame, peak V -band absolute magnitudes of all of the GRB and X-Ray Flash (XRF)-associated SNe with a large sample of local type Ibc SNe, concluding that, when host extinction is considered, the peak magnitudes of the GRB/XRF-SNe cannot be distinguished from the peak magnitudes of non-GRB/XRF SNe.
We study the influence of the environment on the evolution of galaxies by
investigating the luminosity function (LF) of galaxies of different
morphological types at different environmental density levels.
We construct the LFs separately for spiral and elliptical galaxies using data
from the Sloan Digital Sky Survey (SDSS), correcting the luminosities for the
intrinsic absorption. We use the global luminosity density field to define
different environments. The smoothed bootstrap method is used to calculate
confidence regions of the derived luminosity functions.
We find a strong environmental dependency for the LF of elliptical galaxies.
The LF of spiral galaxies is almost environment independent, suggesting that
spiral galaxy formation mechanisms are similar in different environments.
Absorption by the intrinsic dust influences the bright-end of the LF of spiral
galaxies. After attenuation correction, the brightest spiral galaxies are still
about 0.5 mag less luminous than the brightest elliptical galaxies. Despite the
extent of the SDSS survey, the influence of single rich superclusters is
present in the galactic LF of the densest environments.
Two groups [3,4] have confirmed the results of our paper concerning the actual existence of low variance circles in the cosmic microwave background (CMB) sky. They also point out that the effect does not contradict the LCDM model - a matter which is not in dispute. We point out two discrepancies between their treatment and ours, however, one technical, the other having to do with the very understanding of what constitutes a Gaussian random signal. Both groups simulate maps using the CMB power spectrum for LCDM, while we simulate a pure Gaussian sky plus the WMAP's noise, which points out the contradiction with a common statement [3] that "CMB signal is random noise of Gaussian nature". For as it was shown in [5], the random component is a minor one in the CMB signal, namely, about 0.2. Accordingly, the circles we saw are a real structure of the CMB sky and they are not of a random Gaussian nature. Although the structures studied certainly cannot contradict the power spectrum, which is well fitted by LCDM model, we particularly emphasize that the low variance circles occur in concentric families, and this key fact cannot be explained as a purely random effect. It is, however a clear prediction of conformal cyclic cosmology.
The results of photometric decomposition of surface brightness distributions in 85 early-type unbarred galaxies are presented. The SDSS r-images are analysed. Double-tiered exponential disks are found in all galaxies which are studied; the statistics of the disk parameters is derived.
Spectropolarimetry results for the starburst galaxy M82 are presented. The optical emission lines of the filaments in the energetic outflow ("superwind") from the nuclear starburst region of M82 are substantially polarized. The H-alpha polarization degrees and angles measured by our study are consistent with previous narrowband imaging polarimetry data. The polarized emission lines are redshifted with respect to the emission lines in the total light and systemic motion of the galaxy. The emission line intensity ratios [NII]/H-alpha and [SII]/H-alpha in the polarized light are similar to those of the nuclear star-forming region. In addition, the electron density N_e derived from the[SII]6731/6717 line ratio of the polarized light is 600 - 1000 cm^-3 at a distance of more than 1 kpc from the nucleus, whereas the N_e derived from the total light are less than 300 cm^-3. These facts strongly suggest that the emission from the nuclear starburst of M82 is scattered by dust grains entrained and transported outward by the superwind. A simple hollow biconical outflow model shows that the velocity of the outflowing dust grains, v_d, ranges from 100 to 200 km/s near the nucleus, decreases monotonically with the distance from the nucleus, and reaches about 10 km/s at around 1 kpc. The motion of the dust is substantially slower than that of both ionized gas (~600 km/s) and molecular gas (~200 km/s) at the same distance from the nucleus of M82. This indicates that dust grains in the superwind are kinematically decoupled from both gas components at large radii. Since the dust velocity v_d is much less than the escape velocity of M82 (~170 km/s at 1.5 kpc from the nucleus), most of the dust entrained by the superwind cannot escape to intergalactic space, and may fall back into the galaxy disk without any additional acceleration mechanisms (such as radiation pressure).
Studies of a class of infinite one dimensional self-gravitating systems have highlighted that, on the one hand, the spatial clustering which develops may have scale invariant (fractal) properties, and, on the other, that they display "self-similar" properties in their temporal evolution. The relevance of these results to three dimensional cosmological simulations has remained unclear. We show here that the measured exponents characterizing the scale-invariant non-linear clustering are in excellent agreement with those derived from an appropriately generalized "stable-clustering" hypothesis. Further an analysis in terms of "halos" selected with a friend-of-friend algorithm reveals that such structures are, statistically, virialized across the range of scales corresponding to scale-invariance. Thus the strongly non-linear clustering in these models is accurately described as a virialized fractal structure, very much in line with the "clustering hierarchy" which Peebles originally envisaged qualitatively as associated with stable clustering. If transposed to three dimensions these results would imply, notably, that cold dark matter halos (or even subhalos) are 1) not well modeled as smooth objects, and 2) that the supposed "universality" of their profiles is, like apparent smoothness, an artefact of poor numerical resolution.
The Atlas3D project is a multi-wavelength survey combined with a theoretical modeling effort. The observations span from the radio to the millimeter and optical, and provide multi-colour imaging, two-dimensional kinematics of the atomic (HI), molecular (CO) and ionized gas (Hbeta, [OIII] and [NI]), together with the kinematics and population of the stars (Hbeta, Fe5015 and Mgb), for a carefully selected, volume-limited (1.16*10^5 Mpc^3) sample of 260 early-type (elliptical E and lenticular S0) galaxies (ETGs). The models include semi-analytic, N-body binary mergers and cosmological simulations of galaxy formation. Here we present the science goals for the project and introduce the galaxy sample and the selection criteria. The sample consists of nearby (D<42 Mpc) morphologically-selected ETGs extracted from a parent sample of 871 galaxies (8% E, 22% S0 and 70% spirals) brighter than M_K<-21.5 mag (stellar mass M_Star>6*10^9 M_Sun). We analyze possible selection biases and we conclude that the parent sample is essentially complete and statistically representative of the nearby galaxy population. We present the size-luminosity relation for the spirals and ETGs and show that the ETGs in the Atlas3D sample define a tight red sequence in a colour-magnitude diagram, with few objects in the transition from the blue cloud. We describe the strategy of the SAURON integral-field observations and the extraction of the stellar kinematics with the pPXF method. We give an overview of the characteristics of the other main datasets already available for our sample and of the ongoing modelling projects.
Axions differ from ordinary cold dark matter, such as WIMPs or sterile neutrinos, because they form a Bose-Einstein condensate (BEC). As a result, axions accreting onto a galactic halo fall in with net overall rotation. In contrast, ordinary CDM accretes onto galactic halos with an irrotational velocity field. The inner caustics are different in the two cases. It is shown that if the dark matter is axions, the phase space structure of the halos of isolated disk galaxies, such as the Milky Way, is precisely that of the caustic ring model for which observational support exists. The other dark matter candidates predict a far more chaotic phase space structure for galactic halos.
The Dirac-Born-Infeld (DBI) action has been widely studied as an interesting example of a model of k-inflation in which the sound speed of the cosmological perturbations differs from unity. In this article we consider a scalar-tensor theory in which the matter component is a field with a DBI action. Transforming to the Einstein frame, we explore the effect of the resulting coupling on the background dynamics of the fields and the first-order perturbations. We find that the coupling forces the scalar field into the minimum of its effective potential. While the additional scalar field contributes significantly to the energy density during inflation, the dynamics are determined by the DBI field, which has the interesting effect of increasing the number of efolds of inflation and decreasing the boost factor of the DBI field. Focusing on this case, we show, with the benefit of numerical examples, that the power spectrum of the primordial perturbations is determined by the behaviour of the perturbations of the modified DBI field.
We analyze 1298 merging galaxies with redshifts up to z=0.7 from the Canada-France-Hawaii Telescope Legacy Survey, taken from the catalog presented in Bridge et al. (2010). By analyzing the internal colors of these systems, we show that so-called wet and dry mergers evolve in different senses, and quantify the space densities of these systems. The local space density of wet mergers is essentially dentical to the local space density of dry mergers. The evolution in the total merger rate is modest out to z ~ 0.7, although the wet and dry populations have different evolutionary trends. At higher redshifts dry mergers make a smaller contribution to the total merging galaxy population, but this is offset by a roughly equivalent increase in the contribution from wet mergers. By comparing the mass density function of early-type galaxies to the corresponding mass density function for merging systems, we show that not all the major mergers with the highest masses (M_stellar > 10^11 M_solar) will end up with the most massive early-type galaxies, unless the merging timescale is dramatically longer than that usually assumed. On the other hand, the usually-assumed merging timescale of ~ 0.5-1 Gyr is quite consistent with the data if we suppose that only less massive early-type galaxies form via mergers. Since low-intermediate mass ellipticals are 10 --100 times more common than their most massive counterparts, the hierarchical explanation for the origin of early-type galaxies may be correct for the vast majority of early-types, even if incorrect for the most massive ones.
A large number of cosmological parameters have been suggested for obtaining information on the nature of dark energy. In this work, we study the efficacy of these different parameters in discriminating theoretical models of dark energy, using both currently available supernova (SNe) data, and simulations of future observations. We find that the current data does not put strong constraints on the nature of dark energy, irrespective of the cosmological parameter used. For future data, we find that the although deceleration parameter can accurately reconstruct some dark energy models, it is unable to discriminate between different models of dark energy, therefore limiting its usefulness. Physical parameters such as the equation of state of dark energy, or the dark energy density do a good job of both reconstruction and discrimination if the matter density is known to high accuracy. However, uncertainty in matter density reduces the efficacy of these parameters. A recently proposed parameter, Om(z), constructed from the first derivative of the SNe data, works very well in discriminating different theoretical models of dark energy, and has the added advantage of not being dependent on the value of matter density. Thus we find that a cosmological parameter constructed from the first derivative of the data, for which the theoretical models of dark energy are sufficiently distant from each other, and which is independent of the matter density, performs the best in reconstructing dark energy from SNe data.
Gauge-invariant treatments of general-relativistic higher-order perturbations on generic background spacetime is proposed. We show the fact that the linear-order metric perturbation is decomposed into gauge-invariant and gauge-variant parts, which was the important premise of this general framework. This means that the development the higher-order gauge-invariant perturbation theory on generic background spacetime is possible.
We treat a model in which tensor perturbations of de~Sitter spacetime, represented as a spatially flat model, are modified by the effects of the vacuum fluctuations of a massless conformally invariant field, such as the electromagnetic field. We use the semiclassical theory of gravity with the expectation value of the conformal field stress tensor as a source. We first study the stability of de~Sitter spacetime by searching for growing, spatially homogeneous modes, and conclude that it is stable within the limits of validity of the semiclassical theory. We next examine the modification of linearized plane gravity waves by the effects of the quantum stress tensor. We find a correction term which is of the same form as the original wave, but displaced in phase by -\pi/2, and with an amplitude which depends upon the duration of inflation. The magnitude of this effect is proportional to the change in scale factor during inflation. So long as the energy scale of inflation and the proper frequency of the mode at the beginning of inflation are well below the Planck scale, the fractional correction is small. However, modes which are transplanckian at the onset of inflation can undergo a significant correction. The increase in amplitude can potentially have observable consequences through a modification of the power spectrum of tensor perturbations in inflationary cosmology. This enhancement of the power spectrum depends upon the duration of inflation and is greater for shorter wavelengths.
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The temperature fluctuations and polarization of the Cosmic Microwave Background (CMB) are now a well-known probe of the Universe at an infant age of 400,000 years. During the transit to us from the surface of last scattering, the CMB photons are expected to undergo modifications induced by the intervening large-scale structure. Among the expected secondary effects is the weak gravitational lensing of the CMB by the foreground dark matter distribution. We derive a quadratic estimator that uses the non-Gaussianities generated by the lensing effect at the four-point function level to extract the power spectrum of lensing potential fluctuations integrated out to z ~ 1100 with peak contributions from potential fluctuations at z of 2 to 3. Using WMAP 7-year temperature maps, we report the first direct constraints of this lensing potential power spectrum and find that it has an amplitude of A_L = 0.96 +/- 0.60, 1.06 +/- 0.69 and 0.97 +/- 0.47 using the W, V and W+V bands, respectively.
We measure black hole masses for 71 BL Lac objects from the Sloan Digital Sky Survey with redshifts out to z~0.4. We perform spectral decompositions of their nuclei from their host galaxies and measure their stellar velocity dispersions. Black hole masses are then derived from the black hole mass - stellar velocity dispersion relation. We find BL Lac objects host black holes of similar masses, ~10^{8.5} M_sun, with a dispersion of 0.4 dex, similar to the uncertainties on each black hole measurement. Therefore, all BL Lac objects in our sample have the same indistinguishable black hole mass. These 71 BL Lac objects follow the black hole mass - bulge luminosity relation, and their narrow range of host galaxy luminosities confirm previous claims that BL Lac host galaxies can be treated as standard candles. We conclude that the observed diversity in the shapes of BL Lac object spectral energy distributions is not strongly driven by black hole mass or host galaxy properties.
Gas motions in the hot intracluster medium of galaxy clusters have an important effect on the mass determination of the clusters through X-ray observations. The corresponding dynamical pressure has to be accounted for in addition to the hydrostatic pressure support to achieve a precise mass measurement. An analysis of the velocity structure of the ICM for simulated cluster-size haloes, especially focusing on rotational patterns, has been performed, demonstrating them to be an intermittent phenomenon, strongly related to the internal dynamics of substructures. We find that the expected build-up of rotation due to mass assembly gets easily destroyed by passages of gas-rich substructures close to the central region. Though, if a typical rotation pattern is established, the corresponding mass contribution is estimated to be up to ~17% of the total mass in the innermost region, and one has to account for it. Extending the analysis to a larger sample of simulated haloes we statistically observe that (i) the distribution of the rotational component of the gas velocity in the innermost region has typical values of ~200-300 km/s; (ii) except for few outliers, there is no monotonic increase of the rotational velocity with decreasing redshift, as we would expect from approaching a relaxed configuration. Therefore, the hypothesis that the build-up of rotation is strongly influenced by internal dynamics is confirmed, and minor events like gas-rich substructures passing close to the equatorial plane can easily destroy any ordered rotational pattern.
We present the results of a 6.1 square degree survey for clusters of galaxies via their Sunyaev- Zel'dovich (SZ) effect at 31 GHz. From late 2005 to mid 2007 the Sunyaev-Zel'dovich Array (SZA) observed four fields of roughly 1.5 square degrees each. One of the fields shows evidence for significant diffuse Galactic emission, and we therefore restrict our analysis to the remaining 4.4 square degrees. We estimate the cluster detectability for the survey using mock observations of simulations of clusters of galaxies; and determine that, at intermediate redshifts (z ~ 0.8), the survey is 50% complete to a limiting mass (M200 rho mean) of ~ 6.0 x 10^14M_{solar}, with the mass limit decreasing at higher redshifts. We detect no clusters at a significance greater than 5 times the RMS noise level in the maps, and place an upper limit on \sigma_8, the amplitude of mass density fluctuations on a scale of 8h^-1 Mpc, of 0.84 + 0.07 at 95% confidence, where the uncertainty reflects calibration and systematic effects. This result is consistent with estimates from other cluster surveys and CMB anisotropy experiments.
We propose a new ray-tracing algorithm to measure the weak lensing shear and convergence fields directly from N-body simulations. We calculate the deflection of the light rays lensed by the 3-D mass density field or gravitational potential along the line of sight on a grid-by-grid basis, rather than using the projected 2-D lens planes. Our algorithm uses simple analytic formulae instead of numerical integrations in the computation of the projected density field along the line of sight, and so is computationally efficient, accurate and straightforward to implement. This will prove valuable in the interpretation of data from the next generation of surveys that will image many thousands of square degrees of sky.
We have carried out a pilot study for the SCUBA-2 'All-Sky' Survey, SASSy, a wide and shallow mapping project at 850 microns, designed to find rare objects, both Galactic and extragalactic. Two distinct sets of exploratory observations were undertaken, and used to test the SASSy approach and data reduction pipeline. The first was a 0.5 by 0.5 degrees map around the nearby galaxy NGC 2559. The galaxy was easily detected at 156 mJy, but no other convincing sources are present in the map. Comparison with other galaxies with similar wavelength coverage indicates that NGC 2559 has relatively warm dust. The second observations cover 1 square degree around the W5-E HII region. As well as diffuse structure in the map, a filtering approach was able to extract 27 compact sources with signal-to-noise greater than 6. By matching with data at other wavelengths we can see that the SCUBA-2 data can be used to discriminate the colder cores. Together these observations show that the SASSy project will be able to meet its original goals of detecting new bright sources which will be ideal for follow-up observations with other facilities.
The existence of concentric low variance circles in the CMB sky, generated by black-hole encounters in an aeon preceding our big bang, is a prediction of the Conformal Cyclic Cosmology. Detection of three families of such circles in WMAP data was recently reported by Gurzadyan & Penrose (2010). We reassess the statistical significance of those circles by comparing with Monte Carlo simulations of the CMB sky with realistic modeling of the anisotropic noise in WMAP data. We find that the circles are not anomalous and that all three groups are consistent at 3sigma level with a Gaussian CMB sky as predicted by inflationary cosmology model.
The modified gravity with $f(R)=R^{1+\epsilon}$ ($\epsilon>0$) allows a scaling solution where the density of gravity sector follows the density of the dominant fluid. We present initial conditions of background and perturbation variables during the scaling evolution regime in the modified gravity. As a possible dark energy model we consider a gravity with a form $f(R)=R^{1+\epsilon}+qR^{-n}$ ($-1<n \le 0$) where the second term drives the late-time acceleration. We show that our $f(R)$ gravity parameters are very sensitive to the baryon perturbation growth and baryon density power spectrum, and present observational constraints on the model parameters. Our analysis suggests that only the parameter space extremely close to the $\Lambda\textrm{CDM}$ model is allowed.
The statistics of isothermal lines and loops of the Cosmic Microwave Background (CMB) radiation on the sky map is studied and the fractal structure is confirmed in the radiation temperature fluctuation. We estimate the fractal exponents, such as, the fractal dimension $D_{\mathrm{e}}$ of the entire pattern of isothermal lines, the fractal dimension $D_{\mathrm{c}}$ of a single isothermal line, the exponent $\zeta$ in Kor\v{c}ak's law for the size distribution of isothermal loops, the two kind of Hurst exponents, $H_{\mathrm{e}}$ for the profile of the CMB radiation temperature, and $H_{\mathrm{c}}$ for a single isothermal line. We perform the fractal analysis also on the two artificial sky maps simulated by the standard model in physical cosmology, the WMAP best-fit $\Lambda$ Cold Dark Matter ($\Lambda$CDM) model, and by the Gaussian free model of rough surfaces. The temperature fluctuations of the real CMB radiation and of the simulation by the $\Lambda$CDM model are non-Gaussian, in the sense that the displacement of isothermal lines and loops has antipersistent property indicated by $H_{\mathrm{e}} \simeq 0.25 < 1/2$.
The evolution of the curvature perturbation is highly non-trivial for curvaton models with self-interactions and is very sensitive to the parameter values. The final perturbation depends also on the curvaton decay rate $\Gamma$. As a consequence, non-gaussianities can be greatly different from the purely quadratic case, even if the deviation is very small. Here we consider a class of polynomial curvaton potentials and discuss the dynamical behavior of the curvature perturbation. We point out that, for example, it is possible that the non-gaussianity parameter $\fnl\simeq 0$ while $\gnl$ is non-zero. In the case of a curvaton with mass $m\sim {\cal O}(1)$ TeV we show that one cannot ignore non-quadratic terms in the potential, and that only a self-interaction of the type $V_{\rm int}=\sigma^8/M^4$ is consistent with various theoretical and observational constraints. Moreover, the curvaton decay rate should then be in the range $\Gamma=10^{-15}- 10^{-17}$ GeV.
We investigate the emission properties of polycyclic aromatic hydrocarbons (PAHs) in various metallicity environments with the Infrared Spectrograph on board Spitzer. Local giant HII regions are used as references as they enable access to the distinct interstellar medium components that contribute to the mid-infrared spectrum of star-forming galaxies: photodissociation regions (PDRs), photoionized gas, stellar clusters, and embedded regions. Three objects are considered, NGC3603 in the Milky Way, 30Doradus in the Large Magellanic Cloud, and N66 in the Small Magellanic Cloud. From the variations of the PAH/14um ratio, we find that PAHs are destroyed in the ionized gas for a radiation field such that [NeIII]/[NeII]>3. From the variations of the PAH/Hu-alpha ratio, we find that the PAH emission sources in the giant HII regions follow the same photodestruction law regardless of metallicity. We then compare these results with observations of starburst galaxies, HII galaxies, and blue compact dwarf galaxies (BCDs). While the integrated mid-infrared spectra of BCDs are reminiscent of a warm dusty ionized gas, we observe a significant contribution to the PAH emission in starburst galaxies that is not arising from PDRs.
Aimed at understanding the evolution of galaxies in clusters, the GLACE survey is mapping a set of optical lines ([OII]3727, [OIII]5007, Hbeta and Halpha/[NII] when possible) in several galaxy clusters at redshift around 0.40, 0.63 and 0.86, using the Tuneable Filters (TF) of the OSIRIS instrument (Cepa et al. 2005) at the 10.4m GTC telescope. This study will address key questions about the physical processes acting upon the infalling galaxies during the course of hierarchical growth of clusters. GLACE is already ongoing: we present some preliminary results on our observations of the galaxy cluster Cl0024+1654 at z = 0.395; on the other hand, GLACE@0.86 has been approved as ESO/GTC large project to be started in 2011.
The emission from blazars is known to be variable at all wavelengths. The flux variability is often accompanied by spectral changes. Spectral energy distribution (SED) changes must be associated with changes in the spectra of emitting electrons and/or the physical parameters of the jet. Meaningful modeling of blazar broadband spectra is required to understand the extreme conditions within the emission region. Not only is the broadband SED crucial, but also information about its variability is needed to understand how the highest states of emission occur and how they differ from the low states. This may help in discriminating between models. Here we present the results of our SED modeling of the blazar S5 0716+714 during various phases of its activity. The SEDs are classified into different bins depending on the optical brightness state of the source.
We present a new estimation method for mapping the gravitational lensing potential from observed CMB intensity and polarization fields. Our method uses Bayesian techniques to estimate the average curvature of the potential over small local regions. These local curvatures are then used to construct an estimate of a low pass filter of the gravitational potential. By utilizing Bayesian/likelihood methods one can easily overcome problems with missing and/or non-uniform pixels and problems with partial sky observations (E and B mode mixing, for example). Moreover, our methods are local in nature which allow us to easily model spatially varying beams and are highly parallelizable. We note that our estimates do not rely on the typical Taylor approximation which is used to construct estimates of the gravitational potential by Fourier coupling. We present our methodology with a flat sky simulation under nearly ideal experimental conditions with a noise level of 1 $\mu K$-arcmin for the temperature field, $\sqrt{2}$ $\mu K$-arcmin for the polarization fields, with an instrumental beam full width at half maximum (FWHM) of 0.25 arcmin.
Context: Cosmic rays are present in almost all phases of the ISM. PAHs and cosmic rays represent an abundant and ubiquitous component of the interstellar medium. However, the interaction between them has never before been fully investigated. Aims: To study the effects of cosmic ray ion (H, He, CNO and Fe-Co-Ni) and electron bombardment of PAHs in galactic and extragalactic environments. Methods: We calculate the nuclear and electronic interactions for collisions between PAHs and cosmic ray ions and electrons with energies between 5 MeV/nucleon and 10 GeV, above the threshold for carbon atom loss, in normal galaxies, starburst galaxies and cooling flow galaxy clusters. Results: The timescale for PAH destruction by cosmic ray ions depends on the electronic excitation energy Eo and on the amount of energy available for dissociation. Small PAHs are destroyed faster, with He and the CNO group being the more effective projectiles. For electron collisions, the lifetime is independent of the PAH size and varies with the threshold energy To. Conclusions: Cosmic rays process the PAHs in diffuse clouds, where the destruction due to interstellar shocks is less efficient. In the hot gas filling galactic halos, outflows of starburst galaxies and intra-cluster medium, PAH destruction is dominated by collisions with thermal ions and electrons, but this mechanism is ineffective if the molecules are in denser cloudlets and isolated from the hot gas. Cosmic rays can access the denser clouds and together with X-rays will set the lifetime of those protected PAHs. This limits the use of PAHs as a`dye' for tracing the presence of cold entrained material.
We investigate the non-Gaussianity of inflation driven by a single scalar field coupling non-minimally to the Einstein Gravity. We assume that the form of the scalar field is very general with an arbitrary sound speed. For convenience to study, we take the subclass that the non-minimal coupling term is linear to the Ricci scalar $R$. We define a parameter $\mu\equiv\epsilon_h/\epsilon_\theta$ where $\epsilon_h$ and $\epsilon_\theta$ are two kinds of slow-roll parameters, and obtain the dependence of the shape of the 3-point correlation function on $\mu$. We also show the estimator $F_{NL}$ in the equilateral limit.
The Survey Science Centre of the XMM-Newton satellite released the first incremental version of the 2XMM catalogue in August 2008 . With more than 220,000 X-ray sources, the 2XMMi was at that time the largest catalogue of X-ray sources ever published and thus constitutes an unprecedented resource for studying the high-energy properties of various classes of X-ray emitters such as AGN and stars. The advent of the 7th release of the Sloan Digital Sky Survey offers the opportunity to cross-match two major surveys and extend the spectral energy distribution of many 2XMMi sources towards the optical bands. We here present a cross-matching algorithm based on the classical likelihood ratio estimator. The method developed has the advantage of providing true probabilities of identifications without resorting to Monte-Carlo simulations. Over 30,000 2XMMi sources have SDSS counterparts with individual probabilities of identification higher than 90%. Using spectroscopic identifications from the SDSS DR7 catalogue supplemented by extraction from other catalogues, we build an identified sample from which the way the various classes of X-ray emitters gather in the multi dimensional parameter space can be analysed. We investigate two scientific use cases. In the first example we show how these multi-wavelength data can be used to search for new QSO2s. Although no specific range of observed properties allows us to identify Compton Thick QSO2s, we show that the prospects are much better for Compton Thin AGN2 and discuss several possible multi-parameter selection strategies. In a second example, we confirm the hardening of the mean X-ray spectrum with increasing X-ray luminosity on a sample of over 500 X-ray active stars and reveal that on average X-ray active M stars display bluer $g-r$ colour indexes than less active ones (abridged).
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We present the rest-frame optical morphologies of active galactic nucleus (AGN) host galaxies at 1.5<z<3, using near-infrared imaging from the Hubble Space Telescope Wide Field Camera 3, the first such study of AGN host galaxies at these redshifts. The AGN are X-ray selected from the Chandra Deep Field South and have typical luminosities of 1E42 < L_X < 1E44 erg/s. Accreting black holes in this luminosity and redshift range account for a substantial fraction of the total space density and black hole mass growth over cosmic time; they thus represent an important mode of black hole growth in the universe. We find that the majority (~80%) of the host galaxies of these AGN have low Sersic indices indicative of disk-dominated light profiles, suggesting that secular processes govern a significant fraction of the cosmic growth of black holes. That is, many black holes in the present-day universe grew much of their mass in disk-dominated galaxies and not in early-type galaxies or major mergers. The properties of the AGN host galaxies are furthermore indistinguishable from their parent galaxy population and we find no strong evolution in either effective radii or morphological mix between z~2 and z~0.05.
Primordial non-Gaussianity introduces a scale-dependent variation in the clustering of density peaks corresponding to rare objects. This variation, parametrized by the bias, is investigated on scales where a linear perturbation theory is sufficiently accurate. The bias is obtained directly in real space by comparing the one- and two-point probability distributions of density fluctuations. We show that these distributions can be reconstructed using a bivariate Edgeworth series, presented here up to an arbitrarily high order. The Edgeworth formalism is shown to be well-suited for 'local' cubic-order non-Gaussianity parametrized by g_NL. We show that a strong scale-dependence in the bias can be produced by g_NL of order 10,000, consistent with CMB constraints. On correlation length of 80-100 Mpc, the bias may be enhanced by as much as 40-60%. We further examine the bias as a function of mass scale, and also explore the relationship between the clustering and the abundance of massive clusters in the presence of g_NL. We explain why the Edgeworth formalism, though technically challenging, is a very powerful technique for constraining high-order non-Gaussianity with large-scale structures.
NGC 3147, NGC 4698 and 1ES 1927+654 are active galaxies that are classified as Seyfert 2s, based on the line ratios of strong narrow emission lines in their optical spectra. However, they exhibit rapid X-ray spectral variability and/or little indication of obscuration in X-ray spectral fitting, contrary to expectation from the AGN unification model. Using optical spectropolarimetry with LRIS and near-infrared spectroscopy with NIRSPEC at the W. M. Keck Observatory, we conducted a deep search for hidden polarized broad H-alpha and direct broad Pa-beta or Br-gamma emission lines in these objects. We found no evidence for any broad emission lines from the active nucleus of these galaxies, suggesting that they are unobscured, completely "naked" AGNs that intrinsically lack broad-line regions.
We report the discovery of a significant excess of candidate Halpha emitters (HAEs) in the field of the radio galaxy 4C 23.56 at z=2.483. Using the MOIRCS near-infrared imager on the Subaru Telescope we found 11 candidate emission-line galaxies to a flux limit of ~7.5 10^-17 erg s-1 cm-2, which is about 5 times excess from the expected field counts with ~3-sigma significance. Three of these are spectroscopically confirmed as redshifted Halpha at z=2.49. The distribution of candidate emitters on the sky is tightly confined to a 1.2-Mpc-radius area at z=2.49, locating 4C 23.56 at the western edge of the distribution. Analysis of the deep Spitzer MIPS 24 mu m imaging shows that there is also an excess of faint MIPS sources. All but two of the 11 HAEs are also found in the MIPS data. The inferred star-formation rate (SFR) of the HAEs based on the extinction-corrected Halpha luminosity (median SFR >~100 M_solar yr-1) is similar to those of HAEs in random fields at z~2. On the other hand, the MIPS-based SFR for the HAEs is on average 3.6 times larger, suggesting the existence of the star-formation significanly obscured by dust. The comparison of the Halpha-based star-formation activities of the HAEs in the 4C 23.56 field to those in another proto-cluster around PKS 1138-262 at z=2.16 reveals that the latter tend to have fainter Halpha emission despite similar K-band magnitudes. This suggests that star-formation may be suppressed in the PKS 1138-262 protocluster relative to the 4C 23.56 protocluster. This difference among the HAEs in the two proto-clusters at z > 2 may imply that some massive cluster galaxies are just forming at these epochs with some variation among clusters.
We present new Gemini-North/NIRI and VLT/SINFONI \hband\ spectroscopy for a flux limited sample of 40 z~4.8 active galactic nuclei, selected from the Sloan Digital Sky Survey. The sample probably contains the most massive active black holes (BHs) at this redshift and spans a broad range in bolometric luminosity, 2.7x10^46< L_bol < 2.4x10^47 erg/sec. The high-quality observations and the accurate fitting of the MgII(2800A) line, enable us to study, systematically, the distribution of BH mass (M_BH) and normalized accretion rate (L/L_Edd) at z~4.8. We find that 10^8 < M_BH < 6.6x10^9 M_sun, with a median of ~8.4x10^8 M_sun. We also find that 0.2 < L/L_Edd < 3.9 with a median of ~0.6. Most of these sources had enough time to grow to their observed mass at z~4.8 from z=20, assuming a range of seed BH masses, with ~40% that are small enough to be stellar remnants. Compared to previously studied samples at z~2.4 and 3.3, the masses of the z~4.8 BHs are typically lower by ~0.5 dex. and their L/L_Edd is higher by a similar factor. The new z~4.8 sample can be considered as the progenitor population of the most massive BHs at z~2.4 and 3.3. Such an evolutionary interpretation requires that the growth of the BHs from z~4.8 to z~3.3 and z~2.4 proceeds with short duty cycles, of about 10-20%, depending on the particular growth scenario.
We use a large N-body simulation to examine the detectability of HI in emission at redshift z ~ 1, and the constraints imposed by current observations on the neutral hydrogen mass function of galaxies at this epoch. We consider three different models for populating dark matter halos with HI, designed to encompass uncertainties at this redshift. These models are consistent with recent observations of the detection of HI in emission at z ~ 0.8. Whilst detection of 21 cm emission from individual halos requires extremely long integrations with existing radio interferometers, such as the Giant Meter Radio Telescope (GMRT), we show that the stacked 21 cm signal from a large number of halos can be easily detected. However, the stacking procedure requires accurate redshifts of galaxies. We show that radio observations of the field of the DEEP2 spectroscopic galaxy redshift survey should allow detection of the HI mass function at the 5-12 sigma level in the mass range 10^(11.4) M_sun/h < M_halo < 10^(12.5)M_sun/h, with a moderate amount of observation time. Assuming a larger noise level that corresponds to an upper bound for the expected noise for the GMRT, the detection significance for the HI mass function is still at the 1.7-3 sigma level. We find that optically undetected satellite galaxies enhance the HI emission profile of the parent halo, leading to broader wings as well as a higher peak signal in the stacked profile of a large number of halos. We show that it is in principle possible to discern the contribution of undetected satellites to the total HI signal, even though cosmic variance limitation make this challenging for some of our models.
This article reports on a growing body of observational evidence that many powerful lobe dominated (FR II) radio sources likely have jets with high efficiency. This study extends the maximum efficiency line (jet power $\approx$ 25 times the thermal luminosity) defined in Fernandes et (2010) so as to span four decades of jet power. The fact that this line extends over the full span of FR II radio power is a strong indication that this is a fundamental property of jet production that is independent of accretion power. This is a valuable constraint for theorists. For example, the currently popular "no net flux" numerical models of black hole accretion produce jets that are 2 to 3 orders of magnitude too weak to be consistent with sources near maximum efficiency.
This paper aims at robustly determining the redshift of the cluster of galaxies JKCS041 and at putting constraints on the formation epoch of the color-magnitude sequence in two very high redshift clusters. New deep z'-J data show a clear narrow red sequence that is co-centered with, and similarly concentrated on, the extended X-ray emission of the cluster of galaxies JKCS041. The JKCS041 red sequence is 0.32+/-0.06 mag redder in z'-J than the red sequence of the zspec=1.62 IRC0218A cluster, putting JKCS041 at z>>1.62 and ruling out z<~1.49 the latter claimed by a recent paper. The color difference of the two red sequences gives a red-sequence-based redshift of z=2.20+/-0.11 for JKCS041, where the uncertainty accounts for uncertainties in stellar synthesis population models, in photometric calibration, and in the red sequence color of both JKCS041 and IRC0218A clusters. We do not observe any sign of truncation of the red sequence for both clusters down to J=23 mag (1.0e+11 solar masses), which suggests that it is already in place in clusters rich and massive enough to heat and retain hot gas at these high redshifts.
We investigate the validity of the approximate method to describe a strong gravitational lensing which was extended by Alard on the basis of a perturbative approach to an Einstein ring. Adopting an elliptical Navarro-Frenk-White (NFW) lens model, we demonstrate how the approximate method works, focusing on the shape of the image, the magnification, caustics, and the critical line. Simplicity of the approximate method enables us to investigate the lensing phenomena in an analytic way. We derive simple approximate formulas which characterise a lens system near the Einstein ring.
Observational manifestations of some models of modified gravity, which have been suggested to explain the accelerated cosmological expansion, are analyzed for gravitating systems with time dependent mass density. It is shown that if the mass density rises with time, the system evolves to the singular state with infinite curvature scalar. The corresponding characteristic time is typically much shorter than the cosmological time.
From a survey for redshifted HI 21-cm and OH 18-cm absorption in the hosts of a sample of radio galaxies and quasars, we detect HI in three of the ten and OH in none of the fourteen sources for which useful data were obtained. As expected from our recent result, all of the 21-cm detections occur in sources with ultra-violet continuum luminosities of L < 10^23 W/Hz. At these "moderate" luminosities, we also obtain four non-detections, although, as confirmed by the equipartition of detections between the type-1 and type-2 objects, this near-50% detection rate cannot be attributed to unified schemes of active galactic nuclei (AGN). All of our detections are at redshifts of z < 0.67, which, in conjunction with our faint source selection, biases against UV luminous objects. The importance of ultra-violet luminosity (over AGN type) in the detection of 21-cm is further supported by the non-detections in the two high redshift z ~ 3.6 - 3.8 radio galaxies, which are both type-2 objects, while having L > 10^23 W/Hz. Our 21-cm detections in combination with those previously published, give a total of eight (associated and intervening) HI absorbing sources searched and undetected in OH. Using the detected 21-cm line strengths to normalise the limits, we find that only two of these eight may have been searched sufficiently deeply in OH, although even these are marginal.
We have constructed a supercluster catalogue for the galaxies from the SDSS survey main and Luminous Red Galaxy (LRG) samples. We have also created a test catalogue for the galaxies from the Millennium simulation to compare the simulated and observed superclusters and to clarify the methods we use. To delineate superclusters, we calculate luminosity density fields using the B3-spline kernel of the radius of 8 Mpc/h and define regions with densities over a selected threshold as superclusters. We create two types of catalogues, one with an adaptive local threshold and a set of catalogues with different global thresholds. We present supercluster catalogues for both the SDSS main and LRG samples. We describe their properties and compare them with the supercluster catalogues for the Millennium simulation. We find that the superclusters are well-defined systems, and the properties of the superclusters of the main and LRG samples are similar. The Millennium galaxy catalogue provides similar superclusters to those observed.
The eternal inflation scenario predicts that our observable universe resides inside a single bubble embedded in a vast multiverse, the majority of which is still undergoing super-accelerated expansion. Many of the theories giving rise to eternal inflation predict that we have causal access to collisions with other bubble universes, opening up the possibility that observational cosmology can probe the dynamics of eternal inflation. We present the first observational search for the effects of bubble collisions, using cosmic microwave background data from the WMAP satellite. Using a modular algorithm that is designed to avoid a posteriori selection effects, we find four features on the CMB sky that are consistent with being bubble collisions. If this evidence is corroborated by upcoming data from the Planck satellite, we will be able to gain insight into the possible existence of the multiverse.
There are at least three cosmic backgrounds of primordial gravitational waves coming from inflation: those produced during inflation and associated with the stretching of quantum modes; those produced at the violent stage of preheating after inflation; and those associated with the self-ordering of Goldstone modes if inflation ends via a global symmetry breaking scenario, like in hybrid inflation. Each background has its own characteristic spectrum with specific features. We describe in detail the origin of extra peaks in the PGW background from preheating in the case in which inflation ends with the formation of cosmic strings due to an Abelian Higgs model after hybrid inflation. We then discuss the prospects for detecting each gravitational wave background, and distinguishing between them with a very sensitive probe, the local B-mode of the cosmic microwave background polarization.
We report the discovery of the first HeI*\lambda 10830 broad absorption line quasar FBQS J1151+3822. Using new infrared and optical spectra, as well as the SDSS spectrum, we extracted the apparent optical depth profiles as a function of velocity of the 3889A and 10830A HeI* absorption lines. Since these lines have the same lower levels, inhomogeneous absorption models could be used to extract the average true HeI* column density; the log of that number was 14.9. The total hydrogen column density was obtained using Cloudy models. A range of ionization parameters and densities were allowed, with the lower limit on the ionization parameter of log U=-1.4 determined by the requirement that there be sufficient HeI*, and the upper limit on the density of log n=8 determined by the lack of Balmer absorption. Simulated UV spectra showed that the ionization parameter could be further constrained in principle using a combination of low and high ionization lines (such as MgII and PV), but the only density-sensitive line predicted to be observable and not significantly blended was CIII\lambda 1176. We estimated the outflow rate and kinetic energy, finding them to be consistent but on the high side compared with analysis of other objects. Assuming that radiative line driving is the responsible acceleration mechanism, a force multipler model was constructed. A dynamical argument using the model results strongly constrained the density to be log n >= ~7. Consequently, the log hydrogen column density is constrained to be between 21.7 and 22.9, the mass outflow rate to be between 11 and 56 solar masses per year, the ratio of the mass outflow rate to the accretion rate to be between 1.2 and 5.8, and the kinetic energy to be between 1 and 5 x 10^44 erg/s. We discuss the advantages of using HeI* to detect high-column-density BALQSOs and and measure their properties. (Abridged)
This paper presents an overview and introduction to Smoothed Particle Hydrodynamics and Magnetohydrodynamics in theory and in practice. Firstly, we give a basic grounding in the fundamentals of SPH, showing how the equations of motion and energy can be self-consistently derived from the density estimate. We then show how to interpret these equations using the basic SPH interpolation formulae and highlight the subtle difference in approach between SPH and other particle methods. In doing so, we also critique several `urban myths' regarding SPH, in particular the idea that one can simply increase the `neighbour number' more slowly than the total number of particles in order to obtain convergence. We also discuss the origin of numerical instabilities such as the pairing and tensile instabilities. Finally, we give practical advice on how to resolve three of the main issues with SPMHD: removing the tensile instability, formulating dissipative terms for MHD shocks and enforcing the divergence constraint on the particles, and we give the current status of developments in this area. Accompanying the paper is the first public release of the NDSPMHD SPH code, a 1, 2 and 3 dimensional code designed as a testbed for SPH/SPMHD algorithms that can be used to test many of the ideas and used to run all of the numerical examples contained in the paper.
The time-dependent metric of a cosmic string leads to an effective interaction between the string and photons - the "gravitational Aharonov-Bohm" effect -- and causes cosmic strings to emit light. We evaluate the radiation of pairs of photons from cosmic strings and find that the emission from cusps, kinks and kink-kink collisions occurs with a flat spectrum at all frequencies up to the string scale. Further, cusps emit a beam of photons, kinks emit along a curve, and the emission at a kink-kink collision is in all directions. The emission of light from cosmic strings could provide an important new observational signature of cosmic strings that is within reach of current experiments for a range of string tensions.
In this work we study the constraints on the dark matter interaction with the standard model particles, from the observations of dark matter relic density, the direct detection experiments of CDMS and XENON, and the indirect detection of the antiproton-to-proton ratio by PAMELA. A model independent way is adopted in the study by constructing the effective interaction operators between dark matter and standard model particles. The most general 4-fermion operators are investigated. We find that the constraints from different observations are complementary with each other. Especially the spin independent scattering gives very strong constraints for corresponding operators. In some cases the indirect detection of antiproton-to-proton data can actually be more sensitive than the direct detection or relic density for light dark matter (less than 70 GeV).
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