On the pulsation of a star in which there is a prevalent magnetic field

In this paper a simple approximate formula is obtained for the frequency (σ) of radial pulsation of a gaseous star in which there is a prevalent magnetic field. The formula is σ2I = - (3γ - 4) (Ω + B) , where γ is the ratio of the specific heats, I = ∫0Mr2dm (r) , and Ω and B denote the gravitational potential energy and the magnetic energy of the star, respectively. The formula is derived from the virial theorem in the form recently established by Chandrasekhar and Fermi; and it supports their conclusion that the period of pulsation can be made as long as one may desire by letting the magnetic energy approach the upper limit (namely, |Ω|) set by the virial theorem

A model integrating longshore and cross-shore processes for predicting long-term shoreline responses to climate change

We present a shoreline change model for coastal hazard assessment and management planning. The model, CoSMoS-COAST (Coastal One-line Assimilated Simulation Tool), is a transect-based, one-line model that predicts short-term and long-term shoreline response to climate change in the 21st century. The proposed model represents a novel, modular synthesis of process-based models of coastline evolution due to longshore and cross-shore transport by waves and sea level rise. Additionally, the model uses an extended Kalman filter for data assimilation of historical shoreline positions to improve estimates of model parameters and thereby improve confidence in long-term predictions. We apply CoSMoS-COAST to simulate sandy shoreline evolution along 500 km of coastline in Southern California, which hosts complex mixtures of beach settings variably backed by dunes, bluffs, cliffs, estuaries, river mouths, and urban infrastructure, providing applicability of the model to virtually any coastal setting. Aided by data assimilation, the model is able to reproduce the observed signal of seasonal shoreline change for the hindcast period of 1995–2010, showing excellent agreement between modeled and observed beach states. The skill of the model during the hindcast period improves confidence in the model’s predictive capability when applied to the forecast period (2010–2100) driven by GCM-projected wave and sea level conditions. Predictions of shoreline change with limited human intervention indicate that 31% to 67% of Southern California beaches may become completely eroded by 2100 under sea level rise scenarios of 0.93 to 2.0 m

On the Angular Correlation Function of SZ Clusters : Extracting cosmological information from a 2D catalog

We discuss the angular correlation function of Sunyaev-Zel'dovich (SZ)-detected galaxy clusters as a cosmological probe. As a projection of the real-space cluster correlation function, the angular function samples the underlying SZ catalog redshift distribution. It offers a way to study cosmology and cluster evolution directly with the two-dimensional catalog, even before extensive follow-up observations, thereby facilitating the immediate scientific return from SZ surveys. As a simple illustration of the information content of the angular function, we examine its dependence on the parameter pair Om_m, sigma_8 in flat cosmologies. We discuss sources of modeling uncertainty and consider application to the future Planck SZ catalog, showing how these two parameters and the normalization of the SZ flux-mass relation can be simultaneously found when the local X-ray cluster abundance constraint is included.Comment: 11 pages, 5 figures. A&A, 410, 767; corrected typo, published versio

Be stars: one ring to rule them all?

Aims. We report theoretical spectral energy distributions (SEDs), Br$\gamma$ line profiles and visibilities for two scenarios that can explain the disk dissipation of active hot stars an account for the transition from the Be to the B spectroscopic phase. Methods. We use the SIMECA code to investigate these two scenarios: the first one where the disk is formed by successive outbursts of the central star. A low-density region is developing above the star and slowly grows outward and forms a ring-like structure that will gradually excavate the disk. The second one, where a slowly decreasing mass loss, for instance due to a decrease of the radiative force through an opacity change at the base of the photosphere, may also be responsible for the vanishing of the circumstellar disk. Results. We obtain that a clear signature of the disk dissipation following the ring scenario will be the disappearance of the high velocity tails in the emission lines and a nearly constant peaks separation. Moreover, we found that following the ring-like scenario the visibilities must show an increasing second lobe, an increase of the value of the first zero and, assuming an unresolved central star, a first zero of the visibility curves that appends at shorter baselines as far as the disk is been excavate. We propose to use the AMBER instrument on the VLTI to probe if the the ring scenario is the one that rule the Be phenomenon.Comment: 10 page

The detection of the imprint of filaments on cosmic microwave background lensing

Galaxy redshift surveys, such as 2dF, SDSS, 6df, GAMA and VIPERS, have shown that the spatial distribution of matter forms a rich web, known as the cosmic web. The majority of galaxy survey analyses measure the amplitude of galaxy clustering as a function of scale, ignoring information beyond a small number of summary statistics. Since the matter density field becomes highly non-Gaussian as structure evolves under gravity, we expect other statistical descriptions of the field to provide us with additional information. One way to study the non-Gaussianity is to study filaments, which evolve non-linearly from the initial density fluctuations produced in the primordial Universe. In our study, we report the first detection of CMB (Cosmic Microwave Background) lensing by filaments and we apply a null test to confirm our detection. Furthermore, we propose a phenomenological model to interpret the detected signal and we measure how filaments trace the matter distribution on large scales through filament bias, which we measure to be around 1.5. Our study provides a new scope to understand the environmental dependence of galaxy formation. In the future, the joint analysis of lensing and Sunyaev-Zel'dovich observations might reveal the properties of `missing baryons', the vast majority of the gas which resides in the intergalactic medium and has so far evaded most observations

Clustering properties of a type-selected volume-limited sample of galaxies in the CFHTLS

(abridged) We present an investigation of the clustering of i'AB<24.5 galaxies in the redshift interval 0.2<z<1.2. Using 100,000 precise photometric redshifts in the four ultra-deep fields of the Canada-France Legacy Survey, we construct a set of volume-limited galaxy catalogues. We study the dependence of the amplitude and slope of the galaxy correlation function on absolute B-band rest-frame luminosity, redshift and best-fitting spectral type. We find: 1. The comoving correlation length for all galaxies decreases steadily from z~0.3 to z~1. 2. At all redshifts and luminosities, galaxies with redder rest-frame colours have clustering amplitudes between two and three times higher than bluer ones. 3. For bright red and blue galaxies, the clustering amplitude is invariant with redshift. 4. At z~0.5, less luminous galaxies have higher clustering amplitudes of around 6 h-1 Mpc. 5. The relative bias between galaxies with red and blue rest-frame colours increases gradually towards fainter absolute magnitudes. One of the principal implications of these results is that although the full galaxy population traces the underlying dark matter distribution quite well (and is therefore quite weakly biased), redder, older galaxies have clustering lengths which are almost invariant with redshift, and by z~1 are quite strongly biased.Comment: 16 pages, 18 figures, accepted for publication in Astronomy and Astrophysic

Evolution in the bias of faint radio sources to z ~ 2.2

Quantifying how the baryonic matter traces the underlying dark matter distribution is key to both understanding galaxy formation and our ability to constrain the cosmological model. Using the cross-correlation function of radio and near-infrared galaxies, we present a large-scale clustering analysis of radio galaxies to z ~ 2.2. We measure the angular auto-correlation function of Ks90μJy to infer linear bias of radio galaxies in four redshift bins. We find that the bias evolves from b = 0.57 ± 0.06 at z ~ 0.3 to 8.55 ± 3.11 at z ~ 2.2. Furthermore, we separate the radio sources into subsamples to determine how the bias is dependent on the radio luminosity, and find a bias which is significantly higher than predicted by the simulations of Wilman et al., and consistent with the lower luminosity but more abundant FR-I population having a similar bias to the highly luminous but rare FR-IIs. Our results are suggestive of a higher mass, particularly for FR-I sources than assumed in simulations, especially towards higher redshift.Peer reviewe

Anisotropies in the Diffuse Gamma-Ray Background from Dark Matter with Fermi LAT: a closer look

We perform a detailed study of the sensitivity to the anisotropies related to Dark Matter (DM) annihilation in the Isotropic Gamma-Ray Background (IGRB) as measured by the Fermi Large Area Telescope (Fermi-LAT). For the first time, we take into account the effects of the Galactic foregrounds and use a realistic representation of the Fermi-LAT. We consider DM anisotropies of extra-galactic origin and of Galactic origin (which can be generated through annihilation in the Milky Way sub-structures) as opposed to a background of anisotropies generated by sources of astrophysical origin, blazars for example. We find that with statistics from 5 years of observation Fermi is sensitive to a DM contribution at the level of the thermal-relic cross section depending on the DM mass and annihilation mode. The anisotropy method for DM searches has a sensitivity comparable to the usual methods based only on the energy spectrum and thus constitutes an independent and complementary piece of information in the DM puzzle. (abridged)Comment: 17 pages, 9 figures, v2: added discussion on unresolved point sources, matches published version on MNRA

The Canada-France deep fields survey-I: 100,000 galaxies, 1 deg^2: a precise measurement of \omega(\theta) to IAB~25

(abridged) Using the UH8K mosaic camera, we have measured the angular correlation function \omega(\theta) for 100,000 galaxies over four widely separated fields totalling ~1\deg^2 and reaching IAB~25.5. With this sample we investigate the dependence of \omega(\theta) at 1', A_\omega(1'), on sample median IAB magnitude in the range 19.5<I(AB-med)<24. Our results show that A_\omega(1') decreases monotonically to IAB~25. At bright magnitudes, \omega(\theta) is consistent with a power-law of slope \delta = -0.8 for 0.2'<\theta<3.0' but at fainter magnitudes we find \delta ~ -0.6. At the 3\sigma level, our observations are still consistent with \delta=-0.8. Furthermore, in the magnitude ranges 18.5<IAB<24.0 and 18.5<IAB<23.0 we find galaxies with 2.6<(V-I)AB<2.9 have A_\omega(1')'s which are ~10x higher than field values. We demonstrate that our model redshift distributions for the faint galaxy population are in good agreement with current spectroscopic observations. Using these predictions, we find that for low-omega cosmologies and assuming r_0=4.3/h Mpc, in the range 19.5<I(AB-med)<22, the growth of galaxy clustering is \epsilon~0. However, at 22<I(AB-med)<24.0, our observations are consistent with \epsilon>1. Models with \epsilon~0 cannot simultaneously match both bright and faint measurements of A_\omega(1`). We show how this result is a natural consequence of the ``bias-free'' nature of the \epsilon formalism and is consistent with the field galaxy population in the range 22.0<IAB<24.0 being dominated by galaxies of low intrinsic luminosity.Comment: 20 pages, 21 figures, requires natbib.sty, accepted for publication in Astronomy and Astrophysic

Large Scale Pressure Fluctuations and Sunyaev-Zel'dovich Effect

The Sunyaev-Zel'dovich (SZ) effect associated with pressure fluctuations of the large scale structure gas distribution will be probed with current and upcoming wide-field small angular scale cosmic microwave background experiments. We study the generation of pressure fluctuations by baryons which are present in virialized dark matter halos and by baryons present in small overdensities. For collapsed halos, assuming the gas distribution is in hydrostatic equilibrium with matter density distribution, we predict the pressure power spectrum and bispectrum associated with the large scale structure gas distribution by extending the dark matter halo approach which describes the density field in terms of correlations between and within halos. The projected pressure power spectrum allows a determination of the resulting SZ power spectrum due to virialized structures. The unshocked photoionized baryons present in smaller overdensities trace the Jeans-scale smoothed dark matter distribution. They provide a lower limit to the SZ effect due to large scale structure in the absence of massive collapsed halos. We extend our calculations to discuss higher order statistics, such as bispectrum and skewness in SZ data. The SZ-weak lensing cross-correlation is suggested as a probe of correlations between dark matter and baryon density fields, while the probability distribution functions of peak statistics of SZ halos in wide field CMB data can be used as a probe of cosmology and non-Gaussian evolution of large scale structure pressure fluctuations.Comment: 16 pages, 9 figures; Revised with expanded discussions. Phys. Rev. D. (in press