arXiv: 19 April 2011

Early Universe with CMB polarization

Authors: Tarun Souradeep (IUCAA)

arXiv:1104.3202v1

The Universe is the grandest conceivable scale on which the human mind can strive to understand nature. The amazing aspect of cosmology, the branch of science that attempts to understand the origin and evolution of the Universe, is that it is largely comprehensible by applying the same basic laws of physics that we use for other branches of physics. The observed cosmic microwave background (CMB) is understood by applying the basic laws of radiative processes and transfer, masterfully covered in the classic text by S. Chandrasekhar, in the cosmological context. In addition to the now widely acclaimed temperature anisotropy, there is also linear polarization information imprinted on the observed Cosmic Microwave background. CMB polarization already has addressed, and promises to do a lot more, to unravel the deepest fundamental queries about physics operating close to the origin of the Universe.

 

`Standard' Cosmological model & beyond with CMB

Authors: Tarun Souradeep (IUCAA)

arXiv:1104.3201v1

Observational Cosmology has indeed made very rapid progress in the past decade. The ability to quantify the universe has largely improved due to observational constraints coming from structure formation Measurements of CMB anisotropy and, more recently, polarization have played a very important role. Besides precise determination of various parameters of the `standard' cosmological model, observations have also established some important basic tenets that underlie models of cosmology and structure formation in the universe -- `acausally' correlated initial perturbations in a flat, statistically isotropic universe, adiabatic nature of primordial density perturbations. These are consistent with the expectation of the paradigm of inflation and the generic prediction of the simplest realization of inflationary scenario in the early universe. Further, gravitational instability is the established mechanism for structure formation from these initial perturbations. The signature of primordial perturbations observed as the CMB anisotropy and polarization is the most compelling evidence for new, possibly fundamental, physics in the early universe. The community is now looking beyond the estimation of parameters of a working `standard' model of cosmology for subtle, characteristic signatures from early universe physics.

 

 

arXiv: 15 April 2011

Black holes in Einstein-aether and Horava-Lifshitz gravity

Authors: Enrico Barausse, Ted Jacobson, Thomas P. Sotiriou
http://arxiv.org/abs/1104.2889v1
We study spherical black-hole solutions in Einstein-aether theory, a Lorentz-violating gravitational theory consisting of General Relativity with a dynamical unit timelike vector (the "aether") that defines a preferred timelike direction. These are also solutions to the infrared limit of Horava-Lifshitz gravity. We explore parameter values of the two theories where all presently know experimental constraints are satisfied, and find that spherical black-hole solutions of the type expected to form by gravitational collapse exist for all those parameters. Outside the metric horizon, the deviations away from the Schwarzschild metric are typically no more than a few percent for most of the explored parameter regions, which makes them difficult to observe with electromagnetic probes, but in principle within reach of future gravitational-wave detectors. Remarkably, we find that the solutions possess a universal horizon, not far inside the metric horizon, that traps waves of any speed relative to the aether. A notion of black hole thus persists in these theories, even in the presence of arbitrarily high propagation speeds.

Probing the dark matter issue in f(R)-gravity via gravitational lensing

Authors: M. Lubini, C. Tortora, J. Näf, Ph. Jetzer, S. Capozziello
http://arxiv.org/abs/1104.2851v1

Abstract: For a general class of analytic f(R)-gravity theories, we discuss the weak field limit in view of gravitational lensing. Though an additional Yukawa term in the gravitational potential modifies dynamics with respect to the standard Newtonian limit of General Relativity, the motion of massless particles results unaffected thanks to suitable cancellations in the post-Newtonian limit. Thus, all the lensing observables are equal to the ones known from General Relativity. Since f(R)-gravity is claimed, among other things, to be a possible solution to overcome for the need of dark matter in virialized systems, we discuss the impact of our results on the dynamical and gravitational lensing analyses. In this framework, dynamics could, in principle, be able to reproduce the astrophysical observations without recurring to dark matter, but in the case of gravitational lensing we find that dark matter is an unavoidable ingredient. Another important implication is that gravitational lensing, in the post-Newtonian limit, is not able to constrain these extended theories, since their predictions do not differ from General Relativity.

Tomography from the Next Generation of Cosmic Shear Experiments for Viable f(R) Models

Authors: Stefano Camera, Antonaldo Diaferio, Vincenzo F. Cardone
http://arxiv.org/abs/1104.2740v1
We present the cosmic shear signal predicted by two viable cosmological models in the framework of modified-action f(R) theories. We use f(R) models in which the current accelerated expansion of the Universe is a direct consequence of the modified gravitational Lagrangian rather than dark energy (DE), either in the form of vacuum energy/cosmological constant or of a dynamical scalar field (e.g. quintessence). We choose Starobinsky's (St) and Hu & Sawicki's (HS) f(R) models, which are carefully designed to pass the Solar System gravity tests. In order to further support (or rule out) f(R) theories as alternative candidates to the DE hypothesis, we exploit the power of weak gravitational lensing, specifically the cosmic shear signal. We calculate the tomographic shear matrix as it would be measured by the upcoming ESA Cosmic Vision Euclid satellite. We find that the cosmic shear signal is almost completely degenerate with LCDM in the St model but it is easily distinguishable in the HS model. Moreover, we compute the corresponding Fisher matrix for both the St and HS models, thus obtaining forecasts for their cosmological parameters. Finally, we show that the Bayes factor for the Euclid cosmic shear signal would definitely favour the HS model over LCDM for any non-null values of the extra HS parameter c_2.

arXiv: 14 April 2011

The growth of structure in the Szekeres inhomogeneous cosmological models and the matter-dominated era

Authors: Mustapha Ishak, Austin Peel (The University of Texas at Dallas)
http://arxiv.org/abs/1104.2590v1
This study belongs to a series devoted to using the Szekeres inhomogeneous models in order to develop a theoretical framework where cosmological observations can be investigated with a wider range of possible interpretations. While our previous work addressed the question of cosmological distances versus redshift in these models, the current study is a start at looking into the growth rate of large scale structure. The Szekeres models are exact solutions to Einstein's equations that were originally derived with no symmetries. We use here a formulation of the Szekeres models that is due to Goode and Wainwright who considered the models as exact perturbations of a Friedmann-Lemaitre-Robertson-Walker (FLRW) background. Using the Raychaudhuri equation, we write an exact growth equation in a form that splits into two informative parts. The first part, while exact, is identical to the growth equation in the usual linearly perturbed FLRW models. The second part constitutes exact second-order perturbations. We integrate numerically the full exact growth rate equation for the flat Szekeres Class-II case. We find that for the matter-dominated cosmic phase, the Szekeres growth rate is up to a factor of three stronger than the usual linearly perturbed Einstein-de Sitter case, reflecting the effect of exact Szekeres second-order perturbations. We also find that the Szekeres growth rate is stronger than that of the well-known nonlinear spherical collapse model and the difference between the two increases with time, highlighting the distinction when general inhomogeneous models are used. These results will be useful in analyzing structure growth observables in the Szekeres models. Additionally, the enhanced growth found in the Szekeres models during the matter-dominated era could suggest an alternative explanation to the observed large structures that in an FLRW model require a dark matter component.

Dark Matter Results from 100 Live Days of XENON100 Data

Authors: XENON100 Collaboration: E. Aprile, K. Arisaka, F. Arneodo, A. Askin, L. Baudis, A. Behrens, K. Bokeloh, E. Brown, T. Bruch, G. Bruno, J. M. R. Cardoso, W.-T. Chen, B. Choi, D. Cline, E. Duchovni, S. Fattori, A. D. Ferella, F. Gao, K.-L. Giboni, E. Gross, A. Kish, C. W. Lam, J. Lamblin, R. F. Lang, C. Levy, K. E. Lim, Q. Lin, S. Lindemann, M. Lindner, J. A. M. Lopes, K. Lung, T. Marrodan Undagoitia, Y. Mei, A. J. Melgarejo Fernandez, K. Ni, U. Oberlack, S. E. A. Orrigo, E. Pantic, R. Persiani, G. Plante, A. C. C. Ribeiro, R. Santorelli, J. M. F. dos Santos, G. Sartorelli, M. Schumann, M. Selvi, P. Shagin, H. Simgen, A. Teymourian, D. Thers, O. Vitells, H. Wang, M. Weber, C. Weinheimer
http://arxiv.org/abs/1104.2549v1
We present results from the direct search for dark matter with the XENON100 detector, installed underground at the Laboratori Nazionali del Gran Sasso of INFN, Italy. XENON100 is a two-phase time projection chamber with a 62 kg liquid xenon target. Interaction vertex reconstruction in three dimensions with millimeter precision allows to select only the innermost 48 kg as ultra-low background fiducial target. In 100.9 live days of data, acquired between January and June 2010, no evidence for dark matter is found. Three candidate events were observed in a pre-defined signal region with an expected background of 1.8 +/- 0.6 events. This leads to the most stringent limit on dark matter interactions today, excluding spin-independent elastic WIMP-nucleon scattering cross-sections above 7.0x10^-45 cm^2 for a WIMP mass of 50 GeV/c^2 at 90% confidence level.

Isolated dwarf galaxies in the local supercluster and its surroundings

Authors: V. E. Karachentseva, I. D. Karachentsev, M. E. Sharina
http://arxiv.org/abs/1104.2506v1
We present a list of 75 isolated late-type dwarf galaxies which have no neighbors with a relative radial velocity difference of less than 500 km/s or projected separations within 500 kpc. These were selected from $\sim$2000 dwarf galaxies with radial velocities $V_{LG}<3500$ km/s within the volume of the Local supercluster. In terms of their sizes, luminosities, and the amplitudes of their internal motions, the isolated late-type dwarfs do not differ significantly from gas-rich dwarf galaxies in groups and clusters. However, the median mass of neutral hydrogen per unit luminosity for the isolated dwarf galaxies is two times more than that for the late-type galaxies in groups. We have also identified 10 presumably isolated spheroidal dwarf galaxies. The detection of isolated dwarf galaxies populated exclusively by old stars is of great interest for modern cosmological scenarios of galaxy formation.

arXiv: 13 April 2011

Cosmological implications of a viable non-analytical f(R)-gravity model

Authors: Salvatore Capozziello, Nakia Carlevaro, Mariafelicia De Laurentis, Massimiliano Lattanzi, Giovanni Montani
http://arxiv.org/abs/1104.2169v1
We show how power-law corrections to the Einstein-Hilbert action yield a viable extended theory of gravity, passing the Solar-System tests, provided that the power-law exponent n is strictly comprised between 2 and 3. We implement this paradigm on a cosmological setting outlining how the main phases of the Universe thermal history are properly reproduced. As a result, we find two distinct constraints on the characteristic length scale of the model, i.e., a lower bound from the Solar-System test and an upper bound found by requiring the existence of the matter-dominated phase of the Universe evolution. We also show how the extended framework can accommodate the existence of an early de Sitter phase. Within the allowed range of characteristic length scales, the relation between the expansion rate H_I and the energy scale M of inflation is modified, yielding a value of H_I several orders of magnitude smaller than the one found in the standard picture, i.e., H_I ~ M^2/m_pl. The observational implication of this fact is that, quite generally, a tiny value of the tensor-to-scalar ratio r is expected in the extended framework, that will go undetected even by future missions focused on cosmic microwave background polarization, like CMBPol. The suppression of primordial tensor modes also implies that the inflationary scale can be made arbitrarily close to the Planck one without spoiling the current limits on r. Finally, considering the same modified action, an analysis of the propagation of gravitational waves on a Robertson-Walker background is addressed. We find that, in the allowed parameter range, the f(R) correction does not significantly affect the standard evolution.

Nonparametric Reconstruction of the Dark Energy Equation of State from Diverse Data Sets

Authors: Tracy Holsclaw, Ujjaini Alam, Bruno Sanso, Herbie Lee, Katrin Heitmann, Salman Habib, David Higdon
http://arxiv.org/abs/1104.2041v1
The cause of the accelerated expansion of the Universe poses one of the most fundamental questions in physics today. In the absence of a compelling theory to explain the observations, a first task is to develop a robust phenomenology. If the acceleration is driven by some form of dark energy, then, the phenomenology is determined by the dark energy equation of state w. A major aim of ongoing and upcoming cosmological surveys is to measure w and its time dependence at high accuracy. Since w(z) is not directly accessible to measurement, powerful reconstruction methods are needed to extract it reliably from observations. We have recently introduced a new reconstruction method for w(z) based on Gaussian process modeling. This method can capture nontrivial time-dependences in w(z) and, most importantly, it yields controlled and unbaised error estimates. In this paper we extend the method to include a diverse set of measurements: baryon acoustic oscillations, cosmic microwave background measurements, and supernova data. We analyze currently available data sets and present the resulting constraints on w(z), finding that current observations are in very good agreement with a cosmological constant. In addition we explore how well our method captures nontrivial behavior of w(z) by analyzing simulated data assuming high-quality observations from future surveys. We find that the baryon acoustic oscillation measurements by themselves already lead to remarkably good reconstruction results and that the combination of different high-quality probes allows us to reconstruct w(z) very reliably with small error bounds.

Neutron stars in generalized f(R) gravity

Authors: Emilio Santos
http://arxiv.org/abs/1104.2140v2

Abstract: A generalized $f(R)$ gravity theory is considered with the Einstein-Hilbert action $R+aR^2+bR_{\mu \nu} R^{\mu \nu}$, $R_{\mu \nu}$ being Ricci's tensor and R the curvature scalar. The parameters $a$ and $b$ are taken of order 1 km$^2$. A numerical integration is performed of the field equations for a free neutron gas. As in the standard Oppenheimer-Volkoff calculation the star mass increases with increasing central density until about 1 solar mass and then decreases. However a dramatic difference exists in the behaviour of the baryon number, which increases monotonically. The calculation suggests that the theory allows stars in equilibrium with arbitrary baryon number, no matter how large.

Generalizing Galileons

Authors: Mark Trodden, Kurt Hinterbichler
http://arxiv.org/abs/1104.2088v1
The Galileons are a set of terms within four-dimensional effective field theories, obeying symmetries that can be derived from the dynamics of a 3+1-dimensional flat brane embedded in a 5-dimensional Minkowski Bulk. These theories have some intriguing properties, including freedom from ghosts and a non-renormalization theorem that hints at possible applications in both particle physics and cosmology. In this brief review article, we will summarize our attempts over the last year to extend the Galileon idea in two important ways. We will discuss the effective field theory construction arising from co-dimension greater than one flat branes embedded in a flat background - the multiGalileons - and we will then describe symmetric covariant versions of the Galileons, more suitable for general cosmological applications. While all these Galileons can be thought of as interesting four-dimensional field theories in their own rights, the work described here may also make it easier to embed them into string theory, with its multiple extra dimensions and more general gravitational backgrounds.

arXiv: 12 April 2011

Through the Looking Glass: Bright, Highly Magnified Galaxies at z~7 Behind Abell 1703

Authors: L.D. Bradley, R.J. Bouwens, A. Zitrin, R. Smit, D. Coe, H.C. Ford, W. Zheng, G.D. Illingworth, N. Benítez, T.J. Broadhurst
http://arxiv.org/abs/1104.2035v1
We report the discovery of eight strongly lensed Lyman break galaxy (LBG) candidates at z~7 detected in Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging of Abell 1703. The brightest candidate, called A1703-zD1, has an observed (lensed) magnitude of 24.0 AB (26 sigma) in the WFC3/IR F160W band, making it 0.2 magnitudes brighter than the z_850-band dropout recently found behind the Bullet Cluster and 0.7 magnitudes brighter than the previously brightest known z~7.5 galaxy, A1689-zD1. With a cluster magnification of 9.0, this source has an intrinsic magnitude of H_160 = 26.4 AB, a strong J_125 - H_160 break of 1.7 magnitudes, and a photometric redshift of z~6.7. Additionally, we find seven other bright LBG candidates with H_160-band magnitudes of 24.9-26.4, photometric redshifts z~6.4 - 8.8, and magnifications mu~3-40. Stellar population fits to the ACS, WFC3/IR, and \Spitzer/IRAC data for A1703-zD1 and A1703-zD4 yield stellar masses (0.7 - 3.0) x 10^{9} M_sun, stellar ages 5-180 Myr, and star-formation rates ~7.8 M_sun/yr, and low reddening with A_V <= 0.8. The source-plane reconstruction of the exceptionally bright candidate A1703-zD1 exhibits an extended structure, spanning ~4 kpc in the z~6.7 source plane, and shows three resolved star-forming knots of radius r~0.4 kpc.

An analytical model for the accretion of dark matter subhalos

Authors: Xiaohu Yang (SHAO), H.J. Mo (UMass), Youcai Zhang (SHAO), Frank C. van den Bosch (Yale)
http://arxiv.org/abs/1104.1757v1

An analytical model is developed for the mass function of cold dark matter subhalos at the time of accretion and for the distribution of their accretion times. Our model is based on the model of \citet{Zhao09} for the median assembly histories of dark matter halos, combined with a simple log-normal distribution to describe the scatter in the main-branch mass at a given time for halos of the same final mass. Our model is simple, and can be used to predict the un-evolved subhalo mass function, the mass function of subhalos accreted at a given time, the accretion-time distribution of subhalos of a given initial mass, and the frequency of major mergers as a function of time. We test our model using high-resolution cosmological $N$-body simulations, and find that our model predictions match the simulation results remarkably well. Finally, we discuss the implications of our model for the evolution of subhalos in their hosts and for the construction of a self-consistent model to link galaxies and dark matter halos at different cosmic times.

Cosmological Constraints from Galaxy Clustering and the Mass-to-Number Ratio of Galaxy Clusters

Authors: Jeremy L. Tinker, Erin S. Sheldon, Risa H. Wechsler, Matthew R. Becker, Eduardo Rozo, Ying Zu, David H. Weinberg, Idit Zehavi, Michael Blanton, Michael Busha, Benjamin P. Koester
http://arxiv.org/abs/1104.1635v1

Abstract: We place constraints on the average density (Omega_m) and clustering amplitude (sigma_8) of matter using a combination of two measurements from the Sloan Digital Sky Survey: the galaxy two-point correlation function, w_p, and the mass-to-galaxy-number ratio within galaxy clusters, M/N, analogous to cluster M/L ratios. Our w_p measurements are obtained from DR7 while the sample of clusters is the maxBCG sample, with cluster masses derived from weak gravitational lensing. We construct non-linear galaxy bias models using the Halo Occupation Distribution (HOD) to fit both w_p and M/N for different cosmological parameters. HOD models that match the same two-point clustering predict different numbers of galaxies in massive halos when Omega_m or sigma_8 is varied, thereby breaking the degeneracy between cosmology and bias. We demonstrate that this technique yields constraints that are consistent and competitive with current results from cluster abundance studies, even though this technique does not use abundance information. Using w_p and M/N alone, we find Omega_m^0.5*sigma_8=0.465+/-0.026, with individual constraints of Omega_m=0.29+/-0.03 and sigma_8=0.85+/-0.06. Combined with current CMB data, these constraints are Omega_m=0.290+/-0.016 and sigma_8=0.826+/-0.020. All errors are 1-sigma. The systematic uncertainties that the M/N technique are most sensitive to are the amplitude of the bias function of dark matter halos and the possibility of redshift evolution between the SDSS Main sample and the maxBCG sample. Our derived constraints are insensitive to the current level of uncertainties in the halo mass function and in the mass-richness relation of clusters and its scatter, making the M/N technique complementary to cluster abundances as a method for constraining cosmology with future galaxy surveys.

arXiv: 11 April 2011

The Velocity Field Around Groups of Galaxies
F.D.A.Hartwick
http://arxiv.org/abs/1104.1621v1
A statistical method is presented for determining the velocity field
in the immediate vicinity of groups of galaxies using only positional
and redshift information with the goal of studying the perturbation of
the Hubble flow around groups more distant than the Local Group. The
velocities are assumed to obey a Hubble-like expansion law, i.e.
$V=H_{exp}R$ where the expansion rate $H_{exp}$ is to be determined.
The method is applied to a large, representative group catalog and
evidence is found for a sub-Hubble expansion rate within two well
defined radii beyond the virial radii of the groups. This result is
consistent with that of Teerikorpi et al. (2008) who found a similar
expansion law around 3 nearby groups and extends it to a more
representative volume of space.

The Shape of Dark Matter Haloes in the Aquarius Simulations: Evolution
and Memory
Carlos A. Vera-Ciro, Laura V. Sales, Amina Helmi, Carlos S. Frenk,
Julio F. Navarro, Volker Springel, Mark Vogelsberger, Simon D.M. White
http://arxiv.org/abs/1104.1566v1
We use the high resolution cosmological N-body simulations from the
Aquarius project to investigate in detail the mechanisms that
determine the shape of Milky Way-type dark matter haloes. We find
that, when measured at the instantaneous virial radius, the shape of
individual haloes changes with time, evolving from a typically prolate
configuration at early stages to a more triaxial/oblate geometry at
the present day. This evolution in halo shape correlates well with the
distribution of the infalling material: prolate configurations arise
when haloes are fed through narrow filaments, which characterizes the
early epochs of halo assembly, whereas triaxial/oblate configurations
result as the accretion turns more isotropic at later times.
Interestingly, at redshift z=0, clear imprints of the past history of
each halo are recorded in their shapes at different radii, which also
exhibit a variation from prolate in the inner regions to
triaxial/oblate in the outskirts. Provided that the Aquarius haloes
are fair representatives of Milky Way-like 10^12 Msun objects, we
conclude that the shape of such dark matter haloes is a complex,
time-dependent property, with each radial shell retaining memory of
the conditions at the time of collapse.

SNLS3: Constraints on Dark Energy Combining the Supernova Legacy
Survey Three Year Data with Other Probes
M. Sullivan, J. Guy, A. Conley, N. Regnault, P. Astier, C. Balland, S.
Basa, R. G. Carlberg, D. Fouchez, D. Hardin, I. M. Hook, D. A. Howell,
R. Pain, N. Palanque-Delabrouille, K. M. Perrett, C. J. Pritchet, J.
Rich, V. Ruhlmann-Kleider, D. Balam, S. Baumont, R. S. Ellis, S.
Fabbro, H. K. Fakhouri, N. Fourmanoit, S. Gonzalez-Gaitan, M. L.
Graham, M. J. Hudson, E. Hsiao, T. Kronborg, C. Lidmam, A. M. Mourao,
J. D. Neill, S. Perlmutter, P. Ripoche, N. Suzuki, E. S. Walker
http://arxiv.org/abs/1104.1444v1
We present observational constraints on the nature of dark energy
using the Supernova Legacy Survey three year sample (SNLS3) of Guy et
al. (2010) and Conley et al. (2011). We use the 472 SNe Ia in this
sample, accounting for recently discovered correlations between SN Ia
luminosity and host galaxy properties, and include the effects of all
identified systematic uncertainties directly in the cosmological fits.
Combining the SNLS3 data with the full WMAP7 power spectrum, the Sloan
Digital Sky Survey luminous red galaxy power spectrum, and a prior on
the Hubble constant H0 from SHOES, in a flat universe we find
omega_m=0.269+/-0.015 and w=-1.061+0.069-0.068 -- a 6.5% measure of
the dark energy equation-of-state parameter w. The statistical and
systematic uncertainties are approximately equal, with the systematic
uncertainties dominated by the photometric calibration of the SN Ia
fluxes -- without these calibration effects, systematics contribute
only a ~2% error in w. When relaxing the assumption of flatness, we
find omega_m=0.271+/-0.015, omega_k=-0.002+/-0.006, and
w=-1.069+0.091-0.092. Parameterizing the time evolution of w as
w(a)=w_0+w_a(1-a), gives w_0=-0.905+/-0.196, w_a=-0.984+1.094-1.097 in
a flat universe. All of our results are consistent with a flat, w=-1
universe. The size of the SNLS3 sample allows various tests to be
performed with the SNe segregated according to their light curve and
host galaxy properties. We find that the cosmological constraints
derived from these different sub-samples are consistent. There is
evidence that the coefficient, beta, relating SN Ia luminosity and
color, varies with host parameters at >4sigma significance (in
addition to the known SN luminosity--host relation); however this has
only a small effect on the cosmological results and is currently a
sub-dominant systematic.

Supernova Constraints and Systematic Uncertainties from the First 3
Years of the Supernova Legacy Survey
A. Conley, J. Guy, M. Sullivan, N. Regnault, P. Astier, C. Balland, S.
Basa, R.G. Carlberg, D. Fouchez, D. Hardin, I.M. Hook, D.A. Howell, R.
Pain, N. Palanque-Delabrouille, K.M. Perrett, C.J. Pritchet, J. Rich,
V. Ruhlmann-Kleider, D. Balam, S. Baumont, R.S. Ellis, S. Fabbro, H.K.
Fakhouri, N. Fourmanoit, S. Gonzalez-Gaitan, M.L. Graham, M.J. Hudson,
E. Hsiao, T. Kronborg, C. Lidman, A.M. Mourao, J.D. Neill, S.
Perlmutter, P. Ripoche, N. Suzuki, E.S. Walker
http://arxiv.org/abs/1104.1443v1
We combine high redshift Type Ia supernovae from the first 3 years of
the Supernova Legacy Survey (SNLS) with other supernova (SN) samples,
primarily at lower redshifts, to form a high-quality joint sample of
472 SNe (123 low-$z$, 93 SDSS, 242 SNLS, and 14 {\it Hubble Space
Telescope}). SN data alone require cosmic acceleration at >99.9%
confidence, including systematic effects. For the dark energy equation
of state parameter (assumed constant out to at least $z=1.4$) in a
flat universe, we find $w = -0.91^{+0.16}_{-0.20}(\mathrm{stat})
^{+0.07}_{-0.14} (\mathrm{sys})$ from SNe only, consistent with a
cosmological constant. Our fits include a correction for the recently
discovered relationship between host-galaxy mass and SN absolute
brightness. We pay particular attention to systematic uncertainties,
characterizing them using a systematics covariance matrix that
incorporates the redshift dependence of these effects, as well as the
shape-luminosity and color-luminosity relationships. Unlike previous
work, we include the effects of systematic terms on the empirical
light-curve models. The total systematic uncertainty is dominated by
calibration terms. We describe how the systematic uncertainties can be
reduced with soon to be available improved nearby and
intermediate-redshift samples, particularly those calibrated onto
USNO/SDSS-like systems.

Cosmology with Hypervelocity Stars
Abraham Loeb (Harvard)
http://arxiv.org/abs/1102.0007v2
In the standard cosmological model, the merger remnant of the Milky
Way and Andromeda (Milkomeda) will be the only galaxy remaining within
our event horizon once the Universe has aged by another factor of ten,
~10^{11} years after the Big Bang. After that time, the only
extragalactic sources of light in the observable cosmic volume will be
hypervelocity stars being ejected continuously from Milkomeda.
Spectroscopic detection of the velocity-distance relation or the
evolution in the Doppler shifts of these stars will allow a precise
measurement of the vacuum mass density as well as the local matter
distribution. Already in the near future, the next generation of large
telescopes will allow photometric detection of individual stars out to
the edge of the Local Group, and may target the ~10^{5+-1}
hypervelocity stars that originated in it as cosmological tracers.

arXiv: 8 April 2011

Extraterrestrial Life and Censorship
N. Chandra Wickramasinghe (Cardiff University UK)
http://arxiv.org/abs/1104.1314v1
In this article I chronicle a series of landmark events, with which I
was personally involved, that relate to the development of the theory
of cosmic life. The interpretation of events offered here might invite
a sense of incredulity on the part of the reader, but the facts
themselves are unimpeachable in regard to their authenticity. Of
particular interest are accounts of interactions between key players
in an unfolding drama connected with the origins of life. Attempts to
censor evidence incompatible with the cosmic life theory are beginning
to look futile and a long-overdue paradigm shift may have to be
conceded.

Is the Universe homogeneous?
Roy Maartens (Western Cape, ICG, Portsmouth)
http://arxiv.org/abs/1104.1300v1
The standard model of cosmology is based on the existence of
homogeneous surfaces as the background arena for structure formation.
Homogeneity underpins both general relativistic and modified gravity
models and is central to the way in which we interpret observations of
the CMB and the galaxy distribution. However, homogeneity cannot be
directly observed in the galaxy distribution or CMB, even with perfect
observations, since we observe on the past lightcone and not on
spatial surfaces. We can directly observe and test for isotropy, but
to link this to homogeneity, we need to assume the Copernican
Principle. First, we discuss the link between isotropic observations
on the past lightcone and isotropic spacetime geometry: what
observations do we need to be isotropic in order to deduce spacetime
isotropy? Second, we discuss what we can say with the Copernican
assumption. The most powerful result is based on the CMB: the
vanishing of the dipole, quadrupole and octupole of the CMB is
sufficient to impose homogeneity. Real observations lead to
near-isotropy on large scales - does this lead to near-homogeneity?
There are important partial results, and we discuss why this remains a
difficult open question. Thus we are currently unable to prove
homogeneity of the Universe on large-scales, even with the Copernican
Principle. However we can use observations of galaxies and clusters to
test the Copernican Principle itself.

A smoother end to the dark ages
Zoltán Haiman (Columbia University)
http://arxiv.org/abs/1104.1189v1
Independent lines of evidence suggest that the first stars, which
ended the cosmic dark ages, came in pairs, rather than singly. This
could change the prevailing view that the early Universe had a
Swiss-cheese-like appearance.

The effects of galaxy formation on the matter power spectrum: A
challenge for precision cosmology
Marcel P. van Daalen (1 and 2), Joop Schaye (1), C. M. Booth (1),
Claudio Dalla Vecchia (1 and 3) ((1) Leiden Observatory, Leiden
University (2) Max Planck Institute for Astrophysics (3) Max Planck
Institute for Extraterrestrial Physics)
http://arxiv.org/abs/1104.1174v1
Upcoming weak lensing surveys, such as LSST, EUCLID, and WFIRST, aim
to measure the matter power spectrum with unprecedented accuracy. In
order to fully exploit these observations, models are needed that,
given a set of cosmological parameters, can predict the non-linear
matter power spectrum at the level of 1% or better for scales
corresponding to comoving wave numbers 0.1<k<10 h/Mpc. We have
employed the large suite of simulations from the OWLS project to
investigate the effects of various baryonic processes on the matter
power spectrum. In addition, we have examined the distribution of
power over different mass components, the back-reaction of the baryons
on the CDM, and the evolution of the dominant effects on the matter
power spectrum. We find that single baryonic processes are capable of
changing the power spectrum by up to several tens of per cent. Our
simulation that includes AGN feedback, which we consider to be our
most realistic simulation as, unlike those used in previous studies,
it has been shown to solve the overcooling problem and to reproduce
optical and X-ray observations of groups of galaxies, predicts a
decrease in power relative to a dark matter only simulation ranging,
at z=0, from 1% at k~0.3 h/Mpc to 10% at k~1 h/Mpc and to 30% at k~10
h/Mpc. This contradicts the naive view that baryons raise the power
through cooling, which is the dominant effect only for k>70 h/Mpc.
Therefore, baryons, and particularly AGN feedback, cannot be ignored
in theoretical power spectra for k>0.3 h/Mpc. It will thus be
necessary to improve our understanding of feedback processes in galaxy
formation, or at least to constrain them through auxiliary
observations, before we can fulfil the goals of upcoming weak lensing
surveys.

Galaxy Bias and its Effects on the Baryon Acoustic Oscillations Measurements
Kushal T. Mehta, Hee-Jong Seo, Jonathan Eckel, Daniel J. Eisenstein,
Marc Metchnik, Philip Pinto, Xiaoying Xu
http://arxiv.org/abs/1104.1178v1
The baryon acoustic oscillation (BAO) feature in the clustering of
matter in the universe serves as a robust standard ruler and hence can
be used to map the expansion history of the universe. We use high
force resolution simulations to analyze the effects of galaxy bias on
the measurements of the BAO signal. We apply a variety of Halo
Occupation Distributions (HODs) and produce biased mass tracers to
mimic different galaxy populations. We investigate whether galaxy bias
changes the non-linear shifts on the acoustic scale relative to the
underlying dark matter distribution presented by Seo et al (2009). For
the less biased HOD models (b < 3), we do not detect any shift in the
acoustic scale relative to the no-bias case, typically 0.10% \pm
0.10%. However, the most biased HOD models (b > 3) show a shift at
moderate significance (0.79% \pm 0.31% for the most extreme case). We
test the one-step reconstruction technique introduced by Eisenstein et
al. (2007) in the case of realistic galaxy bias and shot noise. The
reconstruction scheme increases the correlation between the initial
and final (z = 1) density fields achieving an equivalent level of
correlation at nearly twice the wavenumber after reconstruction.
Reconstruction reduces the shifts and errors on the shifts. We find
that after reconstruction the shifts from the galaxy cases and the
dark matter case are consistent with each other and with no shift. The
1-sigma systematic errors on the distance measurements inferred from
our BAO measurements with various HODs after reconstruction are about
0.07% - 0.15%.

arXiv: 7 April 2011

Constraints on the dark energy using multiple observations : snare of
principal component analysis
Seokcheon Lee
http://arxiv.org/abs/1104.1137v1
We explore snares in determining the equation of state of dark energy
($\omega$) when one uses the so-called principal component analysis
for multiple observations. We demonstrated drawbacks of principal
component analysis in an earlier paper. We used the Hubble parameter
data generated from a fiducial model using the so-called
Chevallier-Polarski-Linder parameterization. We extend our previous
consideration to multiple observations, the Hubble parameter and the
luminosity distance. We find that the principal component analysis
produces the almost constant $\omega$ even when a fiducial model is a
rapidly varying $\omega$. Thus, resolution of dynamical property of
$\omega$ through PCA is degraded especially when one fits to several
observations.

MOND and the unique void galaxy KK246
Mordehai Milgrom (DPPA, Weizmann Institute)
http://arxiv.org/abs/1104.1118v1
MOND predictions are compared with the mass discrepancy, Gamma (the
dynamical-to-baryon mass ratio) deduced from the recently measured
rotation curve, for the gas-rich, dwarf galaxy KK246, "the only galaxy
observed in the local void". KK246 is special in at least two regards:
a. It is, to my knowledge, the record holder for the largest mass
discrepancy deduced from a rotation curve, Gamma= 15. b. It is very
isolated, residing in a large, very empty void. I also discuss another
extreme case: Andromeda IV, a dwarf considered here for the first time
in light of MOND, with a very large mass discrepancy, Gamma =12, also
conforming accurately to the MOND prediction. In both cases, MOND
predicts Gamma, or the total dynamical mass at the last observed
radius, from only the knowledge of the small mass of baryons. If MOND
is accepted as the root of the mass discrepancy, these are just two
more expected, albeit reassuring, conformities. However, in the
framework of the dark-matter paradigm--where the mass discrepancy is
strongly dependent on the buildup history of a galaxy--every new such
conformity with a tight law is another difficult-to-understand
surprise, and does carry a new import: What, in the LCDM paradigm,
would prevent such galactic baryons from residing in a halo of half,
or twice, the observed rotational velocities, instead of selecting
exactly the velocities predicted by MOND? This conundrum is especially
poignant for KK246, whose great isolation points to a relatively
unique buildup history. This note underscores the individual
importance of each galaxy as a new test, as opposed to the view of
them all as a statistical ensemble.

arXiv: 6 April 2011

Probing the Universe's Tilt with the Cosmic Infrared Background Dipole

D. J. Fixsen, A.Kashlinsky

http://arxiv.org/abs/1104.0901v1

Conventional interpretation of the observed cosmic microwave background (CMB) dipole is that all of it is produced by local peculiar motions. Alternative explanations requiring part of the dipole to be primordial have received support from measurements of large-scale bulk flows. A test of the two hypothesis is whether other cosmic dipoles produced by collapsed structures later than last scattering coincide with the CMB dipole. One background is the cosmic infrared background (CIB) whose absolute spectrum was measured to ~30% by the COBE satellite. Over the 100 to 500 um wavelength range its spectral energy distribution can provide a probe of its alignment with CMB. This is tested with the COBE FIRAS dataset which is available for such a measurement because of its low noise and frequency resolution important for Galaxy subtraction. Although the FIRAS instrument noise is in principle low enough to determine the CIB dipole, the Galactic foreground is sufficiently close spectrally to keep the CIB dipole hidden. A similar analysis is performed with DIRBE, which - because of the limited frequency coverage - provides a poorer a dataset. We discuss strategies for measuring the CIB dipole with future instruments to probe the tilt and apply it to the Planck, Herschel and the proposed Pixie missions. We find that the Planck and Herschel data sets will not allow a robust CIB dipole measurement. The Pixie instrument promises a determination of the CIB dipole and its alignment with either the CMB dipole or the dipole galaxy acceleration vector.

Gamma Ray Bursts as Probes of the Distant Universe

P. Petitjean (IAP), S. D. Vergani (INAF-OAB)

http://arxiv.org/abs/1104.0844v1

We review recent results on the high-redshift universe and the cosmic evolution obtained using Gamma Ray Bursts (GRBs) as tracers of high-redshift galaxies. Most of the results come from photometric and spectroscopic observations of GRB host galaxies once the afterglow has faded away but also from the analysis of the GRB afterglow line of sight as revealed by absorptions in their optical spectrum.

Galaxy Properties from the Ultra-violet to the Far-Infrared: Lambda-CDM models confront observations

R. S. Somerville, R. C. Gilmore, J.R. Primack, A. Dominguez

http://arxiv.org/abs/1104.0669v1

We combine a semi-analytic model of galaxy formation with simple analytic recipes describing the absorption and re-emission of starlight by dust in the interstellar medium of galaxies. We use the resulting models to predict galaxy counts and luminosity functions from the far-ultraviolet to the sub-mm, from redshift five to the present, and compare with an extensive compilation of observations. We find that in order to reproduce the rest-UV and optical luminosity functions at high redshift, we must assume an evolving normalization in the dust-to-metal ratio, implying that galaxies of a given bolometric luminosity (or metal column density) must be less extinguished than their local counterparts. In our best-fit model, we find remarkably good agreement with observations from rest ~1500 Angstroms to ~250 microns. At longer wavelengths, most dramatically in the sub-mm, our models underpredict the number of bright galaxies by a large factor. We show the results of varying several ingredients of the models, including various aspects of the dust attenuation recipe, the dust emission templates, and the cosmology. We use our models to predict the integrated Extragalactic Background Light (EBL), and compare with an observationally-motivated EBL model and with other available observational constraints. The build-up of the EBL over cosmic history and the implications for the attenuation of GeV and TeV gamma rays are explored in a companion paper.

Supernovae type Ia: non-standard candles of the Universe 

A. I. Bogomazov, A. V. Tutukov

We analyze the influence of the evolution of light absorbtion by grey dust in SNe Ia host galaxies and the influence of the evolution of average total mass of coalescing double carbon-oxygen white dwarfs (progenitors of SNe Ia) under the influence of gravitational radiation on the interpretation of Hubble diagrams of SNe Ia. Significant increase in the average energy of SNe Ia due to increase in the total mass of merging dwarfs can be observed at red shift z> 2. The observed dependence of the distance modulus from the red shift in observations of SNe Ia can be explained not only by the assumption about accelerated expansion of the Universe, but also by the evolution of the absorbtion of light by grey dust in various types of host galaxies of SNe Ia, by the effects of observational selection and by the decrease in the average mass of coalescing degenerate dwarfs.

arXiv: 5 April 2011

Radiation from a dust dynamical LTB black hole

Authors: J. T. Firouzjaee, Reza Mansouri
http://arxiv.org/abs/1104.0530v1
Does a black hole immersed in a cosmological FRW background emit Hawking radiation where a globally defined even horizon does not exist? What about the first law of black hole mechanics? We face these questions using an analytical LTB cosmological black hole model recently published. Using the Hamilton-Jacobi method, we show that it is the apparent horizon which contributes to the Hawking radiation. The first law of LTB black hole, decay of composite particles, and the thermal character of the radiation is also dealt with.

Future weak lensing constraints in a dark coupled universe

Authors: Francesco De Bernardis, Matteo Martinelli, Alessandro Melchiorri, Olga Mena, Asantha Cooray

http://arxiv.org/abs/1104.0652v1
Coupled cosmologies can predict values for the cosmological parameters at low redshifts which may differ substantially from the parameters values within non-interacting cosmologies. Therefore, low redshift probes, as the growth of structure and the dark matter distribution via galaxy and weak lensing surveys constitute a unique tool to constrain interacting dark sector models. We focus here on weak lensing forecasts from future Euclid and LSST-like surveys combined with the ongoing Planck cosmic microwave background experiment. We find that these future data could constrain the dimensionless coupling to be smaller than a few $\times 10^{-2}$. The coupling parameter $\xi$ is strongly degenerate with the cold dark matter energy density $\Omega_{c}h^2$ and the Hubble constant $H_0$.These degeneracies may cause important biases in the cosmological parameter values if in the universe there exists an interaction among the dark matter and dark energy sectors.

LCDM: Triumphs, Puzzles and Remedies

Authors: L. Perivolaropoulos (U. of Ioannina)
http://arxiv.org/abs/1104.0539v1
The consistency level of LCDM with geometrical data probes has been increasing with time during the last decade. Despite of these successes, there are some puzzling conflicts between LCDM predictions and dynamical data probes (bulk flows, alignment and magnitude of low CMB multipoles, alignment of quasar optical polarization vectors, cluster halo profiles). Most of these puzzles are related to the existence of preferred anisotropy axes which appear to be unlikely close to each other. A few models that predict the existence of preferred cosmological axes are briefly discussed.

Designing Surveys for Tests of Gravity

Authors: Bhuvnesh Jain (U Penn)
http://arxiv.org/abs/1104.0415v1
Modified gravity theories may provide an alternative to dark energy to explain cosmic acceleration. We argue that the observational program developed to test dark energy needs to be augmented to capture new tests of gravity on astrophysical scales. Several distinct signatures of gravity theories exist outside the linear regime, especially owing to the screening mechanism that operates inside halos like the Milky Way to ensure that gravity tests in the solar system are satisfied. This opens up several decades in length scale and new classes of galaxies at low-redshift that can be exploited by surveys. While theoretical work on models of gravity is in the early stages, we can already identify new regimes which cosmological surveys could target to test gravity. These include: 1. A small scale component that focuses on the interior and vicinity of galaxy and cluster halos. 2. Spectroscopy of low redshift galaxies, especially galaxies smaller than the Milky Way, in environments that range from voids to clusters. 3. A program of combining lensing and dynamical information, from imaging and spectroscopic surveys respectively, on the same (or statistically identical) sample of galaxies.

arXiv; 4 April 2011

Dark Matter in Elliptical Galaxies

Authors: David A. Buote, Philip J. Humphrey (UC Irvine)
We review X-ray constraints on dark matter in giant elliptical galaxies (10^{12} M_sun <~ M_vir <~ 10^{13} M_sun) obtained using the current generation of X-ray satellites, beginning with an overview of the physics of the hot interstellar medium and mass modeling methodology. Dark matter is now firmly established in many galaxies, with inferred NFW concentration parameters somewhat larger than the mean theoretical relation. X-ray observations confirm that the total mass profile (baryons+DM) is close to isothermal (M ~ r), and new evidence suggests a more general power-law relation for the slope of the total mass profile that varies with the stellar half-light radius. We also discuss constraints on the baryon fraction, super-massive black holes, and axial ratio of the dark matter halo. Finally, we review constraints on non-thermal gas motions and discuss the accuracy of the hydrostatic equilibrium approximation in elliptical galaxies.

arXiv: 1 April 2011

Satellites in the Local Group and Other Nearby Groups

Authors: Eva K. Grebel (ARI/ZAH, Heidelberg University)
http://arxiv.org/abs/1103.6234v1
Abstract: In recent years the census of known satellites in our own Local Group and in nearby galaxy groups has increased substantially due to sensitive wide-area surveys. In the Local Group these surveys have more than doubled its known galaxy content and extended the galaxy luminosity function to very faint total magnitudes. Deep ground-based imaging and spectroscopic observations as well as high-resolution imaging with the Hubble Space Telescope have revolutionized our understanding of the chemical evolution and star formation histories of the satellites. We often find long-lasting star formation episodes with low star formation efficiencies. There is evidence for localized, stochastic enrichment, and recent searches are now beginning to uncover even extremely metal-deficient stars. In many satellites evidence for two or more distinct stellar subpopulations is found. Differing fractions of old populations have been detected in all satellites studied in sufficient detail so far. Kinematic measurements support a picture in which satellites are dark-matter dominated, although recent results indicate that the proposed common mass scale for dwarf spheroidal galaxies may not hold for very low-mass satellites. When considering satellite ensembles, we find global morphology-distance and gas-content - distance relations in all groups studied thus far, but individual star formation histories also strongly depend on a given satellite's intrinsic properties.

arXiv: 31 March 2011

Extrasolar Planets in the Classroom

Authors: Samuel J. George
http://arxiv.org/abs/1103.5690v1
The field of extrasolar planets is still, in comparison with other astrophysical topics, in its infancy. There have been about 300 or so extrasolar planets detected and their detection has been accomplished by various different techniques. Here we present a simple laboratory experiment to show how planets are detected using the transit technique. Following the simple analysis procedure describe we are able to determine the planetary radius to be 1.27 +/- 0.20 R_{J} which, within errors agrees with the establish value of 1.32 +/- 0.25 R_{J}.

Title: Dark Energy

Authors: Miao Li, Xiao-Dong Li, Shuang Wang, Yi Wang
http://arxiv.org/abs/1103.5870v1
We review the problem of dark energy, including a survey of phenomenological models and some aspects of data fitting.

Formation rates of Dark Matter Haloes

Authors: Sourav Mitra, Girish Kulkarni, J. S. Bagla, Jaswant K. Yadav
http://arxiv.org/abs/1103.5828v1
We derive an estimate of the rate of formation of dark matter halos per unit volume as a function of the halo mass and redshift of formation. Analytical estimates of the number density of dark matter halos are useful in modeling several cosmological phenomena. We use the excursion set formalism for computing the formation rate of dark matter halos. We use an approach that allows us to differentiate between major and minor mergers, as this is a pertinent issue for semi-analytic models of galaxy formation. We compute the formation rate for the Press-Schechter and the Sheth-Tormen mass function. We show that the formation rate computed in this manner is positive at all scales. We comment on the Sasaki formalism where negative halo formation rates are obtained. Our estimates compare very well with N-Body simulations for a variety of models. We also discuss the halo survival probability and the formation redshift distributions using our method.

A Robust Approach to Constraining Dark Matter from Gamma-Ray Data

Authors: Eric J. Baxter, Scott Dodelson
http://arxiv.org/abs/1103.5779v1
Photons produced in the annihilations of dark matter particles can be detected by gamma-ray telescopes; this technique of indirect detection serves as a cornerstone of the upcoming assault on the dark matter paradigm. The main obstacle to the extraction of information about dark matter from the annihilation photons is the presence of large and uncertain gamma-ray backgrounds. We present a new technique for using gamma-ray data to constrain the properties of dark matter that makes minimal assumptions about the dark matter and the backgrounds. The technique relies on two properties of the expected signal from annihilations of the smooth dark matter component in our galaxy: 1) it is approximately rotationally symmetric around the axis connecting us to the galactic center, and 2) variations from the mean signal are uncorrelated from one pixel to the next. We apply this technique to recent data from the Fermi telescope to generate constraints on the dark matter mass and cross section for a variety of annihilation channels. We quantify the uncertainty introduced into our constraints by uncertainties in the halo profile and by the possibility that the halo is triaxial. The resultant constraint, the flux F \leq 4.5\times10^-6 cm^-2 s^-1 sr^-1 for energies between 1 and 100 GeV at an angle 15 degrees away from the Galactic Center, translates into an upper limit on the velocity weighted annihilation cross section of order 10^-25 cm^3 s^-1 depending on the annihilation mode.

Cosmological UV/IR Divergences and de-Sitter Spacetime

Authors: Wei Xue, Keshav Dasgupta, Robert Brandenberger
http://arxiv.org/abs/1103.0285v2
We consider one loop graviton corrections to scalar field Green's functions in the de Sitter phase of an inflationary space-time, a topic relevant to the computation of cosmological observables beyond linear order. By embedding de-Sitter space into an ultraviolet complete theory such as M-theory we argue that the ultraviolet (UV) cutoff of the effective field theory should be taken to be fixed in physical coordinates, whereas the infrared (IR) cutoff is expanding as space expands. In this context, we demonstrate how to implement three different regularization schemes -- the brute force cutoff regularization, dimensional regularization and Pauli-Villars regularization -- obtaining the same result for the scalar propagator if we use any of the three regularization schemes.

arXiv: 30 March 2011

The EFIGI catalogue of 4458 nearby galaxies with detailed morphology

Authors: Anthony Baillard, Emmanuel Bertin, Valérie de Lapparent, Pascal Fouqué, Stéphane Arnouts, Yannick Mellier, Roser Pelló, Jean-Francois Leborgne, Philippe Prugniel, Dmitry Makarov, Lidia Makarova, Henry J. McCracken, Albert Bijaoui, Lidia Tasca
http://arxiv.org/abs/1103.5734v1

Now that large databases of resolved galaxy images are provided by modern imaging surveys, advanced morphological studies can be envisioned, urging for well defined calibration samples. We present the EFIGI catalogue, a multiwavelength database specifically designed for a dense sampling of all Hubble types. The catalogue merges data from standard surveys and catalogues (Principal Galaxy Catalogue, Sloan Digital Sky Survey, Value-Added Galaxy Catalogue, HyperLeda, and the NASA Extragalactic Database) and provides detailed morphological information. Imaging data are obtained from the SDSS DR4 in the u, g, r, i, and z bands for a sample of 4458 PGC galaxies, whereas photometric and spectroscopic data are obtained from the SDSS DR5 catalogue. Point-Spread Function models are derived in all five bands. Composite colour images of all objects are visually examined by a group of astronomers, and galaxies are staged along the Hubble sequence and classified according to 16 morphological attributes describing their structure, texture, as well as environment and appearance on a five-level scale. The EFIGI Hubble sequence shows remarkable agreement with the RC3 Revised Hubble Sequence. The main characteristics and reliability of the catalogue are examined, including photometric completeness, type mix, systematic trends and correlations. The final EFIGI database is a large sub-sample of the local Universe, with a dense sampling of Sd, Sdm, Sm and Im types compared to magnitude-limited catalogues. We estimate the photometric catalogue to be more than ~ 80% complete for galaxies with 10<g<14. More than 99.5% of EFIGI galaxies have a known redshift in the HyperLeda and NED databases.

The Second Byurakan Survey Galaxies. I. The Optical Database

Authors: M. Gyulzadyan, B. Mclean, V.Zh.Adibekyan, R. J. Allen, D. Kunth, A. Petrosian, J. A. Stepanian
http://arxiv.org/abs/1103.5624v1
A database for the entire catalog of the Second Byurakan Survey (SBS) galaxies is presented. It contains new measurements of their optical parameters and additional information taken from the literature and other databases. The measurements were made using Ipg(near-infrared), Fpg(red) and Jpg(blue) band images from photographic sky survey plates obtained by the Palomar Schmidt telescope and extracted from the STScI Digital Sky Survey (DSS). The database provides accurate coordinates, morphological type, spectral and activity classes, apparent magnitudes and diameters, axial ratios, and position angles, as well as number counts of neighboring objects in a circle of radius 50 kpc. The total number of individual SBS objects in the database is now 1676. The 188 Markarian galaxies which were re-discovered by SBS are not included in this database. We also include redshifts that are now available for 1576 SBS objects, as well as 2MASS infrared magnitudes for 1117 SBS galaxies.

The Cluster Lensing and Supernova Survey with Hubble (CLASH): Strong Lensing Analysis of Abell 383 from 16-Band HST WFC3/ACS Imaging

Authors: A. Zitrin, T. Broadhurst, D. Coe, K. Umetsu, M. Postman, N. Benítez, M. Meneghetti, E. Medezinski, S. Jouvel, L. Bradley, A. Koekemoer, W. Zheng, H. Ford, J. Merten, D. Kelson, O. Lahav, D. Lemze, A. Molino, M. Nonino, M. Donahue, P. Rosati, A. Van der Wel, M. Bartelmann, R. Bouwens, O. Graur, G. Graves, O. Host, L. Infante, S. Jha, Y. Jimenez-Teja, R. Lazkoz, D. Maoz, C. McCully, P. Melchior, L.A. Moustakas, S. Ogaz, B. Patel, E. Regoes, A. Riess, S. Rodney, S. Seitz
http://arxiv.org/abs/1103.5618v2
We examine the inner mass distribution of the relaxed cluster Abell 383 (z=0.189), in deep 16-band HST/ACS+WFC3 imaging taken as part of the CLASH multi-cycle treasury program. Our program is designed to study the dark matter distribution in 25 massive clusters, and balances depth with a wide wavelength coverage, 2000-16000\AA, to better identify lensed systems and generate precise photometric redshifts. This photometric information together with the predictive strength of our strong-lensing analysis method identifies 13 new multiply-lensed images and candidates, so that a total of 27 multiple-images of 9 systems are used to tightly constrain the inner mass profile gradient, $d\log Sigma/d\log r\simeq -0.6\pm 0.1$ (r<160 kpc). We find consistency with the standard distance-redshift relation for the full range spanned by the lensed images, 1.01<z<6.03, with the higher redshift sources deflected through larger angles as expected. The derived inner mass profile is consistent with the results of our independent weak-lensing analysis of wide-field Subaru images, with good agreement in the region of overlap. Combining weak and strong lensing, the overall mass profile is well fitted by an NFW profile with M_{vir}=6.26^{+0.26}_{-0.25} x 10^{14}M_{\odot}/h and a relatively high concentration, c_{vir} = 8.59^{+0.21}_{-0.20}, which lies above the standard c-M relation similar to other well-studied clusters. The critical radius of Abell 383 is modest by the standards of other lensing clusters, r_{E}\simeq16\pm2\arcsec (for z_s=2.55), so the relatively large number of lensed images uncovered here with precise photometric redshifts validates our imaging strategy for the CLASH survey. In total we aim to provide similarly high-quality lensing data for 25 clusters, 20 of which are X-ray selected relaxed clusters, enabling a precise determination of the representative mass profile free from lensing bias.

Gamma-ray bursts as cosmological probes: LambdaCDM vs. conformal gravity

Authors: Antonaldo Diaferio (1,2,3), Luisa Ostorero (1,2,3,4), Vincenzo F. Cardone (5), ((1) Universita` di Torino, (2) INFN Torino, (3) Harvard-Smithsonian Center for Astrophysics, (4) University of Pennsylvania, (5) INAF Monte Porzio Roma)
http://arxiv.org/abs/1103.5501v1
LambdaCDM, for the currently preferred cosmological density Omega_0 and cosmological constant Omega_Lambda, predicts that the Universe expansion decelerates down to redshift z~0.9 and accelerates at later times. On the contrary, the cosmological model based on conformal gravity predicts that the cosmic expansion has always been accelerating. To distinguish between these two very different cosmologies, we resort to gamma-ray bursts (GRBs), which have been suggested to probe the Universe expansion history at z>1, where identified type Ia supernovae (SNe) are rare. We use the full Bayesian approach to infer the cosmological parameters and the additional parameters required to describe the GRB data available in the literature. For the first time, we use GRBs as cosmological probes without any prior information from other data. In addition, when we combine the GRB samples with SNe, our approach neatly avoids all the inconsistencies of most numerous previous methods that are plagued by the so-called circularity problem. We find that the currently available SN and GRB samples are accommodated equally well by LambdaCDM and conformal gravity and do not exclude a continuous accelerated expansion. Nevertheless, the model selection method provided by the Bayesian approach decisively favours LambdaCDM.

Removable Matter-Power-Spectrum Covariance from Bias Fluctuations

Authors: Mark C. Neyrinck (JHU)
http://arxiv.org/abs/1103.5476v1
We find a simple, accurate model for the covariance matrix of the real-space cosmological matter power spectrum on slightly nonlinear scales. The model is based on fluctuations in a multiplicative, scale-independent bias. It has only one parameter, the variance (among realizations) of the variance of the nonlinear density field in cells, with little dependence on the cell size, between 2-8 Mpc/h. Furthermore, we find that the troublesome non-Gaussian part of the covariance can be largely removed if the power spectrum is divided by the variance in cell densities.

The correlation structure of dark matter halo properties

Authors: Akila Jeeson-Daniel (1,2), Claudio Dalla Vecchia (2,3), Marcel R. Haas (2,4), Joop Schaye (2) ((1) MPA (2) Leiden (3) MPE (4) STScI)
http://arxiv.org/abs/1103.5467v1
We investigate the correlation between nine different dark matter halo properties using a rank correlation analysis and a Principal Component Analysis for a sample of haloes spanning five orders of magnitude in mass. We consider mass and dimensionless measures of concentration, age, relaxedness, sphericity, triaxiality, substructure, spin, and environment, where the latter is defined in a way that makes it insensitive to mass. We find that concentration is the most fundamental property. Except for environment, all parameters are strongly correlated with concentration. Concentration, age, substructure, mass, sphericity and relaxedness can be considered a single family of parameters, albeit with substantial scatter. In contrast, spin, environment, and triaxiality are more independent, although spin does correlate strongly with substructure and both spin and triaxiality correlate substantially with concentration. Although mass sets the scale of a halo, all other properties are more sensitive to concentration.

arXiv: 29 March 2011

Extrasolar Asteroid Mining as Forensic Evidence for Extraterrestrial Intelligence

Duncan Forgan, Martin Elvis
http://arxiv.org/abs/1103.5369v1
The development of civilisations like ours into spacefaring, multi-planet entities requires significant raw materials to construct vehicles and habitats. Interplanetary debris, including asteroids and comets, may provide such a source of raw materials. In this article we present the hypothesis that extraterrestrial intelligences (ETIs) engaged in asteroid mining may be detectable from Earth. Considering the detected disc of debris around Vega as a template, we explore the observational signatures of targeted asteroid mining (TAM), such as unexplained deficits in chemical species, changes in the size distribution of debris and other thermal signatures which may be detectable in the spectral energy distribution (SED) of a debris disc. We find that individual observational signatures of asteroid mining can be explained by natural phenomena, and as such they cannot provide conclusive detections of ETIs. But, it may be the case that several signatures appearing in the same system will prove harder to model without extraterrestrial involvement. Therefore signatures of TAM are not detections of ETI in their own right, but as part of "piggy-back" studies carried out in tandem with conventional debris disc research, they could provide a means of identifying unusual candidate systems for further study using other SETI techniques.

What do we really know about Dark Energy?

Ruth Durrer
http://arxiv.org/abs/1103.5331v1
In this paper I discuss what we truly know about dark energy. I shall argue that up to date our single indication for the existence of dark energy comes from distance measurements and their relation to redshift. Supernovae, CMB anisotropies and observations of baryon acoustic oscillations, they all simply tell us that the observed distance to a given redshift is larger than the one expected from a Friedmann Lemaitre universe with matter only and the locally measured Hubble parameter.