Found 94 talks archived in Cosmology

Almost all cosmologists accept nowadays that the redshift of the galaxies is due to the expansion of the Universe (cosmological redshift), plus some Doppler effect of peculiar motions, but can we be sure of this fact by means of some other independent cosmological test? Here I will review some recent tests: CMBR temperature versus redshift, time dilation, the Hubble diagram, the Tolman or surface brightness test, the angular size test, the UV surface brightness limit and the Alcock-Paczynski test. Some tests favour expansion and others favour a static Universe. Almost all the cosmological tests are susceptible to the evolution of galaxies and/or other effects. Tolman or angular size tests need to assume very strong evolution of galaxy sizes to fit the data with the standard cosmology, whereas the Alcock-Paczynski test, an evaluation of the ratio of observed angular size to radial/redshift size, is independent of it.

The standard model of cosmology is based on the Friedmann-Robertson-Walker (FRW) metric. Often written in terms of co-moving coordinates, this elegant and highly practical solution to Einstein's equations is based on the Cosmological principal and Weyl's postulate. But not all of the physics behind such symmetries has yet been recognized. We invoke the fact that the co-moving frame also happens to be in free fall to demonstrate that the FRW metric is apparently valid only for a medium with zero active mass. In other words, the application of FRW appears to require an equation-of-state rho+3p = 0, in terms of the total energy density rho and total pressure p. Though the standard model is not framed in these terms, the optimization of its parameters brings it ever closer to this constraint as the precision of the observations continues to improve. For example, the latest high-precision BAO measurements rule out the standard model at better than the 99.34% C.L. if the zero active mass condition is ignored.

The extragalactic background light (EBL) is the second most energetic diffuse background that fills our Universe. It is produced by star formation processes and supermassive black hole accretion over the history of the  Universe. Thus, it contains fundamental information about galaxy evolution and cosmology. Interestingly, it brings together classical astronomy and high energy astrophysics since gamma-rays from extragalactic sources such as blazars and gamma-ray bursts interact by pair-production with EBL photons. Therefore, it is also essential for extragalactic gamma-ray astronomy to understand precisely and accurately the EBL in order to interpret correctly high energy observations. In this talk, I will review the present EBL knowledge, and describe how we can extract information, such as the value of the expansion rate of the Universe, from the EBL. Finally, the latest all-sky Fermi-LAT catalog of hard sources (E>50 GeV), called 2FHL, and future directions of EBL research will also be discussed.

Current scientific cosmology hosts a plurality of scenarios that articulate in different ways the precision astronomy's observations. However, this palette of alternatives is not taken as the true scientific production. There is a monist tendency to think that scientific results should be represented by a single scenario. The present work seeks to undermine the attempts to justify that tendency and to show that even if a single and final stage is waiting, methodological pluralism also would be the best option to achieve it.

The ``dark flow'' dipole is a statistically significant dipole found at the position of galaxy clusters in filtered maps of Cosmic Microwave Background (CMB) temperature anisotropies. The dipole measured in WMAP 3, 5 and 7 yr data releases was roughly aligned with the all-sky CMB dipole and correlated with cluster X-ray luminosity. We analyzed the final WMAP 9 yr and the first Planck data releases using a catalog of 980 clusters outside the Kp0 mask to test our earlier findings. The dipoles measured on these new data sets are fully compatible with our earlier estimates, being similar in amplitude and direction to our previous results and in disagreement with the results of an earlier study by the Planck Collaboration. Further, in Planck data dipoles are independent of frequency, ruling out the Thermal Sunyaev-Zeldovich as the source of the effect. The signal is dominated by the most massive clusters, with a statistical significance better than 99%, slightly larger than in WMAP. Since both data sets differ in foreground contributions, instrumental noise and other systematics, the agreement between WMAP and Planck dipoles argues against them being due to systematic effects in either of the experiments.

Driven by the potential of large-scale structure (LSS) observations to shed light on the physics behind the accelerated expansion of the Universe, several ground-breaking galaxy surveys are currently under way. These surveys will measure the LSS of the Universe with unprecedented precision, providing new insights not only on the origin of cosmic acceleration, but also on many other important physical parameters. The ongoing Baryon Oscillation Spectroscopic Survey (BOSS) is an example of these new surveys. In this talk I review our theoretical understanding of LSS and the details of the analysis of these measurements. I also describe the cosmological implications of the latest clustering measurements from BOSS, with an emphasis on the problem of understanding cosmic acceleration.

We have learned a great deal about the universe from measurements ofthe cosmic microwave background (CMB). Most of what we have learned so far has been based on the temperature anisotropy combined with measurements of the polarization at angular scales of roughly 10 degrees. We are entering a new era in which the polarization of the CMB will be measured to high accuracy especially at degree angular scales and smaller. With the polarization we can, for example,  measure or limit the presence of gravitational radiation from the early universe and determine the sum of the neutrino masses. The polarization will also give us a new way to determine the cosmological parameters. We review recent results on the CMB polarization with anemphasis on those from the Atacama Cosmology Telescope (ACT) project.

Any viable theory of the formation and evolution of galaxies should be able to broadly account for the emergent properties of the galaxy population, and their evolution with time, in terms of fundamental physical quantities. Yet, when citing the key processes we believe to be central to the story, we often find ourselves listing from a vast and confusing melee of modelling strategies & numerical simulations, rather than appealing to traditional analytic derivations where the connections to the underlying physics are more tangible. By re-examining both complex models and recent observational surveys in the spirit of the classic theories, we will investigate to what extent the trends in the galaxy population can still be seen as an elegant fingerprint of cosmology and fundamental physics.

On March 17 the team responsible for the BICEP2 experiment, a CMB telescope located in the South Pole, announced the discovery of the primordial B-mode signal in the CMB polarization. This discovery inmediatly had a well-deserved impact in the media world-wide. In fact, it is the first observational confirmation of a prediction from the inflationary model, which was proposed at the beginning of the 80s as a solution for some inconsistencies of the Big Bang model. In this talk I will put this discovery in the context of CMB research, with a historical perspective. I will emphasize the importance of this discovery for Cosmology, and for Fundamental Physics, and will finally comment the prospects for the future, in particular the role of experiments like Quijote that have to confirm this signal.

The accelerated expansion of the Universe discovered in the late 90's has opened one of the most intriguing questions of modern  physics. To help to understand its origin, and measure the expansion history of the Universe, large galaxy spectroscopic surveys are being carried out and planned for the future. In this talk, I will review the Baryon Oscillation Spectroscopic Survey (BOSS) and the requirements to achieve its precise results. I will then describe a sample of large-volume high-resolution N-body simulations available at MultiDark database,
that are useful to test the models. Finally, I will present some work I have been doing aimed at producing a large number of mock galaxy catalogs using an improved lagrangian perturbation theory calibrated with these simulations. Mock galaxy catalogs are essential to produce reliable cosmological constraints from these surveys.