Found 76 talks archived in Cosmology
AbstractPeculiar velocities of galaxies, derived using distance estimators, are plagued with systematic effects and are unreliable beyond 100 Mpc/h. In Kashlinsky & Atrio-Barandela (2000) we proposed to measure peculiar velocities of clusters of galaxies using the temperature anisotropies on the Cosmic Microwave Background generated by the hot X-ray emitting. Using this technique we have recently found a bulk flow velocity of amplitude 600-1000 km/s in the same direction as the CMB dipole and encompassing a sphere of 300 Mpc/h radius. We shall discuss the cosmological implications of this measurement.
I will review the status of our understanding of galaxy formation in the prevailing cold dark matter paradigm. After reviewing the successes and failures of the most natural predictions of this scenario I will focus on the consequences of two of its main predictions: the presence of large numbers of low-mass dark matter halos and the prevalence of accretion events during the formation of normal galaxies. In particular, I will discuss the interpretation of the recent discovery of a population of ultra-faint galaxies in the Local Group, and its relation to the profuse cold dark matter substructure expected in the Galactic halo. I will also discuss the importance that accretion events might have had in shaping not only the stellar halo but also the disk component(s) of the Milky Way.
AbstractThe amount of baryons seen in the local Universe falls short by a factor2-5 if compared to the amount of detected baryons at intermediate (z~2)or high (z~1,100) redshift. This is the so called "missing baryon" problem in Cosmology. Hydrodynamical simulations of the large scale structure predict that most of those missing baryons should be in the form of ionized gas present in slightly overdense regions, at a temperature ranging from 10^5 to 10^7 K, conforming the "Warm Hot Intergalactic Medium" (WHIM). This WHIM would not form stars, and would not emit or absorb either in the IR, optical or UV. However, it should interact with the photons of the Cosmic Microwave Background (CMB) through two different channels: (i) Thompson scattering (where there is no energy exchange) and (ii) Compton scattering (where hot electrons transfer energy to the CMB photons, distorting their black body spectrum). I shall review the status of the search for missing baryons in the context of CMB observations and the currently most favored cosmological model. I shall also outline new methods and prospects for detecting this missing gas with upcoming CMB experiments and address the link between the cosmic baryon problem and the search for (so far undetected) bulk flows at scales of ~10 Mpc/h.
AbstractIn our now-standard picture for the growth of structure, dark matter halos are the basic unit of nonlinear structure in the present Universe. I will report results from simulations of galaxy-scale dark halos with more than an order of magnitude better mass resolution than any previously published work. Tests demonstrate detailed convergence for (sub)structures well below a millionth the mass of the final system. Even with such resolution the fraction of halo mass in bound subhalos does not rise above a few percent within the half-mass radius. I will also present a new simulation technique which allows structure in the dark matter distribution to be studied on very much smaller scales. This is required for accurate forecasts of the expected signal both in earth-bound experiments designed to detect dark matter directly, and in indirect detection experiments like GLAST which attempt to image dark matter annihilation radiation at gamma-ray wavelengths.
AbstractSince its discovery in 1964, the cosmic microwave background (CMB) has been one of the basic pillars of the cosmological model. However, it is only very recently that CMB observations have become one of the most powerful tools in modern cosmology, due to the increasing accuracy of the experiments measuring the CMB anisotropies. In this talk, I will present a brief historical perspective of the history of the CMB observations, since the discovery until nowadays, with special emphasis on the implications and the impact of those observations in cosmology. Experiments like COBE, Tenerife, WMAP or PLANCK will be described. The last part of my talk will be devoted to describe the future of this field, and in particular, will be focused on the possibility of the detection of primordial gravitational-waves.
AbstractWe examine the latest results concerning the evolution in the structures of galaxies from the local universe up to z ~ 6. We present results from the COSMOS, EGS and UDF surveys and characterise the structure of galaxies in terms of stellar masses. We find in general that galaxy structure becomes more asymmetric with time, and we use this information to determine the merger history of galaxies and the role of mergers in galaxy formation, placing the first firm constraints on the importance of this formation mode.
- Problems with the dark matter and dark energy hypotheses, and alternative ideasDr. Martin Lopez CorredoiraThursday October 25, 2018 - 10:30 (Aula)