Found 76 talks archived in Cosmology
AbstractWe present recent theoretical and empirical results concerning the accuracy of Cepheid distance estimates based on optical and near-infrared (NIR) Period-Luminosity (PL) relations. In particular, we plan to discuss the dependence of both slope and zero-point on the metal content using a large sample of extragalactic Cepheids. Moreover, we discuss pros and cons of optical and NIR reddening free Period-Wesenheit relations. We also mention the impact that GAIA will have on the precision of the Cepheid distance scale and the role that E-ELT will play in the identification of Cepheids beyond the Local Volume.
A Friedman-like cosmological model, based on noncommutative geometry, is presented. Its Planck level is totally nonlocal with no space and no time. The dynamics on this level is strongly probabilistic which makes the initial singularity statistically insignificant. Space, time and the standard dynamics emerge when one goes from the non-commutative regime (on the Planck level) to the usual "commutative physics".
AbstractSurvey operations with the VISTA telescope with it wide field near IR camera started in Feb 2010, following a science verification phase that started in Oct, 2009. I will describe this new 4.2m wide field telescope and the ESO VISTA Public survey program. I will give details of all ESO six public surveys which will be used for a range of galactic and extragalactic science. I am the PI of the largest, by area, VISTA survey, I will focus my talk on the VISTA Hemisphere Survey and I will show how this survey will be used to find quasars in the Epoch of Reionization at redshift greater than 7. The VISTA Hemisphere Survey (VHS) has been been awarded 300 clear nights on the 4.2m ESO VISTA telescopes. VHS observations started i February, 2010 and the survey will take 5 years to complete. The VHS will cover the whole southern celestial hemisphere (dec<0) to a depth 4 magnitudes fainter than 2MASS/DENIS in at least two wavebands J and K. In the South Galactic Cap, 5000 square degrees will be imaged deeper, including H band, and will have supplemental deep multi-band grizY imaging data provided by the Dark Energy Survey (DES). The remainder of the high galactic latitude sky will be imaged in YJHK and combined with ugriz wavebands from the VST ATLAS, SDSS BOSS and Skymapper optical surveys. The medium term scientific goals include: a huge expansion in our knowledge of the lowest-mass and nearest stars; deciphering the merger history and genesis of our own Galaxy; measurement of large-scale structure out to z=1 and measuring the properties of Dark Energy; discovery of the first quasars with z > 7. In my talk, I will describe the scientific motivation and methodology of the search for quasars with z > 7.
AbstractThe Atacama Cosmology Telescope (ACT) has been observing the southern sky in the millimeter range with an angular resolution at the arc-minute level. An analysis of 228 square degrees observed at 148 GHz along a stripe centered at declination -53 degrees reveals the presence of the Silk damping tail in the temperature angular power spectrum of the Cosmic Microwave Background (CMB). This decaying tail becomes truncated by a rising spectrum at scales corresponding to few arcmins (l ~ 3000) whose origin is compatible with a unclustered population of unresolved point sources and some residual anisotropy due to Compton scattering of CMB photons off free electrons (the Sunyaev-Zel'dovich effect). Comparisons with other observations and constraints on different components giving rise to this secondary spectrum are discussed.
Luminous high-redshift radio galaxies (HzRGs) are associated with the most massive known galaxies in the early Universe. These galaxies have the properties expected of the progenitors of dominant galaxies in rich clusters.
I shall describe the properties of HzRGs and demonstrate how they can be used to study the formation and evolution of galaxies and clusters. I shall also show how LOFAR, the new European radio telescope, can be used to extend these probes into the epoch of reionisation.
In this work we have tried to verify what types of bulges are the descendants and the precursors of the bulges with blue colors observed at intermediate z. These may be the result of intense star formation in the central regions of the disks, related to the phenomenon of pseudo-bulges in the local universe or, alternatively, they may result from rejuvenation processes of old and red classical bulges, formed at high z, perhaps through secular evolution produced by internal or external agents. We can identify and distinguish between these processes analyzing the central surface brightness of the galaxies, μ0. For the general bulge population in the local universe, color is strongly correlated with surface density, in the sense that redder bulges are denser. Classical bulges and pseudo-bulges occupy different regions in a color-μ0 diagram. We have studied the redshift evolution of the relation between the colors and the central surface brightness for samples of spiral galaxy bulges selected from HST/ACS GOODS-N survey, and have analysed the ability of color-μ0 diagram to segregate different types of bulges at z ~ 1. The results show that, up to z ~ 0.8, galaxy nuclear and global colors are strongly correlated with the central surface brightness and, therefore, with the central surface density, in the sense that denser bulges are redder. This suggests that these formed the bulk of their stars at earlier epochs than less dense bulges. For z > 0.8, we find an important fraction of galaxies with high central surface brightness and nuclear colors much bluer than the rest of the galaxy, which probably corresponds to episodes of strong nuclear star formation that may result in the growth of the bulges inside the disks. From simple evolution models we can infer that these nuclei with star formation evolve towards the formation/growth of moderate central surface brightness, intermediate color z ~ 0 pseudobulges rather than classical bulges. These models also argue against rejuvenation processes for z ~ 1 dense and old bulges.
AbstractLarge-scale outflows from galaxies are a crucially important yet poorly understood aspect of galaxy evolution. They redistribute gas and metals into the IGM, regulate star formation, affect the galaxy luminosity function and mass-metallicity relation, etc. Unfortunately, their detailed context in galaxy evolution is difficult to understand: locally, they are identified and studied in heterogeneous manners, while we have only recently begun to study them on cosmological scales and then only in known bright, starbursting galaxies. I will discuss increasing evidence that the so-called ultra-strong MgII intervening quasar absorbers select galactic superwinds over a large range of redshift in a manner independent of luminosity. As superwinds cover a small fraction of the sky at any epoch, only with recent huge quasar absorption lines surveys has it been possible to identify significant numbers of outflows in this manner. I will present new results from several of our studies -- including the measurement of the average SFR of their hosts using [O II] emission from SDSS composite spectra, WIYN, Gemini and WHT imaging of the superwind environments, Gemini/GMOS spectroscopy of superwind host galaxies, and VLT/UVES echellegrams of the absorption lines -- with the aim of understanding the nature of the outflows, their host galaxies, environments, and their evolution over cosmic time.
AbstractThe COSMOS survey is the largest high redshift galaxy evolution survey ever done -- imaging 2 square degrees with all major space-based and ground based observatories. I will describe the key data in the survey and then present recent results on large-scale structures, the dark matter distributions and galaxy evolution.
AbstractThe standard model of cosmology -- the ``Lambda cold dark matter'' model -- is based on the idea that the dark matter is a collisionless elementary particle, probably a supersymmetric particle. This model (which mostly dates back to an early workshop in Santa Barbara in the 1980s) has been famously verified by observations of the cosmic microwave background radiation and the large-scale distribution of galaxies. However, the model has yet to be tested conclusively on the small scales appropriate to most astronomical objects, such as galaxies and clusters. I will review our current understanding of the distribution of dark matter on small scales which derives largely from large cosmological N-body simulations and I will discuss prospects for detecting dark matter, either through its gravitational effect on galaxies and clusters or, more directly, through gamma-ray annihilation radiation.
AbstractThe Sloan Digital Sky Survey is currently the largest spectroscopic survey of extragalactic objects and one of the most ambitious observational programs ever undertaken in astronomy, measuring about 1 million redshifts and thus providing a three dimensional mapping of the local universe up to a depth of several hundreds of Mpc. The main characteristic of galaxy distribution in this survey, and in the Two degree Field Galaxy redshift Survey completed few years ago, is that large scale structures have been found to extend to scales of the order of hundreds of mega parsecs. However the standard determination of a characteristic length scale, statistically describing galaxy correlations, is of only few mega parsecs: the standard explanation of this apparent mismatch is that large scale structures have small amplitude relative to the average density. We show that, in the newest galaxy samples, large scale structures are quite typical and correspond to large fluctuation in the galaxy density field, making the standard interpretation untenable. We show that the standard statistical analysis is affected by systematics which are due to inconsistent assumptions. We point out that standard theoretical models of structure formation are unable to explain the existence of the large fluctuations in the galaxy density field detected in these samples. This conclusion is reached in two ways: by considering the scale, determined by a linear perturbation analysis of a self-gravitating fluid, below which large fluctuations are expected in standard models and through the determination of statistical properties of mock galaxy catalogs generated from cosmological N-body simulations. Finally we discuss the implications of this results in relation to recent attempts to describe inhomogeneous models in general relativity and to the recent discoveries of large scale coherent bulk flows.
- TODAY: The Starlight Foundation: the starry sky as a scientific, cultural, environmental and sustainable economy resource.Dr. A. M. VarelaThursday March 21, 2019 - 10:30 (Aula)
- Properties and evolutionary state of massive stars across the HR diagramDr. Michalis KourniotisThursday March 28, 2019 - 10:30 (Aula)