Found 89 talks archived in Cosmology
I will review the status of the QUIJOTE (Q-U-I JOint TEnerife) experiment, a project led from the IAC with the aim of characterising the polarisation of the Cosmic Microwave Background (CMB) and other galactic or extragalactic physical processes that emit in microwaves in the frequency range 10-42GHz, and at large angular scales (1 degree resolution). QUIJOTE consists of two telescopes and three instruments operating from the Teide Observatory, and started operations about 10 years ago, in November 2012.
I will discuss the status of the project, and I will present the latest scientific results associated with the wide survey carried out with the first QUIJOTE instrument (MFI) at 11, 13, 17 and 19GHz, covering approximately 29000 deg$^2$ with polarisation sensitivities in the range of 35-40 $\mu$K/deg. These MFI maps provide the most accurate description we have of the polarization of the emission of the Milky Way in the microwave range, in a frequency domain previously unexplored by other experiments. These maps provide a unique view of the Galactic
magnetic field as traced by the synchrotron emission. These results have been presented in an initial series of 6 scientific articles published on January 12th, 2023.
Finally, I will describe the prospects for future CMB observations from the Teide Observatory.
Cosmological observations (redshifts, cosmic microwave background radiation, abundance of light elements, formation and evolution of galaxies, large-scale structure) find explanations within the standard Lambda-CDM model, although many times after a number of ad hoc corrections. Nevertheless, the expression ‘crisis in cosmology’ stubbornly reverberates in the scientific literature: the higher the precision with which the standard cosmological model tries to fit the data, the greater the number of tensions that arise. Moreover, there are alternative explanations for most of the observations. Therefore, cosmological hypotheses should be very cautiously proposed and even more cautiously received.
There are also sociological and philosophical arguments to support this scepticism. Only the standard model is considered by most professional cosmologists, while the challenges of the most fundamental ideas of modern cosmology are usually neglected. Funding, research positions, prestige, telescope time, publication in top journals, citations, conferences, and other resources are dedicated almost exclusively to standard cosmology. Moreover, religious, philosophical, economic, and political ideologies in a world dominated by anglophone culture also influence the contents of cosmological ideas.
The search for the primordial B-modes polarization in the cosmic microwave background (CMB) radiation,
carrying the signature of the primordial gravitational waves from the inflation epoch, motivated a significant
technological progress enabling the next generation of CMB instruments (e.g. CMB-S4, LiteBIRD)
to reach an unprecedented sensitivity. However, such a challenging detection demands a very high control
of the instrumental systematics and CMB foreground emissions.
Among those, the galactic dust polarized emission spectral dependence, not yet fully
characterized, could leave a high level of uncertainty in the cosmological polarization data
producing an ambiguous detection of the CMB B-modes.
Characterizing the dust spectral energy distribution (SED) spatial variations became one of
the most critical issues in the quest for primordial B-modes.
In the work that I will present we have used the release of the Planck satellite HFI data
obtained with the software Sroll2 (Delouis+2019, A&A 629, A38), in order to characterize
and compare the SEDs for polarization and total intensity.
The mean SEDs for dust polarization and total intensity from 353 to 100 GHz are confirmed
to be remarkably close. However, the data show evidence for spatial variations of the
polarization SED. These variations are correlated with variations of dust temperature
measured on total intensity data but the correlation is tight only in the Galactic plane.
At higher latitudes, by considering 90% of useful sky fraction and less, the amplitude of the dust
emission residuals in polarization suggests that an additional contribution, coming from
variations of the polarization angle, becomes dominant. Current models, which extrapolate
the SED spatial variations from total intensity to polarization, would be therefore grossly
simplifying and underestimating the foreground signal to CMB polarization.
A key problem that we are facing in cosmology nowadays is that we cannot make accurate predictions with our current theoretical models. We have all of the pieces of the standard model but it doesn't have an analytical solution. The only way to have accurate predictions is to run a cosmological simulation. Then, why not use these simulations as the theory model? Well, for one main reason, if we want to explore the full parameter space comprised in the standard model, we need thousands of such simulations, and they are terribly computationally expensive. We wouldn't be able to do it in years! In this talk, I will tell you how in the last few years we have come up with a way to circumvent this problem.
The light emitted by all galaxies across the history of the Universe is encoded in the intensity of the extragalactic background light (EBL), the diffuse cosmic radiation field at ultraviolet, optical, and infrared wavelengths. The EBL is a source of opacity for very high energy gamma rays via pair production, leaving a characteristic attenuation imprint in the spectra of distant gamma-ray sources. In this seminar, I will report on new measurements of the EBL using gamma-ray data from both the Large Area Telescope on board the Fermi Gamma-ray Space Telescope and ground-based Imaging Atmospheric Cherenkov Telescopes. These unprecedented measurements have allowed us to derive the cosmic star-formation history, the number density of faint galaxies during the re-ionization epoch, and also the expansion rate of the Universe and its matter content. These results demonstrate that gamma-ray astrophysics has matured to the point of providing competitive measurements of cosmic properties previously restricted to techniques used by more traditional astronomy.
The next decade will see a deluge of new cosmological data that will enable us to accurately map out the distribution of matter in the local Universe, image billions of stars and galaxies to unprecedented precision, and create high-resolution maps of the Milky Way. Signatures of new physics as well as astrophysical processes of interest may be hiding in these observations, offering significant discovery potential. At the same time, the complexity of astrophysical data provides significant challenges to carrying out these searches using conventional methods. I will describe how overcoming these issues will require a qualitative shift in how we approach modeling and inference in cosmology, bringing together several recent advances in machine learning and simulation-based (or likelihood-free) inference. I will ground the talk through examples of proposed analyses that use machine learning-enabled simulation-based inference with an aim to uncover the identity of dark matter, while at the same time emphasizing the generality of these techniques to a broad range of problems in astrophysics, cosmology, and beyond.
Meeting ID: 831 9395 9785
In cosmology, it is customary to convert observed redshifts into distances in order to study the large scale distribution of matter probes like galaxies and quasars, and to obtain cosmological constraints thereof. In this talk, I describe a new approach which bypasses such conversion and studies the "field of redshifts" as a new cosmological observable, dubbed thereafter as angular redshift fluctuations (ARF). By comparing linear theory predictions to the output of N-body cosmological simulations, I will show how the ARF are actually sensitive to both the underlying density and radial peculiar velocity fields in the universe, and how one can obtain cosmological and astrophysical constraints from them. And since "the prove of the pudding is in the eating", I will demonstrate how ARF provide, under a very simple setup, competitive constraints on the nature of peculiar velocities and gravity from BOSS DR13 data. Furthermore, I will also show that by combining ARF with maps of the cosmic microwave background (CMB), we can unveil the signature of the missing (and moving) baryons, doubling the amount of detected baryons in disparate cosmic epochs ranging from z=0 up to z=5, and providing today's most precise description of the spatial distribution of baryons in the universe.
We introduce the strong CP problem and the existence of the Axion as a possible solution.
We discuss the possibility that axions are the dark matter of the Universe and the possible ways to
detect it or disprove it using: direct laboratory experiments as well as astrophysical and cosmological
In this talk, we shall review the impact of the neutrino properties on the different cosmological observables. We shall also present the latest cosmological constraints on the neutrino masses and on the effective number of relativistic species. Special attention would be devoted to the role of neutrinos in solving the present cosmological tensions.
- Is the riddle of the astronomical Li origin solved?Dr. Paolo MolaroTuesday January 31, 2023 - 12:30 GMT (Aula)
- What do the neighbors look like? A comparative look at the Milky Way and Andromeda dwarf galaxiesDr. Nicolas MartinTuesday February 14, 2023 - 12:30 GMT (Aula)