Found 62 talks archived in Particle astrophysics, physical data and processes
Thursday February 10, 2011
Dr. Christophe Morisset
Instituto de Astronomía, UNAM, Mexico
Abstract
We revisit the question of the ionization of the diffuse medium in late type galaxies, by studying NGC 891, the prototype of edge-on spiral galaxies. The most important challenge for the models considered so far was the observed increase of [O III]/Hβ, [O II]/Hβ and [N II]/Hα with increasing distance to the galactic plane. We propose a scenario based on the expected population of massive OB stars and hot low-mass evolved stars (HOLMES) in this galaxy to explain this observational fact. In the framework of this scenario we construct a finely meshed grid of photoionization models. For each value of the galactic latitude z we look for the models which simultaneously fit the observed values of the [O III]/Hβ, [O II]/Hβ and [N II]/Hα ratios. For each value of z we find a range of solutions which depends on the value of the oxygen abundance. The models which fit the observations indicate a systematic decrease of the electron density with increasing z. They become dominated by the HOLMES with increasing z only when restricting to solar oxygen abundance models, which argues that the metallicity above the galactic plane should be close to solar. They also indicate that N/O increases with increasing z.
Tuesday December 14, 2010
Dr. Karsten Berger
Instituto de Astrofísica de Canarias, Spain
Abstract
This seminar talk will give a short overview of the current status of the field of Astroparticle Physics. The subject includes a great variety of instruments working in different energy ranges (from a few MeV to 1020 eV) and studying different particles (neutrinos, protons, gamma-rays and more). Finally, a short discussion regarding the connection between the observations and the physics at the Large Hadron Collider will be discussed.
Thursday November 25, 2010
Prof. Frank Close
University of Oxford, UK
Abstract
Rutherford discovered the atomic nucleus in 1912 in an experiment on a table top. The LHC will be producing its first major results by 2012, involving teams of thousands and apparatus that is bigger than Rutherford's entire laboratory. How did science come to this, and what are the questions the LHC hopes to answer? What is Higgs' boson, and is it really Higgs that invented it? I will explore the role of symmetry and asymmetry in physics, and illustrate how the ideas that have been associated with Higgs' name have a long history.
Tuesday November 23, 2010
Dr. Karsten Berger
Instituto de Astrofísica de Canarias, Spain
Abstract
This seminar talk will give a short overview of the current status of the field of Astroparticle Physics. The subject includes a great variety of instruments working in different energy ranges (from a few MeV to 1020 eV) and studying different particles (neutrinos, protons, gamma-rays and more). Finally, a short discussion regarding the connection between the observations and the physics at the Large Hadron Collider will be discussed.
Thursday November 11, 2010
Dr. Jaime de la Cruz Rodríguez
The Institute for Solar Physics of the Royal Swedish Academy of Science.
Abstract
Fibrils are thin elongated features visible in the solar chromosphere in and around magnetized regions. Because of their visual appearance they have been traditionally considered a tracer of the magnetic field lines. In this work we challenge that notion for the first time by comparing their orientation to that of the magnetic field, obtained via high-resolution spectro-polarimetric observations of Ca II lines. The short answer to the question posed in the title is that mostly yes, but not always.
Thursday November 4, 2010
Dr. Felix Mirabel
CEA, Service d'Astrophysique, France
Abstract
The so called "dark ages" of the universe began about 400.000 years after the Big Bang as matter cooled down and space became filled with neutral hydrogen for hundreds of millions years. How the Universe was heated and reionized during the first billion years after the Big Bang is a question of topical interest in cosmology. I will show that current theoretical models on the formation and collapse of primordial stars suggest that a large fraction of massive stars should have imploded, forming high-mass black hole X-ray binaries. Then, I will review the recent observations of compact stellar remnants in the near and distant universe that support this theoretical expectation, showing that the thermal (UV and soft X-rays) and non-thermal (hard X-rays, winds and jets) emission from a large population of stellar black holes in high mass binaries heated the intergalactic medium over large volumes of space, complementing the reionization by their stellar progenitors. Feedback from accreting stellar black holes at that epoch would have prevented the formation of the large quantities of low mass dwarf galaxies that are predicted by the cold dark matter model of the universe. A large population of black hole binaries may be important for future observations of gravitational waves as well as for the existing and future atomic hydrogen radio surveys of HI in the early universe.
Friday October 29, 2010
Mr. Hugo Messias
Centro de Astronomia e Astrofísica da Universidade de Lisboa, Portugal
Abstract
In this talk, I will cover our contribution to the study of extremely red galaxy (ERG) populations presenting a multi-wavelength analysis of these objects, selected in the GOODS-South/Chandra Deep Field South field. By using all the photometric (from X-rays to radio) and spectroscopic information available on large deep samples of extremely red objects (EROs, 645 sources), infrared EROs (IEROs, 294 sources) and distant red galaxies (DRGs, 350 sources), we derive redshift distributions, identify AGN powered and star-formation powered galaxies (based on X-ray properties and a new IR AGN diagnostic developed by us), and, using the radio observations of this field, estimate robust (AGN- and dust-unbiased) star formation rate densities (SFRD) for these populations. Applying a redshift separation (1 ≤ z < 2 and 2 ≤ z ≤ 3) we find a significant rise (a factor of 1.5 — 3) of SFRD for EROs and DRGs toward high-z, while none is observed for IEROs. As expected, we find a significant overlap between the ERG populations, and investigate the properties of "pure" (galaxies that conform to only one of the three considered ERG criteria) and "combined" (galaxies conforming to all three criteria) sub-populations. We find ERG sub-populations with no AGN activity and intense star-formation rates. With average values of ~180 M⊙/yr at 2 ≤ z < 3, they reasonably contribute to the global star-formation rate density, reaching a > 20% level. Strong AGN behaviour is not observed in the ERG population, with AGN only increasing the average radio luminosity of ERGs by 10 — 20%. However, AGN are frequently found (in up to 27% of the ERG population), and would increase the SFRD estimate by over 100%. Thus, and while the contribution of SF processes to the radio luminosity in galaxies with AGN remains uncertain, a comprehensive identification of AGN in these populations is necessary to obtain meaningful results. The dust content to each population is also derived by correlating UV and Radio SFRs, giving a higher obscuration for more active SF sources. Also, know to be amongst the most massive galaxies in the high-z universe, I will show that ERGs may constitute up to 60% of the total mass in the universe at 1 ≤ z ≤ 3. Finally, preliminary and promising results are presented on the morphologies of ERGs (CAS and Gini/M20 parameters) based on the v1.9 ACS GOODS-S images.
Wednesday October 20, 2010
Dr. Beatriz Ruiz Granados
Instituto de Astrofísica de Canarias, Spain
Abstract
Recent observations of the rotation curve of M31 show a rise of the outer part that cannot be understood in terms of standard dark matter models or perturbations of the galactic disc by M31's satellites. In this talk, we show a possible explanation of this dynamical feature based on the influence of the magnetic field within the thin disc. We have considered standard mass models for the luminous mass distribution, a Navarro-Frenk-White model to describe the dark halo, and we have added up the contribution to the rotation curve of a magnetic field in the disc. We have found a significant improvement of the fit in the outer part when magnetic effects are considered. Our best-fit requires a field strength of ~ 4μG which is compatible with the observations of the magnetic fields in M31.
Thursday April 15, 2010
Dr. André Milone
Instituto Nacional de Pesquisas Espaciais, Brazil
Abstract
The current databases of empirical star spectra for modelling single-aged stellar populations (SSPs) generally do not chemically characterize their stars completely. Spectral properties of stars and their populations may change considerably if the elemental abundance ratios E/Fe differ from the solar-scaled values. We intend to build up robust integrated spectral energy distribution of SSPs older than 1 Gyr by adopting the MILES database (Medium-resolution Isaac Newton Telescope Library of Empirical Spectra) and taking into account the Mg/Fe ratio of its stars. Magnesium is a proxy of the alpha-capture elements and the alpha/Fe ratio has been widely used as an indicator of the star formation time scale. In this talk, I present how accurate and extensive our compilation and determination of [Mg/Fe] were obtained around MILES to compute state-of-the-art SSP models. Published high resolution measurements were adopted to define a uniform scale of [Mg/Fe] and calibrate our results at medium resolution that were based on the spectral synthesis of two strong Mg features.
Friday March 26, 2010
Dr. Josep María Trigo
Instituto de Ciencias del Espacio, Spain
Abstract
Short-lived nuclides (SLNs) were incorporated to the solar nebula at the time of condensation of the first minerals from the vapor phase. The study of the isotopic ratios preserved in primitive meteorites provides clues on the stellar sources that produced these SLN, being supernovae and Asymptotic Giant Branch stars (AGBs) candidates. On the other hand, stellar grains were also preserved in primitive meteorites and Interplanetary Dust Particles (IDPs). Their survival demonstrates that the solar nebula was not so hot as first researchers proposed in the 60s. Interestingly, the available stellar grain abundances in primitive meteorites (chondrites) depend of the physico-chemical processes suffered by their parent bodies: metamorphism, aqueous alteration, etc. An evaluation of the primordial presolar grain abundances in the protoplanetary disk at the time these materials formed would allow a comparison with the derived from theoretical models. For gaining insight on these processes we should study the most primitive meteorites (the chondrites), but also even more pristine materials arrived from comets, particularly these captured in the stratosphere as IDPs, or collected from 81P/Wild 2 comet by Stardust (NASA) spacecraft.Upcoming talks
- Properties and origin of thick disks in external galaxiesDr. Francesca PinnaThursday January 16, 2025 - 10:30 GMT (Aula)
- Seminar by Luigi TibaldoLuigi TibaldoTuesday January 21, 2025 - 12:30 GMT (Aula)
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