Katarina Markovič

Univerzitetni Observatorij München

ponedeljek, 16. 1. 2012, ob 11h v F6

(POZOR! neobičajen termin)

Meritve iz fizike delcev še vedno ne izključujejo okolice nekaj kiloelektronvoltov za maso delcev temne snovi. Takšna masa bi pomenila, da termični učinek teh delcev na porazdelitev mase v zgodnjem vesolju ni zanemarljiv! Temno snov, ki lahko zatre perturbacije gostote na majhnih razdaljah, imenujemo topla temna snov (angl. Warm Dark Matter – WDM). Nerelativistične delce hladne temne snovi (angl. Cold Dark Matter ali CDM) ločimo od tople temne snovi po njihovi porazdelitvi hitrosti v zgodnjem vesolju. Učinek tople temne snovi je razviden kot zmanjšanje spektra moči perturbacij na majhnih skalah. Na žalost pa se ta “odtis” močno zmanjša med nelinearno evolucijo porazdelitve mase v vesolju. Modeliranje nelinearnih struktur dandanes je že v “hladnem” scenariju nepopolno, v “toplem” scenariju pa je še v povojih. Vendar pa vstop v dobo kozmologije visoke natančnosti zahteva izpopolnitev teorij, če se želimo izogniti omejitvam sistematičnih napak iz teorije in slediti natančnosti eksperimentov.

Drejc Kopač

FMF, Univerza v Ljubljani

torek, 20. 12. 2011, ob 12h v F3
(POZOR! sprememba ure in predavalnice)

We will discuss an unusual gamma-ray burst GRB 101225A, which was detected on the Christmas Day 2010. After presenting the observations and the obtained data, we will focus on two different theoretical interpretations for this event, published in the December 2011 issue of the Nature journal (Thöne et al. 2011 and Campana et al. 2011). The “dual personality” of this gamma-ray burst is clearly a signature that many phenomena in high-energy astrophysics are not yet explained, but more (strange) events will help us advance in the field.

Članke si oglejte preko povezav v povzetku predavanja (odebeljeni tekst).

Dunja Fabjan

CO Vesolje-SI in Univerza v Ljubljani

torek, 29. 11. 2011, ob 14h v F5

Najnovejša rentgenska opazovanja jate galaksij v Perzeju so pokazala, da bi naj bil delež mase plina na razdalji virialnega radija večji od pričakovanega (Simionescu et al. 2011). Simulacije jat galaksij (Nagai & Lau 2011) nazorno kažejo, da je vzrok v zgoščinah plina in da so le-te odvisne od fizikalnih procesov znotraj jate.
Ogledali si bomo rezultate, ki jih je pred kratkim objavila skupina astronomov (Eckert et al. 2011), ki je uporabila arhivske podatke nedavno “upokojenega” rentgenskega satelita ROSAT in jih primerjala s tremi različnimi serijami simulacij jat galaksij.

Članke si oglejte preko povezav v povzetku predavanja (odebeljeni tekst). Če nimate dostopa do revij (Full Refereed Journal Article) si lahko članek ogledate preko povezave na astro-ph arhive (arXiv e-print).

Ponedeljkov fizikalni kolokvij

Vid Iršič in prof. Tomaž Zwitter

Fakulteta za matematiko in fiziko, Univerza v Ljubljani

ponedeljek, 14. 11. 2011, ob 16.15 v predavalnici F1

Pred predavanjem so vsi udeleženci vabljeni na čaj!

The fact that the Universe is expanding has been known ever since Edwin Hubble’s discovery in late 1920s that distant galaxies recede from each other at velocities proportional to distances between them. A shock to scientific community came in the late 1990s when two independent groups discovered that the Universe is not only expanding but is doing so at an ever increasing rate. Both groups were using distant supernovae as standard candles to measure distances that stretch billions of kilometers over space. The results were compatible with predictions of general theory of relativity with additional term, cosmological constant, which was postulated by Einstein himself which he later disregarded and dubbed it his greatest bundle. The discovery for which this year’s Nobel prize is awarded proved this bundle to be of a more brilliant type. However, even though the mathematical construction exists to explain this phenomena we are no closer to understand it in the framework of standard model of particle physics.

Gal Matijevič

Fakulteta za matematiko in Fiziko, Univerza v Ljubljani

torek, 8. 11. 2011, ob 14h v F5

Dandanes je količina podatkov v mnogih novih astronomskih bazah tolikšna, da je ročno pregledovanje takšnih baz skrajno nepraktično in pogosto povsem nemogoče. K sreči obstaja širok nabor računalniških metod, s katerimi je mogoče skrite zakonitosti v podatkih odkrivati preprosto in učinkovito. Ogledali si bomo relativno novo metodo z imenom Locally Linear Embedding – LLE, ki sta jo prva predstavila Roweis in Saul (2000), nedavno pa je bila uspešno uporabljena za klasifikacijo galaktičnih spektrov pregleda neba SDSS (Vanderplas in Connolly, 2009). Pokazali bomo še, kako je s to metodo mogoče razlikovati med spektri pregleda neba RAVE in kako jo uporabimo za klasifikacijo prekrivalnih dvojnic misije Kepler.

Članka si oglejte na povezavah v povzetku predavanja (odebeljeni tekst).

Petr Heinzel

Director of the Astronomical Institute (Czech Republic)

petek, 30. 9. 2011, ob 11h v F5

The Astronomical Institute in Ondřejov near Prague is one of the oldest scientific institutions in the Czech Republic and belongs to the Academy of Sciences. The informal talk will be about the research in astronomy covered by the Astronomical Institute. Currently the institute participates in ESO and ESA projects, as the Czech republic became a member state of these organisations in 2007 and 2008, respectively, and in the European Association of Solar Telescopes. Some brief information will also be given about the history of astronomy in the Czech Republic and about czech research institutes doing astronomy nowadays.

Stefano Covino

INAF – Brera Astronomical Observatory

torek, 7. 6. 2011, ob 14h v F5

The host galaxies of long GRBs represent a class of objects of great interest. First of all, studying their properties we can derive information about the progenitors of these events. In addition, these galaxy can be selected, thanks to the GRB afterglow brightness, to very high-redshifts providing a sample of objects that would have escaped any other luminosity-biased galaxy survey. In this talk I will review their main features and discuss the importance in the field of the advent of new generation spectrographs as the ESO X-shooter.

Luca Zappacosta

INAF – Astronomical Observatory of Rome

torek, 31. 5. 2011, ob 14h v F5

About half of the ordinary matter is still missing from the census of the baryons in the local universe. Cosmological simulations show that they should be hidden in the large-scale filamentary distribution of the cosmic web as warm-hot (logT=5-7 K) tenuous (10^-6 – 10^-5 cm^-3) intergalactic gas (WHIM) weakly emitting in the Far UV/X-rays and therefore very difficult to detect with current instruments. Focusing on the X-rays, where the majority of the missing baryons can be identified, I will show and discuss the most promising WHIM detections.

Gregory Ruchti

Johns Hopkins University (USA), Max Planck Institut for Astrophysics – Garching (Germany)

torek, 24. 5. 2011, ob 14h v F5

Models of the formation of the thick disk of the Milky Way Galaxy make specific predictions about the chemical abundance properties of the metal-weak (and oldest) stellar population in the thick disk. We have undertaken the study of the elemental abundances and kinematic properties of a sample of 319 candidate metal-poor thick-disk stars selected from the RAVE spectroscopic survey of bright stars. Our aim is to differentiate among the present scenarios of the formation of the thick disk. In this study, we measured the abundances of several alpha-elements and found that the thick-disk ratios are enhanced, implying that enrichment proceeded by purely core-collapse supernovae. Further, the sample probes distances ranging out to about 2 kpc from the Sun, allowing for the investigation of the gradients in the thick disk. I will discuss the results from these investigations and how they compare to the predictions made by present models of the formation of the thick disk.

Giuseppe Murante

INAF – Astronomical Observatory of Torino

torek, 10. 5. 2011, ob 12h v F6 (Pozor: sprememba ure in predavalnice!)

We present a new multi-phase sub-resolution model for star formation and feedback in SPH numerical simulations of galaxy formation. Our model, called MUPPI (MUlti-Phase Particle Integrator), describes each gas particle as a multi-phase system, with cold and hot gas phases, coexisting in pressure equilibrium, and a stellar component.

Cooling of the hot tenuous gas phase feeds the cold gas phase. We compute the cold gas molecular fraction using the phenomenological relation of Blitz & Rosolowsky between this fraction and the external disk pressure, that we identify with the SPH pressure. Stars are formed out of molecular gas with a given efficiency, which scales with the dynamical time of the cold phase.

Our prescription for star formation is not based on imposing the Schmidt-Kennicutt relation, which is instead naturally produced by MUPPI. Energy from supernova explosions is deposited partly into the hot phase of the gas particles, and partly to that of neighboring particles. Mass and energy flows among the different phases of each particle are described by a set of ordinary differential equations which we explicitly integrate for each gas particle, instead of relying on equilibrium solutions. This system of equations also includes the response of the multi-phase structure to energy changes associated to the thermodynamics of the gas.

We apply our model to isolated disk galaxy simulations as well as to cosmological re-simulation of DM haloes potentially harbouring disk galaxies. MUPPI does reproduce the basic properties of the inter-stellar medium in disk galaxies and generates the correct SK relation both in isolated galaxies and in cosmological ones. We show the effect of having an efficient termal feedback on the gas accretion history of cosmological galaxies.

Series of talks on Gamma Ray Astronomy

Andrea Melandri

INAF – Astronomical Observatory of Brera

v torek, 12. 4. 2011 ob 9:15 v F5

Series of talks on Gamma Ray Astronomy

Paolo D’Avanzo

INAF – Astronomical Observatory of Brera

torek, 5. 4. 2011 ob 9:15 v F5

Series of talks on Gamma Ray Astronomy

Andrea Melandri

INAF – Astronomical Observatory of Brera

v torek, 5. 4. 2011 ob 8:15 v F5

Fabio Fontanot

INAF – OATS

torek, 5. 4. 2011, ob 14h v F5

The modeling of AGN feedback is of fundamental importance in order to understand the complex interplay between the various physical mechanisms shaping the observed properties of galactic populations and the evolution of their stellar masses and star formation rates. In particular, in the current theoretical paradigm of galaxy formation, AGN feedback plays a crucial role in regulating the levels of activity in galaxies, including the onset of cooling flows and star formation, as well as the triggering of galactic winds leading to the removal of the gas from the host galaxy. Only in recent years, however, the detailed study of the dependence of galaxy activity on stellar mass, parent halo mass and hierarchy (i.e. centrals or satellites) has been made possible thanks to the availability of large samples of galaxies and to the improved determination of their physical properties.

In my contribution, I will compare the fraction of galaxy belonging to different activity classes (i.e. star-forming, AGN and radio active) with the predictions of four semi-analytical models for galaxy formation and evolution, implementing different approaches for the growth of Supermassive Black Holes and the subsequent AGN feedback. I will employ empirical conversion laws to estimate the equivalents of the observed activity indicators from the predicted gas accretion rates ( line strength and radio power) and star formation rates ( emission line). I will demonstrate that the models are able to reproduce the overall distribution of the fraction of galaxies belonging to the different activity classes as a function of stellar mass and halo mass: star forming galaxies and strong radio sources are preferentially associated with low-mass and high-mass galaxies/halos respectively.

However, I will also highlight some relevant discrepancies between observations and model predictions. In SAMs predictions a relevant fraction of Dark Matter Halo with mass larger than solar masses and/or galaxy with mass larger than solar masses hosts a bright radio source and the radio brightness is expected to depend strongly on the mass of the parent halo mass, at variance with the available observational constraints. Finally I will also discuss the importance of the AGN fraction as a powerful discriminant between the different approaches to the problem of growth of Supermassive Black Holes.

Series of talks on Gamma Ray Astronomy

Paolo D’Avanzo

INAF – Astronomical Observatory of Brera

torek, 29. 3. 2011, ob 9:15 v F5

Elisabetta Bissaldi

Institute of Astro and Particle Physics, University of Innsbruck

torek, 29. 3. 2011, ob 14h v F5

In the first couple of years since the launch of the Fermi Observatory, the Gamma–ray Burst Monitor (GBM) has detected over 680 Gamma–Ray Bursts (GRBs), of which 18 were also detected by the Large Area Telescope (LAT) above 100 MeV. Besides GRBs, GBM has triggered on other transient sources, such as Soft Gamma Repeaters (SGRs), Terrestrial Gamma–ray Flashes (TGFs) and solar flares. I will first present the science highlights of the GBM observations.

I will then focus on the analysis of a sample of 50 bright GRBs detected up to more than 1 MeV with GBM, which were collected during the first year of Fermi operations. For each burst, time-integrated burst spectra are fitted with different models. Fit parameter distributions are presented and discussed in the framework of earlier BATSE results.

Priddey Robert

torek, 15. 3. 2011, ob 14h v F5

Leta 1609 je mož po imenu Galileo za vedno spremenil svet. Leta 2009 ga je dekle po imenu Celeste zopet spremenila. Sedaj mora popraviti, kar je storila.

“Zvezdni sel” je pred kratkim izšel pri DMFA kot DVD z gradivom, ki služi za učni pripomoček pri astronomiji. Film so posneli profesionalni astronomi na Univerzi v Hertfordshire in je posvečen je 400-letnici astronomskih teleskopov (1609-2009).
Po predvajanju filma se bomo pogovorili o zgodovini astronomije (Galilejev svet, ukrivljenost prostora in časa, širjenje vesolja in temna snov) ter izmenjali mnenja o študiju astronomije in poklicu astronoma.

Več: Portal v Vesolje

Anna Gregorio

University of Trieste, INAF and INFN

torek, 18. 1. 2011, ob 14h v F3

The Planck satellite represents the most precise thermometer ever built up to now. Thanks to its accuracy, in the next future Planck will provide fundamental information on our primordial Universe. After a review of the Planck scientific goals, I will concentrate on its working principle and the on-board instrumentation. I will then talk about its measurements giving few preliminary results.

Giovanni Vladilo

Astronomical Observatory of Trieste – INAF

torek, 11. 1. 2011, ob 14h v F3

In the first part of this talk I will provide a brief introduction to astrobiology, the science that studies the origin, evolution and distribution of life in the Universe. I will then summarize the main results of searches for life in the Solar System. Finally, I will introduce the observational studies of extrasolar planets and discuss their importance to search for habitable environments and signatures of life outside the Earth.

Ponedeljkov fizikalni kolokvij

Anže Slosar

Brookhaven National Laboratory, Upton, NY

ponedeljek, 10. 1. 2011, ob 16.15 v predavalnici F1

The Lyman-alpha forest is a series of absorption features in the spectra of distant quasars, blue-ward of the Lyman-alpha emission line. These features arise as the light from the quasar is absorbed by the intervening neutral hydrogen. This gives one-dimensional information about the fluctuations in the neutral hydrogen density along the line of sight to the quasar. When spectra of many quasars are combined, it allows one to build a three-dimensional image of the fluctuations in the neutral hydrogen density and thus infer the corresponding fluctuations in the matter density. This makes the Lyman-alpha forest a unique probe of the distant Universe, opening a novel window on understanding dark energy, dark matter, neutrino properties and inflation. BOSS experiment has detected, for the first time, correlations in the Lyman-alpha forest fluctuations to cosmological distances. It will measure around 160,000 high redshift quasars and constrain dark energy. BigBOSS will be even fierecer and measure spectra of around a million high-redshift quasars.