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On the Origin and Growth of Cosmic Magnetic Fields

On the Origin and Growth of Cosmic Magnetic Fields

dr. Alexander M. Beck

University Observatory Munich, Germany

v sredo, 19. oktobra, ob 12. uri v predavalnici F3 (Jadranska 19, Ljubljana)

The origin of magnetic fields in high-redshift and present-day galaxies is a long-standing problem. In this talk, we present a model for the seeding and evolution of magnetic fields in protogalaxies. Supernova (SN) explosions during the assembly of a protogalaxy self-consistently provide magnetic seed fields, which are subsequently amplified by compression, shear flows and random motions.

We present cosmological simulations with the GADGET code of Milky Way-like galactic halo formation using a standard LCDM cosmology and analyse the strength and distribution of the evolving magnetic field. We analyse the intrinsic rotation measure (RM) of the forming galactic halo over redshift. The mean halo intrinsic RM peaks between redshifts z=4 and z=2 and reaches absolute values around 1000 rad/m$^2$. Towards redshift z=0, the intrinsic RM values decline to a mean value below 10 rad/m$^2$. At high redshifts, the distribution of individual starforming and thus magnetized regions is widespread leading to a widespread distribution of large intrinsic Rms.

Our model for the evolution of galactic magnetic fields solves the joint problem of magnetic field seeding and subsequent amplification and distribution. The magnetic fields in galaxies are a direct consequence of the very basic processes of star and galaxy formation.

Cosmic-Ray Acceleration in galactic Interactions and its implications

Cosmic-Ray Acceleration in galactic Interactions and its implications

prof. Tijana Prodanović

University of Novi Sad, Serbia

v sredo, 15. junija, ob 14. uri v predavalnici F5 (Jadranska 19, Ljubljana)

It has been shown that galactic interaction and mergers can give rise to large-scale tidal shocks that propagate through their gas. As a result, this can give rise to a new population of cosmic rays, additional to standard galactic cosmic rays present in star-forming galaxies. We investigate the impact of this tidal cosmic-ray population on the nucleosynthesis of lithium in interacting systems in the context of the cosmological lithium problem. Moreover we also demonstrate that the development of these interaction shock-waves and may also have far reaching consequences on our understanding of galactic evolution and star formation history, by affecting the far-infrared radio correlation observed in star-forming galaxies.

Relativistične N-body simulacije in njihova uporaba v kozmologiji

Relativistične N-body simulacije in njihova uporaba v kozmologiji

Mateja Gosenca

Univerza v Sussexu (UK)

v ponedeljek, 6. junija, ob 14. uri v predavalnici F4 (Jadranska 19, Ljubljana)

Numerične simulacije delcev temne snovi se uporabljajo za modeliranje nastanka struktur v vesolju. Večina teh simulacij temelji na enačbah Newtonove mehanike. Za veliko problemov, ki jih takšne simulacije naslavljajo, je to odlična poenostavitev. Toda za modeliranje struktur, ki nastanejo zelo zgodaj, velikostnih skal blizu kozmološkega horizonta in relativističnih virov perturbacij, takšna aproksimacija ne zadostuje. Predstavila bom razvoj simulacij, ki namesto Newtonove gravitacije uporabljajo enačbe splošne relativnosti in hkrati delcem dovolijo relativistične hitrosti. Predvsem slednje je idealno za modeliranje tako imenovanih ultrakompaktnih minihalojev, ki predstavljajo edinstveno možnost detekcije prvobitnega spektra moči na majhnih velikostnih skalah. Poleg tega se s tem odpirajo vrata simulacijam modelov modificirane gravitacije, ki ponujajo eno od teoretsko najbolj zanimivih razlag pojava temne energije.

GALAH in difuzne medzvezdne črte

GALAH in difuzne medzvezdne črte

dr. Janez Kos

The University of Sydney, Sydney Institute for Astronomy

v sredo, 16. decembra 2015, ob 12. uri v predavalnici F3 (Jadranska 19, Ljubljana)

Na področju difuznih medzvezdnih črt smo dosegli velik preskok z opazovanji spektroskopskega pregleda neba RAVE; prvič je postal mogoč tri dimenzionalni vpogled v strukturo medzvezdne snovi tudi izven galaktične ravnine. RAVE je pred kratkim končal z opazovanji, začel pa se je nov pregled neba imenovan GALAH (GALactic Archaeology with Hermes), ki se lahko smatra za nekakšnega nadgrajenega naslednika RAVE-a.
GALAH ponuja spektre v štirih pasovih vidnih in bližnje IR svetlobe z resolucijo R=28 000 in razmerjem signala proti šumu nad 100. V astrodebati bom predstavil napredek in nove izzive pri opazovanju difuznih medzvezdnih črt v GALAH-ju. Govoril bom tudi o ostalih raziskovalnih projektih, ki potekajo v okviru projekta GALAH in o raziskovalnih priložnostih, ki so še vedno na voljo vsem, ki imajo/imamo dostop do GALAH-jevih spektrov.

Relativistic effects in Lyman-alpha forest

Relativistic effects in Lyman-alpha forest

dr. Vid Iršič

ICTP Trieste, Italy

v torek, 6. oktobra 2015, ob 13. uri v predavalnici F4 (Jadranska 19, Ljubljana)

As the observations move out to larger scales the validity of a simple Newtonian description starts to come into question. Recent years have seen a lot of effort put into understanding and possibly measuring the signal of relativistic effects and/or weak gravitational lensing in the 2-point statistics of the galaxy clustering.
I will present the first study to extend the formalism to a different tracer of underlying matter at unique redshift range (z = 2 − 5). Furthermore, I will show a comprehensive application of the calculations to the Quasar-Lyman-alpha cross-correlation function. The results indicate that the signal of relativistic effects can be as large as 30% at Baryonic Acoustic Oscillation (BAO) scale, which is much larger than anticipated and mainly due to the large differences in density bias factors of our tracers.

A search for Galactic transients disguised as gamma-ray bursts

A search for Galactic transients disguised as gamma-ray bursts

Aurora Clerici

University of Ferrara

v torek, 8. septembra 2015, ob 14. uri v predavalnici F6 (Jadranska 19, Ljubljana)

A significant fraction of cosmological gamma-ray bursts (GRBs) are characterised by a fast rise and exponential decay (FRED) temporal structure. This is not a distinctive feature of this class, since it is observed in many Galactic transients and is likely descriptive of a sudden release of energy followed by a diffusion process. We searched for possible Galactic intruders disguised as FRED GRBs in the Swift catalogue. We tested the degree of isotropy through the dipole and the quadrupole moment distributions. In addition, we searched for possible indicators of a Galactic origin among the spectral and temporal properties of individual GRBs. In this talk, we will present the results of our analysis.

For more information see http://arxiv.org/abs/1508.04898

Space coronagraphy with ESA

Space coronagraphy with ESA

Prof. Petr Heinzel

Astronomical Institute, Czech Academy of Sciences

v četrtek, 11. junija 2015, ob 14. uri v predavalnici F2 (Jadranska 19, Ljubljana)

Solar coronagraphs are special telescopes designed to observe the corona and various coronal structures (e.g. prominences) out of solar eclipses. Most efficient are the space coronagraphs, where the observations are not influenced by the Earth atmosphere. I will briefly review previous coronagraphic missions of ESA (European Space Agency) and show some new results obtained with one of them, namely UVCS on board of the SOHO satellite. These results concern large solar eruptions called Coronal Mass Ejections (CME) and their spectroscopic diagnostics. ESA is currently developing two new space coronagraphs, METIS for Solar Orbiter mission (launch 2018) and ASPIICS for Proba-3 mission (launch 2018). The latter one is particularly interesting because it will simulate, for the first time, a total solar eclipse from space.

Finally, I will also mention how CME’s can be detected on other active stars, with their potential influence on exoplanets.

Planetarna meglica Sh2-71 in njena nenavadna centralna zvezda

Planetarna meglica Sh2-71 in njena nenavadna centralna zvezda

Teo Močnik

University of Keele, UK

v ponedeljek, 8. junija 2015, ob 13. uri v predavalnici F4 (Jadranska 19, Ljubljana)

Planetarne meglice, ene najbolj fotogeničnih objektov na nočnem nebu, obsegajo pravo paleto različnih oblik in velika večina jih ni sferično simetričnih. Kaj povzroča to nesimetrijo v izvrženem ioniziranem materialu umirajoče zvezde je še danes uganka. Navidezna centralna zvezda bipolarne planetarne meglice Sh2-71 je ena redkih kandidatinj, ki se uvršča na seznam tesnih centralnih dvojnic in tako predstavlja poligon za razvijanje teorij o nastanku nesimetričnih oblik planetarnih meglic. Najnovejša fotometrična in spektroskopska opazovanja razkrivajo presenetljivo spremenljivost in nakazujejo, da je centralna zvezda tesna dvojnica Be + sdO s precesirajočim Be diskom. Tak sistem centralne zvezde je sicer potrebno obravnavati kot nedokončen, a izmed vseh doslej obravnavanih modelov najbolje pojasni opazovane spektrofotometrične lastnosti zvezde in obenem ponudi razlago za bipolarno obliko planetarne meglice.

Modeliranje šuma v astronomskih podatkih

Modeliranje šuma v astronomskih podatkih

dr. Gal Matijevič

Leibniz-Institut für Astrophysik Potsdam

v ponedeljek, 25. maja 2015, ob 13. uri v predavalnici F4 (Jadranska 19, Ljubljana)

Večina informacij, ki jih dobimo o vesolju onkraj Osončja, pride do nas prek svetlobe. Vsak astronomski posnetek vsebuje poleg signala, ki nas zanima, tudi šum. Del celotnega prispevka šuma je posledica končnega števila fotonov, ki zadanejo detektor in ga lahko modeliramo kot Poissonski proces. Toda skoraj nikoli to ni edini vir šuma.

V obdelanih posnetkih lahko ponavadi zaznamo druge vire sistematičnih in intrinzinčnih variacij, ki so posledica optike, detektojev, obdelave ali pa procesov, ki se odvijajo na astronomskem objektu in jih ne znamo ali ne želimo modelirati. V primeru, da celoten šum npr. v spektru zvezde še vedno obravnavamo, kot da je normalno porazdeljen, lahko zaidemo v težave.

V predavanju si bomo ogledali nekaj orodij, s katerimi lahko efektivno modeliramo celoten šum. Pokazali bomo, da je tak pristop ključen in da so v nasprotnem primeru naše rešitve sistematično premaknjene in navidezno bolj natančne.

The nature of GeV Galactic Center excess emission: options and their testability

The nature of GeV Galactic Center excess emission: options and their testability

dr. Gabrijela Zaharijaš

University of Nova Gorica

v ponedeljek, 25. maja 2015, ob 13. uri v predavalnici F4 (Jadranska 19, Ljubljana)

Several groups have recently claimed evidence for an unaccounted gamma-ray excess over the diffuse backgrounds at few GeV in the Fermi-LAT data in a region around the Galactic Center, consistent with putative signals of long sought for WIMP dark matter particles. However, several conventional astrophysical explanation of this emission appear viable and need to be understood and accounted for, before any robust inference can be made about dark matter signals. In particular, we show that the main features of this excess can be reproduced if they originate in the inverse Compton emission from high-energy electrons injected in a burst event of ~ [latex]10^52[/latex]-10^53[/latex] erg roughly O( [latex]10^6[/latex]) years ago and we discuss the testability of this prediction. Another convincing astrophysical candidate for this emission is an unresolved population of MSP. There have been several works studying this possibility and reaching in some cases opposite conclusions. Here we reassess these claims by adopting a phenomenological approach and make clear predictions for the next generation experiments, which due to their improved angular resolution at few GeV should be able to test the point source origin of the excess.