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

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

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

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

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