Polarizirano zračenje radio galaksija na niskim radio frekvencijama

master's thesis

• Title (english): Polarised emission of galaxies at low radio frequencies
• Author: Dario Barišić
• Mentor: Vibor Jelić (mentor)
• Mentor: Krešimir Pavlovski (mentor)
• Committee member: Krešimir Pavlovski (predsjednik povjerenstva)
• Committee member: Vibor Jelić (član povjerenstva)
• Committee member: Ivica Smolić (član povjerenstva)
• Committee member: Vernesa Smolčić (član povjerenstva)
• Committee member: Maro Cvitan (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2018-11-19, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

U ovom radu bavimo se potragom za polariziranim zračenjem radiogalaksija koristeći polarimetrijska promatranja na 150 MHz prikupljena LOFAR teleskopom u području centriranom na sjajnoj radiogalaksiji 3C196 (RA = 8h13m36s, DEC = +48°13'03'') koje obuhvaća oko 50 kvadratnih stupnjeva. Ukupno smo pronašli 10 polariziranih radioizvora. Analizom slika iz FIRST kataloga na 1.4 GHz ustanovili smo da su 9 izvora radiogalaksije FR-II tipa koje su luminoznije prema rubovima, a preostali izvor je kvazar. Izračunati postotci polarizacije izvora na 150 MHz pokazuju znatno veću depolarizaciju u odnosu na mjerenja iz NVSS kataloga na frekvencijama oko 1.4 GHz. Za pojedine izvore postoje velike razlike između Faradayevih dubina dobivenih iz LOFAR-ovih mjerenja i onih koje se navode u NVSS katalogu, što pripisujemo niskoj rezoluciji u Faraday prostoru za NVSS-ova mjerenja. Usporedbom dobivenih vrijednosti ukupnog intenziteta s onima na drugim frekvencijama, koje smo pronašli u VLSS (74 MHz), NVSS (1.4 GHz) i WENSS (325 MHz) katalozima, dobili smo vrijednosti spektralnih indeksa koji u prosjeku iznose 0.753. Dobivena je gustoća od jednog izvora na 5 kvadratnih stupnjeva neba.

Abstract (english)

In this Diploma thesis we are searching for polarized emission of the radio galaxies in a field centred at a bight radio galaxy 3C196 (RA = 8h13m36s, DEC = +48°13'03''), covering an area of 50 square degrees. In our analysis we are using LOFAR polarimetric observations at 150 MHz. In total we have found 10 polarized radio sources. By analysing the FIRST images of these sources we concluded that one source is a quasar, while all the others are FR-II radio galaxies, which are the brightest at the edges. Their degree of polarization at 150 MHz is smaller than at 1.4 GHz (NVSS catalogue), due to significantly higher wavelenght dependent depolarization. There is some discrepancy in obtained rotation measures if compared with the ones at 1.4 GHz. This can be attributed to much poorer resolution in Faraday depth at higher radio frequencies. We also compared the amount of emission obtained in total intensity with catalogues at other frequencies (VLSS - 74 MHz, WENSS - 325 MHz, NVSS - 1.4 GH). Based on this comparison we calculated the spectral indices of the sources, mounting to 0.753 in average. We found a density of 1 source per 5 square degrees.

• Keywords: sinkrotronsko zračenje; radiogalaksija; Faradayeva dubina; spektralni indeksi
• Keywords (english): synchrotron emission; radio galaxy; rotation measure; spectral indices
• Language: croatian
• URN:NBN: urn:nbn:hr:217:992842
• Study programme: Title: Physics; specializations in: Research; Course: Research; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra fizike (magistar/magistra fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2018-11-20 13:12:09