Faradayevi momenti južnih galaktičkih širina u pregledu neba LoTSS

master's thesis

• Title (english): Faraday moments at South Galactic latitudes in the LoTSS sky survey
• Author: Lovorka Gajović
• Mentor: Vibor Jelić (mentor)
• Committee member: Vibor Jelić (predsjednik povjerenstva)
• Committee member: Matko Milin (član povjerenstva)
• Committee member: Vernesa Smolčić (član povjerenstva)
• Committee member: Krešimir Kumerički (član povjerenstva)
• Committee member: Ivica Smolić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2021-07-09, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

Cilj pregleda neba LoTSS je promatranje cijelog sjevernog neba teleskopom LOFAR na niskim radiofrekvencijama (približno 150 MHz). U Mliječnoj stazi polarizirano radiozračenje na niskim frekvencijama je sinkrotronsko zračenje koje proizvode visokoenergetski elektroni. U meduzvjezdanoj materiji, u kojoj je prisutno magnetsko polje, zbog Faradayeve rotacije se zakreće kut polarizacije emitiranog sinkrotronskog zračenja. Budući da Faradayeva rotacija ovisi o kvadratu valne duljine zračenja, možemo iskoristiti Faradayevu tomografiju i metodom RM sinteze raspetljati opaženo zračenje po Faradayevim dubinama što nam daje raspodjelu ionizacije i magnetskog polja u meduzvjezdanoj materiji duž doglednice. U ovom radu smo spojili 186 zasebnih opažanja pregleda neba LoTSS u mozaik koji prekriva približno 1400 kvadratnih stupnjeva neba na južnim galaktičkim širinama. Izračunali smo nulti Faradayev moment koji odgovara ukupnom intenzitetu zračenja po Faradayevim dubinama, prvi Faradayev moment koji predstavlja srednju vrijednost Faradayeve dubine utežnjenu intenzitetom i drugi Faradayev moment koji označava polovicu utežnjene širine u Faradayevom spektru. Najbitnija značajka dobivenog mozaika je gradijent emisije po Faradayevim dubinama koji se proteže sa zapadne prema istočnoj strani vidnog polja. U najstrmijem dijelu gradijenta emisija se pomakne približno 4⁰ na nebu za svaki rad m-2 Faradayeve dubine. Usporedili smo rezultate s kartom ukupne galaktičke Faradayeve rotacije i pokazali da je emisija koju LoTSS opaža nastala na manjim udaljenostima od skale galaksije.

Abstract (english)

The goal of the LoTSS sky survey is to observe the whole North sky with the LOFAR telescope at very low radio frequencies (approximately 150 MHz). At low frequencies, most of the polarized emission of the Milky Way is synchrotron radiation produced by high energy electrons. Faraday rotation changes the angle of polarization when the radiation passes through magnetized interstellar medium. Faraday rotation is proportional to the square of the wavelength of radiation. Therefore, we can use Faraday tomography and rotation measure (RM) synthesis method to disentangle the observed emission over the range of Faraday depths. Faraday depth gives us the distribution of ionised interstellar medium and magnetic field along the line of sight. In this work we combined 186 single LoTSS observations into a mosaic which covers approximately 1400 square degrees of the sky at South Galactic latitudes. We calculated the Faraday moments. The zero moment represents the total intensity of radiation over the whole Faraday spectrum. The first moment is the average Faraday depth weighted by intensity. The second moment is a half of the weighted width of the Faraday spectrum. The most significant feature of the mosaic is a gradient of intensity over multiple Faraday depths which covers the field of view from west to east. At the steepest part of the gradient the emission moves on average 4⁰ on the sky when the Faraday depth changes by 1 rad m-2. We compared our results to the Galactic Faraday rotation sky map and concluded that the emission observed in the LoTSS survey is produced at distances closer to us compared to the size of the whole galaxy.

• Keywords: lokalna međuzvjezdana materija; sinkrotronsko zračenje; Faradayevi momenti; magnetsko polje
• Keywords (english): local interstellar medium; synchrotron radiation; Faraday moments; magnetic fields
• Language: croatian
• URN:NBN: urn:nbn:hr:217:772688
• 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; Embargo expiration date: 2022-07-09
• Created on: 2021-07-23 11:37:18