Depolarizacijski kanali u radiopolarimetrijskim promatranjima

master's thesis

• Title (english): Depolarization Canals in Radiopolarimetry Observations
• Author: David Prelogović
• Mentor: Vibor Jelić (mentor)
• Mentor: Vernesa Smolčić (mentor)
• Committee member: Vibor Jelić (predsjednik povjerenstva)
• Committee member: Vernesa Smolčić (član povjerenstva)
• Committee member: Ivica Smolić (član povjerenstva)
• Committee member: Krešimir Pavlovski (član povjerenstva)
• Committee member: Krešimir Kumerički (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2019-07-17, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

Nedavna polarimetrijska mjerenja radioteleskopa LOFAR ukazala su na postojanje dugih i ravnih depolarizacijskih kanala na području neba znanom kao polje 3C 196. Mogući uzroci njihovog nastanka i dalje su nejasni. Radiopolarimetrijska mjerenja baziraju se na Faradayevoj rotaciji, tj. zakretanju ravnine polarizacije zračenja prilikom prolaska kroz međuzvjezdanu materiju (plazmu). Kut rotacije ovisan je o gustoći elektrona i jakosti magnetskog polja, pa nagle promjene u magnetskom polju ili uski turbulentni medij nastao prolaskom zvijezde, mogući su uzroci depolarizacije kojima ćemo se baviti u ovom istraživanju. U prvom ćemo slučaju kao mjere orijentacije magnetskog polja koristiti promatranja neutralnog vodika i polarizaciju termalne prašine, a u drugom mjerenja položaja, brzina i svojstava zvijezda u blizini 3C 196 polja. Analizu radiozračenja provodimo metodom Rotation Measure Synthesis, a kvantitativnu detekciju linearnih struktura Rolling Hough Transform algoritmom. Iz uočenih korelacija različitih vrsta međuzvjezdane materije zaključujemo o snažnom utjecaju magnetskog polja u njihovom oblikovanju. S druge strane, tragovi zvijezda pokazali su se kao potencijalni izvori nekih depolarizacijskih kanala, ali problem u konačnici ostavljaju otvorenim.

Abstract (english)

The radio polarimetric observations exploit the fact that the polarisation angle of the radio emission is Faraday rotated as the emission passes through the interstellar medium, specifically plasma. The amount of rotation depends on the electron density and the magnetic field strength. Recent polarimetric observations with the LOFAR radio telescope revealed long and straight depolarization canals in the part of the sky known as the 3C 196 field. The origin of these canals is still not well understood and in this work, we will investigate two possibilities. The first is associated with sudden changes in the magnetic field direction and the second with narrow and turbulent ionising trails of stars. In our work, we use the observations of the neutral hydrogen emission and polarized dust emission as measures of the magnetic field orientation. We also use the GAIA measurements of the stars in the proximity of the 3C 196 field. The radio polarimetric observations are analysed using the Rotation Measure Synthesis, while the quantitative analysis of linear structures is done using the Rolling Hough Transform algorithm. We find a good alignment between different interstellar medium phases, indicating an important role of the magnetic fields. In contrary, a connection between the depolarization canals and the star-trails is inconclusive, calling for further analysis.

• Keywords: depolarizacijski kanali; Faradayeva rotacija; LOFAR; plazma; neutralni vodik; prašina; tragovi zvijezda; RM sinteza; RHT
• Keywords (english): depolarization canals; Faraday rotation; LOFAR; plasma; neutral hydrogen; dust; startrails; RM Synthesis; RHT
• Language: croatian
• URN:NBN: urn:nbn:hr:217:385694
• 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: 2019-08-26 15:56:38