Variable sources in large optical sky surveys

doctoral thesis

• Title (croatian): Promjenjivi izvori u velikim optičkim pregledima neba
• Author: Marta Fatović
• Mentor: Lovro Palaversa (mentor)
• Committee member: Vibor Jelić (predsjednik povjerenstva)
• Committee member: Lovro Palaversa (član povjerenstva)
• Committee member: Ana Babić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2024-10-24, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

This thesis studies periodic variability in large optical sky surveys, focusing on long-period variable sources. A primary challenge in studying these objects is accurately determining their periods. The first part of this thesis addresses this by introducing a set of filters to reliably identify periods of sources in the SDSS S82, which were previously classified as non-variable. Five quasars with plausible periodic variability were identified by applying several criteria to the light curves. These criteria included requiring at least 25 data points, matching periods in the SDSS gri filters within 0.1%, and ensuring good agreement with a simple sinusoidal model. Potential aliases were filtered out by requiring distinct periods and calculated uncertainties that were not multiples of one year. Additionally, Kuiper statistics were used to ensure no significant gaps or clustering of points in each phase light curve. In the second part of this thesis, the focus is on one of the previously detected quasars with the shortest period of 278 days. This quasar is analyzed using new observations of MgII lines and archived SDSS spectra, providing three epochs of MgII observations. The key findings include the discovery that the newly observed MgII line exhibits a double-peaked profile that changes over time. By comparing synthetic magnitudes with photometric data as well as using the PoSKI model, which analyzes emission lines and light curves of candidate supermassive binary black holes (SMBBH), a correlation was found suggesting a closely orbiting SMBBH. The latest release Gaia DR3, included light curves for all objects within a field centered on the Andromeda Galaxy. The final scientific part of this thesis focuses on identifying Mira stars in the M31 galaxy and determining their periods. For the first time, a period-luminosity (PL) relation for Mira variables in the M31 galaxy has been established using Gaia filters. This relation is compared with PL relations for multiple galaxies presented in other works, using 2MASS data. Although the method can be improved, the results are promising and lay the groundwork for future research utilizing Gaia’s light curves for the entire sky.

Abstract (croatian)

Ova disertacija istražuje dugoperiodičnu promjenjivost u velikim optičkim pregledima neba. Periodički promjenjivi izvori ključni su za procjenu udaljenosti u svemiru. Osim toga, promatranje periodične promjenjivosti u AGN-ovima može pružiti uvid u mogućnost sustava dvojnih crnih rupa, čime se postavlja temelj za proučavanje gravitacijskih valova. Glavni izazov u proučavanju promjenjivih izvora je točno određivanje njihovih perioda. U poglavlju 4 uvedene su metode filtracije za pouzdano određivanje perioda objekata prethodno klasificiranih kao nepromjenjivi. Identificirano je pet kvazara s mogućom periodičkom promjenjivošću u SDSS ugriz filtrima, pri čemu je kvazar s najkraćim periodom odabran za daljnje istraživanje. Buduća istraživanja će imati koristi od nadolazećih osjetljivih pregleda neba, poix Prošireni sažetak put Rubin Observatory Legacy Survey of Space and Time, koji će biti učinkovitiji u otkrivanju periodične promjenjivosti. U poglavlju 5 analiziran je jedan od pet identificiranih kvazara koristeći nove MgII linije i arhivirane SDSS spektre, pružajući tri epohe MgII opažanja. Primjenom PoSKI modela utvrđena je povezanost između opaženog ponašanja i modeliranog sustava, sugerirajući prisutnost SMBBH u bliskoj orbiti. Za potvrdu SMBBH sustava potrebna su opsežna promatranja, uključujući daljnje spektroskopsko praćenje i fotometrijska opažanja. Promatranja radio emisije mogla bi pružiti jedinstvenu dijagnostiku okruženja SMBBH sustava. Gaia satelit započeo je svoja znanstvena opažanja 2014. godine, značajna za proučavanje promjenjivih izvora jer Gaia mapira cijelo nebo. U poglavlju 6 identificirane su Mira zvijezde u M31 galaksiji i određeni su njihovi periodi. Po prvi put uspostavljena je PL relacija za Mire u M31 galaksiji koristeći Gaia filtre. Analiza periodičnosti Mira u M31 može se poboljšati uključivanjem čimbenika poput gibanja zvijezda u Andromedi, boje i svih triju Gaia filtera pri izračunu perioda. Gaia DR4 pružit će podatke o krivuljama sjaja za sve opažene izvore, omogućujući primjenu ove metode na druge galaksije.

• Keywords: long-period variability; red giants; active galactic nuclei; supermassive binary black hole; quasar; light curve; MgII spectral line
• Keywords (croatian): dugoperiodična varijabilnost; crveni divovi; aktivne galaktičke jezgre; supermasivna binarna crna rupa; kvazar; krivulja sjaja; MgII spektralna linija
• Language: english
• URN:NBN: urn:nbn:hr:217:027966
• Promotion: 2024
• Study programme: Title: Doctoral study; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti u području prirodnih znanosti (doktor/doktorica znanosti u području prirodnih znanosti)
• Type of resource: Text
• Extent: 106 str.
• File origin: Born digital
• Access conditions: Open access
• Created on: 2024-12-04 14:07:40