http://hdl.handle.net/123456789/11 http://hdl.handle.net/123456789/5795 UTICAJ INTERAKCIJA UDALJENIH GALAKSIJA NA NJIHOVO NETERMALNO RADIO ZRAČENJE Pavlović, Mrina The studyofgalaxiesthroughhighredshiftsarekeytounderstandingthe evolutionofgalaxiesthroughcosmictimes.Assuchobjectsareverydifficultto observedirectly,theyaremainlyexaminedusingempiricallyderivedtoolssuchas the numerouscorrelationsbetweentheirdifferentparametriccharacteristics,one of thembeingthelinearrelationshipbetweenfar-infraredandradioemissionin star-forming galaxies,namedtheFarInfrared-Radio(FIR)Correlation.Although the correlationwasconsideredtobestableintermsoflinearity,recentworks, whichincludegalaxiesathighredshifts(0 < z< 6), showedalargedeviation from thecorrelationinthesesystems.Thegoalofthisdoctoraldissertationis an examinationofthephysicalprocessesthatleadtothiskindofbehavior.As a possiblecauseofthisevolution,wewillassumeforthefirsttime,andexamine interactionsbetweengalaxies(collisionsandcloseapproaches).Interactionsbe- tweengalaxiesleadtotheformationofshockwavesonlargescalesthatcanlead to changesintherelationshipbetweeninfraredandradioemissions.Ourhypoth- esis wastestedinseveralstadiumsandthemainresultsareasfollows:1.We developedmodelsoftheevolutionoftheFIRcorrelationwithredshiftasfunctions of thegalaxyinteractionrate.Wetestedthemodelsonasampleofgalaxieswith an alreadydeterminedmorphologyseparatelyfordiscgalaxiesandforgalaxies that haverecentlybeenorarecurrentlyinteracting-irregulargalaxies. 2. Inasmallsampleof34galaxiesthatwetookfrompaperMiettinenetal.(2017), it wasshownthatthereisanindicationthattheinteractionbetweengalaxiescan beresponsiblefortheevolutionofthecorrelationwiththeredshift. 3. Thenextanalysiswasperformedonamuchlargersampleofstar-forming galaxies takenfromCOSMOSfield,wherewedidnotfindanyevolutionofcorre- lation withtheredshift.Also,itwasshownthatthemeanvalueofthecorrelation parameter islowerinirregulargalaxiesthanindiskgalaxies. Although recentobservationsindicatedanevolutionoftheFIRcorrelation with redshift,theresultsofthisresearchfailedtoreproducethatevolutionand showedthattheFIRcorrelationisstablewithredshift.However,itwasalso shownthatduetotheinteractionofgalaxies,theevolutionoftheFIRcorrelation is possibleiftherepresentationofinteractingsystemsinthesampleishigher. Sat, 01 Jan 2022 00:00:00 GMT http://hdl.handle.net/123456789/5793 IN- SITU DUST DETECTION USING RADIO ANTENNAS OF DIFFERENT SPACECRAFT - SPACE OBSERVATIONS AND MODELING Racković Babić, Kristina Interplanetary dust grains contain important information about the Solar System. Analyzing these particles is an important aspect of the heliosphere study. Dust impacts have been observed using radio and wave instruments onboard the spacecraft since the 1980s. The interaction between the impact-generated plasma cloud and antenna – spacecraft system elements generates the characteristic signal waveform. The present work focuses on the detection and interpretation of the dust generated signals from radio instruments onboard various spacecraft orbiting at 1 AU. In the first part of the thesis, we aim to develop a model which links the observed electric signals to the dust impact properties.We propose a new model which takes into account the effect of impact - ionization - charge collection and electrostatic-influence. Our model provides an analytical expression for the pulse. It allows us to measure the amount of total ion charge, the fraction of escaping charge, the rise timescale, and the relaxation timescale. The proposed model is simple and convenient for large data fitting. To validate the model, we use the Time Domain Sampler (TDS) subsystem of the STEREO/WAVES instrument, which generates high-cadence time series of voltage pulses for each monopole. Since the beginning of the STEREO mission in 2007, we have collected all the dust events detected by S/WAVES/TDS simultaneously on all three monopoles at 1 AU. Our study confirms that the rise time vastly exceeds the spacecraft’s short timescale of electron collection by the spacecraft. Aside from electron dynamics, we also obtained interesting results regarding the cloud’s electron temperature. The presented model provides an effective tool for analyzing vii dust waveforms, and is applicable for different space missions which investigate the distribution of dust particles, e.g., Solar Orbiter and Parker Solar Probe. In the second part of the thesis, we focus on the interstellar dust (ISD). Interplanetary and interstellar dust are the two main dust populations at 1 AU. Our objective is to search for interstellar dust by analyzing the data sets collected by STEREO and Wind, starting from the beginning of the missions. Between 2007 and 2012, while being at the solar minimum with a solar dipole pointing southward, all three spacecraft recorded ISD flux at 1 AU. However, before and after that period, the disappearance of the interstellar component was noticeable. The observed change of the impact rate suggests that the flux of interstellar dust at 1 AU varies with the solar cycle. Each time the magnetic dipole field changes its polarity during the solar cycle, small interstellar grains experience focusing or defocusing. Consequently, the dust grains are systematically deflected either towards, or away from the solar magnetic equator plane by the solar wind magnetic field which thus affects the dust dynamics and the total interstellar dust flux in the inner heliosphere. Our study provides the first quantitative description of the time variation of ISD flux at 1 AU. Sat, 01 Jan 2022 00:00:00 GMT http://hdl.handle.net/123456789/5790 PROMENA V I R MAGNITUDA IZABRANIH KVAZARA I POVEZIVANJE SISTEMA GAIA SA SISTEMOM ICRF Jovanović, Miljana One of the main objectives of the Gaia mission of the European Space Agency is to construct a celestial reference frame at the wavelengths of the optical domain, Gaia CRF. This frame needs a link to the International Celestial Reference Frame – ICRF which is fixed with respect to distant objects (quasars). The objects serving for the purpose of linking are required to be visible in both domains (optical and radio). A set of 47 such objects has been proposed and included which in the radio domain have no detected extended emission. The mentioned objects are active galactic nuclei (AGN) the brightness of which varies over the whole electromagnetic spectrum. The brightness change may be due to activity in different AGN regions, but also to external factors. Such variations can lead to changes in the photocentre position and, consequently, to changes of the object coordinates. In order to establish which objects are suitable for linking these two frames we have examined the brightness variation in the optical domain. The objects have been observed from 2013 in the V and R bands. We have analysed the brightness, colour (V − R) and optical spectral index (α). It has been established that for the majority of objects the brightness is variable, or possibly variable. Almost 15% of all objects have significant changes in their brightness (more than 1 mag), only ∼10% are stable with minor brightness changes of ∼0.3 mag. The results concerning the change analysis of the colour and α are also presented. Based on these results 17 objects are chosen as suitable for linking ICRF to Gaia CRF. The results of the analysis, as well as the observed values, are essential for the examination of these objects because of their importance in astrometry, also in astrophysics. These data are relevant to a better understanding of formation and evolution of galaxies. Mon, 01 Jan 2024 00:00:00 GMT http://hdl.handle.net/123456789/5766 ANALIZA PROMENLJIVOSTI AKTIVNIH GALAKTIČKIH JEZGARA KOMBINOVANOM PRIMENOM SAMOORGANIZUJUĆIH MAPA I NEURONSKIH PROCESA Čvorović - Hajdinjak, Iva This doctoral dissertation addresses the development and application of advanced methods for analyzing the temporal variability of active galactic nuclei (AGN) through the modeling of their optical light curves. The research integrates unsupervised and generative learning techniques, by combining Self- Organizing Maps (SOM) for data preprocessing and Conditional Neural Processes (CNP) for light curve prediction. For the first time in the study of AGN light curves, clustering via SOM has been implemented for preprocessing, alongside the application of CNP for modeling variability. This innovative approach facilitates a more effective modeling of light curves characterized by uneven sampling and missing observations. The QNPy software package was developed and optimized for large-scale parallel processing of extensive time series data. The proposed methodology was validated using light curves from the All-Sky Automated Survey for SuperNovae (ASAS-SN) and the SWIFT/BAT mission, covering a broad range of time scales and variability. The analysis prove that clustering light curves with SOM enhances the performance of neural process, particularly for objects exhibiting simpler variability patterns. The effects of SOM hyperparameters on clustering and prediction performance were carefully examined. The models were validated using loss function and mean squared error evaluations on real data. The proposed methodology shows strong potential for scalable processing of the large time-series data, anticipated in upcoming projects such as the Vera C. Rubin Observatory’s Legacy Survey of Space and Time, enabling automated classification, anomaly detection, and the extraction of scientifically significant objects from catalogs containing hundreds of millions of sources. Sun, 01 Jun 2025 00:00:00 GMT