Galaxy modelling: dynamical methods and applications
Date
2016-06-20
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Abstract
Käesoleva doktoritöö eesmärk on välja töötada meetod, millega on võimalik modelleerida ga-laktikate dünaamikat, võttes arvesse võimalikke efekte, mis mõjutavad mudel- ja vaatlusandmete võrdlemist.
Dünaamiline modelleerimine võimaldab uurida, kuidas on mass jaotunud galaktikates. Üks levinud meetodeid on Jeansi võrrandite kasutamine, millest leitakse vastavalt tihedusjaotusele tähtede liik-umine. Klassikalisel juhul ei ole see ühene ülesanne – liikumine ja tihedusjaotus on kõdunud. Teine probleem on, et Jeansi võrrandites on rohkem muutujaid kui võrrandeid, mistõttu süsteem ilma li-saeeldusteta ei lahendu. Doktoritöö näitab, et kasutades mitteklassikalist suurust – kolmandat liiku-misintegraali –, on võimalik Jeansi võrrandid lahendada ning saada süsteemile lahend.
Doktoritöös uuriti erinevaid protsesse, mis mõjutavad galaktikate dünaamilist modelleerimist. Mudeli sisend (tihedusjaotus) peab olema täpne – uurimise tulemusena leiti, et fotomeetriliste andmete põhjal saadav stellaarne jaotus on pädev, kuid sellest leitud täheketta paksuse kasutamisel peab olema ettevaatlik. Mudeli väljundit mõjutavad kõigi punktide arvesse võtmine piki vaatejoont ning atmosfääri ja spektrograafi põhjustatud konvolutsioon. Viimased on eriti olulised kaugete ga-laktikate vaatluste korral.
Koostatud kinemaatiline mudel võimaldas veel uurida üht huvitavat efekti, mille on tekitanud tolm. Kuna tolm varjab enda taga olevat valgust, siis galaktikate meiepoolsemad piirkonnad domineerivad heledustes, ja seega ka kinemaatikas. Taoline “nihe” põhjustab kinemaatiliste parameetrite ebatäpsusi kuni 20% ulatuses.
The aim of the present Thesis was to develop a method to study the dynamics of galaxies and vari-ous effects that could affect the comparison of the model calculations with observations. Measured kinematic quantities provide us with a possibility to constrain the mass distribution of galaxies. A common way for it is to model the kinematics via solving the Jeans equations – the equations de-rived from collisionless Boltzmann equation to describe the stellar motions. From the classical point of view, the task is degenerated: one cannot distinguish the distortions of velocities from different mass distributions. In addition, a shortcoming of using the Jeans equations is that there are more variables than equations, and therefore the problem is not solvable by itself – we must use additional constraints. One possible source of constraints is a non-classical conserved quantity (third integral of motion) – a variable that is constant along the stellar orbit. This Thesis provided a new solution by choosing a specific form for the third integral of motion, which allows us to solve the Jeans equations. In the Thesis, we also studied various effects influencing the model input and output. We studied how well the stellar density distribution that is needed for the model input can be found from pho-tometric observations. Most parameters can be restored well, except the flatness of the component, for which the accuracy is moderate. For making the output of the model comparable with observa-tions, one has to take into account all the points on sightline and the convolution due to atmosphere and spectrograph slit. In case of high redshift galaxies, the effect can be very important. Our kinematic model allowed us to study an interesting topic – how much the presence of dust af-fects the kinematic parameters. The dust in galaxies hinders the visibility of the far side of galaxy, and therefore suppresses the influence of the kinematic parameters of that region.
The aim of the present Thesis was to develop a method to study the dynamics of galaxies and vari-ous effects that could affect the comparison of the model calculations with observations. Measured kinematic quantities provide us with a possibility to constrain the mass distribution of galaxies. A common way for it is to model the kinematics via solving the Jeans equations – the equations de-rived from collisionless Boltzmann equation to describe the stellar motions. From the classical point of view, the task is degenerated: one cannot distinguish the distortions of velocities from different mass distributions. In addition, a shortcoming of using the Jeans equations is that there are more variables than equations, and therefore the problem is not solvable by itself – we must use additional constraints. One possible source of constraints is a non-classical conserved quantity (third integral of motion) – a variable that is constant along the stellar orbit. This Thesis provided a new solution by choosing a specific form for the third integral of motion, which allows us to solve the Jeans equations. In the Thesis, we also studied various effects influencing the model input and output. We studied how well the stellar density distribution that is needed for the model input can be found from pho-tometric observations. Most parameters can be restored well, except the flatness of the component, for which the accuracy is moderate. For making the output of the model comparable with observa-tions, one has to take into account all the points on sightline and the convolution due to atmosphere and spectrograph slit. In case of high redshift galaxies, the effect can be very important. Our kinematic model allowed us to study an interesting topic – how much the presence of dust af-fects the kinematic parameters. The dust in galaxies hinders the visibility of the far side of galaxy, and therefore suppresses the influence of the kinematic parameters of that region.
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Keywords
galaktikad, modelleerimine (teadus), dünaamika (füüs.), meetodid, rakendused, galaxies, modelling (science), dynamics (physics), methods, applications