Tracing galaxy evolution by their present-day luminosity function
Date
2011-04-14
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Abstract
Galaktikad, mis koosnevad kuni sadadest miljarditest tähtedest, gaasist ja tolmust, on ühed tähelepanuväärsemad süsteemid Universumis. Juba visuaalsete vaatluste põhjal on näha, et neid on väga mitmesuguseid: spiraalseid, elliptilisi ning korrapäratu kujuga. Selline mitmekesisus tekitab küsimuse, kuidas galaktikad on tekkinud? Galaktikate tekkimine ja evolutsioon hõlmab mitmeid erinevaid füüsikalisi protsesse ja sõltub paljudest faktoritest. Tänapäeva kosmoloogias on selle mõistmine üks aktuaalsemaid probleeme.
Käesoleva töö eesmärgiks on uurida, kuidas galaktikate evolutsioon sõltub Universumi suuremastaabilisest struktuurist. Selleks kasutame galaktikate heledusfunktsiooni - vaadeldud galaktikate heleduste jaotust, Uurides galaktikate heledusfunktsiooni sõltuvana suuremastaabilisest struktuurist, järeldasime, et elliptiliste galaktikate evolutsioon sõltub tugevalt ümbritsevast suuremastaabilisest keskkonnast, seevastu spiraalsete galaktikate heledusfunktsioon jääb erineva tihedusega piirkondades muutumatuks. Elliptiliste galaktikate heleduste üldine sõltuvus globaalsest ümbrusest oli oodatav, kuna elliptilised galaktikad tekivad vastavalt praegusele galaktikate tekke paradigmale peamiselt galaktikate ühinemise tulemusel. Spiraalgalaktikate heledusfunktsiooni sarnasus erinevates piirkondades näitab aga, et spiraalgalaktikate tekkimine erinevates tingimustes on sarnane. Kuna hierarhilise kuhjumise teooria järgi peaksid ka spiraalgalaktikad sõltuma ümbritsevast globaalsest keskkonnast, piirab see tulemus spiraalgalaktikate tekke võimalikke viise.
Käesoleva töö tulemused näitasid selgelt, et lisaks lokaalsele (gruppide) ümbrusele on galaktikate evolutsioonis oluline ka globaalne, suuremastaabiline ümbrus. Loodetavasti aitab suuremastaabilise ümbruse mõju arvestamine lahendada mitmeid probleeme galaktikate tekke stsenaariumides.
Galaxies, which are complex objects containing up to several tens of billions stars, as well as gas and dust, are remarkable objects. The Universe contains a very diverse “zoo” of galaxies: there are galaxies with a discy shape and spiral structure, elliptical galaxies, and even galaxies, which show no sign of structure. This variety of galaxies leads to the basic question: how the galaxies form and evolve and which processes shape the structure of galaxies? Due to the complexity of galaxy formation and evolution, this question is still an unresolved puzzle and it is one of the biggest challenges in modern cosmology. The present thesis is based on large galaxy surveys and concentrates on the large-scale structure: how galaxy evolution is related to the surrounding large-scale environment of superclusters and voids. To study the evolution of galaxies, we use the luminosity function, which is in this respect one of the most fundamental of all cosmological observables. One of the principal results of the present study was the conclusion that the evolution of spiral galaxies is almost independent of the global environment, especially for blue and red spirals separately, showing that the formation of spiral galaxies has to be similar in all environments. Meanwhile, the luminosity function of elliptical galaxies depends strongly on the environment. This shows that the global environmental density is an important factor (via merging history) in the formation of elliptical galaxies. The results of the present study show clearly, that besides the local/group environment, the global (supercluster-void) environment plays also an important role in the formation and evolution of galaxies. Accounting for the role of global environment can help to solve several problems in the present picture of galaxy formation and evolution.
Galaxies, which are complex objects containing up to several tens of billions stars, as well as gas and dust, are remarkable objects. The Universe contains a very diverse “zoo” of galaxies: there are galaxies with a discy shape and spiral structure, elliptical galaxies, and even galaxies, which show no sign of structure. This variety of galaxies leads to the basic question: how the galaxies form and evolve and which processes shape the structure of galaxies? Due to the complexity of galaxy formation and evolution, this question is still an unresolved puzzle and it is one of the biggest challenges in modern cosmology. The present thesis is based on large galaxy surveys and concentrates on the large-scale structure: how galaxy evolution is related to the surrounding large-scale environment of superclusters and voids. To study the evolution of galaxies, we use the luminosity function, which is in this respect one of the most fundamental of all cosmological observables. One of the principal results of the present study was the conclusion that the evolution of spiral galaxies is almost independent of the global environment, especially for blue and red spirals separately, showing that the formation of spiral galaxies has to be similar in all environments. Meanwhile, the luminosity function of elliptical galaxies depends strongly on the environment. This shows that the global environmental density is an important factor (via merging history) in the formation of elliptical galaxies. The results of the present study show clearly, that besides the local/group environment, the global (supercluster-void) environment plays also an important role in the formation and evolution of galaxies. Accounting for the role of global environment can help to solve several problems in the present picture of galaxy formation and evolution.
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Keywords
dissertatsioonid, astronoomia, galaktikad, galaktikate evolutsioon, kosmoloogia, heledusfunktsioon, galaxy evolution