Galaxies and non-galactic baryons in cosmic filaments

Abstract

Galaktikad on ühed huvitavamad taevas vaadeldavad objektid. Need on erineva kujuga, vankriratta või CD-plaadi kettakujulistest spiraalsetest kuni ilmetute kanamuna kujuga el- liptilisteni. Sada aastat tagasi mõõdeti esimest korda galaktikate kaugusi ja sai ilmsiks, et need on meist tohutult kaugel asuvad tähtede kogumikud. Ka meie Päike asub ühes galakti- kas, Linnutee, mis on ainult üks miljarditest teistest galaktikatest meie universumis.

Tänu teleskoopidega tehtud taevaülevaadetele, mille eesmärk on galaktikate täpsete asu- kohtade määramine, on saanud selgeks, et galaktikad ei asu üksteise suhtes juhuslikult, vaid eelistatud paigutuses. Mõned neist on tihedas koosluses üksteise lähedal, parvedes. Parvede vahel on pikad galaktikate ahelad, filamendid. On ka piirkondasid, kus on väga vähe või po- le üldse galaktikaid, tühikud. Seda jaotust võib ette kujutada kui inimeste jaotust Maa peal, kus parved on suurlinnad, filamendid suuremad teed, mille lähedal on väiksemad linnad ja tühikud väheasustatud alad.

Samuti on leitud, et galaktikad erinevad sõltuvalt nende keskkondade tihedusest. Par- vedes on hilisemas arengujärgus galaktikad: suuremad ja vanemad. Tühikud on vastandina väiksemate ja noorte galaktikate ala. Filamendid on vahepealsed, kus leidub palju erine- vaid galaktikaid. Nad esinevad ka väga erinevates keskkondades asudes nii tühikutes kui ka parvede kogumite vahel.

Selle teesi eesmärgiks on iseloomustada just filamentides asuvaid galaktikaid. Prae- guseni pole veel selge kuidas filamendi keskkond mõjutab galaktikate arengut. Probleemi lahendamiseks kasutasime kaasautoritega nii avalikult kättesaadavaid vaaltusandmeid kui ka Tartu Ülikooli Tartu Observatooriumi teadlaste kogemust galaktikate konfiguratsioonide iseloomustamises. Selle töö tulemusena leidsime, et filamentides on galaktikad väiksema tähetekke aktiivsusega ja üldiselt hilisemas arengufaasis kui eeldaks ainuüksi keskkonna tiheduse põhjal. Edaspidi on vaja veel uurida galaktikaid, et nende olemusest aru saada.

Galaxies are some of the most interesting objects visible in the sky. They have different shapes, from cartwheel or CD-like disky spirals to featureless egg-shaped ellipticals. One hundred years ago the distances of galaxies were first measured and it became apparent that they are collections of stars at vast distances from us. Even the Sun is located within a galaxy, the Milky Way, which is just one of billions of other galaxies in our universe.

Sky surveys with telescopes have measured exact positions of galaxies. From these we know that galaxies are not situated randomly, but in preferred configurations. Some are in dense associations, clusters. Clusters are connected by long chains of galaxies, filaments. There are regions where there are very few or no galaxies at all, voids. This configuration can be imagined as similar to human populations on Earth, where the clusters are big cities, filaments highways with nearby towns and the voids regions of sparse inhabitation.

It has also been determined that galaxies differ based on the density of their environ- ment. In clusters galaxies are more likely in a later stage of evolution: larger and older. Voids in contrast are territories of small young galaxies. Filaments are intermediate, where many different types of galaxies are found. Filaments also inhabit a variety of environments, inside voids and between dense clusters.

The goal of this thesis is to characterise galaxies in filaments. It is still not well unders- tood how the filament environment affects the evolution of galaxies. In order to gain insight into this problem we utilised publicly available observational data and the expertise of the scientists at the Tartu University Tartu Observatory in identifying galaxy configurations. As the result of this work we found that galaxies in filaments are less star forming and general- ly more evolved than would be expected based on density alone. However more research is needed to fully understand the nature of galaxies.