Diffuse interstellar bands as a tool for exploring galactic interstellar medium

Vogrinčič, Rok (author), Kos, Janez (mentor)

Diffuse interstellar bands (DIBs) are interstellar absorption features observed in spectra of stars reddened by dust. These bands were discovered in the early 20th century, and to date, approximately 500 of them have been identified in the optical and near-infrared wavelengths. Their exact nature is unknown, but they are likely linked to large carbon-based molecules in gaseous form, that are stable in the cold diffuse interstellar medium. Only recently has the Fullerene cation $C_{60}$ been confirmed as a carrier through laboratory studies focused on a few near-infrared DIBs. DIBs are characterized by their broad widths, spanning several \AA, which is why they are referred to as diffuse. The goal of this thesis is to explore DIBs in approximately one million spectra observed in the wavelength range from 4700 to 7900 \AA, obtained by the GALAH survey. We produce $\sim$400,000 spectra of interstellar medium (ISM) absorption features and present the first extensive DIB catalogue of the GALAH survey which contains 183 DIBs. We create a synthetic DIB spectrum at unit reddening which may permit us to narrow down the possible carriers of DIBs and explore the composition of the ISM and ultimately better model dust and star formation as well as to correct Galactic and extragalactic observations. We find that DIBs are a valuable tool for studying the galactic ISM. By utilizing the extensive DIB database from the GALAH sky survey and precise measurements of stellar positions and distances provided by Gaia, we can investigate both DIB clouds and different components of the ISM, such as interstellar dust, neutral and molecular hydrogen. We find positive and moderately high correlation between DIBs and dust reddening using various surveys of interstellar dust. We utilize two DIB families based on the sensitivity of DIBs to UV radiation. Correlations between DIBs, reddening, and other ISM tracers reveal some commonalities between the DIB families. We also study the spatial distribution of DIB carriers, explore DIB dependencies on other ISM tracers, and investigate Doppler splitting and positions of DIB clouds in the Galaxy. Our findings align with previous studies, but comparisons are limited due to diverse observing instruments, methods and sometimes poorly sampled parts of the sky.

• Language: English
• Keywords: methods: data analysis, Astronomical data bases: catalogues, Astronomical data bases: surveys, ISM: abundances, ISM: clouds, ISM: dust, extinction, ISM: general, ISM: lines and bands, ISM: molecules, ISM: structure
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2023
• PID: 20.500.12556/RUL-151234
• COBISS.SI-ID: 166387459
• Publication date in RUL: 01.10.2023

Secondary language

• Language: Slovenian
• Title: Difuzni medzvezdni pasovi kot orodje za raziskovanje galaktične medzvezdne snovi

Abstract

Difuzni medzvezdni pasovi (DIB) so medzvezdne absorpcije, ki jih opazimo v spektrih zvezd, ki so pordečene od medzvezdnega prahu. Te pasove so odkrili v začetku 20. stoletja, do danes jih je bilo v območju vidne in bližnje infrardeče svetlobe identificiranih približno 500. Njihov natančen izvor ni znan, so pa verjetno povezani z velikimi molekulami na osnovi ogljika, v plinasti obliki, ki so stabilne v hladni difuzni medzvezdni snovi. Šele pred kratkim je bil z laboratorijskimi študijami, osredotočenimi na nekaj DIBov v bližnjem infrardečem območju valovnih dolžin, kot nosilec DIBa potrjen kation fulerena $C_{60}$. DIBe imenujemo difuzne, saj so za njih značilne široke absorpcijske črte, ki merijo nekaj \AA. Cilj tega dela je raziskati DIBe v približno milijonu zvezdnih spektrov, opazovanih v območju valovnih dolžin med 4700 in 7900 \AA, pridobljenih s pregledi neba GALAH. V delu ustvarimo $\sim $400.000 absorpcijskih spektrov medzvezdne snovi (ISM spektri) in predstavimo prvi obsežen katalog 183 DIBov opazovanih s pregledi neba GALAH. Ustvarimo sintetični spekter DIBov pri pordečitvi ene magnitude, kar nam lahko omogoči, da zožimo možne kandidate za nosilce DIBov in raziščemo sestavo medzvezdne snovi, izboljšamo fizikalne modele prahu in nastajanja zvezd ter naredimo popravke pri galaktičnih in izven-galaktičnih opazovanjih. Ugotavljamo, da so DIBi dragoceno orodje za raziskovanje galaktične medzvezdne snovi. Z uporabo obsežne podatkovne baze DIBov iz pregleda neba GALAH in natančnih meritev položajev in razdalj do zvezd, ki jih zagotavlja vesoljska misija Gaia, lahko raziskujemo tako oblake DIBov kot različne komponente medzvezdne snovi: medzvezdni prah, nevtralni in molekularni vodik. Z uporabo različnih raziskav medzvezdnega prahu, izmerimo pozitivno in zmerno visoko korelacijo med DIBi in pordečitvijo zaradi prahu. DIBe glede na njihovo občutljivost na ultravijolično (UV) sevanje razdelimo v dve družini. Korelacije med DIBi, pordečitvijo in drugimi sledilci medzvezdne snovi, razkrivajo nekatere skupne značilnosti med družinami DIBov. Preučujemo tudi prostorsko porazdelitev nosilcev DIBov, raziskujemo odvisnost DIBov od drugih sledilcev medzvezdne snovi ter Dopplersko razcepitev DIBov in položaje oblakov DIB nosilcev v Galaksiji. Naše ugotovitve so v skladu s prejšnjimi študijami, vendar so primerjave omejene zaradi različnih opazovalnih instrumentov, metod in v nekaterih primerih zaradi slabo vzorčenih delov neba.

• Keywords: metode: analiza podatkov, Astronomske baze podatkov: katalogi, Astronomske baze podatkov: raziskave, ISM: zastopanost, ISM: oblaki, ISM: prah, ekstinkcija, ISM: splošno, ISM: črte in pasovi, ISM: molekule, ISM: struktura