Gas and dust in early galaxy evolution
Doktorsavhandling, 2021

In order to study the content of distant galaxies without focusing solely on the brightest objects -- the tip of the iceberg -- I developed a tool:  LineStacker. As its name indicates this tool was designed to perform spectral stacking analyses. Stacking allows to shed light on otherwise invisible features, by averaging together observations of many sources from a common galaxy population.

Spectral lines emitted or absorbed by galaxies and the intergalactic medium carry information on the content of galaxies as well as their dynamics. The luminosity of certain atomic and molecular spectral lines is known to correlate with fundamental physical properties of galaxies, such as star formation rate. In addition, the shape of the lines can trace global dynamics of galaxies or peculiar events such as outflows.

In this context, I used LineStacker to study distant galaxies by observing the average spectral lines, or continuum emission, emitted by a particular galaxy population. In this thesis I present the tool LineStacker in detail and with a specific emphasis on the statistical tools included with it.

In addition, I showcase three different analyses where we used LineStacker to study galaxy evolution. In the two first we studied ionized carbon, [CII], in galaxies at redshift z∼6.
One project focused on the faint outflow signatures below the main [CII] line, while the other project focused on the overall [CII] emission from faint, gravitationally lensed galaxies. Finally, in the last analysis, we studied the overall dust mass as well as the comoving dust mass density and their evolution with redshift. The results from all the analyses highlight the power and efficiency of stacking as a method, and the necessity to go beyond studying the brightest objects.

Galaxies: evolution -- Galaxies: high-redshift -- methods: stacking -- methods: data analysis -- techniques: interferometric

EE-salen, Edit-huset, Elektrogården 1, Göteborg
Opponent: Prof, Linda Tacconi, Max Planck Institute for Extraterrestrial Physics, Germany


Jean Baptiste Jolly

Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik

ALMA Lensing Cluster Survey: A spectral stacking analysis of [C II] in lensed z similar to 6 galaxies

Astronomy and Astrophysics,; Vol. 652(2021)

Artikel i vetenskaplig tidskrift

LINESTACKER: A spectral line stacking tool for interferometric data

Monthly Notices of the Royal Astronomical Society,; Vol. 499(2020)p. 3992-4010

Artikel i vetenskaplig tidskrift

A spectral stacking analysis to search for faint outflow signatures in z ∼6 quasars

Astronomy and Astrophysics,; Vol. 631(2019)

Artikel i vetenskaplig tidskrift

ALMA Lensing Cluster Survey: Average dust, gas, and star-formation properties of cluster and field galaxies from stacking analysis

Monthly Notices of the Royal Astronomical Society,; Vol. 526(2023)p. 2423-2439

Artikel i vetenskaplig tidskrift

Galaxer är stora gravitationellt bundna strukturer av gas, damm och mörk materia. De flesta galaxer har ett supermassivt svart hål i deras mitt och består av några hundra miljarder stjärnor. En av de stora frågorna i astronomi är hur dessa galaxer har utvecklats genom universums historia, dvs under de senaste 13.7 miljarder åren.
Genom att titta långt bort i universum ser vi universum så som det var förr i tiden, vilket tillåter oss att se de tidiga stadierna av galaxernas utveckling. Studerandet av dessa tidiga galaxer tillåter oss att förstå hur de har utvecklats till de galaxer vi ser idag i det närliggande universumet.

Den här avhandlingen har två syften: att fokusera på evolutionen av galaxer under de första miljarder åren efter Big Bang och att utveckla en metod for att utmana känslighetsgränsen för observationer. Genom mitt arbete har jag utvecklat en metod och ett verktyg för att stacka radiointerferometrisk spektrallinjedata, LineStacker, som jag sedan använde för att studera gas innehållet i galaxer, mer specifikt undersökte jag joniserat kol i tidiga galaxer. Därutöver har jag även utfört en storskalig studie av evolutionen av damm i galaxer observerade genom gravitationslinser.

Galaxies are large systems of gas, dust, and dark matter gravitationally bound. Most galaxies contain a super-massive black-hole in their center, and are typically composed of a few hundred billion stars. One of the big question of astronomy is how these galaxies have evolved trough the age of the Universe, i.e. in 13.7 billion years. By looking far in space we observe the universe as it was back in time, allowing us to see the early stages of galaxy evolution. Studying these early galaxies allows us to understand how they evolved toward the galaxies that we see today, in the local universe.

The focus of this thesis is two fold: to focus on the evolution of galaxies in the first million years after the Big Bang, and to develop methodology to push the sensitivity limit of observation. Through my work I developed a method for stacking radio-interferometric spectral line data. I then used this tool, LineStacker, to study the gas content of galaxies, more specifically by searching for ionized carbon in early galaxies. Further, I also conducted a large scale study to look at the evolution of the dust in gravitationally lensed galaxies.


Astronomi, astrofysik och kosmologi


Grundläggande vetenskaper



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5038



EE-salen, Edit-huset, Elektrogården 1, Göteborg


Opponent: Prof, Linda Tacconi, Max Planck Institute for Extraterrestrial Physics, Germany

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