Public defence in Space science and technology, M.Sc.(Tech.) Irene Varglund

The title of the thesis: A multifrequency view on the characteristics and evolution of narrow-line Seyfert 1 galaxies

Thesis defender: Irene Varglund
Opponent: Prof. Dragana Ilić, University of Belgrade, Serbia
Custos: Prof. Anne Lähteenmäki, Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering

Narrow-line Seyfert 1 (NLS1) galaxies behave similarly to their older and bigger quasar siblings, despite their smaller size and earlier evolutionary stage. Although the supermassive black holes in these sources range from low to intermediate, these sources are still capable of launching one of the most energetic phenomena in the Universe: near lightspeed travelling powerful plasma jets that strongly emit in radio. Originally these sources were classified as non-detectable at radio frequencies, however, this has been proven wrong by, for example, detections at the Metsähovi Radio Observatory. As a result, astronomers have had to rethink the traditional jet paradigm as well as NLS1 galaxy classification system. One of the main issues in studying these extraordinary sources is that they are difficult to accurately classify as their key spectral line features can be highly similar to other sources. 

In this doctoral thesis, NLS1 galaxies have been studied in both optical and radio frequencies. The main aims of this thesis have been to obtain as clean a sample of NLS1 galaxies as possible, study the host galaxy morphologies of both jetted and non-jetted sources, and to study the diverse radio properties of NLS1 galaxies. Through this it is possible to obtain a more comprehensive understanding of the NLS1 galaxy class which can guide in understanding AGN and AGN evolution in general. 

One of the main achievements of this thesis is obtaining the largest and cleanest sample of NLS1 galaxies currently available through meticulous scrutinizing of spectral line features. Other results include providing more evidence that both the jetted and non-jetted NLS1 galaxies have predominantly disk-like host galaxies, thus contradicting the traditional jet paradigm. Furthermore, some NLS1 galaxies showcase unforeseen AGN variability, possibly showcasing a completely new type of variability. Finally, this thesis provides undisputable proof that NLS1 galaxies as a class can be detected at radio frequencies. 

This thesis and future research will be capable of providing irrefutable proof of NLS1 galaxy properties. The sample obtained in this thesis will be further studied in upcoming studies with higher resolution data to guarantee a 100% clean sample. With a completely clean sample, it is finally possible to study the characteristics of this galaxy class at various frequencies without the interference of impostor sources. 

Key words: NLS1 galaxies, supermassive black hole, astrophysical jets, active galaxies

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/

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Doctoral theses in the School of Electrical Engineering: https://aaltodoc.aalto.fi/handle/123456789/53