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The different neighbours around Type-1 and Type-2 active galactic nuclei
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
2014 (English)In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 10, no 6, 417-420 p.Article in journal (Refereed) Published
Abstract [en]

One of the most intriguing open issues in galaxy evolution is the structure and evolution of active galactic nuclei (AGN) that emit intense light believed to come from an accretion disk near a super massive black hole(1,2). To understand the zoo of different AGN classes, it has been suggested that all AGN are the same type of object viewed from different angles(3). This model-called AGN unification-has been successful in predicting, for example, the existence of hidden broad optical lines in the spectrum of many narrow-line AGN. But this model is not unchallenged(4) and it is debatable whether more than viewing angle separates the so-called Type-1 and Type-2 AGN. Here we report the first large-scale study that finds strong differences in the galaxy neighbours to Type-1 and Type-2 AGN with data from the Sloan Digital Sky Survey (SDSS; ref. 5) Data Release 7 (DR7; ref. 6) and Galaxy Zoo(7,8). We find strong differences in the colour and AGN activity of the neighbours to Type-1 and Type-2 AGN and in how the fraction of AGN residing in spiral hosts changes depending on the presence or not of a neighbour. These findings suggest that an evolutionary link between the two major AGN types might exist.

Place, publisher, year, edition, pages
2014. Vol. 10, no 6, 417-420 p.
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-228468DOI: 10.1038/NPHYS2951ISI: 000336969500016OAI: oai:DiVA.org:uu-228468DiVA: diva2:734249
Available from: 2014-07-15 Created: 2014-07-15 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Active Galactic Nuclei in galaxy surveys: Empirical paths to the fiery hearts of cosmic beasts
Open this publication in new window or tab >>Active Galactic Nuclei in galaxy surveys: Empirical paths to the fiery hearts of cosmic beasts
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Some galaxies emit excessive amounts of light from their centers, caused by accretion of gas onto super-massive black holes (SMBH). These galactic cores are often referred to as Active Galactic Nuclei (AGN) and they come in many different forms, distinguishable by their emission properties. The AGN classes fall into two major categories: those with narrow Balmer lines, and those with broad Balmer lines. The AGN Unification theory of radio-quiet AGN predicts the two classes to differ mainly in the viewing angle of the observer who may, or may not, see the central engine due to dust obscuration in the foreground.

In this PhD thesis, I explore the limits of the radio-quiet AGN Unification. In its most famous and simple form, the obscurer is a parsec-sized dust doughnut surrounding the accretion disk. I show that the galaxy neighbours to the two types of AGN are different, in disagreement with the simplest form of unification (Paper I). The two AGN classes differ in their [OIII]5007 luminosity, as well as in their star-formation history (Paper II), suggesting that we must incorporate galactic dust into the concept of AGN Unification, as well as differences in the luminosity of the central engine. I also present a novel, data-driven method to pinpoint the relative spatial origin of certain emission lines in AGN (Paper III). Finally, we conclude the thesis by discussing an anti-transient survey targeted at finding signatures of extra-terrestrial intelligence (Paper IV). This survey can, as a side effect, also be useful to find extreme, variable AGN that challenge both AGN Unification and evolutionary theories.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 47 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1458
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:uu:diva-308359 (URN)978-91-554-9765-1 (ISBN)
Public defence
2017-01-13, Polhemsalen, Ångströmslaboratoriet, Lägerhyddsv. 1, Uppsala, 13:30 (English)
Opponent
Supervisors
Available from: 2016-12-22 Created: 2016-11-24 Last updated: 2016-12-28Bibliographically approved

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Villarroel, Beatriz RodriguezKorn, Andreas J.

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