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Active Galactic Nuclei in galaxy surveys: Empirical paths to the fiery hearts of cosmic beasts
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
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. , p. 47
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: urn:nbn:se:uu:diva-308359ISBN: 978-91-554-9765-1 (print)OAI: oai:DiVA.org:uu-308359DiVA, id: diva2:1049505
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
List of papers
1. The different neighbours around Type-1 and Type-2 active galactic nuclei
Open this publication in new window or tab >>The different neighbours around Type-1 and Type-2 active galactic nuclei
2014 (English)In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 10, no 6, p. 417-420Article 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.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-228468 (URN)10.1038/NPHYS2951 (DOI)000336969500016 ()
Available from: 2014-07-15 Created: 2014-07-15 Last updated: 2017-12-05Bibliographically approved
2. AGN luminosity and stellar age: two missing ingredients forAGN unification as seen with iPTF supernovae
Open this publication in new window or tab >>AGN luminosity and stellar age: two missing ingredients forAGN unification as seen with iPTF supernovae
Show others...
2017 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 837, no 2, article id 110Article in journal (Refereed) Published
Abstract [en]

Active galactic nuclei (AGNs) are extremely powerful cosmic objects, driven by accretion of hot gas upon super-massive black holes. The zoo of AGN classes is divided into two major groups, with Type-1 AGNs displaying broad Balmer emission lines and Type-2 narrow ones. For a long time it was believed that a Type-2 AGN is a Type-1 AGN viewed through a dusty kiloparsec-sized torus, but an emerging body of observations suggests more than just the viewing angle matters. Here we report significant differences in supernova (SN) counts and classes in the first study to date of SNe near Type-1 and Type-2 AGN host galaxies, using data from the intermediate Palomar Transient Factory, the Sloan Digital Sky Survey Data Release 7, and Galaxy Zoo. We detect many more SNe in Type-2 AGN hosts (size of effect similar to 5.1 sigma) compared to Type-1 hosts, which shows that the two classes of AGN are located inside host galaxies with different properties. In addition, Type-1 and Type-2 AGNs that are dominated by star formation according to Wide-field Infrared Survey Explorer colors m(W1) - m(W2) < 0.5 and are matched in 22 mu m absolute magnitude differ by a factor of ten in L[O III] lambda 5007 luminosity, suggesting that when residing in similar types of host galaxies Type-1 AGNs are much more luminous. Our results demonstrate two more factors that play an important role in completing the current picture: the age of stellar populations and the AGN luminosity. This has immediate consequences for understanding the many AGN classes and galaxy evolution.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-308356 (URN)10.3847/1538-4357/aa5d5a (DOI)000401172400008 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2016-11-24 Created: 2016-11-24 Last updated: 2017-06-15Bibliographically approved
3. Data-driven dissection of emission-line regions in Seyfert galaxies
Open this publication in new window or tab >>Data-driven dissection of emission-line regions in Seyfert galaxies
2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 596, no A20Article in journal (Refereed) Published
Abstract [en]

Aims. Indirectly resolving the line-emitting gas regions in distant active galactic nuclei (AGN) requires both high-resolution photometry and spectroscopy (i.e. through reverberation mapping). Emission in AGN originates on widely different scales; the broad-line region (BLR) has a typical radius less than a few parsec, the narrow-line region (NLR) extends out to hundreds of parsecs. But emission also appears on large scales from heated nebulae in the host galaxies (tenths of kpc). Methods. We propose a novel, data-driven method based on correlations between emission-line fluxes to identify which of the emission lines are produced in the same kind of emission-line regions. We tested the method on Seyfert galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) and Galaxy Zoo project. Results. We demonstrate the usefulness of the method on Seyfert-1s and Seyfert-2 objects, showing similar narrow-line regions (NLRs). Preliminary results from comparing Seyfert-2s in spiral and elliptical galaxy hosts suggest that the presence of particular emission lines in the NLR depends both on host morphology and eventual radio-loudness. Finally, we explore an apparent linear relation between the final correlation coefficient obtained from the method and time lags as measured in reverberation mapping for Zw229-015.

National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:uu:diva-308352 (URN)10.1051/0004-6361/201628752 (DOI)000390797900058 ()
Funder
Max Planck Society
Available from: 2016-11-24 Created: 2016-11-24 Last updated: 2017-11-29Bibliographically approved
4. Our Sky Now And Then: Searches For Lost Stars And Impossible Effects As Probes Of Advanced Extraterrestrial Civilizations
Open this publication in new window or tab >>Our Sky Now And Then: Searches For Lost Stars And Impossible Effects As Probes Of Advanced Extraterrestrial Civilizations
2016 (English)In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 152, no 3, article id 76Article in journal (Refereed) Published
Abstract [en]

Searches for extraterrestrial intelligence using large survey data often look for possible signatures of astroengineering. We propose searching for physically impossible effects caused by highly advanced technology by carrying out a search for disappearing galaxies and Milky Way stars. We select similar to 10 million objects from USNO-B1.0 with low proper motions (mu < 20 mas yr(-1)) imaged on the sky in two epochs. We search for objects not found at the expected positions in the Sloan Digital Sky Survey (SDSS) by visually examining images of similar to 290,000 USNO-B1.0 objects with no counterpart in the SDSS. We identify some spurious targets in the USNO-B1.0. We find one candidate of interest for follow-up photometry, although it is very uncertain. If the candidate eventually is found, it defines the probability of observing a disappearing-object event in the last decade to less than one in one million in the given samples. Nevertheless, because the complete USNO-B1.0 data. set is 100 times larger than any of our samples, we propose an easily accessible citizen science project in search of USNO-B1.0 objects that have disappeared from the SDSS.

Keyword
astrobiology, extraterrestrial intelligence, surveys
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-305484 (URN)10.3847/0004-6256/152/3/76 (DOI)000383804300024 ()
Available from: 2016-10-18 Created: 2016-10-18 Last updated: 2017-11-29Bibliographically approved

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