Universität zu Köln

Vitale, Mariangela (2014). Multi-wavelength Studies of Active Galactic Nuclei: The Link between Black Hole Accretion and Galaxy Evolution. PhD thesis, Universität zu Köln.

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Abstract

The discovery of general correlations between black hole and properties of the host galaxy has led to the hypothesis of a co-evolution between the two. The black hole-host co-evolution might be explained by black hole accretion and stellar mass build-up of the galaxy being fueled by the same gas. Gas is made available once a galaxy is created, or is gained in successive interactions with neighboring galaxies. The black hole-host co-evolution is one of the most debated topics of modern extragalactic astrophysics. However, strong observational evidence of it is still missing. Active Galactic Nuclei (AGN) - the bright, accreting black holes at the center of massive galaxies - can play an important role in shaping the physical properties of the galaxies they occupy. Most of galaxies are found to be either active (they form new stars) and blue spirals, or passive and red ellipticals. Galaxies having intermediate properties are often found to harbor an AGN at their centers. This fact has been related to some AGN showing jets and gas outflows, which might interact with the interstellar medium of the galaxies, creating or destroying the conditions for star formation. A combined multi-wavelength study of AGN and hosting galaxies at intermediate redshifts can help us probing the degree of co-evolution, and the way the so-called AGN feedback may regulate star formation in galaxies. Feedback might lead to the morphological and color transformation of the host. To observe the transformation, I have studied large samples of normal galaxies and AGN hosts in the optical and radio domains. This approach is particularly useful, since optical spectral information can trace host galaxy properties, while AGN activity is visible in the radio. Moreover, this study allows investigating the connection between optical and radio emission from galaxies, and their possible common origin. This PhD work explores the chance of an evolutionary sequence for galaxies of a given mass. The sequence would start with merger/interaction triggered bursts of star formation, followed by stellar mass build-up and accretion onto black hole. Once the black hole at the center of the galaxy is active, it might induce once-in-a-time or recurrent AGN feedback, eventually stopping the star-formation process in the hosting galaxy. From this point on, galaxies evolve passively. The stages of galaxy evolution can be represented by spectral classes as defined by optical emission-line diagnostic diagrams. The latter are based on the strength of low-ionization optical lines. The classes are: star-forming, composites (galaxies with mixed contribution to line emission, coming from both star formation and AGN activity), Seyfert, and LINER galaxies.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Vitale, Mariangela vitale@ph1.uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-57299
Date:	April 2014
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	Natural sciences and mathematics Physics
Uncontrolled Keywords:	Keywords Language Galaxies English Black hole UNSPECIFIED Galaxy evolution UNSPECIFIED
Date of oral exam:	9 April 2014
Referee:	Name Academic Title Eckart, Andreas Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/5729