Universität zu Köln

Misquitta, Persis ORCID: 0000-0003-3168-9448 (2023). An Optical Spectroscopic Study of Interacting Galaxies at Low/Intermediate Redshift. PhD thesis, Universität zu Köln.

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Abstract

Evolution of galaxies, how their central supermassive black holes, stellar populations, and morphology grow and change over cosmic time, is one of the fundamental questions in astrophysics. External and internal processes can bring about this evolution. Interaction of galaxies is an external process where two or more galaxies collide against each other or experience a fly-by. It is important to study galaxies in different phases of inter- action and over the electromagnetic spectrum in order to have a concrete understanding of the process. Within the scope of this thesis, we study a total of 12 pairs/triplets of interacting galaxies. Ten out of twelve of these galaxy pairs/triplets were chosen from a larger sample of 500 SDSS-FIRST selected galaxies. With eight pairs and two triplets, the sample consists of 22 galaxies in total. The remaining two galaxy pairs are SDSSJ134420.86+663717.8 and Mrk231. SDSSJ134420.86+663717.8 is made up of two galaxies, while Mrk231 is in a late stage merger, such that the progenitor galaxies are no longer distinguishable. All three projects are based on optical long slit spectroscopy of galactic nuclear regions using the Multi-Object Double Spectrographs mounted on the Large Binocular Telescope (LBT) located on Mount Graham in Arizona. Additionally, in the case of Mrk231, six off-nuclear positions were observed. Archival mid-infrared and radio continuum data were available for the SDSS-FIRST sample. At least one of the two, or three, galaxies involved in an interaction was detected by FIRST at 1.4 GHz. The archival data were used in conjunction with the LBT observations to check for possible correlations between the emission in optical, mid-infrared, and radio regimes. The nuclear ionisation ratios of the radio-detected galaxies in our sample fall in the composite or transition region of the optical diagnostic diagram. Additionally, the radio-detected galaxies in our sample host the more massive supermassive black hole in the pair or triplet of interacting galaxies. SDSSJ134420.86+663717.8 consists of two galaxies, A and B. Based on the nature of the optical spectra, galaxy A seems to host a Seyfert Type 1 active galactic nucleus, while the nuclear region of galaxy B seems to have a star-forming nature. Both of the nuclei fall in the composite or transition region of the optical diagnostic diagram. The mass of the supermassive black hole at the centre of galaxy A is ∼ 2×107 M⊙, while the supermassive black hole at the centre of galaxy B has a mass of ∼ 3×107 M⊙. A simple N-body simulation shows that for an almost orthogonal approach of the progenitor galaxies, the resultant model resembles SDSSJ134420.86+663717.8 morphologically and kinematically. Mrk231 is an ultra-luminous infrared, radio-quiet galaxy that seems to be in a late stage of merger, as evidenced by the existence of two tidal tails. The central region of the galaxy hosts a Seyfert Type 1 active galactic nucleus as well as an extremely intense circum-nuclear starburst. The spectrum of the centre of Mrk231 consists of a continuum originating in the extreme starburst overlaid by emission lines from the active galactic nucleus and broad absorption lines from broad absorption line clouds that are associated with the nucleus but located at a distance from it. The mass of the central supermassive black hole is estimated to be ∼ 2×108 M⊙. Broad Hα emission is detected at a distance of ∼ 1.7 kpc from the centre of Mrk231. Such high velocities could be attributed to outflows associated with the active galactic nucleus as well as the extreme starburst happening in the circum-nuclear region of Mrk231. Careful examination of acquisition images taken with the LBT as well as archival SDSS and DSS images shows that in addition to the two previously reported tidal tails, there exists a third diffuse tidal tail-like structure that might be indicative of an interaction with a third (dwarf) galaxy. The study of these 12 pairs/triplets of galaxies shows that interactions lead to energetic phenomena at the centres of at least one of the galaxies involved in the merger. While it is not clear which galaxy gets favoured to be more energetic, it could be connected to the mass of the central supermassive black hole.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Misquitta, Persis misquitta@ph1.uni-koeln.de orcid.org/0000-0003-3168-9448 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-705516
Date:	28 July 2023
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language Galaxy interactions, active galactic nuclei, starburst, star-formation, galaxy evolution, galaxy dynamics and kinematics English
Date of oral exam:	24 February 2023
Referee:	Name Academic Title Eckart, Andreas Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/70551