Krips, Melanie (2005). High Resolution Multi-Wavelength Study of Active Galaxies. PhD thesis, Universität zu Köln.


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This PhD thesis presents a study of active galaxies carried out from cm- to mm-wavelengths with high angular resolution. The mechanism of the activity in these objects is supposed to be strongly correlated with the accretion of matter onto a super-massive black hole in their centres. One approach to increase the understanding of these highly interesting sources is to observe and analyse the molecular gas. The characteristics of its distribution and dynamics are indispensible diagnostic tools to investigate the accretion processes at different angular scales. A second approach is the study of emission originating in the direct vicinity of the black hole, such as non-thermal radio emission. To account for different activity levels, five objects were chosen ranging from nearby, Low Luminosity Active Galaxies (LLAGs; NGC3718 at z=0.003 and NGC1068 at z=0.004) to higher redshifted, High LAGs (HLAGs; HE1029-1831 at z=0.039, 3C48 at z=0.367, and Q0957+561 at z=1.414). The first two sources are part of the NU(clei of)-GA(laxy) project, that aims at analysing the distribution and kinematics of the molecular gas at high angular resolution/sensitivity in a sample of 30 nearby LLAGs. HE1029-1831 is part of a complementary sample of nearby HLAGs with similar aims. All sources were observed in carbon-monoxide (CO), known to be a good molecular gas tracer, with the IRAM Plateau de Bure Interferometer (PdBI) providing high sensitivity and high angular resolution. CO emission was detected in all five galaxies. In NGC3718, the molecular gas disk, having roughly two hundred million solar masses, is highly warped. The distribution of the gas reveals large scale asymmetries witnessing a possible tidal tail interaction with a close companion, and as well small scale asymmetries most likely tracing accretion onto the nucleus. The appearance of the molecular gas in NGC1068 is quite complex, too. Besides two spiral arms at a radius of 1kpc and a nuclear bar with a length of roughly 2kpc, a nuclear ring becomes visible. Indications for a strongly rotating and compact nuclear gas component are found in the maps, supporting previous findings. As a byproduct, new information on the mm continuum was gained indicating a turnover in the Spectral Energy Distribution similar to what is detected for the central source of our own galaxy. HE1029-1831 appears to be a gas rich host galaxy with a barred gas distribution and gas mass of 8 Giga sun masses. The striking velocity gradient across the bar indicates a bar-driven gas inflow in this system. The CO emission in 3C48 gives further evidence for a merger hypothesis that was strongly debated in the past. The IRAM PdBI maps show two distinct dynamical systems of which one is centered almost on the nucleus itself and the second one closer to a second bright component that was recently also detected in the Near-Infrared and can be likely associated with a second nucleus. Finally, also in the highest redshifted object of this study, Q0957+561, CO emission was detected towards both lensed images. This is the second system at the redshift range of 1-2 in which CO emission was found. The CO emission is associated with a rotating gas disk of 50 Giga sun masses. As a further gas tracer, HCN was observed in a subsample of the NUGA survey. CO, although being a good gas tracer, preferentially measures low to moderate gas densities and is thus not well suited for comparisons with stellar characteristics such as star formation. HCN, however, is supposed to trace denser parts of the gas. To obtain hence a more complete picture, IRAM 30m observations were carried out to detect HCN in the NUGA galaxies which are regarded as a first step for follow-up interferometric observations. A strong correlation between the Far-Infrared luminosities, being a diagnostic tool for star formation, and HCN luminosities is found in this sample consistent with other studies. To investigate the emission of the central most parts in LLAGN at radio wavelengths and their differences or similarities to HLAGs, snap-shot observations of seven NUGA galaxies with local and very long baseline interferometers were conducted at two different wavelengths. The results for the LLAGs are similar to what is usually found for HLAGs supporting the idea that LLAGs might only be scaled down HLAGs in terms of activity, i.e. the responsible physical processes are similar. Besides compact radio emission, also extended and diffuse emission, including jets, were detected. Furthermore, a strong correlation between radio and X-ray luminosities was found indicating connected emission processes. The radio emission is mainly produced by synchrotron radiation which can be Compton-scattered towards higher energies, thus explaining the observed correlation. This set of radio observations is so far the most sensitive study with the highest angular resolution of such weak radio LLAGs.

Item Type: Thesis (PhD thesis)
Translated title:
Studie über aktive Galaxien bei verschiedenen Wellenlängen und hoher räumlicher AuflösungGerman
CreatorsEmailORCIDORCID Put Code
Krips, Melaniekrips@þh1.uni-koeln.deUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-14439
Date: 2005
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:
Aktive Galaxien , Molekulares Gas , Radiokontinuum , AkkretionsmechanismenGerman
active galaxies , molecular gas , radio continuum , accretion mechanismEnglish
Date of oral exam: 2 February 2005
NameAcademic Title
Eckart, AndreasProf.Dr
Refereed: Yes


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