University of Cologne 1st Physikalisches Institut projects

Codes: UK03

Physics of Low-Luminosity Radio Nuclei

Aim of this project is to address the global radio and molecular gas properties of a representative  sample of galaxies hosting low-luminosity quasi-stellar objects. An abundant supply of gas is  necessary to fuel both the active galactic nucleus and any circum-nuclear star-burst activity of  quasi-stellar objects (QSOs). The connection between ultra-luminous infrared galaxies and the host  properties of QSOs is a subject to a controversial debate. Nearby low-luminosity QSOs are ideally suited to study the properties of their host galaxies because of their higher frequency of occurrence  compared to high-luminosity QSOs in the same comoving volume and because of their small cosmological distance.

Representative samples are selected from QSO and radio surveys. The abundance of molecular gas and the importance of star formation is being probed through infrared- and mm-spectroscopy. The nuclear activity is tested through radio interferometric observations that aim at distinguishing between contributions from  non-thermal nuclei and super nova remanents in these low luminosity nuclei.

Contact: Prof. Dr. Andreas Eckart (eckart@ph1.uni-koeln.de)

Site: Cologne, 1st Physics Institute, University of Cologne

Codes: UK04

NIR Studies of the Black Hole at the Center of our Galaxy

The compact source Sgr A* that can be associated with the massive black hole at the center of the Milky Way shown a strong variability from the radio to the X-ray wavelength domain. The most recent results from a near-infrared observations revealed polarized NIR flare emission of Sgr A*. This can be interpreted as emission from spots which are on relativistic orbits around Sgr A*. Emission from a possible jet or outflow from such a disk can also contribute. We also find that the variable NIR emission of Sgr A* is highly polarized and consists of a contribution of a non- or weakly polarized main flare with highly polarized sub-flares. The flare activity shows a possible quasi-periodicity of 20 min consistent with previous observations. The highly variable and polarized emission supports that the NIR emission is non-thermal and is consistent with emission from a jet or temporary disk. Alternative explanations for the high central mass concentration involving boson or fermion balls are increasingly unlikely. Observations with the VLT, VLTI and in future with the LBT will allow us to better discriminate Sgr A* from the surrounding stars, to register the light curves with a higher signal to noise, and to further develop the theoretical models.

Contact: Prof. Dr. Andreas Eckart (eckart@ph1.uni-koeln.de)

Site: Cologne, 1st Physics Institute, University of Cologne

 
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