Siegel der Universität

Universität zu Köln
Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Nearby QSOs: A sample of low-luminosity type-1 QSOs

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Active galactic nuclei (AGN) have been subject to lively discussions in extragalactic astrophysics for many years. A unified model has been established explaining the numerous appearances of AGN with varying orientation relative to the line of sight.

Other models deal with the evolution of AGN and the interaction between the active nucleus and the galaxy hosting it. These models take account of enhanced star formation during the evolutionary process and the demand of an abundant supply of material to fuel the AGN.

To gather further insights and to be able to test existing models of AGNs, the environment hosting the nucleus should be studied in more detail. Therefore it is necessary to separate the AGN and star-burst regions and determine the properties of the hosts stellar population and interstellar medium.
Quasi-stellar objects (QSOs) with their exceptionally optically bright nuclei form a very interesting subgroup among AGN, since they are the most active ones of their species. Though, because of the nuclei's dominating radiation outshining their surroundings, it is challenging to observe the galaxies that host QSOs.

Nevertheless, with sophisticated observation techniques, namely with the use of Interferometers such as IRAM or BIMA in the mm-wavelength - or LBT and VLT in the NIR domain, high resolution imaging observations of the closest of these objects can be performed. In combination with additional multi-wavelength data, detailed studies of the properties of nearby QSO host galaxies are possible.

Conclusions from these nearby objects again allow a detailed interpretation of high-z QSO host data.

Our Sample

  • Our sample is formed by a set of closest QSOs for which detailed studies of their hosts can be performed.
  • The sources were selected from the Hamburg/ESO survey for bright QSOs (Wisotzki+00).
  • Only objects with a redshift z < 0.06 have been selected. At the chosen redshift range several important diagnostic emmission and absorption lines, such as the CO(2-0) rotation vibrational band head absorption, are still accessable in the K-band.


Busch et al. analyze near-infrared longslit spectra of eleven sources. Diagnostic line ratios point at an excitation due to the mixing of star formation and nuclear activity. Black hole mass estimates from the broad components of hydrogen recombination lines are used to study the M-L relation and support the results of Busch et al. (2014) that LLQSO are located below the M-L relation of inactive galaxies.
For details, read Busch et al. 2016: A low-luminosity type-1 QSO sample. V. Overluminous host spheroids and their excitation mechanisms!
Moser et al. study low CO transitions of three sources with the Submillimeter Array (SMA). We derive molecular and dynamical masses. The data indicates that the centres of the observed LLQSOs are heavily affected by violent star formation.
For details, read Moser et al. 2016: A low-luminosity type-1 QSO sample . IV. Molecular gas contents and conditions of star formation in three nearby Seyfert galaxies!
Tremou et al. analyze optical spectra from the Hamburg/ESO survey (HES) and the Six Degree Field Galaxy Survey (6dFGS) of all 99 sources. In the BPT diagnostic diagram only 50-60% show clear AGN ionization. This points at a significant contribution of star formation to the ionization of these sources.
For details, read Tremou et al. 2015: A low-luminosity type-1 QSO sample. III. Optical spectroscopic properties and activity classification!
We analyze near-infrared integral-field spectroscopy data of the LLQSO HE 1029-1831. We observe circumnuclear star formation regions and determine their star formation history. At least in this particular case, the offset in published MBH-Lbulge relations of inactive galaxies (as discussed in Busch+ 2014) is caused by younger stellar populations and thus a lower mass-to-light ratio.
For details, read Busch et al. 2015: A low-luminosity type-1 QSO sample: II. Tracing circumnuclear star formation in HE 1029-1831 with SINFONI!
Busch et al. analyze 20 LLQSOs in the near-infrared JHK-bands: A careful bulge-disk-bar-AGN decomposition with BUDDA provides bulge-luminosities. We show that the observed LLQSOs do not follow published MBH-Lbulge relations of inactive galaxies.
For details, read Busch et al. 2014: A low-luminosity type-1 QSO sample. I. Overluminous host spheroidals or undermassive black holes!

People currently working on this Project

  • Gerold Busch
  • Andreas Eckart
  • Nastaran Fazeli
  • Lydia Moser
  • Julia Scharwächter
  • Mónica Valencia-S.