Results on Southern Compact Groups of galaxies
As itemised on the page about observations, a multi-wavelength database leads to a multitude of derived quantities characterising the properties of SCGs and their member galaxies.
Group membership
Group membership is defined by applying the criteria developed by Iovino (2002), based on optical imaging and spectroscopy. HI line observations are used to cross-check the recession velocities of galaxies with HI gas.
HI gas properties
HI line observations provide us with the usual information about the distribution and kinematics of HI gas in galaxies, and in addition an estimate of or upper limit on the amount of intergalactic HI gas present in the groups.
At the same time, HI is an excellent tracer of disturbances, because it is the most volatile component of a galaxy, which accordinly will react first to external forces.
A comparison of the HI properties of galaxies in SCGs with those of field galaxies reveals whether there are any systemactic differences, such as e.g. the removal of gas from the galaxy disks in the course of gravitational interactions, which can lead to HI deficiencies.
All these are essential parameters to know in a comparison of the evolution of galaxies in SCGs with field galaxies and thereby the influence of gravitational interactions and mergers on galaxy evolution.
Signs of gravitational disturbances
As mentioned above, the presence of HI tidal features, such as tails or plumes, are tell-tale signs of galaxy interactions. Optical imaging provides an addtional way of searching for such features in gas-poor galaxies, if the stellar population has reacted to external gravitational forces.
Starburst vs. AGN activity
Optical spectroscopy of the nuclear areas is used to determine which type of activity is ongoing in the central areas of galaxies in SCGs. Radio continuum observations can be used to assist in this determination and also the X-ray properties of nuclear emission sources provide valuable clues.
The distinction of the different types of (circum-)nuclear activity is important for the determination of possible enhancements compared to field galaxies (starburst vs. LINER vs. AGN).
Level and distribution of star formation activity
Based on the currently available database, star formation rates are determined from radio continuum flux densities.
Stellar population studies
Optical and near-infrared imaging provide us with information on the distribution of stars in SCG member galaxies and their colours.
Group dynamics
The dispersions of the member galaxies' recession velocities (primarily from optical spectroscopy) are used to determine the total virialised mass of SCGs studied by us.
Recession velocities and HI line widths also provide crucial inputs to models of interactions of pairs of galaxies in SCGs.
