Structural parameters of compact stellar systems

The objective of this thesis is to establish the observational properties and structural parameters of compact stellar systems that are brighter or larger than the standard globular cluster. We consider a standard globular cluster to be fainter than MV ~ -11 mag and to have an effective radius of ~3 pc. We perform simulations to further understand observations and the relations between fundamental parameters of dense stellar systems. With the aim of establishing the photometric and structural properties of Ultra- Compact Dwarfs (UCDs) and extended star clusters we first analyzed deep F475W (Sloan g) and F814W (I) Hubble Space Telescope images obtained with the Advanced Camera for Surveys. We fitted the light profiles of ~5000 point-like sources in the vicinity of NGC 4874 one of the two central dominant galaxies of the Coma cluster. Also, NGC 4874 has one of the largest globular cluster systems in the nearby universe. We found that 52 objects have effective radii between ~10 and 66 pc, in the range spanned by extended star clusters and UCDs. Of these 52 compact objects, 25 are brighter than MV ~ -11 mag, a magnitude conventionally thought to separate UCDs and globular clusters. We have discovered both a red and a blue subpopulation of Ultra-Compact Dwarf (UCD) galaxy candidates in the Coma galaxy cluster.