Home Research Interests Publications Conference contributions CV Resources


  
 • Extragalactic Globular Cluster Systems
    • Globular Clusters in Dwarf Galaxies
    • Nuclear Globular Clusters
    • Horizontal branch morphology
    • Galaxy formation and evolution
KK 197
Top: Hubble Space Telescope (ACS) image (from V and I filters) of the dwarf spheroidal galaxy KK 197. A zoom at its nuclear GC is shown in the bottom left corner. Bottom: Spectroscopic age and metallicity estimate using full spectrum fitting analysis. Two highly probable solutions for GC age at same metallicity reveals the effect of hot, blue HB stars (Georgiev et al. in prep.).
kk197_spec_70.jpg
My main research interests are related to the properties of stellar and star cluster populations in dwarf galaxies in the context of galaxy formation and evolution.

According to the hierarchical galaxy formation scenario, the assembly of massive present-day galaxies involved numerous mergers of small pre-galactic entities. In particular, dwarf irregular galaxies (the main targets of my research) are widely regarded as being the closest match of such galaxy building blocks.

Hence, a study of their old globular clusters (GCs), whose properties reflect the physical conditions at the time of their early formation, and comparison with GCs in massive galaxies can be used to quantify the contribution of dwarf galaxies to the assembly of today's massive galaxies and their globular cluster system.

An excellent example for the need of such a study is the Milky Way globular cluster system, because it is found to harbor a sub-population of GCs whose properties (colors, luminosities, chemical compositions, horizontal-branch morphologies, structural parameters and orbital kinematics) suggest that they might have formed in lower-mass satellites and were later incorporated into the Milky Way. In particular, the GC properties in combination with the specific frequencies (the number of GCs per unit galaxy luminosity/mass, i.e. the specific GC formation efficiency) are very useful tools to perform the aforementioned study.

The horizontal branch (HB) morphology of old GCs is an important parameter because it can significantly affect the age of the GC estimated from  integrated light optical absorption line indices spectroscopy. Hot, blue HB stars enhance high-order Balmer lines which render younger GC age. To tackle this GCs' age-HB degeneracy, I am working on a method that utilizes a full spectrum fitting analysis.

A robust estimate of the GCs' properties (age, metallicity, mass, structural parameters) allows one to draw conclusions on the host galaxy star formation history, driven by accretions, mergers and galaxy-galaxy interactions in galaxy groups and clusters.


Last update November 2011
Also links back/forward to: