Young stellar structures in four nearby galaxies
  A cluster finding method was developed and applied in four Local Group
Galaxies (SMC, M31, M33 and NGC 6822). The aim is to study the young stellar
population of these galaxies by identifying stellar structures in small and
large scales. Also our aim is to assess the potential of using the observations
of ESA's space mission Gaia for the study of nearby galaxies resolved in stars.
The detection method used is a Hierarchical technique based on a modified
friends of friends algorithm. The identified clusters are classified in five
distinct categories according to their size. The data for our study were used
from two ground based surveys, the Local Group Galaxy Survey and the Maggelanic
Clouds Spectroscopic Survey. Relatively young main sequence stars were selected
from the stellar catalogs and were used by the detection algorithm. Multiple
young stellar structures were identified in all galaxies with size varying from
very small scales of a few pc up to scales larger than 1 kpc. The same cluster
finding method was used in six spiral galaxies observed with the Hubble Space
Telescope in a previous study. The average size in each category of the
identified structures in the Local Group galaxies presents values consistent
with the identified structures in the relatively distant spiral galaxies. Most
of the structures consist of stars within the observational limits of Gaia's
instruments. It is expected that Gaia's observations will contribute
significantly on the study of the young stellar population of nearby galaxies.
