Abstract details

I'll present a summary of our systematic and homogeneous analysis of the surface number counts and population gradients of the resolved stars in surroundings of the nearby disk galaxies, observed with space- (Hubble & Spitzer) and ground-based telescopes. We examine the radial (in-plane) and vertical (extraplanar) distributions as a function of stellar age by tracking changes in the color-magnitude diagram of face-on and edge-on galaxies. In particular, I will focus on our recent extensive study of three Local Group disk galaxies, IC1613, NGC6822 and IC10. Our data show that the scale length and height of a stellar population increases with age, with oldest of the detected red giant branch population (RGB) identified at large galactocentric radii or extraplanar height, out to typically a few kpc. In the most massive of the studied galaxies there is evidence for a break in number density and color gradients of evolved RGB stars, which plausibly correspond to the thick disk and halo components of the galaxies. The results may imply that all massive spiral galaxies not only have a thick disk but also poses an extended halo, while dwarf disk galaxies have solely a thin/thick disk component. When complemented with detailed chemical abundance and kinematic information from spectra of these stars, our optical/near-IR photometric data will allow us to shed light on fundamental questions about the evolution of disk galaxies, such as disk heating versus merger scenarios and a role of these mechanisms in forming the stellar disks and halo.