The expected imaging capabilities of future Extremely Large Telescopes ( ELTs ) will offer the unique possibility to investigate the stellar population of distant galaxies from the photometry of the stars in very crowded fields .
Using simulated images and photometric analysis we explore here two representative science cases aimed at recovering the characteristics of the stellar populations in the inner regions of distant galaxies .
Specifically : case A ) at the center of the disk of a giant spiral in the Centaurus Group , ( \mu _ { B } \sim 21 , distance of 4.6 Mpc ) ; and , case B ) at half of the effective radius of a giant elliptical in the Virgo Cluster ( \mu _ { I } \sim 19.5 , distance of 18 Mpc ) .
We generate synthetic frames by distributing model stellar populations and adopting a representative instrumental set up , i.e .
a 42 m Telescope operating close to the diffraction limit .
The effect of crowding is discussed in detail showing how stars are measured preferentially brighter than they are as the confusion limit is approached .
We find that ( i ) accurate photometry ( \sigma \sim 0.1 , completeness \mathrel { \hbox to 0.0 pt { \lower 3.0 pt \hbox { $ \sim$ } } \raise 2.0 pt \hbox { $ > $ } } 90 % ) can be obtained for case B ) down to I \sim 28.5 , J \sim 27.5 allowing us to recover the stellar metallicity distribution in the inner regions of ellipticals in Virgo to within \sim 0.1 dex ; ( ii ) the same photometric accuracy holds for the science case A ) down to J \sim 28.0 , K \sim 27.0 , enabling to reconstruct of the star formation history up to the Hubble time via simple star counts in diagnostic boxes .
For this latter case we discuss the possibility of deriving more detailed information on the star formation history from the analysis of their Horizontal Branch stars .
We show that the combined features of high sensitivity and angular resolution of ELTs may open a new era for our knowledge of the stellar content of galaxies of different morphological type up to the distance of the Virgo cluster .