Context :

Aims : The extraplanar stellar populations of highly-inclined disk galaxies ICÂ 2233 , ICÂ 5052 , NGCÂ 4631 and NGCÂ 5023 are analyzed with the goal to quantify their vertical extent and structure .

Methods : Based on the single-star photometry , we separate different stellar populations and analyze their spatial distribution .

Results : On archival images obtained with the Hubble Space Telescope ACS/WFC the surroundings of these galaxies are well resolved into stars with the red giant population ( RGB ) identified far above the galaxy mid-planes .
We find that there are a profound change in slope of the number density profile of the evolved RGB stars at extraplanar height of 4 - 8 Â kpc , that possibly reflects a truncation of the thick disk and reaching the 2 - 3 times more extended oblate stellar component ( “ the halo ” ) .
This structure is consistent with our previous studies of both edge-on and face-on disk galaxies in the Local Universe ( Tikhonov et al .
2005a , b ) and allow us to improve the spatial model of the stellar components of a typical spiral galaxy .
In NGCÂ 4631 , the revealed asymmetry of its stellar thick disk and halo , is likely caused by the neighbor dwarf galaxy NGCÂ 4627 .
Based on the tip of the red giant branch method ( TRGB ) we estimated a distance of 10.42 \pm 0.38 Â Mpc for ICÂ 2233 , 5.62 \pm 0.20 Â Mpc for ICÂ 5052 , 7.11 \pm 0.13 Â Mpc for NGCÂ 4631 ( 6.70 \pm 0.15 for its satellite NGCÂ 4627 ) and 6.14 \pm 0.15 Â Mpc for NGCÂ 5023 .
We confirm the presence of slight extraplanar metallicity gradient of evolved stars at NGCÂ 5023 and ICÂ 5052 , based on the systematic changes of the colour distribution of red giant stars .

Conclusions :