We present the results of deep multicolour CCD imaging with the SAO RAS 6 m telescope of the pair of extremely metal-deficient gas-rich dwarf galaxies SBS 0335–052 E and W. The total magnitudes in U,B,V,R and I bands and the integrated fluxes of H \alpha emission are measured for both galaxies , and their integrated colours are derived .
The analysis of their surface brightness ( SB ) distributions is performed with the use of the azimuthally-averaged SB profiles .
The latter were modeled by the central Gaussian component and the underlying exponential ‘ disk ’ , mainly contributing in the outermost , very low SB regions .
The colours of these LSB components are used to estimate the age of the oldest visible stellar population .
For the interpretation of the observed LSB colours their contamination by the nebular emission of ionized gas is accounted for by the use of the distribution of H \alpha flux .
We compare the derived ‘ gas-free ’ colours with the colours predicted by the evolution synthesis models from the PEGASE.2 package , considering three SF histories : a ) instantaneous starburst , b ) continuous star formation with constant SFR , and c ) continuous exponentially fading SF ( e-fold time of 3 Gyr ) .
We conclude that the ‘ gas-free ’ colours of the LSB component of the Eastern galaxy can be best consistent with the instantaneous starburst population ( ages of \lesssim 100 Myr ) .
Models with continuous SF give less consistent results , but can be considered as acceptable .
For such scenarios , the ‘ gas-free ’ colours require ages of \lesssim 400 Myr .
For the Western galaxy , the situation is in general similar .
But the colour ( V - R ) appears to be quite red and implies a significantly older component .
We briefly discuss the possible evolution sequence between SBS 0335–052 , HI 1225+01 and other extremely metal-deficient galaxies based on the merger scenario .