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We present a detailed study of the stellar and HI structure of the dwarfirregular galaxies SextansA and SextansB, members of the NGC3109 association.We use newly obtained deep (r~26.5) and wide field g,r photometry to extend theSurface Brightness (SB) profiles of the two galaxies down to mu_V~ 31.0mag/arcsec^2. We find that both galaxies are significantly more extended thanwhat previously traced with surface photometry, out to ~4 kpc from theircenters along their major axis. Older stars are found to have more extendeddistribution with respect to younger populations. We obtain the first estimateof the mean metallicity for the old stars in SexB, from the color distributionof the Red Giant Branch, <[Fe/H]>=-1.6. The SB profiles show significantchanges of slope and cannot be fitted with a single Sersic model. Both galaxieshave HI discs as massive as their respective stellar components. In both casesthe HI discs display solid-body rotation with maximum amplitude of ~50 km/s(albeit with significant uncertainty due to the poorly constrainedinclination), implying a dynamical mass ~10^{9}~M_sun, a mass-to-light ratioM/L_V~25 and a dark-to-barionic mass ratio of ~10. The distribution of thestellar components is more extended than the gaseous disc in both galaxies. Wefind that the main, approximately round-shaped, stellar body of Sex~A issurrounded by an elongated low-SB stellar halo that can be interpreted as atidal tail, similar to that found in another member of the same association(Antlia). We discuss these, as well as other evidences of tidal disturbance, inthe framework of a past passage of the NGC3109 association close to the MilkyWay, that has been hypothesized by several authors and is also supported by therecently discovered filamentary configuration of the association itself.

The extended structure of the dwarf irregular galaxies Sextans A and Sextans B. Signatures of tidal distortion in the outskirts of the Local Group