tokens: 8 of Savino et al. 2019 ) is about 0.5–0.6 × 10 −4 M ⊙ yr −1 , in good agreement with the SFR of about 0.4 × 10 −4 M ⊙ yr −1 measured in our work. The both measurements show the comparable total stellar mass 3.13 × 10 6 M ⊙ (4.2 × 10 6 M ⊙ ). The bottom panel of Fig. 4 shows the stellar mass formed in the last 2 Gyr versus the galaxy absolute magnitudes. The percentage of the mass formed is small for all the objects. This plot could demonstrate how intensive is the residual SF in dSph galaxies depending on the degree of isolation of the object. Highly isolated galaxies clearly show recent residual SF (>10 per cent of the total stellar mass), while within the virial radius it is practically zero. And XVIII and Tucana are situated beyond the virial radius (but within the LG zero-velocity sphere). Following the logic of the above plot, they should be located between those two extreme cases. None the less, Tucana is again out of the trend, located among the galaxies inside the virial radius. It also could be an argument in favour that in the past this dwarf was among the closer satellites of M 31. Simpson et al. ( 2018 ) predicted quenching of SF in satellite galaxies of the LG from a suite of 30 cosmological zoom simulations of MW-like host galaxies. The authors found that systems within host galaxy R 200 are comprised of two populations: first infall and ‘backsplash’ galaxies that have had a much more extended interaction with the host. Backsplash galaxies that do not returned to the host by z = 0, exhibit quenching properties similar to galaxies within R 200 and are distinct from other external systems. The last scenario are well match with the SF properties of Tucana dSph. It should be noted that the results are affected by the well-known problem of age–metallicity degeneration in the process of SFH measurement, and some dependence of the results on the isochrone set used (Williams et al. 2017 ). Besides, the obtained CMDs are somewhat not deep enough, in the sense that the photometric limit is brighter than MSTO. At the same time, uniform data set and its homogeneous processing should reduce the influence of these factors on the results of our comparative analysis to a minimum. When analysing SFHs of dwarf satellite galaxies in the nearby galaxy groups (first of all, the LG), one should take into account, that even in a particular mass range and fixed environment, there is a large degree of scatter in the SFHs, frequently noted in various researches (see e.g. Garrison-Kimmel et al. 2019 ). The mentioned study has used a set of about 500 dwarf galaxies taken from FIRE-2 (The Feedback In Realistic Environments 2) simulations to explore how their SFHs vary with environment. They conclude, that the satellites ( d ≤ 300 kpc) tend to form their stars earlier than equivalent 300 d 1000 kpc dwarfs, consistent with the picture, where interactions with MW-mass hosts inhibit SF. A galaxy could loss its gas due to ram pressure effects and tidal
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