ner_tags: O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O B-CelestialObject O O O O O O O O O O B-CelestialObject I-CelestialObject O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O B-CelestialObject O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O B-CelestialObject O O O O O B-CelestialObject I-CelestialObject O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O
tokens: tidal forces from the Milky Way, or any other physical process 9 9 For example, relaxation cannot be responsible for the spatial distribution of the different stellar populations in Carina since the relaxation times in dwarf galaxies are much larger than the age of the universe (e.g., Freeman 2008 ). , were not strong enough to move a significant fraction of these stars to the outer region. Otherwise, a large number of intermediate-age stars would be present in the outskirts of Carina, and thus we would not observe such a strong break in the SFH and MDF of Carina between the intermediate and outer regions. Since the radial trends in Carina do not seem to be governed by the tidal influence of the Milky Way, we suggest that this hints that the SFH is not dominated by tidal forces either. In this line, the fact that we find two episodes of star formation in Carina instead of three, as has often been claimed (Hurley-Keller et al. 1998 ; Rizzi et al. 2003 ; Pilkington Gibson 2012 ; McMonigal et al. 2014 ), makes it harder to explain the star-formation episodes in Carina as being the result of periodic close passages to the Milky Way (as done in Pasetto et al. 2011 ), even more so since proper motions suggest that the orbital period of Carina is close to 2 Gyr (Piatek et al. 2003 ; Pasetto et al. 2011 ). Another mechanism proposed to explain the SFH of Carina is gas accretion from the Milky Way (e.g., Lemasle et al. 2012 ; de Boer et al. 2014 ). In this view, the first episode would have ended because of gas depletion, and subsequent star formation would have been stopped for a few gigayears until the dwarf galaxy renewed its gas content thanks to an inflow from the Milky Way. Even though this is a plausible scenario, the in-falling gas should have had the same metallicity as the stars from the end of the first episode to reproduce the age–metallicity relation in Carina. A simpler way to explain why the metallicity of the stars at the end of the first episode coincides with that of the stars at the beginning of the second episode is to assume that the gas that formed the second episode in Carina was enriched within the same galaxy by the first generation of stars. Internal evolution would also be consistent with the mean metallicities and ages at different Carina regions, which according to what we see in Figure 9 are roughly constant throughout the extent of the galaxy. This would not necessarily be the case if the gas that formed those stars had been accreted at different moments and each region had different levels of influence from each inflow. For all these reasons, we conclude that the SFH of Carina must be dominated by internal evolution. Our interpretation is that, after the first episode formed the majority of the stars in Carina, the physical conditions of the gas made the galaxy unable to form stars for a few gigayears, until it contracted to activate star formation again. We claim that the temporal gap in star formation in Carina might