The Milky Way's inner region is dominated by a stellar bar and a boxy-peanutshaped bulge. However, which stellar populations inhabit the inner Galaxy orhow star formation proceeded there is still unknown. The difficulty in studyingthese stars stems from their location in dense regions that are stronglyimpacted by extinction and crowding effects. In this work, we use starformation histories computed in the solar neighbourhood using GaiaColour-Magnitude Diagram fitting to shed light onto the evolution of thecentral regions of our Galaxy. For that, we have obtained precise agedistributions for the non-negligible amount of super metal-rich stars ([M/H]$\sim$ 0.5) in the solar neighbourhood (more than 5$\%$ of the total starswithin 400 pc of the plane). Assuming that these stars were born in the innerGalaxy and migrated outwards, those distributions should be indicative of thetrue stellar age distribution in the inner Galaxy. Surprisingly, we find thatthese age distributions are not continuous but show clear signs of episodicstar formation ($\sim$~13.5, 10.0, 7.0, 4.0, 2.0 and less than 1~Gyr ago).Interestingly, with the exception of the 4~Gyr event, the timings of thedetected events coincide with the formation of the primitive Milky Way and withknown merging events or satellite encounters (Gaia-Enceladus-Sausage,Sagittarius dwarf galaxy, and the Magellanic Clouds), suggesting that thesecould have induced enhanced and global star-forming episodes. These results arecompatible with a scenario in which Gaia-Enceladus-Sausage is responsible forthe formation of the bar 10 Gyr ago. However, we cannot associate any accretioncounterpart with the 4-Gyr-ago event, leaving room for a late formation of thebar, as previously proposed. A qualitative comparison with the AurigaSuperstars simulations suggesting a possible link to bar dynamics and satelliteaccretion. [Abridged]

The extremely-low-luminosity, compact Milky Way satellite Ursa Major III /UNIONS 1 (UMaIII/U1; $L_V = 11 \ L_{\odot}$; $a_{1/2} = 3$ pc) was found tohave a substantial velocity dispersion at the time of its discovery ($\sigma_v= 3.7^{+1.4}_{-1.0} \rm \ km \ s^{-1}$), suggesting that it might be anexceptional, highly dark-matter-dominated dwarf galaxy with very few stars.However, significant questions remained about the system's dark matter contentand nature as a dwarf galaxy due to the small member sample ($N=11$), possiblespectroscopic binaries, and the lack of any metallicity information. Here, wepresent new spectroscopic observations covering $N=16$ members that bothdynamically and chemically test UMaIII/U1's true nature. From higher-precisionKeck/DEIMOS spectra, we find a 95% confidence level velocity dispersion limitof $\sigma_v< 2.3 \rm \ km \ s^{-1}$, with a $\sim$120:1 likelihood ratio nowfavoring the expected stellar-only dispersion of $\sigma_* \approx 0.1 \rm \ km\ s^{-1}$ over the original $3.7 \rm \ km \ s^{-1}$ dispersion. There is now noobservational evidence for dark matter in the system. From Keck/LRIS spectratargeting the Calcium II K line, we also measure the first metallicities for 12member stars, finding a mean metallicity of $\rm [Fe/H] = -2.65 \; \pm \, 0.1$(stat.) $\pm \,0.3$ (zeropoint) with a metallicity dispersion limit of$\sigma_{\rm [Fe/H]} < 0.35$ dex (at the 95% credible level). Together, theseproperties are more consistent with UMaIII/U1 being a star cluster, though thedwarf galaxy scenario is not fully ruled out. Under this interpretation,UMaIII/U1 ranks among the most metal-poor star clusters yet discovered and ispotentially the first known example of a cluster stabilized by a substantialpopulation of unseen stellar remnants.