The recent Planck Legacy 2018 release has confirmed the presence of anenhanced lensing amplitude in CMB power spectra compared to that predicted inthe standard $\Lambda$CDM model. A closed universe can provide a physicalexplanation for this effect, with the Planck CMB spectra now preferring apositive curvature at more than $99 \%$ C.L. Here we further investigate theevidence for a closed universe from Planck, showing that positive curvaturenaturally explains the anomalous lensing amplitude and demonstrating that italso removes a well-known tension within the Planck data set concerning thevalues of cosmological parameters derived at different angular scales. We showthat since the Planck power spectra prefer a closed universe, discordanceshigher than generally estimated arise for most of the local cosmologicalobservables, including BAO. The assumption of a flat universe could, therefore,mask a cosmological crisis where disparate observed properties of the Universeappear to be mutually inconsistent. Future measurements are needed to clarifywhether the observed discordances are due to undetected systematics, or to newphysics, or simply are a statistical fluctuation.

A scenario for the formation of the bi-modality in the chemical space[$\alpha$/Fe] vs [Fe/H] of the Milky Way was recently proposed in which$\alpha$-enhanced stars are produced early and quickly in clumps. Besidesaccelerating the enrichment of the medium with $\alpha$-elements, these clumpsscatter the old stars, converting in-plane to vertical motion, forming ageometric thick disc. In this paper, by means of a detailed analysis of thedata from smooth particle hydrodynamical simulations, we investigate thegeometric properties (in particular of the chemical thick disc) produced inthis scenario. For mono-age populations we show that the surface radial densityprofiles of high-[$\alpha$/Fe] stars are well described by single exponentials,while that of low-[$\alpha$/Fe] stars require broken exponentials. This breakis sharp for young populations and broadens for older ones. The position of thebreak does not depend significantly on age. The vertical density profiles ofmono-age populations are characterized by single exponentials, which flaresignificantly for low-[$\alpha$/Fe] stars but only weakly (or not at all) forhigh-[$\alpha$/Fe] stars. For low-[$\alpha$/Fe] stars, the flaring leveldecreases with age, while for high-[$\alpha$/Fe] stars it weakly increases withage (although with large uncertainties). All these properties are in agreementwith observational results recently reported for the Milky Way, making this aplausible scenario for the formation of the Galactic thick disc.

Using Hubble Space Telescope ACS/WFC data we present the photometry andspatial distribution of resolved stellar populations of four fields within theextended ultraviolet disk (XUV disk) of M83. These observations show a clumpydistribution of main-sequence stars and a mostly smooth distribution of redgiant branch stars. We constrain the upper-end of the initial mass function(IMF) in the outer disk using the detected population of main-sequence starsand an assumed constant star formation rate (SFR) over the last 300 Myr. Bycomparing the observed main-sequence luminosity function to simulations, wedetermine the best-fitting IMF to have a power law slope $\alpha=-2.35 \pm 0.3$and an upper-mass limit $\rm M_{u}=25_{-3}^{+17} \, M_\odot$. This IMF isconsistent with the observed H$\alpha$ emission, which we use to provideadditional constraints on the IMF. We explore the influence of deviations fromthe constant SFR assumption, finding that our IMF conclusions are robustagainst all but strong recent variations in SFR, but these are excluded bycausality arguments. These results, along with our similar studies of othernearby galaxies, indicate that some XUV disks are deficient in high-mass starscompared to a Kroupa IMF. There are over one hundred galaxies within 5 Mpc,many already observed with HST, thus allowing a more comprehensiveinvestigation of the IMF, and how it varies, using the techniques developedhere.