GN-z11 was photometrically selected as a luminous star-forming galaxycandidate at redshift z > 10 based on Hubble Space Telescope (HST) imagingdata. Follow-up HST near-infrared grism observations detected a continuum breakthat was explained as the Ly-alpha break corresponding to z = 11.09(+0.08-0.12). However, its accurate redshift remained unclear. Here we report aprobable detection of three ultraviolet (UV) emission lines from GN-z11, whichcan be interpreted as the [C III] 1907, C III] 1909 doublet and O III] 1666 atz = 10.957+/-0.001 (when the Universe was only ~420 Myr old, or ~3% of itscurrent age). This is consistent with the redshift of the previous grismobservations, supporting GN-z11 as the most distant galaxy known to date. ItsUV lines likely originate from dense ionized gas that is rarely seen at lowredshifts, and its strong [C III] and C III] emission is partly due to anactive galactic nucleus (AGN) or enhanced carbon abundance. GN-z11 is luminousand young, yet moderately massive, implying a rapid build-up of stellar mass inthe past. Future facilities will be able to find the progenitors of suchgalaxies at higher redshift and probe the cosmic epoch in the beginning ofre-ionization.

The cusp-core problem is one of the main challenges of the cold dark matterparadigm on small scales: the density of a dark matter halo is predicted torise rapidly toward the center as rho ~ r^alpha with alpha between -1 and -1.5,while such a cuspy profile has not been clearly observed. We have carried outthe spatially-resolved mapping of gas dynamics toward a nearby ultra-diffusegalaxy (UDG), AGC 242019. The derived rotation curve of dark matter is wellfitted by the cuspy profile as described by the Navarro-Frenk-White model,while the cored profiles including both the pseudo-isothermal and Burkertmodels are excluded. The halo has alpha=-(0.90+-0.08) at the innermost radiusof 0.67 kpc, Mhalo=(3.5+-1.2)E10 Msun and a small concentration of 2.0+-0.36.AGC 242019 challenges alternatives of cold dark matter by constraining theparticle mass of fuzzy dark matter to be < 0.11E-22 eV or > 3.3E-22 eV , thecross section of self-interacting dark matter to be < 1.63 cm2/g, and theparticle mass of warm dark matter to be > 0.23 keV, all of which are in tensionwith other constraints. The modified Newtonian dynamics is also inconsistentwith a shallow radial acceleration relationship of AGC 242019. For the feedbackscenario that transforms a cusp to a core, AGC 242019 disagrees with thestellar-to-halo-mass-ratio dependent model, but agrees with thestar-formation-threshold dependent model. As a UDG, AGC 242019 is in adwarf-size halo with weak stellar feedback, late formation time, a normalbaryonic spin and low star formation efficiency (SFR/gas).

We use the Keck Cosmic Web Imager integral-field unit spectrograph to: 1)measure the global stellar population parameters for the ultra-diffuse galaxy(UDG) Dragonfly 44 (DF44) to much higher precision than previously possible forany UDG, and 2) for the first time measure spatially-resolved stellarpopulation parameters of a UDG. We find that DF44 falls below themass--metallicity relation established by canonical dwarf galaxies both in andbeyond the Local Group. We measure a flat radial age gradient ($m_{\rm age}\sim +0.01_{-0.08}^{+0.07}$ log Gyr kpc$^{-1}$) and a flat-to-positivemetallicity gradient ($m_{\rm [Fe/H]} \sim +0.08_{-0.11}^{+0.11}$ dexkpc$^{-1}$), which are inconsistent with the gradients measured in similarlypressure-supported dwarf galaxies. We also measure a flat-to-negative [Mg/Fe]gradient ($m_{\rm [Mg/Fe]} \sim -0.18_{-0.17}^{+0.17}$ dex kpc$^{-1}$) suchthat the central $1.5$ kpc of DF44 has stellar population parameters comparableto metal-poor globular clusters. Overall, DF44 does not have internalproperties similar to other dwarf galaxies and is inconsistent with it havingbeen puffed up through a prolonged, bursty star-formation history, as suggestedby some simulations. Rather, the evidence indicates that DF44 experienced anintense epoch of "inside-out" star formation and then quenched early andcatastrophically, such that star-formation was cut off more quickly than incanonical dwarf galaxies.