There has long been evidence that low-mass galaxies are systematically larger in radius, of lower central stellar mass density, and of lower central phase-space density, than are star clusters of the same luminosity. The larger radius, at a comparable value of central velocity dispersion, implies a larger mass at similar luminosity, and hence significant dark matter, in dwarf galaxies, compared to no dark matter in star clusters. We present a synthesis of recent photometric and kinematic data for several of the most dark-matter dominated galaxies. There is a bimodal distribution in half-light radii, with stable star clusters always being smaller than ∼ 30pc, while stable galaxies are always larger than ∼ 120pc. We extend the previously known observational relationships and interpret them in terms of a more fundamental pair of intrinsic properties of dark matter itself: dark matter forms cored mass distributions, with a core scale length of greater than about 100pc, and always has a maximum central mass density with a narrow range. The dark matter in dSph galaxies appears to be clustered such that there is a mean volume mass density within the stellar distribution which has the very low value of about 0.1 M ⊙ pc −3 (about 5GeV/c 2 cm −3 ). All dSphs have velocity

We confirm and extend the recent finding that the central surface density r_0*rho_0 galaxy dark matter halos, where r_0 and rho_0 are the halo core radius and central density, is nearly constant and independent of galaxy luminosity. Based on the co-added rotation curves of about 1000 spiral galaxies, mass models of individual dwarf irregular and spiral galaxies of late and early types with high-quality rotation curves and, galaxy-galaxy weak lensing signals from a sample of spiral and elliptical galaxies, we find that log(r_0*rho_0) = 2.15 +- 0.2, in units of log(Msol/pc^2). We also show that the observed kinematics of Local Group dwarf spheroidal galaxies are consistent with this value. Our results are obtained for galactic systems spanning over 14 magnitudes, belonging to different Hubble Types, and whose mass profiles have been determined by several independent methods. In the same objects, the approximate constancy of rho_0*r_0 is in sharp contrast to the systematical variations, by several orders of magnitude, of galaxy properties, including rho_0 and central stellar surface density.Comment: Accepted for publication in MNRAS. 9 pages, 4 figure

We present radial velocities and chemical abundances of O, Na, Mg, Al, Si, Ca, Cr, Fe, Co, Ni, and Cu for a sample of 156 red giant branch stars in two Galactic bulge fields centered near (l,b)=(+5.25,-3.02) and (0,-12). The (+5.25,-3.02) field also includes observations of the bulge globular cluster NGC 6553. The results are based on high resolution (R∼20,000), high signal-to-noise (S/N 70) FLAMES-GIRAFFE spectra obtained through the ESO archive. However, we only selected a subset of the original observations that included spectra with both high S/N and that did not show strong TiO absorption bands. The present work extends previous analyses of this data set beyond Fe and the α-elements Mg, Si, Ca, and Ti. While we find reasonable agreement with past work, the data presented here indicate that the bulge may exhibit a different chemical composition than the local thick disk, especially at [Fe/H] -0.5. In particular, the bulge [α/Fe] ratios may remain enhanced to a slightly higher [Fe/H] than the thick disk and the Fe-peak elements Co, Ni, and Cu appear enhanced compared to the disk. There is also some evidence that the [Na/Fe] (but not [Al/Fe]) trends between the bulge and local disk may be different at low and high metallicity. We also find that the velocity dispersion decreases as a function of increasing [Fe/H] for both fields, and do not detect any significant cold, high velocity population. A comparison with chemical enrichment models indicates that a significant fraction of hypernovae are required to explain the bulge abundance trends, and that initial mass functions that are steep, top-heavy (and do not include strong outflow), or truncated to avoid including contributions from stars >40 M ⊙ are ruled out, in particular because of disagreement with the Fe-peak abundance data. For most elements, the NGC 6553 stars exhibit nearly identical abundance trends to comparable metallicity bulge field stars. However, the star-to-star scatter and mean [Na/Fe] ratios appear higher in the cluster, perhaps indicating additional self-enrichment.

Half of all the elements in the universe heavier than iron were created by rapid neutron capture. The theory for this astrophysical 'r-process' was worked out six decades ago and requires an enormous neutron flux to make the bulk of these elements. 1 Where this happens is still debated. 2 A key piece of missing evidence is the identification of freshly-synthesised r-process elements in an astrophysical site. Current models 3-5 and circumstantial evidence 6 point to neutron star mergers as a probable r-process site, with the optical/infrared 'kilonova' emerging in the days after the merger a likely place to detect the spectral signatures of newly-created neutron-capture elements. 7-9 The kilonova, AT2017gfo, emerging from the gravitational-wave-discovered neutron star merger, GW170817, 10 was the first kilonova where detailed spectra were recorded. When these spectra were first reported 11, 12 it was argued that they were broadly consonant with an outflow of radioactive heavy elements, however, there was no robust identification of any element. Here we report the identification of the neutron-capture element strontium in a re-analysis of these spectra. The detection of a neutron-capture element associated with the collision of two extreme-density stars establishes the origin of r-process elements in neutron star mergers, and demonstrates that neutron stars comprise neutron-rich matter 13 .The most detailed information available for a kilonova comes from a series of spectra of AT2017gfo taken over several weeks with the medium resolution, ultraviolet (320 nm) to near-infrared (2,480 nm) spectrograph, X-shooter, mounted at the Very Large Telescope at the European Southern Observatory. These spectra 11, 12 , allow us to track the evolution of the kilonova's primary electromagnetic output from 1.5 days until 10 days after the event. Detailed modelling of these spectra has yet to be done owing to the limited understanding of the phenomenon and the expectation that a very large number of moderate to weak lanthanide lines with unknown oscillator strengths would dominate the spectra 14,15 . Despite the expected complexity, we sought to identify individual elements in the early spectra because these spectra are well-reproduced by relatively simple models 11 .The first epoch spectrum can be reproduced over the entire observed spectral range with a single-temperature blackbody with an observed temperature 4, 800 K. The two major deviations short of 1 µm from a pure blackbody are due to two very broad (∼ 0.2c) absorption components. These components are observed centred at about 350 nm and 810 nm (Fig. 1). The shape of the ultraviolet absorption component is not well constrained because it lies close to the edge of our sensitivity limit and may simply be cut off below about 350 nm. The presence of the absorption feature at 810 nm at this epoch has been noted in earlier publications 11,12 .The fact that the spectrum is very well reproduced by a single temperature blackbody in the first epoch suggests a population of states 0.3...