ALBERT

Description: The nucleosynthetic site of the rapid (r) neutron-capture process is currently being debated. The direct detection of the neutron star merger GW170817, through gravitational waves and electromagnetic radiation, has confirmed such events as important sources of the r-process elements. However, chemical evolution models are not able to reproduce the observed chemical abundances in the Milky Way when neutron star mergers are assumed to be the only r-process site and realistic time distributions of such events are taken into account. Now for the first time, we combine all the available observational evidence of the Milky Way and its dwarf galaxy satellites to show that the data can only be explained if there are (at least) two distinct r-process sites: a quick source with timescales comparable to core-collapse supernovae, tquick ≲ 108 yr, and a delayed source with characteristic timescales tdelayed ≳ 4 Gyr. The delayed r-process source most probably originates in neutron star mergers, as the timescale fits well with that estimated for GW170817. Given the short timescales of the quick source, it is likely associated with massive stars, though a specific fast-track channel for compact object mergers cannot be excluded at this point. Our approach demonstrates that only by looking at all the available data will we be able to solve the puzzle that is the r-process.

Description: The slow (s) and intermediate (i) neutron (n) capture processes occur both in asymptotic giant branch (AGB) stars, and in massive stars. To study the build-up of the s- and i-products at low metallicity, we investigate the abundances of Y, Ba, La, Nd, and Eu in 98 stars, at −2.4 〈  [Fe/H] 〈  −0.9, in the Sculptor dwarf spheroidal galaxy. The chemical enrichment from AGB stars becomes apparent at [Fe/H] ≈ −2 in Sculptor, and causes [Y/Ba], [La/Ba], [Nd/Ba] and [Eu/Ba] to decrease with metallicity, reaching subsolar values at the highest [Fe/H] ≈ −1. To investigate individual nucleosynthetic sites, we compared three n-rich Sculptor stars with theoretical yields. One carbon-enhanced metal-poor (CEMP-no) star with high [Sr, Y, Zr] 〉  +0.7 is best fit with a model of a rapidly-rotating massive star, the second (likely CH star) with the i-process, while the third has no satisfactory fit. For a more general understanding of the build-up of the heavy elements, we calculate for the first time the cumulative contribution of the s- and i-processes to the chemical enrichment in Sculptor, and compare with theoretical predictions. By correcting for the r-process, we derive [Y/Ba]s/i = −0.85 ± 0.16, [La/Ba]s/i = −0.49 ± 0.17, and [Nd/Ba]s/i = −0.48 ± 0.12, in the overall s- and/or i-process in Sculptor. These abundance ratios are within the range of those of CEMP stars in the Milky Way, which have either s- or i-process signatures. The low [Y/Ba]s/i and [La/Ba]s/i that we measure in Sculptor are inconsistent with them arising from the s-process only, but are more compatible with models of the i-process. Thus we conclude that both the s- and i-processes were important for the build-up of n-capture elements in the Sculptor dwarf spheroidal galaxy.

Description: We use high-resolution (≈10 pc), zoom-in simulations of a typical (stellar mass $M_star simeq 10^{10}, { m M}_{odot }$) Lyman Break Galaxy (LBG) at z ≃ 6 to investigate the stellar populations of its six dwarf galaxy satellites, whose stellar [gas] masses are in the range log (M⋆/M⊙) ≃ 6−9 [log (Mgas/M⊙) ≃ 4.3−7.75]. The properties and evolution of satellites show no dependence on the distance from the central massive LBG (

Description: We present the results from the search for Lyman Alpha emitters (LAEs) in the proximity of 11 C iv absorption systems at z 〉 4.7 in the spectrum of the QSO J1030+0524, using data from MUSE. We have found multiple LAE candidates close to four C iv systems at $z_{ m {{C,{small IV}}}}=4.94$–5.74 with $log _{10}(N_{ m{{C,{small IV}}}}[$cm−2]) 〉 13.5. At z = 5–6, C iv systems with W$_0( m {{C,{small IV}}})〉 0.2$ Å seem more likely to have galaxies with Lyα emission within ρ 〈 200 proper kpc (4/5 cases), than the C iv systems with W$_0( m {{C,{small IV}}}) 0.5 Å is in the range $11, {lesssim}, ho , {lesssim}, 200$ proper kpc (pkpc). Furthermore, all candidates are in the luminosity range 0.18–1.15 L$^{star }_{ m{{Lyalpha}}}(z=5.7)$, indicating that the environment of C iv systems within 200 pkpc is populated by the faint end of the Lyα luminosity function. We report a 0.28 L$^{star }_{ m {{Lyalpha}}}$ galaxy at a separation of ρ = 11 pkpc from a strong C iv absorption ($log _{10}(N_{ m {{C,{small IV}}}}[$cm−2]) = 14.52) at $z_{ m {{C,{small IV}}}}=5.72419$. The prevalence of sub-L$^{star }_{ m {{Lyalpha}}}$ galaxies in the proximity of z 〉 4.9 C iv systems suggest that the absorbing material is rather young, likely ejected in the recent past of the identified galaxies. The connection between faint LAEs and high-ionization absorption systems reported in this work, is potentially a consequence of the role of low mass galaxies in the early evolution of the circum-galactic and intergalactic media.