Context.
The chemical enrichment in the interstellar medium (ISM) of galaxies is regulated by several physical processes: star birth and death, grain formation and destruction, and galactic inflows ...and outflows. Understanding such processes and their relative importance is essential to following galaxy evolution and the chemical enrichment through the cosmic epochs, and to interpreting current and future observations. Despite the importance of such topics, the contribution of different stellar sources to the chemical enrichment of galaxies, for example massive stars exploding as Type II supernovae (SNe) and low-mass stars, as well as the mechanisms driving the evolution of dust grains, such as for example grain growth in the ISM and destruction by SN shocks, remain controversial from both observational and theoretical viewpoints.
Aims.
In this work, we revise the current description of metal and dust evolution in the ISM of local low-metallicity dwarf galaxies and develop a new description of Lyman-break galaxies (LBGs) which are considered to be their high-redshift counterparts in terms of star formation, stellar mass, and metallicity. Our goal is to reproduce the observed properties of such galaxies, in particular (i) the peak in dust mass over total stellar mass (sMdust) observed within a few hundred million years; and (ii) the decrease in sMdust at a later time.
Methods.
We fitted spectral energy distribution of dwarf galaxies and LBGs with the “Code Investigating GALaxies Emission”, through which the total stellar mass, dust mass, and star formation rate are estimated. For some of the dwarf galaxies considered, the metal and gas content are available from the literature. We computed different prescriptions for metal and dust evolution in these systems (e.g. different initial mass functions for stars, dust condensation fractions, SN destruction, dust accretion in the ISM, and inflow and outflow efficiency), and we fitted the properties of the observed galaxies through the predictions of the models.
Results.
Only some combinations of models are able to reproduce the observed trend and simultaneously fit the observed properties of the galaxies considered. In particular, we show that (i) a top-heavy initial mass function that favours the formation of massive stars and a dust condensation fraction for Type II SNe of around 50% or more help to reproduce the peak of sMdust observed after ≈100 Myr from the beginning of the baryon cycle for both dwarf galaxies and LBGs; (ii) galactic outflows play a crucial role in reproducing the observed decline in sMdust with age and are more efficient than grain destruction from Type II SNe both in local galaxies and at high-redshift; (iii) a star formation efficiency (mass of gas converted into stars) of a few percent is required to explain the observed metallicity of local dwarf galaxies; and (iv) dust growth in the ISM is not necessary in order to reproduce the values of sMdust derived for the galaxies under study, and, if present, the effect of this process would be erased by galactic outflows.
High precipitation in boreal northeastern North America could help forests withstand the expected temperature-driven increase in evaporative demand, but definitive evidence is lacking. Using a ...network of tree-ring collections from 16,450 stands across 583,000 km² of boreal forests in Québec, Canada, we observe a latitudinal shift in the correlation of black spruce growth with temperature and reduced precipitation, from negative south of 49°N to largely positive to the north of that latitude. Our results suggest that the positive effect of a warmer climate on growth rates and growing season length north of 49°N outweighs the potential negative effect of lower water availability. Unlike the central and western portions of the continent's boreal forest, northeastern North America may act as a climatic refugium in a warmer climate.
ABSTRACT
Rapid neutron capture process (r-process) elements have been detected in a large fraction of metal-poor halo stars, with abundances relative to iron (Fe) that vary by over two orders of ...magnitude. This scatter is reduced to less than a factor of 3 in younger Galactic disc stars. The large scatter of r-process elements in the early Galaxy suggests that the r-process is made by rare events, like compact binary mergers and rare sub-classes of supernovae. Although being rare, neutron star mergers alone have difficulties to explain the observed enhancement of r-process elements in the lowest metallicity stars compared to Fe. The supernovae producing the two neutron stars already provide a substantial Fe abundance where the r-process ejecta from the merger would be injected. In this work we investigate another complementary scenario, where the r-process occurs in neutron star-black hole mergers in addition to neutron star mergers. Neutron star-black hole mergers would eject similar amounts of r-process matter as neutron star mergers, but only the neutron star progenitor would have produced Fe. Furthermore, a reduced efficiency of Fe production from single stars significantly alters the age–metallicity relation, which shifts the onset of r-process production to lower metallicities. We use the high-resolution (20 pc)3/cell inhomogeneous chemical evolution tool ‘ICE’ to study the outcomes of these effects. In our simulations, an adequate combination of neutron star mergers and neutron star-black hole mergers qualitatively reproduces the observed r-process abundances in the Galaxy.
Abstract
We address the deficiency of odd-Z elements P, Cl, K and Sc in Galactic chemical evolution models through an investigation of the nucleosynthesis of interacting convective O and C shells in ...massive stars. 3D hydrodynamic simulations of O-shell convection with moderate C-ingestion rates show no dramatic deviation from spherical symmetry. We derive a spherically averaged diffusion coefficient for 1D nucleosynthesis simulations, which show that such convective–reactive ingestion events can be a production site for P, Cl, K and Sc. An entrainment rate of 10−3 M⊙ s−1 features overproduction factors OPs ≈ 7. Full O–C shell mergers in our 1D stellar evolution massive star models have overproduction factors OPm > 1 dex but for such cases 3D hydrodynamic simulations suggest deviations from spherical symmetry. γ-process species can be produced with overproduction factors of OPm > 1 dex, for example, for 130, 132Ba. Using the uncertain prediction of the 15 M⊙, Z = 0.02 massive star model (OPm ≈ 15) as representative for merger or entrainment convective–reactive events involving O- and C-burning shells, and assume that such events occur in more than 50 per cent of all stars, our chemical evolution models reproduce the observed Galactic trends of the odd-Z elements.
ABSTRACT
We present new observational data for the heavy elements molybdenum (Mo, Z = 42) and ruthenium (Ru, Z= 44) in F-, G-, and K-stars belonging to different substructures of the Milky Way. The ...range of metallicity covered is −1.0 < Fe/H < + 0.3. The spectra of Galactic disc stars have a high resolution of 42 000 and 75 000 and signal-to-noise ratio better than 100. Mo and Ru abundances were derived by comparing the observed and synthetic spectra in the region of Mo i lines at 5506, 5533 Å for 209 stars and Ru i lines at 4080, 4584, 4757 Å for 162 stars using the LTE approach. For all the stars, the Mo and Ru abundance determinations are obtained for the first time with an average error of 0.14 dex. This is the first extended sample of stellar observations for Mo and Ru in the Milky Way disc, and together with earlier observations in halo stars it is pivotal in providing a complete picture of the evolution of Mo and Ru across cosmic time-scales.
The Mo and Ru abundances were compared with those of the neutron-capture elements (Sr, Y, Zr, Ba, Sm, Eu). The complex nucleosynthesis history of Mo and Ru is compared with different Galactic Chemical Evolution (GCE) simulations. In general, present theoretical GCE simulations show underproduction of Mo and Ru at all metallicities compared to observations. This highlights a significant contribution of nucleosynthesis processes not yet considered in our simulations. A number of possible scenarios are discussed.
We run a three-dimensional Galactic chemical evolution (GCE) model to follow the propagation of 53Mn from supernovae of type Ia (SNIa), 60Fe from core-collapse supernovae (CCSNe), 182Hf from ...intermediate mass stars (IMSs), and 244Pu from neutron star mergers (NSMs) in the Galaxy. We compare the GCE of these short-lived radioactive isotopes (SLRs) to recent detections on the deep-sea floor. We find that although these SLRs originate from different sites, they often arrive conjointly on Earth.
Abstract
Aluminium-26 is a short-lived radionuclide with a half-life of 0.72 Myr, which is observed today in the Galaxy via
γ
-ray spectroscopy and is inferred to have been present in the early solar ...system via analysis of meteorites. Massive stars are considered the main contributors of
26
Al. Although most massive stars are found in binary systems, the effect, however, of binary interactions on the
26
Al yields has not been investigated since Braun & Langer. Here we aim to fill this gap. We have used the MESA stellar evolution code to compute massive (10
M
⊙
≤
M
≤ 80
M
⊙
) nonrotating single and binary stars of solar metallicity (
Z
= 0.014). We computed the wind yields for the single stars and for the binary systems where mass transfer plays a major role. Depending on the initial mass of the primary star and orbital period, the
26
Al yield can either increase or decrease in a binary system. For binary systems with primary masses up to ∼35–40
M
⊙
, the yield can increase significantly, especially at the lower mass end, while above ∼45
M
⊙
the yield becomes similar to the single-star yield or even decreases. Our preliminary results show that compared to supernova explosions, the contribution of mass loss in binary systems to the total
26
Al abundance produced by a stellar population is minor. On the other hand, if massive star mass loss is the origin of
26
Al in the early solar system, our results will have significant implications for the identification of the potential stellar, or stellar population, source.
We analyze the nucleosynthesis yields of various Type Ia supernova explosion simulations including pure detonations in sub-Chandrasekhar mass white dwarfs; double detonations and pure helium ...detonations of sub-Chandrasekhar mass white dwarfs with an accreted helium envelope; a violent merger model of two white dwarfs; and deflagrations and delayed detonations in Chandrasekhar mass white dwarfs. We focus on the iron peak elements Mn, Zn, and Cu. To this end, we also briefly review the different burning regimes and production sites of these elements, as well as the results of abundance measurements and several galactic chemical evolution studies. We find that super-solar values of Mn/Fe are not restricted to Chandrasekhar mass explosion models. Scenarios including a helium detonation can significantly contribute to the production of Mn, in particular the models proposed for calcium-rich transients. Although Type Ia supernovae are often not accounted for as production sites of Zn and Cu, our models involving helium shell detonations can produce these elements in super-solar ratios relative to Fe. Our results suggest a re-consideration of Type Ia supernova yields in galactic chemical evolution models. A detailed comparison with observations can provide new insight into the progenitor and explosion channels of these events.
PDF
