Aims. We investigate the chemical evolutionary history of the dwarf spheroidal galaxies Leo 1 and Leo 2 by means of predictions from a detailed chemical evolution model compared to observations. The ...model adopts up to date nucleosynthesis and takes into account the role played by supernovae of different types (Ia, II), allowing us to follow in detail the evolution of several chemical elements (H, D, He, C, N, O, Mg, Si, S, Ca, Fe, Ba, and Eu). Methods. Each galaxy model is specified by the prescriptions of the star formation rate and by the galactic wind efficiency chosen to reproduce the main features of these galaxies, in particular the stellar metallicity distributions and several abundance ratios. These parameters are constrained by the star formation histories of the galaxies as inferred by the observed color–magnitude diagrams, indicating extended star formation episodes occurring at early epochs, but also with hints of intermediate stellar populations. Results. The main observed features of the galaxies Leo 1 and Leo 2 can be very well explained by chemical evolution models according to the following scenarios: the star formation occurred in two long episodes at 14 Gyr and 9 Gyr ago that lasted 5 and 7 Gyr, respectively, with a low efficiency (ν = 0.6 Gyr-1) in Leo 1, whereas the star formation history in Leo 2 is characterized by one episode at 14 Gyr ago that lasted 7 Gyr, also with a low efficiency (ν = 0.3 Gyr-1). In both galaxies an intense wind (nine and eight times the star formation rate – wi = 9 and 8 in Leo 1 and Leo 2, respectively) takes place which defines the pattern of the abundance ratios and the shape of the stellar metallicity distribution at intermediate to high metallicities. Conclusions. The observational constraints can only be reproduced with the assumption of gas removal by galactic winds.
Aims. We study the nucleosynthesis of several neutron capture elements (barium, europium, lanthanum, and yttrium) in local group dwarf spheroidal (dSph) galaxies and in the Milky Way by comparing the ...predictions of detailed chemical evolution models with the observed data. We analyse the differences in the abundance patterns of these two types of galaxies in order to understand their formation and evolution. Methods. We compare the evolution of Ba/Fe, Eu/Fe, La/Fe, Y/Fe, Ba/Y, Ba/Eu, Y/Eu, and La/Eu observed in dSph galaxies and in our Galaxy with predictions of detailed chemical evolution models. The models for all dSph galaxies and for the Milky Way are able to reproduce several observational features of these galaxies, such as a series of abundance ratios and the stellar metallicities distributions. The Milky Way model adopts the two-infall scenario, whereas the most important features of the models for the dSph galaxies are the low star-formation rate and the occurrence of intense galactic winds. Results. We predict that the s-r/Fe ratios in dSphs are generally different than the corresponding ratios in the Milky Way, at the same Fe/H values. This is interpreted as a consequence of the time-delay model coupled with different star formation histories. In particular, the star-formation is less efficient in dSphs than in our Galaxy and it is influenced by strong galactic winds. Our predictions are in very good agreement with the available observational data. Conclusions. The time-delay model for the galactic chemical enrichment coupled with different histories of star formation in different galaxies allow us to succesfully interpret the observed differences in the abundance ratios of s- and r-process elements, as well as of α-elements in dSphs and in the Milky Way. These differences strongly suggest that the main stellar populations of these galaxies could not have had a common origin and, consequently, that the progenitors of local dSphs might not be the same objects as the building blocks of our Galaxy.
Aims. In order to verify the effects of the most recent data on the evolution of Carina and Sagittarius Dwarf Spheroidal Galaxies (dSph) and to set tight constraints on the main parameters of ...chemical evolution models, we study in detail the chemical evolution of these galaxies through comparisons between the new data and the predictions of a model, already tested to reproduce the main observational constraints in dSphs. Methods. Several abundance ratios, such as α/Fe , Ba/Fe and Eu/Fe, in Sagittarius and Carina and the metallicity distribution of stars in Carina are compared to the predictions of our models adopting the observationally derived star formation histories in these galaxies. Results. These new comparisons confirm our previously suggested scenario for the evolution of these galaxies, and allow us to better fix the star formation and wind parameters. In particular, for Carina the comparison between the new observed metallicity distribution of stars and our predictions indicates that the best efficiency of star formation for this galaxy is $\nu = 0.15$ Gyr-1, that the best wind efficiency parameter is wi = 5 (the wind rate is five times stronger than the star formation rate), and that the star formation history, which produces the best fit to the observed metallicity distribution of stars is characterized by several episodes of activity. In the case of Sagittarius there are now much more data on abundances and our results suggest that $\nu=3$ Gyr-1 and wi=9, again in agreement with our previous work. Finally, we show new predictions for N/Fe and C/Fe ratios for the two galaxies suggesting a scenario for Sagittarius very similar to the one of the solar vicinity in the Milky Way, except for a slight decrease of N/Fe ratio at high metallicities due to the galactic wind which is not present in the Milky Way. For Carina we predict a larger N/Fe ratio at low metallicities, reflecting the lower star formation efficiency of this galaxy relative to Sagittarius and the Milky Way.
Theoretical Λcold dark matter (ΛCDM) cosmological models predict a much larger number of low-mass dark matter haloes than has been observed in the Local Group of galaxies. One possible explanation is ...the increased difficulty of detecting these haloes if most of the visible matter is lost at early evolutionary phases through galactic winds. In this work we study the current models of triggering galactic winds in dwarf spheroidal galaxies (dSph) from supernovae, and study, based on 3D hydrodynamic numerical simulations, the correlation of the mass-loss rates and important physical parameters as the dark matter halo mass and its radial profile, and the star formation rate. We find that the existence of winds is ubiquitous, independent of the gravitational potential. Our simulations revealed that the Rayleigh-Taylor Instability (RTI) may play a major role on pushing matter out of these systems, even for very massive haloes. The instability is responsible for 5-40 per cent of the mass loss during the early evolution of the galaxy, being less relevant at t > 200 Myr. There is no significant difference in the mass-loss rates obtained for the different dark matter profiles studied (NFW and logarithmic). We have also found a correlation between the mass-loss rate and both the halo mass and the rate of supernovae, as already reported in previous works. Besides, the epoch in which most of the baryon galactic matter is removed from the galaxy varies depending on the SN rate and gravitational potential. The later, combined to the importance of the RTI in each model, may change our understanding about the chemical evolution of dwarf galaxies, as well as in the heavy element contamination of the intergalactic medium at high redshifts.
ABSTRACT As is usual in dwarf spheroidal galaxies, today the Local Group galaxy Ursa Minor is depleted of its gas content. How this galaxy lost its gas is still a matter of debate. To study the ...history of gas loss in Ursa Minor, we conducted the first three-dimensional hydrodynamical simulations of this object, assuming that the gas loss was driven by galactic winds powered only by type II supernovae (SNe II). The initial gas setup and supernova (SN) rates used in our simulations are mainly constrained by the inferred star formation history and the observed velocity dispersion of Ursa Minor. After 3 Gyr of evolution, we found that the gas removal efficiency is higher when the SN rate is increased, and also when the initial mean gas density is lowered. The derived mass-loss rates are systematically higher in the central regions ( pc), even though such a relationship has not been strictly linear in time and in terms of the galactic radius. The filamentary structures induced by Rayleigh-Taylor instabilities and the concentric shells related to the acoustic waves driven by SNe can account for the inferred mass losses from the simulations. Our results suggest that SNe II are able to transfer most of the gas from the central region outward to the galactic halo. However, other physical mechanisms must be considered in order to completely remove the gas at larger radii.
We aim to reproduce the chemical evolution of the bulge of M31 using a detailed chemical evolution model, including radial gas flows coming from the disc. We study the impact of the initial mass ...function, the star formation rate and the time-scale for bulge formation on the metallicity distribution function of stars. We compute several models of chemical evolution using the metallicity distribution of dwarf stars as an observational constraint for the bulge of M31. Then, using the model that best reproduces the metallicity distribution function, we predict the X/Feversus Fe/H relations for several chemical elements (O, Mg, Si, Ca, C, N). Our best model for the bulge of M31 is obtained by using a robust statistical method and assumes a Salpeter initial mass function, a Schmidt–Kennicutt law for star formation with an exponent k = 1.5, an efficiency of star formation of ∼15 ± 0.27 Gyr−1 and an infall time-scale of ∼0.10 ± 0.03 Gyr. Our results suggest that the bulge of M31 formed very quickly as a result of an intense star formation rate and an initial mass function flatter than in the solar vicinity but similar to that inferred for the Milky Way bulge. The α/Fe ratios in the stars of the bulge of M31 should be high for most of the Fe/H range, as observed in the Milky Way bulge. These predictions await future data to be proven.
Abstract
SHADOWS 1, 2 is an intended future beam dump experiment in the CERN North Area, aiming to search for feebly interacting particles (FIPs) 3 created in 400 GeV/c proton interactions. Due to ...its proposed off-axis location alongside the K12 beamline 4, the SHADOWS detector can be placed potentially very close to the beam dump, enabling it to search for FIPs in unexplored parts of the parameter space. In order to guarantee good quality of a potential signal, it is crucial to reduce any backgrounds of Standard Model particles as much as possible. The dominant background downstream the beam dump is caused by muons 1. This introduces the need of a dedicated muon sweeping system consisting of magnetised iron blocks (MIBs) to actively mitigate this background component. We present the conceptional design studies in the framework of the Conventional Beams Working Group of the Physics Beyond Colliders Initiative at CERN 5, 6.
We predict the metallicity distribution of stars and the age–metallicity relation for six dwarf spheroidal (dSph) galaxies of the Local Group by means of a chemical evolution model that is able to ...reproduce several observed abundance ratios, and the present-day total mass and gas content of these galaxies. The model adopts up-to-date nucleosynthesis and takes into account the role played by supernovae of different types (II, Ia) allowing us to follow in detail the evolution of several chemical elements (H, D, He, C, N, O, Mg, Si, S, Ca and Fe). Each galaxy model is specified by the prescriptions of the star formation rate and by the galactic wind efficiency chosen to reproduce the main features of these galaxies. These quantities are constrained by the star formation histories of the galaxies as inferred by the observed colour–magnitude diagrams (CMD). The main conclusions are: (i) five of the six dSph galaxies are characterized by very low star formation efficiencies (ν= 0.005–0.5 Gyr−1) with only Sagittarius having a higher one (ν= 1.0 –5.0 Gyr−1); (ii) the wind rate is proportional to the star formation rate and the wind efficiency is high for all galaxies, in the range wi= 6–15; (iii) a high wind efficiency is required in order to reproduce the abundance ratios and the present-day gas mass of the galaxies; (iv) the predicted age–metallicity relation implies that the stars of the dSphs reach solar metallicities in a time-scale of the order of 2–6 Gyr, depending on the particular galaxy; (v) the metallicity distributions of stars in dSphs exhibit a peak around Fe/H∼−1.8 to −1.5 dex, with the exception of Sagittarius, which shows a peak around Fe/H∼−0.8 dex; (iv) the predicted metallicity distributions of stars suggest that the majority of stars in dSphs are formed in a range of metallicity in agreement with the one of the observed stars.
Aims. Based on XMM-Newton, Chandra, and optical DR10-SDSS data, we investigate the metal enrichment history of the group NGC 4325 (z = 0.026). To complete the analysis we used chemical evolution ...models and studied the optical spectrum of the central dominant galaxy through its stellar population analysis and emission line diagnostics to analyse its role in the metal enrichment of the intra-group medium. Methods. We used X-ray 2D spectrally resolved maps to resolve structure in temperature and metallicity. We also derived gas and total masses within r2500 and r500 assuming hydrostatic equilibrium and spherical symmetry. To perform stellar population analysis we applied the spectral fitting technique with STARLIGHT to the optical spectrum of the central galaxy. We simulated the chemical evolution of the central galaxy. Results. While the temperature, pseudo-pressure, and pseudo-entropy maps showed no inhomogeneities, the spatial distribution of the metallicity shows a filamentary structure in the core of this group, which is spatially correlated with the central galaxy, suggesting a connection between the two. The analysis of the optical spectrum of the central galaxy showed no contribution by any recent AGN activity. Using the star formation history as input to chemical evolution models, we predicted the iron and oxygen mass released by supernovae (SNe) winds in the central galaxy up to the present time. Conclusions. Comparing the predicted amount of mass released by the NGC 4325 galaxy to the ones derived through X-ray analysis we conclude that the winds from the central galaxy alone play a minor role in the IGM metal enrichment of this group inside r2500. The SNe winds are responsible for no more than 3% of it and of the iron mass and 21% of the oxygen mass enclosed within r2500. Our results suggest that oxygen has been produced in the early stages of the group formation, becoming well mixed and leading to an almost flat profile. Instead, the iron distribution is centrally peaked, indicating that this element is still being added to the IGM specifically in the core by the SNIa. A possible scenario to explain the elongated metal-rich structure in the core of the NGC 4325 is a past AGN activity, in which our results suggest an episode older than ~107−108 yrs and younger than 5 × 108. Through the overall distribution of the galaxies, we found no signs of recent merger in the group centre that could explain the metal-rich structure.
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