Quantifying the uncertainties of chemical evolution studies

Abstract

Context. Galactic chemical evolution models are useful tools for interpreting the large body of high-quality observational data on the chemical composition of stars and gas in galaxies that have become available in recent years. Aims. This is the second paper of a series that aims at quantifying the uncertainties in chemical evolution model predictions related to the underlying model assumptions. Specifically, it deals with the uncertainties due to the choice of the stellar yields. Methods. We adopted a widely used model for the chemical evolution of the Galaxy to test the effects of changing the stellar nucleosynthesis prescriptions on the predicted evolution of several chemical species. Up-to-date results from stellar evolutionary models were carefully taken into account. Results. We find that, except for a handful of elements whose nucleosynthesis in stars is well understood by now, large uncertainties still affect model predictions. This is especially true for the majority of the iron-peak elements, but also for much more abundant species such as carbon and nitrogen. The main causes of the mismatch we find among the outputs of different models assuming different stellar yields and among model predictions and observations are (i) the adopted location of the mass cut in models of type II supernova explosions; (ii) the adopted strength and extent of hot bottom burning in models of asymptotic giant branch stars; (iii) the neglection of the effects of rotation on the chemical composition of the stellar surfaces; (iv) the adopted rates of mass loss and of (v) nuclear reactions; and (vi) the different treatments of convection. Conclusions. Our results suggest that it is mandatory to include processes such as hot bottom burning in intermediate-mass stars and rotation in stars of all masses in accurate studies of stellar evolution and nucleosynthesis. In spite of their importance, both these processes still have to be better understood and characterized. As for massive stars, presupernova models computed with mass loss and rotation are available in the literature, but they still wait for a self-consistent coupling with the results of explosive nucleosynthesis computations.

Planetary nebulae as observational constraints in chemical evolution models for NGC 6822

“…This is found in several works on chemical evolution models (e.g., Chiappini et al 2003;Carigi et al 2005;Mollá et al 2006;Romano et al 2010;Kobayashi et al 2011). The prediction of our model is 7.4σ higher than the value observed in H ii regions, therefore we consider that the N yields adopted for LIMS are in general overestimated the models.…”

“…The determination of this type of elements in stars is not so reliable and in previous papers (e.g., Timmes et al 1995;Romano et al 2010;Kobayashi et al 2011) the authors were not able to test Ne, Cl, and Ar yields owing to the lack of stellar abundances.…”

The new semi-analytic code GalICS 2.0 – reproducing the galaxy stellar mass function and the Tully–Fisher relation simultaneously

“…ESN, ΨSN, R and y are determined by stellar evolution. We have used the values for a Chabrier (2003) initial mass function with Romano et al (2010)'s stellar yields (see Vincenzo et al 2016) and we have not allowed them to vary. Okamoto et al (2008) find that cosmic reionization suppresses gas accretion onto haloes up to Mreio = 6.5 × 10 9 h −1 0 M⊙ at z = 0.…”

The metal contents of two groups of galaxies

“…Iwamoto et al 1999;Woosley et al 2002). Carbon and nitrogen are produced by a variety of sources, the relative importance of which is still under debate (for an overview of possible sources of several elements, see Romano et al 2010, and references therein). Based on optical observations of stars in our galaxies, A&A 531, A15 (2011) most authors conclude that superwinds of massive metal-poor stars enriched the gas with carbon early in the Galaxy disk's evolution.…”