Abstract
ABSTRACT We study the effects of the integrated galactic initial mass function (IGIMF) and dust evolution on the abundance patterns of high redshift starburst galaxies. In our chemical models, the rapid collapse of gas clouds triggers an intense and rapid star formation episode, which lasts until the onset of a galactic wind, powered by the thermal energy injected by stellar winds and supernova explosions. Our models follow the evolution of several chemical elements (C, N, α-elements, and Fe) both in the gas and dust phases. We test different values of β, the slope of the embedded cluster mass function for the IGIMF, where lower β values imply a more top-heavy initial mass function (IMF). The computed abundances are compared to high-quality abundance measurements obtained in lensed galaxies and from composite spectra in large samples of star-forming galaxies in the redshift range 2 ≲ z ≲ 3. The adoption of the IGIMF causes a sensible increase of the rate of star formation with respect to a standard Salpeter IMF, with a strong impact on chemical evolution. We find that in order to reproduce the observed abundance patterns in these galaxies, either we need a very top-heavy IGIMF (β < 2) or large amounts of dust. In particular, if dust is important, the IGIMF should have β ≥ 2, which means an IMF slightly more top-heavy than the Salpeter one. The evolution of the dust mass with time for galaxies of different mass and IMF is also computed, highlighting that the dust amount increases with a top-heavier IGIMF.
Highlights
The stellar initial mass function (IMF) influences most observable properties of stellar populations, as it regulates the relative fractions of low- and high-mass stars within them
4.1 The effects of the integrated galactic initial mass function (IGIMF) on the galactic star formation history In Figures 2-4 we show the impact of the IMF on the evolution of the star formation rate (SFR), Type Ia and core collapse (CC)-SN rates, as well as gas, stellar mass and energetic budget for the starburst models of Table 1
The models computed adopting the W11 IGIMF exhibit larger SFR values than the ones computed with a Salpeter IMF
Summary
The stellar initial mass function (IMF) influences most observable properties of stellar populations, as it regulates the relative fractions of low- and high-mass stars within them. The bulk of Fe in a galaxy is known to be produced by Type Ia supernovae (SNe) over timescales that can even reach or exceed the Hubble time (Matteucci & Greggio 1986; Matteucci & Recchi 2001). Owing to these differences, chemical abundance ratios have been used as powerful instruments for reconstructing the star formation history of galaxies. Another fundamental issue yet to be clarified concerns the universality of the IMF, as in principle in the local Universe it could be different from high redshift galaxies (e.g. Larson 1998), which are likely to be characterised by different physical conditions
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