Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-11-21
Mon.Not.Roy.Astron.Soc. 349 (2004) L43
Astronomy and Astrophysics
Astrophysics
Accepted for publication in MNRAS; 6 pages, 3 figures
Scientific paper
10.1111/j.1365-2966.2004.07754.x
Studies of the broad emission-line regions (BLRs) in quasars have revealed solar or higher enrichment levels up to the highest redshifts. In combination with the presence of large amounts of dust in QSOs at $z$ about 6, this implies that substantial amounts of star formation and nucleosynthesis took place at significantly earlier epochs. Here, we examine whether a top-heavy stellar initial mass function (IMF) is indicated by current data, by modelling the contributions from different regions of the IMF, including Type Ia/II and pair instability supernovae, to the metal synthesis in BLRs. We find that, in order to reproduce the observations of roughly solar values of N/C and Fe/Mg in these objects, (i) stars with a present-day IMF are sufficient, regardless of their metallicity, (ii) zero-metallicity stars with a top-heavy IMF severely underproduce N/C, and (iii) the contribution of Type Ia SNe is not strongly required by the data. Therefore, stars of mass about 1-40 $M_\odot$ must have existed at $z$ about 10-20, possibly coeval with any hypothesized stars of masses exceeding about 100 $M_\odot$ at these epochs. This is in agreement with the nucleosynthetic abundance pattern detected in extremely metal-poor stars in the galactic halo.
Ferrara Andrea
Schneider Raffaella
Venkatesan Aparna
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