Vazdekis, A.; Ferreras, I.; Weidner, C.; La Barbera, F.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society: Letters, Volume 448, Issue 1, p.L82-L86
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3
2015
Citations
43
Refereed citations
41
Description
Spectroscopic analyses of gravity-sensitive line strengths give growing
evidence towards an excess of low-mass stars in massive early-type
galaxies (ETGs). Such a scenario requires a bottom-heavy initial mass
function (IMF). However, strong constraints can be imposed if we take
into account galactic chemical enrichment. We extend the analysis of
Weidner et al. and consider the functional form of bottom-heavy IMFs
used in recent works, where the high-mass end slope is kept fixed to the
Salpeter value, and a free parameter is introduced to describe the slope
at stellar masses below some pivot mass scale (M < MP =
0.5 M⊙). We find that no such time-independent
parametrization is capable to reproduce the full set of constraints in
the stellar populations of massive ETGs - resting on the assumption that
the analysis of gravity-sensitive line strengths leads to a mass
fraction at birth in stars with mass M < 0.5 M⊙ above
60 per cent. Most notably, the large amount of metal-poor gas locked in
low-mass stars during the early, strong phases of star formation results
in average stellar metallicities [M/H] ≲ -0.6, well below the solar
value. The conclusions are unchanged if either the low-mass end cutoff,
or the pivot mass are left as free parameters, strengthening the case
for a time-dependent IMF.
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