Bibcode
La Barbera, F.; Ferreras, I.; Vazdekis, A.; de la Rosa, I. G.; de Carvalho, R. R.; Trevisan, M.; Falcón-Barroso, J.; Ricciardelli, E.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 433, Issue 4, p.3017-3047
Advertised on:
8
2013
Número de citas
245
Número de citas referidas
232
Descripción
We perform a spectroscopic study to constrain the stellar initial mass
function (IMF) by using a large sample of 24 781 early-type galaxies
from the Sloan Digital Sky Survey-based Spheroids Panchromatic
Investigation in Different Environmental Regions survey. Clear evidence
is found of a trend between IMF and central velocity dispersion
(σ0), evolving from a standard Kroupa/Chabrier IMF at
σ0 ˜ 100 km s-1 towards a more
bottom-heavy IMF with increasing σ0, becoming steeper
than the Salpeter function at σ0 ≳ 220 km
s-1. We analyse a variety of spectral indices, combining
gravity-sensitive features, with age- and metallicity-sensitive indices,
and we also consider the effect of non-solar abundance variations. The
indices, corrected to solar scale by means of semi-empirical
correlations, are fitted simultaneously with the (nearly solar-scaled)
extended MILES (MIUSCAT) stellar population models. Similar conclusions
are reached when analysing the spectra with a hybrid approach, combining
constraints from direct spectral fitting in the optical with those from
IMF-sensitive indices. Our analysis suggests that σ0,
rather than [α/Fe], drives the variation of the IMF. Although our
analysis cannot discriminate between a single power-law (unimodal) IMF
and a low-mass (≲0.5 M⊙) tapered (bimodal) IMF,
robust constraints can be inferred for the fraction in low-mass stars at
birth. This fraction (by mass) is found to increase from ˜20 per
cent at σ0 ˜ 100 km s-1, up to
˜80 per cent at σ0 ˜ 300 km s-1.
However, additional constraints can be provided with stellar
mass-to-light (M/L) ratios: unimodal models predict M/L significantly
larger than dynamical M/L, across the whole σ0 range,
whereas a bimodal IMF is compatible. Our results are robust against
individual abundance variations. No significant variation is found in Na
and Ca in addition to the expected change from the correlation between
[α/Fe] and σ0.
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