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Systematic variations of the Initial Mass Functionof
early-type galaxies • Francesco La Barbera (INAF/OAC, IT)•
Ignacio Ferreras (UCL/MSSL, UK)• Alejandro Vazdekis (IAC, ES)•
Ignacio Martín Navarro (IAC, ES)• Reinaldo R. de Carvalho (INPE,
BR)• Carsten Weidner (IAC, ES) • Jesús Falcón Barroso (IAC, ES)•
Ignacio G. de la Rosa (IAC, ES)• Marina Trevisan (INPE, BR)•
Beatriz Barbuy (IAG, BR)• Elena Ricciardelli (Valencia, ES)
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Sample and Models
SPIDER sample of 39,993 bright (Mr200/Å, no sky contamination
issues
unimodal (single power-law) IMF
bimodal (low-mass tapered; Vazdekis+’96) IMF
MILES extended (MIUSCAT) SSP models (Vazdekis+’12)
0.06
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Spectral indices vs. σ and [α/Fe](Ferreras+’13; La
Barbera+’13)
Mg4780, TiO1, TiO2, NaI8190, CaT
IMF (4700
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Fitting results – observed vs. model indicesIM
F sl
o pe
Metallicity
IMF
slo p
e
Metallicity
All (optical+NIR) indices point to an increase of age, [Z/H],
and IMF slope with σ0(see Conroy & van Dokkum ‘12;
Spiniello+’14a, b)
(Ferreras+’13; La Barbera+’13)
Unimodal and bimodal models fit equally well (i.e. cannot be
singled out from indices)
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IMF slope and M*/L vs. σ
Trend from a Kroupa-like IMF (σ≤150km/s), to a bottom-heavy IMF
at high σ.F 0
.5=
Indices constrain the mass fraction in low-mass stars at birth
in the IMF, F0.5.
(Ferreras+’13; La Barbera+’13)
dynamical Mdyn/LMdyn∝5Reσ2
stellar M*/L
Bimodal 2x smaller than unimodal M*/L. one can have strong
IMF-sensitive features, but “low” M*/L (see Smith&Lucey
2013)(see Läsker+’13)
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(Vazdekis+’96,’97; Weidner+’13)The time-dependent IMF of
ETGs
F0.5=0.6
F0.5=0.3
Kroupa-like IMF matches age-metallicity of ETGs, but not
F0.5
bottom-heavy at all times never reaches metallicity [Z/H]>-1
!!
F0.5=0.6F0.5=0.5
D
B
time-dependent IMF is needed to match simultaneously: - age and
[Z/H]- F0.5- fraction of stellar remnants (i.e. LMXB rates; see
Peacock+’14)
A
Chemical enrichment toy models (Ferreras&Silk2000a,b)
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Martín-Navarro et al. (arXiv:1404.6533)
… suggest that the bottom-heavy IMF is confined to the galaxy
central regions.
A bottom-heavy IMF in the cores of ETGs ?
…. of optical+NIR features ….
Long-slit observations at 10.4m GTC….
(see POSTER by I. Martín-Navarro)
See also arXiv:1407.4455: “The stellar initial mass function at
z>1” by Martìn-Navarro et al.
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SummarySignificant trend of IMF slope to increase with σ for the
whole population of ETGs
σ, rather than [Mg/Fe], seems to drive the IMF trend.
We cannot distinguish different IMF models (unimodal vs.
bimodal) with line strengths, implying a large uncertainty on
M*/L.
In contrast, the fraction in low-mass (
