systematic variations of the initial mass function of early …systematic variations of the initial...
TRANSCRIPT
-
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)
-
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
-
Spectral indices vs. σ and [α/Fe](Ferreras+’13; La Barbera+’13)
Mg4780, TiO1, TiO2, NaI8190, CaT
IMF (4700
-
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)
-
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)
-
(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)
-
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.
-
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 (