SPIDER VIII – constraints on the stellar initial mass function of early-type galaxies from a variety of spectral features

Barbera, F. La; Ferreras, Ignacio; Vazdekis, Alexandre; Rosa, I. G. de la; Carvalho, R. R. de; Trevisan, M.; Falcón-Barroso, J.; Ricciardelli, E.

doi:10.1093/mnras/stt943

Cited by 281 publications

(300 citation statements)

References 98 publications

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“…There are indications that the light of stars in massive early type galaxies is consistent with populations formed with a bottom-heavy IMF, as given by the analysis of their spectral features (van Dokkum & Conroy 2010Ferreras et al 2013;La Barbera et al 2013;; in other works, the mass-to-light ratio of massive early type galaxies is constrained by using dynamical tools (Cappellari et al 2012;Dutton et al 2012;Tortora et al 2013) or strong gravitational lensing Treu et al 2010). However, these methods present a degeneracy in the sense that a higher ratio of less massive stars implies either a bottom heavy IMF or a top heavy IMF, since massive stars end their lives in short time-scales and contribute to the total emitted light only during star formation events and shortly after.…”

Section: Discussionmentioning

confidence: 96%

Chemoarchaeological downsizing in a hierarchical universe: impact of a top-heavy IGIMF

Gargiulo¹,

Cora²,

Padilla³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We make use of a semi-analytical model of galaxy formation to investigate the origin of the observed correlation between [α/Fe] abundance ratios and stellar mass in elliptical galaxies. We implement a new galaxy-wide stellar initial mass function (Top Heavy Integrated Galaxy Initial Mass Function, TH-IGIMF) in the semi-analytic model SAG and evaluate its impact on the chemical evolution of galaxies. The SFR-dependence of the slope of the TH-IGIMF is found to be key to reproducing the correct [α/Fe]-stellar mass relation. Massive galaxies reach higher [α/Fe] abundance ratios because they are characterized by more top-heavy IMFs as a result of their higher SFR. As a consequence of our analysis, the value of the minimum embedded star cluster mass and of the slope of the embedded cluster mass function, which are free parameters involved in the TH-IGIMF theory, are found to be as low as 5 M ⊙ and 2, respectively. A mild downsizing trend is present for galaxies generated assuming either a universal IMF or a variable TH-IGIMF. We find that, regardless of galaxy mass, older galaxies (with formation redshifts 2) are formed in shorter time-scales ( 2 Gyr), thus achieving larger [α/Fe] values. Hence, the time-scale of galaxy formation alone cannot explain the slope of the [α/Fe]-galaxy mass relation, but is responsible for the big dispersion of [α/Fe] abundance ratios at fixed stellar mass. We further test the hyphothesis of a TH-IGIMF in elliptical galaxies by looking into mass-to-light ratios, and luminosity functions. Models with a TH-IGIMF are also favoured by these constraints. In particular, mass-to-light ratios agree with observed values for massive galaxies while being overpredicted for less massive ones; this overprediction is present regardless of the IMF considered.

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Section: Discussionmentioning

confidence: 96%

Chemoarchaeological downsizing in a hierarchical universe: impact of a top-heavy IGIMF

Gargiulo¹,

Cora²,

Padilla³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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“…These SSP models also allow for variations on the IMF slope and shape. The IMF has recently been reported to be non-universal (e.g., Cappellari et al 2012;Conroy & van Dokkum 2012;Spiniello et al 2012;La Barbera et al 2013;Ferreras et al 2013) and to have a strong impact on the derived stellar population properties (Ferré-Mateu et al 2013). However, Martín-Navarro et al (2015) have recently shown that for the compact massive relic galaxy NGC 1277, changing the IMF does not modify the derived age properties.…”

Section: Discussionmentioning

confidence: 99%

Massive Relic Galaxies Challenge the Co-Evolution of Super-Massive Black Holes and Their Host Galaxies

Ferré-Mateu

Mezcua

Trujillo

et al. 2015

ApJ

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We study a sample of eight massive galaxies that are extreme outliers (3-5σ) in the M • − M bulge local scaling relation. Two of these galaxies are confirmed to host extremely large super-massive black holes (SMBHs), whereas the virial mass estimates for the other six are also consistent with having abnormally large SMBHs. From the analysis of their star formation histories and their structural properties, we find that all of these extreme outliers can be considered to be relic galaxies from the early (z ∼ 2) universe: i.e., they are compact (R 2 e < kpc) and have purely old stellar populations (t 10  Gyr). In order to explain the nature of such deviations from the local relations, we propose a scenario in which the hosts of these über-massive SMBHs are galaxies that have followed a different evolutionary path than the two-phase growth channel assumed for massive galaxies. Once the SMBH and the core of the galaxy are formed at z ∼ 2, the galaxy skips the second phase, remaining structurally untouched and without further mass and size increase. We show that if the outliers had followed the normal evolutionary path by growing in size via merger activity, the expected (mild) growth in mass would place them closer to the observed local relations. Our results suggest that the SMBH growth epoch for the most massive galaxies stopped ∼10 Gyr ago.

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“…In this section, we discuss alternative methods to estimate [Mg/Fe], by either comparing the linestrengths of selected (Mg and Fe) spectral features to predictions of either α-enhanced (as in, e.g., TMJ11) or base models (see La . To this end, we rely on a subsample of 4, 671 nearby (z ∼ 0.07) ETGs from the SDSS-based SPIDER sample, restricting the analysis to the best-quality spectra, with S/N > 25 perÅ in the spectral regions of the Mgb, Fe 5270 and Fe 5335 features (see La Barbera et al 2013 As discussed in La Fig. 30.…”

Section: The Proxy For [Mg/fe]mentioning

confidence: 99%

Evolutionary stellar population synthesis with MILES – II. Scaled-solar and α-enhanced models

Vazdekis

Coelho

Cassisi

et al. 2015

Monthly Notices of the Royal Astronomical Society

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320

394

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We present models that predict spectra of old-and intermediate-aged stellar populations at 2.51Å (FWHM) with varying [α/Fe] abundance. The models are based on the MILES library and on corrections from theoretical stellar spectra. The models employ recent [Mg/Fe] determinations for the MILES stars and BaSTI scaled-solar and α-enhanced isochrones. We compute models for a suite of IMF shapes and slopes, covering a wide age/metallicity range. Using BASTI, we also compute "base models" matching The Galactic abundance pattern. We confirm that the α-enhanced models show a flux excess with respect to the scaled-solar models blue-ward ∼4500Å, which increases with age and metallicity. We also confirm that both [MgFe] and [MgFe] ′ indices are [α/Fe]-insensitive. We show that the sensitivity of the higher order Balmer lines to [α/Fe] resides in their pseudo-continua, with narrower index definitions yielding lower sensitivity. We confirm that the α-enhanced models yield bluer (redder) colours in the blue (red) spectral range. To match optical colours of massive galaxies we require both α-enhancement and a bottom-heavy IMF. The comparison of Globular Cluster line-strengths with our predictions match the [Mg/Fe] determinations from their individual stars. We obtain good fits to both full spectra and indices of galaxies with varying [α/Fe]. Using thousands of SDSS galaxy spectra we obtain a linear relation between a proxy for the abundance,

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SPIDER VIII – constraints on the stellar initial mass function of early-type galaxies from a variety of spectral features

Cited by 281 publications

References 98 publications

Chemoarchaeological downsizing in a hierarchical universe: impact of a top-heavy IGIMF

Chemoarchaeological downsizing in a hierarchical universe: impact of a top-heavy IGIMF

Massive Relic Galaxies Challenge the Co-Evolution of Super-Massive Black Holes and Their Host Galaxies

Evolutionary stellar population synthesis with MILES – II. Scaled-solar and α-enhanced models

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