IMF variations in unresolved stellar populations: Challenges

AbstractThis talk focuses on the challenges facing the recent discovery of variations of the stellar initial mass function in massive early-type galaxies, with special emphasis on the constraints via gravity-sensitive spectral features.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stt943 ◽

2013 ◽

Vol 433 (4) ◽

pp. 3017-3047 ◽

Cited By ~ 170

Author(s):

F. La Barbera ◽

I. Ferreras ◽

A. Vazdekis ◽

I. G. de la Rosa ◽

R. R. de Carvalho ◽

...

Keyword(s):

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Spectral Features ◽

Early Type ◽

Stellar Initial Mass Function

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Simple interpolation functions for the galaxy-wide stellar initial mass function and its effects in early-type galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2562 ◽

2019 ◽

Vol 490 (1) ◽

pp. 848-867 ◽

Cited By ~ 2

Author(s):

J Dabringhausen

Keyword(s):

Formation Rate ◽

Stellar Populations ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Early Type ◽

The Galaxy ◽

Stellar Initial Mass Function ◽

Stellar Masses ◽

Interpolation Functions

ABSTRACT The galaxy-wide stellar initial mass function (IGIMF) of a galaxy is thought to depend on its star formation rate (SFR). Using a catalogue of observational properties of early-type galaxies (ETGs) and a relation that correlates the formation time-scales of ETGs with their stellar masses, the dependencies of the IGIMF on the SFR are translated into dependencies on more intuitive parameters like present-day luminosities in different passbands. It is found that up to a luminosity of approximately 109 L⊙ (quite independent of the considered passband), the total masses of the stellar populations of ETGs are slightly lower than expected from the canonical stellar initial mass function (IMF). However, the actual mass of the stellar populations of the most luminous ETGs may be up to two times higher than expected from a simple stellar population model with the canonical IMF. The variation of the IGIMF with the mass of ETGs is presented here also as convenient functions of the luminosity in various passbands.

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The IMF-SFH connection in massive early-type galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316007808 ◽

2015 ◽

Vol 11 (S315) ◽

Author(s):

I. Ferreras ◽

C. Weidner ◽

A. Vazdekis ◽

F. La Barbera

Keyword(s):

Age Distribution ◽

Stellar Populations ◽

Mass Function ◽

Initial Mass Function ◽

Population Synthesis ◽

Early Type ◽

Massive Galaxies ◽

Stellar Initial Mass Function ◽

The Many ◽

The Imf

The stellar initial mass function (IMF) is one of the fundamental pillars in studies of stellar populations. It is the mass distribution of stars at birth, and it is traditionally assumed to be universal, adopting generic functions constrained by resolved (i.e. nearby) stellar populations (e.g., Salpeter 1955; Kroupa 2001; Chabrier 2003). However, for the vast majority of cases, stars are not resolved in galaxies. Therefore, the interpretation of the photo-spectroscopic observables is complicated by the many degeneracies present between the properties of the unresolved stellar populations, including IMF, age distribution, and chemical composition. The overall good match of the photometric and spectroscopic observations of galaxies with population synthesis models, adopting standard IMF choices, made this issue a relatively unimportant one for a number of years. However, improved models and observations have opened the door to constraints on the IMF in unresolved stellar populations via gravity-sensitive spectral features. At present, there is significant evidence of a non-universal IMF in early-type galaxies (ETGs), with a trend towards a dwarf-enriched distribution in the most massive systems (see, e.g., van Dokkum & Conroy 2010; Ferreras et al. 2013; La Barbera et al. 2013). Dynamical and strong-lensing constraints of the stellar M/L in similar systems give similar results, with heavier M/L in the most massive ETGs (see, e.g., Cappellari et al. 2012; Posacki et al. 2015). Although the interpretation of the results is still open to discussion (e.g., Smith 2014; La Barbera 2015), one should consider the consequences of such a bottom-heavy IMF in massive galaxies.

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