scholarly journals Initial Mass Function for Massive Galaxies at z ~ 1

2014 ◽  
Vol 10 (S311) ◽  
pp. 136-139
Author(s):  
Shravan Shetty ◽  
Michele Cappellari

AbstractWe present the results on the stellar Initial Mass Function (IMF) normalisation of 68 massive (M* = 1011 - 1012M⋖) Early-Type Galaxies (ETGs) at redshift of ~1. This was achieved by deriving the stellar Mass-to-Light ratio (M/L) of the galaxies through axis-symmetric dynamical modelling and comparing it to the same derived via stellar population modelling through full spectrum fitting. The study also employs an Abundance Matching technique to account for the dark matter within the galaxies. The results demonstrate that massive ETGs at high redshifts on average have a Salpeter-like IMF normalisation, while providing observational evidence supporting previous predictions of low dark matter fraction in the inner regions (<1Re) of galaxies at higher redshift.

2012 ◽  
Vol 8 (S295) ◽  
pp. 225-228
Author(s):  
E. M. Corsini ◽  
G. A. Wegner ◽  
J. Thomas ◽  
R. P. Saglia ◽  
R. Bender ◽  
...  

AbstractWe studied the stellar populations, distribution of dark matter, and dynamical structure of a sample of 25 early-type galaxies in the Coma and Abell~262 clusters. We derived dynamical mass-to-light ratios and dark matter densities from orbit-based dynamical models, complemented by the ages, metallicities, and α-element abundances of the galaxies from single stellar population models. Most of the galaxies have a significant detection of dark matter and their halos are about 10 times denser than in spirals of the same stellar mass. Calibrating dark matter densities to cosmological simulations we find assembly redshifts zDM ≈ 1–3. The dynamical mass that follows the light is larger than expected for a Kroupa stellar initial mass function, especially in galaxies with high velocity dispersion σeff inside the effective radius reff. We now have 5 of 25 galaxies where mass follows light to 1–3 reff, the dynamical mass-to-light ratio of all the mass that follows the light is large (≈ 8–10 in the Kron-Cousins R band), the dark matter fraction is negligible to 1–3 reff. This could indicate a ‘massive’ initial mass function in massive early-type galaxies. Alternatively, some of the dark matter in massive galaxies could follow the light very closely suggesting a significant degeneracy between luminous and dark matter.


Author(s):  
I. Ferreras ◽  
C. Weidner ◽  
A. Vazdekis ◽  
F. La Barbera

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.


2016 ◽  
Vol 57 (2) ◽  
pp. 2.32-2.36 ◽  
Author(s):  
Ignacio Ferreras ◽  
Francesco La Barbera ◽  
Alexandre Vazdekis

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