scholarly journals Variations of the stellar Initial Mass Function in semi-analytic models: Implications for the mass assembly of galaxies in the GAEA model

2019 ◽  
Vol 15 (S341) ◽  
pp. 124-128
Author(s):  
Fabio Fontanot
Keyword(s):  
Galaxy Evolution ◽  
Mass Function ◽  
Spectroscopic Studies ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Initial Mass ◽  
Chemical Enrichment ◽  
Statistical Indicator ◽  
Stellar Initial Mass Function ◽  
Stellar Masses

AbstractA wealth of observations recently challenged the notion of a universal stellar initial mass function (IMF) by showing evidences in favour of a variability of this statistical indicator as a function of galaxy properties. I present predictions from the semi-analytic model gaea (GAlaxy Evolution and Assembly), which features (a) a detailed treatment of chemical enrichment, (b) an improved stellar feedback scheme, and (c) implements theoretical prescriptions for IMF variations. Our variable IMF realizations predict intrinsic stellar masses and mass-to-light ratios larger than those estimated from synthetic photometry assuming a universal IMF. This provides a self-consistent interpretation for the observed mismatch between photometrically inferred stellar masses of local early-type galaxies and those derived by dynamical and spectroscopic studies. At higher redshifts, the assumption of a variable IMF has a deep impact on our ability to reconstruct the evolution of the galaxy stellar mass function and the star formation history of galaxies.

scholarly journals Impact of metallicity and star formation rate on the time-dependent, galaxy-wide stellar initial mass function

2018 ◽  
Vol 620 ◽  
pp. A39 ◽  
Author(s):  
T. Jeřábková ◽  
A. Hasani Zonoozi ◽  
P. Kroupa ◽  
G. Beccari ◽  
Z. Yan ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Probability Density Distribution ◽  
Star Forming ◽  
The Galaxy ◽  
Stellar Initial Mass Function ◽  
Stellar Masses

The stellar initial mass function (IMF) is commonly assumed to be an invariant probability density distribution function of initial stellar masses. These initial stellar masses are generally represented by the canonical IMF, which is defined as the result of one star formation event in an embedded cluster. As a consequence, the galaxy-wide IMF (gwIMF) should also be invariant and of the same form as the canonical IMF; gwIMF is defined as the sum of the IMFs of all star-forming regions in which embedded clusters form and spawn the galactic field population of the galaxy. Recent observational and theoretical results challenge the hypothesis that the gwIMF is invariant. In order to study the possible reasons for this variation, it is useful to relate the observed IMF to the gwIMF. Starting with the IMF determined in resolved star clusters, we apply the IGIMF-theory to calculate a comprehensive grid of gwIMF models for metallicities, [Fe/H] ∈ (−3, 1), and galaxy-wide star formation rates (SFRs), SFR ∈ (10−5, 105) M⊙ yr−1. For a galaxy with metallicity [Fe/H] < 0 and SFR > 1 M⊙ yr−1, which is a common condition in the early Universe, we find that the gwIMF is both bottom light (relatively fewer low-mass stars) and top heavy (more massive stars), when compared to the canonical IMF. For a SFR < 1 M⊙ yr−1 the gwIMF becomes top light regardless of the metallicity. For metallicities [Fe/H] > 0 the gwIMF can become bottom heavy regardless of the SFR. The IGIMF models predict that massive elliptical galaxies should have formed with a gwIMF that is top heavy within the first few hundred Myr of the life of the galaxy and that it evolves into a bottom heavy gwIMF in the metal-enriched galactic centre. Using the gwIMF grids, we study the SFR−Hα relation and its dependency on metallicity and the SFR. We also study the correction factors to the Kennicutt SFRK − Hα relation and provide new fitting functions. Late-type dwarf galaxies show significantly higher SFRs with respect to Kennicutt SFRs, while star-forming massive galaxies have significantly lower SFRs than hitherto thought. This has implications for gas-consumption timescales and for the main sequence of galaxies. We explicitly discuss Leo P and ultra-faint dwarf galaxies.

scholarly journals The Dawes Review 8: Measuring the Stellar Initial Mass Function

2018 ◽  
Vol 35 ◽  
Author(s):  
A. M. Hopkins
Keyword(s):  
Galaxy Evolution ◽  
Fundamental Property ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Fundamental Field ◽  
Stellar Initial Mass Function ◽  
Almost All ◽  
Further Development ◽  
New Framework

Abstract The birth of stars and the formation of galaxies are cornerstones of modern astrophysics. While much is known about how galaxies globally and their stars individually form and evolve, one fundamental property that affects both remains elusive. This is problematic because this key property, the birth mass distribution of stars, referred to as the stellar initial mass function, is a key tracer of the physics of star formation that underpins almost all of the unknowns in galaxy and stellar evolution. It is perhaps the greatest source of systematic uncertainty in star and galaxy evolution. The past decade has seen a growing variety of methods for measuring or inferring the initial mass function. This range of approaches and evolving definitions of the quantity being measured has in turn led to conflicting conclusions regarding whether or not the initial mass function is universal. Here I review this growing wealth of approaches, and highlight the importance of considering potential initial mass function variations, reinforcing the need to carefully quantify the scope and uncertainties of measurements. I present a new framework to aid the discussion of the initial mass function and promote clarity in the further development of this fundamental field.

scholarly journals Measuring the stellar initial mass function

2019 ◽  
Vol 15 (S352) ◽  
pp. 98-98
Author(s):  
Andrew Hopkins
Keyword(s):  
Galaxy Evolution ◽  
Fundamental Property ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Fundamental Field ◽  
Stellar Initial Mass Function ◽  
Almost All ◽  
Further Development ◽  
The Imf

AbstractThe birth of stars and the formation of galaxies are cornerstones of modern astrophysics. While much is known about how galaxies globally and their stars individually form and evolve, one fundamental property that affects both remains elusive. This is problematic because this key property, the stellar initial mass function (IMF), is a key tracer of the physics of star formation that underpins almost all of the unknowns in galaxy and stellar evolution. It is perhaps the greatest source of systematic uncertainty in star and galaxy evolution. The past decade has seen a growing number and variety of methods for measuring or inferring the shape of the IMF, along with progressively more detailed simulations, paralleled by refinements in the way the concept of the IMF is applied or conceptualised on different physical scales. This range of approaches and evolving definitions of the quantity being measured has in turn led to conflicting conclusions regarding whether or not the IMF is universal. Here I summarise the growing wealth of approaches to our understanding of this fundamental property that defines so much of astrophysics, and highlight the importance of considering potential IMF variations, reinforcing the need for measurements to quantify their scope and uncertainties carefully. I present a new framework to aid the discussion of the IMF and promote clarity in the further development of this fundamental field.

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

2019 ◽  
Vol 490 (1) ◽  
pp. 848-867 ◽  
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.

scholarly journals The stellar initial mass function of the solar neighbourhood revealed by Gaia

2019 ◽  
Vol 489 (2) ◽  
pp. 2377-2394 ◽  
Author(s):  
A Sollima
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Solar Neighbourhood ◽  
Initial Mass ◽  
Galactic Disc ◽  
Formation History ◽  
Stellar Initial Mass Function ◽  
Metallicity Distribution

Abstract I use a sample of more than 120 000 stars in the solar neighbourhood, with parallaxes, magnitudes and colours estimated with unprecedented accuracy by the second data release of the Gaia mission, to derive the initial mass function of the Galactic disc. A full-forward technique is used to take into account, for the population of unresolved binaries, the metallicity distribution and the star formation history, including their variation across the Galactic disc, as well as all the observational effects. The shape of the initial mass function is well represented by a segmented power law with two breaks at characteristic masses. It has a maximum at M ∼ 0.15 M⊙ with significant flattening (possibly a depletion) at lower masses and a slope of α = −1.34 ± 0.07 in the range 0.25 < M/M⊙ < 1. Above 1 M⊙, the initial mass function shows an abrupt decline with a slope ranging from α = −2.68 ± 0.09 to α = −2.41 ± 0.11, depending on the adopted resolution of the star formation history.

scholarly journals Is the stellar initial mass function universal?

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