The Variation of Integrated Star Initial Mass Functions among Galaxies

By C. Weidner, Pavel Kroupa. 2005

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The integrated galaxial initial mass function (IGIMF) is the relevant distribution function containing the information on the distribution of stellar remnants, the number of supernovae, and the chemical enrichment history of a galaxy. Since most stars form in embedded star clusters with different masses, the IGIMF becomes an integral of the assumed (universal or invariant) stellar IMF over the embedded star cluster mass function (ECMF). For a range of reasonable assumptions about the IMF and the ECMF we find the IGIMF to be steeper (containing fewer massive stars per star) than the stellar IMF, but below a few solar masses it is invariant and identical to the stellar IMF for all galaxies. However, the steepening sensitively depends on the form of the ECMF in the low-mass regime. Furthermore, observations indicate a relation between the star formation rate of a galaxy and the most massive young stellar cluster in it. The assumption that this cluster mass marks the upper end of a young-cluster mass function leads to a connection of the star formation rate and the slope of the IGIMF above a few solar masses. The IGIMF varies with the star formation history of a galaxy. Notably, large variations of the IGIMF are evident for dE, dIrr, and LSB galaxies with a small to modest stellar mass. We find that for any galaxy the number of supernovae per star (NSNS) is suppressed relative to that expected for a Salpeter IMF. Dwarf galaxies have a smaller NSNS than massive galaxies. For dwarf galaxies the NSNS varies substantially depending on the galaxy assembly history and the assumptions made about the low-mass end of the ECMF. The findings presented here may be of some consequence for the cosmological evolution of the number of supernovae per low-mass star and the chemical enrichment of galaxies of different mass.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/c1ebe46fdf7cc2894762c34dfa6d04aad7a56087

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Citations in the corpus

THE STELLAR INITIAL MASS FUNCTION OF ULTRA-FAINT DWARF GALAXIES: EVIDENCE FOR IMF VARIATIONS WITH GALACTIC ENVIRONMENT (2013, background): “Since alphaabundances are related to supernova Type II enrichment, it is plausible that star formation rates or specific star formation density is the controlling physical parameter (Weidner & Kroupa 2005).”
The maximum stellar mass, star-cluster formation and composite stellar populations (2005, methodology): “Following-on from our discussion in Weidner & Kroupa (2005) we explore how a different ECMF affects the IGIMF.”
A Universal Stellar Initial Mass Function? A critical look at variations in extreme environments (2010, methodology): “Summing the IMFs of a galaxy’s constituent stellar populations (i.e. clusters, associations, and distributed field populations) produces an Integrated Galaxy Initial Mass Function (IGIMF; Weidner & Kroupa 2005).”
(Star)bursts of FIRE: observational signatures of bursty star formation in galaxies (2015, background): “In our simulations, these effects are caused mostly by bursty star formation without accounting for IMF variations (as done in Kroupa & Weidner 2003; Weidner & Kroupa 2005) or stochastic IMF sampling.”
On the Normalization of the Cosmic Star Formation History (2006, background): “A modified Salpeter form with a turnover below1M⊙, though, is still a reasonable model (e.g., Baldry & Glazebrook 2003), and other currently favoured IMFs include those of Kroupa (2001), Baldry & Glazebrook (2003), and Weidner & Kroupa (2005, 2006).”
A comprehensive set of simulations studying the influence of gas expulsion on star cluster evolution (2007, background): “Star clusters can therefore be viewed as the fundamental building blocks of galaxies since the galactic disc velocity distribution (Kroupa 2002, 2005), the galactic stellar mass function (Weidner & Kroupa 2005) and the galacticfield binary-star population (Kroupa 1995) are all established by them.”
Evidence for top-heavy stellar initial mass functions with increasing density and decreasing metallicity (2012, background): “3) has been made use of in Weidner et al. (2011) to include the evidence for a systematically varying IMF into the framework of the theory of the integrated galactic IMF (IGIMF, i.e. the stellar IMF of whole galaxies, Kroupa & Weidner 2003; Weidner & Kroupa 2005).”
Radial variations in the stellar initial mass function of early-type galaxies (2014, background): “Nevertheless, it is not clear at present how the most developed theoretical mechanisms describing variations in the IGIMF over galactic scales (Weidner & Kroupa 2005) can also explain local variations.”
Galaxies as simple dynamical systems: observational data disfavor dark matter and stochastic star formation (2014, methodology): “14) is not unique, as yet another formulation at the classical level has recently been presented (see [11, 235] for details) and implemented in the Phantom of Ramses (POR) simulation code (Lüghausen, Famaey & Kroupa 2014, [236]).”
COMPARISON OF Hα AND UV STAR FORMATION RATES IN THE LOCAL VOLUME: SYSTEMATIC DISCREPANCIES FOR DWARF GALAXIES (2009, background): “On the theoretical side, Kroupa & Weidner (2003) and Weidner & Kroupa (2005, 2006) have formulated a model based on both statistical arguments and observational constraints which produces IMFs that appear to be steeper for galaxies with lower SFRs.”
The stellar and sub-stellar IMF of simple and composite populations (2011, methodology): “1 in Weidner & Kroupa 2005, as derived by Weidner et al. 2004 using observed maximum star cluster masses).”
THE ACS NEARBY GALAXY SURVEY TREASURY. VIII. THE GLOBAL STAR FORMATION HISTORIES OF 60 DWARF GALAXIES IN THE LOCAL VOLUME (2011, background): “…be attributed to a wide range of effects including temporary episodes between massive star formation (e.g., Skillman et al. 2003a), a stochastically sampled or systematically varying IMF (e.g., Eldridge 2010; Weidner & Kroupa 2005), and/or leakage of ionizing photons (e.g., Ferguson et al. 1996).”
A GALEX ULTRAVIOLET IMAGING SURVEY OF GALAXIES IN THE LOCAL VOLUME (2010, background): “Briefly, in the “integrated galactic stellar initial mass function” (IGIMF; Kroupa & Weidner 2003; Weidner & Kroupa 2005, 2006), it is assumed that: (i) all stars form in clusters; (ii) the maximum mass of a star formed in a cluster is a deterministic function of the cluster mass, and this maximum…”
The relation between the most-massive star and its parental star cluster mass (2009, background): “7 The IGIMF concept is discussed in great detail in Kroupa & Weidner (2003) and Weidner & Kroupa (2005) and subsequent papers.”
The metallicity distribution of bulge clump giants in Baade’s window (2011, background): “…near solar metallicities MD consistent with high α-elements ratios, Ballero et al. (2007b) had to assume a flatter IMF than in the solar neighbourhood but also (see Ballero et al. 2007a) flatter than the stellar IMF of Kroupa (2001) and the IMF integrated over galaxies of Weidner & Kroupa (2005).”
Evidence for a Nonuniversal Stellar Initial Mass Function from the Integrated Properties of SDSS Galaxies (2007, background): “Weidner & Kroupa (2005) use a universal IMF with the assumption that stars are born in clusters where the maximum cluster mass is related to the star formation rate.”
Galaxy and Mass Assembly (GAMA): the star formation rate dependence of the stellar initial mass function (2011, methodology): “Whether the IGIMF is universal (Elmegreen 2006) or differs from the star cluster IMF (Weidner & Kroupa 2005, 2006) is again a much debated subject.”