Evidence for top-heavy stellar initial mass functions with increasing density and decreasing metallicity

By M. Marks, Pavel Kroupa, Joerg Dabringhausen, M. Pawlowski. 2012

197 citations recorded by the source corpus.

ABSTRACT Residual-gas expulsion after cluster formation has recently been shown to leave animprint in the low-mass present-day stellar mass function (PDMF) which allowedthe estimation of birth conditions of some Galactic globular clusters (GCs) such asmass, radius and star formation eﬃciency. We show that in order to explain theircharacteristics (masses, radii, metallicity, PDMF) their stellar initial mass function(IMF) must have been top-heavy. It is found that the IMF is required to becomemore top-heavy the lower the cluster metallicity and the larger the pre-GC cloud-core density are. The deduced trends are in qualitative agreement with theoreticalexpectation. The results are consistent with estimates of the shape of the high-massend of the IMF in the Arches cluster, Westerlund 1, R136 and NGC 3603, as wellas with the IMF independently constrained for ultra-compact dwarf galaxies (UCDs).The latter suggests that GCs and UCDs might have formed along the same channel orthat UCDs formed via mergers of GCs. A fundamental plane is found which describesthe variation of the IMF with density and metallicity of the pre-GC cloud-cores. Theimplications for the evolution of galaxies and chemical enrichment over cosmologicaltimes are expected to be major.Keywords: stars: formation – stars: mass-function – stars: early-type – stars: late-type – globular clusters: general

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/8eb756f8e6556d42d1190e323dd0165c65e76496

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Citations in the corpus

Merging black holes in young star clusters (2019, methodology): “We choose the initial SC half mass radius rh according to the Marks & Kroupa relation (Marks et al. 2012), which relates the total mass of the SC MSC with its initial half mass radius rh: rh = 0.10 +0.07 −0.04 pc ( MSC M )0.13±0.04 .”
The Close Binary Fraction of Solar-type Stars Is Strongly Anticorrelated with Metallicity (2018, background): “Although some observations indicate that the IMF becomes top-heavy toward lower metallicities (Marks et al. 2012; Geha et al. 2013; Kroupa et al. 2013), this trend is not statistically significant until the metallicity falls below at least [Fe/H]−1.5.”
The stellar and sub-stellar IMF of simple and composite populations (2011, methodology): “The dependence of α3 on cluster-forming cloud density ρ (stars plus gas) can be parametrised for m > 1M⊙ as (Marks et al. 2012) α3 = α2, ρ < 9.5× 104M⊙/pc3, α3 = 1.86− 0.43 log10 ( ρcl/(10 6M⊙ pc −3) ) , ρ ≥ 9.5× 104M⊙/pc3.”
Massive black hole binaries from runaway collisions: the impact of metallicity (2016, background): “On the other hand, a relatively fast gas expulsion due to stellar winds and SN explosions can lead to the expansion of the cluster (Marks et al. 2008, 2012; Leigh et al. 2013), reducing the efficiency of stellar collisions.”
THE STELLAR INITIAL MASS FUNCTION OF ULTRA-FAINT DWARF GALAXIES: EVIDENCE FOR IMF VARIATIONS WITH GALACTIC ENVIRONMENT (2013, background): “…properties of the stellar birth cloud such as the gas density, metallicity, or turbulent velocity (e.g.,; Larson 2005; Bate 2009; Myers et al. 2011; Marks et al. 2012; Hopkins 2012), however, IMF observations are largely invariant within the Milky Way (Bochanski et al. 2010; Covey et al. 2008).”
Galaxies as simple dynamical systems: observational data disfavor dark matter and stochastic star formation (2014, background): “This evidence for top-heavy IMFs in massively star-bursting clusters appears from four entirely independent data sets: (i) the elevated dynamical M/L ratios of UCDs [289,290], (ii) the higher incidence of LMXBs in UCDs [291], (iii) globular clusters in the Milky Way which have “damaged” present-day ”
Evolutionary roads leading to low effective spins, high black hole masses, and O1/O2 rates for LIGO/Virgo binary black holes (2017, background): “Notably, both theoretical arguments (see Klencki et al. 2018, for an overview) and observations of some GCs in the Milky Way (Marks & Kroupa 2012; Marks et al. 2012) seem to point towards a top-heavy IMF12 in lowmetallicity galaxies, which are likely an important formation site of massive BH-BH…”
Cusp-core transformations in dwarf galaxies: observational predictions (2012, background): “Indeed, both the IMF and stellar evolution models are poorly constrained at low metallicity and/or at high redshift, and more generally in extreme galactic environments (Marks et al. 2012).”
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “…either on direct comparisons of stellar and cluster masses in the Milky Way (Kroupa & Weidner 2003; Weidner & Kroupa 2006; Weidner et al. 2010, 2013), or on indirect indicators such as X-ray binary populations (Dabringhausen et al. 2009, 2012) and globular cluster properties (Marks et al. 2012).”