研究成果・発表論文

The formation of globular clusters with top-heavy initial mass functions

Fukushima, Hajime,   & Yajima, Hidenobu


要旨

We study the formation of globular clusters (GCs) in massive compact clouds with the low metallicity of Z = 10-3 Zbyperformingthree-dimensionalradiative- hydrodynamicsimulations.Consideringtheuncertaintyoftheinitialmassfunction(IMF)ofstarsformedinlow- metallicityandhigh-densityclouds,weinvestigatetheimpactsoftheIMFonthecloudconditionfortheGCformationwiththerangeofthepower- lawindexofIMFasγ = 1-2.35. We find that the threshold surface density (Σthr) for the GC formation increases from 800 Mpc^-2atγ = 2.35 to 1600 Mpc^-2atγ = 1.5 in the cases of clouds with Mcl = 106 Mbecausetheemissivityofionizingphotonsperstellarmassincreasesasγ decreases. For γ < 1.5, Σthr saturates with ~ 2000 Mpc^-2thatisquiterareandobservedonlyinlocalstarburstgalaxiesduetoe.g.mergerprocesses.Thus,wesuggestthatformationsitesoflow- metallicityGCscouldbelimitedonlyintheveryhigh-surfacedensityregions.WealsofindthatΣthr can be modelled by a power-law function with the cloud mass (Mcl) and the emissivity of ionizing photons (s*) as Mcl-15s*25. Based on the relation between the power-law slope of IMF and Σthr, future observations with e.g. the JWST can allow us to constrain the IMF of GCs.




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