Non-universal stellar initial mass functions: large uncertainties in star formation rates at z ≈ 2–4 and other astrophysical probes

• Published in: Monthly notices of the Royal Astronomical Society Vol. 517; no. 2; pp. 2471 - 2484
• Main Authors: Ziegler, Joshua J, Edwards, Thomas D P, Suliga, Anna M, Tamborra, Irene, Horiuchi, Shunsaku, Ando, Shin’ichiro, Freese, Katherine
• Format: Journal Article
• Language: English
• Published: United Kingdom Oxford University Press 27.09.2022
• Subjects: galaxies: luminosity function; mass function; methods: data analysis; neutrinos; stars: formation; stars: luminosity function; supernovae: general
• ISSN: 0035-8711; 1365-2966; 1365-2966
• DOI: 10.1093/mnras/stac2748

ABSTRACT We explore the assumption, widely used in many astrophysical calculations, that the stellar initial mass function (IMF) is universal across all galaxies. By considering both a canonical broken-power-law IMF and a non-universal IMF, we are able to compare the effect of different IMFs on multiple observables and derived quantities in astrophysics. Specifically, we consider a non-universal IMF that varies as a function of the local star formation rate, and explore the effects on the star formation rate density (SFRD), the extragalactic background light, the supernova (both core-collapse and thermonuclear) rates, and the diffuse supernova neutrino background. Our most interesting result is that our adopted varying IMF leads to much greater uncertainty on the SFRD at $z \approx 2-4$ than is usually assumed. Indeed, we find an SFRD (inferred using observed galaxy luminosity distributions) that is a factor of $\gtrsim 3$ lower than canonical results obtained using a universal IMF. Secondly, the non-universal IMF we explore implies a reduction in the supernova core-collapse rate of a factor of $\sim 2$, compared against a universal IMF. The other potential tracers are only slightly affected by changes to the properties of the IMF. We find that currently available data do not provide a clear preference for universal or non-universal IMF. However, improvements to measurements of the star formation rate and core-collapse supernova rate at redshifts $z \gtrsim 2$ may offer the best prospects for discernment.