Table 1 Pop III stellar IMFs

IMF name	IMF exponent α_III	Minimum stellar mass \({M}_{\min }\) (M_⊙)	Maximum stellar mass \({M}_{\max }\) (M_⊙)	Relative specific X-ray emissivity f_X,III
Sal (that is, Salpeter¹⁰³)	2.35	0.8	250.0	0.29
Int-2	2.00	2.0	180.0	2.85
Int-1	1.00	2.0	180.0	35.27
Int-0.5	0.50	2.0	180.0	46.40
Int-0	0.00	2.0	180.0	75.24
Top	0.00	10.0	500.0	3.21

Each IMF is a truncated power law with minimum mass \({M}_{\min }\), maximum mass \({M}_{\max }\) and exponent α_III (see equation (2)). The Sal¹⁰³ and Top IMFs represent intentionally extreme bottom-heavy and top-heavy scenarios, respectively, and the four Int IMFs allow us to explore the effects of varying the IMF slope while keeping the boundaries fixed. In this study, we consider Pop III stars between 0.8 M_⊙ and 500 M_⊙. The lower limit is motivated by stellar archaeology surveys¹⁶ finding that Pop III stars below this mass threshold must have been rare. The upper limit is set to 500 M_⊙ because more massive stars experience early photodisintegration of their atmospheres, resulting in us being unable to model their spectra reliably²⁴. Also given is f_X,III, the computed X-ray emissivity of Pop III star-forming halos per unit star formation rate for each IMF (Methods); for convenience, these values are normalized so that f_X,III = 1 corresponds to \(3\times 1{0}^{40}\,{\rm{erg}}\,{{\rm{s}}}^{-1}\,{{\rm{M}}}_{\odot }^{-1}\,\mathrm{yr}\), the specific X-ray emissivity expected for Pop II star-forming halos based on low-redshift observations and simulations⁸¹.

Quick links

Search