Early Enrichment Population Theory at High Redshift

Abstract

An early enrichment population (EEP) has been theorized to produce the observed intracluster medium (ICM) metallicity of galaxy clusters. This population likely existed at high redshifts (z ∼ 10), relics of which we posit exist today as dwarf galaxies. Previous work has argued that the initial mass function (IMF) of the EEP must be flatter than those found at lower redshifts, but with considerable uncertainties. In this work, we present a more quantitative model for the EEP and demonstrate how observational constraints can be applied to the IMF using supernova Type Ia (SN Ia) rates, delay time distributions (DTDs), and the luminosity functions (LFs) of galaxy clusters. We determine best-fit values for the slope and mass break of the IMF by comparing IMFs from literature with observed DTDs and the low-luminosity component (M(R) > −12) of the Coma LF. We derive two best-fit IMFs, flatter than standard IMFs: (1) αlo = −0.13 ± 0.24 for 0.07 < M/M⊙ < 1.75 and αhi = 0.53 ± 0.01 for 1.75 < M/M⊙ < 150; and (2) αlo = 1.06 ± 0.11 for 0.07 < M/M⊙ < 6 and αhi = 0.53 ± 0.01 for 6 < M/M⊙ < 150. We compare these with sl-5 from M. Loewenstein (2013), with α = 0.5 for 0.07 < M/M⊙ < 8 and α = 0.3 for 8 < M/M⊙ < 150. This EEP model, along with stars formed at later times, can produce the observed ICM metallicity, is consistent with observations, and predicts a significant rise in the SN Ia rate at increasing redshift.