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$\sim$10), relics of which we posit exist today as dwarf galaxies. Previous work argues that the initial mass function (IMF) of the EEP must be flatter than those found at lower redshifts, but with considerable uncertainties. In this work, we present a more quantitative model for the EEP and demonstrate how observational constraints can be applied to the IMF using supernova Type Ia (SN Ia) rates, delay time distribution (DTD), and the luminosity function (LF) of galaxy clusters. We determine best-fit values for the slope and mass break of the IMF by comparing IMFs from literature with observed DTDs, and the low-luminosity component ($M(R)> -12$) of the Coma LF. We derive two best-fit IMFs, flatter than standard IMFs: (1) $\alpha_{lo} = -0.13 \pm 0.24$ for $0.07 < M/M_\odot < 1.75$ and $\alpha_{hi} = 0.53 \pm 0.01$ for $1.75 < M/M_\odot < 150$, and (2) $\alpha_{lo} = 1.06 \pm 0.11$ for $0.07 < M/M_\odot < 6$ and $\alpha_{hi} = 0.53 \pm 0.01$ for $6 < M/M_\odot < 150$. We compare these with \textit{sl-5} from \cite{Loew2013}, with $\alpha=0.5$ for $0.07 < M/M_\odot < 8$, and $\alpha=0.3$ for $8 < M/M_\odot < 150$. 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.