$\hat{I}\pm$-MC: Self-consistent $\hat{I}\pm$-enhanced stellar population models covering a wide range of age, metallicity, and wavelength

Abstract

We present new stellar population models, $\hat{I}\pm$-MC, self-consistently taking into account non-solar $[\hat{\mathrm{I}}\pm /Fe]$ abundances for both isochrones and stellar spectra. The $\hat{I}\pm$-MC models are based on $\hat{I}\pm$-enhanced MIST isochrones and C3K spectral libraries, which are publicly available in FSPS. Our new models cover a wide range of ages ($\log (age/yr)=5.0-10.3$), metallicities ($[Fe/H]=[-2.5,+0.5]$ in steps of 0.25, $[\hat{\mathrm{I}}\pm /Fe]=-0.2,+0.0,+0.2,+0.4,+0.6$), and wavelengths ($0.1-2.5\hat{\mathrm{I}}¼\mathrm{m}$). We investigate the separate and combined effects of $\hat{I}\pm$-enhanced isochrones and stellar spectral libraries on simple stellar populations (SSPs), including their broadband colors, spectral indices, and full spectra. We find that the primary effect of $\hat{I}\pm$-enhancement in isochrones is to lower the overall continuum levels and redden the continuum shapes, while $\hat{I}\pm$-enhancement in stellar spectra mainly affects individual spectral lines. At constant $[Fe/H]$, $\hat{I}\pm$-enhancement has significant impacts on the broadband colors by $\sim 0.1-0.4\mathrm{mag}$ across all ages ($0.01-10\mathrm{Gyr}$). The effects of $\hat{I}\pm$-enhancement on colors at fixed $[Z/H]$ are smaller, by $\sim 0.1-0.2\mathrm{mag}$. The spectral indices involving $\hat{I}\pm$-elements, Ca4227 and Mg b, increase with $[\hat{\mathrm{I}}\pm /Fe]$ (both at fixed $[Fe/H]$ and fixed $[Z/H]$) due to enhanced $\hat{I}\pm$-abundances. At constant $[Fe/H]$, $\hat{I}\pm$-enhancement weakens most Fe-sensitive and Hydrogen Balmer lines. Our new self-consistent $\hat{I}\pm$-enhanced models will be essential in deriving accurate physical properties of high-redshift galaxies, where $\hat{I}\pm$-enhancement is expected to be common.

Submitted to ApJ. Comments welcome