α-MC: Self-consistent α-enhanced Stellar Population Models Covering a Wide Range of Age, Metallicity, and Wavelength

We present new stellar population models, α-MC, self-consistently taking into account nonsolar [α/Fe] abundances for both isochrones and stellar spectra. The α-MC models are based on α-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, [α/Fe] = −0.2, +0.0, +0.2, +0.4, +0.6), and wavelengths (0.1–2.5 μm). We investigate the separate and combined effects of α-enhanced isochrones and stellar spectral libraries on simple stellar populations, including their broadband colors, spectral indices, and full spectra. We find that the primary effect of α-enhancement in isochrones is to lower the overall continuum levels and redden the continuum shapes, while α-enhancement in stellar spectra mainly affects individual spectral lines. At constant [Fe/H], α-enhancement has significant impacts on the broadband colors by ∼0.1–0.4 mag across all ages (0.01–10 Gyr). The effects of α-enhancement on colors at fixed [Z/H] are smaller, by ∼0.1–0.2 mag. The spectral indices involving α-elements, Ca4227 and Mg b, increase with [α/Fe] (both at fixed [Fe/H] and fixed [Z/H]) due to enhanced α-abundances. At constant [Fe/H], α-enhancement weakens most Fe-sensitive and hydrogen Balmer lines. Our new self-consistent α-enhanced models will be essential in deriving accurate physical properties of high-redshift galaxies, where α-enhancement is expected to be common.