The Impact of the Initial Mass Function on the Evolution of M/L

The Initial Mass Function (IMF) represents the distribution of stellar masses of stars formed in one star formation event and is one of the most crucial ingredients to understand the formation and evolution of stellar populations and galaxies. We use Flexible Stellar Population Synthesis (FSPS) to study the impact of five different IMFs (Chabrier, Kroupa, Salpeter, bottom-light, and bottom-heavy) on the time evolution of the stellar mass-to-light ratio (M/L). We investigate a range of stellar metallicities from sub- to super-solar and star-formation histories in FSPS to explore their impact on M/L evolution. We then use Prospector, a package to conduct principled inference of stellar population properties, to model the 50-band GALEX ultraviolet to the MIPS 24 μm photometry from UltraVISTA DR3 (Marsan et al. 2022) of a sample of spectroscopically confirmed ultra-massive galaxies at 3 < z < 4 with estimated dynamical masses from measurements of stellar absorption velocity dispersions and size (Forrest et al. 2022, submitted) to derive photometric stellar masses with different IMF assumptions. We present the comparison of the dynamical masses and photometric stellar masses, and their implications on the IMFs of distant massive galaxies and find that M/L differences over cosmic time from a bottom-heavy IMF lead to significant variations in stellar mass measurements and derived stellar properties compared to those derived using a standard Chabrier IMF.