Recovering stellar population properties and redshifts from broadband photometry of simulated galaxies: Lessons for SED modeling

We present a detailed analysis of our ability to determine stellar masses, ages, reddening, and extinction values, and star formation rates (SFRs) of high-redshift galaxies by modeling broadband spectral energy distributions (SEDs) with stellar population synthesis. In order to do so, we computed synthetic optical-to-NIR SEDs for model galaxies taken from hydrodynamical merger simulations placed at redshifts 1.5 ≤ z ≤ 2.9. Viewed under different angles and during different evolutionary phases, the simulations represent a wide variety of galaxy types (disks, mergers, spheroids). We show that simulated galaxies span a wide range in SEDs and color, comparable to those of observed galaxies. In all star-forming phases, dust attenuation has a large effect on colors, SEDs, and fluxes. The broadband SEDs were then fed to a standard SED modeling procedure, and resulting stellar population parameters were compared to their true values. Disk galaxies generally show a decent median correspondence between the true and estimated mass and age, but suffer from large uncertainties (Δlog M = -0.06^+0.06_-0.13, Δlog age_w = +0.03^+0.19_-0.42). During the merger itself, we find larger offsets: ΔlogM = -0.13^+0.10 _-0.14 and Alogage_w = -0.12^+0.40 _-0.26. E(B - V) values are generally recovered well, but the estimated total visual absorption AV is consistently too low, increasingly so for larger optical depths (ΔA_V = -0.54^+0.40 _-0.46 in the merger regime). Since the largest optical depths occur during the phases of most intense star formation, it is for the highest SFRs that we find the largest underestimates (Δlog SFR = -0.44 ^+0.32_-0.31 in the merger regime). The masses, ages, E(B - V), A_V, and SFRs of merger remnants (spheroids) are very well reproduced. We discuss possible biases in SED modeling results caused by mismatch between the true and template star formation history (SFH), dust distribution, metallicity variations, and active galactic nucleus contribution. Mismatch between the real and template SFH, as is the case during the merging event, drives the age, and consequently mass estimate, down with respect to the true age and mass. However, the larger optical depth toward young stars during this phase reduces the effect considerably. Finally, we tested the photometric redshift code EAZY on the simulated galaxies placed at high redshift. We find a small scatter in Δz/(1 + z) of 0.031.