Using model spectral energy distributions to study galaxy masses : now and in the future

Abstract

The determination of galaxy masses is an essential tool for our understanding of galaxy evolution. Looking at 67 local galaxies, we find that galaxy stellar masses are underestimated using traditional methods that assume homogeneous stellar populations as compared to spatially resolved methods. The underestimate is correlated with specific star-formation rate (sSFR), and is as high as 25% in high-SFR nearby galaxies. At higher redshifts we find a similar effect, except the linear trend with sSFR becomes much more dramatic: unresolved mass measurements may be too low by factors of two to five for the highest sSFR galaxies. The increasing mass correction with sSFR resolves a long-standing discrepancy between the directly observed star-formation rate density and that implied by the stellar mass density. A definitive confirmation of this trend will require observations with JWST. We use the spatially resolved data of our high redshift galaxies to create simulations of the JWST's NIRISS instrument, and find that analysis tools need to ensure they can account for spatially inhomogeneous spectra within a galaxy in order to obtain the most accurate line emission measurements. Additionally, we examine how photometric redshifts can be improved for future space-based weak lensing missions such as Euclid. Weak lensing tomography depends critically upon accurate redshift estimation in order to map the three dimensional mass distribution of the universe. We demonstrate the poor quality of photometric redshifts these missions would expect without optical bandpasses and show how the addition of a U and/or G filter could remove their reliance on ground-based surveys.