Probing cosmic dawn with wide-range galaxy SED modeling

Understanding the properties of the first generation of galaxies is an ongoing challenge. While advances in deep field observation have led to the identification of large numbers of galaxies at z > 6, there are very few observed galaxies at this range that are sufficiently bright (m_ab < 25) to perform high signal-to-noise spectroscopy on them. Further complicating meaningful work with these high-z galaxies is the difficulty in optically distinguishing bright but distant galaxies from nearby ones that have been obscured by dust. We have identified new candidate z > 6 galaxies in HST images of massive galaxy clusters, providing a new sample of five highly magnified and intrinsically faint candidate galaxies. Of this sample, we examine two strongly lensed galaxies that appear as multiple images on the sky, collected by the HST WFC3 with ground-based NIR imaging as supplementary data. Both are characterized by a drop-off in their spectra corresponding to a specific spectral feature that sets a lower bound on the redshift. These dropout galaxies are contrasted with three galaxies collected by SDSS, which have a distinctly different spectra while having similar apparent magnitudes at the observed wavelengths. Using the open-source SED modeling software Prospector, we demonstrate that the redshift, mass, and age of the high-z galaxies can not only be constrained with limited available data, but that the associated high-z galaxies can be successfully distinguished from dusty low-z galaxies. Our work results in two new bright (m_ab ~24) strongly lensed z > 6 galaxies, providing a path forward for future analysis on the early era of galaxy formation.