Stellar Properties of Galaxies in the Cosmic Dawn: What can we learn before JWST?

Constraints on physical properties of galaxies in the redshift range z ~ 6-10 are key for a full understanding of the process of reionization and early galaxy evolution, including the onset of star formation. As rest-frame optical wavelengths fall into the near infrared at these redshifts, Spitzer/IRAC fluxes become essential to constrain these properties. I will present results on the basic stellar properties (star formation rates, stellar masses, and ages) of a previously unknown z ~ 8 multiply imaged system behind HFF cluster A370 and the highlights from my study of ~200 z ~ 6-10 galaxy candidates from the Reionization Lensing Cluster Survey (RELICS) and companion Spitzer-RELICS surveys using photometric redshift fitting using HST and Spitzer fluxes. I will also discuss our spectroscopic follow-up program with Keck, as well as why these objects are perfect laboratories for JWST to study in great detail the physical properties of galaxies in the early universe.