Monday

The epoch of reionisation when the Universe transformed from a neutral state to an ionised state in an important phase change in the history of our Universe. But what were the first luminous sources responsible for this phase change and when exactly did they form? These are some of the major unanswered questions in extragalactic astronomy. The James Webb Space Telescope (JWST) will be launched in 2021 and will search for the First Light objects in the redshift range of z = 10 − 15. Observing these galaxies will be routine with JWST, however, until then, our best chance to study these systems is through deep observations of lensing clusters with the Hubble Space Telescope (HST) by using them as ‘Cosmic Telescopes’. Therefore, to extend its reach even farther beyond its technical capabilities before JWST is launched, the HST observed six massive clusters of galaxies as gravitational lenses to find the faintest and earliest galaxies in the Universe, ∼10-100 times fainter than any previously studied, as a part of the Hubble Frontier Fields (HFF) program. In this talk, I will present how we detect and examine the objects behind HFFs lensing clusters. We have developed a novel method to subtract the massive foreground galaxies from these clusters, allowing for a deeper and cleaner detection of the faintest systems. With photometry from HST, Spitzer and K-band imaging, I will present new measurements of the UV spectral slopes, galaxy stellar mass functions, UV luminosity functions, stellar mass density, and UV luminosity density for galaxies from z = 6 − 9 in the Hubble Frontier Fields. I will further discuss how these results reveal new information on PopIII stellar populations as well as on the faint-end of the mass function from the faintest galaxies at high-z, unveiling the potential science that can be done with JWST.