Monday

One of the key question of modern extragalactic astronomy is to determine when the first generation of stars and galaxies started to bathe the Universe in light. According to the most recent simulations, this "Cosmic Dawn" occurred ~200 Myr after the Big-Bang (corresponding to a redshift of z~20). The recent claim of the detection of a redshifted 21cm absorption in the CMB suggests that the formation of the first generation of stars and galaxies happened at z~17. However, observing these galaxies at very high-redshift (z>11) is well beyond the capabilities of current ground-based and space instruments. However recently high redshift galaxies discovered at fascinating distances z>8, were interpreted in terms of ages and intense star formation histories. These galaxies are revealed mature with ages of 500 million years, starting just after the Big-Bang. Such early systems with significant stellar masses and star formation rates which decline with time are not easily reproduced by contemporary numerical simulations. In this talk I will discuss the spectral energy distributions and physical properties of six galaxies whose photometric redshifts suggest they lie beyond a redshift z>9. Each was selected on account of a prominent excess seen in the Spitzer/IRAC 4.5micron band which, for a redshift above z=9, likely indicates the presence of a rest-frame Balmer break. In addition to constraining the earlier star formation activity on the basis of fits using stellar population models with BAGPIPES, we have undertaken the necessary, but challenging, follow-up spectroscopy for each candidate using various combinations of Keck/MOSFIRE, VLT/X-shooter, Gemini/FLAMINGOS2 and ALMA. Our analysis of this enlarged sample provides further support for a cosmic star formation history extending beyond redshifts z>10 and demonstrates that the James Webb Space Telescope will have the capabilities of tracing earlier progenitors of such systems.