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Special Presentations

Hunting the First Galaxies with Hubble and Gravitational Lensing

Presented by: Dan Coe (STScI)
Category: Science Colloquia   Duration: 1 hour   Broadcast date: March 14, 2013
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The first galaxies are the frontier of extragalactic astronomy. How and when did they form, and how did they contribute to reionization? We have made progress toward answering these questions by obtaining deep infrared observations with the Hubble Space Telescope, revealing distant galaxies in the epoch of reionization (z > 6). I will discuss how gravitational lensing enables more efficient searches for high-redshift galaxies and led to our discovery of MACS0647-JD at z ~ 10.8 (420 Myr after the Big Bang), a strong candidate for the most distant galaxy yet known. This discovery by the CLASH Multi-Cycle Treasury program is consistent with expectations extrapolated from lower redshifts (4 < z < 8) suggesting sufficient numbers of faint galaxies at early times to reionize the universe. However, this discovery is in tension with the lower number densities of z > 9 candidates identified in deep field observations including the Ultra Deep Field. With the combined powers of HST and gravitational lensing, the upcoming Frontier Fields will resolve this discrepancy and place new constraints on reionization by obtaining magnified images of distant galaxies with the faintest intrinsic magnitudes yet observed (AB mag > 31).