Bright galaxies at z=9-11 from pure-parallel HST observations: Building a unique sample for JWST with Spitzer/IRAC
Abstract
The combination of observations taken by Hubble and Spitzer revealed the unexpected presence of sources as bright as our own Milky Way as early as 400 Myr after the Big Bang, potentially highlighting a new highly efficient regime for star formation in L>L* galaxies at very early times. Yet, the sample of high-quality z>8 galaxies that have both HST and Spitzer/IRAC imaging is still very small, particularly at high luminosities. We propose here to remedy this situation and efficiently follow-up with Spitzer/IRAC the most promising z>8 sources from our Hubble Brightest of Reionizing Galaxies (BoRG) survey, which covers a footprint on the sky similar to CANDELS, provides a deeper search than ground-based surveys like UltraVISTA, and is robust against cosmic variance because of its 180 independent lines of sight. The proposed new 3.6 micron observations will continue the Spitzer cycle 12 BORG911 program and target 15 additional fields, leveraging over 300 new HST orbits (350 sqarcmin) to identify a final sample of about 5 to 10 bright galaxies at z >= 8.5. For optimal time use (just over 22 hours), our goal is to readily discriminate between z>8 sources (undetected or marginally detected in IRAC) and z~2 interlopers (strongly detected in IRAC) with just 1-2 hours per pointing. The high-quality candidates that we will identify with IRAC will be ideal targets for further studies to investigate the reionization state of the inter-galactic medium through near-IR Keck/VLT spectroscopy. They will also be uniquely suited to measurement of the redshift and stellar population properties through JWST/NIRSPEC observations, with the potential to elucidate how the first generations of stars are assembled in the earliest stages of the epoch of reionization.
- Publication:
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Spitzer Proposal
- Pub Date:
- August 2016
- Bibcode:
- 2016sptz.prop13103B