Confirmation of a Large, Robust Sample of z=9-10 Galaxies in the CANDELS Fields
Abstract
The galaxy population at z > 8 probes the earliest phases of galaxy evolution, constraining the physical processes regulating gas cooling and star formation. Previous studies using an incomplete filter set found few galaxies at z > 9, implying a sharp drop in the star formation rate (SFR) density. This would be inconsistent with the observed increase in the stellar-mass to halo-mass (SMHM) ratio from z=4 to z=7. Either this SMHM evolutionary trend reverses course just before z=8 (disfavored by the data), or the SFR density at z>9 is larger.
We have built a sample of 11 bright (H<26.5) z=9-10 candidate galaxies in the CANDELS fields, 3X larger than previous samples in these fields, leveraging a HST+Spitzer photometric redshift selection method. This sample favors continued SMHM evolution, but most candidates have significant integrated redshift probability at z < 8 due to incomplete photometric coverage. We propose followup F105W and F140W imaging that will cover gaps in the wavelength coverage - a robust measurement in F105W will reject lower-redshift solutions, while a detection in F140W will provide a second detection band, ensuring no sources are spurious. This imaging can be accomplished in only 14 orbits, an efficient use leveraging thousands of archival HST orbits and Spitzer/IRAC hours invested in these fields. Studying these earliest galaxies is one of the main science themes of the James Webb Space Telescope (JWST). Our proposed followup F105W and F140W imaging will yield a reference sample of robust z=9-10 candidate galaxies ready for spectroscopic observations in JWST Cycle 1 (six candidates are in a field due to be observed by a selected ERS program).- Publication:
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HST Proposal
- Pub Date:
- June 2019
- Bibcode:
- 2019hst..prop15862F