A Census of Star-Forming Galaxies in the z~9-10 Universe based on HST+Spitzer Observations Over 19 CLASH clusters: Three Candidate z~9-10 Galaxies and Improved Constraints on the Star Formation Rate Density at z~9

Abstract: We utilise a two-color Lyman-Break selection criterion to search for z~9-10 galaxies over the first 19 clusters in the CLASH program. A systematic search yields three z~9-10 candidates. While we have already reported the most robust of these candidates, MACS1149-JD, two additional z~9 candidates are also found and have H_{160}-band magnitudes of ~26.2-26.9. A careful assessment of various sources of contamination suggests <~1 contaminants for our z~9-10 selection. To determine the implications of these search results for the LF and SFR density at z~9, we introduce a new differential approach to deriving these quantities in lensing fields. Our procedure is to derive the evolution by comparing the number of z~9-10 galaxy candidates found in CLASH with the number of galaxies in a slightly lower redshift sample (after correcting for the differences in selection volumes), here taken to be z~8. This procedure takes advantage of the fact that the relative volumes available for the z~8 and z~9-10 selections behind lensing clusters are not greatly dependent on the details of the lensing models. We find that the normalization of the UV LF at z~9 is just 0.28_{-0.20}^{+0.39}\times that at z~8, ~1.4_{-0.8}^{+3.0}x lower than extrapolating z~4-8 LF results. While consistent with the evolution in the UV LF seen at z~4-8, these results marginally favor a more rapid evolution at z>8. Compared to similar evolutionary findings from the HUDF, our result is less insensitive to large-scale structure uncertainties, given our many independent sightlines on the high-redshift universe.

A Census of Star-Forming Galaxies in the $z\sim9$-10 Universe

The paper explores the identification and characterization of star-forming galaxies in the high-redshift universe, specifically at $z\sim9$-10. Utilizing the Hubble and Spitzer telescopes, the research spans observations over 19 clusters in the Cluster Lensing And Supernova survey with Hubble (CLASH) program. The study unveils three candidate galaxies in the described redshift range and aims to refine constraints on the star formation rate (SFR) density during this epoch.

The study employs a two-color Lyman-Break selection criterion, effectively applying it to identify potential high-redshift candidates. This approach, in tandem with careful assessments of contamination sources, allows a reliable selection process, ultimately yielding three promising galaxy candidates at $z\sim9$-10.

Key findings include:
1. The fraction of $z\sim9$ galaxy candidates is reported as $0.28_{-0.20}^{+0.39}\times$ of the $z\sim8$ population. This reflects a decrease in normalization of the UV luminosity function (LF) as one moves to higher redshifts.
2. The study suggests potential rapid evolution in the UV LF at $z>8$, implying a significant shift in the star formation activity as the universe ages.
3. Compared to similar studies using the Hubble Ultra Deep Field (HUDF), this research benefits from diverse sightlines, reducing large-scale structure uncertainties.
4. The study introduces a differential approach to derive the evolution in LF and SFR density in lensing fields. This method helps compare the number of high-redshift galaxy candidates across different epochs while accounting for selection differences due to lensing.

The implications of such research are manifold, impacting both theoretical models and observational strategies. Understanding galaxy formation and evolution during such early cosmic times provides crucial insights into the processes driving reionization. Moreover, this informs models predicting the build-up of stellar mass in the universe. Future studies could benefit significantly from next-generation telescopes and enhanced imaging techniques, potentially extending the frontier of observable large-scale structure in the high-redshift universe.

Overall, the paper showcases a methodical approach to understanding galaxy formation in the early universe, suggesting a possible accelerated evolutionary process commencing at $z>8$. The ongoing and future observations could further refine these findings, impacting the established cosmological models.