A Search for H-Dropout Lyman Break Galaxies at z~12-16 (2112.09141v4)

Abstract: We present two bright galaxy candidates at z~12-13 identified in our H-dropout Lyman break selection with 2.3 deg2 near-infrared deep imaging data. These galaxy candidates, selected after careful screening of foreground interlopers, have spectral energy distributions showing a sharp discontinuity around 1.7 um, a flat continuum at 2-5 um, and non-detections at <1.2 um in the available photometric datasets, all of which are consistent with z>12 galaxy. An ALMA program targeting one of the candidates shows a tentative 4sigma [OIII]88um line at z=13.27, in agreement with its photometric redshift estimate. The number density of the z~12-13 candidates is comparable to that of bright z~10 galaxies, and is consistent with a recently proposed double power-law luminosity function rather than the Schechter function, indicating little evolution in the abundance of bright galaxies from z~4 to 13. Comparisons with theoretical models show that the models cannot reproduce the bright end of rest-frame ultraviolet luminosity functions at z~10-13. Combined with recent studies reporting similarly bright galaxies at z~9-11 and mature stellar populations at z~6-9, our results indicate the existence of a number of star-forming galaxies at z>10, which will be detected with upcoming space missions such as James Webb Space Telescope, Nancy Grace Roman Space Telescope, and GREX-PLUS.

• The paper presents the detection of two promising H-dropout LBG candidates at z~12-13 using deep near-infrared imaging.
• The study leverages ALMA follow-up that tentatively detected an [OIII] 88µm line, suggesting one candidate is at z=13.27 with active star formation.
• The research compares observed luminosity functions with theoretical models, highlighting the need for deeper spectroscopy with JWST and future missions.

Overview of "A Search for H-Dropout Lyman Break Galaxies at $z\sim12-16$" by Harikane et al.

This paper investigates an ambitious observational program aimed at identifying high-redshift galaxies from the early universe, particularly those at redshifts $z\sim12-16$. The authors present the results of a search for $H$-band dropout Lyman Break Galaxies (LBGs), relying on techniques proven effective for identifying galaxies at earlier times. These searches leverage deep imaging data from various telescopes, and while constraints are thus far primarily photometric, these efforts hold significance for guiding future spectroscopic campaigns, particularly with upcoming space missions like the James Webb Space Telescope (JWST).

Key Findings and Results

1. Identification of Candidates: Two promising LBG candidates were identified, showing a discernible break at wavelengths consistent with $z\sim12-13$ redshift. Photometric datasets, particularly those covering the near-infrared spectrum, were used to select galaxies on the basis of their dropout features at the $H$-band.
2. ALMA Observations: Submillimeter follow-up with the Atacama Large Millimeter/submillimeter Array (ALMA) tentatively detected an {\sc [Oiii]} $88 \mu$m line from one candidate, dubbed HD1, believed to be at $z = 13.27$. This detection, though not definitive, suggests the proposed redshift of the object and underscores the potential metallicity and star-formation properties of early galaxies.
3. Luminosity Functions and Comparison to Models: The paper computes the number density of the detected $z\sim13$ galaxies and compares them with theoretical predictions. Current models, as explained, are not well-aligned with observations at high luminosities, suggesting either an underestimation in the models of how quickly galaxies could form and grow at such early times or the presence of AGN activity misidentified as stellar light.
4. Implications for Future Surveys: The work highlights the scalability and need for deeper imaging and spectroscopy to firmly confirm the nature and properties of these candidates. Future infrared space telescopes such as JWST, GREX-PLUS, and the Nancy Grace Roman Space Telescope will be pivotal in expanding the number of known high-redshift galaxies. The findings imply that these missions could discover thousands of galaxies beyond $z \sim 10$, depending on their survey strategies and depths.

Implications and Speculations

• Cosmic Structure Formation: Detecting galaxies at such high redshifts informs models of cosmic structure formation, particularly the timeline and mechanisms by which these earliest systems assembled their mass.
• Refinement of Semi-Analytic Models: The dissonance between observed abundances of high $z$ galaxies and predictions from semi-analytic models suggests the need for refined assumptions regarding star formation efficiencies, the interstellar medium conditions, and feedback mechanisms affecting nascent galaxies.
• AGN Contribution and Detection: The potential presence of black holes accreting mass in these early galaxies could suggest significant contributions of AGNs to the ionizing photon budget of the early universe, with implications for the reionization epoch.

In summary, the paper shines a light on the dawn of galactic formation and offers an early glimpse into a future where such galaxies are not singular anomalies in the observational catalog but rather routine elements of cosmic surveys, providing a deeper understanding of the universe's formative years. The observational techniques and findings of this paper act as a foundational blueprint for the daunting task of mapping the farthest expanses of the universe.