GOLDRUSH. IV. Luminosity Functions and Clustering Revealed with ∼4,000,000 Galaxies at z ∼ 2–7: Galaxy–AGN Transition, Star Formation Efficiency, and Implication for Evolution at z > 10

Abstract

We present new measurements of rest-UV luminosity functions and angular correlation functions from 4,100,221 galaxies at z ∼ 2–7 identified in the Subaru/Hyper Suprime-Cam survey and CFHT Large Area U-band Survey. The obtained luminosity functions at z ∼ 4–7 cover a very wide UV luminosity range of ∼ 0.002 – 2000 L UV * combined with previous studies, confirming that the dropout luminosity function is a superposition of the active galactic nucleus (AGN) luminosity function dominant at M UV ≲ −24 mag and the galaxy luminosity function dominant at M UV ≳ −22 mag, consistent with galaxy fractions based on 1037 spectroscopically identified sources. Galaxy luminosity functions estimated from the spectroscopic galaxy fractions show the bright-end excess beyond the Schechter function at ≳2σ levels, possibly made by inefficient mass quenching, low dust obscuration, and/or hidden AGN activity. By analyzing the correlation functions at z ∼ 2–6 with HOD models, we find a weak redshift evolution (within 0.3 dex) of the ratio of the star formation rate (SFR) to the dark matter accretion rate, SFR / M ̇ h , indicating the almost constant star formation efficiency at z ∼ 2–6, as suggested by our earlier work at z ∼ 4–7. Meanwhile, the ratio gradually increases with decreasing redshift at z < 5 within 0.3 dex, which quantitatively reproduces the cosmic SFR density evolution, suggesting that the redshift evolution is primarily driven by the increase of the halo number density due to the structure formation, and the decrease of the accretion rate due to the cosmic expansion. Extrapolating this calculation to higher redshifts assuming the constant efficiency suggests a rapid decrease of the SFR density at z > 10 with ∝ 10−0.5(1+z), which will be directly tested with the James Webb Space Telescope.

High Equivalent Width of Hα+[N ii] Emission in z ∼ 8 Lyman-break Galaxies from IRAC 5.8 μm Observations: Evidence for Efficient Lyman-continuum Photon Production in the Epoch of Reionization

“…The To our knowledge, this measurement constitutes the first detection of Hα from broadband photometry in the population of star-forming galaxies at z > 6.5 typically probed by Lymanbreak selections (e.g., Bouwens et al 2015bBouwens et al , 2022aFinkelstein et al 2015;Bowler et al 2017;Harikane et al 2022). Recent attempts at measuring the intensity of Hα at z ∼ 8 for individual sources in HFF cluster fields were unsuccessful (e.g., Asada & Ohta 2022), likely due to the much shallower coverage available in the IRAC 5.8 μm band over those fields combined with the relatively low magnification values for the considered sources.…”

“…The black solid curve in Figure 3 presents the result of applying a redshift-dependent M å /L optical ratio to the analytical expression for the sSFR(z) evolution. This factor was estimated from our default template set (Section 2), assuming galaxies started forming stars at z ∼ 20 (e.g., Mawatari et al 2020;Harikane et al 2022). 13 We applied a global normalization factor from fitting the curve to the available observations (χ red = 4.7).…”

ALMA Confirmation of an Obscured Hyperluminous Radio-Loud AGN at $z=6.853$ Associated with a Dusty Starburst in the 1.5 deg$^2$ COSMOS Field

“…Within the past few years, several deep wide-area (>deg 2 ) optical+near-infrared imaging surveys have reached (near) completion (Lawrence et al 2007;McCracken et al 2012;Jarvis et al 2013;Inoue et al 2020;Aihara et al 2022), providing large samples of UVbright (−23 M UV −21) Lyman-break 𝑧 7 galaxies (Bowler et al 2017(Bowler et al , 2020Stefanon et al 2019;Bouwens et al 2021a;Endsley et al 2021a;Harikane et al 2022;Schouws et al 2022a). This has in turn led to substantial improvements in our understanding of the UV-luminous reionization-era galaxy population.…”

Groups and Protocluster Candidates in the CLAUDS and HSC-SSP Joint Deep Surveys

“…We calculate the galaxy luminosity functions at i band in all redshift bins. Note that more comprehensive studies of the luminosity functions based on the CLAUDS and HSC data set have been carried out at UV and U bands (Ono et al 2018;Moutard et al 2020;Harikane et al 2022;C. Liu et al 2022, in preparation).…”