JWST, ALMA, and Keck Spectroscopic Constraints on the UV Luminosity Functions at z~7-14: Clumpiness and Compactness of the Brightest Galaxies in the Early Universe

Abstract

We present the number densities and physical properties of the bright galaxies spectroscopically confirmed at $z\sim 7-14$. Our sample is composed of 60 galaxies at $z_{\mathrm{spec}}\sim 7-14$, including recently-confirmed galaxies at $z_{\mathrm{spec}}=12.34-14.32$ with JWST, as well as new confirmations at $z_{\mathrm{spec}}=6.583-7.643$ with $-24<M_{\mathrm{UV}}<-21$ mag using ALMA and Keck. Our JWST/NIRSpec observations have also revealed that very bright galaxy candidates at $z\sim 10-13$ identified from ground-based telescope images before JWST are passive galaxies at $z\sim 3-4$, emphasizing the necessity of strict screening and spectroscopy in the selection of the brightest galaxies at $z>10$. The UV luminosity functions derived from these spectroscopic results are consistent with a double power-law function, showing tensions with theoretical models at the bright end. To understand the origin of the overabundance of bright galaxies, we investigate their morphologies using JWST/NIRCam high-resolution images obtained in various surveys including PRIMER and COSMOS-Web. We find that $\sim 70\%$ of the bright galaxies at $z\sim 7$ exhibit clumpy morphologies with multiple sub-components, suggesting merger-induced starburst activity, which is consistent with SED fitting results showing bursty star formation histories. At $z\gtrsim 10$, bright galaxies are classified into two types of galaxies; extended ones with weak high-ionization emission lines, and compact ones with strong high-ionization lines including NIV]$\hat{I}»$1486, indicating that at least two different processes (e.g., merger-induced starburst and compact star formation/AGN) are shaping the physical properties of the brightest galaxies at $z\gtrsim 10$ and are responsible for their overabundance.

34 pages, 22 figures, Accepted for Publication in ApJ