[Paper Review] EPOCHS Paper II: The Ultraviolet Luminosity Function from $7.5

Nathan Adams, Christopher J. Conselice+35 more|arXiv (Cornell University)|Apr 26, 2023

Atmospheric Ozone and Climate17 citations

TL;DR

This study derives the ultraviolet luminosity function and star formation rate density for 7.5<z<13.5 using 180 arcmin^2 of JWST/PEARLS blank-field data, finding z=8–9 densities consistent with HST, z=12.5 densities higher than simulations, and overall support for galaxy-driven reionization up to z~8.

ABSTRACT

We present an analysis of the ultraviolet luminosity function (UV LF) and star formation rate density of distant galaxies ($7.5 &lt; z &lt; 13.5$) in the `blank' fields of the Prime Extragalactic Areas for Reionization Science (PEARLS) survey combined with Early Release Science (ERS) data from the CEERS, GLASS, NGDEEP surveys/fields and the first data release of JADES. We use strict quality cuts on EAZY photometric redshifts to obtain a reliable selection and characterisation of high-redshift ($z&gt;6.5$) galaxies from a consistently processed set of deep, near-infrared imaging. Within an area of 180 arcmin$^{2}$, we identify 1046 candidate galaxies at redshifts $z&gt;6.5$ and we use this sample to study the ultraviolet luminosity function (UV LF) in four redshift bins between $7.5

Motivation & Objective

• Measure the ultraviolet luminosity function (UV LF) and star formation rate density (SFRD) of distant galaxies in the redshift range 7.5<z<13.5.
• Construct a robust high-redshift galaxy sample from consistently processed JWST NIRCam imaging across multiple surveys to minimize systematics.
• Assess how the UV LF evolves with redshift and compare results to past HST measurements and theoretical predictions.
• Evaluate the role of cosmic variance in shaping high-redshift galaxy densities and implications for reionization.
• Lay groundwork for future derivations of galaxy properties (e.g., stellar masses, star formation properties) in the early Universe.

Proposed method

• Reprocess JWST NIRCam imaging from PEARLS, CEERS, GLASS, NGDEEP, JADES and SMACS in a consistent pipeline to produce 0.03 arcsec/pixel mosaics.
• Perform forced photometry in 0.32 arcsecond apertures with PSF-corrected fluxes and representative aperture corrections.
• Estimate photometric depths per field using NMAD of 200 empty apertures to obtain realistic photometric errors.
• Use EAZY-py with Larson et al. (2023a) templates (bluer, emission-line–rich) for photometric redshifts; enforce robust high-z selection criteria across multiple metrics (P(z), chi^2, delta chi^2, and size checks).
• Identify and remove brown dwarfs via SED fitting with Sonora Bobcat templates to minimize stellar contamination.
• Limit the UV LF measurement to redshift bins within 7.5<z<13.5 and to unlensed, blank-field regions to avoid lensing model uncertainties.

Experimental results

Research questions

• RQ1 What is the ultraviolet luminosity function in four redshift bins between 7.5<z<13.5 in deep, blank JWST fields?
• RQ2 How does the derived UV LF compare to past HST measurements and to early JWST results across z~8–12?
• RQ3 What does the star formation rate density implied by the UV LF indicate about the efficiency of star formation and the drivers of reionization at z>6.5?
• RQ4 To what extent does cosmic variance affect inferred high-z galaxy number densities in small-area JWST surveys?

Key findings

• 1046 candidate galaxies with z>6.5 identified within 180 arcmin^2.
• UV LF measurements in four redshift bins between 7.5<z<13.5 are obtained for a robust high-z sample.
• Galaxy number densities at z=8 and z=9 are consistent with past HST observations.
• z=10.5 densities lie between early JWST results and past HST results, suggesting cosmic variance as a possible cause of previously high densities.
• UV-luminous galaxy densities at z=12.5 are higher than predictions from simulations.
• Star formation rate density is largely consistent with a constant star formation efficiency and slightly lower than some previous JWST-based estimates, supporting galaxy-driven reionization at z≤8.