The evolution of the galaxy UV luminosity function at redshifts z ~ 8-15 from deep JWST and ground-based near-infrared imaging

Abstract

We re-reduce and analyse the available James Webb Space Telescope (JWST) ERO and ERS NIRCam imaging (SMACS0723, GLASS, CEERS) in combination with the latest deep ground-based near-infrared imaging in the COSMOS field (provided by UltraVISTA DR5) to produce a new measurement of the evolving galaxy UV luminosity function (LF) over the redshift range 𝑧 = 8 − 15. This yields a new estimate of the evolution of UV luminosity density (𝜌 UV ), and hence cosmic star-formation rate density (𝜌 SFR ) out to within < 300 Myr of the Big Bang. Our results confirm that the high-redshift LF is best described by a double power-law (rather than a Schechter) function, and that the LF and the resulting derived 𝜌 UV (and thus 𝜌 SFR ), continues to decline gradually and steadily over this redshift range (as anticipated from previous studies which analysed the pre-existing data in a consistent manner). We provide details of the 55 high-redshift galaxy candidates, 44 of which are new, that have enabled this new analysis. Our sample contains 6 galaxies at 𝑧 ≥ 12, one of which appears to set a new redshift record as an apparently robust galaxy candidate at 𝑧 16.7, the properties of which we therefore consider in detail. The advances presented here emphasize the importance of achieving high dynamic range in studies of early galaxy evolution, and re-affirm the enormous potential of forthcoming larger JWST programmes to transform our understanding of the young Universe.

The brightest galaxies at Cosmic Dawn

“…Thus a reduction in dust attenuation may play an important role in explaining excesses of bright 𝑧 ∼ > 8 galaxies (e.g., Bowler et al 2020). Indeed, we note that of the brightest 𝑧 ∼ > 11 candidates found with JWST, all show very blue UV slopes 𝛽 ∼ < − 2.1, indicating negligible dust attenuation (Naidu et al 2022;Atek et al 2022;Donnan et al 2022). Though c.f.…”

“…The James Webb Space Telescope (JWST) is pushing our observational horizon even further, expanding our view to 5𝜇m (with the ★ E-mail: charlotte.mason@nbi.ku.dk NIRCam instrument, Rieke et al 2005), making it possible to observe rest-frame UV emission from 𝑧 ∼ < 30 galaxies, when the universe is just 100 Myr old. Interestingly, recent works have shown JWST to preliminary confirm HST galaxy counts at 𝑧 ∼ 7 − 9 (Leethochawalit et al 2022b) but claimed discovery of a relatively high number of galaxy candidates at 𝑧 ∼ 10 − 17 from early release science observations, suggesting the excess of sources relative to UV LF predictions extends to higher redshifts (Castellano et al 2022;Naidu et al 2022;Morishita & Stiavelli 2022;Donnan et al 2022;Atek et al 2022;Finkelstein et al 2022). It is too early to draw definitive conclusions, as these sources are not spectroscopically confirmed and the photometric candidates are based on reductions using preliminary calibrations (indeed, some of the same sources are reported with significantly different fluxes by different groups), and cover small fields subject to cosmic variance (e.g., Trenti & Stiavelli 2008).…”

Stress Testing $Λ$CDM with High-redshift Galaxy Candidates

“…This rapid rise indicates that the mass reservoir available for the most massive galaxies increases quickly and that, to first order, the most massive galaxies at 𝑧 = 20 should be significantly less massive than the most massive galaxies at 𝑧 = 10 (however, hierarchical assembly guarantees that individual halo mass accretion histories are flatter than these curves). The stars on the plot show several of the high-redshift galaxy candidates detected in JWST observations (from Atek et al 2022;Donnan et al 2022;Finkelstein 2016;Labbé et al 2022;Naidu et al 2022) that are intrinsically rare in terms of their stellar content at that redshift; the candidates must be hosted by halos with cumulative comoving number densities that are at most 10 −2 − 10 −8 Mpc −3 and could be significantly smaller.…”

“…My analysis is in many ways similar to Behroozi & Silk (2018), who connected cumulative number densities of dark matter halos to high-redshift galaxy stellar mass functions, though I also consider the maximal cumulative stellar mass density allowed in ΛCDM. The question of the consistency of stellar mass functions and the underlying cosmological dark matter halo mass functions has become considerably more urgent since the very recent release of the first data from JWST, and with it, a swarm of high-redshift galaxy candidates (Atek et al 2022;Castellano et al 2022;Donnan et al 2022;Finkelstein et al 2022;Labbé et al 2022;Morishita & Stiavelli 2022;Naidu et al 2022;Yan et al 2022). With these values, the linear matter power spectrum is specified at all times relevant for structure formation.…”

On the ages of bright galaxies $\sim 500$ Myr after the Big Bang: insights into star formation activity at $z \gtrsim 15$ with JWST

“…Now, with JWST, a new window into galaxies in the even earlier (𝑧 12) Universe is opening (e.g. Naidu et al 2022;Donnan et al 2022;Castellano et al 2022).…”