Seeing sharper and deeper: JWST's first glimpse of the photometric and spectroscopic properties of galaxies in the epoch of reionisation

Abstract

We analyse the photometric and spectroscopic properties of four galaxies in the epoch of reionisation (EoR) within the SMACS 0723 JWST Early Release Observations field. Given the known spectroscopic redshifts of these sources, we investigated the accuracy with which photometric redshifts can be derived using NIRCam photometry alone, finding that F115W imaging is essential to distinguish between 𝑧 ∼ 8 galaxies with high equivalent width (EW) [O III] 𝜆5007 emission and 𝑧 ∼ 10 Balmer break galaxies. We find that all four sources exhibit strong (> 0.6 mag) F356W−F444W colours, which sit at the extreme end of theoretical predictions from numerical simulations. We find that these galaxies deviate (by ≈ 0.5 dex) from the local correlation between [O III] 𝜆5007/H𝛽 and [Ne III] 𝜆3869/[O II], which is consistent with the predictions from simulations of high-redshift galaxies. We measure the [O III] 𝜆5007 rest-frame equivalent widths both directly from the spectroscopy, and indirectly as inferred from the strong F356W−F444W colours, finding large [O III] 𝜆5007 EWs of 400-1000 Å. The [O III] 𝜆5007 and H𝛽 EWs are consistent with those seen in extreme, intensely star-forming dwarf galaxies in the local Universe. Our structural analysis indicates that these galaxies are resolved, exhibiting irregular shapes with bright clumps and colour gradients. In line with the predictions from the FLARES hydrodynamic simulations, such intense star formation and extreme nebular conditions are likely the norm, rather than the exception, in the EoR. Finally, although star-forming galaxies and AGN often occupy similar regions within the [O III] 𝜆5007/H𝛽-[O II]/H𝛿 plane, we find that AGN exhibit distinct, red colours in the F150W−F200W, F200W−F277W plane.

A lensed protocluster candidate at z = 7.66 identified in JWST observations of the galaxy cluster SMACS0723−7327

“…Our redshift measurements are consistent with the values previously measured by other groups (e.g. Curti et al 2022, Carnall et al 2022, Atek et al 2022, Katz et al 2022, Trussler et al 2022.…”

JWST NIRCam+NIRSpec: Interstellar medium and stellar populations of young galaxies with rising star formation and evolving gas reservoirs

“…This possibly indicates that we enter at 𝑧 > 7 another epoch of galaxy formation, where galactic systems are out of equilibrium and evolve more stochastically. Consistent with this, other studies find high ionization, low metallicity and high pressure in the interstellar medium (ISM; Katz et al 2022;Schaerer et al 2022;Rhoads et al 2022;Trump et al 2022;Trussler et al 2022).…”

“…These three objects have been discussed in several recent papers (e.g., Arellano-Córdova et al 2022;Carnall et al 2022;Curti et al 2022;Katz et al 2022;Rhoads et al 2022;Schaerer et al 2022;Trump et al 2022;Trussler et al 2022). The different studies rely on different measurement techniques, but also on different reduction and calibration pipelines, making comparisons difficult.…”

High-Redshift Galaxy Candidates at $z = 9-13$ as Revealed by JWST Observations of WHL0137-08

“…Analyses of these z ∼ 9 − 16 candidates observed in JWST imaging further reveal young stellar ages ∼ 10−100 Myr (Whitler et al 2022;Furtak et al 2022), younger than the median ages ∼ 100 Myr measured at slightly lower redshifts z ∼ 7 − 9 (Leethochawalit et al 2022;Endsley et al 2022). Evidence that some of these galaxies are extremely young, < 10 Myr, z ∼ 7 − 9 is provided by very strong emission lines in NIRSpec spectroscopy (Carnall et al 2022;Tacchella et al 2022;Trussler et al 2022), with flux excesses also clearly observed in photometry, especially when imaging is available in four NIRCam long-wavelength filters F277W, F356W, F410M, and F444W.…”