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1. JWST UNCOVER: discovery of z > 9 galaxy candidates behind the lensing cluster Abell 2744

   https://doi.org/10.1093/mnras/stad1998  

   Atek, Hakim ; Chemerynska, Iryna ; Wang, Bingjie ; Furtak, Lukas J. ; Weibel, Andrea ; Oesch, Pascal ; Weaver, John R. ; Labbé, Ivo ; Bezanson, Rachel ; van Dokkum, Pieter ; et al ( August 2023 , Monthly Notices of the Royal Astronomical Society)

   We present the results of a search for high-redshift (z > 9) galaxy candidates in the JWST UNCOVER survey, using deep NIRCam and NIRISS imaging in seven bands over ∼45 arcmin2 and ancillary Hubble Space Telescope (HST) observations. The NIRCam observations reach a 5σ limiting magnitude of ∼29.2 AB. The identification of high-z candidates relies on a combination of a dropout selection and photometric redshifts. We find 16 candidates at 9 < z < 12 and three candidates at 12 < z < 13, eight candidates are deemed very robust. Their lensing amplification ranges from μ = 1.2 to 11.5. Candidates have a wide range of (lensing corrected) luminosities and young ages, with low stellar masses [6.8 < log(M⋆/M⊙) < 9.5] and low star formation rates (SFR = 0.2–7 M⊙ yr−1), confirming previous findings in early JWST observations of z > 9. A few galaxies at z ∼ 9−10 appear to show a clear Balmer break between the F356W and F444W/F410M bands, which helps constrain their stellar mass. We estimate blue UV continuum slopes between β = −1.8 and −2.3, typical for early galaxies at z > 9 but not as extreme as the bluest recently discovered sources. We also find evidence for a rapid redshift-evolution of the mass-luminosity relation and a redshift evolution of the UV continuum slope for a given range of intrinsic magnitude, in line with theoretical predictions. These findings suggest that deeper JWST observations are needed to reach the fainter galaxy population at those early epochs, and follow-up spectroscopy will help better constrain the physical properties and star formation histories of a larger sample of galaxies.

    

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2. High-redshift Galaxy Candidates at z = 9–10 as Revealed by JWST Observations of WHL0137-08

   https://doi.org/10.3847/1538-4357/acecfe  

   Bradley, Larry D. ; Coe, Dan ; Brammer, Gabriel ; Furtak, Lukas J. ; Larson, Rebecca L. ; Kokorev, Vasily ; Andrade-Santos, Felipe ; Bhatawdekar, Rachana ; Bradač, Maruša ; Broadhurst, Tom ; et al ( September 2023 , The Astrophysical Journal)

   We report the discovery of four galaxy candidates observed 450–600 Myr after the Big Bang with photometric redshifts betweenz∼ 8.3 and 10.2 measured using James Webb Space Telescope (JWST) NIRCam imaging of the galaxy cluster WHL0137−08 observed in eight filters spanning 0.8–5.0μm, plus nine Hubble Space Telescope filters spanning 0.4–1.7μm. One candidate is gravitationally lensed with a magnification ofμ∼ 8, while the other three are located in a nearby NIRCam module with expected magnifications ofμ≲ 1.1. Using SED fitting, we estimate the stellar masses of these galaxies are typically in the range$\log M_{\star }/M_{\odot }$= 8.3–8.7. All appear young, with mass-weighted ages <240 Myr, low dust contentA_V< 0.15 mag, and specific star formation rates sSFR ∼0.25–10 Gyr⁻¹for most. Onez∼ 9 candidate is consistent with an age <5 Myr and an sSFR ∼10 Gyr⁻¹, as inferred from a strong F444W excess, implying [Oiii]+Hβrest-frame equivalent width ∼2000 Å, although an olderz∼ 10 object is also allowed. Anotherz∼ 9 candidate is lensed into an arc 2.″4 long with a magnification ofμ∼ 8. This arc is the most spatially resolved galaxy atz∼ 9 known to date, revealing structures ∼30 pc across. Follow-up spectroscopy of WHL0137−08 with JWST/NIRSpec will be useful to spectroscopically confirm these high-redshift galaxy candidates and to study their physical properties in more detail.

    

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3. Low-mass bursty galaxies in JADES efficiently produce ionizing photons and could represent the main drivers of reionization

   https://doi.org/10.1093/mnras/stad3605  

   Simmonds, C. ; Tacchella, S. ; Hainline, K. ; Johnson, B. D. ; McClymont, W. ; Robertson, B. ; Saxena, A. ; Sun, F. ; Witten, C. ; Baker, W. M. ; et al ( November 2023 , Monthly Notices of the Royal Astronomical Society)

   We use deep imaging from the JWST Advanced Deep Extragalactic Survey (JADES) to study the evolution of the ionizing photon production efficiency, ξion. We estimate ξion for a sample of 677 galaxies at z ∼ 4–9 using NIRCam (Near-Infrared Camera) photometry. Specifically, combinations of the medium and wide bands F335M–F356W and F410M–F444W to constrain emission lines that trace ξion: Hα and [O iii]. Additionally, we use the spectral energy distribution fitting code prospector to fit all available photometry and infer galaxy properties. The flux measurements obtained via photometry are consistent with FRESCO (First Reionisation Epoch Spectroscopic Complete Survey) and NIRSpec-derived fluxes. Moreover, the emission-line-inferred measurements are consistent with the prospector estimates. We also confirm the observed ξion trend with redshift and MUV, and find: log ξion(z, MUV) = (0.05 ± 0.02)z + (0.11 ± 0.02)MUV + (27.33 ± 0.37). We use prospector to investigate correlations of ξion with other galaxy properties. We see a clear correlation between ξion and burstiness in the star formation history of galaxies, given by the ratio of recent to older star formation, where burstiness is more prevalent at lower stellar masses. We also convolve our ξion relations with luminosity functions from the literature, and constant escape fractions of 10 per cent and 20 per cent, to place constraints on the cosmic ionizing photon budget. By combining our results, we find that if our sample is representative of the faint low-mass galaxy population, galaxies with bursty star formation are efficient enough in producing ionizing photons and could be responsible for the reionization of the Universe.

    

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4. Simulating JWST deep extragalactic imaging surveys and physical parameter recovery

   https://doi.org/10.1051/0004-6361/202037450  

   Kauffmann, O. B. ; Le Fèvre, O. ; Ilbert, O. ; Chevallard, J. ; Williams, C. C. ; Curtis-Lake, E. ; Colina, L. ; Pérez-González, P. G. ; Pye, J. P. ; Caputi, K. I. ( August 2020 , Astronomy & Astrophysics)

   null (Ed.)

   We present a new prospective analysis of deep multi-band imaging with the James Webb Space Telescope (JWST). In this work, we investigate the recovery of high-redshift 5 <   z  <  12 galaxies through extensive image simulations of accepted JWST programs, including the Early Release Science in the EGS field and the Guaranteed Time Observations in the HUDF. We introduced complete samples of ∼300 000 galaxies with stellar masses of log( M * / M ⊙ ) > 6 and redshifts of 0 <   z  <  15, as well as galactic stars, into realistic mock NIRCam, MIRI, and HST images to properly describe the impact of source blending. We extracted the photometry of the detected sources, as in real images, and estimated the physical properties of galaxies through spectral energy distribution fitting. We find that the photometric redshifts are primarily limited by the availability of blue-band and near-infrared medium-band imaging. The stellar masses and star formation rates are recovered within 0.25 and 0.3 dex, respectively, for galaxies with accurate photometric redshifts. Brown dwarfs contaminating the z  >  5 galaxy samples can be reduced to < 0.01 arcmin −2 with a limited impact on galaxy completeness. We investigate multiple high-redshift galaxy selection techniques and find that the best compromise between completeness and purity at 5 <   z  <  10 using the full redshift posterior probability distributions. In the EGS field, the galaxy completeness remains higher than 50% at magnitudes m UV  <  27.5 and at all redshifts, and the purity is maintained above 80 and 60% at z  ≤ 7 and 10, respectively. The faint-end slope of the galaxy UV luminosity function is recovered with a precision of 0.1–0.25, and the cosmic star formation rate density within 0.1 dex. We argue in favor of additional observing programs covering larger areas to better constrain the bright end. 

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5. Brown Dwarf Candidates in the JADES and CEERS Extragalactic Surveys

   https://doi.org/10.3847/1538-4357/ad20d1  

   Hainline, Kevin N. ; Helton, Jakob M. ; Johnson, Benjamin D. ; Sun, Fengwu ; Topping, Michael W. ; Leisenring, Jarron M. ; Baker, William M. ; Eisenstein, Daniel J. ; Hausen, Ryan ; Hviding, Raphael E. ; et al ( March 2024 , The Astrophysical Journal)

   By combining the James Webb Space Telescope (JWST)/NIRCam JADES and CEERS extragalactic data sets, we have uncovered a sample of 21 T and Y brown dwarf candidates at best-fit distances between 0.1 and 4.2 kpc. These sources were selected by targeting the blue 1–2.5μm colors and red 3–4.5μm colors that arise from molecular absorption in the atmospheres ofT_eff< 1300 K brown dwarfs. We fit these sources using multiple models of substellar atmospheres and present the resulting fluxes, sizes, effective temperatures, and other derived properties for the sample. If confirmed, these fits place the majority of the sources in the Milky Way thick disk and halo. We observe proper motions for seven of the candidate brown dwarfs, with directions in agreement with the plane of our Galaxy, providing evidence that they are not extragalactic in nature. We demonstrate how the colors of these sources differ from selected high-redshift galaxies, and explore the selection of these sources in planned large-area JWST NIRCam surveys. Deep imaging with JWST/NIRCam presents an an excellent opportunity for finding and understanding these ultracool dwarfs at kiloparsec distances.

    

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