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1. ALESS-JWST: Joint (Sub)kiloparsec JWST and ALMA Imaging of z  ~ 3 Submillimeter Galaxies Reveals Heavily Obscured Bulge Formation Events

   https://doi.org/10.3847/1538-4357/ad9a52  

   Hodge, J A; da_Cunha, E; Kendrew, S; Li, J; Smail, I; Westoby, B A; Nayak, O; Swinbank, A M; Chen, C-C; Walter, F; et al (January 2025, The Astrophysical Journal)

   Abstract We present JWST NIRCam imaging targeting 13z ~ 3 infrared-luminous (L_IR ∼ 5 × 10¹²L_⊙) galaxies from the ALESS survey with uniquely deep, high-resolution (0 $\stackrel{\text{″}}{.}$ 08–0 $\stackrel{″}{.}$ 16) Atacama Large Millimeter/submillimeter Array 870μm imaging. The 2.0–4.4μm (observed frame) NIRCam imaging reveals the rest-frame near-infrared stellar emission in these submillimeter-selected galaxies at the same (sub)kiloparsec resolution as the 870μm dust continuum. The newly revealed stellar morphologies show striking similarities with the dust continuum morphologies at 870μm, with the centers and position angles agreeing for most sources, clearly illustrating that the spatial offsets reported previously between the 870μm and Hubble Space Telescope morphologies were due to strong differential dust obscuration. The F444W sizes are 78% ± 21% larger than those measured at 870μm, in contrast to recent results from hydrodynamical simulations that predict larger 870μm sizes. We report evidence for significant dust obscuration in F444W for the highest-redshift sources, emphasizing the importance of longer-wavelength MIRI imaging. The majority of the sources show evidence that they are undergoing mergers/interactions, including tidal tails/plumes—some of which are also detected at 870μm. We find a clear correlation between NIRCam colors and 870μm surface brightness on  ∼1 kpc scales, indicating that the galaxies are primarily red due to dust—not stellar age—and we show that the dust structure on  ∼kpc scales is broadly similar to that in nearby galaxies. Finally, we find no strong stellar bars in the rest-frame near-infrared, suggesting the extended bar-like features seen at 870μm are highly obscured and/or gas-dominated structures that are likely early precursors to significant bulge growth. 

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2. COSMOS-Web: Intrinsically Luminous z ≳ 10 Galaxy Candidates Test Early Stellar Mass Assembly

   https://doi.org/10.3847/1538-4357/ad2075  

   Casey, Caitlin M; Akins, Hollis B; Shuntov, Marko; Ilbert, Olivier; Paquereau, Louise; Franco, Maximilien; Hayward, Christopher C; Finkelstein, Steven L; Boylan-Kolchin, Michael; Robertson, Brant E; et al (April 2024, The Astrophysical Journal)

   Abstract We report the discovery of 15 exceptionally luminous 10 ≲z≲ 14 candidate galaxies discovered in the first 0.28 deg²of JWST/NIRCam imaging from the COSMOS-Web survey. These sources span rest-frame UV magnitudes of −20.5 >M_UV> −22, and thus constitute the most intrinsically luminousz≳ 10 candidates identified by JWST to date. Selected via NIRCam imaging, deep ground-based observations corroborate their detection and help significantly constrain their photometric redshifts. We analyze their spectral energy distributions using multiple open-source codes and evaluate the probability of low-redshift solutions; we conclude that 12/15 (80%) are likely genuinez≳ 10 sources and 3/15 (20%) likely low-redshift contaminants. Three of ourz∼ 12 candidates push the limits of early stellar mass assembly: they have estimated stellar masses ∼ 5 × 10⁹M_⊙, implying an effective stellar baryon fraction ofϵ_⋆∼ 0.2−0.5, whereϵ_⋆≡M_⋆/(f_bM_halo). The assembly of such stellar reservoirs is made possible due to rapid, burst-driven star formation on timescales < 100 Myr where the star formation rate may far outpace the growth of the underlying dark matter halos. This is supported by the similar volume densities inferred forM_⋆∼ 10¹⁰M_⊙galaxies relative toM_⋆∼ 10⁹M_⊙—both about 10⁻⁶Mpc⁻³—implying they live in halos of comparable mass. At such high redshifts, the duty cycle for starbursts would be of order unity, which could cause the observed change in the shape of the UV luminosity function from a double power law to a Schechter function atz≈ 8. Spectroscopic redshift confirmation and ensuing constraints of their masses will be critical to understand how, and if, such early massive galaxies push the limits of galaxy formation in the Lambda cold dark matter paradigm. 

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3. High-redshift JWST predictions from IllustrisTNG: dust modelling and galaxy luminosity functions

   https://doi.org/10.1093/mnras/staa137  

   Vogelsberger, Mark; Nelson, Dylan; Pillepich, Annalisa; Shen, Xuejian; Marinacci, Federico; Springel, Volker; Pakmor, Rüdiger; Tacchella, Sandro; Weinberger, Rainer; Torrey, Paul; et al (March 2020, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The James Webb Space Telescope (JWST) promises to revolutionize our understanding of the early Universe, and contrasting its upcoming observations with predictions of the Λ cold dark matter model requires detailed theoretical forecasts. Here, we exploit the large dynamic range of the IllustrisTNG simulation suite, TNG50, TNG100, and TNG300, to derive multiband galaxy luminosity functions from z = 2 to z = 10. We put particular emphasis on the exploration of different dust attenuation models to determine galaxy luminosity functions for the rest-frame ultraviolet (UV), and apparent wide NIRCam bands. Our most detailed dust model is based on continuum Monte Carlo radiative transfer calculations employing observationally calibrated dust properties. This calibration results in constraints on the redshift evolution of the dust attenuation normalization and dust-to-metal ratios yielding a stronger redshift evolution of the attenuation normalization compared to most previous theoretical studies. Overall we find good agreement between the rest-frame UV luminosity functions and observational data for all redshifts, also beyond the regimes used for the dust model calibrations. Furthermore, we also recover the observed high-redshift (z = 4–6) UV luminosity versus stellar mass relation, the H α versus star formation rate relation, and the H α luminosity function at z = 2. The bright end (MUV > −19.5) cumulative galaxy number densities are consistent with observational data. For the F200W NIRCam band, we predict that JWST will detect ∼80 (∼200) galaxies with a signal-to-noise ratio of 10 (5) within the NIRCam field of view, $$2.2\times 2.2 \, {\rm arcmin}^{2}$$, for a total exposure time of $$10^5\, {\rm s}$$ in the redshift range z = 8 ± 0.5. These numbers drop to ∼10 (∼40) for an exposure time of $$10^4\, {\rm s}$$. 

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4. Beyond UVJ: Color Selection of Galaxies in the JWST Era

   https://doi.org/10.3847/1538-4357/aca294  

   Antwi-Danso, Jacqueline; Papovich, Casey; Leja, Joel; Marchesini, Danilo; Marsan, Z C; Martis, Nicholas S.; Labbe, Ivo; Muzzin, Adam; Glazebrook, Karl; Straatman, Caroline M.; et al (February 2023, The Astrophysical journal)

   We present a new rest-frame color–color selection method using synthetic us − gs and gs − is, (ugi)s colors to identify star-forming and quiescent galaxies. Our method is similar to the widely used U − V versus V − J (UVJ) diagram. However, UVJ suffers known systematics. Spectroscopic campaigns have shown that UVJ-selected quiescent samples at z ≳ 3 include ∼10%–30% contamination from galaxies with dust-obscured star formation and strong emission lines. Moreover, at z > 3, UVJ colors are extrapolated because the rest-frame band shifts beyond the coverage of the deepest bandpasses at <5 μm (typically Spitzer/IRAC 4.5 μm or future JWST/NIRCam observations). We demonstrate that (ugi)s offers improvements to UVJ at z > 3, and can be applied to galaxies in the JWST era. We apply (ugi)s selection to galaxies at 0.5 < z < 6 from the (observed) 3D-HST and UltraVISTA catalogs, and to the (simulated) JAGUAR catalogs. We show that extrapolation can affect (V − J)0 color by up to 1 mag, but changes $${({g}_{s}-{i}_{s})}_{0}$$ color by ≤0.2 mag, even at z ≃ 6. While (ugi)s-selected quiescent samples are comparable to UVJ in completeness (both achieve ∼85%–90% at z = 3–3.5), (ugi)s reduces contamination in quiescent samples by nearly a factor of 2, from ≃35% to ≃17% at z = 3, and from ≃60% to ≃33% at z = 6. This leads to improvements in the true-to-false-positive ratio (TP/FP), where we find TP/FP ≳2.2 for (ugi)s at z ≃ 3.5 − 6, compared to TP/FP < 1 for UVJ-selected samples. This indicates that contaminants will outnumber true quiescent galaxies in UVJ at these redshifts, while (ugi)s will provide higher-fidelity samples. 

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5. Euclid : A UV-faint quasar in a highly luminous star-forming host galaxy at z  ≈ 7.7

   https://doi.org/10.1051/0004-6361/202659319  

   Belladitta, S; Decarli, R; Bañados, E; Walter, F; Yang, D; Guarneri, F; Jahnke, K; Bisogni, S; Bosman, S_E I; Fan, X; et al (July 2026, Astronomy & Astrophysics)

   Constraining the co-evolution of supermassive black holes and their host galaxies in the first billion years after the Big Bang is essential for understanding the formation of the earliest cosmic structures. Here, we present IRAM/NOrthern Extended Millimeter Array (NOEMA) observations of thez ≈ 7.7 quasar EUCL J125308.55+705432.3, recently discovered in the first data release of the Euclid Wide Survey. We report the most distant detections of [C II]158 μm and cold dust emission in a quasar host to date. The [C II]emission line sets the systemic redshift atz = 7.6980 ± 0.0004. The source exhibits luminosities ofL_FIR = 3.6 × 10¹² L_⊙andL_[C II]= 2 × 10⁹L_⊙, respectively, a dust mass of 1.4 × 10⁸ M_⊙, and a dynamical mass in the range 0.33 − 1.3 × 10¹⁰ M_⊙. Remarkably, despite being nearly two magnitudes fainter in the rest-frame UV (M₁₄₅₀ = −24.06) than previously knownz ≈ 7.5 quasars (⟨M₁₄₅₀⟩ ∼ − 26.5), EUCL J125308.55+705432.3 exhibits the brightest [C II]emission among them. This indicates that the host galaxy is actively star-forming, with a star-formation rate > 250M_⊙yr⁻¹, consistent with recent findings that UV-faint quasars atz > 6 preferentially reside in [C II]-luminous galaxies. The UV-faintness likely reflects dust obscuration or sub-Eddington accretion, rather than lower host mass, suggesting these systems are at a different stage in their evolution compared to UV-bright quasars. These IRAM/NOEMA observations highlight the power of combiningEuclid’s wide-area quasar discovery potential with submillimetre follow-up observations to characterise the host galaxies of early supermassive black holes across a broader redshift and luminosity range than previously accessible. 

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