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Abstract:

We analyze 99 photometrically selected Little Red Dots (LRDs) at z ≈ 4–8 in the GOODS fields, leveraging ultradeep JADES NIRCam short-wavelength (SW) data. Among the 99 selected LRDs, we examine the morphology of 30. The remaining 69 appear predominantly compact, with sizes ≲400 pc and no extended components even in stacked SW images. However, their unresolved nature may partly reflect current depth limitations, which could prevent the detection of faint diffuse components. Among the 30 morphologically analyzed LRDs, 50% show multiple associated components, while the rest exhibit highly asymmetric structures, despite appearing as single sources. This diversity in rest-frame UV morphologies may point to interactions or strong internal feedback. We find median stellar masses of log10(M⋆/M⊙)=9.07−0.08+0.11 for pure stellar models with AV≈1.16−0.21+0.11 mag, and log10(M⋆/M⊙)=9.67−0.27+0.17 for models including active galactic nuclei (AGNs) with AV≈2.74−0.71+0.55 mag, in line with recent studies suggesting higher masses and dust content for AGN-fitted LRDs. NIRSpec spectra are available for 15 sources, six of which are also in the morphological sample. Broad Hα is detected in 40% (FWHM = 1200–2900 km s−1), and one source shows broad Hβ emission. Emission line ratios indicate a composite nature, consistent with both AGN and stellar processes. Altogether, these results suggest that LRDs are a mixed population, and their rest-frame UV morphology reflects this complexity. Morphological studies of larger samples could provide a new way to understand what drives their properties and evolution.

Abstract:

The high-redshift UV luminosity function provides important insights into the evolution of early galaxies. JWST has revealed an unexpectedly large population of bright (MUV ≲ −20) galaxies at z ≳ 10, implying fundamental changes in the star-forming properties of galaxies at increasingly early times. However, constraining the fainter population (MUV ≳ −18) has been more challenging. In this work, we present the z ≳ 9 UV luminosity function from the JWST Advanced Deep Extragalactic Survey. We calculate the UV luminosity function from several hundred z ≳ 9 galaxy candidates that reach UV luminosities of MUV ∼ −17 in redshift bins of z ∼ 8.5–12 (309 candidates) and z ∼ 12–16 (63 candidates). We search for candidates at z ∼ 16–22.5 and find none. We also estimate the z ∼ 14–16 luminosity function from the z ≥ 14 subset of the z ∼ 12–16 sample. Consistent with other measurements, we find an excess of bright galaxies that is in tension with many theoretical models, especially at z ≳ 12. However, we also find high number densities at −18 ≲ MUV ≲ −17, suggesting that there is a larger population of faint galaxies than expected, as well as bright ones. From our parametric fits for the luminosity function, we find steep faint-end slopes of −2.5 ≲ α ≲ −2.3, suggesting a large population of faint (MUV ≳ −17) galaxies. Combined, the high normalization and steep faint-end slope of the luminosity function could imply that the reionization process is appreciably underway as early as z = 10.

Abstract:

Distant quasars (QSOs) in galaxy overdensities are considered key actors in the evolution of the early Universe. In this work, we performed an analysis of the kinematic and physical properties of the BR1202-0725 system at z ∼ 4.7, one of the most overdense fields known in the early Universe, consisting of a QSO, a sub-millimetre galaxy (SMG), and three Lyman- α emitters. We used data from the JWST/NIRSpec integral field unit to analyse the rest-frame optical emission of each source in the system. Based on the continuum and Balmer line emission, we estimated a bolometric luminosity of log( L bol /[erg s −1 ]) = 47.2 ± 0.4 and a black hole mass of log( M BH / M ⊙ ) = 10.1 ± 0.5 for the QSO, which are consistent with previous measurements obtained with ground-based observations. The NIRSpec spectra of the SMG revealed, instead, unexpected [O  III ] and H α +[N  II ] profiles. The overall [O  III ] line profile is blueshifted by more than 700 km s −1 relative to the systemic velocity of the galaxy. Additionally, both the [O  III ] and H α +[N  II ] lines show prominent broad (∼1300 km s −1 ), blueshifted wings associated with outflowing ionized gas. The analysis of NIRSpec and X-ray observations indicates that the SMG likely hosts an accreting supermassive black hole, which is 91̽»¨ed by the following results: (i) the excitation diagnostic diagram is consistent with ionization from an active galactic nucleus (AGN); (ii) the X-ray luminosity is higher than 10 44 erg s −1 ; and (iii) it hosts a fast outflow ( v out ∼ 5000 km s −1 ), comparable to the ones observed in luminous QSOs. Therefore, the QSO-SMG pair of BR1202-0725 represents one of the highest-redshift double AGNs found to date, with a projected separation of 24 kpc. Finally, we investigated the environment of this system and found four new galaxies, detected in both [O  III ] and H α emission, at the same redshift of the QSO and within a projected distance of 5 kpc from it. This overdense system includes at least ten galaxies in a field of view of only 980 kpc 2 .

Abstract:

We investigate the unusual emission-line luminosity ratios observed in the JWST Deep Extragalactic Survey (JADES) NIRSpec spectroscopy of GN-z11, which reveal exceptionally strong emission lines and a significant detection of the rarely observed N iii] , multiplet. These features suggest an elevated N/O abundance, challenging existing models of stellar populations and nebular emission. To assess whether Wolf–Rayet (WR) stars can account for the observed line ratios, we construct a suite of stellar and nebular models incorporating high-resolution stellar spectral libraries, enabling a more accurate treatment of WR evolution and its influence on the ionizing radiation field. We find that the inclusion of WR stars is essential for reproducing the observed position of GN-z11 in the C iii]/He ii versus C iii]/C iv diagnostic plane, resolving discrepancies from previous studies. The model-derived metallicity (0.07 Z/Z 0.15), ionization parameter (−2), and stellar ages are consistent with the literature estimates. However, our models underpredict the N iii/O iii] ratio, suggesting that WR stars alone cannot fully explain the nitrogen enrichment. This suggests that additional mechanisms, such as rapid chemical enrichment in a young, metal-poor environment, may be necessary to explain the nitrogen excess. While our models successfully reproduce most observed line ratios, further refinements to the models are needed to fully characterize the stellar populations and the enrichment processes of high-redshift galaxies like GN-z11.