@article{21045,
  abstract     = {The abundant population of little red dots (LRDs), compact objects with red UV to optical colors and broad Balmer lines at high redshift, is revealing new insights into the properties of early active galactic nuclei (AGN). Perhaps the most surprising features of this population are the presence of Balmer absorption and ubiquitous strong Balmer breaks. Recent models link these features to an active supermassive black hole (SMBH) cocooned in very dense gas (NH ∼ 1024 cm−2). We present a stringent test of such models using VLT/MUSE observations of A2744-45924, the most luminous LRD known to date (LHα ≈ 1044 erg s−1), located behind the Abell-2744 lensing cluster at z = 4.464 (μ = 1.8). We detect a moderately extended Lyα nebula (h ≈ 5.7 pkpc), spatially offset from the point-like Hα seen by JWST by ≈1.6 pkpc. The Lyα emission is narrow (FWHM = 270 ± 15 km s−1), and faint (Lyα = 0.07Hα) compared to Lyα nebulae typically observed around quasars of similar luminosity. We detect compact N IV]λ1486 emission, spatially aligned with Hα, and a spatial shift in the far-UV continuum matching the Lyα offset. We discuss that Hα and Lyα have distinct physical origins: Hα originates from the AGN, while Lyα is powered by star formation. In the environment of A2744-45924, we identified four extended Lyα halos (Δz < 0.02, Δr < 100 pkpc). Their Lyα luminosities match the expectations based on Hα emission, and show no evidence for radiation from A2744-45924 affecting its surroundings. The lack of strong, compact, and broad Lyα and the absence of a luminous extended halo, suggest that the UV AGN light is obscured by dense gas cloaking the SMBH with a covering factor close to unity.},
  author       = {Torralba Torregrosa, Alberto and Matthee, Jorryt J and Pezzulli, Gabriele and Urrutia, Tanya and Gronke, Max and Mascia, Sara and D’Eugenio, Francesco and Di Cesare, Claudia and Eilers, Anna Christina and Greene, Jenny E. and Iani, Edoardo and Ishikawa, Yuzo and Mackenzie, Ruari and Naidu, Rohan P. and Navarrete, Benjamín and Kotiwale, Gauri},
  issn         = {1432-0746},
  journal      = {Astronomy and Astrophysics},
  publisher    = {EDP Sciences},
  title        = {{A weak Ly α halo for an extremely bright little red dot. Indications of enshrouded supermassive black hole growth}},
  doi          = {10.1051/0004-6361/202555596},
  volume       = {705},
  year         = {2026},
}

@article{21341,
  abstract     = {We aim to characterise the mass-metallicity relation (MZR) and the 3D correlation between the stellar mass, metallicity, and star formation rate (SFR) known as the fundamental metallicity relation (FMR) for galaxies at 5 < z < 7. Using ∼800 [O III] selected galaxies from deep NIRCam grism surveys, we present our stacked measurements of direct-Te metallicities, which we used to test recent strong-line metallicity calibrations. Our measured direct-Te metallicities (0.1–0.2 Z⊙ for M★ ≈ 5 × 107 − 9 M⊙, respectively) match recent JWST/NIRSpec-based results. However, there are significant inconsistencies between observations and hydrodynamical simulations. We observe a flatter MZR slope than the SPHINX20 and FLARES simulations, which cannot be attributed to selection effects. With simple models, we show that the effect of an [O III] flux-limited sample on the observed shape of the MZR is strongly dependent on the FMR. If the FMR is similar to the one in the local Universe, the intrinsic high-redshift MZR should be even flatter than is observed. In turn, a 3D relation where SFR correlates positively with metallicity at fixed mass would imply an intrinsically steeper MZR. Our measurements indicate that metallicity variations at fixed mass show little dependence on the SFR, suggesting a flat intrinsic MZR. This could indicate that the low-mass galaxies at these redshifts are out of equilibrium and that metal enrichment occurs rapidly in low-mass galaxies. However, being limited by our stacking analysis, we are yet to probe the scatter in the MZR and its dependence on SFR. Large carefully selected samples of galaxies with robust metallicity measurements can put tight constraints on the high-redshift FMR and help us to understand the interplay between gas flows, star formation, and feedback in early galaxies.},
  author       = {Kotiwale, Gauri and Matthee, Jorryt J and Kashino, Daichi and Vijayan, Aswin P. and Torralba Torregrosa, Alberto and Di Cesare, Claudia and Iani, Edoardo and Bordoloi, Rongmon and Leja, Joel and Maseda, Michael V. and Tacchella, Sandro and Shivaei, Irene and Heintz, Kasper E. and Danhaive, A. Lola and Mascia, Sara and Kramarenko, Ivan and Navarrete, Benjamín and Mackenzie, Ruari and Naidu, Rohan P. and Sobral, David},
  issn         = {1432-0746},
  journal      = {Astronomy & Astrophysics},
  publisher    = {EDP Sciences},
  title        = {{Rapid, out-of-equilibrium metal enrichment indicated by a flat mass-metallicity relation at z ∼ 6 from NIRCam grism spectroscopy}},
  doi          = {10.1051/0004-6361/202556597},
  volume       = {706},
  year         = {2026},
}

@article{21451,
  abstract     = {The population of the little red dots (LRDs) may represent a key phase of supermassive black hole (SMBH) growth. A cocoon of dense excited gas is emerging as a key component to explain the most striking properties of LRDs, such as strong Balmer breaks and Balmer absorption, as well as the weak IR emission. To dissect the structure of LRDs, we analyzed new deep JWST/NIRSpec PRISM and G395H spectra of FRESCO-GN-9771, one of the most luminous known LRDs at z = 5.5. These spectra reveal a strong Balmer break, broad Balmer lines, and very narrow [O III] emission. We revealed a forest of optical [Fe II] lines, which we argue are emerging from a dense (nH = 109 − 10 cm−3) warm layer with electron temperature Te ≈ 7000 K. The broad wings of Hα and Hβ have an exponential profile due to electron scattering in this same layer. The high Hα : Hβ : Hγ flux ratio of ≈10.4 : 1 : 0.14 is an indicator of collisional excitation and resonant scattering dominating the Balmer line emission. A narrow Hγ component, unseen in the other two Balmer lines due to outshining by the broad components, could trace the ISM of a normal host galaxy with a star formation rate of ∼5 M⊙ yr−1. The warm layer is mostly opaque to Balmer transitions, producing a characteristic P Cygni profile in the line centers suggesting outflowing motions. This same layer is responsible for shaping the Balmer break. The broadband spectrum can be reasonably matched by a simple photoionized slab model that dominates the λ > 1500 Å continuum and a low-mass (∼108 M⊙) galaxy that could explain the narrow [O III], with only a subdominant contribution to the UV continuum. Our findings indicate that Balmer lines are not directly tracing the gas kinematics near the SMBH and that the BH mass scale is likely much lower than virial indicators suggest.},
  author       = {Torralba Torregrosa, Alberto and Matthee, Jorryt J and Pezzulli, Gabriele and Naidu, Rohan P. and Ishikawa, Yuzo and Brammer, Gabriel B. and Chang, Seok Jun and Chisholm, John and De Graaff, Anna and D’Eugenio, Francesco and Di Cesare, Claudia and Eilers, Anna Christina and Greene, Jenny E. and Gronke, Max and Iani, Edoardo and Kokorev, Vasily and Kotiwale, Gauri and Kramarenko, Ivan and Ma, Yilun and Mascia, Sara and Navarrete, Benjamín and Nelson, Erica and Oesch, Pascal and Simcoe, Robert A. and Wuyts, Stijn},
  issn         = {1432-0746},
  journal      = {Astronomy & Astrophysics},
  publisher    = {EDP Sciences},
  title        = {{The warm outer layer of a little red dot as the source of [Fe ii] and collisional Balmer lines with scattering wings}},
  doi          = {10.1051/0004-6361/202557537},
  volume       = {707},
  year         = {2026},
}

@article{21452,
  abstract     = {Galaxies exhibit a tight correlation between their star formation rate (SFR) and stellar mass over a wide redshift range known as the star-forming main sequence (SFMS). With JWST, the SFMS can now be investigated at high redshifts down to masses of ∼106 M⊙, using sensitive star formation rate tracers such as the Hα emission, which allow us to probe the variability in the star formation histories. We present inferences of the SFMS based on 316 Hα-selected galaxies at z ∼ 4 − 5 with log(M★/M⊙) = 6.4 − 10.6. These galaxies were identified behind the Abell 2744 lensing cluster with NIRCam grism spectroscopy from the survey All the Little Things (ALT). At face value, our data suggest a shallow slope in the SFMS (SFR ∝ M★α, with α = 0.45). After we corrected this for the Hα-flux limited nature of our survey using a Bayesian framework, the slope steepened to α = 0.59+0.10−0.09, whereas current data on their own are inconclusive on the mass dependence of the scatter. These slopes differ significantly from the slope of ∼1 that is expected from the observed evolution of the galaxy stellar mass function and from simulations. When we fixed the slope to α = 1, we found evidence for a decreasing intrinsic scatter with stellar mass (from ∼0.5 dex at M★ = 108 M⊙ to 0.4 dex at M★ = 1010 M⊙). This difference might be explained by a (combination of) luminosity-dependent SFR(Hα) calibration, a population of (mini)-quenched low-mass galaxies, or underestimated dust attenuation in high-mass galaxies. Future deep observations with different facilities can quantify these processes, which will enable us to achieve better insights into the variability of the star formation histories.},
  author       = {Di Cesare, Claudia and Matthee, Jorryt J and Naidu, Rohan P. and Torralba, Alberto and Kotiwale, Gauri and Kramarenko, Ivan and Blaizot, Jeremy and Rosdahl, Joakim and Leja, Joel and Iani, Edoardo and Adamo, Angela and Covelo-Paz, Alba and Furtak, Lukas J. and Heintz, Kasper E. and Mascia, Sara and Navarrete, Benjamín and Oesch, Pascal A. and Romano, Michael and Shivaei, Irene and Tacchella, Sandro},
  issn         = {1432-0746},
  journal      = {Astronomy & Astrophysics},
  publisher    = {EDP Sciences},
  title        = {{The slope and scatter of the star-forming main sequence at z ∼ 5: Reconciling observations with simulations}},
  doi          = {10.1051/0004-6361/202557790},
  volume       = {707},
  year         = {2026},
}

@article{19930,
  abstract     = {We present an analysis of the UV continuum slope, β, using a sample of 726 galaxies with z > 4, selected from a mixture of JWST ERS, GTO, and GO observational programs. We considered only spectroscopic data obtained with the low-resolution (R ∼ 30 − 300) PRISM/CLEAR NIRSpec configuration. Studying the correlation between β and MUV, we find an overall decreasing trend, described by β = ( − 0.055 ± 0.017)MUV + ( − 2.98 ± 0.34). This is consistent with previous studies, where brighter galaxies show redder β values. However, when analyzing the trend in separate redshift bins, we find that at high redshift the relation becomes much flatter and is consistent with a flat slope within 1σ. Furthermore, we find that β tends to decrease with redshift, following β = ( − 0.075 ± 0.010)z + ( − 1.496 ± 0.056). This is consistent with most recent results showing a steepening of the spectra at higher z. We selected a sample of galaxies with extremely blue slopes (i.e., β < −2.6). Such slopes are steeper than predicted by stellar evolution models – even for dust-free, young, metal-poor populations – when the contribution of nebular emission is included. We selected 44 extremely blue galaxies (XBGs) and investigated the possible physical origin of their steep slopes by comparing them to a subsample of redder galaxies (matched in Δz = ±0.5 and ΔMUV = ±0.2). We find that XBGs have younger stellar populations, stronger ionization fields, lower dust attenuation, and lower but not pristine metallicity (∼10% Z⊙) compared to red galaxies. However, these properties alone cannot explain the extreme β values. Using indirect inference of Lyman continuum escape with the most recent models, we estimated the escape fraction fesc > 10% in at least 25% of the XBGs, whereas all the red sources exhibit much lower fesc values. A reduced nebular continuum contribution – resulting from either a high escape fraction or a bursty star formation history – is likely the origin of the extremely blue slopes.},
  author       = {Dottorini, D. and Calabrò, A. and Pentericci, L. and Mascia, Sara and Llerena, M. and Napolitano, L. and Santini, P. and Roberts-Borsani, G. and Castellano, M. and Amorin, R. and Dickinson, M. and Fontana, A. and Hathi, N. and Hirschmann, M. and Koekemoer, A. M. and Lucas, R. A. and Merlin, E. and Morales, A. and Pacucci, F. and Wilkins, S. and Arrabal Haro, P. and Bagley, M. and Finkelstein, S. L. and Kartaltepe, J. and Papovich, C. and Pirzkal, N.},
  issn         = {1432-0746},
  journal      = {Astronomy & Astrophysics},
  publisher    = {EDP Sciences},
  title        = {{Evolution of the UV slope of galaxies at cosmic morning (z > 4): The properties of extremely blue galaxies}},
  doi          = {10.1051/0004-6361/202453267},
  volume       = {698},
  year         = {2025},
}

@article{19967,
  abstract     = {Context. Investigating the ionizing emission of star-forming galaxies and the escape fraction of ionizing photons is critical to understanding their contribution to reionization and their impact on the surrounding environment. The number of ionizing photons available to reionize the intergalactic medium (IGM) depends on not only the abundance of galaxies but also their efficiency in producing ionizing photons (ξion). This quantity is thus fundamental to quantify the role of faint versus bright sources in driving this process, as we must assess their relative contribution to the total ionizing emissivity.

Aims. Our goal is to estimate the ξion using Balmer lines (Hα or Hβ) in a sample of 761 galaxies at 4 ≤ z ≤ 10 selected from different JWST spectroscopic surveys. We aim to determine the redshift evolution of ξion and the relation of ξion with the physical properties of the galaxies.

Methods. We used the available HST and JWST photometry to perform a spectral energy distribution (SED) fitting in the sample to determine their physical properties and relate them with ξion. We used the BAGPIPES code for the SED fitting and assumed a delayed exponential model for the star formation history. We used the NIRSpec spectra from prism or grating configurations to estimate Balmer luminosities, and then constrained ξion values after dust correction.

Results. We find a mean value of 1025.22 Hz erg−1 for ξion in the sample with an observed scatter of 0.42 dex. We find an increase in the median values of ξion with redshift from 1025.09 Hz erg−1 at z ∼ 4.18 to 1025.28 Hz erg−1 at z ∼ 7.14, confirming the redshift evolution of ξion found in other studies. Regarding the relation between ξion and physical properties, we find a decrease in ξion with increasing stellar mass, indicating that low-mass galaxies are efficient producers of ionizing photons. We also find an increase in ξion with increasing specific star formation rate (sSFR) and increasing UV absolute magnitude. This indicates that faint galaxies and galaxies with high sSFR are also efficient producers. We also investigated the relation of ξion with the rest-frame equivalent width (EW) of [OIII]λ5007 and find that galaxies with the higher EW([OIII]λ5007) are more efficient producers of ionizing photons, with the best fit leading to the relation log(ξion)  =  0.43 × log(EW[OIII])+23.99. Similarly, we find that galaxies with higher O32 = [OIII]λ5007/[OII]λλ3727,3729 and lower gas-phase metallicities (based on the R23 = ([OIII]λλ4959,5007+[OII]λλ3727,3729)/Hβ calibration) show higher ξion values.},
  author       = {Llerena, M. and Pentericci, L. and Napolitano, L. and Mascia, Sara and Amorín, R. and Calabrò, A. and Castellano, M. and Cleri, N. J. and Giavalisco, M. and Grogin, N. A. and Hathi, N. P. and Hirschmann, M. and Koekemoer, A. M. and Nanayakkara, T. and Pacucci, F. and Shen, L. and Wilkins, S. M. and Yoon, I. and Yung, L. Y.A. and Bhatawdekar, R. and Lucas, R. A. and Wang, X. and Arrabal Haro, P. and Bagley, M. B. and Finkelstein, S. L. and Kartaltepe, J. S. and Merlin, E. and Papovich, C. and Pirzkal, N. and Santini, P.},
  issn         = {1432-0746},
  journal      = {Astronomy & Astrophysics},
  publisher    = {EDP Sciences},
  title        = {{The ionizing photon production efficiency of star-forming galaxies at z ∼ 4–10}},
  doi          = {10.1051/0004-6361/202453251},
  volume       = {698},
  year         = {2025},
}

@article{20661,
  abstract     = {We analyse James Webb Space Telescope (JWST) Near Infrared Imager and Slitless Spectrograph (NIRISS) and Near Infrared Spectrograph (NIRSpec) spectroscopic observations in the Abell 2744 galaxy cluster field. From approximately 120 candidates, we identify 12 objects with at least two prominent emission lines among [O II] λ3727, H β λ4861, [O III] λ4959, [O III] λ5007, and H α λ6563 that are spectroscopically confirmed by both instruments. Our key findings reveal systematic differences between the two spectrographs based on source morphology and shutter aperture placement. Compact objects show comparable or higher
integrated flux in NIRSpec relative to NIRISS (within 1σ uncertainties), while extended sources consistently display higher flux in NIRISS measurements. This pattern reflects NIRSpec’s optimal coverage for compact objects while potentially undersampling extended sources. Quantitative analysis demonstrates that NIRSpec recovers at least 63 per cent of NIRISS-measured flux when the slit covers >15 per cent of the source or when Re < 1 kpc. For lower coverage or larger effective radii, the recovered flux varies from 24 per cent to 63 per cent. When studying the H α λ6563/[O III] λ5007 emission line ratio, we observe that
measurements from these different spectrographs can vary by up to ∼0.3 dex, with significant implications for metallicity and star formation rate characterizations for individual galaxies. These results highlight the importance of considering instrumental effects when combining multi-instrument spectroscopic data and demonstrate that source morphology critically influences flux
recovery between slit-based and slitless spectroscopic modes in JWST observations.},
  author       = {Dalmasso, Nicolò and Watson, Peter J. and Treu, Tommaso and Trenti, Michele and Vulcani, Benedetta and Nanayakkara, Themiya and Bradač, Maruša and Jones, Tucker and Boyett, Kristan and Wang, Xin and Mascia, Sara and Pentericci, Laura},
  issn         = {1365-2966},
  journal      = {Monthly Notices of the Royal Astronomical Society},
  number       = {2},
  pages        = {1915--1925},
  publisher    = {Oxford University Press},
  title        = {{Quantifying spectroscopic flux variations between JWST NIRISS and NIRSpec: Slit losses in emission line measurements of z ∼ 1-3 galaxies}},
  doi          = {10.1093/mnras/staf1837},
  volume       = {544},
  year         = {2025},
}

@article{20932,
  abstract     = {Identifying Lyman continuum (LyC) leakers at intermediate redshifts is crucial for understanding the properties of cosmic reionizers because the opacity of the intergalactic medium (IGM) prevents the direct detection of LyC emission from sources during the Epoch of Reionization (EoR). In this study, we confirm two new LyC candidate leakers at z ∼ 3 in the Abell 2744 cluster field, with absolute escape fractions (fesc) of 0.83−0.80+0.15 and 0.74−0.70+0.23, respectively. The LyC emission was detected using HST/WFC3/F275W and F336W imaging. These two candidate leakers appear to be faint (MUV = −17.61 ± 0.06 and −18.22 ± 0.10), exhibit blue UV continuum slopes (β = −2.43 ± 0.05 and −1.92 ± 0.09), have low masses (M★ ∼ 107.51 ± 0.03 and 107.17 ± 0.15 M⊙) and Lyα equivalent widths of 90 ± 3 Å and 28 ± 12 Å, respectively. These two LyC candidate leakers were detected in a catalog of 91 spectroscopically confirmed sources using public spectra from the JWST and/or MUSE. We also analyzed properties that were proposed as indirect indicators of LyC emission, such as Lyα, the O32 ratio, and M★. We created a galaxy subsample that was selected according to these properties, stacked the LyC observations of this subsample, and assessed the limits of the escape fractions in the stacks. We aim to enhance our understanding of LyC escape mechanisms and improve our predictions of the LyC fesc during the EoR by analyzing the individual candidates and the stacks in the context of the currently limited sample of known LyC leakers at z ∼ 3.},
  author       = {Liu, Y. and Mascia, Sara and Pentericci, L. and Watson, P. and Alavi, A. and Bergamini, P. and Bradač, M. and Calabrò, A. and Glazebrook, K. and Henry, A. and Llerena, M. and Merlin, E. and Metha, B. and Nanayakkara, T. and Napolitano, L. and Roy, N. and Siana, B. and Vanzella, E. and Vulcani, B. and Wang, X.},
  issn         = {1432-0746},
  journal      = {Astronomy & Astrophysics},
  publisher    = {EDP Sciences},
  title        = {{A Lyman continuum analysis of ∼100 galaxies at z spec∼ 3 in the Abell 2744 cluster field}},
  doi          = {10.1051/0004-6361/202556410},
  volume       = {704},
  year         = {2025},
}

@article{21060,
  abstract     = {Compact, star-forming galaxies with high star formation rate surface densities (ΣSFR) are often efficient Lyman continuum (LyC) emitters at z ≤ 4.5, likely because intense stellar feedback creates low-density channels that allow photons to escape. Irregular or disturbed morphologies, such as those resulting from mergers, can also facilitate LyC escape by creating anisotropic gas distributions. We investigated the influence of galaxy morphology on LyC production and escape at redshifts 5 ≤ z ≤ 7 using observations from various James Webb Space Telescope (JWST) surveys. Our sample consists of 436 sources, which are predominantly low-mass (∼10^8.15 M), star-forming galaxies with ionizing photon efficiency (ξion) values consistent with canonical expectations. Since direct measurements of fesc are not possible during the Epoch of  Reionization (EoR), we predicted fesc for high-redshift galaxies by applying survival analysis to a subsample of LyC emitters from the Low-Redshift Lyman Continuum Survey (LzLCS), selected to be direct analogs of reionization-era galaxies. We find that these galaxies exhibit, on average, modest predicted escape fractions (∼0.04). In addition, we evaluated the correlation between morphological features and LyC emission. Our findings indicate that neither ξion nor the predicted fesc values show a significant correlation with the presence of merger signatures. This suggests that in low-mass galaxies at z ≥ 5, strong morphological disturbances are not the primary mechanism driving LyC emission and leakage. Instead, compactness and star formation activity likely play a more pivotal role in regulating LyC escape. },
  author       = {Mascia, Sara and Pentericci, L. and Llerena, M. and Calabrò, A. and Matthee, Jorryt J and Flury, S. and Pacucci, F. and Jaskot, A. and Amorín, R. O. and Bhatawdekar, R. and Castellano, M. and Cleri, N. and Costantin, L. and Davis, K. and Di Cesare, Claudia and Dickinson, M. and Fontana, A. and Guo, Y. and Giavalisco, M. and Holwerda, B. W. and Hu, W. and Huertas-Company, M. and Jung, Intae and Kartaltepe, J. and Kashino, D. and Koekemoer, A. M. and Lucas, R. A. and Lotz, J. and Napolitano, L. and Jogee, S. and Wilkins, S.},
  issn         = {1432-0746},
  journal      = {Astronomy & Astrophysics},
  publisher    = {EDP Sciences},
  title        = {{Little impact of mergers and galaxy morphology on the production and escape of ionizing photons in the early Universe}},
  doi          = {10.1051/0004-6361/202553760},
  volume       = {701},
  year         = {2025},
}