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P. G. Pérez-González

Publications and source records attributed to P. G. Pérez-González.

At least 19 recordsLinked to original sources
arXiv2026

Too many or too bright? Status and perspectives in the study of the UV Luminosity Function at z>10

The finding that galaxies in the first 500Myr were much more numerous and/or brighter than expected is often cited as one of the main discoveries of the James Webb Space Telescope in its first four years of operation. This result is now solidly based on an impressive number of surveys that have detected, spectroscopically confirmed, and characterized a relatively large sample of galaxies up to z=14.44, the redshift of the most distant galaxy currently known. This finding has motivated the introduction of additional physical mechanisms into theoretical models to reproduce the observed numbers and luminosities. These results contrast with the failure, despite ongoing efforts, to confirm any galaxy candidate beyond this redshift. This review summarizes the status of the search for and characterization of galaxies at z>9, focusing on the evolution of the UV Luminosity Function (UVLF), which is the main statistical description of the galaxy population that can be obtained at these redshifts. We first provide a comprehensive overview of the full set of JWST data obtained so far. We perform a 'meta--analysis' on the entire data set and provide a simple yet effective description of the global evolution of the UVLF, averaging over the various surveys. We also compare these results extensively with theoretical models that were developed to match the new JWST observations and that explore different physical mechanisms able to drive the observed evolution. We conclude with a summary of the contrasting results regarding the search for galaxy candidates at z>15, and outline the requirements for future surveys aimed at breaking this barrier.

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arXiv2026

A tidal disruption event in a quasar at redshift 7.19

We report a long-lived nuclear transient in GNz7q, a red quasar at $z=7.19$ powered by a $\sim3\times10^{7}\,M_\odot$ black hole and hosted by a compact, dusty starburst galaxy. The transient was identified in more than two decades of imaging with HST, Spitzer, and JWST. After a rapid rise, the source faded smoothly by $Δm\simeq1.1$ mag in the rest-frame ultraviolet over $\sim2$ rest-frame yr, with coherent, wavelength-dependent evolution across 1--5 $μ$m that places GNz7q above the 99.9th percentile of the SDSS quasar variability distribution and is absent at $z\gtrsim5$. The duration and energetics disfavor superluminous supernovae, and stochastic quasar variability reproduces the multi-band evolution with a probability of $\lesssim10^{-5}$. A panchromatic model combining a thermal continuum with a $t^{-5/3}$ decline reproduces the light curves, yielding a peak bolometric luminosity of $\simeq3\times10^{45}$ erg s$^{-1}$ and a radiated energy of $\simeq1.5\times10^{53}$ erg, which imply the tidal disruption of a star of a few solar masses and place the event among the most energetic tidal disruption events (TDEs) known. A redshifted, extremely broad Balmer-line component in independent JWST/NIRSpec spectroscopy is consistent with a transient, non-virialized broad-line region. JWST/MIRI photometry further reveals delayed mid-infrared emission from $\simeq1500$ K dust at a sub-parsec radius, consistent with a dust echo of the flare. The relatively low black-hole mass and dense star-forming nucleus of GNz7q are conditions under which TDEs are expected to be most efficient. These observations provide a time-domain view of episodic black-hole fueling and its dusty nuclear environment 700 million years after the Big Bang. Wide-field surveys with Roman and Euclid in the near-infrared, complemented by LSST at lower redshifts, may uncover such transients in large numbers.

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arXiv2026

Cosmic Noon Galaxies in the Hubble Ultra Deep Field with MIRI Wide-Field Slitless Spectroscopy

We present results from a survey of the Hubble Ultra-Deep Field using the Wide-Field Slitless Spectroscopic (WFSS) capability of the Mid-Infrared Instrument (MIRI) on JWST, demonstrating the capabilities of this new mode. We describe the data reduction and calibration methodology, and estimate calibration uncertainties. From our observations we obtain spectra of 47 galaxies with confirmed spectroscopic redshifts, with a maximum z_spec of 3.712. In the final sample we target in particular the 3.3 um Polycyclic Aromatic Hydrocarbon (PAH) feature, which has recently gathered interest as a star formation rate indicator and diagnostic for the dust grain size distribution in star forming galaxies from the local Universe to intermediate redshifts. The feature falls into the WFSS wavelength region for redshifts 0.67 to 3.1 - providing full coverage of the peak star formation ``Cosmic Noon'' era (1 < z < 3) and connecting dust properties in this critical galaxy evolution period with local-Universe and low-redshift observations. Using the galaxies in our sample in this redshift regime, we test correlations identified in lower-redshift samples in the near-infrared or targeted programs in the mid-infrared, finding the WFSS spectra, even with large calibration uncertainties, show good agreement with complementary samples. The 3.3 um PAH luminosities follow previously established correlations with total IR luminosity and SED-derived star formation rates, confirming this feature's power as tracer of dust-obscured star formation. Our work illustrate the potential of the MIRI WFSS mode for studies of Cosmic Noon-era galaxies in particular in an observationally efficient way.

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arXiv2026

Rapid quenching and early gas depletion in the core of a galaxy protocluster at z=2.2

Understanding how galaxy evolution is affected in forming high-z overdensities is a major open question in modern astrophysics. Here, we present the average properties of the quiescent galaxy population recently identified in the core of the Spiderweb protocluster at z = 2.16. By stacking observations from the Hubble Space Telescope (HST; F160W imaging and G141 grism spectroscopy), the James Webb Space Telescope (JWST; PaBeta narrowband imaging), and the Atacama Large Millimeter/submillimeter Array (ALMA; 1.2 mm dust continuum imaging), we constrained their ensemble star formation history (SFH), residual dust-obscured star formation, and cold gas mass, respectively. The inferred average SFH indicates steady stellar mass growth, with progenitor SFRs consistent with those of massive Halpha emitters (HAEs) in the same structure. This is followed by rapid quenching, on average 500 Myr prior to observation. No significant age differences are found between active galactic nucleus (AGN) hosts and non-AGN systems. We find weak PaBeta emission for 80% of the sample, yet with dust-obscured star formation rates consistent with quiescence in all but one source (ID 443) excluded from the sample. Our galaxies remain individually and globally undetected in the dust continuum, yielding an average gas fraction fgas= Mmol/Mstar<7%, consistent with previously reported gas depletion trends with stellar mass observed in neighboring HAEs. We thus find the Spiderweb protocluster to host a sizable population of gas-depleted, massive quenched galaxies in its core, likely descending from main-sequence galaxy progenitors and building the first elements of the red sequence in this high-z forming cluster.

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arXiv2026

Mass--size evolution and the emerging passive--density relation revealed by JWST/NIRCam in the Spiderweb protocluster

We investigate how the environment affects galaxy structure in the Spiderweb protocluster at $z=2.16$ using JWST/NIRCam F115W, F182M, and F410M imaging (rest-frame $\sim 3500$Å to $1.4\,μ$m). We perform homogeneous multi-wavelength parametric modelling of the single-Sérsic and bulge--disc decomposition for the Spiderweb member sample of 103 galaxies within the JWST field of view (up to $\sim 2\times R_{200}$). Star-forming galaxies follow a mass--size relation broadly consistent with the field, with a mildly steeper trend at the high-mass end within uncertainties. Passive galaxies exhibit a flatter mass--size relation, and their typical size (intercept at fixed stellar mass) lies between that of the coeval field and cluster passive populations, indicating an intermediate evolutionary stage. In both star-forming and passive systems, bulges are systematically more compact than discs. Galaxy sizes decrease slightly with increasing wavelength, whereas ALMA-detected dusty star-forming galaxies exhibit a much steeper wavelength dependence, consistent with centrally concentrated, obscured star formation. The passive fraction depends primarily on local density: it resembles the field at $Σ\lesssim 100$--$200\,{\rm gal\,Mpc^{-2}}$ and rises to $\sim60\%$ at $Σ\gtrsim 1000\,{\rm gal\,Mpc^{-2}}$, although with relatively large uncertainties due to the small number of galaxies in the highest-density bins, with no significant additional dependence on clustercentric distance. We also find a weak but significant correlation between local density and Sérsic index (strongest in F410M), but no clear correlation with effective radius or the star-formation rate surface density $Σ_{\rm SFR}$. These results support a picture in which quenching and structural transformation are already advanced, while the size growth is still ongoing.

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arXiv2026

Dissecting the Obscured Core of GN20: an Active Galactic Nucleus Outshone by Young Stars

We investigate the relative contributions of star formation and AGN activity to the total energy budget of GN20, one of the most luminous dusty star-forming galaxies known at $z>4$, through spatially resolved spectral energy distribution decomposition. We perform Bayesian SED fitting with CIGALE on two spatially distinct apertures: the nuclear core (r=0.14", $\sim$1kpc physical) and the full galaxy (r=1.4", 9.9 kpc), combining JWST/NIRCam and MIRI broadband imaging, JWST/NIRSpec PRISM IFU pseudo-continuum photometry spanning 42 wavelength bins across rest-frame $0.12$--$1.05μ$m, and archival HST and millimeter interferometry data from NOEMA and PdBI. The integrated SED is dominated by stellar-heated dust, with only a marginal AGN contribution at galaxy-wide scales ($f_\mathrm{AGN}^\mathrm{int}=0.09\pm0.02$). The nuclear core, however, requires a significant AGN component ($f_\mathrm{AGN}=0.34\pm0.05$) to account for a mid-infrared excess at rest-frame $\sim$2.5--3.6$μ$m characteristic of AGN-heated torus dust. The AGN accounts for $\sim34\%$ of the nuclear infrared luminosity but only $\sim9\%$ of the total integrated $L_\mathrm{IR}$, explaining its weak signature in integrated diagnostics and its consistency with existing upper limits from Spitzer spectroscopy. The inferred black hole mass places GN20 within the local $M_\mathrm{BH}$--$M_\mathrm{bulge}$ relation at the Eddington limit, and in the overmassive regime at sub-Eddington accretion rates, suggesting early and rapid black hole assembly concurrent with the dominant starburst. GN20 exemplifies a class of systems where nuclear-scale SED decomposition, enabled by the angular resolution and infrared sensitivity of JWST, is the only means to uncover a buried AGN overwhelmed by galaxy-wide star formation.

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arXiv2026

PRISMS. U37126, a very blue, ISM-naked starburst at z=10.255 with nearly 100% Lyman continuum escape fraction

We present very deep (~11h) JWST/MIRI low-resolution spectroscopy of the rest-frame optical emission of U37126, a UV-bright (M_UV ~ -20), mildly lensed ($μ\simeq 2.2$) galaxy at z=10.255. The continuum emission is well detected in both NIRSpec and MIRI spectra, yet no nebular recombination or metal emission lines are observed (EW(Hbeta+[OIII])<300A and EW(Halpha)<400A, at 3sigma). Combined with the exceptionally blue UV continuum slope, beta_UV ~ -2.9, and weak/flat Balmer break, these constraints indicate a stellar population dominated by very young and massive stars with a strongly suppressed nebular contribution. Comparisons with synthetic stellar population models indicate that U37126 requires both a very high ionizing photon production efficiency, log(Xi_ion / Hz erg^-1) ~ 25.75, and a nearly unit LyC escape fraction, of fesc>86% (3sigma) based on Halpha flux limit and fesc=0.94+/-0.06 derived independently from SED fitting. The best-fit SED yields a (de-lensed) stellar mass of Mstar ~ 10^7.8 Msun and a star-formation rate of SFR~10Msun/yr (sSFR~160 Gyr^-1), that along with its very compact size, reff~61pc, yields very high stellar mass and star-formation-rate surface densities, Sigma_M ~ 3x10^3 Msun/pc^2 and Sigma_SFR ~ 400 Msun/yr/kpc^2. Together with the lack of detectable nebular emission, these properties suggest that U37126 is undergoing an ``ISM-naked'' starburst phase, possibly driven by an extremely efficient gas-to-star conversion followed by strong feedback that has cleared the remaining gas from its stellar core, allowing most LyC photons to escape. Finally, we show that even a small fraction of galaxies like U37126 (~ 3%-6%), with extreme LyC production and escape, could contribute disproportionately (~ 50%-100%) to the ionizing photon budget during cosmic reionization.

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arXiv2026

GA-NIFS: The interplay between feedback and star formation at 3 < z < 9 probed by JWST/NIRSpec IFU

The study of starburst- and AGN-driven feedback is fundamental for understanding the processes that shape galaxy growth, quench star formation, and drive the co-evolution of galaxies and their central black holes. We present a spatially resolved study of six galaxies at $3 < z < 9$, including starburst- and AGN-dominated systems, observed with JWST/NIRSpec IFU in low- ($R \sim 100$) and high-resolution ($R \sim 2700$) mode. Previous analysis of $R \sim 2700$ data revealed ionized outflows in all these galaxies. We explore possible links between outflows and stellar population properties to assess the mechanisms driving galaxy evolution at early epochs. Combining the spatially resolved stellar population analysis with the outflow properties, we find that the most massive galaxies ($M_\star > 5 \times 10^{10} M_\odot$) with strong AGN-driven ionized outflows show evidence of past quenching episodes occurring within the last $\sim 100$--$300$ Myr, mainly in the nuclear regions ($r < 3$ kpc). In contrast, higher-redshift ($z > 5$) and less massive ($M_\star < 10^{10} M_\odot$) starburst galaxies with powerful (starburst-driven) outflows appear to have experienced continuous growth, with no clear sign of quenching. Massive galaxies with weaker outflows do not show evidence of quenching in their history. One massive AGN host (GS20936) shows evidence for a recent ($10$--$30$ Myr) rejuvenation phase, likely fueled by a recent major merger. These results suggest that (AGN-driven) outflows can already play a key role in shaping the SFHs of massive galaxies at early cosmic epochs.

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arXiv2026

Ly$α$ visibility from z = 4.5 to 11 in the UDS field: Evidence for a high neutral hydrogen fraction and small ionized bubbles at z $\sim$ 7

The resonant scattering nature of Ly$α$ photons interacting with neutral hydrogen makes Ly$α$ emitters (LAEs) robust tracers of the intergalactic neutral hydrogen fraction, and thus sensitive probes of cosmic reionization. We present an extensive study of the Ly$α$ evolution from galaxies at 4.5 $\leq$ z $\leq$ 11 in the UDS field, observed as part of the CAPERS survey, and complemented with spectra from the DAWN JWST Archive. The combined sample includes 651 spectroscopically confirmed Ly$α$-break galaxies, among which we find 73 S/N>3 LAEs in JWST-NIRSpec PRISM spectra. We trace the redshift evolution of the LAE fraction with EW$_0$ >25 A (X$_{\mathrm{Lyα}}$) between z = 5 and z = 9, extending such an analysis to the UDS field for the first time. At z = 5 and 6, the UDS results agree with the average JWST X$_{\mathrm{Lyα}}$ values from multiple fields. However, JWST measurements are consistently lower than ground-based results. To investigate this, we compare JWST observations to a population of star-forming galaxies at z$\sim$6 observed with VLT-FORS2. We find that a Ly$α$ slit-loss of 35 $\pm$ 10% in JWST spectra accounts for the offset, as the resonant Ly$α$ emission is more spatially extended than the stellar continuum. From z = 6 to 7, the UDS field shows a significant drop in Ly$α$ visibility, from which we infer a neutral hydrogen fraction of X$_{\mathrm{HI}}$ = 0.7--0.9. Finally, we identify two robust ionized bubbles at z = 7.29 and 7.77, with radii of $R_{\mathrm{ion}}$ = 0.6 and 0.5 physical Mpc and photometric overdensities of N/$\langle$N$\rangle$ = 3 and 4, based on candidate counts down to the photometric completeness limit. Compared to the large ionized region at z$\sim$7 in the EGS field, these results indicate significant field-to-field variation, supporting a patchy, inhomogeneous reionization process.

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arXiv2026

MIDIS: The identification of deep MIRI-red sources as candidates for extreme Balmer-break and line emitting galaxies at high-z

We investigate the detection and nature of 5.6~μm MIRI-red sources in the MIRI Deep Imaging Survey (MIDIS), covering 2.4~arcmin$^2$ in the Hubble Ultra Deep Field. MIDIS is the deepest JWST/MIRI survey to date, probing faint limits and enabling studies of rare high-redshift galaxy populations. We define MIRI-red sources as those detected at 5$σ$ significance in MIRI/F560W with red colors: $m_{\rm F444W} - m_{\rm F560W} \ge 0.5$. Using an empirical methodology, we estimate the purity and completeness of MIRI detections and find that a 5-sigma detection at 28.75 mag has a purity of 92\% and completeness of 54\%. We identify seven MIRI-red galaxy candidates, including an F115W dropout consistent with a high-redshift galaxy candidate. We explore possible physical origins for the MIRI-red population, including active galactic nuclei, dust-obscured galaxies, extreme emission-line galaxies, evolved stellar populations, and Little Red Dots (LRDs). Given the proximity of the F444W and F560W filters and the depth of MIDIS, MIRI-red galaxies are consistent with emission-line galaxies with $EW_0(Hα) \ge 750$ Å or $EW_0(Hβ+ [OIII]) \ge 600$ Å, or high-redshift Balmer breaks of at least 1.6. We also discuss an extreme MIRI-red galaxy undetected in F444W, a potential MIRI-only source, for which we derive $EW_0(Hα) \sim 6000$ Å and $EW_0(Hβ+ [OIII]) \sim 4000$ Å, or high-$z$ LRD analogs with Balmer breaks of 6.3. Finally, we find fewer MIRI-red detections than expected from extrapolations of the H$α$ or H$β$+[OIII] line luminosity functions, consistent with previous deep searches, while the absence of $z>10$ LRD candidates agrees with theoretical expectations for the MIDIS volume.

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arXiv2026

MIRI spectrophotometry of GN-z11: Detection and nature of an optical red continuum component

We present new MIRI F560W, F770W and F1000W imaging of GN-z11, extending the previous rest-frame coverage from 0.38 to 0.86$μ$m. We report significant detections (14$σ$) in the F560W and F770W images, and a marginal detection (3.2$σ$) in F1000W. Here, we analyse its SED combining new MIRI imaging data with archival NIRSpec/Prism and MRS spectroscopy, and NIRCam imaging. The continuum emission shows a flat energy distribution, in f$_ν$, up to 0.5$μ$m, compatible with the presence of a mixed stellar population of young (4$\pm$1 Myr) and mature (63$\pm$23 Myr) stars that also account for the [O III], H$β$ and H$α$ emission lines. The continuum at rest-frame 0.66$μ$m shows a 36$\pm$3% flux excess above the predicted flux for a mixed stellar population, pointing to the presence of an additional source contributing at these wavelengths. This excess increases to 91$\pm$28% at rest-frame 0.86$μ$m, although with a large uncertainty due to the marginal detection in the F1000W filter. We consider that hot dust emission in the dusty torus around a type 2 AGN could be responsible for the observed excess. Alternatively, this excess could be due to hot dust emission or to a photoluminiscence dust process (Extended Red Emission, ERE) under the extreme UV radiation field, as observed in some local metal-poor galaxies and in young compact starbursts. The presence of a type 1 AGN is not supported by the observed SED since high-z QSOs contribute at wavelengths above rest-frame 1$μ$m, and an additional ad-hoc red source would be required to explain the observed flux excess at 0.66 and 0.86$μ$m. Additional deep MIRI imaging covering the rest-frame near-IR are needed to confirm the flux detection at 10$μ$m with higher significance, and to discriminate between the different hot dust emission in the extreme starburst and AGN scenarios with MIRI imaging at longer wavelengths.

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arXiv2026

PRISMS. UNCOVER-26185, a metal-poor SFG at z=10.05 with no evidence for a X-ray-luminous AGN

This work presents the first results of the PRImordial galaxy Survey with MIRI Spectroscopy (PRISMS), a JWST cycle 4 program (PID 8051) aimed at the characterization of a relatively large sample of ten galaxies about 500 Myr after the Big Bang. Here, we present deep (13.9 hours) spectroscopy with the MIRI LRS of the lensed galaxy UNCOVER-26185 at a redshift of z=10.054. It is a faint UV galaxy (UV absolut magnitude of -18.83 mag) previously identified as a X-ray luminous AGN. MIRI LRS detects the H$β$+[OIII]4960,5008 complex and H$α$ emission line with a significance of 10$σ$ and 8$σ$, respectively, as well as the optical continuum emission at rest-frame 0.45 $μ$m and 0.57 $μ$m with a signal-to-noise ratio of 6-7. The UV-to-optical spectral energy distribution, combining continuum and emission lines, is compatible with: (i) a low stellar (A$_V$= 0.2) and nebular (A$_V$=0.0) extinction, (ii) a SFH composed by a young (7 Myr) starburst and an intermediate-age (65 Myr) stellar population, and (iii) a total stellar mass of 1.7$\times$10$^{8}$ M$_{\odot}$. The H$α$-derived star-formation rate is 1.3 M$_{\odot}$ yr$^{-1}$. The low optical emission line ratios locate UNCOVER-26185 as the most metal-poor (Z = 0.04 Z$_{\odot}$), and as outlier with the lowest ionization (logU=-2.5) galaxy identified so far at redshifts above 9. With no evidence of an active galactic nuclei in the rest-frame UV-to-optical spectrum, UNCOVER-26185 has the properties of a metal-poor, main-sequence star-forming galaxy at redshift 10, with ISM and ionization properties very different than those of the already studied UV-bright galaxies at redshifts beyond 10. PRISMS is starting to explore the population of intermediate-UV luminosity galaxies at z=10, covering UV absolute magnitudes in the range of -17.9 to -20.5, fainter than those of UV-bright galaxies studied so far.

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arXiv2026

There Is More to Outshining: 2D Dust Effects on Stellar Mass Estimates at $3 \leq z < 9$ with JWST in the JADES Field

Dust attenuation modifies the observed spectral energy distribution (SED), leading to biases in the properties inferred from integrated SED fitting. As spatially resolved SED modeling becomes feasible for large high-redshift samples, it is increasingly important to assess how dust attenuation affects resolved mass estimates. We evaluate the impact of dust attenuation on stellar mass estimates derived from integrating spatially resolved SED fitting results. We perform spatially resolved and integrated SED fitting on a sample of 3408 galaxies at $3 \leq z < 9$ from the GOODS South field, combining deep NIRCam from the JWST Advanced Deep Extragalactic Survey (JADES) and HST/ACS imaging from GOODS and CANDELS. We compare galaxy-integrated properties derived from fitting the summed SED with those obtained from spatially resolved SED modeling. Using a two-component dust attenuation model with a variable slope, we investigate how the dust attenuation slope, A(V), and stellar population properties contribute to discrepancies in the resulting stellar mass estimates. Resolved stellar masses are systematically higher than integrated estimates, with a median offset of +0.24 dex. Resolved analyses recover higher dust attenuations ($ΔA(V)\approx +0.08$ mag), lower birth cloud fractions ($Δμ\approx -0.28$), and grayer attenuation curves ($Δδ_{\mathrm{ISM}} = +0.08$), arising from preferential sampling of compact star-forming regions. Integrated fits underestimate stellar ages by $\sim23\%$ at $z < 5$ and 31$\%$ at $z \gtrsim 5$. The stellar mass offset correlates strongly with the age difference and the attenuation slope difference, indicating that age-dependent outshining and spatially varying dust geometry are primary drivers of the discrepancy between resolved and integrated stellar masses.

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arXiv2026

Ultra High-Redshift or Closer-by, Dust-Obscured Galaxies? Deciphering the Nature of Faint, Previously Missed F200W-Dropouts in CEERS

The James Webb Space Telescope (JWST) is revolutionizing our understanding of the Universe by unveiling faint, near-infrared dropouts previously beyond our reach, ranging from exceptionally dusty sources to galaxies up to redshift $z \sim 14$. In this paper, we identify F200W-dropout objects in the Cosmic Evolution Early Release Science (CEERS) survey which are absent from existing catalogs. Our selection method can effectively identify obscured low-mass ($\log \text{M}_* \leq 9$) objects at $z \leq 6$, massive dust-rich sources up to $z \sim 12$, and ultra-high-redshift ($z > 15$) candidates. Primarily relying on NIRCam photometry from the latest CEERS data release and supplementing with Mid-Infrared/(sub-)mm data when available, our analysis pipeline combines multiple SED-fitting codes, star formation histories, and CosMix - a novel tool for astronomical stacking. Our work highlights three $2 15$, with best-fit masses compatible with $Λ$CDM and a standard baryons-to-star conversion efficiency. Their bi-modal redshift probability distributions suggest they could also be $z<1.5$ dwarf galaxies with extreme dust extinction. We also identify a strong line emitter galaxy at $z \sim 5$ mimicking the near-infrared emission of a $z \sim 13$ galaxy. Our sample holds promising candidates for future follow-ups. Confirming ultra high-redshift galaxies or lower-z dusty dwarfs will offer valuable insights into early galaxy formation, evolution with their central black holes and the nature of dark matter, and/or cosmic dust production mechanisms in low-mass galaxies, and will help us to understand degeneracies and contamination in high-z object searches.

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arXiv2025

HELM's deep: Highly Extincted Low-Mass galaxies seen by JWST

The dust content of star-forming galaxies is generally positively correlated with their stellar mass. However, some recent JWST studies have shown the existence of a population of dwarf galaxies with an unexpectedly large dust attenuation. Using the Cosmic Evolution Early Release Science Survey (CEERS) data, we identified a sample of 1361 highly extincted low-mass (HELM) galaxies, defined as dwarf galaxies ($M_*<10^{8.5}$) with Av>1mag or more massive galaxies with an exceptionally high dust attenuation given their stellar mass (i.e., $Av>1.6log_{10}(M_*/Mo)-12.6$). The selection is performed using the multiparameter distribution obtained through a comprehensive spectral energy distribution fitting analysis, based on optical to near-infrared data. After excluding possible contaminants, like brown dwarfs, little red dots, high-z (z>8.5) and ultra-high-z (z>15) galaxies, the sample mainly includes sources at z<1, with a tail extending up to z=7.2. The sample has a median stellar mass of $10^7$ Mo and a median dust attenuation of Av=2mag. We analysed the morphology, environment and star-formation rate of these sources to investigate the reason of their large dust attenuation. In particular, HELM sources have sizes (effective radii, Re) similar to non-dusty dwarf galaxies and no correlation is visible between the axis ratios (b/a) and the dust attenuation. This findings indicate that it is unlikely that the large dust attenuation is due to projection effects, but a prolate or a disk-on oblate geometry are still possible, at least for a subsample of the sources. We have found that the distribution of HELM sources is slightly skewed toward more clustered environments than non-dusty dwarfs and tend to be slightly less star forming. This finding, if confirmed by spectroscopic follow-up, indicates that HELM sources could be going through some environmental processes, such as galaxy interactions.

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arXiv2025

JWST reveals extended stellar disks for ALMA-bright dusty star-forming galaxies in the Spiderweb protocluster

We present JWST/NIRCam imaging of dusty star-forming galaxies (DSFGs) detected by Atacama Large Millimeter/submillimeter Array (ALMA) in the Spiderweb protocluster at $z=2.16$. We identify 22 DSFGs detected by both ALMA and JWST, 10 of which are spectroscopically confirmed as protocluster members. This is the first systematic analysis of a statistical DSFG sample in $z\sim2$ protocluster environments using JWST/NIRCam data. Most of the DSFG members exhibit very red colors and reside in the dusty star-forming region of the rest-frame UVJ diagram, indicating strong dust obscuration. The Gini-M20 diagram suggests that most DSFGs in this protocluster are late-type disks, with a significant fraction displaying clumpy and disturbed rest-frame UV/optical morphologies, but few showing clear merger signatures. The DSFG members exhibit relatively large stellar disks and effective radii with a median stellar mass of log(M/Msun) = 10.8 +/- 0.3, placing them above coeval field DSFGs and typical protocluster galaxies in the size-mass relation at both rest-frame optical and near-infrared wavelengths. These sizes are comparable to those of more evolved field DSFGs at z~1-2, indicating accelerated structural growth in dense environments. Moreover, these DSFG members show a decreasing trend in stellar size from shorter to longer wavelengths, with a moderately steep slope comparable to coeval field DSFGs. These results may support an inside-out growth scenario for protocluster evolution, in which massive galaxies near the center are more evolved and more strongly affected by AGN feedback and environmental effects, e.g., ram-pressure stripping. We propose that the cold gas accretion at the protocluster outskirts drives intense star formation and stellar disk growth in ALMA-detected DSFGs, which are expected to evolve into massive elliptical galaxies at later stages.

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arXiv2025

JADES: Carbon-enhanced, Nitrogen-normal compact galaxy at z=11.2

Over the past few years \textit{JWST} has been a major workhorse in detecting and constraining the metal enrichment of the first galaxies in the early Universe and finding the source of the ionisation of their interstellar medium. In this work, we present new deep JWST/NIRSpec spectroscopy of GS-z11-1, a galaxy at z = 11.28, in which we report the detection of multiple rest-frame UV and optical emission lines: CIII]$λλ$1907,09, CIV]$λλ$1548,51, [OII]$λλ$3726,29, [NeIII]$λ$3869, H$γ$ and tentative evidence for HeII$λ$1640. The ionisation properties of GS-z11-1 are consistent with star formation, with potential contribution from an active galactic nucleus (AGN). We estimate a galaxy stellar mass of log(M$_{*}$/M$_{\odot}$) = 7.8$\pm$0.2 and log(SFR/(M$_{\odot}$ yr$^{-1}$))= 0.32$\pm$0.11 for the fiducial SF-only models. We measured C/O from the SED modelling of C/O = 1.20$\pm0.15 \times$ solar. This is one of the highest C/O abundances at z$>$10, and it is consistent with either PopII and PopIII enrichment paths. Despite this source being extremely compact, with a half-light radius of 73$\pm$10 pc, we see no increased equivalent width of NIV] and NIII] emission lines as seen in some other compact sources at similar redshifts, a potential signature of second-generation stars in GCs. Overall, this galaxy exhibits low metallicity and high ionisation parameter consistent with intense star-formation or AGN activity in the early Universe, possibly observed before the enrichment by the second generation of stars in proto-globular clusters in the core of the galaxy.

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arXiv2025

Pushing JWST to the extremes: search and scrutiny of bright galaxy candidates at z$\simeq$15-30

We designed customized Lyman-break color selection techniques to identify galaxy candidates in the redshift ranges $15 \leq z \leq 20$ and $20 \leq z \leq 28$. The selection was performed on the ASTRODEEP-JWST multi-band catalogs of the CEERS, Abell-2744, JADES, NGDEEP, and PRIMER survey fields, covering a total area of $\sim0.2$ sq. deg. We identify five candidates at $15 \leq z \leq 20$, while no objects are found based on the $z\gtrsim20$ color selection criteria. Despite exhibiting a $>$1.5 mag break, all the objects display multimodal redshift probability distributions across different SED-fitting codes and methodologies. The alternative solutions correspond to poorly understood populations of low-mass quiescent or dusty galaxies at z$\sim$3-7. This conclusion is supported by the analysis of five F200W-dropout objects that we find to be interlopers on the basis of NIRSpec PRISM spectra: four dusty star-forming galaxies at z$\sim$2.2-6.6, and a passive galaxy at z=4.91 with log$(M_{\rm star}/{\rm M}_{\odot}) \lesssim$ 9. We measured the UV luminosity function under different assumptions on the contamination level within our sample. We find that if even a fraction of the candidates is indeed at $z\gtrsim15$, the resulting UV LF points to a very mild evolution compared to estimates at $z<15$, implying a significant tension with existing theoretical models. In particular, confirming our bright ($M_{\text{UV}}<-21$) candidates would require substantial revisions to the theoretical framework. In turn, if all these candidates will be confirmed to be interlopers, we conclude that future surveys may need ten times wider areas to select $M_{\text{UV}}\lesssim-20$ galaxies at $z>15$. Observations in the F150W and F200W filters at depths comparable to those in the NIRCam LW bands are also required to mitigate contamination from rare red objects at z$\lesssim$8.

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