arXiv subjects

Emanuele Daddi

Publications and source records attributed to Emanuele Daddi.

At least 37 records · Page 2Linked to original sources

arXiv2026

From Grism to IFU: Revising the Redshift and Nature of the Massive Dusty Galaxy S1 with JWST and ALMA

We report a revised spectroscopic redshift for the dusty massive galaxy S1, previously inferred with an exceptionally high baryon-to-star conversion efficiency from NIRCam slitless grism data at $z_{\rm grism}=5.58$. Our new JWST/NIRSpec IFU observations reveal multiple rest-frame optical and NIR emission lines, yielding a secure spectroscopic redshift of $z_{\rm spec}=3.2439\pm0.0002$. We show that the earlier grism-based redshift resulted from contamination by a nearby galaxy whose dispersed spectral trace overlaps with S1, illustrating a known challenge of slitless spectroscopy when only a single dispersion angle and single emission feature are available. In addition, we present new ALMA 1 mm observations, which robustly detect dust emission ($S_{\rm 1mm}=0.99\pm0.03$ mJy) and show a dust half-light radius ($R_{\rm e,1mm}=0.73\pm0.10$ kpc) slightly smaller than the stellar size ($R_{\rm e, F444W} = 0.97\pm0.01$ kpc). Using the revised redshift and compiled multi-wavelength photometry, we update the UV-to-FIR SED and find that S1 is less extreme than previously inferred, yet remains a very massive (log$M_{\star}/M_{\odot}\sim10.6$), heavily obscured star-forming galaxy. The updated SED modeling reveals S1 to be a very dust- and gas-rich system with a moderate star formation rate and a long gas depletion time ($τ_{\rm dep} \sim 1.4$ Gyr), deviating from SMGs and OFGs, but more closely resembling typical massive main-sequence galaxies. We note that, although this revision reduces the number of ultra-massive galaxies reported in Xiao et al. 2024, it does not alter the main conclusions of that work. Overall, our study clarifies the nature of S1 and underscores the importance of multi-line spectroscopic confirmation, slitless observations at multiple position angles, and IFU data for robust redshift and physical characterization of rare massive galaxies in the early Universe.

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arXiv2026

Illuminating the Physics of Cosmic Origin and Evolution: A UK Space Frontiers 2035 White Paper

Understanding the Universe's origins and evolution remains one of the most fundamental challenges in modern cosmology. This white paper explores three key science priorities in this field: unravelling the physics of cosmic inflation, investigating the accelerating expansion of the Universe, and precisely measuring the sum of the neutrino masses. Achieving these goals requires a dedicated survey to map the large-scale structure at high redshift in unprecedented detail. We describe how this can be achieved through a mission concept called SIRMOS, providing a high-throughput, highly multiplexed spectroscopic capability to obtain accurate redshifts for over 100 million galaxies over a wide sky area. Such a survey would leverage the deepest existing wide-area photometric catalogues for targeting, with spectra offering continuous 1.25-2.5~$μ$m wavelength coverage at moderate resolution, allowing precise redshift measurements in the $1<z<4$ range with minimal bias. We outline the scientific opportunities this presents. Recent years have seen significant advances in instrumentation, including digital micromirror devices, complex telescope mirrors, large detector arrays, and data processing pipelines. While these technologies have been demonstrated in terrestrial applications, such a survey is a unique opportunity to apply these proven capabilities in space to address fundamental questions in cosmology. Participation in such a mission will simultaneously deliver a compelling science case, help align UK Space Agency and STFC strategies, demonstrate the UK's growing capability in end-to-end space missions, and strengthen the national space economy through high-value industrial participation.

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arXiv2026

Galaxies in the Epoch of Reionization Are All Bark and No Bite -- Plenty of Ionizing Photons, Low Escape Fractions

Early results from JWST suggest that epoch-of-reionization (EoR) galaxies produce copious ionizing photons, which, if they escape efficiently, could cause reionization to occur too early. We study this problem using \jwst\ imaging and prism spectroscopy for 412 galaxies at 4.5 < z < 9.0. We fit these data simultaneously with stellar-population and nebular-emission models that include a parameter for the fraction of ionizing photons that escape the galaxy, $f_\mathrm{esc}$. We find that the ionization production efficiency, $ξ_\mathrm{ion}$ = Q(H) / L(UV), increases with redshift and decreasing UV luminosity, but shows significant scatter, $σ( \log ξ_\mathrm{ion})$ = 0.3 dex. The inferred escape fractions averaged over the population are low, ranging from $\langle f_\mathrm{esc} \rangle$ = $2.6\pm 1.4$\% at 6 < z < 9 to $6.5\pm 2.2$\% at 4.5 < z < 6 with weak or no indication of evolution with redshift. This implies that in our models most of the ionizing photons need to be absorbed to account for the nebular emission. We compute the impact of our results on reionization, including the distributions for $ξ_\mathrm{ion}$ and $f_\mathrm{esc}$, and the evolution and uncertainty of the UV luminosity function. Considering galaxies brighter than M(UV) < -16 mag, we would produce an IGM hydrogen-ionized fraction of $x_e = 0.5$ at 5.3 < z < 5.8, possibly too late compared to constraints from from QSO sightlines. Including fainter galaxies, M(UV) < -14 mag, we obtain $x_e = 0.5$ at 6.0 < z < 8.1, fully consistent with QSO and CMB data. This implies that EoR galaxies produce plenty of ionizing photons, but these do not efficiently escape. This may be a result of high gas column densities combined with burstier star-formation histories, which limit the time massive stars are able to clear channels through the gas for ionizing photons to escape.

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arXiv2026

Discovery of a gas-enshrouded broad-line AGN at z $\sim$ 7

The Lyman-alpha (Ly$α$) absorption profile in star-forming galaxies serves as a powerful tracer of the extended, dense neutral hydrogen in their surroundings during the Epoch of Reionization (EoR). We report a unique galaxy, A2744-z7DLA, at $z\approx 6.87$ gravitationally lensed by the foreground galaxy cluster Abell 2744, which exhibits both moderate Ly$α$ emission and damped Ly$α$ absorption, suggesting the presence of a dense neutral hydrogen environment. Our analysis suggests that the UV continuum turnover near Ly$α$ is more likely shaped by a damped Ly$α$ system rather than nebular continuum from two photon process. We analyze the physical properties of A2744-z7DLA with spectroscopic and photometric data from the JWST and the HST. The galaxy shows a compact morphology ($r_e \sim 0.3\ {\rm kpc}$) and a broadened H$α$ emission line, suggesting possible AGN activity. The broad component of H$α$ has a FWHM of $2721 \pm 200\ {\rm km\ s^{-1}}$, corresponding to a black hole mass of $M_{\rm BH}=2.90^{+2.35}_{-1.28}\times 10^7 M_\odot$ and a black hole-to-stellar mass ratio of $\log (M_{\rm BH}/M_{\rm stellar}) = -1.58^{+0.45}_{-0.34}$. The Balmer decrement ($\rm Hα/Hβ$) yields a dust attenuation of $\rm A_V \approx 1.15 \pm 0.23$, indicating that this system is less dust-rich than some "little red dots". Furthermore, we perform SED fitting using both stellar and AGN models. The results show that the UV and optical wavelengths are dominated by star-forming regions, while the AGN component contributes primarily at longer wavelengths. This work provides new insights into the interplay between star formation, neutral gas, and potential AGN activity in galaxies during the EoR.

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arXiv2026

Cosmic Vine: High abundance of massive galaxies and dark matter halos in a forming cluster at z=3.44

The Cosmic Vine is a massive protocluster at z=3.44 in the JWST CEERS field, offering an ideal laboratory for studying the early phases of cluster formation. Using the data from the DAWN JWST Archive, we conduct a comprehensive study on the large-scale structure, stellar mass function (SMF), quiescent members, and dark matter halos in the Cosmic Vine. First, we spectroscopically confirm 136 galaxies in the Vine at z=3.44, and an additional 47 galaxies belonging to a diffuse foreground structure at z=3.34 which we dub the Leaf. We identify four subgroups comprising the Cosmic Vine and two subgroups within the Leaf. Second, we identified 11 quiescent members with log(M*/Msun)=9.5-11.0, the largest sample of quiescent galaxies in overdense environments at z>3, which gives an enhanced quiescent galaxy number density 2x10^(-4)cMpc^(-3) that is three times above the field level at log(M*/Msun) > 10. Notably, these quiescent members form a tight red sequence on the color-magnitude diagram, making it one of the earliest red sequences known to date. Third, by constructing the SMFs for both star-forming and quiescent members, we find that both SMFs are top-heavy, with a significantly enhanced quiescent fraction at log(M*/Msun)>10.5 compared to field counterparts. The stellar mass-size analysis reveals that star-forming members are more compact at higher masses than their field counterparts. Finally, we estimate a halo mass of log(Mh/Msun)=13.2+-0.3 for the protocluster core, and log(Mh/Msun)=11.9-12.4 for satellite subgroups. The phase-space analysis indicates that three subgroups are likely infalling to the core. This work reveals a high abundance of massive galaxies and dark matter halos in a forming cluster, demonstrating the accelerated assembly of massive galaxies in massive halos when the Universe was less than 2 billion years old.

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arXiv2026

Galactic bars are already mature at Cosmic Noon: bar strength and flatness at z ~ 1.5

In this work, we explore the nature of $z>1$ galactic bars. Once thought to be highly transient, our results demonstrate otherwise. Our sample consists of nine massive ($>10^{10.5}\,\rm M_{\odot}$) star-forming barred-spiral galaxies at $z_{\rm spec} \sim 1.5$. Using rest-frame near-IR (F444W) JWST/NIRCam imaging, we apply ellipse fitting along with 1D and 2D morphological modeling to directly measure bar properties. We find that five galaxies host flat surface brightness profiles (bar Sérsic index $<0.4$), indicative of highly evolved, "mature" bars. By contrast, only two galaxies show exponential profiles, characteristic of young bars, and these are also shorter in absolute length than the flat bars. We therefore conclude that a large fraction of bars at this epoch have already matured, thereby indicating the presence of well-settled disks required to facilitate bar formation and sustained evolution well before $z\sim1.5$. To assess the gravitational impact of the bars, we calculate the maximum transverse-to-radial force ratio ($Q_{b}$). We find that $Q_{b}$ values are comparable to, or weaker than, those of bars in the local Universe, Seven of the nine bars show only a marginal increase in strength with maturity (from exponential to flat bars). Contrarily however, the remaining two bars are flat, but have the lowest $Q_{b}$ values in our sample. We hence propose that the mature bars at $z\sim 1.5$ may experience phases of weakening due to rapid gas inflows and/or minor mergers. In conclusion, our work sheds light on the rapidly evolving nature of high-z bars and paves the way for larger statistical studies.

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arXiv2025

Mysteries of Capotauro: investigating the puzzling nature of an extreme F356W-dropout

JWST has uncovered a diverse population of extreme near-infrared dropouts, including ultra high-redshift ($z>15$) galaxy candidates, dust-obscured galaxies challenging dust production theories, sources with strong Balmer breaks - possibly compact AGN in dense environments - and cold, sub-stellar Galactic objects. This work presents Capotauro, a F356W-dropout in the CEERS survey with F444W AB magnitude of $\sim27.68$ and a sharp $>3$ mag flux drop between $3.5{-}4.5\,μ$m, undetected below $3.5\,μ$m. We combine JWST/NIRCam, MIRI, and NIRSpec/MSA data with HST/ACS and WFC3 observations to perform a spectro-photometric analysis of Capotauro using multiple SED-fitting codes. Our setup tests $z\geq15$ as well as $z<10$ dusty, Balmer-break or strong-line galaxy solutions, and the possibility of Capotauro being a Milky Way sub-stellar object. Among extragalactic options, our analysis favors interpreting the sharp drop as a Lyman break at $z\sim32$, consistent with the epoch of formation of the first stars and black holes, with only $\sim0.5\%$ of the posterior volume at $z<25$. Lower-redshift solutions struggle to reproduce the extreme break, suggesting that if Capotauro lies at $z<10$, it must show a non-standard combination of strong dust attenuation and/or Balmer breaks, making it a peculiar interloper. Alternatively, its properties match a very cold (Y2-Y3 type) brown dwarf or a free-floating exoplanet with a record-breaking combination of low temperature and large distance ($T_{\mathrm{eff}}<300\,\mathrm{K}$, $d\gtrsim130\,\mathrm{pc}$, up to $\sim2\,\mathrm{kpc}$). While current data cannot determine its nature, Capotauro emerges as a remarkably unique object in all plausible scenarios, and a compelling target for follow-up.

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arXiv2025

Stellar Morphology of Optically Dark or Faint Galaxies at $z>3$ with JWST

JWST offers an unprecedented view of optically dark or faint galaxies (OFGs), previously missed by HST. They are likely massive, heavily dust-obscured star-forming galaxies (SFGs) that substantially contribute to the cosmic SFR density at $z>$3. To identify drivers of their high dust attenuation and their role in early universe galaxy evolution, we analyse the stellar morphology of 65 OFGs (from 1892 SFGs at 3$<z<$4) using NIRCam/F444W imaging from the PRIMER and CEERS fields. We study correlations between dust attenuation ($A_v$) and galaxy properties, like stellar mass, size, and orientation, and compare scaling relations between OFGs and typical SFGs. We find that OFGs are ~8-9 times more massive and ~4 times more dust attenuated than the parent sample. Structurally, OFGs resemble parent SFGs in median $R_e$ and median $Σ_{R_e}$ but may be slightly rounder on average. While $A_v$ strongly correlates with stellar mass, it does not show significant dependence on stellar mass-normalised effective radius and stellar mass surface density, Sérsic index, axis ratio, or SFR surface density. The mass-size and mass-surface density relations place OFGs as a higher-mass extension of SFGs, with no concrete proof of evolutionary differences between them. This suggests that OFGs are heavily dust-obscured primarily due to their high stellar masses, which facilitates dust production and retention, with older stellar populations likely contributing as well. Although some OFGs exhibit high $Σ_\mathrm{R_e}$ and occupy regions of the mass-size plane similar to quiescent galaxies, the overall sample is not representative of this. Their current structures resemble typical SFGs, with no concrete signs of rapid compaction. Diversity in their physical properties shows that OFGs span a range of evolutionary states with few showing reduced star formation, while most remain actively star-forming.

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arXiv2025

Investigating the Growth of Little Red Dot Descendants at z<4 with the JWST

One of JWST's most remarkable discoveries is a population of compact red galaxies known as Little Red Dots (LRDs). Their existence raises many questions about their nature, origin, and evolution. These galaxies show a steep decline in number density-nearly two orders of magnitude-from $z=6$ to $z=3$. In this study, we explore their potential evolution by identifying candidate descendants in CEERS, assuming a single evolutionary path: the development of a blue star-forming outskirt around the red compact core. Our color-magnitude selection identifies galaxies as red as LRDs at $z<4$, surrounded by young, blue stellar outskirts. Morphological parameters were derived from single Sérsic profile fits; physical properties were obtained from SED fitting using a stellar-only model. These "post-LRD" candidates show LRD-like features with $M_\ast \sim 10^{10} \ M_\odot $, central densities ($ Σ_\ast \sim 10^{11} \ M_\odot \ \text{kpc}^{-2}$ ), compact sizes, and red rest-frame colors, but with an added extended component. Their number density at $z = 3 \pm 0.5$ ( $ \sim 10^{-4.15} \, \text{Mpc}^{-3} $) matches that of LRDs at $5 < z < 7$ , supporting a possible evolutionary link. We observe a redshift-dependent increase in outskirts mass fraction and galaxy size-from $\sim 250$ pc at $ z = 5 $ to $\sim 600$ pc at $ z = 3 $-suggesting global stellar growth. Meanwhile, the core remains red and compact, but the V-shaped SED fades as the outskirts grow. These findings support an evolutionary scenario in which LRDs gradually acquire an extended stellar component over cosmic time by cold accretion. This may explain the apparent decline in their observed number density at lower redshift.

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arXiv2025

Ly-alpha emission reveals two satellite halos around massive groups at z ~ 3: the puzzling case of a quiescent central galaxy

We present the discovery and characterisation of two Ly$α$ nebulae (LANs), RO-1001-Sat and RO-0959-Sat, as satellite structures of two giant LANs at $z=2.920$ and 3.092. They are found neighbouring two out of four known giant LANs at $z\sim3$ in our MUSE follow-up observations, reinforcing the idea that Ly$α$ emission can be used to trace massive dark matter halos at high-$z$. This high occurrence of massive satellite halos agrees with simulations. With sizes of $\simeq80\times160$ and $80\times100~\mathrm{pkpc}^2$, the two nebulae are both $\sim$300pkpc from the main LANs. The Ly$α$ emission is only shifted by $\simeq100-300$ km s$^{-1}$ between each of the two pairs, suggesting connections via large-scale structure. RO-1001-Sat and RO-0959-Sat are estimated to have log$(M_\mathrm{h}/M_\odot)\simeq13.2\pm0.3$ and $12.8\pm0.3$, putting them potentially close to the regime of cold-mode accretion. The central brightest galaxies in the two halos are morphologically distinct despite having similar stellar mass $\sim10^{11}M_\odot$, one being an elliptical quiescent galaxy in RO-1001-Sat and the other being a dusty star-forming spiral in RO-0959-Sat. Intriguingly, the quiescent galaxy aligns well with the peak of the LAN as well as the potential well of the host halo, making it the first clear-cut case where the cold gas ought to be accreting onto the galaxy but with no observable star formation, either due to morphological quenching or, more likely, radio-mode feedback from an active galactic nucleus. Finally, we show a tentative detection of a Ly$α$ filament connecting RO-1001 and RO-1001-Sat. This work shows how panoramic MUSE (and in the future, BlueMUSE) observations of massive halo seeds can be used to efficiently search for additional halos, unveiling their large-scale structure and enabling the study of Ly$α$-selected galaxy groups.

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arXiv2025

Resolving the dusty star-forming galaxy GN20 at z=4.055 with NOEMA and JWST: A similar distribution of stars, gas and dust despite distinct apparent profiles

We present high-resolution (0.13"-0.23") NOEMA observations of the dust continuum emission at 1.1 mm (rest-frame 220 micron) and JWST/NIRCam and MIRI imaging of the z=4.055 starburst galaxy GN20. The sensitive NOEMA imaging at 1.6 kpc resolution reveals extended dust emission, ~14 kpc in diameter (r_e~2.5 kpc, b/a=0.5), that is centrally asymmetric and clumpy. The dust emission is as extended as the stellar emission and the molecular gas traced by CO(2-1), with a common center, and is brightest in the strongly-obscured nuclear part of the galaxy. Approximately one-third of the total dust emission emerges from the nucleus and the most prominent clump to the south, and (only) 60% from the central 3.5x1.5 kpc (0.5"-0.2"), implying that the starburst is very extended. The combined JWST and NOEMA morphology suggests GN20 experienced a recent interaction or merger, likely invigorating the starburst. The radial surface brightness profiles of the molecular gas and near-IR stellar emission are similar, while in contrast, the dust emission appears significantly more concentrated. Through self-consistent radiative transfer modeling of the integrated and resolved CO and dust emission, we derive an $M_{mol}=2.9^{+0.4}_{-0.3}\times10^{11}$ Msun with $α_{CO}=2.8^{+0.5}_{-0.3}$. We find that the extended dust implies a lower global dust optical depth than previously reported, but a high dust mass of $M_{dust}=5.7^{+0.8}_{-0.6}\times 10^{9}$ Msun and gas-to-dust ratio of ~50. Furthermore, we show the distinct apparent radial profiles of the gas and dust can be explained purely by radiative transfer effects and the observations are consistent with the gas and dust mass being similarly distributed throughout the starburst. The latter highlights the importance of accounting for radiative transfer effects when comparing molecular gas and dust distributions from different tracers.

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arXiv2025

The Bigfoot: A footprint of a Coma cluster progenitor at z=3.98

Protoclusters, galaxy clusters' high redshift progenitors, hold the keys to understanding the formation and evolution of clusters and their member galaxies. However, their cosmological distances and spatial extensions (tens of Mpc) have inhibited complete mapping of their structure and constituent galaxies, which is key to robustly linking protoclusters to their descendants. Here we report the discovery of the Bigfoot, a tridimensional structure at $z = 3.98$ including 11 subgroups traced by 55 (700) spectroscopic (photometric) redshifts with JWST, extending over $15\times 37$ $\times 49{\rm{cMpc^3}}$ in the PRIMER-UDS field. Bigfoot's large-scale and mass function of member galaxies closely match constrained simulations' predictions for the progenitors of today's most massive clusters (${M_0} > 10^{15} {M_{_ \odot }}$). All subgroups with ${M_{\rm{h}}} > {10^{12.5}}{M_{_ \odot }}$ exhibit enhanced fractions of massive galaxies ($>{10^{10.0} {M_{_ \odot }}}$) compared to lower-mass halos and the field, demonstrating the accelerated formation of massive galaxies in massive halos. The presence of this massive protocluster with a large central halo (${10^{13.0} {M_{_ \odot }}}$) in a JWST deep field bears important cosmological implication that favors high ${σ_8}$ of PLANCK cosmology over low-redshift probes.

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arXiv2025

Investigating the influence of radio-faint AGN activity on the infrared-radio correlation of massive galaxies

It is well-known that star-forming galaxies (SFGs) exhibit a tight correlation between their radio and infrared emissions, commonly referred to as the infrared-radio correlation (IRRC). Recent empirical studies have reported a dependence of the IRRC on the galaxy stellar mass, in which more massive galaxies tend to show lower infrared-to-radio ratios (qIR) with respect to less massive galaxies. One possible, yet unexplored, explanation is a residual contamination of the radio emission from active galactic nuclei (AGN), not captured through "radio-excess" diagnostics. To investigate this hypothesis, we aim to statistically quantify the contribution of AGN emission to the radio luminosities of SFGs located within the scatter of the IRRC. Our VLBA program "AGN-sCAN" has targeted 500 galaxies that follow the qIR distribution of the IRRC, i.e., with no prior evidence for radio-excess AGN emission based on low-resolution (~ arcsec) VLA radio imaging. Our VLBA 1.4 GHz observations reach a 5-sigma sensitivity limit of 25 microJy/beam, corresponding to a radio brightness temperature of Tb ~ 10^5 K. This classification serves as a robust AGN diagnostic, regardless of the host galaxy's star formation rate. We detect four VLBA sources in the deepest regions, which are also the faintest VLBI-detected AGN in SFGs to date. The effective AGN detection rate is 9%, when considering a control sample matched in mass and sensitivity, which is in good agreement with the extrapolation of previous radio AGN number counts. Despite the non-negligible AGN flux contamination (~ 30%) in our individual VLBA detections, we find that the peak of the qIR distribution is completely unaffected by this correction. We conclude that residual AGN contamination from non-radio-excess AGN is unlikely to be the primary driver of the M* - dependent IRRC.

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arXiv2025

Under the glare of a luminous quasar, the FIR continuum is still an excellent tracer of the ISM down to the central kiloparsec

Contamination-free assessments of the interstellar medium and star formation in quasar host galaxies, particularly based on the far-infrared, offer insights into the role of supermassive black holes in galaxy evolution. Motivated by predictions of quasar heating of dust on both nuclear and galaxy-wide scales, we perform two-component (host galaxy + point source) modeling of high-resolution (~0.1") ALMA observations of the FIR continuum in Band 5 (lambda_rest~500 um) of three highly luminous quasars (L_bol~10^47 erg/s), powered by supermassive black holes having M_BH~10^9 M_sun, at z=2. We include Band 9 (lambda_rest~154 um; 0.06" and 0.3") data at high S/N which places further constraints on the unresolved nuclear component in two cases. To break the degeneracy between quasar and stellar heating, we use CO (J=5-4), observed in Band 5, to gauge the expected contribution of star formation to the infrared luminosity. We find very good agreement between the strength and spatial distribution of the extended continuum component and its prediction based on CO (J=5-4). This is supported by the location of our three quasars along the L_(CO 5-4)-L_(IR, SFR) luminosity relation for inactive star-forming galaxies. As a consequence, there is no evidence for additional continuum emission on extended scales which could be attributed to quasar-heated dust. As expected, the nuclear (i.e., torus) contribution is present and subdominant (12% in Band 9 for one quasar with a typical star-forming host) or non-existent (<8% in Band 9 for the starbursting host). Based on the continuum and CO, the presence of substantial levels of ongoing star formation agrees with previous estimates from unresolved ALMA continuum observations which finds SFRs consistent with star-forming main-sequence galaxies. Therefore, our results do not provide evidence for a quasar-mode feedback, even for the most luminous cases at z=2.

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arXiv2025

Noema formIng Cluster survEy (NICE): A Census of Star Formation and Cold Gas Properties in Massive protoclusters at 1.5<z<4

Massive protoclusters at z~1.5-4, the peak of the cosmic star formation history, are key to understanding the formation mechanisms of massive galaxies in today's clusters. However, studies of protoclusters at these high redshifts remain limited, primarily due to small sample sizes and heterogeneous selection criteria. In this work, we conduct a systematic investigation of the star formation and cold gas properties of member galaxies of eight massive protoclusters in the COSMOS field, using the statistical and homogeneously selected sample from the Noema formIng Cluster survEy (NICE). Our analysis reveals a steep increase in the star formation rates per halo mass ($Σ_{\rm SFR} /M_{\rm halo}$) with redshifts in these intensively star-forming protoclusters, reaching values one to two orders of magnitude higher than those observed in the field at z>2. We further show that, instead of an enhancement of starbursts, this increase is largely driven by the concentration of massive and gas-rich star-forming galaxies in the protocluster cores. The member galaxies still generally follow the same star formation main sequence as in the field, with a moderate enhancement at the low mass end. Notably, the most massive protocluster galaxies ($M_\star$>8$\times$10$^{10}$M$_\odot$) exhibit higher $f_{\rm gas}$ and $τ_{\rm gas}$ than their field counterparts, while remaining on the star forming main sequence. These gas-rich, massive, and star-forming galaxies are predominantly concentrated in the protocluster cores and are likely progenitors of massive ellipticals in the center of today's clusters. These results suggest that the formation of massive galaxies in such environments is sustained by substantial gas reservoirs, which support persistent star formation and drive early mass assembly in forming cluster cores.

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arXiv2025

A PAH deficit in the starburst core of a distant spiral galaxy

We present high-resolution and spatially-matched observations with JWST and ALMA of a starburst galaxy (PACS-830) at $z=1.46$. The NIRCam observations mainly trace the stellar light while the CO ($J$=5--4) observations map the dense molecular gas at kpc scales. Both datasets reveal the morphology to be that of a gas/dust rich bulge with two extending arms, together resembling a grand-design spiral galaxy. The more pronounced arm contributes 21 $\pm$ 6\% of the total CO emission. These results demonstrate that starburst activity at high redshift can be triggered, without undergoing a highly disruptive major merger. We assess the strength and distribution of star formation using two tracers: (1) Polycyclic Aromatic Hydrocarbons (PAHs) emission detected at $8~μ$m ($L_8$) with a MIRI/F1800W image, and (2) $L_\mathrm{IR}$, inferred from the CO ($J$=5--4) map. The spatial profiles of the $L_\mathrm{IR}$ and $L_8$ are dissimilar, thus leading to a significant deficit of mid-IR ($L_8$) emission in the nucleus. We hypothesize that this is due to the destruction of PAH molecules by the intense ionizing radiation field or decreased emission in the photodissociation region, as seen in nearby star-forming regions and consistent with the galaxy-wide properties of distant starbursts. This study reveals spatial variations in the $L_8$ to $L_\mathrm{IR}$ ratio for the first time at $z>1$, in agreement with expectations from theory. Our analysis underscores the pivotal role of joint high-resolution observations with JWST and ALMA in discerning the different phases of the interstellar medium (ISM) and revealing internal physics in galaxy substructures.

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arXiv2025

No [CII] or dust detection in two Little Red Dots at z$_{\rm spec}$ > 7

Little Red Dots (LRDs) are compact, point-like sources characterized by their red color and broad Balmer lines, which have been debated to be either dominated by active galactic nuclei (AGN) or dusty star-forming galaxies (DSFGs). Here we report two LRDs (ID9094 and ID2756) at z$_{\rm spec}$>7, recently discovered in the JWST FRESCO GOODS-North field. Both satisfy the "v-shape" colors and compactness criteria for LRDs and are identified as Type-I AGN candidates based on their broad H$β$ emission lines (full width at half maximum: 2280$\pm$490 km/s for ID9094 and 1070$\pm$240 km/s for ID2756) and narrow [OI] lines ($\sim$ 300-400 km/s). To investigate their nature, we conduct deep NOEMA follow-up observations targeting the [CII] 158${\rm μm}$ emission line and the 1.3 mm dust continuum. We do not detect [CII] or 1.3 mm continuum emission for either source. Notably, in the scenario that the two LRDs were DSFGs, we would expect significant detections: $>16σ$ for [CII] and $>3σ$ for the 1.3 mm continuum of ID9094, and $>5σ$ for [CII] of ID2756. Using the 3$σ$ upper limits of [CII] and 1.3 mm, we perform two analyses: (1) UV-to-FIR spectral energy distribution (SED) fitting with and without AGN components, and (2) comparison of their properties with the L$_{[CII]}$-SFR$_{tot}$ empirical relation. Both analyses are consistent with a scenario where AGN activity may contribute to the observed properties, though a dusty star-forming origin cannot be fully ruled out. Our results highlight the importance of far-infrared observations for studying LRDs, a regime that remains largely unexplored.

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arXiv2025

Coevolution of halo and quasar properties in dense environments: CARLA J1017+6116 at z=2.8

Radio-loud active galactic nuclei, in particular radio-loud quasars, are fueled by accretion onto supermassive black holes and are among the most energetic sources in the Universe. While their impact on their surroundings - from the interstellar medium to the circumgalactic medium - is well recognized, the specific mechanisms remain uncertain. In this study we analyze deep Keck Cosmic Web Imager observations of the Lyman-alpha (Lya) halo surrounding the radio-loud quasar at the center of the cluster CARLA J1017+6116 at redshift z = 2.8. As is known from previous observations, the cluster hosts a high fraction of early-type galaxies, and the star formation of its spectroscopically confirmed cluster members is typical of or higher than that of galaxies on the main sequence. We find that the Lya halo extends at least 16 arcsec (128 pkpc) down to a surface brightness level of 1e-19 erg/s/cm^2/arcsec^2, with a total observed Lya luminosity of log10(L/Lsun) = 43.35 +- 0.05. The halo has distinct kinematic regions with asymmetries suggestive of complex interactions between the quasar and the intracluster medium, possibly driven by a combination of biconical feedback and episodic activity. Despite the quasar classification, our reanalysis of very long baseline interferometry data finds no evidence of extended jet structures; we instead find compact and variable radio emission that could indicate episodic jet activity or suppression by the dense interstellar medium. Combining these observations with imaging obtained with the Hubble Space Telescope, we identified one Lya-emitting source within the quasar halo. While mechanical feedback from a jet appears limited or episodic, radiative feedback likely plays a dominant role in shaping the extended Lya halo, highlighting the complex interplay between quasar-driven processes and the surrounding dense environment.

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