arXiv subjects

Pablo G. Pérez-González

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

At least 55 records · Page 3Linked to original sources

arXiv2025

Spider-Webb: Spatially-Resolved Evidence of Inside-Out Quenching in the Spiderweb Protocluster at $z \sim 2$

We present a spatially-resolved analysis of galaxy quenching within the Spiderweb Protocluster at $z \sim 2.16$, combining deep imaging from the James Webb Space Telescope (JWST) and the Hubble Space Telescope (HST). Utilizing pixel-by-pixel spectral energy distribution fitting, we derive maps of stellar mass, star formation rate (SFR), specific SFR (sSFR), and rest-frame UVJ colors. Quiescent galaxies, predominantly found at $\log(M_*/M_{\odot}) \geq 10.5$, exhibit clear mass-dependent inside-out quenching, with central sSFR approximately an order of magnitude lower than outer regions, while lower-mass star-forming galaxies show flat sSFR profiles. Central star formation activity fundamentally anti-correlates with Sérsic index, indicating reduced activity in bulge-dominated systems. Spatially resolved UVJ colors reveal heterogeneous internal star formation, distinguishing star-forming regions in quiescent hosts from those in globally star-forming systems. These findings demonstrate that quenching mechanisms were effectively operating by $z \sim 2$, with the observed inside-out patterns and morphological correlations consistent with AGN-driven feedback processes. Our study provides key observational constraints on galaxy evolution during this critical epoch.

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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

Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Cosmology and High-z Universe

Full sky coverage with 30-40 meter-class telescopes is essential to answer fundamental questions in Astrophysics, Cosmology, and Physics, such as the composition of the Universe and the formation of the first stars and supermassive black holes. An ELT/TMT-like telescope in the Northern Hemisphere is a fundamental and necessary facility to provide multiplexing of observing power, diversity of instrumentation, rapid response, and statistical power required to address the questions and the problems, current and future, unveiled by full sky observatories such as JWST, Euclid, or Roman space telescopes. The Northern ELT/TMT will expedite the study of unique, extreme, rare, transient, and/or high-energy events which will give the most information about fundamental Physics problems in the era of multi-messenger and time-domain Astronomy.

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arXiv2025

GA-NIFS: the highest-redshift ring galaxy candidate from a head-on collision

Collisional ring galaxies are a rare class of interacting systems, making up only ~0.01% of galaxies in the local Universe. Their formation is typically attributed to a head-on collision of a massive galaxy with a compact satellite (intruder), triggering density waves that, propagating outward, produce the characteristic ring morphology. Here, we present the discovery and detailed analysis of GS18660, the most distant ring galaxy known to date, at z=3.08, identified in JWST/NIRSpec IFS observations as part of the GA-NIFS programme. This work aims to characterise the physical and dynamical properties of GS18660 and shed light into the formation of its ring. Specifically, we analyse the ionized gas properties, stellar populations, and gas kinematics of the system, and use the observed geometry to constrain the timescale of the collision. Our analysis is based on NIRSpec IFS data, including low-resolution (R~100) spectroscopy covering ~0.2-1.3um rest-frame, and high-resolution (R~2700) spectroscopy covering 0.4-0.8um rest-frame. Multi-wavelength techniques are applied to derive nebular gas conditions and stellar population properties. Gas kinematic analysis reveals that GS18660 exhibits a rotating disk component with an additional radial expansion velocity of ~200 km/s, consistent with a propagating collisional wave. Nebular line diagnostics indicate intense star formation (SFR ~100 Msun/yr) along the ring and in the nucleus. Stellar population analysis shows that the most recent star formation episode, occurring within the last ~50 Myr, predominantly took place in the ring. We also identify a close companion, the intruder galaxy responsible for the collision, moving away with a relative velocity of ~425 km/s. The evidence strongly favours a collisional origin for the ring in GS18660, though the presence of a recently formed bar (and hence a resonance ring) cannot be completely excluded.

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arXiv2025

GA-NIFS: Understanding the ionization nature of EGSY8p7/CEERS-1019. Evidence for a star formation-driven outflow at z = 8.6

Understanding the physical conditions and feedback mechanisms in early massive galaxies is essential to uncover how they formed and evolved during the first billion years of the Universe. In this context, the galaxy EGSY8p7/CEERS-1019 at z=8.6 provides an excellent benchmark, given its stellar mass of $10^{9.3}M_\odot$ and elevated N/O abundance despite its sub-solar metallicity. In this study, we present new JWST/NIRSpec observations offering the first spatially resolved spectroscopy of this galaxy, with higher sensitivity and spectral resolution than previous studies. We identify broad (FWHM=650km/s) H$β$ and [OIII] emission components whose emission is located between the two rest-frame UV clumps of the galaxy and extended over a distance of $\sim1kpc$. The morphology and kinematics of these components indicate that the broad emission arises from outflowing gas rather than from an AGN broad-line region. The kinetic energy injection rate from stellar feedback is an order of magnitude higher than that of the outflow, while the radiation pressure rate is comparable to the outflow momentum rate. These results suggest that stellar feedback alone can drive the outflow, with radiation pressure potentially providing the required momentum transfer. We derive a low mass-loading factor ($η=0.16$) and ionizing photon escape fraction ($f_{esc}=0.021\pm0.014$). Together with the high electron density measured ($n_e=2200cm^{-3}$), these results support the interpretation that most of the gas remains confined within the galaxy. Comparisons of diagnostic emission-line ratios with photoionization and shock models support a star-formation-driven ionization scenario, ruling out any excitation by AGN radiation. Finally, the absence of detectable Wolf-Rayet features suggests that alternative mechanisms must be considered to explain the high N/O ratio in this galaxy.

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arXiv2025

PRIMER & JADES reveal an abundance of massive quiescent galaxies at 2 < z < 5

We select a mass-complete sample of 225 quiescent galaxies at $z>2$ with $M_* > 10^{10}\ \mathrm{M}_\odot$ from PRIMER and JADES photometry spanning a total area of $\simeq320$ sq. arcmin. We restrict our analysis to only area with optical coverage in three $HST$ ACS filters, and provide evidence that this is important for selecting the most complete and clean samples of $z>2$ massive quiescent galaxy candidates. We investigate the contamination in our sample via $JWST$ NIRSpec spectroscopic validation, $Chandra$ X-ray imaging, and ALMA interferometry, calculating a modest total contamination fraction of $12.9_{-3.1}^{+4.0}$ per cent. The removal of $HST$ data increases star-forming galaxy contamination by $\simeq10$ per cent and results in a $\simeq20$ per cent loss of candidates recovered from $HST$+$JWST$ data combined. We calculate massive quiescent galaxy number densities at $2 3$, with discrepancies of up to $\simeq 1$ dex. We place 14 of our $z>3$ massive quiescent galaxies on the BPT and WHaN diagrams using medium-resolution spectroscopic data from the EXCELS survey. We find a very high incidence of faint AGN in our sample, at a level of $\simeq50$ per cent, consistent with recent results at cosmic noon. This is interesting in the context of maintenance-mode feedback, which is invoked in many simulations to prevent quenched galaxies from re-igniting star formation. To properly characterise the evolution of early massive quiescent galaxies, greater coverage in optical filters and significantly larger spectroscopic samples will be required.

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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

Witnessing downsizing in the making: quiescent and breathing galaxies at the dawn of the Universe

[Shortened for arXiv] We conduct a systematic search for $\log(M_\ast/M_\odot) \geq 9.5$ quiescent galaxies at $z > 3$ in six extragalactic deep fields observed with NIRCam, with the goal of extracting their physical and statistical features in a uniform and self-consistent manner. We exploit the ASTRODEEP-JWST photometric catalogs to single out robust candidates, including sources quenched only a few tens of Myr before the observation. We apply a SED-fitting procedure which explores three functional forms of star formation history and the $χ^2$ probabilities of the solutions, with additional checks to minimise the contamination from interlopers, tuning our selection criteria against available spectroscopic data from the DAWN archive and simulated catalogs. We select 633 candidates, which we rank by a reliability parameter based on the probabilities of the quiescent and alternative star-forming solutions, with 291 candidates tagged as "gold". According to the best-fit models, 79\% of the massive ($\log(M_\ast/M_\odot) \geq 10.5$) quiescent galaxies at $3 < z < 5$ stopped forming stars at least 150 Myr before the time of observation, while 89\% of low-mass sources have been quenched for less than 150 Myr. The abundance of low-mass old quiescent systems does not increase significantly with time from $z = 5$ to 3: low-mass objects seem to be experiencing a short episode of quenching followed by rejuvenation (``breathing''), consistent with a downsizing scenario of galaxy formation. We also find an abrupt drop in the density of massive quiescent candidates at $z > 5$. We derive estimates for the number density of early passive galaxies up to $z = 10$ and compare them against various models: tensions with data remain in the modeling of the observed bimodality of time passed since quenching as a function of mass.

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arXiv2025

JWST PRIMER: A deep JWST study of all ALMA-detected galaxies in PRIMER COSMOS -- dust-obscured star-formation history back to z $\simeq$ 7

We use the deep NIRCam and MIRI imaging from the JWST PRIMER survey to study the properties of (sub)mm sources detected by ALMA in the centre of the COSMOS field, with the aim of better constraining the history of dust-enshrouded star formation. The wealth of ALMA data in this field enabled us to isolate a robust sample of 128 (sub)mm sources within the 175 sq. arcmin of the PRIMER COSMOS survey footprint, spanning two decades in (sub)mm flux density. The JWST imaging is deep/red enough to reveal secure galaxy counterparts for all of these sources. Moreover, 52% of the galaxies have spectroscopic redshifts, enabling us to refine the photo-zs for the remaining galaxies. Armed with this robust redshift information, we calculate the star-formation rates (SFR) and stellar masses of all 128 ALMA-detected galaxies, and place them in the context of other galaxies in the field. We find that the vast majority of star formation is dust-enshrouded in the ALMA-detected galaxies, with SFR ranging from ~1000 down to ~20 solar masses per year. We also find that virtually all (126/128) have high stellar masses, at all redshifts, with log(M/Msun) > 10. The unusually high quality of our sample enables us to make a robust estimate of the contribution of the ALMA-detected galaxies to cosmic star-formation rate density from z = 2 out to z = 7. Finally, to correct for the fact that the deep ALMA pointings cover < 20% of the PRIMER COSMOS area, we use our knowledge of all other massive galaxies in the field to produce a completeness-corrected estimate of dust-enshrouded star-formation rate density over cosmic time. This confirms that UV-visible star formation dominates at z > 4, but also indicates that dust-enshrouded star formation likely still made a significant contribution at higher redshifts: extrapolation of our results suggest a ~20% contribution at z = 8, and potentially still ~5% at z = 10.

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arXiv2025

Net-zero gas inflow: Measurement of the gas consumption history of a massive quiescent galaxy

JWST is discovering increasing numbers of quiescent galaxies 1--2 billion years after the Big Bang, whose redshift, high mass, and old stellar ages indicate that their formation and quenching were surprisingly rapid. This fast-paced evolution seems to require that feedback from AGN (active galactic nuclei) be faster and/or more efficient than previously expected \citep{Xie24}. We present deep ALMA observations of cold molecular gas (the fuel for star formation) in a massive, fast-rotating, post-starburst galaxy at $z=3.064$. This galaxy hosts an AGN, driving neutral-gas outflows with a mass-outflow rate of $60\pm20$ M$_{\odot}$ yr$^{-1}$, and has a star-formation rate of $<5.6$ M$_{\odot}$ yr$^{-1}$. Our data reveal this system to be the most distant gas-poor galaxy confirmed with direct CO observations (molecular-gas mass $< 10^{9.1}$ M$_{\odot}$; <0.8 % of its stellar mass). Combining ALMA and JWST observations, we estimate the gas-consumption history of this galaxy, showing that it evolved with net zero gas inflow, i.e., gas consumption by star formation matches the amount of gas this galaxy is missing relative to star-forming galaxies. This could arise both from preventive feedback stopping further gas inflow, which would otherwise refuel star formation or, alternatively, from fine-tuned ejective feedback matching precisely gas inflows. Our methods, applied to a larger sample, promise to disentangle ejective vs preventive feedback.

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arXiv2025

The CEERS Photometric and Physical Parameter Catalog

We present the Cosmic Evolution Early Release Science Survey (CEERS) catalog, including space-based photometry, photometric redshifts, and physical parameters for more than 80,000 galaxies. The imaging used for this catalog comes from the CEERS survey, which has NIRCam coverage over ~100 sq. arcmin of the Extended Groth Strip (EGS) in seven filters from 1.15$μ$m to 4.44$μ$m. Alongside these data, we also include ancillary HST imaging in seven filters from 0.435$μ$m to 1.6$μ$m. We used Source Extractor with hot and cold detection settings to extract photometry. We derive photometric redshifts using the spectral energy distribution (SED) modeling code, LePHARE, and estimate their accuracy using spectroscopically confirmed galaxies out to $z\sim10$, with $σ_{NMAD}$ ranging from 0.035-0.073, depending strongly on galaxy magnitude and redshift. We compute stellar masses, star formation rates, and E(B-V) using three different SED fitting codes with different templates and assumptions about the galaxy star formation histories. All of these measurements, as well as the full mosaics in all filters, and redshift probability distribution functions, are made available via the CEERS DR1.0 data release.

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arXiv2025

The rise of the galactic empire: luminosity functions at $z\sim17$ and $z\sim25$ estimated with the MIDIS$+$NGDEEP ultra-deep JWST/NIRCam dataset

We present a sample of six F200W and three F277W dropout sources identified as $16 16$ candidates present mass-weighted ages around 30 Myr, and attenuations $\mathrm{A(V)}<0.1$ mag. Their average stellar mass is $\mathrm{M}_\bigstar\sim10^{7}\,\mathrm{M}_\odot$, implying a stellar-to-baryon mass fraction around 10% if the emissivity increases with redshift, or significantly higher otherwise. Three candidates present very blue UV spectral slopes ($β\sim-3$) compatible with Pop III young ($\lesssim10$ Myr) stars and/or high escape fractions of ionizing photons; the rest have $β\sim-2.5$ similar to $z=10-12$ samples.

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arXiv2025

Very bright, very blue, and very red: JWST CAPERS analysis of highly luminous galaxies with extreme UV slopes at $\mathbf{z = 10}$

We present JWST/NIRSpec PRISM observations of three luminous ($M_{\rm UV}<-20$) galaxies at $z\sim10$ observed with the CAPERS Cycle 3 program. These galaxies exhibit extreme UV slopes compared to typical galaxies at $z=10$. Of the three sources, two of them are a close pair (0.22 - arcsec) of blue galaxies at $z=9.800\pm0.003$ and $z=9.808\pm0.002$ with UV slopes of $β=-2.87\pm0.15$ and $β=-2.46\pm0.10$ respectively, selected from PRIMER COSMOS NIRCam imaging. We perform spectrophotometric modeling of the galaxies which suggests extremely young stellar ages and a lack of dust attenuation. For the bluest galaxy, its UV slope also suggests significant Lyman continuum escape. In contrast, the third source (selected from CEERS NIRCam imaging) at $z=9.942\pm0.002$ exhibits a red UV slope with $β=-1.51\pm0.08$. We rule out the possibility of a strong nebular continuum due to the lack of a Balmer jump and find no evidence to support the presence of active galactic nucleus continuum due to a lack of strong UV emission lines and no broad component to H$γ$ or H$β$. Instead, it is most likely that the red UV slope is due to dust-reddening ($A_{\rm V}\simeq0.9$) implying a significant level of dust-obscured star-formation only $\simeq480\, \rm Myr$ after the Big Bang. Under standard assumptions for dust attenuation, EGS-25297 would be the most intrinsically UV-luminous galaxy ($M_{\mathrm{UV,corr}}\simeq -22.4^{+0.7}_{-1.1}$) yet spectroscopically confirmed at $z \sim 10$. This work highlights that luminous galaxies at $z\gtrsim10$ have a diversity of dust properties and that spectroscopy of these galaxies is essential to fully understand star-formation at $z\gtrsim10$.

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arXiv2025

Discovery of Multiply Ionized Iron Emission Powered by an Active Galactic Nucleus in a z~7 Little Red Dot

Some of the most puzzling discoveries of NASA's JWST in the early Universe surround the surprising abundance of compact red sources, which show peculiar continuum shapes and broad hydrogen spectral lines. These sources, dubbed ``Little Red Dots'' or LRDs, have been the subject of intense inquiry in the literature. Any of the proposed explanations, from accreting super-massive black holes ensconced in ultra-dense gas to extremely compact star-systems, has significant implications for the earliest phases of galaxy evolution. Part of the difficulty in concretely identifying the physical mechanisms that drive their rest ultra-violet/optical spectral properties is the lack of bona fide signatures -- either star-formation or accreting super-massive black hole, that uniquely discriminate between competing interpretations. In this work, we report the discovery of several spectral features that strongly favor the existence of an accreting super-massive black hole in an LRD witnessed in the first 800 Myr of cosmic time, including several rare iron transitions and a possible [FeVII]. Additionally, we report on the properties of significant Balmer absorption and find that the small widths and relative depths of the absorption feature suggest the source of the absorber is at or beyond the outer edge of the broad-line region and does it fully cover the accreting SMBH in the center of the system. The detection of these iron features, coupled with the properties of the Balmer absorption, unveils an alternative scenario for LRDs -- one where there are direct sight-lines from the accretion disk to gas on scales at (or beyond) the broad-line gas region.

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arXiv2025

GA-NIFS: an extended [OIII] halo around the sub-Eddington quasar J1342+0928 at z=7.54

The James Webb Space Telescope (\textit{JWST}) opened a new observational window on the primordial Universe. Here we present new JWST NIRSpec integral field spectroscopy (IFS) observations of the $z=7.54$ quasar ULAS J1342+0928 obtained as part of the Galaxy Assembly with NIRSpec IFS (GA-NIFS) GTO programme. The new data-set obtained with both the prism ($R\sim100$) and the high-resolution grating ($R\sim2700$) allow for a complete description of the quasar emission from the rest-frame UV to optical bands. The low-resolution data reveal the presence of [\ion{O}{iii}] emission on $\sim$7 kpc scales, well above the typical galaxy size at this redshift, likely associated with a past outflow event. Additionally, the high-resolution observations show a more energetic ionised outflow on nuclear scales ($\lesssim 0.6$ kpc). The total ionised mass outflow rate ranges between 50 and 300 $\rm M_{\odot} \, yr^{-1}$ where the significant spread is mostly due to the lack of tight constraints on the electron density. This range overlaps in part with the star formation rate range (85--545 $\rm M_{\odot} \, yr^{-1}$), implying that the nuclear outflow could ultimately lead to an early star formation quenching. By employing an accretion disc modelling, for the first time on \textit{JWST} data, we manage to robustly estimate the black hole mass and the bolometric luminosity, $\rm \log(M_{BH}/(M_{\odot}))=9.2\pm 0.2$ and $\rm \log(L_{bol}/(erg \, s^{-1}))=46.8\pm 0.1$, respectively. We derive an Eddington ratio of $\rm λ_{Edd}\sim 0.4$, challenging the paradigm of widespread super-Eddington accretion in quasars at the epoch of reionisation.

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arXiv2025

A direct black hole mass measurement in a Little Red Dot at the Epoch of Reionization

Recent discoveries of faint active galactic nuclei (AGN) at the redshift frontier have revealed a plethora of broad \Halpha emitters with optically red continua, named Little Red Dots (LRDs), which comprise 15-30\% of the high redshift broad line AGN population. Due to their peculiar spectral properties and X-ray weakness, modeling LRDs with standard AGN templates has proven challenging. In particular, the validity of single-epoch virial mass estimates in determining the black hole (BH) masses of LRDs has been called into question, with some models claiming that masses might be overestimated by up to 2 orders of magnitude, and other models claiming that LRDs may be entirely stellar in nature. We report the direct, dynamical BH mass measurement in a strongly lensed LRD at $z = 7.04$. The combination of lensing with deep spectroscopic data reveals a rotation curve that is inconsistent with a nuclear star cluster, yet can be well explained by Keplerian rotation around a point mass of 50 million Solar masses, consistent with virial BH mass estimates from the Balmer lines. The Keplerian rotation leaves little room for any stellar component in a host galaxy, as we conservatively infer $M_{\rm BH}/M_{*}>2$. Such a ''naked'' black hole, together with its near-pristine environment, indicates that this LRD is a massive black hole seed caught in its earliest accretion phase.

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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

Accelerated quenching and chemical enhancement of massive galaxies in a $z\sim4$ gas-rich halo

Stars in galaxies form when baryons radiatively cool down and fall into gravitational wells whose mass is dominated by dark matter. Eventually, star formation quenches as gas is depleted and/or perturbed by feedback processes, no longer being able to collapse and condense. We report the first spatially resolved spectroscopic observations, using the JWST/NIRSpec IFU, of a massive, completely quiescent galaxy (Jekyll) and its neighborhood at $z=3.714$, when the Universe age was 10% of today's. Jekyll resides in a massive dark matter halo (with mass M$_\mathrm{DM}>10^{12}$ M$_\odot$) and forms a galaxy pair with Hyde, which shows very intense dust-enshrouded star formation (star formation rate $\sim300$ M$_\odot$yr$^{-1}$). We find large amounts of kinematically perturbed ionized and neutral gas in the circumgalactic medium around the pair. Despite this large gas reservoir, Jekyll, which formed $10^{11}$ M$_\odot$ in stars and chemically enriched early (first billion years of the Universe) and quickly (200-300 Myr), has remained quiescent for over 500 Myr. The properties of the gas found around the two galaxies are consistent with intense, AGN-induced photoionization, or intense shocks. However, with the current data no obscured or unobscured AGN is detected in the central galaxy (Jekyll) nor in the very active and dust rich star-forming galaxy (Hyde).

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