Sebastiano Cantalupo

We investigate the multiphase circumgalactic medium during the epoch of reionization ( z > 6) by cross-correlating cool- C II and warm-ionized C IV absorption systems with star-forming [O III ] emitters. JWST/NIRCam wide-field slitless spectroscopy from the EIGER survey was combined with medium- and high-resolution optical and NIR spectra of six background quasars, including new VLT/X-Shooter observations of PSO J159-02. We analyzed the relation between 16 C II and 14 C IV absorbers (log( N ) > 13.0) and 136 galaxies within an impact parameter of R _⊥ ≤ 1000 pkpc and a line-of-sight separation of Δ v ≤ 500 km s ⁻¹ . We detected a statistically significant excess of both ions around galaxies compared to a randomized background. The C IV covering fraction remains enhanced up to ∼1 pMpc, whereas C II drops to the background level beyond ∼0.5 pMpc, demonstrating that the warm-ionized phase is more spatially extended than cooler gas. Jointly, the 3D galaxy-absorber spatial clustering is significantly weaker than the galaxy-galaxy autocorrelation. This provides direct physical evidence that early carbon enrichment is not confined to the virial radius of massive star-forming systems; rather, a substantial fraction of these metals permeates the diffuse intergalactic medium or is injected by a widespread population of faint undetected dwarf galaxies. Finally, we note a rapid radial decline of the C IV covering fraction compared with lower-redshift samples at z < 2 and z ∼ 3 − 4, which indicates an evolving circumgalactic medium ionization structure where early metals predominantly reside in lower ionization states. In conclusion, we determine a conservative lower limit for the observed carbon mass of M _{C  II +C  IV} ≥ 2.8 × 10 ⁶ M _⊙ within 300 pkpc.

Context . Galaxy protoclusters (PCs) at z ≳ 2 are dense regions extending up to a few megaparsec in which the availability of cold gas and the elevated rates of galaxy interactions trigger intense often dust-obscured star formation in the member galaxies. These same mechanisms are also expected to promote supermassive black hole (SMBH) growth, but this possible effect remains unclear, largely due to the heterogeneous galaxy selections and active galactic nucleus (AGN) identification methods employed in previous studies. Aims . We quantitatively assessed the effect of the PC environment on SMBH growth by measuring the incidence of X-ray AGN among dusty star-forming galaxies (DSFGs) in PCs and in a homogeneously selected control sample of field galaxies. We also investigated the physical mechanisms that drive any difference between the two environments. Methods . We considered the DSFG population of ALMA-detected galaxies in the submillimeter/millimeter continuum of seven PCs at 2 < z < 4.5 and constructed a selection-matched control field sample from the COSMOS survey. We statistically compared the incidence of X-ray selected AGN in the PC and control samples and the physical properties of the host galaxies as obtained through uniform spectral energy distribution fitting. Results . We found a significantly higher X-ray AGN fraction in PCs by ≈2.7×, which is different from the field expectation with a Poisson significance p = 3×10 ⁻⁴ . Similar values were obtained by splitting the sample into two redshift bins, ≈2.7× at z = 2–3 and ≈2.6× at z = 3–4.5, with significances of p = 0.003 and 0.03, respectively. The field and PC DSFG samples are well matched in stellar mass, star-formation rate, and dust mass, indicating that the observed enhancement is not driven by selection effects or systematically higher host masses. In particular, AGN in PCs are hosted by galaxies with similar stellar masses and star formation rates as field AGN. Conclusions . Our results provide quantitative and unbiased evidence that the dense PC environment enhances the AGN incidence and in turn SMBH growth among DSFGs beyond what is expected from host galaxy properties alone, likely through an increased gas availability and interaction-driven fueling. At higher redshift, current statistics limit firm conclusions, but the observed trends suggest that environmental triggering of AGN can operate already at z ≳ 4. This work represents a first step toward a homogeneous assessment of the overall environmental effects on SMBH growth across cosmic time.

Context. Numerical efforts increasingly resolve the small-scale structure of the circumgalactic medium (CGM), but the dynamical impact of ionising radiation on its cold 10 ⁴ K component remains poorly understood. Aims. We investigated the evolution of static cold gas structures exposed to the extreme-ultraviolet (EUV) radiation of quasars. Methods. We developed an analytical framework to describe the evolution of such clouds, introducing a new threshold that defines when a cloud becomes radiation-shielded. The framework was validated using radiation-hydrodynamic simulations of single static clouds. Results. The framework predicts three evolutionary regimes: (i) an optically thin regime, in which radiation uniformly ionises the cloud; (ii) a radiation-shielded regime, where the cloud remains largely unaffected; and (iii) a “rocket-effect” regime, in which an ionisation front propagates through the cloud, ionising the illuminated side while compressing the opposite side and accelerating the surviving cold clump. In this latter regime, the cloud’s Lyman- α (Ly α ) luminosity can increase by up to one order of magnitude compared to the optically thin case. Such luminosities are as high as 70% of the values obtained from a fluorescent regime without considering hydrodynamical response. Unless the cloud is self-shielded, at least ∼50 − 60% of Ly α emission arises from recombination. Applying this framework to both a population of clouds along a line of sight and a ray propagating inside a single cold stream, we find that the cold inter-galactic medium (IGM) and CGM around bright quasars ( L _ν, LL ∼ 10 ^31.6 erg s ⁻¹ Hz ⁻¹ ) is likely fully ionised, whereas the one around faint quasars ( L _ν, LL ∼ 10 ^28.6 erg s ⁻¹ Hz ⁻¹ ) predominantly experiences a rocket-effect regime. Conclusions. These results imply that the hydrodynamical response of cold CGM structures to quasar radiation must be considered when deriving CGM and IGM physical properties from observations, particularly for faint quasars.

Gas flows between galaxies and the circumgalactic medium (CGM) play a central role in galaxy evolution and can become observable as giant nebulae when illuminated by quasars. We present an ensemble study of nebulae around 30 UV-luminous quasars at z ≈ 0.4–1.4 from the CUBS and MUSEQuBES surveys, 27 of which are detected in extended [O II ] and/or [O III ] emission. Based on a joint analysis of nebular morphology and surrounding galaxy environments, we introduce three morpho-kinematic classifications. We identify eleven irregular, large-scale (>50 kpc) systems, many of which are likely interaction-related; twelve compact host-galaxy-scale nebulae, likely tracing CGM/interstellar medium (ISM) gas; and four systems with complex morphologies of uncertain origin. We introduce a quantitative measure of the spatial and kinematic association between nebulae and quasar-host group galaxies, finding a statistically significant association for ten nebulae, most of which are irregular, large-scale nebulae, consistent with qualitative analysis. Radio jets are detected in six systems, with no strong correlation found between radio activity and nebular emission. The [O II ] nebulae are more asymmetric than their Ly α counterparts at z > 2, but bear more similarity to H I gas observed in 21 cm around local elliptical galaxies. Blueshifted–redshifted patterns, likely tracing gas rotation, are observed in roughly 30% of the systems, though disturbed kinematics suggest that feedback may also be important. These results show that giant quasar nebulae are not a uniform class of objects, but instead arise through multiple pathways shaped by host-galaxy gas, galaxy interactions, group environments, and quasar activity, with the most striking cases associated with galaxy interactions.

We present an analysis of a partial Lyman limit system at z = 0.87641 detected in the Hubble Space Telescope/Cosmic Origins Spectrograph spectrum of the background quasar LBQS 0107−0235. The absorber exhibits a simple kinematic structure, with the metal-lines and the H i Lyman-series absorption well described by a single component. Photoionization modeling yields a gas metallicity of one-tenth solar and a hydrogen number density of n _H ≈ 8.5 × 10 ⁻⁴ cm ⁻³ ( log 10 ( n H / cm − 3 ) ≈ − 3.1 ). At the absorber redshift, the Very Large Telescope/MUSE data show two galaxies (G1 and G2) at normalized impact parameters of ρ / R _vir ≈ 0.9 and velocity separations of ∣Δ v ∣ = 18 and 99 km s ⁻¹ , respectively, from the absorber. Both galaxies have rotating disks with stellar masses of M _* ≈ 6 × 10 ⁹ and ≈2.2 × 10 ¹⁰ M _⊙ . Their 100 Myr averaged star formation rates are ≈2.5 and ≈2.2 M _⊙ yr ⁻¹ , although their instantaneous rates place G2 on the star-forming main sequence and G1 above it, which is actively star-forming at this redshift. The absorber is positioned very close to the projected major axis of both galaxies. The absorber’s orientation, kinematics, and subsolar metallicity ( log 10 ( Z / Z ⊙ ) = − 1.05 ) are consistent with the absorption tracing a subsolar metallicity inflowing stream, although a galaxy–galaxy interaction origin cannot be excluded. We discuss these scenarios in the context of cosmological simulations of cold-mode accretion and circumgalactic medium gas flows around galaxies with halos of the mass M _h ≲ 10 ¹² M _⊙ .

We investigate the azimuthal dependence of H i and O vi -bearing gas in the circumgalactic medium (CGM) of 113 isolated galaxies in the redshift range 0.12 < z < 0.75, including 91 new measurements from the MUSE Quasar-fields Blind Emitters Survey (MUSEQuBES). Of these, measurements for 46 galaxies lie within the virial radius ( R _vir ), including 36 non-face-on systems for which azimuthal angle ( ϕ ) measurements are robust. The H i covering fraction ( κ _{H I} ) within R _vir of low-mass (7 < log 10 ( M ⋆ / M ⊙ ) ≤ 9) galaxies, for a threshold column density of log 10 ( N ( H I ) / cm − 2 ) = 14.5 , exhibits an enhancement along both the disk plane ( ϕ ≲ 20°) and in the polar direction ( ϕ ≳ 70°). In contrast, such a bimodal distribution is not observed for higher mass galaxies (9 < log 10 ( M ⋆ / M ⊙ ) ≤ 11.3). Similarly, the O vi covering fraction ( κ _{O VI} ), for a threshold of log 10 ( N ( O VI ) / cm − 2 ) = 14.0 , shows a tentative enhancement along both the projected major and minor axes for low-mass galaxies. In contrast, O vi -bearing gas around higher-mass galaxies appears more uniformly distributed, with no significant azimuthal dependence. Finally, using the halo circular-velocity-normalized pixel-velocity two-point correlation function (TPCF), we find that O vi absorbers are kinematically narrower along the disk plane compared to the polar directions of the host galaxies with similar stellar mass distributions. The observed isotropic distribution of O vi in high-mass halos suggests that its spatial distribution is governed by global halo properties; however, the O vi kinematics retain memory of the site of origin.

While the warm ( T ∼ 10 ⁴ K), ionized gas in the circumgalactic medium (CGM) at z > 3 is now routinely observed around bright quasars in Ly α emission, little is known about the CGM hot phase ( T ∼ 10 ⁷ K). Here, we report the analysis of 634 ks of Chandra X-ray observations in the MQN01 Cosmic Structure, a region containing one of the brightest Ly α nebulae and the largest galaxy overdensity known at z > 3. We detect ≈66 net counts (≈8 σ ) of X-ray emission in the 0.5–2 keV band extending to at least ∼30 kpc from the brightest quasar in MQN01. The morphology and spectrum are consistent with thermal emission from hot plasma in collisional ionization equilibrium. Quasi-stellar object (QSO) photoionization is found to have a negligible impact, and alternative scenarios such as inverse Compton scattering are disfavoured. A joint spatial and spectral Markov chain Monte Carlo (MCMC) analysis provides consistency with a β model with a steep density profile ( β ≃ 2.0 ^+1.4 _−0.8 , r _core = 36 ⁺¹³ ₋₁₆ kpc) and an average gas temperature of kT ≃ (1.8 ± 0.4) keV. Assuming that the QSO resides within a virialized halo, whose virial temperature is equal to the observed gas temperature, the implied halo mass and virial radius would be M _vir ∼ 3 × 10 ¹³ M _⊙ and ∼190 kpc. Further assuming that the observed emission traces the brighter inner region of a distribution extending to the virial radius, the extrapolated hot gas mass would be M _hot ≈ 2.6 ^+1.7 _−0.6 × 10 ¹² M _⊙ , which is ≃ 8.3 ^+3.0 _−9.8 % of M _vir , or 56 ⁺⁶⁵ ₋₂₀ % of the theoretical cosmological baryon budget of the halo. The hot gas also emits an exceptionally high X-ray luminosity, with a measured L _2 − 10 = 2.25 _−1.38 ^+0.77 × 10 ⁴⁵ erg s ⁻¹ within the central 30 kpc. This system is a clear outlier in the L _X – T _X plane, indicating a thermodynamic state distinct from that of evolved lower-redshift hot halos. The cooling time in the inner 15-30 kpc is comparable to the local dynamical time (1 < t _cool / t _ff < 10), suggesting that the gas could become locally unstable in the absence of heating or feedback. Moreover, the thermal pressure associated with the detected CGM hot phase is large enough to confine the cold and dense clumps, which are required to reproduce the high Ly α emission associated with the inner regions of the MQN01 structure. Although limited to a single system, our results provide unique information on the multi-phase properties of the CGM (or proto-intracluster medium) and a view of the nascent thermal hot gas phase observed in local galaxy clusters.

Recent JWST observations have unveiled a large number of quiescent galaxies at z ≳ 3, bringing potential challenges to current galaxy formation models. Since star formation is expected to be fed by external gas accretion, knowledge about the circumgalactic media (CGM) of these galaxies is essential to understanding how they quench. In this work, we present the discovery of a massive, passive galaxy ( M _★ ≃ 10 ¹¹ M _⊙ ) within the MUSE Quasar Nebula 01 (MQN01) large-scale structure at z ≃ 3.25, containing one of the largest overdensities of galaxies and active galactic nuclei (AGNs) found so far at z ≳ 3. This passive galaxy has a star formation rate of 4 ₋₂ ⁺⁶ M _⊙ yr, placing it more than 1 dex below the star-forming main sequence, and it has no detectable molecular gas ( M _H2 < 2 × 10 ¹⁰ M _⊙ within a 700 km s ⁻¹ window, if assuming r ₄₁ = 0.34 and α _CO = 4 M _⊙ K ⁻¹ km ⁻¹ s pc ² ). Surprisingly, it is located at the center of a large cool gas reservoir, as traced by bright Ly α and H α emission. Deep multiwavelength information unique to this field, including spectroscopic and Chandra X-ray observations, suggests that an external mechanism could keep this cool gas reservoir in a dynamically hot, turbulent state, thus reducing its ability to efficiently accumulate within the galaxy. In particular, we discuss the possibility that the agent of this external energy injection is the AGN jet from a nearby star-forming galaxy located at a projected distance of 48 kpc and detected in both X-ray and radio. Additional or alternative energy injection mechanisms could involve the gravitational interaction between these two galaxies. In all scenarios, the elevated ionizing field provided by the AGN overdensity, including the nearby AGN, can illuminate the passive galaxy’s cool CGM and make it visible through fluorescent emission. Our study demonstrates that the star formation rates of high-redshift galaxies could be substantially reduced and maintained at a low level even within gas-rich and overdense environments in particular situations.

The formation and evolution of galaxies is regulated by the exchange of gas with the surrounding large-scale structures on circum- and intergalactic scales, yet little is known about the complex processes shaping the cycle of baryons in and out of galaxies. In this work, we present a multiline study of the gas surrounding a z ≈ 3.66 quasar known to host one of the brightest Ly α nebulae at high redshift, MUSE Quasar Nebula 04 (MQN04). By combining a high-resolution MUSE detection of nonresonant He II emission with a precise measurement of the redshift of the quasar host via the ALMA CO(4–3) line, we study the kinematics of the cool ionized gas down to #x2248; 1 kpc from the quasar. The MUSE observations reveal complex clumpy structures as well as diffuse emission extended over ≈100 kpc and blueshifted by ≈0 − 800 km s ⁻¹ relative to the quasar systemic redshift, suggesting that the circumgalactic medium is highly asymmetric. The analysis of the He II /Ly α line ratio, and the presence of a low-column density (≈ 10 ^14.6 cm ⁻² ) H I absorber along the quasar sightline suggests that MQN04 resides in a highly ionized medium. This is also supported by the gas kinematics, which, except in the most central region, shows consistent velocity shifts across the different tracers, indicative of relatively weak radiative transfer effects. Based on its morphology and kinematics, we conclude that the extended He II emission may arise from merger-driven tidal stripping or inflows of gas illuminated by the quasar radiation. On comoving megaparsec scales, we discover a large concentration ( δ ≈ 41) of star-forming galaxies lying within |Δ v _QSO | ≲ 1000 km s ⁻¹ from the quasar. MQN04 is therefore one of the most overdense environments discovered at this epoch.

We present the mass-metallicity relation for star-forming galaxies in the protocluster MUSE Quasar Nebula 01 (MQN01) field, a massive cosmic-web node at z ∼ 3.245, hosting one of the highest overdensities of galaxies and active galactic nuclei found so far at z > 3. Through James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) spectra and images from JWST and Hubble Space Telescope (HST), we identified a sample of nine star-forming galaxies in the MQN01 field with a detection of nebular emission lines (H β , [OIII], H α , [NII]), covering the mass range of 10 ^7.5 M _⊙ − 10 ^10.5 M _⊙ . We present the relations of the emission line flux ratios versus stellar mass for the sample and derive the gas-phase metallicity (12 + log(O/H)) based on the strong-line diagnostics of [OIII] λ 5008/H β and [NII] λ 6585/H α . Compared to the typical field galaxies at similar redshifts, MQN01 galaxies show relatively higher [NII] λ 6585/H α and lower [OIII] λ 5008/H β at the same stellar mass, which implies a higher metallicity by about 0.26 ± 0.07 dex than on the field mass-metallicity relation. These differences decrease when we consider the fundamental metallicity relation, that is, when we also take the galaxy star formation rates into account. We argue that these results are consistent with a scenario in which galaxies in overdense regions assemble their stellar mass more efficiently (or, equivalently, start forming mass at earlier epochs) than field galaxies at similar redshifts.