Institut d'Astrophysique de Paris

[This corrects the article DOI: 10.3389/fpain.2026.1722394.].

Abstract Supermassive black hole (SMBH) growth plausibly occurs via runaway astrophysical black hole mergers in nuclear star clusters that form intermediate mass black hole seeds at high redshifts. Such a model yields an order-of-magnitude higher rate of tidal disruption events than that of compact-object captures. Our prediction, normalized to our proposed resolution of SMBH seeding, yields detectable tidal disruption event rates at high redshift. The resulting dense gas cocoons generate compact galactic nuclei, each incorporating a central, massive, black hole star, with comparable masses in gas, stars, and massive black holes within a scale of around a parsec as inferred from the various Little Red Dot spectral signatures.

ABSTRACT We present JWST/NIRSpec IFU observations of the $z=7.152$ galaxy system B14-65666, as part of the GA-NIFS survey. Line and continuum emission in this massive system ($\log _{10}(M_*/{\rm M}_{\odot })=9.8\pm 0.2$) is resolved into two strong cores surrounded by diffuse emission, as seen in recent JWST/NIRCam imaging. Our data set contains detections of [O ii]$\lambda \lambda 3726{,}3729$, [Ne iii]$\lambda \lambda 3869{,}3968$, Balmer lines, [O iii]$\lambda \lambda 4959{,}5007$, He i$\lambda 5875$, and weak [O iii]$\lambda 4363$. Each spectrum is fit with a model that consistently incorporates interstellar medium conditions (i.e. electron temperature, $T_{\rm e}$, electron density, $n_{\rm e}$, and colour excess, $E(B-V)$). The resulting line fluxes are used to constrain the gas-phase metallicity ($Z_{\rm g}\sim 0.2\mathrm{ -}0.3$ solar) and H$\beta$-based star formation rate for each region. Common line ratio diagrams (O32–R23, R3–R2, Ne3O2–R23) reveal that each line-emitting region lies at the intersection of low- and high-redshift galaxies, suggesting low ionization and higher metallicity compared to the predominantly lower-mass galaxies studied with the JWST/NIRSpec IFU so far at $z\gt 5.5$. Spaxel-by-spaxel fits reveal evidence for both narrow (FWHM $\lt 400$ km s$^{-1}$) and broad (FWHM $\gt 500$ km s$^{-1}$) line emission, the latter of which likely represents tidal interaction or outflows. Comparison to ALMA [C ii]158$\mu$m and [O iii]88$\mu$ m data shows a similar velocity structure, and we explore optical-far infrared diagnostics. The two core galaxies both lie on the mass-metallicity relation at $z\gt 4$, but show contrasting properties (e.g. $M_*$, $Z_{\rm g}$), suggesting distinct evolutionary pathways. Combining the NIRSpec IFU and ALMA data sets, our analysis opens new windows into the merging system B14-65666.

Quasars at the dawn of cosmic time ( z > 6) are fundamental probes for investigating the early coevolution of supermassive black holes and their host galaxy. Nevertheless, their infrared spectral energy distribution currently remains poorly constrained because the photometric coverage that probes the far-infrared wavelength range in which the dust modified blackbody is expected to peak (∼80 μm) is limited. We studied the high-frequency dust emission via a dedicated ALMA Band 8 (∼400 GHz) campaign targeting 11 quasar host galaxies at 6 < z < 7. Combined with archival observations in other ALMA bands, this program enables a detailed characterization of their infrared emission, which allowed us to derive dust masses ( M d ), dust emissivity indexes ( β ), dust temperatures ( T d ), infrared luminosities ( L IR ), and associated star formation rates (SFRs). Our analysis confirmed that dust temperature is higher in this sample (34−65 K) than in local main-sequence galaxies, and this finding can be linked to the increased star formation efficiency we derived, as also suggested by the [CII] 158 μm deficit. Most remarkably, we note that the average value of T d of this sample does not differ from the one that is observed in luminous, ultraluminous and hyperluminous infrared galaxies at different redshifts that show no signs of hosting a quasar. Finally, our findings suggest that the presence of a bright AGN does not significantly bias the derived infrared properties, although further high frequency observations with a high spatial resolution might reveal more subtle effects on subkiloparsec scales.

Context. We investigate the origin of inter-band continuum time delays in active galactic nuclei (AGNs) in order to study the structure and properties of their accretion disks. Aims. We aim to measure the inter-band continuum time delays through photometric monitoring of Seyfert galaxy Fairall 9 to construct the lag-spectrum. Additionally, we explain the observed features in the Fairall 9 lag-spectrum and discuss the potential drivers behind them based on our newly collected data from the Obserwatorium Cerro Murphy (OCM) telescope. Methods. We initiated a long-term, continuous AGN photometric monitoring program in 2024 titled Hubble constant constraints through AGN Light curve Observations (HALO) using intermediate and broadband filters. Here, we present the first results from HALO, focusing on photometric light curves and continuum time-delay measurements for Fairall 9. To complement these observations and extend the wavelength coverage of the lag-spectrum, we also reanalyzed archival Swift light curves and spectroscopic data available in the literature. Results. Using HALO and Swift light curves, we measured inter-band continuum delays to construct the lag-spectrum of Fairall 9. Excess lags appear in the u and U bands (Balmer continuum contamination) and in the I band (Paschen jump and dust emission from the torus). Overall, the lag-spectrum deviates significantly from standard disk model predictions. Conclusions. We find that inter-band delays deviate from the power law, τ λ ∝ λ β , due to broad-line region scattering, reprocessing, and dust contributions at longer wavelengths. Power-law fits are therefore not well suited to characterizing the nature of the time delays.

The extragalactic background light (EBL) fluctuations in the optical/near-IR encode the cumulative integrated galaxy light (IGL), diffuse intra-halo light (IHL), and high-$z$ sources from the epoch of reionisation (EoR), but they are difficult to disentangle with auto-spectra alone. We aim to decompose the EBL into its principal constituents using multi-band intensity mapping combined with cosmic shear and galaxy clustering. We develop a joint halo-model framework in which IHL follows a mass- and redshift-dependent luminosity scaling, IGL is set by an evolving Schechter luminosity function, and EoR emission is modelled with Pop II/III stellar emissivities and a binned star-formation efficiency. Using mock surveys in a flat $Λ$CDM cosmology with ten spectral bands spanning 0.75-5.0$\rm μm$ in the NEP deep fields over about 100$°^2$ with source detections down to AB=20.5 for masking, and six redshift bins to $z=2.5$, we fit auto- and cross-power spectra using a MCMC method. The combined SPHEREx$\times$Euclid analysis recovers all fiducial parameters within 1$σ$ and reduces 1$σ$ uncertainties on IHL parameters by 10-35% relative to SPHEREx EBL-only, while EoR star-formation efficiency parameters improve by 20-35%. Cross-correlations reveal a stronger coupling of IHL than IGL to the shear field, enhancing component separation; conversely, the EoR contribution shows negligible correlation with cosmic shear and galaxy clustering, aiding its isolation in the EBL. Relative to the SPHEREx EBL-only case, the inferred IHL fraction as a function of halo mass is significantly tightened over $10^{11}-10^{14} M_{\odot}$, with uncertainties reduced by 5-30%, and the resulting star-formation rate density constraints extend to $z\sim 11$, with uncertainty reductions of 22-31%.

We investigate how the orbital evolution and mass distribution of infalling satellite galaxies shape the phase-space and radial distributions of intracluster light (ICL) relative to the underlying cluster dark matter (DM) halo. Using N-body simulations, we follow the tidal stripping and orbital evolution of satellite galaxies as they are accreted into a live cluster halo, systematically varying satellite-to-host mass ratio and orbital circularity. We measure the specific orbital energy and angular momentum of stripped stellar and DM material, finding that the stripped stars consistently occupy lower-energy and lower-angular momentum regions of phase-space than the stripped DM. The magnitude of this difference increases strongly towards more equal satellite--to--host mass ratios, while the dependence on orbital circularity is weak. We construct a predictive model for the phase-space properties of stripped stars and DM from a whole infalling satellite population and find that the resulting phase-space difference between the components are driven primarily by the characteristic mass of the infalling satellite stellar mass function. We find that the ICL is always more centrally concentrated than the DM. The magnitude of this offset depends on the characteristic mass and increases towards higher characteristic masses. Comparisons with four independent cosmological hydrodynamical simulations show that, once the infalling satellite stellar mass function is matched, the model reproduces the radial stellar-to-DM density profile offsets to better than the inter-simulation scatter. This demonstrates that the radial relationship between the ICL and the DM distribution is largely governed by satellite demographics. With adequate constraints on the infalling satellite population, ICL density profiles can therefore be used as informative tracers of the underlying radial DM distribution in clusters.

Changing-look active galactic nuclei (CLAGNs) represent a rare class of AGNs that undergo transitions from type 1 (characterized by the presence of broad emission lines in their spectra) to type 2 (absence of broad emission lines) or vice versa, over timescales ranging from months to years. Such brief periods of variation can significantly constrain the physical processes involved in the accretion of matter onto the AGN central supermassive black hole. Since normal type 1 and type 2 AGNs are known to show different polarization properties, detailed investigations of the CLAGN polarization can shed light on the underlying mechanisms responsible for the changing-look phenomenon. In this paper we present new (spectro)polarimetric observations of two changing-look AGNs located in the core of the inclined spiral galaxies NGC 1365 and NGC 2992. Both AGNs are radio emitters, thereby enabling a comparison of their polarization to the radio jet axis, which defines the accretion disk geometry. In the case of NGC 1365, the AGN shows polarization characteristics consistent with those observed in type 1 Seyferts, in particular polarization parallel to the radio jet. This intrinsic polarization is modified by the wavelength-dependent dichroic extinction that occurs in the galaxy bar and that rotates the polarization angle at the shortest wavelengths. Measuring the polarization of NGC 1365 when the AGN is in a type 2 state would be particularly interesting to see if its polarization becomes perpendicular to the radio axis, as observed in normal type 2 AGNs, or if it remains parallel. NGC 2992, on the other hand, is so inclined that dichroic dust extinction in the disk completely dominates the polarization of the AGN, thus overwhelming any polarization due to scattering. Consequently, the polarization properties remain essentially constant between the different AGN states, and the faint broad lines observed in the polarized flux are most likely not scattered light. Differential dilution between the continuum and the narrow-line polarizations can explain the unusually high polarization measured in the emission lines.

Abstract We present [O iii] 88 μm observations towards four Herschel-selected dusty star-forming galaxies (DSFGs; log10μLIR/L⊙ = 13.5 − 14 at z = 2.9 − 4) using the Atacama Compact Array (ACA) in Bands 9 and 10. We detect [O iii] emission in all four targets at >3σ, finding line luminosity ratios ($L_{\rm [O_{III}]} / L_{\rm IR} = 10^{-4.2}$ to 10−3) similar to local spiral galaxies, and an order of magnitude lower when compared with local dwarf galaxies as well as high-redshift Lyman-break galaxies. Using the short-wavelength capabilities of the ACA, these observations bridge the populations of galaxies with [O iii] emission at low redshift from space missions and at high redshift from ground-based studies. The difference in [O iii] emission between these DSFGs and other high-redshift galaxies reflects their more evolved stellar populations (>10 Myr), larger dust reservoirs (Mdust ∼ 109 − 11 M⊙), metal-rich interstellar medium (Z ∼ 0.5 − 2 Z⊙), and likely weaker ionization radiation fields. Ancillary [C ii] emission on two targets provide $L_\mathrm{[O\, \rm \small {III}]}/L_\mathrm{[C\, \rm \small {II}]}$ ratios at 0.3 − 0.9, suggesting that ionized gas represents a smaller fraction of the total gas reservoir in DSFGs, consistent with theoretical models of DSFGs as transitional systems between gas-rich, turbulent disks and more evolved, gas-poor galaxies. Expanding samples of DSFGs with [O iii] emission will be key to place this heterogeneous, poorly-understood galactic phase in its astrophysical context.

The ongoing Euclid mission aims to measure spectroscopic redshifts for approximately two million galaxies using the H $α$ line emission detected in near-infrared slitless spectroscopic data from the Euclid Deep Fields (EDFs). These measurements will reach a flux limit of $5\times 10^{-17}\,{\rm erg}\,{\rm cm}^{-2}\,{\rm s}^{-1}$ in the redshift range $0.4<z<1.8$, opening the door to numerous investigations involving galaxy evolution, extending well beyond the mission's core objectives. The achieved H $α$ luminosity depth will lead to a sufficiently high sampling, enabling the reconstruction of the large-scale galaxy environment. We assess the quality of the reconstruction of the galaxy cosmic web environment with the expected spectroscopic dataset in EDFs. The analysis is carried out on the Flagship and GAEA galaxy mock catalogues. The quality of the reconstruction is first evaluated using geometrical and topological statistics measured on the cosmic web, namely the length of filaments, the area of walls, the volume of voids, and its connectivity and multiplicity. We then quantify how accurately gradients in galaxy properties with distance from filaments can be recovered. As expected, the small-scale redshift-space distortions, have a strong impact on filament lengths and connectivity, but can be mitigated by compressing galaxy groups before skeleton extraction. The cosmic web reconstruction is biased when relying solely on H $α$ emitters. This limitation can be mitigated by applying stellar mass weighting during the reconstruction. However, this approach introduces non-trivial biases that need to be accounted for when comparing to theoretical predictions. Redshift uncertainties pose the greatest challenge in recovering the expected dependence of galaxy properties, though the well-established stellar mass transverse gradients towards filaments can still be observed.