Bartolomeo Trefoloni

The large population of broad-line active galactic nuclei (AGNs) observed with the James Webb Space Telescope (JWST) at z ≳ 4 provides a new view of the black hole–galaxy connection in the first gigayear of cosmic history. We used the JADES survey-level dataset and developed a forward-modelling Bayesian framework that explicitly accounts for broad H α detectability and incorporates selection effects into the likelihood function. With this approach, we constrain the black hole–stellar mass ( M _BH – M _★ ) relation to be log M _BH = −4.06 ^+0.50 _−0.51 + 1.17 ^0.06 _−0.06 log M _★ , with an intrinsic orthogonal scatter of σ _int = 0.63 ^+0.14 _−0.11 dex. The slope and normalization are consistent with local determinations, indicating that the average scaling was already established by z ∼ 4–6. This suggests that the primary evolution of the relation occurs in its dispersion rather than in its mean normalization. In contrast, the substantially larger intrinsic scatter relative to the nearby Universe reveals a wider diversity of black hole–galaxy growth histories, likely driven by bursty accretion, delayed feedback, and differences in merger or seeding histories. Future JWST samples will be crucial to test whether this increased scatter is a persistent feature of the high-redshift Universe.

Quasar accretion models predict a broad range of optical and ultraviolet properties that depend primarily on black hole mass and accretion rate. Yet, most optically selected luminous quasars display strikingly similar continuum spectra. We show that this uniformity can be explained by a nearly constant luminosity-to-mass (‘Eddington’) ratio, λ _EDD and by thermal emission from a standard, optically thick, geometrically thin accretion disc. A standard disc with an Eddington ratio λ _EDD ∼ 0.1 reproduces both the black hole mass–luminosity distribution of Sloan Digital Sky Survey (SDSS) quasars and their principal continuum properties. In this framework, the spectral energy distribution (SED) peaks beyond the observable ultraviolet range for nearly all sources. We show that the few quasars expected to be cold enough to shift the peak into the observable region indeed show this behaviour. This scenario is further supported by an analysis of the relation between the luminosity of the main broad emission lines and the continuum luminosity (i.e. the ‘Baldwin effect’). We find that (1) the observed slopes of the line–continuum relations match the expectations from the standard disc model, if we assume that the line emission is a good proxy of the ionizing luminosity; (2) the dispersions of the line-continuum luminosity relations are very small (as small as 0.13 dex), suggesting that the physics of the disc-broad line region system is dominated by only one parameter (the black hole mass) with a nearly constant Eddington ratio; (3) our hypothesis of constant λ _EDD ∼ 0.1 provides a black hole mass estimate (based on the observed luminosity) with a smaller error than the virial estimate. Finally, we note that these results are strictly valid only for SDSS quasars; sources selected using other criteria may exist in different accretion states.

The population of active galactic nuclei (AGNs) newly discovered by the James Webb Space Telescope (JWST) exhibits peculiar properties that distinguish it from both local type I AGNs and high-redshift quasars. Most of these sources are compact, appearing as ‘little dots’; among them, the sub-class (10−30% of the total) characterised by significantly red optical colours is known as ‘little red dots’ (LRDs). In this work, we introduce the analogous term ‘little blue dots’ (LBDs) to characterise the remaining (bluer) sources (70−90%). We present a comparative analysis of two bright prototypical representatives, which we refer to as the Rosetta stones of the two classes: GN-28074 at z=2.26 as the red Rosetta stone and GS-3073 at z=5.55 as the blue Rosetta stone. Both Rosetta stones exhibit non-Gaussian broad Balmer lines, better described by exponential or double-Gaussian profiles rather than single Gaussians, similarly to normal low-redshift type I AGNs, indicating that non-Gaussian wings are not unique to LRDs. They are both extremely X-ray weak, showing strong auroral λ 4363 emission, weak hot dust mid-IR emission, and no time variability. However, they do differ in terms of excitation diagnostics: the λ 4686 line is undetected in the red Rosetta, but strongly detected in the blue Rosetta in both narrow and broad components, with the latter being much broader than hydrogen Balmer lines. This supports BLR stratification and disfavours the cocoon electron-scattering scenario in LBDs. An additional difference is the presence of prominent Balmer absorption in the red Rosetta, which is indicative of extremely dense gas along the line of sight and also happens to be absent in the blue Rosetta. Taken together, these results suggest that LRDs and LBDs share the same central engine as standard type I AGNs, while differing in terms of the amount and geometry of dense gas surrounding the accretion disk and/or in their accretion properties.

Context. Strong outflows from active galactic nuclei are frequently observed in objects with lower coronal X-ray luminosity. This intrinsic X-ray weakness is considered a requirement for the formation of radiatively driven winds. Aims. To obtain an unbiased view on the connection between X-ray emission and the presence of powerful winds in the most luminous quasar phase, we present an X-ray analysis of a sample of extremely luminous, radio-quiet quasars with signatures of strong outflows in their rest-frame ultraviolet (UV) emission spectra. Methods. We study the Chandra X-ray spectral properties of 10 objects, selected from the Sloan Digital Sky Survey Data Release 16 quasar catalogue based on their UV luminosities and C IV emission line blueshifts, comparing them to typical optically blue quasars. Results. Our analysis reveals that seven out of 10 quasars in our sample have photon indices Γ > 1.7. Only two out of 10 objects exhibiting outflows with velocities exceeding 1400 km/s are X-ray ‘weak’, consistent with the fraction of X-ray ‘weak’ objects generally observed in quasar populations. Notably, one of the objects identified as X-ray ‘weak’ is likely an intrinsically X-ray ‘normal’ quasar that is heavily obscured. We observe a tentative indication at a ∼2 σ confidence level that the correlation between the excessively low X-ray flux level and the presence of C IV emission-line outflows might emerge at wind velocities greater than 3000 km/s. Conclusions. Our study provides additional evidence that the relationship between X-ray emission and the presence of winds is intricate. Our findings emphasise the need for X-ray observations of a larger sample of UV-selected quasars with confirmed strong emission-line outflows to unravel the nuanced interplay between winds and X-ray emission.

The James Webb Space Telescope (JWST) has discovered a large population of active galactic nuclei (AGN) in the early Universe. A large fraction of these AGN revealed a significant lack of X-ray emission; the observed X-ray luminosity upper limits were 2–3 dex lower than expected. We explored the radio emission of these AGN, focusing on the JWST-selected broad-line AGN (BLAGN, or type 1) in the GOODS-N field, one of the fields with the best combination of deep radio observations and statistics of JWST-selected, spectroscopically confirmed BLAGN. We used deep radio data at different frequencies (144 MHz, 1.5 GHz, 3 GHz, 5.5 GHz, 10 GHz), and we find that none of the 37 sources investigated is detected at any of these frequencies. Similarly, the radio stacking analysis does not reveal any detection down to an rms of ∼0.15 μJy beam ⁻¹ , corresponding to a 3 σ upper limit at rest frame 5 GHz of L _5GHz = 2 × 10 ³⁹ erg s ⁻¹ at the mean redshift of the sample z ∼ 5.1. We compared this and the upper limits of the individual sources with expected radio luminosities estimated assuming different AGN scaling relations to check whether they are consistent with the standard BLAGN spectral energy distribution. For most of the sources the radio luminosity upper limits are still compatible with expectations for radio-quiet (RQ) AGN; nevertheless, the more stringent stacking upper limits and the fact that no detection is found might suggest that JWST-selected BLAGN are weaker than standard AGN, even at radio frequencies. The probability of having none of the BLAGN detected in none of the investigated radio images is expected to be on average very low ( P < 10 ⁻⁴ ). We discuss some scenarios that could explain the possible radio weakness, such as free-free absorption from a dense medium or the lack of either a magnetic field or a corona, possibly as a consequence of super-Eddington accretion. These scenarios would also explain the observed X-ray weakness. We also conclude that ∼1 dex more sensitive radio observations are needed to better constrain the level of radio emission (or lack thereof) for the bulk of these sources. The Square Kilometer Array Observatory (SKAO) will likely play a crucial role in assessing the properties of this AGN population.

Recent JWST observations have revealed a large population of intermediate/low-luminosity active galactic nuclei (AGNs) at early times with peculiar properties, different from local AGNs or luminous quasars. To better understand the physical conditions in the broad-line regions (BLRs) of these early AGNs, we used the optical Fe II (4434–4684 Å) and the broad Hβemission, and the ratio between their equivalent widths R_Fe, as a probe on a purposefully assembled sample. Specifically, we gathered a sample of 31 high redshift (⟨z⟩ = 6.5) AGNs, observed by JWST, with broad Hβdetection both in the high and low luminosity regimes (respectively 14 faint AGNs and 17 quasars), to investigate their optical Fe II emission properties. In addition, we carefully selected control samples at lower z. We found that the population of faint AGNs (log(L_Hβ,br/(erg s⁻¹)) ≲ 44) exhibits a significantly lower Fe II emission than their local counterparts having a mean (median) R_Fe < 0.24 (0.12) versus R_Fe ≃ 0.90 (0.79) in the control sample. At the same time, the quasars at the epoch of reionisation observed by JWST present a Fe II emission profile that closely resembles that observed at z < 3. We argue that the weakness of the Fe II bump in the faint JWST AGNs might be due to the reduced metallicity of their broad line region (≲0.5 Z_⊙), while luminous quasars have already reached chemical maturity (∼Z_⊙ or higher). Lastly, we highlight an intriguing similarity between the spectral properties of the high redshift population of faint AGNs with those harboured in local metal poor dwarf galaxies.

The transformative era opened by the James Webb Space Telescope (JWST) on the high-z Universe allows us to investigate the early stages of supermassive black hole (SMBH) evolution, with the first results showing a greater than expected number of active galactic nuclei (AGNs) at very early times. In this work, we spectroscopically select narrow-line AGNs (NLAGNs) among the ∼300 publicly available medium-resolution spectra of the Cosmic Evolution Early Release Science Survey (CEERS). Using both traditional and newly identified emission line NLAGN diagnostics diagrams, we identified 52 NLAGNs at 2 ≲ z ≲ 9, on which we performed a detailed multiwavelength analysis. We also identified four new z ≲ 2 broad-line AGNs (BLAGNs), in addition to the eight previously reported z > 4.5 BLAGNs. We found that the traditional BPT diagnostic diagrams are not suited to identifying high-z AGNs, while most of the high-z NLAGN were selected using the recently proposed AGN diagnostic diagrams based on the [O III] λ4363 auroral line or high-ionization emission lines. We compared the emission line velocity dispersion and the obscuration levels of the sample of NLAGNs with those of the parent sample without finding significant differences between the two distributions, suggesting a population of AGNs heavily buried and not significantly impacting the host galaxies’ physical properties, as was further confirmed by spectral energy distribution fitting. The bolometric luminosities of the high-z NLAGNs selected in this work are ∼1.5 dex below the ones sampled by surveys before JWST, potentially explaining the weak impact of these AGNs. Finally, we investigated the X-ray properties of the selected NLAGNs and of the sample of high-z BLAGNs. We found that all but four NLAGNs are undetected in the deep X-ray image of the field, as well as all the high-z BLAGNs. We did not obtain a detection even by stacking the undetected sources, resulting in an X-ray weakness of ∼1 − 2 dex from what was expected based on their bolometric luminosities. To discriminate between a heavily obscured AGN scenario or an intrinsic X-ray weakness of these sources, we performed a radio (1.4GHz) stacking analysis, which did not reveal any detection and left open the questions about the origin of the X-ray weakness.

A fundamental ingredient in the unified model of active galactic nuclei (AGN) is the obscuring torus, whose innermost, hottest region dominates the near infrared (NIR) emission. Characterising the change in the torus properties and its interplay with the primary AGN emission is key for our understanding of AGN physics, evolution, and classification. Its covering factor (CF) is largely responsible for the classification of AGN on the basis of the detection of broad emission lines. It is still not clear whether the torus properties evolve over time and how they relate with the accretion parameters of the nucleus. In this work, we aim at investigating the evolution of the NIR properties with the redshift (z) and the bolometric luminosity (L_bol) in a sample of AGN. To this end, we assembled a large dataset of ∼36 000 type 1 AGN between 0.5 < z < 2.9 and 45.0 < log(L_bol/(erg s)) < 48.0 with UV, optical, and near-infrared photometry. We produced average spectral energy distributions (SED) in different bins of the z − L_bol parameter space to estimate how the NIR SED evolves according to these parameters. We find that the NIR luminosity decreases for increasing L_bol at any redshift. At the same time, the shape of the NIR SED in our sample is consistent with a non-evolution with z. As a consequence, all the explored proxies for the CF exhibit significant anti-correlations with L_bol, but not with z. Additionally, the CF also shows a shallower anti-correlation with the Eddington ratio (λ_Edd), yet the current systematic uncertainties, as well as the limited dynamical range, do not allow us to precisely constrain the role of the Eddington ratio. Lastly, we derived the covering factor from the ratio between the NIR and optical luminosity and we employed it to set a lower limit for the X-ray obscuration at different redshifts.