arXiv subjects

F. Vito

Publications and source records attributed to F. Vito.

At least 19 recordsLinked to original sources

arXiv2026

Exploring the AGN population in protoclusters: results from the TNG300 simulation and comparison with observations

In this work, we investigate the physical properties and cosmic evolution of galaxies and AGN in a sample of 280 protoclusters identified in the TNG300 simulation, selected to end up in $z = 0$ clusters with $M_{200, \rm c} > 10^{14} \, {\rm M_{\odot}}$. Our goal is to provide the first statistical view of AGN activity enhancement in a uniformly defined sample of overdense environments, and to identify the physical mechanisms driving it. We identify protoclusters as the progenitors of present-day galaxy clusters through merger-tree reconstruction and compare their galaxy and AGN populations with a control sample of field galaxies across the redshift range $0 \leq z \leq 6$. We investigate galaxy and SMBH demographics, AGN fractions, bolometric luminosity functions, and the SMBH accretion rate density, consistently applying homogeneous selection criteria in all environments. We find that TNG300 protoclusters host systematically more massive galaxies and SMBHs than the field by up to $1 \, {\rm dex}$ at all redshifts, with signatures of accelerated galaxy evolution already visible at $z \sim 3-4$. The AGN fraction increases with stellar mass in both environments and, at fixed host-galaxy stellar mass, is broadly consistent between protoclusters and field galaxies, indicating no strong environmental triggering of SMBH accretion. However, when analysed as a function of redshift, protoclusters exhibit a significant enhancement of AGN activity (by a factor $> 2$), particularly at high luminosities and early cosmic times. We show that this enhancement primarily arises from differences in the stellar-mass distributions of galaxies in overdense regions, where massive systems assemble earlier than in the field. Consistently, protoclusters dominate the bright end of the AGN bolometric luminosity function and contribute up to $\sim 50\%$ of the total SMBH accretion rate density at $z \sim 6$.

astro-ph.GA↗

arXiv2026

SKA$-$VLBI view of AGN jets in the early Universe

Active Galactic Nuclei (AGN) are among the brightest sources in the Universe, and those that are also jetted are uniquely valuable at the earliest epochs, because their relativistic outflows can regulate the gas supply of their host galaxies, potentially affecting both early star formation and the rapid growth of supermassive black holes (SMBHs). Their compact, high-brightness-temperature radio cores provide the sharpest beacons for very long baseline interferometry (VLBI), enabling direct constraints on Doppler boosting, jet duty cycles, and jet$-$environment coupling at extreme redshifts. In this White Paper, we discuss how the SKA-VLBI will provide sub-$\mu$Jy sensitivity together with milliarcsecond (mas) angular resolution to image and characterise jetted AGN at $z>6$ across SKA-Mid and SKA-Low frequencies. These observations can directly test SMBHs ($>10^6$ M$_{\odot}$) formation/evolution models (including jet-assisted super-Eddington phases) and infer the geometry of the Universe, directly probing the cosmological framework at high precision. Synergies with current and next-generation multi-band facilities will also be crucial to fully understand their host galaxies and their environment, providing an unprecedented panchromatic knowledge of the first jetted AGN.

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arXiv2026

The WISSHFUL program: the highest redshift UFO discovered in a non-lensed QSO

We present the first results from the WISSHFUL program, an XMM-Newton heritage program targeting luminous QSOs at Cosmic Noon. We report on recent simultaneous XMM-Newton and NuSTAR observations of the Super-Eddington accreting quasar WISSH13 at z=3.294, which provide the highest quality broadband X-ray spectrum to date for a non-lensed QSO at this redshift. Physical modeling of the continuum reveals a soft photon index ($\Gamma\sim2$) and strong reflection ($R\sim1.4-1.8$), despite the weak narrow Fe emission, and a low high-energy cut-off ($E_{cut}\sim60-80$ keV, $kTe = 15-20$ keV, depending on the model adopted). Most notably, we detect two significant (at $96.7\%$ and $98.9\%$ confidence level, respectively) absorption features at $\sim7.5$ and $\sim10$ keV rest-frame, interpreted as a blueshifted blend of Fe XXV He$\alpha$ and Fe XXVI Ly$\alpha$. These features indicate the presence of two kinematic components of a highly ionized, high column Ultra-Fast Outflow (UFO) with a velocity of $v_{out}\sim0.1c$ and $v_{out}\sim0.3c$, respectively. The slower wind is consistently detected in an archival 2017 XMM-Newton observation, whereas the faster wind is detected only in 2024. This stratified and variable wind exhibits extreme energetics, with a mass outflow rate of $\dot{M}_{out}\sim20M_{\odot}/yr$ (corresponding to $15\% \dot{M}_{acc}$) for each component, and a kinetic power of the order of $\sim1$ and $\sim10\%$ of the bolometric luminosity, respectively. While this represents one of the most powerful UFOs ever detected, its kinetic power is a similar fraction of the QSO's bolometric luminosity compared to lower-redshift AGN. We present several theoretical frameworks to explain the peculiar accretion and ejection properties of this remarkable QSO at Cosmic Noon.

astro-ph.HE↗

arXiv2026

Euclid: Disky titans -- surprisingly high star formation efficiency in two brightest group galaxies at $z\sim 0.75$

We present the discovery of two disky titans in the first data release of the Euclid satellite. These sources are massive ($M>10^{11} M_\odot$) star-forming (SFR $\sim 20 M_\odot$/yr) discs located in strong over-densities at intermediate redshift ($z\sim 0.75$). They represent an small fraction of the massive galaxies in over-dense regions (just four candidates in more than 20 deg2 analysed in this study), and their existence is puzzling considering the abundance of passive and bulge-dominated sources commonly found at the centre of groups and clusters at low redshift. Firstly, our analysis shows that these objects are located in massive groups ($M_h\sim 10^{13.8} M_\odot$), where rapid accretion of cold gas should be prevented from the formation of a static hot halo. Despite this, a millimetre follow-up with NOEMA shows significant cold gas reservoirs $M_{h_2} \sim 10^{10.3} M_\odot$) within these sources. Secondly, our morphological analysis shows the presence of a massive and passive bulge in these galaxies, which is expected to stabilise the disc against fragmentation thereby suppressing further star formation. However, these sources lie on the Schmidt-Kennicutt relation or even slightly above. Building on these observations, we propose a scenario where these disky titans are the product of a merger-induced rejuvenation episode, in which the most massive galaxy of a group accretes cold gas from another member and briefly restarts star-formation. Such scenario is supported by a comparison with the TNG300 simulation and easily explains the surviving of star-formation activity in massive galaxies in over-dense environments as temporary stages in a more complex evolution. More in general, our study showcases the ability of Euclid to find rare objects thanks to the unprecedented statistics offered by its surveys and the scientific potential residing in the synergy between Euclid and other facilities observing at longer wavelengths.

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arXiv2025

A deep X-ray look to the most obscured quasar at z~3.6 and its environment

The most luminous and obscured quasars (QSOs) detected in infrared all-sky surveys could represent a key co-evolutionary phase from nuclear to circum-galactic (CG) scales in the formation of massive galaxies. In this context, Hot Dust Obscured Galaxies (Hot DOGs) at z ~2-4 provide a unique opportunity to study the link between cosmic mass assembly and nuclear accretion in high-z luminous QSOs/galaxies. W0410-0913 (hereafter W0410-09) is a luminous ($\rm ~L_{\rm bol} \sim 6.4 \times10^{47} \rm erg\ s^{-1}$) obscured QSO at z = 3.631, with a 30 kpc CG Ly$\alpha$ nebula (CGLAN), smaller than the ~ 100 kpc nebulae around unobscured Type-I QSOs, and an exceptional overdense environment of ~ 19 Ly$\alpha$ emitters (LAEs) within 300 kpc and $\pm$ 200 $\rm km ~s^{-1}$ of the Hot DOG. We aim to detect and characterize nuclear accretion in W0410-09 and its environment. Exploiting a deep proprietary ~280 ks Chandra observation, using empirical and physically motivated models for obscured sources, we show that W0410-09 exhibits Compton-thick obscuration ($\rm~ N_H > 10^{24} \rm cm^{-2}$) and high intrinsic luminosity ($\rm ~L_{2-10} > 10^{45} \rm erg ~s^{-1}$), making it one of the most luminous obscured QSOs at z $>$ 3.5. With the exclusion of W0410-09 we do not detect X-ray emission from any of the 19 LAEs, except for a 3$\sigma$ signal in the 6-7 keV rest-frame band, interpreted as Fe K$\alpha$ emission, suggesting the presence of heavily obscured yet undetected AGN emission in several LAEs. Including W0410-09, the estimated AGN fraction is $f_{\rm AGN}^{\rm LAE} = 5^{+12}_{-4}$%, potentially up to ~35% if unresolved obscured AGN are considered as suggested by the Fe K$\alpha$ line detection. We conclude that W0410-09 is in a critical transitional blow-out phase, during which powerful QSO-driven outflows are clearing the nuclear obscuration, ultimately leading to an unobscured luminous quasar.

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arXiv2025

The WISSH quasar project. XII. X-ray view of the most luminous quasi-stellar objects at Cosmic Noon

To improve our knowledge of nuclear emission in luminous QSOs at Cosmic Noon, we studied the X-ray emission of the WISE/SDSS-selected hyper-luminous (WISSH) QSO sample: 85 broad-line AGN with $L_{bol}>few\times 10^{47}\,erg\,s^{-1}$ at $z\sim 2-4$. Our aim is to characterise their X-ray spectra and explore relations between X-ray luminosity and other bands, comparing powerful QSOs with the general AGN population. We performed spectral analysis for about half of the sample; 16 sources were analysed via their hardness ratio; for the others we estimated their intrinsic luminosity $L_{2-10\,keV}$. Only 8 sources are undetected. We report a large dispersion in $L_{2-10\,keV}$ despite the narrow distribution of $L_{bol}$, $L_{2500\,\r{A}}$ and $\lambda L_{6\,\mu m}$ (about one-third of the sources classified as X-ray weak). This suggests differences in X-ray corona and accretion flow physics between hyper-luminous and less powerful AGN. X-ray photon index distribution is consistent with that of lower-$z$, lower-$L_{bol}$ AGN, and does not depend on the Eddington ratio ($\lambda_{Edd}$) or X-ray weakness. Most WISSH QSOs with intrinsic absorption estimates show little to no obscuration ($N_H \le 5\times 10^{22}\,cm^{-2}$). Among the obscured sources we find blue QSOs without broad absorption lines within the "forbidden region" of the $Log(N_H)-Log(\lambda_{Edd})$ plane, typically occupied by dust-reddened QSOs and associated with intense feedback. We confirm a correlation between $L_{2-10\,keV}$ and CIV line blueshift, a tracer of nuclear ionized outflows. Multi-wavelength data and complete X-ray coverage enabled the investigation of the disk-corona interplay at the highest luminosity regimes. The broad distribution of bolometric correction and X-ray - to - optical index suggest caution when using $L_{bol}$, $L_{2500\,\r{A}}$ or $L_{6\,\mu m}$ as direct X-ray proxy for individual luminous QSOs.

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arXiv2025

The properties of X-ray selected AGN in protoclusters pinpointed by Enormous Lya Nebulae

Protoclusters of galaxies are overdense regions of the Universe characterized by large gas reservoirs. Such environments make them perfect laboratories to investigate galaxy-AGN co-evolution and the growth of SMBHs. Galaxies living in such a dense regions are expected to growth efficiently their SMBH, resulting in a higher incidence of AGN than in the field. Some protoclusters exhibit extended Ly$\alpha$ nebulae in their central region, pinpointing the presence of massive gas reservoirs, but whose main powering mechanism is still debated. We aim to investigate the AGN population, and AGN enhancement, in three protoclusters at 2.3 < z < 3.2 which host enormous Ly$\alpha$ nebulae (ELANe). Additionally, we search for the presence of X-ray diffuse emission in the same region of the Ly$\alpha$ nebulae to reveal multi-phase gas in these protoclusters. We use deep (190-270 ks) Chandra observations to identify AGN among the protocluster members and perform X-ray spectral analysis to derive the properties of those sources. We compare the AGN fraction and space density with those observed in other known protoclusters and from the field environment. We find 11 X-ray detected AGN in the three protoclusters. Each structure hosts a central, X-ray powerful (log$(L_{\rm X}/{\rm erg \, s^{-1}}) \sim 45-46$), QSO, while the other X-ray sources are mostly moderately luminous (log$(L_{\rm X}/{\rm erg \, s^{-1}}) \sim 44$) and obscured Compton-Thin AGN. The fraction of AGN in our targets is comparable with estimates for other protoclusters, and significantly higher than what is found for low-redshift clusters. We also find a significant enhancement (2-4 dex) of AGN density with respect to the field and to non active galaxies in the protoclusters. Finally, we find no significant soft X-ray diffuse emissions from the nebulae, thus ruling out gravitational heating as the main powering mechanism of the ELANe.

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arXiv2025

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) XXII. Chandra observations of narrow-line quasar candidates at z>6

We report on Chandra X-ray observations of four narrow-line quasar candidates at z~6, selected from the SHELLQs project, based on the Subaru Hyper Suprime-Cam survey. These objects are characterised by narrow (FWHM<310 km/s), luminous (>1e44 erg/s) Lya and faint UV continuum (M_1450 = -22 - -21), prompting us to examine whether they are obscured luminous AGN at the epoch of reionization. However, none of these objects were detected by Chandra, giving an upper limit to their rest-frame 2-10 keV luminosity (Lx) of 2e44 erg/s (2 sigma), assuming a spectral slope Gamma=2. Subsequent rest-frame optical spectroscopy of these objects by the JWST-NIRSpec, presented in a companion paper, show weak broad Balmer emission at the base of narrow cores. With the scaling relation for low-redshift AGN, the observed strong [OIII]5007 flux of these sources would predict Lx to be around 1e45 erg/s, which is well above the Chandra upper limits. These optical spectra and X-ray quietness are reminiscent of JWST-selected broad-line AGN. We attribute the weak broad Balmer emission to the broad-line regions hidden partially by optically-thick obscuring matter which also hides the optical and X-ray continuum emission from the accretion disc. Compton-thick obscuration, which would strongly suppress X-ray emission, could be due to a dense inter-stellar medium that is often present in galaxies at high redshifts. Alternatively, the same effect could be obtained from an inflated disc at the innermost radii in a supercritical accretion flow, when the disc is viewed at inclined angles.

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arXiv2024

The radio properties of the JWST-discovered AGN

We explore the radio emission of JWST-selected Broad Line AGN (BLAGN, or type 1) in the GOODS-N field. We use 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 the aforementioned frequencies. Similarly, the radio stacking analysis does not reveal any detection down to an rms of ${\sim 0.15}\mu$Jy beam$^{-1}$, corresponding to a $3\sigma$ upper limit at rest frame 5 GHz of $L_{5GHz}=2\times10^{39}$ erg s$^{-1}$ at the mean redshift of the sample $z\sim 5.1$. We compared this and individual sources upper limits with expected radio luminosities estimated assuming different AGN scaling relations, {to check whether these 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. Indeed, 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 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 $\sim$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.

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arXiv2024

HYPERION: broad-band X-ray-to-near-infrared emission of Quasars in the first billion years of the Universe

We aim at characterizing the X-ray-to-optical/near-infrared broad-band emission of luminous QSOs in the first Gyr of cosmic evolution to understand whether they exhibit differences compared to the lower-\textit{z} QSO population. Our goal is also to provide for these objects a reliable and uniform catalog of SED fitting derivable properties such as bolometric and monochromatic luminosities, Eddington ratios, dust extinction, strength of the hot dust emission. We characterize the X-ray/UV emission of each QSO using average SEDs from luminous Type 1 sources and calculate bolometric and monochromatic luminosities. Finally we construct a mean SED extending from the X-rays to the NIR bands. We find that the UV-optical emission of these QSOs can be modelled with templates of $z\sim$2 luminous QSOs. We observe that the bolometric luminosities derived adopting some bolometric corrections at 3000 \AA\ ($BC_{3000\text{\AA}}$) largely used in the literature are slightly overestimated by 0.13 dex as they also include reprocessed IR emission. We estimate a revised value, i.e. $BC_{3000\text{\AA}}=3.3 $ which can be used for deriving $L_\text{bol}$ in \textit{z} $\geq$ 6 QSOs. A sub-sample of 11 QSOs is provided with rest-frame NIR photometry, showing a broad range of hot dust emission strength, with two sources exhibiting low levels of emission. Despite potential observational biases arising from non-uniform photometric coverage and selection biases, we produce a X-ray-to-NIR mean SED for QSOs at \textit{z} $\gtrsim$ 6, revealing a good match with templates of lower-redshift, luminous QSOs up to the UV-optical range, with a slightly enhanced contribution from hot dust in the NIR.

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arXiv2024

HYPERION. Shedding light on the first luminous quasars: A correlation between UV disc winds and X-ray continuum

One of the main open questions in the field of luminous ($L_{\rm bol}>10^{47}\,\rm erg\,s^{-1}$) quasars (QSOs) at $z \gtrsim 6$ is the rapid formation ($< 1\,$Gyr) of their supermassive black holes (SMBHs). For this work we analysed the relation between the X-ray properties and other properties describing the physics and growth of both the accretion disc and the SMBH in QSOs at the Epoch of Reionization (EoR). The sample consists of 21 $z>6$ QSOs, which includes 16 sources from the rapidly grown QSOs from the HYPERION sample and five other luminous QSOs with available high-quality archival X-ray data. We discovered a strong and statistically significant ($>3\sigma$) relation between the X-ray continuum photon index ($\Gamma$) and the $\rm C\,IV$ disc wind velocity ($v_{\rm C\,IV}$) in $z>6$ luminous QSOs, whereby the higher the $v_{\rm C\,IV}$, the steeper the $\Gamma$. This relation suggests a link between the disc-corona configuration and the kinematics of disc winds. Furthermore, we find evidence at $>2-3\sigma$ level that $\Gamma$ and $v_{\rm C\,IV}$ are correlated to the growth rate history of the SMBH. Although additional data are needed to confirm it, this result may suggest that, in luminous $z>6$ QSOs, the SMBH predominantly grows via fast accretion rather than via initial high seed BH mass.

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arXiv2024

X-ray view of a massive node of the Cosmic Web at z~3 I. An exceptional overdensity of rapidly accreting SMBHs

Exploring SMBH population in protoclusters offers valuable insights into how environment affects SMBH growth. However, research on AGN within these areas is still limited by the small number of protoclusters known at high redshift and by the availability of associated deep X-ray observations. To understand how different environments affect AGN triggering and growth at high redshift, we investigated the X-ray AGN population in the field of the MUSE Quasar Nebula 01 (MQN01) protocluster at z ~3.25. This field is known for hosting the largest Lya nebula in the Borisova+16 sample, and one of the largest overdensities of UV-continuum selected and sub-mm galaxies found so far at this redshift. We conducted a ultra deep Chandra X-ray survey (634 ks) observation of the MQN01 field and produced a comparative analyses of the properties of the X-ray AGNs detected in MQN01 against those observed in other selected protoclusters, such as Spiderweb and SSA22. By combining the X-ray, deep MUSE and ALMA data of the same field, we identified six X-ray AGNs within a volume of 16 cMpc^2 and \pm 1000 km/s, corresponding to an X-ray AGN overdensity of ~1000. This overdensity increases at the bright end, exceeding what was observed in the Spiderweb and SSA22 within similar volumes. The AGN fraction measured in MQN01 is significantly higher (f_AGN > 20%) than in the field and increases with stellar masses, reaching a value of 100% for log(M*/Msun) > 10.5. Lastly, we observe that the average specific accretion rate (\lambda_sBHAR) for SMBH populations in MQN01 is higher than in the field and other protoclusters, generally increasing as one moves toward the center of the overdensity. Our results, especially the large fraction of highly accreting SMBHs in the inner regions of the MQN01 overdensity, suggest that protocluster environments offer ideal physical conditions for SMBH triggering and growth.

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arXiv2024

The X-ray enhancements of radio-loud quasars at high redshift: New results at $z = 4\text{ -- }7$

Highly radio-loud quasars (HRLQs; $\log R>2.5$) at $z\gtrsim 4$ show apparent enhanced X-ray emission compared to matched HRLQs at lower redshifts, perhaps due to a redshift-dependent fractional contribution to the X-ray luminosity from inverse-Compton scattering of cosmic microwave background photons (IC/CMB). Using new {\it Chandra} observations and archival X-ray data, we investigate this phenomenon with an optically flux-limited sample of 41 HRLQs at $z = 4$--5.5 all with sensitive X-ray coverage, the largest sample utilized to date by a wide margin. X-ray enhancements are assessed using X-ray-to-optical flux ratios and spectral energy distributions. We confirm the presence of X-ray enhancements at a 4.9--5.3$\sigma$ significance level, finding that the median factor of enhancement is $\approx 1.8$ at our sample median redshift of $z\approx 4.4$. Under a fractional IC/CMB model, the expected enhancement at lower redshifts is modest; e.g., $\approx 4$% at $z\approx 1.5$. We also investigate a sample of seven radio-loud quasars (RLQs; $\log R>1$) at even higher redshifts of $z=5.6$--6.8, using new and archival X-ray data. These RLQs also show evidence for X-ray enhancements by a median factor of $\approx 2.7$ at a 3.7--4.9$\sigma$ significance level. The X-ray spectral and other properties of these $z=5.6$--6.8 RLQs, however, pose challenges for a straightforward fractional IC/CMB interpretation of their enhancements.

astro-ph.HE↗

arXiv2024

AGN X-ray luminosity function and absorption function in the Early Universe ($3\leq z \leq 6$)

The XLF of AGN offers a robust tool to study the evolution and the growth of SMBHs over cosmic time. Owing to the limited area probed by X-ray surveys, optical surveys are routinely used to probe the accretion in the high redshift Universe $z\geq 3$. However, optical surveys may be incomplete because they are strongly affected by dust redenning. In this work, we derive the XLF and its evolution at high redshifts using a large sample of AGNs selected in different fields with various areas and depths covering a wide range of luminosities. Additionally, we put the tightest yet constraints on the absorption function in this redshift regime. In particular, we use more than 600 soft X-ray selected high-z sources in the Chandra Deep fields, the Chandra COSMOS Legacy survey and the XMM-XXL northern field. We derive the X-ray spectral properties for all sources via spectral fitting, using a consistent technique and model. For modeling the parametric form of the XLF and the absorption function, we use a Bayesian methodology allowing us to correctly propagate the uncertainties for the observed X-ray properties of our sources and also the absorption effects. The evolution of XLF is in agreement with a pure density evolution model similar to what is witnessed at optical wavelengths, although a luminosity dependent density evolution model cannot be securely ruled out. A large fraction ($60\%)$ of our sources are absorbed by column densities of $\rm N_H \geq 10^{23} cm^{-2} $, while $17$\% of the sources are CTK. Our results favor a scenario where both the ISM of the host and the AGN torus contribute to the obscuration. The derived BHAD is in agreement with the simulations, if one takes into account that the X-ray AGN are hosted by massive galaxies, while it differs from the one derived using JWST data. The latter could be due to the differences in the AGN and host-galaxy properties.

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arXiv2023

HYPerluminous quasars at the Epoch of ReionizatION (HYPERION). A new regime for the X-ray nuclear properties of the first quasars

The existence of luminous quasars (QSO) at the Epoch of Reionization (EoR; i.e. z>6) powered by supermassive black holes (SMBH) with masses $\gtrsim10^9~M_\odot$ challenges models of early SMBH formation. To shed light on the nature of these sources we started a multiwavelength programme based on a sample of 18 HYPerluminous quasars at the Epoch of ReionizatION (HYPERION). These are the luminous QSOs whose SMBH must have had the fastest mass growth during the Universe first Gyr. In this paper we present the HYPERION sample and report on the first of the 3 years planned observations of the 2.4 Ms XMM-Newton Multi-Year Heritage program on which HYPERION is based. The goal of this program is to accurately characterize the X-ray nuclear properties of QSOs at the EoR. Through a joint X-ray spectral analysis of 10 sources, in the rest-frame $\sim2-50$ keV range, we report a steep average photon index ($\Gamma\sim2.4\pm0.1$). Absorption is not required. The average $\Gamma$ is inconsistent at $\geq4\sigma$ level with the canonical 1.8-2 value measured in QSO at z<6. This spectral slope is also much steeper than that reported in lower-z QSOs with similar luminosity or accretion rate, thus suggesting a genuine redshift evolution. Alternatively, we can interpret this result as the presence of an unusually low-energy cutoff $E_{cut}\sim20$ keV on a standard $\Gamma=1.9$ power-law. We also report on mild indications that HYPERION QSOs show higher soft X-ray emission at 2 keV compared to the UV one at 2500A than expected by lower-z luminous AGN. We speculate that a redshift-dependent coupling between the corona and accretion disc or intrinsically different coronal properties may account for the steep spectral slopes, especially in the presence of powerful winds. The reported slopes, if confirmed at lower luminosities, may have an important impact on future X-ray AGN studies in the early Universe.

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arXiv2023

AGN feedback in an infant galaxy cluster: the LOFAR-Chandra view of the giant FRII radio galaxy J103025+052430 at z=1.7

In the nearby universe jets from AGN are observed to have a dramatic impact on their surrounding extragalactic environment. Their effect at the `cosmic noon' (z>1.5), the epoch when star formation and AGN activity peak, is instead much less constrained. Here we present a study of the giant (750 kpc) radio galaxy 103025+052430 located at the centre of a protocluster at redshift z=1.7, with a focus on its interaction with the external medium. We present new LOFAR observations at 144 MHz, which we combine with VLA 1.4 GHz and 0.5-7 keV Chandra archival data. The new map at 144 MHz confirms that the source has a complex morphology, possibly consistent with the `hybrid morphology' classification. The large size of the source gave us the possibility to perform a resolved radio spectral index analysis, a very unique opportunity for a source at such high redshift. This reveals a tentative flattening of the radio spectral index at the edge of the backflow in the Western lobe, which might be indicating plasma compression. The spatial coincidence between this region and the thermal X-ray bubble C suggests a causal connection between the two. Contrary to previous estimates for the bright X-ray component A, we find that inverse Compton scattering between the radio-emitting plasma of the Eastern lobe and the CMB photons can account for a large fraction (~45%-80%) of its total 0.5-7 keV measured flux. Finally, the X-ray bubble C, which is consistent with a thermal origin, is found to be significantly overpressurised with respect to the ambient medium. This suggests that it will tend to expand and release its energy in the surroundings, contributing to the overall intracluster medium heating. Overall, 103025+052430 gives us the chance to investigate the interaction between AGN jets and the surrounding gas in a system that is likely the predecessor of the rich galaxy clusters we all well know at z=0.

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arXiv2023

The universal shape of the X-ray variability power spectrum of AGN up to $z\sim 3$

We study the ensemble X-ray variability properties of Active Galactic Nuclei (AGN) over a large range of timescales (20 ks $\leq T\leq$ 14 yrs), redshift ($0\leq z \lesssim 3$), luminosities ($10^{40}$ erg s$^{-1}\leq L_X\leq 10^{46}$ erg s$^{-1}$) and black hole (BH) masses ($10^6 \leq $M$_\odot \leq 10^9$). We propose the use of the variance-frequency diagram, as a viable alternative to the study of the power spectral density (PSD), which is not yet accessible for distant, faint and/or sparsely sampled AGN. We show that the data collected from archival observations and previous literature studies are fully consistent with a universal PSD form which does not show any evidence for systematic evolution of shape or amplitude with redshift or luminosity, even if there may be differences between individual AGN at a given redshift or luminosity. We find new evidence that the PSD bend frequency depends on BH mass and, possibly, on accretion rate. We finally discuss the implications for current and future AGN population and cosmological studies.

astro-ph.HE↗

arXiv2022

NuSTAR observations of a heavily X-ray obscured AGN in the dwarf galaxy J144013+024744

We present a multi-wavelength analysis of the dwarf Seyfert-2 galaxy J$144013+024744$, a candidate obscured active galactic nucleus (AGN) thought to be powered by an intermediate-mass black hole (IMBH, $M_\bullet \approx 10^{4-6} M_\odot$) of mass $M_{\bullet} \sim 10^{5.2}M_\odot$. To study its X-ray properties, we targeted J$144013+024744$ with NuSTAR for $\approx 100$ ks. The X-ray spectrum was fitted with absorbed power law, Pexmon and a physical model (RXTorus). A Bayesian X-ray analysis was performed to estimate the posteriors. The phenomenological and the physical models suggest the AGN to be heavily obscured by a column density of $N_{\rm H} = (3.4-7.0)\times10^{23}$ cm$^{-2}$. In particular, the RXTorus model with a sub-solar metallicity suggests the obscuring column to be almost Compton-thick. We compared the $2-10$ keV intrinsic X-ray luminosity with the inferred X-ray luminosities based on empirical scaling relations for unobscured AGNs using $L_{\rm [OIV](25.89\mu {\rm m})}$, $L_{[{\rm OIII}](5007 {\rm angstrom})}$, and $L_{6\rm \mu m}$ and found that the high-excitation $[{\rm OIV}]$ line provides a better estimate of the intrinsic $2-10$ keV X-ray luminosity ($L_{2-10}^{\rm int} \sim 10^{41.41}{\rm erg s}^{-1}$). Our results suggest that J$144013+024744$ is the first type-2 dwarf galaxy that shows X-ray spectroscopic evidence for obscuration. The column density that we estimated is among the highest measured to date for IMBH-powered AGNs, implying that a typical AGN torus geometry might extend to the low-mass end. This work has implications for constraining the black hole occupation fraction in dwarf galaxies using X-ray observations.

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