arXiv subjects

Giorgio Lanzuisi

Publications and source records attributed to Giorgio Lanzuisi.

At least 19 recordsLinked to original sources

arXiv2026

Detection of episodic Ultra-fast Outflows in the Low-luminosity quasar Mrk 205 using XMM-Newton data

Ultra-fast outflows (UFOs) from Active Galactic Nuclei (AGN) are winds which reach velocities up to 0.3c, and show mass outflow rates of 0.01-1 $M_{\odot} yr^{-1}$ and kinetic energies of $10^{42-45}$ erg/s. Their extreme properties allow UFOs to carry substantial kinetic power, sufficient to drive AGN feedback by injecting energy and momentum into the interstellar medium, regulating the host galaxy evolution and the supermassive black hole growth. In this work, we present a detailed analysis of XMM-Newton X-ray spectra of the low-luminosity quasar Mrk205. We find evidence of multi-component ultra-fast outflows, traced by two components detected in the high-resolution data, showing velocities in the range of $\sim$0.07c to $\sim$0.1c. In addition, we marginally detected an ultra-fast outflow feature in the Fe K band. According to our analysis, Mrk 205 shows episodes of wind launches, rather than persistent winds. We further discuss whether the energy carried by the UFOs in Mrk 205 is capable of producing significant feedback on its host galaxy.

astro-ph.HE↗

arXiv2026

AGN X-ray coronae at high luminosity: A broadband study of RBS 229 and PG 1407+265

Context. The X-ray emission of active galactic nuclei (AGNs) is commonly interpreted as arising from Comptonisation in a hot corona above the accretion disc. A prominent soft X-ray excess is also observed in many sources and is often explained by a warm Comptonising layer. Aims. We investigate the X-ray-emitting coronae of the luminous radio-quiet quasars PG 1407+265 ($z=0.94$) and RBS 229 ($z=0.334$), testing whether a two-corona scenario consistently describes their broadband spectra. Methods. We combine XMM-Newton EPIC and Optical Monitor data with simultaneous NuSTAR observations and long-term Swift monitoring, and model the spectra using Comptonisation models. Results. Both quasars are X-ray loud relative to the standard $α_{\rm OX}$-$L_{\rm UV}$ relation, with PG 1407+265 showing the strongest deviation. Their spectra are well reproduced by a warm, optically thick Comptonising component accounting for the soft excess and a hot corona producing the hard X-ray continuum. Both sources show high-energy cut-offs at approximately 70-80 keV. RBS 229 exhibits moderate reflection and a weak neutral Fe K-alpha line, while no significant reflection features are detected in PG 1407+265. The warm-corona parameters of RBS 229 remain consistent across epochs, whereas PG 1407+265 shows strong variability, including an extreme soft-excess episode extending to approximately 3 keV in the rest frame. Conclusions. These results constrain AGN coronae in the poorly explored high-luminosity regime. The cut-offs are broadly consistent with trends in AGN luminosity and accretion rate and remain below the runaway pair-production limit. The contrasting variability suggests that the warm corona responds to changes in the accretion flow while remaining within a narrow range of physical conditions.

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arXiv2026

PACHA: Probing AGN Coronae with High-redshift AGN

The X-ray emission of active galactic nuclei (AGN) is generally attributed to inverse Compton scattering of accretion-disk photons by hot electrons in a compact corona. In local AGN, directly constraining coronal properties is challenging because the high-energy cutoff often lies beyond the NuSTAR bandpass. High-redshift, luminous quasars enable systematic constraints on the high-energy cutoff, as cosmological redshift shifts the spectal cutoff into the observable hard X-ray band. We present first results from the ``Probing the AGN Coronae with High-redshift AGN'' (PACHA) project, based on quasi-simultaneous NuSTAR and XMM-Newton observations of 13 radio-quiet AGN at $z>1$. We constrain the high-energy cutoff and coronal temperature at 90\% confidence level for 10 and 9 sources, respectively. The sample exhibits a mean cutoff energy of $E_{\rm cut}=80.8\pm8.1$ keV and a mean coronal temperature of $kT_{\rm e}=18.4\pm1.6$ keV, both significantly lower than those measured in local {\it Swift}-BAT AGN, while the mean optical depth ($τ=4.8\pm0.3$) is significantly higher. The uncertainties are at 1~$σ$. Combining our high-redshift sample with local AGN, we find a potential anti-correlation between cutoff energy and both X-ray luminosity and black hole mass, with no significant dependence on Eddington ratio. Within a hybrid coronal framework, the inferred temperatures lie well below the pair-production limits for purely thermal coronae, indicating a substantial efficient Compton cooling and/or non-thermal electron component. The detection of low coronal temperatures in high-luminosity AGN is broadly consistent with predictions from recent radiation MHD simulations that consider purely thermal electron populations, implying that non-thermal electrons may not be the primary drivers of the observed coronal properties in these systems.

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arXiv2026

Rapid growth in a dual AGN during a gas-rich merger at z~4.5

The late stages of galaxy mergers - when two supermassive black holes (SMBHs) reach kiloparsec-scale separations - represent a critical phase for understanding SMBH growth, galaxy co-evolution, and the progenitors of low-frequency gravitational waves. Yet confirmed close-separation (<3 kpc) dual active galactic nuclei (AGNs) remain confined to the local Universe, despite predictions that such systems should be common in the merger-rich early Universe. Here we report the discovery of LID-1166, a dual AGN with a projected separation of ~1.5 kpc at z~4.5, representing the first such system known beyond the local Universe. Spatially resolved JWST/NIRSpec integral-field spectroscopy reveals two spatially and kinematically distinct narrow-line emission components with a line-of-sight velocity offset of ~ -164 km/s. Both components additionally exhibit broad Ha emission, including a compact off-nuclei broad Ha component associated with the companion source, confirming two actively accreting SMBHs. Independent ALMA [CII] 158 um observations reveal corresponding spatially and kinematically distinct cold gas components associated with the same nuclei, demonstrating that the system is a gas-rich merger. While undergoing super-Eddington accretion during a late-stage merger, the SMBHs already lie on the local black hole-host mass relation for massive elliptical galaxies within the uncertainties, suggesting that rapid, obscured growth may help establish this relation early in cosmic history. LID-1166 reveals a previously hidden phase of SMBH growth and points to a missing population of heavily obscured, merger-driven dual AGNs at high redshift.

astro-ph.GA↗

arXiv2026

No evolution in the number density of little red dots from cosmic dawn to cosmic noon

We present our search for little red dots (LRDs) in the "J1030 field", a region of the sky around the $z\sim 6.3$ quasar SDSS J1030+0524, observed by the JWST EIGER program. Over 154 point-like sources selected in a JWST-based photometric catalog, we find five broad line emitters (with $FWHM \gtrsim 1000\ \rm km s^{-1}$) that are red ($F200W - F356W > 0$) and are undetected in the X-rays. We use these sources to derive the bolometric luminosity function (LF) of LRDs at $z = 2.4$ and $z = 4.5$. At $z = 2.4$, the space density of LRDs is only a factor of $\sim 2$ lower than that of all pre-JWST active galactic nuclei (AGNs) with bolometric luminosity $L_{\rm bol} \gtrsim 3 \times 10^{44}\ \rm erg\ s^{-1}$. At $z = 4.5$, our estimate is consistent with those derived for LRDs based on larger areas of the sky. A similar behaviour is observed in the black hole mass function. More importantly, we study the number density of LRDs from cosmic dawn to cosmic noon. We find that there is no significant evolution in the abundance of LRDs with $L_{\rm bol} \gtrsim 3 \times 10^{44}\ \rm erg\ s^{-1}$ at $z > 2$. We speculate that the drop at $z < 4$ seen by other studies is due to their sampling of only the bright-end of the LRDs LF. At cosmic noon, the abundance of LRDs is $n = 3.4^{+5.6}_{-2.4} \times 10^{-5}\ \rm Mpc^{-3}$, which is a factor of $\sim 350$ larger than recent model predictions and is comparable with that of X-ray selected AGNs with similar bolometric luminosity. Our result may imply that, if LRDs are the early, rapid stages of supermassive black hole growth, as suggested by some models, then the formation of black hole seeds can be efficient down to epochs as recent as cosmic noon. Alternatively, LRDs may simply be a high-accretion phase in already mature black holes.

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arXiv2026

Little Red and Blue Dots: AGN-excited narrow lines, Lyman-$α$ emission, and resemblance to standard quasars

We present an analysis of a sample of 36 Little Red and Blue Dots (LRDs and LBDs) at $2.26<z<7.89$, identified by JWST in the GOODS fields. While both categories are selected to have broad Balmer lines, both of them are extremely X-ray weak. Both classes share the same location on various diagnostic diagrams, consistent with AGN excitation (with some deviations which can be ascribed to low metallicity), although their weak HeII emission suggests a generally softer ionizing spectrum than ordinary AGN. LRDs display Ly$α$ emission stronger than normal star-forming galaxies, and with a broad component consistent with the broad component of H$α$. Overall, these findings indicate that LRDs and LBDs are both powered by growing black holes and their ionizing radiation escapes to ionize the surrounding interstellar medium (ISM). The broad Balmer lines ($Hα_b$ and $Hβ_b$) have different apparent properties: LBDs have EW(H$α_b$) and $Hα_b/Hβ_b$ broadly consistent with normal AGN, while LRDs have higher values of both quantities, although still in the tail of the quasars distribution. LRD models in which a gas envelope completely encases the black hole, are inconsistent with these results -- these scenarios need modification to include clumpiness, or a (classical) equatorial geometry, letting ionizing photons reach the ISM. The different broad Balmer properties imply that LBDs cannot simply be LRDs with more galaxy contribution. Scenarios in which LRDs are simply dust-obscured LBDs seem broadly consistent with the observations. Finally, these results indicate that LRDs' bolometric luminosities estimated assuming isotropic emission and complete covering by the absorber are inadequate. The few X-ray-detected LRDs suggest no deviation from the standard AGN bolometric corrections, once absorption is accounted for.

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arXiv2026

Unveiling the dynamics of the ultra-fast outflow in IRAS 13224-3809 with X-ray spectroscopy

IRAS 13224-3809 is one of the most intensively studied narrow-line Seyfert 1 galaxies, with a rich literature reporting diverse and sometimes contrasting interpretations of its complex X-ray spectra and variability. Notably, a fast and variable ultra-fast outflow (UFO) was discovered in this source, sparking debate over its nature and driving mechanisms. Motivated by these open questions, we present a systematic, time- and flux-resolved reanalysis of the full 2016 XMM-Newton (1.5 Ms) and NuSTAR (500 ks) datasets, employing careful background treatment and equal-count spectral selections. We uniformly apply three spectral models, including photo-ionized absorption, broad emission, and relativistic reflection, to all intervals. We unambiguously confirm the presence of a strong, variable outflow with velocities exceeding 0.2$c$, and find that models including absorption consistently reveal robust physical trends: a velocity-luminosity correlation of the UFO, persistently large line widths, and no compelling equivalent-width-flux anti-correlation. When emission or reflection components are included, the significance of the absorption features decreases, but significant UFO detections remain in most intervals. We also report clear evidence for rapid acceleration of the wind in response to X-ray flares, with the outflow carrying momentum and kinetic power sufficient to drive an efficient AGN feedback. The observed rapid response favors magnetic driving, analogous to coronal mass ejections, over radiative acceleration. Our results reconcile contrasting previous claims and underline the need for high-resolution spectroscopy to resolve the wind substructure. The observed UFO variability and structure are consistent with a multiphase, clumpy wind produced by thermal and hydrodynamic instabilities, with magnetic reconnection providing the rapid acceleration mechanism.

astro-ph.HE↗

arXiv2026

Discovery of ultra-fast outflows with v$_{\rm out}>0.3 \rm c$ in local bright active galactic nuclei

Ultra-fast outflows (UFOs) are mildly relativistic (outflow velocity $v_{out}>0.1c$) nuclear winds detected as blueshifted absorption lines from highly ionized, dense gas in the X-ray spectra of active galactic nuclei. The AGN feedback mechanism is believed to be powered by these outflows, which can inject a large amount of energy and momentum into the surrounding interstellar medium, shaping the coevolution of the AGNs and their host galaxies. We performed a systematic search and rigorous statistical assessment of the presence of UFOs in the 7-12 keV band, in a sample of bright local AGNs. This study also aims to understand whether the presence and characteristics of UFOs depend on the state of the sources, by studying the relations between the incidence of UFOs and the accretion properties of AGNs. We collected X-ray spectroscopic flux-limited XMM data of 33 observations of local (z<0.2) type 1 AGNs. We modeled their spectra in the 2-12 keV band using a combination of direct-continuum and reflection components and searched for absorption features. This represents the first systematic search for UFOs up to 12 keV. We performed Monte Carlo simulations to assess the statistical significance of the detected lines. We report strong detections of UFOs in six sources of the sample at the >95% confidence level via MC simulations, corresponding to a fraction of 18% in our sample. From the observed energies of each absorption line, we evaluated the respective wind velocities, which in some cases exceed 40\% of the speed of light. The velocity distribution found in this work is therefore shifted to higher energies than those found in previous searches for UFOs in local sources, which were limited to 10 keV. Moreover, our analysis shows no correlation between the accretion properties of the SMBHs and the presence of winds. Furthermore, our study highlights the temporal variability of UFOs.

astro-ph.HE↗

arXiv2026

Radio selection of heavily obscured AGN in the J1030 field: unraveling a missing Compton-thick population

We tested the effectiveness of radio selection to discover heavily obscured AGNs, particularly at high-z, and we measured their abundance for the first time from a radio perspective. We consider the radio sources detected in the J1030 field, which is one of the fields with the deepest combination of 1.4 GHz radio and X-ray observations. We defined a radio excess parameter as the ratio between the star formation rate (SFR) that would correspond to the observed radio luminosity and the one directly derived from the spectral energy distribution (SED) fitting, $\rm REX=SFR_{1.4GHz}/SFR^{corr}_{SED}$. We then select as radio excess AGN those sources with $\rm REX>8.5$, corresponding to a $3σ$ excess above the median value. In this way, we find 145 radio-excess sources falling into the \textit{Chandra} X-ray image footprint but without X-ray detection. From the deep X-ray upper limits, we estimated a lower limit to the obscuration of each radio-excess AGN, finding on average $\log (N_H/\rm{cm^{-2}})>23.7$. A CTK AGN scenario is also supported by the results of the X-ray stacking analysis performed on sources at $z>1.5$, which revealed X-ray luminosities and hardness ratios compatible with very highly obscured AGN. Finally, we computed the number density of these radio-selected CTK AGN. While at $z\sim 2$ the radio number density agrees well with the CTK AGN predictions of different population synthesis models, at $z\sim3$ the radio selection returns a CTK AGN number density $\sim 2-3$ times larger than what is predicted by the X-ray models and observations. This result supports the effectiveness of radio emission in selecting the most obscured sources, unraveling a population of AGN potentially missed by X-rays surveys at $z>3$, paving the way to a synergistic use of the future radio and X-ray facilities such as the \textit{SKAO} and \textit{NewAthena}.

astro-ph.GA↗

arXiv2025

JWST-discovered AGN: evidence for heavy obscuration in the type-2 sample from the first stacked X-ray detection

One of the most puzzling properties of the high-redshift AGN population recently discovered by JWST, including both broad-line and narrow-line sources, is their X-ray weakness. With very few exceptions, and regardless of the optical classification, they are undetected at the limits of the deepest Chandra fields, even when stacking signals from tens of sources in standard observed-frame energy intervals (soft, hard, and full bands). It has been proposed that their elusive nature in the X-ray band is due to heavy absorption by dust-free gas or intrinsic weakness, possibly due to high, super-Eddington accretion. In this work, we perform X-ray stacking in three customized rest-frame energy ranges (1-4, 4-7.25, and 10-30 keV) of a sample of 50 Type 1 and 38 Type 2 AGN identified by JWST in the CDFS and CDFN fields. For the Type 2 sub-sample, we reach a total of about 210 Ms exposure, and we report a significant ($\sim 3σ$) detection in the hardest (10-30 keV rest frame) band, along with relatively tight upper limits in the rest frame softer energy bands. The most straightforward interpretation is in terms of heavy obscuration due to gas column densities well within the Compton thick regime ($> 2 \times 10^{24} $cm$^{-2}$) with a large covering factor, approaching 4$π$. The same procedure applied to the Type 1 sub-sample returns no evidence for a significant signal in about 140 Ms stacked data in any of the adopted bands, confirming their surprisingly elusive nature in the X-ray band obtained with previous stacking experiments. A brief comparison with the current observations and the implications for the evolution of AGN are discussed.

astro-ph.GA↗

arXiv2025

An Extremely-High Velocity Outflow in SMSS J2157-3602, the most luminous quasar in the first 1.3 Gyr

We report the discovery of an extremely high-velocity outflow (EHVO) in the most luminous ($L\rm_{Bol}$ $\sim$ 2.29 $\times$ 10$^{48}$ erg/s) QSO, SMSS J2157-3602, at z=4.692. Combined XSHOOTER and NIRES observations reveal that the EHVO reaches a maximum velocity of v$_\mathrm{max} \sim 0.13c$ and persists over rest-frame timescales of a few months to one year. SMSS J2157-3602 also exhibits one of the highest balnicity index discovered in an EHVO so far. In addition, the blueshifted CIV emission traces a high-velocity (v$\rm_{CIV}^{50}\sim$ 4660 km/s) outflow from the broad-line region. Thanks to an XMM-Newton observation, we also discover the X-ray weak nature of this QSO, which likely prevents the overionization of the innermost disk atmosphere and facilitates the efficient launch of the detected EHVO and BLR winds. The extraordinary luminosity of SMSS J2157-3602 and the extreme velocity of the EHVO make it a unique laboratory for testing AGN driven feedback under extreme conditions. Current uncertainties on the outflow's location and column density strengthen the case for dedicated follow-up, which will be essential to assess the full feedback potential of this remarkable quasar.

astro-ph.GA↗

arXiv2025

A big red dot at cosmic noon

We report the discovery of a little red dot (LRD), dubbed BiRD ('big red dot'), at $z=2.33$ in the field around the $z=6.3$ quasar SDSSJ1030+0524. Using NIRCam images, we identified it as a bright outlier in the $F200W-F356W$ color vs $F356W$ magnitude diagram of point sources in the field. The NIRCam/WFSS spectrum reveals the emission from HeI$λ10830$ and PaG line, both showing a narrow and a broad ($FWHM\gtrsim 2000\ \rm kms^{-1}$) component. The HeI line is affected by an absorption feature, tracing dense gas with HeI column density in the $2^3S$ level $N\sim 0.5-1.2\times 10^{14}\rm cm^{-2}$, depending on the location of the absorber, which is outflowing at the speed of $Δv \sim -830\ \rm kms^{-1}$. As observed in the majority of LRDs, BiRD does not show X-ray or radio emission. The BH mass and the bolometric luminosity, both inferred from the PaG broad component, amount to $M_{\rm BH}\sim 10^8\rm M_{\odot}$ and $L_{\rm bol}\sim 2.9\times 10^{45}\rm ergs^{-1}$, respectively. Intriguingly, BiRD presents strict analogies with other two LRDs spectroscopically confirmed at cosmic noon, GN-28074 ("Rosetta Stone") at $z=2.26$ and RUBIES-BLAGN-1 at $z=3.1$. The blueshifted HeI absorption detected in all three sources suggests that gas outflows may be common in LRDs. We derive a first estimate of the space density of LRDs at $z<3$ based on JWST data, as a function of $L_{\rm bol}$ and BH mass. The space density is only a factor of $\sim 2-3$ lower than that of UV-selected quasars with comparable $L_{\rm bol}$ and $z$, meaning that the contribution of LRDs to the broader AGN population is also relevant at cosmic noon. A similar trend is also observed in terms of BH masses. If, as suggested by recent theories, LRDs probe the very first and rapid growth of black hole seeds, our finding may suggest that the formation of black hole seeds remains efficient at least up to cosmic noon.

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arXiv2025

Unveiling faint X-ray AGN populations in the NewAthena era: Insights from cosmological simulations

Recent observations expanded our understanding of galaxy formation and evolution, yet key challenges persist in the X-ray regime, crucial for studying Active Galactic Nuclei (AGN). These limitations drive the development of next-generation observatories such as ESA's NewAthena. Now in phase B (preliminary design), the mission requires extensive testing to ensure compliance with its scientific goals, particularly given the uncertainties surrounding high redshift AGN. This work leverages the IllustrisTNG cosmological simulation to build an X-ray AGN mock catalogue and assess the performance of NewAthena's WFI. We created a Super Massive Black Hole (SMBH) light cone, spanning 10 deg2, with corrections to account for the limited resolution of the simulation and X-ray properties derived in post-processing. The resulting catalogue reveals a 5* overabundance of faint AGN compared to current X-ray constraints, an inconsistency potentially resolved by invoking a higher Compton-thick (CTK) fraction and intrinsic X-ray weakness, as suggested by recent JWST findings. An end-to-end survey simulation using SIXTE predicts 250000 AGN detections, including 20,000 at z > 3 and 35 in the Epoch of Reionization (z > 6); notably, only AGN with LX > 43.5 erg/s are detectable at z > 6. The analysis also forecasts a significant population of detectable CTK AGN, even beyond z > 4. These findings suggest X-ray observations will, for the first time, probe a significant AGN population in the EoR, offering new insights into SMBH growth. They also provide key input for refining NewAthena's mission design and optimizing its survey strategy.

astro-ph.GA↗

arXiv2025

Intervening nuclear obscuration changing the X-ray look of the $z\approx6$ QSO CFHQS J164121+375520

X-ray observations of the optically selected $z=6.025$ QSO CFHQS J164121+375520 (hereafter J1641) revealed that its flux dropped by a factor $\gtrsim7$ from 2018, when it was a bright and soft X-ray source, to 2021. Such a strong variability amplitude has not been observed before among $z>6$ QSOs, and the underlying physical mechanism was unclear. We carried out a new X-ray and rest-frame UV monitoring campaign of J1641 over 2022-2024. We detected J1641 with Chandra in the 2-7 keV band, while no significant emission is detected at softer X-ray energies, making J1641 an X-ray changing look QSO at $z>6$. Comparing with the 2018 epoch, the 0.5-2 keV flux dropped dramatically by a factor $>20$. We ascribe this behaviour to intervening, and still ongoing, obscuration by Compton-thick gas intercepting our line of sight between 2018 and 2021. The screening material could be an inner disk or a failed nuclear wind that increased their thickness. Another possibility is that we have witnessed an occultation event due to dust-free clouds located at sub-pc/pc scales, similar to those recently invoked to explain the remarkable X-ray weakness of AGN discovered by JWST. These interpretations are also consistent with the lack of strong variations of the QSO rest-frame UV lightcurve over the same period. Future monitoring of J1641 and the possible discovery of other X-ray changing look QSOs at $z>6$ will provide us with precious information about the physics of rapid supermassive black-hole growth at high redshift.

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arXiv2025

Unveiling the origin of XMM-Newton soft proton flares: I. Design and validation of a response matrix for proton spectral analysis

Low-energy (<300 keV) protons entering the field of view of XMM-Newton are observed in the form of a sudden increase in the background level, the so-called soft proton flares, affecting up to 40% of the mission observing time. In-flight XMM-Newton's observations of soft protons represent a unique laboratory to validate and improve our understanding of their interaction with the mirror, optical filters, and X-ray instruments. At the same time, such models would link the observed background flares to the primary proton population encountered by the telescope, converting XMM-Newton into a monitor for soft protons. We built a Geant4 simulation of XMM-Newton, including a verified mass model of the X-ray mirror, the focal plane assembly, and the EPIC MOS and pn-CCDs. We encoded the energy redistribution and proton transmission efficiency into a redistribution matrix file (RMF) and an auxiliary response file (ARF). For the validation, three averaged soft proton spectra, one for each filter configuration, were extracted from a collection of 13 years of MOS observations of the focused non X-ray background and analysed with Xspec. The best-fit model is in agreement with the power-law distribution predicted from independent measurements for the XMM-Newton orbit, spent mostly in the magnetosheath and nearby regions. For the first time we are able to link detected soft proton flares with the proton radiation environment in the Earth's magnetosphere, while proving the validity of the simulation chain in predicting the background of future missions. Benefiting from this work and contributions from the Athena instrument consortia, we also present the response files for the Athena mission and updated estimates for its focused charged background.

astro-ph.IM↗

arXiv2024

An X-ray Significantly Variable, Luminous, Type 2 Quasar at z = 2.99 with a Massive Host Galaxy

We present a comprehensive X-ray analysis and spectral energy distribution (SED) fitting of WISEA J171419.96+602724.6, an extremely luminous type 2 quasar at $z$ = 2.99. The source was suggested as a candidate Compton-thick (column density N$_{\rm H}>$1.5 $\times$ 10$^{24}$ cm$^{-2}$) quasar by a short XMM-Newton observation in 2011. We recently observed the source with deep NuSTAR and XMM-Newton exposures in 2021 and found that the source has a lower obscuration of N$_{\rm H}\sim$5 $\times$ 10$^{22}$ cm$^{-2}$ with an about four times lower flux. The two epochs of observations suggested that the source was significantly variable in X-ray obscuration, flux, and intrinsic luminosity at 2-3~$σ$ in less than 2.5 years (in the source rest frame). We performed SED fitting of this source using CIGALE thanks to its great availability of multiwavelength data (from hard X-rays to radio). The source is very luminous with a bolometric luminosity of $L_{\rm BOL}\sim$ 2.5 $\times$ 10$^{47}$ erg s$^{-1}$. Its host galaxy has a huge star formation rate (SFR) of $\sim$1280 Solar mass yr$^{-1}$ and a huge stellar mass of $\sim$1.1 $\times$ 10$^{12}$ Solar mass. The correlation between the SFR and stellar mass of this source is consistent with what was measured in the high-$z$ quasars. It is also consistent with what was measured in the main-sequence star-forming galaxies, suggesting that the presence of the active nucleus in our target does not enhance or suppress the SFR of its host galaxy. The source is an Infrared hyper-luminous, obscured galaxy with significant amount of hot dust in its torus and shares many similar properties with hot, dust obscured galaxies.

astro-ph.GA↗

arXiv2024

Investigating the interplay between the coronal properties and the hard X-ray variability of active galactic nuclei with NuSTAR

Active galactic nuclei (AGN) are extremely variable in the X-ray band down to very short timescales. However, the driver behind the X-ray variability is still poorly understood. Previous results suggest that the hot corona responsible for the primary Comptonized emission observed in AGN is expected to play an important role in driving the X-ray variability. In this work, we investigate the connection between the X-ray amplitude variability and the coronal physical parameters; namely, the temperature ($kT$) and optical depth ($τ$). We present the spectral and timing analysis of 46 {\it NuSTAR} observations corresponding to a sample of 20 AGN. For each source, we derived the coronal temperature and optical depth through X-ray spectroscopy and computed the normalized excess variance for different energy bands on a timescale of $10$ ks. We find a strong inverse correlation between $kT$ and $τ$, with correlation coefficient of $r<-0.9$ and negligible null probability. No clear dependence was found among the temperature and physical properties, such as the black hole mass or the Eddington ratio. We also see that the observed X-ray variability is not correlated with either the coronal temperature or optical depth under the thermal equilibrium assumption, whereas it is anticorrelated with the black hole mass. These results can be interpreted through a scenario where the observed X-ray variability could primarily be driven by variations in the coronal physical properties on a timescale of less than $10$~ks; whereas we assume thermal equilibrium on such timescales in this work, given the capability of the currently available hard X-ray telescopes. Alternatively, it is also possible that the X-ray variability is mostly driven by the absolute size of the corona, which depends on the supermassive black hole mass, rather than resulting from any of its physical properties.

astro-ph.HE↗

arXiv2024

Fast SMBH growth in the SPT2349--56 protocluster at $z=4.3$

Protoclusters at $z>2$ are gas-rich regions characterized by high star-formation activity. The same physical properties that enhance star formation in protoclusters are also thought to boost the growth of SMBHs. We aim to test this scenario by probing the AGN content of SPT2349-56, a massive, gas-rich, and highly star-forming protocluster core at $z=4.3$ discovered as an overdensity of DSFGs, via Chandra (200 ks) observations, and comparing the results with the field environment. We detected two protocluster members, corresponding to an AGN fraction among DSFGs of $\approx10\%$. This value is consistent with other protoclusters at $z=2-4$, but higher than the AGN incidence among DSFGs in the field environment. Both AGN are heavily obscured sources and hosted in star-forming galaxies with $\approx3\times10^{10}\,\mathrm{M_\odot}$ stellar masses. We estimate that the ISM in the host galaxies can contribute significantly to the nuclear obscuration. One of the two AGN is highly luminous ($L_X=2\times10^{45}\,\mathrm{erg\,s^{-1}}$) and Compton-thick ($N_H=2\times10^{24}\,\mathrm{cm^{-2}}$), and likely powered by a $M_{BH}>6\times10^8\,\mathrm{M_\odot}$ SMBH. Its high accretion rate suggests that it is in the phase of efficient growth required to explain the presence of extremely massive SMBHs in the centers of local galaxy clusters. Considering SPT2349-56 and DRC, a similar protocuster at $z=4$, we find that gas-rich protocluster cores at $z\approx4$ enhance the triggering of luminous (log$\frac{L_X}{\mathrm{erg\,s^{-1}}}=45-46$) AGN by 3-5 orders of magnitude with respect to the field environment. Our results indicate that gas-rich protoclusters at high redshift boost the growth of SMBHs, which will likely impact the subsequent evolution of the structures, and thus represent key science targets to obtain a complete understanding of the relation between environment and galaxy evolution.

astro-ph.GA↗