arXiv subjects

Cristian Vignali

Publications and source records attributed to Cristian Vignali.

At least 19 recordsLinked to original sources

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.

astro-ph.HE↗

arXiv2026

WST instrument Exposure Time Calculator: full simulation of multi-mode spectrograph performance from source to detector

We present a comprehensive Exposure Time Calculator (ETC) developed for the Wide-field Spectroscopic Telescope (WST) concept. The WST, currently in its conceptual phase, is designed as a next-generation large spectroscopic survey facility featuring three complementary observing modes: an Integral Field Spectrograph (IFS) covering 370-930 nm at R of about 4800; a high-resolution Multi-Object Spectrograph (MOS-HR) with four bands at R of about 40000; and a low-resolution Multi-Object Spectrograph (MOS-LR) with four channels at R of about 3800-4900. The ETC simulates the complete photon-propagation path from astronomical source to detector, incorporating wavelength-dependent system throughput (telescope transmission, instrumental optics, detector quantum efficiency), accurate sky background via ESO SkyCalc integration, and a comprehensive noise treatment (photon noise, sky background, read-out noise, dark current). The computational core is implemented as the "pyetc_wst" Python library built on the MPDAF framework, supporting multiple target spectral energy distributions (stellar templates, blackbody, power-law, emission lines, and user-uploaded spectra with arbitrary redshift) and spatial morphologies (point sources and Sersic extended profiles). Four operational modes enable flexible exposure-time optimization. Full spectral outputs include wavelength-dependent signal-to-noise ratio (SNR), source and sky photon counts, noise decomposition by component, and simulated extracted spectra. An interactive web interface, together with a REST API and a command-line tool, complete the user experience and enable batch survey-design workflows.

astro-ph.IM↗

arXiv2026

A pilot sample of Planck-selected strongly lensed sub-mm galaxies: NOEMA observations and physical characterisation

The extreme brightness of high-$z$ strongly lensed galaxies detected by Planck surveys, thanks to their exceptionally large gravitational magnifications, offers a unique opportunity to investigate in extraordinary detail their structure and kinematics during their active star-formation phase. As a step in this direction, we present and analyse NOEMA imaging and spectroscopic data for four lensed high-z galaxy candidates. We performed continuum and line imaging of the sources at 2 and 3 mm bands down to $1''.2$ spatial resolution and 40 $\rm{km}\,{\rm s}^{-1}$ spectral resolution, reconstructed and fitted the line profiles, and produced moment maps of the line emission to investigate the spatial distribution and kinematics of the molecular gas. We also carried out the gravitational lens modelling for one of the sources. The continuum images showed multiple components for at least two of the sources, strongly supporting the strong lensing scenario. We detected with high S/N ratios two CO lines for all sources, at CO(3-2), CO(4-3) and CO(5-4) transitions; for one source, we also detected the [CI](1-0) line. We derived accurate spectroscopic redshifts $2.3 \lesssim z \lesssim 3.3$, with $1σ$ uncertainties $δz \approx 10^{-4}$ in redshift. All four sources lie well above the CO line luminosity-linewidth relation for unlensed galaxies, providing independent confirmation of their strongly lensed nature. Three sources exhibit broad (FWHM$\gtrsim 400\,{\rm km}\,{\rm s}^{-1}$), double-peaked line profiles and substantial velocity gradients, while the last one shows relatively narrow, single-peaked lines and no detectable velocity gradients, possibly indicating a nearly face-on geometry or intrinsically simple kinematics.

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.

astro-ph.GA↗

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.

astro-ph.GA↗

arXiv2026

Beyond the Dot: an LRD-like nucleus at the Heart of an IR-Bright Galaxy and its implications for high-redshift LRDs

Little Red Dots (LRDs) are compact, red sources discovered by JWST at high redshift ($z \gtrsim 4$), marked by distinctive 'V-shaped' spectral energy distributions (SEDs) and often interpreted as rapidly accreting Active Galactic Nuclei (AGNs). Their true nature remains unclear, however, and their evolutionary connection to their lower-redshift counterparts is still poorly constrained. Thus, we present WISEA J123635.56+621424.2, here dubbed {\it the Saguaro}, a $z=2.0145$ galaxy in GOODS-North, as a possible analog of high-redshift LRDs and a potential missing link in their evolutionary path toward lower-redshift systems. It features a compact LRD-like nucleus surrounded by a face-on spiral host. Its connection to LRDs includes that: (1) its nuclear spectrum shows a clear `V-shaped'' SED; and (2) when redshifted to $z=7$, surface-brightness dimming makes the host undetectable, thus mimicking an LRD. This suggests that high-redshift LRDs may be embedded in extended hosts. To test this, we stack rest-frame UV images of 99 photometrically selected LRDs, revealing faint, diffuse emission. Stacking in redshift bins reveals mild radial growth, consistent with the expected galaxy size evolution. A simple analytic model confirms that surface-brightness dimming alone can explain their compact appearance. Lastly, we show that {\it the Saguaro} is not unique by describing similar objects from the literature at $z\lesssim3.5$. Taken together, our results support a scenario in which LRDs may not be a distinct population, but could instead be the visible nuclei of galaxies undergoing a short-lived, perhaps AGN-dominated, evolutionary phase, with their compact, red appearance driven largely by observational biases.

astro-ph.GA↗

arXiv2026

Strong environmental AGN enhancement among DSFGs in z > 2 protoclusters

Galaxy protoclusters (PCs) at z > 2 are dense regions in which cold gas availability and elevated galaxy interaction rates trigger intense, often dust-obscured, star formation. These mechanisms are also expected to promote super-massive black hole (SMBH) growth, but this effect remains unclear, largely due to heterogeneous galaxy selections and active galactic nuclei (AGN) identification methods in previous studies. We quantitatively assess the impact of PC environment on SMBH growth by measuring the incidence of X-ray AGN among dusty star-forming galaxies (DSFGs) in PCs and in a homogeneously selected control field sample, and investigate the physical mechanisms driving any difference. We consider ALMA-detected DSFGs in sub-mm/mm continuum of seven PCs at 2 < z < 4.5, and construct a selection-matched control sample from the COSMOS survey. We statistically compare X-ray AGN incidence and host galaxy physical properties obtained through uniform spectral energy distribution fitting. We find a significant enhancement of X-ray AGN fraction in PCs by ~2.7x (Poisson significance p = 3e-4). Similar values are found in two redshift bins: ~2.7x at z = 2-3 (p = 0.003) and ~2.6x at z = 3-4.5 (p = 0.03). PC and field DSFG samples are well matched in stellar mass, star-formation rate, and dust mass, ruling out selection effects or systematically higher host masses as the driver. Our results provide quantitative evidence that the dense PC environment enhances AGN incidence and SMBH growth in DSFGs beyond what host galaxy properties alone predict, likely through increased gas availability and interaction-driven fueling. This work is a first step toward a homogeneous assessment of environmental effects on SMBH growth across cosmic time.

astro-ph.GA↗

arXiv2026

Enhanced activity in close dual-AGN systems in the local Universe

We present the study of an X-ray selected sample of active galactic nuclei (AGN) in pairs at projected spatial separations 1 <$ r_p$/kpc < 100 at z < 0.1, using XMM-Newton and Chandra data. The pair sample is derived from an initial pool of approximately 2,000 X-ray-selected AGN, and is composed of both AGN-AGN pairs (so called dual AGN) and AGN-galaxy pairs. From this selection, we find that approximately 10% of AGN reside in pairs, and about 4% are paired with another AGN. We performed a detailed X-ray and SDSS optical spectral analysis for AGN in duals and X-ray analysis for AGN in AGN-galaxy pairs, to characterise their absorption properties and investigate the possible triggering mechanisms. We then investigated how obscuration, luminosity, and Eddington ratio depend on projected separation $r_p$. Amongst all AGN in pairs, we found that ~55% are obscured (with hydrogen column density $N_H$ > $10^{22}$ cm$^{-2}$), amongst which ~6% are Compton-thick ($N_H$ > $10^{24}$ cm$^{-2}$). The fraction of absorbed AGN is significantly higher in late-stage mergers ($r_p$ < 30 kpc) compared to early-stage mergers ($r_p$ > 60 kpc). Amongst the AGN in pairs, we also observed an average excess of AGN pairs with respect to a control sample of inactive galaxies in pairs, and that such excess significantly increases with decreasing $r_p$ only for obscured AGN. Finally, in dual-AGN systems, both the bolometric luminosity and the Eddington ratio of the less massive black hole in the pair increase as the separation decreases. These findings suggest that mergers may have an important role in triggering AGN accretion and activity.

astro-ph.GA↗

arXiv2026

Milky-Way-like stars in a galaxy core 8 billion years ago revealed by gravitational lensing

The assembly of stellar-dominated cores in elliptical galaxies is key to understanding how cosmic structures evolved. Gravitational lensing offers unique insights into the nature of their stars. We report the discovery of the smallest known quadruply lensed quasar (radius ~0.2"), whose lensing galaxy at redshift 1.055 (5.5 billion years after the Big Bang) features a lensing mass of only ~2x10^10 M_sun. A Bayesian analysis, based on the system's exceptional properties and standard scaling relations, allowed us to sample the central galactic initial mass function with unmatched accuracy and in a previously uncharted regime in terms of mass and redshift. We found it consistent with the Milky Way one, while excluding bottom-heavy functions. This suggests that the core either grew slowly or underwent early disruptive events altering its stellar build-up, in contrast with the classical view that bulges form rapidly and remain unchanged by later interactions.

astro-ph.GA↗

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↗

arXiv2026

Constraining the synchrotron peak and estimating the VHE brightness of a sample of extreme high synchrotron peak blazars

We present the results of a multi-wavelength study of a population of X-ray bright ($\rm log(F_{0.2-12 \ keV})>-12.5$), non-$γ$-ray detected high and extreme high synchrotron peak (HSP, EHSP; $\rm log(ν_{\rm peak,\ Hz})>16$) BL Lacs to $i$) put stronger constraints on the synchrotron peak location and shape and $ii$) model their expected behaviour in the very high-energy band. First, we performed an X-ray spectral analysis, using XMM-Newton, Chandra, Swift-XRT, and eROSITA data, and fitting the spectra using both a power law and a log parabola model. Out of 78 sources in the initial sample, 17 were best described by a log parabola model, a result that supports a scenario where the synchrotron peak falls in the X-ray band. Among these 17 sources, we further selected the 10 objects dominated by the jet emission, with no significant contamination of the host galaxy. We performed a $γ$-ray analysis of \lat\ data for these objects, obtaining upper limits providing information on their flux in the 100 MeV - 300 GeV energy range. We then modelled the broadband SED of these objects with JetSeT using two models: one assuming a log parabola for the electron distribution and the other one with a broken power law electron distribution, using parameters consistent with those describing the emission of the prototypical EHSP 1ES 0229+200. We found the models to be generally consistent with the available multi-wavelength detections and upper limits. Furthermore, they confirmed that a subsample of sources could display relevant emission in the TeV energy range, even potentially reaching the threshold for detectability by the Cherenkov Telescope Array Observatory.

astro-ph.HE↗

arXiv2026

New Hard X-Ray and Multiwavelength Study of the PeVatron Candidate PWN G0.9+0.1 in the Galactic Center Region

We present a new X-ray study and multiwavelength spectral energy distribution (SED) modeling of the young pulsar wind nebula (PWN) powered by the energetic pulsar PSR J1747-2809, inside the composite supernova remnant (SNR) G0.9+0.1, located in the Galactic Center region. The source is detected by NuSTAR up to 30 keV with evidence for the synchrotron burnoff effect in the changing spatial morphology with increasing energy. The broadband 2-30 keV spectrum of PWN G0.9+0.1 is modeled by a single power law with photon index $Γ=2.11\pm0.07$. We combined the new X-ray data with the multiwavelength observations in radio, GeV, and TeV gamma rays and modeled the SED, applying a one-zone and a multi-zone leptonic model. The comparison of the models is successful, as we obtained physically compatible results in the two cases. Through the one-zone model, we constrain the age of the system to $\sim2.2$ kyr, as well as reproduce the observed PWN and SNR radio sizes. In both the one-zone and multi-zone leptonic models, the electron injection spectrum is well-described by a single power law with spectral index $p \sim 2.6$ and a maximum electron energy of $\sim2$ PeV, suggesting the source could be a leptonic PeVatron candidate. We estimate the average magnetic field to be $B_{\rm PWN} \sim 20\ μ$G. We also report the serendipitous NuSTAR detection of renewed X-ray activity from the very faint X-ray transient XMMU J174716.1-281048 and characterize its spectrum.

astro-ph.HE↗

arXiv2025

The link between galaxy merger, radio jet expansion and molecular outflow in the ULIRG IRAS 00183-7111

The ultraluminous infrared galaxy (ULIRG) IRAS 00183-7111 ($z=0.328$) is one of the three ULIRGs that are currently known to host an active galactic nucleus (AGN) with small-scale radio jets. We present a detailed study of the link between galaxy merger, AGN ignition, radio jet expansion and kpc-scale molecular outflow in IRAS 00183-7111, using high-resolution Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the $^{12}$CO(1-0) and $^{12}$CO(3-2) lines and very deep $i$-band VLT Survey Telescope (VST) imaging. The latter allows us to put constraints on the assembly history of the system, suggesting that it formed through a major merger between two gas-rich spirals, likely characterised by a prograde encounter and no older than $\approx2$~Gyr. The recent merger channelled about $(1.5\pm0.3)\times10^{10}$~M\textsubscript{$\odot$} of molecular gas in the central regions of the remnant, as traced by the CO detections. The spatial correlation between the CO distribution and the radio core suggests that this gas likely contributed to the ignition of the AGN and thus to the launch of the radio jets. Furthermore, by comparing the relative strength of the two CO transitions, we find extreme gas excitation (i.e.\,$T_{\rm ex}\gg50$~K) around the radio lobes, supporting the case for a jet-ISM interaction. A qualitative study of the CO kinematics also demonstrates that, despite the overall disturbed dynamical state with no clear signs of regular rotation, at least one non-rotational kinematic component can be identified and likely associated to an outflow with $v_{\rm out}\approx439$~km~s$^{-1}$ and $\dot{M_{\rm out}}\approx 609$~M$_{\odot}$~yr$^{-1}$.

astro-ph.GA↗

arXiv2025

Black hole merger rates for LISA and LGWA from semi-analytical modelling of light seeds

With the upcoming space- and Moon-based gravitational-wave detectors, LISA and LGWA respectively, a new era of GW astronomy will begin with the possibility of detections of the mergers of intermediate-mass black holes (IMBHs) and supermassive black holes (SMBHs). We generate populations of synthetic black hole (BH) binaries with masses ranging from the intermediate ($10^3-10^5 M_\odot$) to the supermassive regime ($>10^5 M_\odot$), formed from the dynamical processes of merging halos and their residing galaxies, assuming that each galaxy is initially seeded with a single black hole at its centre. The aim is to estimate the rate of these BH mergers which could be detected by LISA and LGWA. Using PINOCCHIO cosmological simulation and a semi-analytical model based on GAEA, we construct a population of merging BHs by implementing a "light" seeding scheme and calculating the merging timescales using the Chandrasekhar prescription. We provide upper and lower limits of dynamical friction timescale by varying the mass of the infalling object to create "pessimistic" and "optimistic" merger rates respectively. We find that for our synthetic population of MBHs, both LGWA and LISA are able to detect more than $15$ binary IMBH mergers per year in the optimistic case, while in the pessimistic case less than $\sim5$ detections would be possible considering the entire lifetime of the detectors. For SMBHs, the rates are slightly lower in both cases. Most mergers below $z\approx4$ are detected in the optimistic case, although mergers beyond $z=8$ are also detectable at a lower rate. We find that LGWA is better suited for high-SNR IMBH detections at higher redshift, while LISA is more sensitive to massive SMBHs. Joint observations will probe the full BH mass spectrum and constrain BH formation and seeding models.

astro-ph.CO↗

arXiv2025

The Faintest, Extremely Variable X-ray Tidal Disruption Event from a Supermassive Black Hole Binary?

Tidal disruption events (TDEs), which occur when stars enter the tidal radii of supermassive black holes (SMBHs) and are subsequently torn apart by their tidal forces, represent intriguing phenomena that stimulate growing research interest and pose an increasing number of puzzles in the era of time-domain astronomy. Here we report an unusual X-ray transient, XID 935, discovered in the 7 Ms Chandra Deep Field-South, the deepest X-ray survey ever. XID 935 experienced an overall X-ray dimming by a factor of more than 40 between 1999 and 2016. Not monotonically decreasing during this period, its X-ray luminosity increased by a factor $> 27$ within 2 months, from $L_{\rm 0.5-7\ keV}<10^{40.87}$ erg s$^{-1}$ (10 October 2014 -- 4 January 2015) to $L_{\rm 0.5-7\ keV}=10^{42.31\pm 0.20}$ erg s$^{-1}$ (16 March 2015). The X-ray position of XID 935 is located at the center of its host galaxy with a spectroscopic redshift of 0.251, whose optical spectra do not display emission characteristics associated with an active galactic nucleus. The peak 0.5--2.0 keV flux is the faintest among all the X-ray-selected TDE candidates to date. Thanks to a total exposure of $\sim 9.5$ Ms in the X-ray bands, we manage to secure relatively well-sampled, 20-year-long X-ray light curves of this deepest X-ray-selected TDE candidate. We find that a partial TDE model could not explain the main declining trend. An SMBH binary TDE model is in acceptable accordance with the light curves of XID 935; however, it fails to match short-timescale fluctuations exactly. Therefore, the exceptional observational features of XID 935 provide a key benchmark for refining quantitative TDE models and simulations.

astro-ph.HE↗

arXiv2025

Tracing AGN-Galaxy Co-Evolution with UV Line-Selected Obscured AGN

Understanding black hole-galaxy co-evolution and the role of AGN feedback requires complete AGN samples, including heavily obscured systems. In this work, we present the first UV line-selected ([Nev]3426 and CIV1549) sample of obscured AGN with full X-ray-to-radio coverage, assembled by combining data from the Chandra COSMOS Legacy survey, the COSMOS2020 catalogue, IR photometry from XID+, and radio observations from the VLA and MIGHTEE surveys. Using CIGALE to perform spectral energy distribution (SED) fitting, we analyse 184 obscured AGN at 0.6 < z < 1.2 and 1.5 < z < 3.1, enabling detailed measurements of AGN and host galaxy properties, and direct comparison with SIMBA hydrodynamical simulations. We find that X-ray and radio data are essential for accurate SED fits, with the radio band proving critical when X-ray detections are missing or in cases of poor IR coverage. Comparisons with matched non-active galaxies and simulations suggest that the [NeV]-selected sources are in a pre-quenching stage, while the CIV-selected ones are likely quenched by AGN activity. Our results indicate that [NeV] and CIV selections target galaxies in a transient phase of their co-evolution, characterised by intense, obscured accretion, and pave the way for future extensions with upcoming large area high-z spectroscopic surveys.

astro-ph.GA↗

arXiv2025

Narrow line AGN selection in CEERS: spectroscopic selection, physical properties, X-ray and radio analysis

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 4.5 BLAGNs. We found that most of the high-z NLAGN were selected using the recently proposed AGN diagnostic diagrams based on the [Oiii] $λ$4363 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 ~1.5dex 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.

astro-ph.GA↗

arXiv2025

The Dual Nature of GHZ9: Coexisting Active Galactic Nuclei and Star Formation Activity in a Remote X-ray Source at z = 10.145

We present James Webb Space Telescope (JWST)/NIRSpec PRISM spectroscopic characterization of GHZ9 at z= 10.145 $\pm$ 0.010, currently the most distant source detected by the Chandra X-ray Observatory. The spectrum reveals several UV high-ionization lines, including CII, SiIV, NIV], CIV, HeII, OIII], NIII], and CIII]. The prominent rest-frame equivalent widths (EW(CIV)$\simeq$65A, EW(OIII])$\simeq$28A, EW(CIII])$\simeq$48A) show the presence of a hard active galactic nucleus (AGN) radiation field, while line ratio diagnostics are consistent with either AGN or star formation as the dominant ionizing source. GHZ9 is nitrogen-enriched (6--9.5 (N/O)$_{\odot}$), carbon-poor (0.2--0.65 (C/O)$_{\odot}$), metal-poor (Z = 0.01--0.1 Z$_{\odot}$), and compact ($<$ 106 pc), similarly to GN-z11, GHZ2, and recently discovered N-enhanced high redshift objects. We exploited the newly available JWST/NIRSpec and NIRCam data set to perform an independent analysis of the Chandra data confirming that GHZ9 is the most likely JWST source associated with X-ray emission at 0.5-7 keV. Assuming a spectral index $Γ$ = 2.3 (1.8), we estimate a black hole (BH) mass of 1.60 $\pm$ 0.31 (0.48 $\pm$ 0.09) $\times$ 10$^8$M$_{\odot}$, which is consistent either with Eddington-accretion onto heavy ($\geq$ 10$^6$ M$_{\odot}$) BH seeds formed at z=18, or super-Eddington accretion onto a light seed of $\sim$ 10$^2-10^4$ M$_{\odot}$ at z = 25. The corresponding BH-to-stellar mass ratio M$_{BH}$/M$_{star}$= 0.33$\pm$0.22 (0.10$\pm$0.07), with a stringent limit $>$0.02, implies an accelerated growth of the BH mass with respect to the stellar mass. GHZ9 is the ideal target to constrain the early phases of AGN-galaxy coevolution with future multi-frequency observations.

astro-ph.GA↗