Nico Cappelluti

The detection of subsolar mass black holes is a milestone of modern astrophysics as it would open a window either onto new stellar physics or could potentially unveil the nature of dark matter as primordial black holes (PBHs). On 2025 November 12, the LIGO–Virgo–KAGRA (LVK) collaboration reported the compact binary merger candidate S251112cm, a system with no obvious electromagnetic counterpart, consistent with binary black hole merger with a chirp mass in the range 0.1–0.87 M _⊙ . The probability that at least one component has mass 99%. Inspired by this trigger, we tested if a population of PBHs formed at the quantum chromodynamics epoch with a broad mass function could account for a signal of this type. Our results, corresponding to a predicted event rate of 0.8 yr ⁻¹ as seen by LVK O3b, suggest that the observed merger rate of 0.2 3 − 0.218 + 0.86 yr − 1 ( 95 % C.L. ) if the trigger is confirmed as an astrophysical event would be compatible with such a model. Our predicted detection rate is also in agreement with current LVK expectations for stellar-mass binaries, remaining consistent with a scenario in which a nonnegligible fraction of the 3–200 M _⊙ mergers observed by LVK originate from PBHs. If confirmed, this detection would place a lower limit to the PBH abundance f _PBH > 0.04 for our adopted model.

Spitzer-based source-subtracted cosmic infrared background (CIB) fluctuations at arcminute-to-degree scales indicate the presence of new populations, whereas subarcminute power arises from known z ≲ 6 galaxies. We reconstruct the evolution of the near-IR CIB anisotropies on subarcminute scales by known galaxy populations. This method is based on, and significantly advanced over, the empirical reconstruction by Helgason et al. which is combined with the halo model connecting galaxies to their host dark matter halos. The modeled CIB fluctuations from known galaxies produce the majority of the observed small-scale signal down to statistical uncertainties of z . Our analysis spanning several Spitzer datasets allows us to narrow the estimated contributions of remaining known galaxies to the CIB anisotropies to be probed potentially from surveys by new and upcoming space missions such as Euclid, SPHEREx, and Roman. Of these, the Roman surveys have the best prospects for measuring the source-subtracted CIB and probing the nature of the underlying new populations at λ < 2 μ m, followed by Euclid’s surveys, while for SPHEREx the source-subtracted CIB signal from them appears significantly overwhelmed by the CIB from remaining known galaxies.

The James Webb Space Telescope North Ecliptic Pole (NEP) Time-Domain Field (TDF) has been monitored by Nuclear Spectroscopic Telescope Array (NuSTAR) and XMM-Newton with a regular cadence for 5 yr, starting in 2019. The survey has accumulated 3.5 Ms of NuSTAR exposure and 228 ks quasi-simultaneous XMM-Newton observations covering 0.31 deg ² . This paper presents the results from the most recent 2 years’ worth of 2 Ms NuSTAR and 166 ks XMM observations in NuSTAR cycles 8 and 9. These observations reached a 20% area flux of 2.20 × 10 ⁻¹⁴ erg cm ⁻² s ⁻¹ in the 8–24 keV band. Note that 75 NuSTAR sources and 274 XMM-Newton sources are detected at 99% reliability level. The log N –log S measured in cycles 8+9 are consistent with those measured in the previous cycle 5+6 NuSTAR NEP survey, but in a larger area (0.3 deg ² compared with 0.19 deg ² ). The slope of the cycles 8+9 8−24 keV log N –log S curve is flatter than other works ( α ₈₉ = 1.13 ± 0.46), but is consistent with the Euclidean value of α = 1.50. In addition, we found ∼36% of the NuSTAR sources to be heavily obscured ( N _H ≥ 10 ²³ cm ⁻² ). The Compton-thick ( N _H ≥ 10 ²⁴ cm ⁻² ) active galactic nuclei fraction is 9 − 8 + 18 % in the NEP-TDF, which is consistent with the measurements in previous surveys.

Identifying active galactic nuclei (AGNs) using only one wavelength region may miss AGNs with characteristics unfavorable for the identification method, which introduces bias in the sample. To better understand these selection effects, we compare the multiwavelength properties of 2584 X-ray- and IR-selected AGNs at z < 3 in the COSMOS field. The X-ray-selected sample consists of the 2219 AGNs with intrinsic 0.5–10 keV X-ray luminosity greater than 10 ⁴³ erg s ⁻¹ ; the 993 IR-selected AGNs are identified by their high-contrast, power-law IR colors using Spitzer/IRAC observations. We find that both selection methods miss a significant fraction of AGNs, as only 24.3% of AGNs (628 out of the total of 2584 AGNs) are recovered by both selection criteria. X-ray selection can capture the most diverse range of multiwavelength spectral emission features, while IRAC selection is biased against AGNs with a steeply decreasing power flux ( λF _λ ) between 1 and 6 μ m. For AGNs with X-ray detections, IRAC-selected sources are 2.5× more X-ray luminous than AGNs not identified by their IR colors. IRAC-selected AGNs without detectable X-rays are obscured, as they have a mean X-ray correction factor log ( L X , obs / L X , int ) = −1.4; 28.5%–42.2% of these AGNs are Compton-thick (according to estimated column densities). Only 1.4% of X-ray-selected AGNs are Compton-thick. The AGN selection technique used significantly impacts the overall characteristics of the resulting AGN sample.

The James Webb Space Telescope (JWST) North Ecliptic Pole (NEP) Time-Domain Field (TDF) has been monitored by NuSTAR and XMM-Newton with a regular cadence for five years starting in 2019. The survey has accumulated 3.5Ms of NuSTAR exposure and 228 ks quasi-simultaneous XMM-Newton observations covering 0.31 deg^2. This paper presents the results from the most recent two-years' 2Ms NuSTAR and 166 ks XMM observations in NuSTAR cycles 8 and 9. These observations reached a 20%-area flux of 2.20 x 10^-14 erg cm^-2 s^-1 in the 8-24 keV band. 75 NuSTAR sources and 274 XMM-Newton sources are detected at 99% reliability level. The logN-logS measured in cycles 8+9 are consistent with those measured in the previous cycle 5+6 NuSTAR NEP survey, but in a larger area (0.3 deg^2 compared with 0.19 deg^2). The slope of the cycles 8+9 8-24 keV logN-logS curve is flatter than other works (α89 = 1.13 +/- 0.46), but is consistent with the Euclidean value of α = 1.50. In addition, we found ~36% of the NuSTAR sources to be heavily obscured (NH >= 10^23 cm^-2). The Compton-thick (NH >= 10^24 cm^-2) (CT-) AGN fraction is 9+18-8% in the NEP-TDF, which is consistent with the measurements in previous surveys.

Galaxy clusters, the most massive, dark-matter-dominated, and most recently assembled structures in the Universe, are key tools for probing cosmology. However, uncertainties in scaling relations that connect cluster mass to observables like X-ray luminosity and temperature remain a significant challenge. In this paper, we present the results of an extensive investigation of 329 simulated clusters from IllustrisTNG300 cosmological simulations. Our analysis involves cross-correlating dark matter and the hot X-ray-emitting gas, considering both the 3D and 2D projected distributions to account for projection effects. We demonstrate that this approach is highly effective in evaluating the dynamical state of these systems and validating the often-utilized assumption of hydrostatic equilibrium, which is key for inferring cluster masses and constructing scaling relations. Our study revisits both the X-ray luminosity–mass and X-ray temperature–mass scaling relations, and demonstrates how the scatter in these relations correlates with the clusters’ dynamical state. We demonstrate that matter–gas coherence enables the identification of an optimal set of relaxed clusters, reducing scatter in scaling relations by up to 40%. This innovative approach, which integrates higher-dimensional insights into scaling relations, might offer a new path to further reduce uncertainties in determining cosmological parameters from galaxy clusters.

We leverage James Webb Space Telescope (JWST) data from the COSMOS-Web survey in order to provide updated measurements on the auto-power spectrum of the now resolved cosmic near-infrared background (CIB) and its coherence with the unresolved soft cosmic X-ray background (CXB) observed by Chandra at z > 6. Maps of the CIB in the F277W and F444W NIRCam filters are constructed with sources fainter than m _AB = 25 and cross-correlated with the CXB in the [0.5–2] keV band. We find that on scales between 1″ and 1000″ the CIB–CXB cross-power in both NIRCam filters is statistically significant, with signal-to-noise ratios (S/Ns) of 4.80 and 6.20, respectively, from redshifts 0 ≤ z ≤ 13. In our high-z (6 ≤ z ≤ 13) interval we find coherence in both filters, with S/Ns of 7.32 and 5.39, respectively. These results suggest that there are X-ray-emitting galaxies resolved by JWST, including star-forming galaxies and active galactic nuclei. We fit the large-scale biasing of the IR sources producing the CIB as a function of z with results consistent with prior measurements, and place constraints on the CXB flux and biasing at low and high z. The CXB flux measurements presented in this study suggest that approximately 94% of the [0.5–2] keV CXB is resolved, and this value is consistent within 2σ with the complete resolution of the [0.5–2] keV CXB.

The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015–2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14 000 deg² of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance.

The recent tension in the value of the cosmological parameter S 8 ≡ σ 8 ( Ω M / 0.3 ) 1 / 2 , which represents the amplitude of the matter density fluctuations of the Universe, has not been resolved. In this work, we present constraints on S ₈ with the X-ray angular power spectra of clusters and groups measured with the half-sky map from eROSITA All Sky Survey Data Release 1 (eRASS1). Thanks to the extensive sky coverage of eRASS1, it achieves unprecedented precision compared to previous power spectrum measurements. Using a well-calibrated, physical halo gas model that includes astrophysics of feedback and nonthermal pressure support, we obtain S 8 = 0.8 0 − 0.01 + 0.02 with 1σ uncertainty that is competitive against other cosmological probes. Our derived S ₈ value is smaller than the primary cosmic microwave background measurements from Planck, but still consistent to within 1σ. We also obtain constraints on the astrophysics of feedback, nonthermal pressure, equation of state in cluster cores, and gas boundaries in clusters and groups. We discuss how additional X-ray observations, and cosmological surveys in microwave and optical, will further improve the cosmological constraints with the angular power spectrum. Our work demonstrates that the angular power spectrum of clusters and groups is a promising probe of both cosmology and astrophysics.

We present a composite machine learning framework to estimate posterior probability distributions of bulge-to-total light ratio, half-light radius, and flux for active galactic nucleus (AGN) host galaxies within z < 1.4 and m < 23 in the Hyper Supreme-Cam (HSC) Wide survey. We divide the data into five redshift bins: low (0 < z < 0.25), mid (0.25 < z < 0.5), high (0.5 < z < 0.9), extra (0.9 < z < 1.1), and extreme (1.1 < z < 1.4), and train our models independently in each bin. We use PSFGAN to decompose the AGN point-source light from its host galaxy, and invoke the Galaxy Morphology Posterior Estimation Network (GaMPEN) to estimate morphological parameters of the recovered host galaxy. We first trained our models on simulated data, and then fine-tuned our algorithm via transfer learning using labeled real data. To create training labels for transfer learning, we used GALFIT to fit ∼20,000 real HSC galaxies in each redshift bin. We comprehensively examined that the predicted values from our final models agree well with the GALFIT values for the vast majority of cases. Our PSFGAN + GaMPEN framework runs at least three orders of magnitude faster than traditional light-profile fitting methods, and can be easily retrained for other morphological parameters or on other data sets with diverse ranges of resolutions, seeing conditions, and signal-to-noise ratios, making it an ideal tool for analyzing AGN host galaxies from large surveys coming soon from the Rubin-LSST, Euclid, and Roman telescopes.