The awe-inspiring distances of the cosmos are hard to visualise, so how can we be certain we are measuring them correctly? Chanda Prescod-Weinstein explains
Double black hole mergers in nuclear star clusters: eccentricities, spins, masses, and the growth of massive seeds
We investigate the formation of intermediate-mass black holes (IMBHs) through hierarchical mergers of stellar-origin black holes (BHs), as well as BH mergers formed dynamically in nuclear star clusters. Using a semi-analytical approach that incorporates probabilistic, mass-function–dependent double-BH (DBH) pairing, binary–single encounters, and a mass-ratio–dependent prescription for energy dissipation in hardening binaries, we find that IMB Hs with masses of order 10²–10⁴ M⊙ can be formed solely through hierarchical mergers on timescales of a few hundred Myr to a few Gyr. Clusters with escape velocities ≳ 400 km s⁻¹ inevitably form high-mass IMB Hs. The spin distribution of IMB Hs with masses ≳ 10³ M⊙ is strongly clustered at χ ≈ 0.15, while for lower masses it peaks at χ ≈ 0.7. Eccentric mergers are more frequent for equal-mass binaries containing first- and second-generation BHs. Metal-rich, young, dense clusters can produce up to 20 of their DBH mergers with eccentricity ≥ 0.1 at 10 Hz, and ~ 2–9 of all in-cluster mergers form at > 10 Hz. Nuclear star clusters are therefore promising environments for the formation of highly eccentric DBH mergers, detectable with current gravitational-wave detectors. Clusters of extreme mass (∼ 10⁸ M⊙) and density (∼ 10⁸ M⊙ pc⁻³) can have about half of their DBH mergers with primary masses ≥ 100 M⊙. The fraction of in-cluster mergers increases rapidly with increasing escape velocity, approaching unity for Vesc ≳ 200 km s⁻¹. The cosmological DBH merger rate from nuclear clusters varies from ≲ 0.01 to 1 Gpc⁻³ yr⁻¹, where the large uncertainties stem from cluster initial conditions, number-density distributions, and the redshift evolution of nucleated galaxies.
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arXiv:2405.05772v3 Announce Type: replace
Abstract: We report the detection of continuum excess in the rest-frame UV between 3000 {\AA} and 3550 {\AA} in the JWST/NIRSpec spectrum of GN-z11, a luminous galaxy $z=10.603$. The shape of the continuum excess resembles a Balmer continuum but has a break around 3546 {\AA}. The fitting result of this excess depends on the assumed origin of the continuum. If the continuum of GN-z11 is dominated by a stellar population with a small Balmer break, the apparent blueshift of the Balmer continuum is not significant and the best-fit Balmer continuum model indicates a temperature of $T_e = 1.78^{+0.25}_{-0.21}\times 10^4$ K. In contrast, if the continuum is dominated by AGN emission, a nebular continuum model cannot fit the spectrum properly. The absence of the Balmer jump indicates an electron temperature of $\sim 3\times 10^4$ K, significantly higher than the temperature of $T_{e}({\rm O^{2+}}) = 1.36\pm 0.13\times 10^{4}$ K inferred from [OIII]$\lambda 4363$ and [OIII]$\lambda 5007$. The temperature difference can result from mixing of different ionized regions: the Balmer emission mainly arises from dense and hot clouds in the Broad Line Region, whereas the forbidden lines originate from less dense and colder gas. An alternative explanation for the observed continuum excess is the FeII emission, which shows a characteristic jump blueward of the Balmer limit as previously seen in the spectra of many lower-redshift quasars. Through comparisons with Cloudy models, we show an Fe abundance above $\sim 1/3$ solar is likely needed, which could be achieved via enrichment from Type-Ia supernovae, hypernovae, or pair-instability supernovae.
Optimizing Data Delivery and Scalable HI Profile Classification for the SKA Era: Infrastructure and Science Challenges at the Spanish SRC
This talk presents ongoing work at the Spanish SKA Regional Centre (esSRC) in the context of the SRC Net 0.1. The first part focuses on the development of efficient data delivery techniques from the distributed Rucio-based storage system to the SRC infrastructure and, ultimately, to user workspaces. Several approaches have been evaluated to support science-ready access, yet current solutions often involve unnecessary data duplication in user areas, resulting in increased usage of storage and computational resources. To address this, we have prototyped mechanisms based on file linking, caching, and data reuse, enabling more efficient access paths for users. While these methods show promising improvements in terms of performance and resource usage, challenges remain, particularly in terms of orchestration, scalability, and compatibility with existing workload managers. The second part presents advances in the automated classification of neutral hydrogen (HI) profiles using machine learning methods, building on previous work [Parra et al., 2024, arXiv:2501.11657]. We outline a roadmap for extending these techniques to handle the data volumes expected from the SKA Observatory. This includes developing scalable pipelines capable of ingesting and processing large spectral datasets in a reproducible and efficient manner, and adapting the classification models to cope with the diversity and complexity of the SKA data products.
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Nature, Published online: 02 July 2025; doi:10.1038/d41586-025-01979-z
The James Webb Space Telescope has detected molecular hydrogen in a nearby galaxy that has a very low proportion of metals. This implies that considerable quantities of molecular gas can form at low metallicities, and provides insight into similarly metal-poor galaxies in the early Universe.
arXiv:2507.00351v1 Announce Type: new
Abstract: We present Dark from Light (DfL) - a novel method to infer the dark sector in wide-field galaxy surveys, leveraging a machine learning approach trained on contemporary cosmological simulations. The aim of this algorithm is to provide a fast, straightforward, and accurate route to estimating dark matter halo masses and group membership in wide-field spectroscopic galaxy surveys. This approach requires a highly limited number of input parameters and yields full probability distribution functions for the output halo masses. To achieve this, we train a series of Random Forest (RF) regression models on the IllustrisTNG and EAGLE simulations at z=0-3, which provide model-dependent mappings from luminous tracers to dark matter halo properties. We incorporate the individual regression models into a virial group-finding algorithm (DfL), which outputs halo properties for observational-like input data. We test the method at z=0-2 for both the EAGLE and IllustrisTNG models, as well as in a cross-validation mode. We demonstrate that known halo masses can be recovered with a mean systematic bias of $\langle b \rangle = \pm 0.10\,$dex (resulting from simulation choice), a mean statistical uncertainty of $\langle \sigma \rangle = 0.12 \,$dex across epochs, and a central - (core) satellite classification accuracy of 96%. We establish that this approach yields superior halo mass recovery to standard abundance matching applied to groups identified through a friends-of-friends algorithm. Additionally, we compare the outputs of DfL to observational constraints on the $M_* - M_{\rm Halo}$ relation from strong gravitational lensing at $z \sim 0$, demonstrating the promise of this novel approach. Finally, we systematically quantify how DfL performs on observational-like input data with varying stellar mass uncertainty and spectroscopic incompleteness, enabling robust error calibration.
Double black hole mergers in nuclear star clusters: eccentricities, spins, masses, and the growth of massive seeds
We investigate the formation of intermediate-mass black holes (IMBHs) through hierarchical mergers of stellar-origin black holes (BHs), as well as BH mergers formed dynamically in nuclear star clusters. Using a semi-analytical approach that incorporates probabilistic, mass-function–dependent double-BH (DBH) pairing, binary–single encounters, and a mass-ratio–dependent prescription for energy dissipation in hardening binaries, we find that IMB Hs with masses of order 10²–10⁴ M⊙ can be formed solely through hierarchical mergers on timescales of a few hundred Myr to a few Gyr. Clusters with escape velocities ≳ 400 km s⁻¹ inevitably form high-mass IMB Hs. The spin distribution of IMB Hs with masses ≳ 10³ M⊙ is strongly clustered at χ ≈ 0.15, while for lower masses it peaks at χ ≈ 0.7. Eccentric mergers are more frequent for equal-mass binaries containing first- and second-generation BHs. Metal-rich, young, dense clusters can produce up to 20 of their DBH mergers with eccentricity ≥ 0.1 at 10 Hz, and ~ 2–9 of all in-cluster mergers form at > 10 Hz. Nuclear star clusters are therefore promising environments for the formation of highly eccentric DBH mergers, detectable with current gravitational-wave detectors. Clusters of extreme mass (∼ 10⁸ M⊙) and density (∼ 10⁸ M⊙ pc⁻³) can have about half of their DBH mergers with primary masses ≥ 100 M⊙. The fraction of in-cluster mergers increases rapidly with increasing escape velocity, approaching unity for Vesc ≳ 200 km s⁻¹. The cosmological DBH merger rate from nuclear clusters varies from ≲ 0.01 to 1 Gpc⁻³ yr⁻¹, where the large uncertainties stem from cluster initial conditions, number-density distributions, and the redshift evolution of nucleated galaxies.
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arXiv:2506.22999v1 Announce Type: new
Abstract: The recent measurement of baryonic acoustic oscillations (BAO) by the Dark Energy Spectroscopic Instrument (DESI) reveals a mild tension with observations of the cosmic microwave background (CMB) within the standard $\Lambda$CDM cosmological model. This discrepancy leads to a preference for a total neutrino mass that is lower than the minimum value inferred from neutrino oscillation experiments. Alternatively, this tension can be eased within $\Lambda$CDM by assuming a higher optical depth ($\tau \simeq 0.09$), but such a value conflicts with large-scale CMB polarization data. We point out that cosmic birefringence, as suggested by recent Planck reanalyses, resolves this discrepancy if the birefringence angle varies significantly during reionization. Specifically, we consider the fact that the measured cosmic birefringence angle $\beta_0=0.34\pm0.09\,(1\,\sigma)\,$deg has the phase ambiguity, i.e., the measured rotation angle is described by $\beta=\beta_0+180n\,$deg ($n\in \mathbb{Z}$). We show that cosmic birefringence induced by axion-like particles with nonzero $n$ suppresses the reionization bump, allowing a higher $\tau$ consistent with data. We provide a viable parameter space where the birefringence effect simultaneously accounts for the low-$\ell$ polarization spectra, the Planck $EB$ correlations, and the elevated value of $\tau$, suggesting a key role for cosmic birefringence in current cosmological tensions.
arXiv:2401.10328v2 Announce Type: replace
Abstract: The spectra of high-redshift ($z\gtrsim 6$) quasars contain valuable information on the progression of the Epoch of Reionization (EoR). At redshifts $z<6$, the observed Lyman-series forest shows that the intergalactic medium (IGM) is nearly ionized, while at $z>7$ the observed quasar damping wings indicate high neutral gas fractions. However, there remains a gap in neutral gas fraction constraints at $6\lesssim z \lesssim 7$ where the Lyman series forest becomes saturated but damping wings have yet to fully emerge. In this work, we use a sample of 18 quasar spectra at redshifts $6.0
arXiv:2506.22147v1 Announce Type: new
Abstract: JWST has revealed a large population of active galactic nuclei (AGN) in the distant universe, which are challenging our understanding of early massive black hole seeding and growth. We expand the exploration of this population to lower luminosities by stacking $\sim 600$ NIRSpec grating spectra from the JWST Advanced Deep Extragalactic Survey (JADES) at $3
arXiv:2410.14404v3 Announce Type: replace
Abstract: According to CMB measurements, baryonic matter constitutes about $5\%$ of the mass-energy density of the universe. A significant population of these baryons, for a long time referred to as `missing', resides in a low density, warm-hot intergalactic medium (WHIM) outside galaxy clusters, tracing the ``cosmic web'', a network of large scale dark matter filaments. Various studies have detected this inter-cluster gas, both by stacking and by observing individual filaments in compact, massive systems. In this paper, we study short filaments (< 10 Mpc) connecting massive clusters ($M_{500} \approx 3\times 10^{14} M_{\odot}$) detected by the Atacama Cosmology Telescope (ACT) using the scattering of CMB light off the ionised gas, a phenomenon known as the thermal Sunyaev-Zeldovich (tSZ) effect. The first part of this work is a search for suitable candidates for high resolution follow-up tSZ observations. We identify four cluster pairs with an intercluster signal above the noise floor (S/N $>$ 2), including two with a tentative $>2\sigma$ statistical significance for an intercluster bridge from the ACT data alone. In the second part of this work, starting from the same cluster sample, we directly stack on ${\sim}100$ cluster pairs and observe an excess SZ signal between the stacked clusters of $y=(7.2^{+2.3}_{-2.5})\times 10^{-7}$ with a significance of $3.3\sigma$. It is the first tSZ measurement of hot gas between clusters in this range of masses at moderate redshift ($\langle z\rangle\approx 0.5$). We compare this to the signal from simulated cluster pairs with similar redshifts and separations in the THE300 and MAGNETICUM Pathfinder cosmological simulations and find broad consistency. Additionally, we show that our measurement is consistent with scaling relations between filament parameters and mass of the embedded halos identified in simulations.
arXiv:2503.02927v2 Announce Type: replace
Abstract: We investigate the impact of ionizing external ultraviolet (UV) radiation on low-mass haloes ($M_{h}<10^{10}M_\odot$) at high redshift using $1140M_\odot$ baryonic resolution zoom-in simulations of seven regions from the THESAN-ZOOM project. We compare three simulation sets that differ in the treatment of external UV radiation: one employing a uniform UV background initiated at z=10.6 in addition to radiation transport for local sources, another with the same background starting at z=5.5, and the default configuration in which the large-scale radiation field from the parent THESAN-1 simulation box acts as a boundary condition. The multi-phase interstellar medium (ISM) model, combined with its high mass resolution, allows us to resolve all star-forming haloes and capture the back-reaction of ionizing radiation on galaxy properties during the epoch of reionization. When present, external UV radiation efficiently unbinds gas in haloes with masses below $10^9M_\odot$ and suppresses subsequent star formation. As a result, in simulations with early reionization, minihaloes fail to form stars from pristine gas, leading to reduced metal enrichment of gas later accreted by more massive haloes. Consequently, haloes with masses below $10^{10}M_\odot$ at all simulated epochs (z>3) exhibit lower metallicities and altered metallicity distributions. The more accurate and realistic shielding from external UV radiation, achieved through self-consistent radiative transfer, permits the existence of a cold but low-density gas phase down to z=3. These findings highlight the importance of capturing a patchy reionization history in high-resolution simulations targeting high-redshift galaxy formation. We conclude that at minimum, a semi-numerical model that incorporates spatially inhomogeneous reionization and a non-uniform metallicity floor is necessary to accurately emulate metal enrichment in minihaloes.
arXiv:2506.20824v1 Announce Type: new
Abstract: We present constraints on isotropic cosmic birefringence induced by axion-like particles (ALPs), derived from the analysis of cosmic microwave background (CMB) polarization measurements obtained with the high-frequency channels of Planck. Recent measurements report a hint of isotropic cosmic birefringence, though its origin remains uncertain. The detailed dynamics of ALPs can leave characteristic imprints on the shape of the $EB$ angular power spectrum, which can be exploited to constrain specific models of cosmic birefringence. We first construct a multi-frequency likelihood that incorporates an intrinsic nonzero $EB$ power spectrum. We also show that the likelihood used in previous studies can be further simplified without loss of generality. Using this framework, we simultaneously constrain the ALP model parameters, the instrumental miscalibration angle, and the amplitudes of the $EB$ power spectrum of a Galactic dust foreground model. We find that, if ALPs are responsible for the observed cosmic birefringence, ALP masses at $\log_{10}m_{\phi}[{\rm eV}]\simeq-27.8$, $-27.5$, $-27.3$, $-27.2$, $-27.1$, as well as $\log_{10}m_{\phi}[{\rm eV}]\in[-27.0,-26.5]$, are excluded at more than $2\,\sigma$ statistical significance.
The Most Ambitious Radio Astronomy Endeavour of the 21st Century? Science, Technology and Engineering Dialogues in a Large-scale Project
The presentation will open with some reflections on the early part of the Square Kilometre Array (SKA) project, where questions asked about engineering realities constraining science aspirations were raised. Early encounters between Scientists and Engineers considered Radio Frequency Interference (RFI) as one of the constraints. Some formative developments of this specific Radio Astronomy (RA) project, with a focus on the XDM , KAT7 and then MeerKAT in South Africa, will be introduced and related to unexpected RFI . The picture will then be widened to unpack an understanding of RFI and ElectroMagnetic Compatibility (EMC) for RA and science projects more generally. Two European examples will be considered. A short diversion into the language that EMC engineers use in RFI and what RA presents as uv-plane data will be taken.
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Title TBC
The presentation will open with some reflections on the early part of the Square Kilometre Array (SKA) project, where questions asked about engineering realities constraining science aspirations were raised. Early encounters between Scientists and Engineers considered Radio Frequency Interference (RFI) as one of the constraints. Some formative developments of this specific Radio Astronomy (RA) project, with a focus on the XDM , KAT7 and then MeerKAT in South Africa, will be introduced and related to unexpected RFI . The picture will then be widened to unpack an understanding of RFI and ElectroMagnetic Compatibility (EMC) for RA and science projects more generally. Two European examples will be considered. A short diversion into the language that EMC engineers use in RFI and what RA presents as uv-plane data will be taken.
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arXiv:2506.20042v1 Announce Type: new
Abstract: The reliable detection of the global 21-cm signal, a key tracer of Cosmic Dawn and the Epoch of Reionization, requires meticulous data modelling and robust statistical frameworks for model validation and comparison. In Paper I of this series, we presented the Beam-Factor-based Chromaticity Correction (BFCC) model for spectrometer data processed using BFCC to suppress instrumentally induced spectral structure. We demonstrated that the BFCC model, with complexity calibrated by Bayes factor-based model comparison (BFBMC), enables unbiased recovery of a 21-cm signal consistent with the one reported by EDGES from simulated data. Here, we extend the evaluation of the BFCC model to lower amplitude 21-cm signal scenarios where deriving reliable conclusions about a model's capacity to recover unbiased 21-cm signal estimates using BFBMC is more challenging. Using realistic simulations of chromaticity-corrected EDGES-low spectrometer data, we evaluate three signal amplitude regimes -- null, moderate, and high. We then conduct a Bayesian comparison between the BFCC model and three alternative models previously applied to 21-cm signal estimation from EDGES data. To mitigate biases introduced by systematics in the 21-cm signal model fit, we incorporate the Bayesian Null-Test-Evidence-Ratio (BaNTER) validation framework and implement a Bayesian inference workflow based on posterior odds of the validated models. We demonstrate that, unlike BFBMC alone, this approach consistently recovers 21-cm signal estimates that align with the true signal across all amplitude regimes, advancing robust global 21-cm signal detection methodologies.
arXiv:2506.20667v1 Announce Type: new
Abstract: Noise maps from CMB experiments are generally statistically anisotropic, due to scanning strategies, atmospheric conditions, or instrumental effects. Any mis-modeling of this complex noise can bias the reconstruction of the lensing potential and the measurement of the lensing power spectrum from the observed CMB maps. We introduce a new CMB lensing estimator based on the maximum a posteriori (MAP) reconstruction that is minimally sensitive to these instrumental noise biases. By modifying the likelihood to rely exclusively on correlations between CMB map splits with independent noise realizations, we minimize auto-correlations that contribute to biases. In the regime of many independent splits, this maximum closely approximates the optimal MAP reconstruction of the lensing potential. In simulations, we demonstrate that this method is able to determine lensing observables that are immune to any noise mis-modeling with a negligible cost in signal-to-noise ratio. Our estimator enables unbiased and nearly optimal lensing reconstruction for next-generation CMB surveys.
