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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.

• Speaker: Prof. Howard Reader
• Tuesday 01 July 2025, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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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.

arXiv:2503.14452v2 Announce Type: replace Abstract: We present power spectra of the cosmic microwave background (CMB) anisotropy in temperature and polarization, measured from the Data Release 6 maps made from Atacama Cosmology Telescope (ACT) data. These cover 19,000 deg$^2$ of sky in bands centered at 98, 150 and 220 GHz, with white noise levels three times lower than Planck in polarization. We find that the ACT angular power spectra estimated over 10,000 deg$^2$, and measured to arcminute scales in TT, TE and EE, are well fit by the sum of CMB and foregrounds, where the CMB spectra are described by the $\Lambda$CDM model. Combining ACT with larger-scale Planck data, the joint P-ACT dataset provides tight limits on the ingredients, expansion rate, and initial conditions of the universe. We find similar constraining power, and consistent results, from either the Planck power spectra or from ACT combined with WMAP data, as well as from either temperature or polarization in the joint P-ACT dataset. When combined with CMB lensing from ACT and Planck, and baryon acoustic oscillation data from DESI DR1, we measure a baryon density of $\Omega_b h^2=0.0226\pm0.0001$, a cold dark matter density of $\Omega_c h^2=0.118\pm0.001$, a Hubble constant of $H_0=68.22\pm0.36$ km/s/Mpc, a spectral index of $n_s=0.974\pm0.003$, and an amplitude of density fluctuations of $\sigma_8=0.813\pm0.005$. Including the DESI DR2 data tightens the Hubble constant to $H_0=68.43\pm0.27$ km/s/Mpc; $\Lambda$CDM parameters agree between the P-ACT and DESI DR2 data at the $1.6\sigma$ level. We find no evidence for excess lensing in the power spectrum, and no departure from spatial flatness. The contribution from Sunyaev-Zel'dovich (SZ) anisotropy is detected at high significance; we find evidence for a tilt with suppressed small-scale power compared to our baseline SZ template spectrum, consistent with hydrodynamical simulations with feedback.

arXiv:2503.14454v2 Announce Type: replace Abstract: We use new cosmic microwave background (CMB) primary temperature and polarization anisotropy measurements from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) to test foundational assumptions of the standard cosmological model and set constraints on extensions to it. We derive constraints from the ACT DR6 power spectra alone, as well as in combination with legacy data from Planck. To break geometric degeneracies, we include ACT and Planck CMB lensing data and baryon acoustic oscillation data from DESI Year-1, and further add supernovae measurements from Pantheon+ for models that affect the late-time expansion history. We verify the near-scale-invariance (running of the spectral index $d n_s/d\ln k = 0.0062 \pm 0.0052$) and adiabaticity of the primordial perturbations. Neutrino properties are consistent with Standard Model predictions: we find no evidence for new light, relativistic species that are free-streaming ($N_{\rm eff} = 2.86 \pm 0.13$, which combined with external BBN data becomes $N_{\rm eff} = 2.89 \pm 0.11$), for non-zero neutrino masses ($\sum m_\nu < 0.082$ eV at 95% CL), or for neutrino self-interactions. We also find no evidence for self-interacting dark radiation ($N_{\rm idr} < 0.134$), early-universe variation of fundamental constants, early dark energy, primordial magnetic fields, or modified recombination. Our data are consistent with standard BBN, the FIRAS-inferred CMB temperature, a dark matter component that is collisionless and with only a small fraction allowed as axion-like particles, a cosmological constant, and the late-time growth rate predicted by general relativity. We find no statistically significant preference for a departure from the baseline $\Lambda$CDM model. In general, models introduced to increase the Hubble constant or to decrease the amplitude of density fluctuations inferred from the primary CMB are not favored by our data.

arXiv:2506.18974v1 Announce Type: new Abstract: The Euclid mission and other next-generation large-scale structure surveys will enable high-precision measurements of the cosmic matter distribution. Understanding the impact of baryonic processes such as star formation and AGN feedback on matter clustering is crucial to ensure precise and unbiased cosmological inference. Most theoretical models of baryonic effects to date focus on two-point statistics, neglecting higher-order contributions. This work develops a fast and accurate emulator for baryonic effects on the matter bispectrum, a key non-Gaussian statistic in the nonlinear regime. We employ high-resolution $N$-body simulations from the BACCO suite and apply a combination of cutting-edge techniques such as cosmology scaling and baryonification to efficiently span a large cosmological and astrophysical parameter space. A deep neural network is trained to emulate baryonic effects on the matter bispectrum measured in simulations, capturing modifications across various scales and redshifts relevant to Euclid. We validate the emulator accuracy and robustness using an analysis of \Euclid mock data, employing predictions from the state-of-the-art FLAMINGO hydrodynamical simulations. The emulator reproduces baryonic suppression in the bispectrum to better than 2$\%$ for the $68\%$ percentile across most triangle configurations for $k \in [0.01, 20]\,h^{-1}\mathrm{Mpc}$ and ensures consistency between cosmological posteriors inferred from second- and third-order weak lensing statistics.

Earth, a Cosmic Spectacle

Louise Beer, IoA Artist in Residence, will share a presentation that considers the philosophical impacts of dark skies, and how having access to them can help us to understand better loss and grief, our individual connection to the deep time history of Earth and the Universe, and the cosmic significance of the climate crisis. Louise will share her 2024 British Council-funded project, Earth, a Cosmic Spectacle which was developed in collaboration with astronomer Dr Ian Griffin and Tūhura Otago Museum in Aotearoa New Zealand. In this project, the artist invited astronomers, biologists, and geologists to gaze into the dark skies of New Zealand and anonymously write a letter exploring how their knowledge of Earth’s long and gradual development, starting from the dawn of the Universe, shapes their understanding of the cosmic significance of the climate crisis.

• Speaker: Louise Beer
• Tuesday 24 June 2025, 13:15-13:45
• Venue: Hoyle Lecture theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.

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arXiv:2502.00946v2 Announce Type: replace Abstract: We present a transfer function-based method to estimate angular power spectra from filtered maps for cosmic microwave background (CMB) surveys. This is especially relevant for experiments targeting the faint primordial gravitational wave signatures in CMB polarisation at large scales, such as the Simons Observatory (SO) small aperture telescopes. While timestreams can be filtered to mitigate the contamination from low-frequency noise, usual methods that calculate the mode coupling at individual multipoles can be challenging for experiments covering large sky areas or reaching few-arcminute resolution. The method we present here, although approximate, is more practical and faster for larger data volumes. We validate it through the use of simulated observations approximating the first year of SO data, going from half-wave plate-modulated timestreams to maps, and using simulations to estimate the mixing of polarisation modes induced by an example of time-domain filtering. We show its performance through an example null test and with an end-to-end pipeline that performs inference on cosmological parameters, including the tensor-to-scalar ratio $r$. The performance demonstration uses simulated observations at multiple frequency bands. We find that the method can recover unbiased parameters for our simulated noise levels.

arXiv:2407.04607v2 Announce Type: replace Abstract: We infer the growth of large scale structure over the redshift range $0.4\lesssim z \lesssim 1$ from the cross-correlation of spectroscopically calibrated Luminous Red Galaxies (LRGs) selected from the Dark Energy Spectroscopic Instrument (DESI) legacy imaging survey with CMB lensing maps reconstructed from the latest Planck and ACT data. We adopt a hybrid effective field theory (HEFT) model that robustly regulates the cosmological information obtainable from smaller scales, such that our cosmological constraints are reliably derived from the (predominantly) linear regime. We perform an extensive set of bandpower- and parameter-level systematics checks to ensure the robustness of our results and to characterize the uniformity of the LRG sample. We demonstrate that our results are stable to a wide range of modeling assumptions, finding excellent agreement with a linear theory analysis performed on a restricted range of scales. From a tomographic analysis of the four LRG photometric redshift bins we find that the rate of structure growth is consistent with $\Lambda$CDM with an overall amplitude that is $\simeq5-7\%$ lower than predicted by primary CMB measurements with modest $(\sim2\sigma)$ statistical significance. From the combined analysis of all four bins and their cross-correlations with Planck we obtain $S_8 = 0.765\pm0.023$, which is less discrepant with primary CMB measurements than previous DESI LRG cross Planck CMB lensing results. From the cross-correlation with ACT we obtain $S_8 = 0.790^{+0.024}_{-0.027}$, while when jointly analyzing Planck and ACT we find $S_8 = 0.775^{+0.019}_{-0.022}$ from our data alone and $\sigma_8 = 0.772^{+0.020}_{-0.023}$ with the addition of BAO data. These constraints are consistent with the latest Planck primary CMB analyses at the $\simeq 1.6-2.2\sigma$ level, and are in excellent agreement with galaxy lensing surveys.

Conditions in our little pocket of the universe seem to be just right for life - and the much-debated anthropic principle forces us to wonder why

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.

• Speaker: Prof. Howard Reader
• Tuesday 01 July 2025, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

Add to your calendar or Include in your list

arXiv:2503.03806v2 Announce Type: replace Abstract: Population III (Pop III) stars are the first stars in the Universe, forming from pristine, metal-free gas and marking the end of the cosmic dark ages. Their formation rate is expected to sharply decline after redshift $z \approx 15$ due to metal enrichment from previous generations of stars. In this paper, we analyze 14 zoom-in simulations from the THESAN-ZOOM project, which evolves different haloes from the THESAN-1 cosmological box down to redshift $z=3$. The high mass resolution of up to $142 M_\odot$ per cell in the gas phase combined with a multiphase model of the interstellar medium (ISM), radiative transfer including Lyman-Werner radiation, dust physics, and a non-equilibrium chemistry network that tracks molecular hydrogen, allows for a realistic but still approximate description of Pop III star formation in pristine gas. Our results show that Pop III stars continue to form in low-mass haloes ranging from $10^6 M_\odot$ to $10^9 M_\odot$ until the end of reionization at around $z=5$. At this stage, photoevaporation suppresses further star formation in these minihaloes, which subsequently merge into larger central haloes. Hence, the remnants of Pop III stars primarily reside in the satellite galaxies of larger haloes at lower redshifts. While direct detection of Pop III stars remains elusive, these results hint that lingering primordial star formation could leave observable imprints or indirectly affect the properties of high-redshift galaxies. Explicit Pop III feedback and specialized initial mass function modelling within the THESAN-ZOOM framework would further help interpreting emerging constraints from the James Webb Space Telescope.

Now, an international group of astronomers led by the University of Cambridge have shown that we will be able to learn about the masses of the earliest stars by studying a specific radio signal – created by hydrogen atoms filling the gaps between star-forming regions – originating just a hundred million years after the Big Bang.

By studying how the first stars and their remnants affected this signal, called the 21-centimetre signal, the researchers have shown that future radio telescopes will help us understand the very early universe, and how it transformed from a nearly homogeneous mass of mostly hydrogen to the incredible complexity we see today. Their results are reported in the journal Nature Astronomy.

“This is a unique opportunity to learn how the universe’s first light emerged from the darkness,” said co-author Professor Anastasia Fialkov from Cambridge’s Institute of Astronomy. “The transition from a cold, dark universe to one filled with stars is a story we’re only beginning to understand.”

The study of the universe’s most ancient stars hinges on the faint glow of the 21-centimetre signal, a subtle energy signal from over 13 billion years ago. This signal, influenced by the radiation from early stars and black holes, provides a rare window into the universe’s infancy.

Fialkov leads the theory group of REACH (the Radio Experiment for the Analysis of Cosmic Hydrogen). REACH is a radio antenna and is one of two major projects that could help us learn about the Cosmic Dawn and the Epoch of Reionisation, when the first stars reionised neutral hydrogen atoms in the universe.

Although REACH, which captures radio signals, is still in its calibration stage, it promises to reveal data about the early universe. Meanwhile, the Square Kilometre Array (SKA)—a massive array of antennas under construction—will map fluctuations in cosmic signals across vast regions of the sky.

Both projects are vital in probing the masses, luminosities, and distribution of the universe's earliest stars. In the current study, Fialkov – who is also a member of the SKA – and her collaborators developed a model that makes predictions for the 21-centimetre signal for both REACH and SKA, and found that the signal is sensitive to the masses of first stars.

“We are the first group to consistently model the dependence of the 21-centimetre signal of the masses of the first stars, including the impact of ultraviolet starlight and X-ray emissions from X-ray binaries produced when the first stars die,” said Fialkov, who is also a member of Cambridge’s Kavli Institute for Cosmology. “These insights are derived from simulations that integrate the primordial conditions of the universe, such as the hydrogen-helium composition produced by the Big Bang.”

In developing their theoretical model, the researchers studied how the 21-centimetre signal reacts to the mass distribution of the first stars, known as Population III stars. They found that previous studies have underestimated this connection as they did not account for the number and brightness of X-ray binaries – binary systems made of a normal star and a collapsed star – among Population III stars, and how they affect the 21-centimetre signal.

Unlike optical telescopes like the James Webb Space Telescope, which capture vivid images, radio astronomy relies on statistical analysis of faint signals. REACH and SKA will not be able to image individual stars, but will instead provide information about entire populations of stars, X-ray binary systems and galaxies.

“It takes a bit of imagination to connect radio data to the story of the first stars, but the implications are profound,” said Fialkov.

“The predictions we are reporting have huge implications for our understanding of the nature of the very first stars in the Universe,” said co-author Dr Eloy de Lera Acedo, Principal Investigator of the REACH telescope and PI at Cambridge of the SKA development activities. “We show evidence that our radio telescopes can tell us details about the mass of those first stars and how these early lights may have been very different from today’s stars.

“Radio telescopes like REACH are promising to unlock the mysteries of the infant Universe, and these predictions are essential to guide the radio observations we are doing from the Karoo, in South Africa.”

The research was supported in part by the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI). Anastasia Fialkov is a Fellow of Magdalene College, Cambridge. Eloy de Lera Acedo is an STFC Ernest Rutherford Fellow and a Fellow of Selwyn College, Cambridge.

 

Reference:
T. Gessey-Jones et al. ‘Determination of the mass distribution of the first stars from the 21-cm signal.’ Nature Astronomy (2024). DOI: 10.1038/s41550-025-02575-x

Understanding how the universe transitioned from darkness to light with the formation of the first stars and galaxies is a key turning point in the universe’s development, known as the Cosmic Dawn. However, even with the most powerful telescopes, we can’t directly observe these earliest stars, so determining their properties is one of the biggest challenges in astronomy.

This is a unique opportunity to learn how the universe’s first light emerged from the darknessAnastasia FialkovESA/Webb, NASA, ESA, CSAThe image shows a deep galaxy field, featuring thousands of galaxies of various shapes and sizes

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arXiv:2506.14870v1 Announce Type: new Abstract: We present a broad-line active galactic nucleus (AGN) at z = 5.077, observed with both NIRSpec/MSA and NIRSpec/IFU by the JADES and BlackTHUNDER surveys. The target exhibits all the hallmark features of a 'Little Red Dot' (LRD) AGN. The combination of spatially resolved and high-resolution spectroscopy offers deeper insight into its nature. The H$\alpha$ line has multiple components, including two broad Gaussians, yielding a black-hole mass of $\log(M_{\rm BH}/M_\odot) = 7.65$, while the narrow [O III]$\lambda$5007 gives a galaxy dynamical mass of $\log(M_{\rm dyn}/M_\odot) = 9.1$, suggesting a dynamically overmassive black hole relative to the host galaxy. The target has two satellites, and is immersed in a 7-kpc wide pool of ionized gas. A spatially detached outflow is also tentatively detected. H$\alpha$ shows strong absorption with high equivalent width (EW), ruling out a stellar origin, and with velocity and velocity dispersion of v = -13 km s$^{-1}$ and $\sigma$ = 120 km s$^{-1}$. There is tentative evidence (2.6 $\sigma$) of temporal variability in the EW of the H$\alpha$ absorber over two rest-frame months. If confirmed, this would suggest a highly dynamic environment. Notably, while the H$\alpha$ absorber is clearly visible and even dominant in the high-resolution G395H observations, it is not detected in the medium-resolution G395M data of the same epoch. This implies that the current incidence rate of absorbers in LRDs - and especially of rest-frame absorbers - may be severely underestimated, because most LRDs rely on lower-resolution spectroscopy. In this context, the high incidence rate of rest-frame absorbers in LRDs may indicate a configuration that is either intrinsically stationary, such as a rotating disc, or that exhibits time-averaged stability, such as an oscillatory 'breathing mode' accretion of cyclic expansion and contraction of the gas around the SMBH.

WST: science. status and plans

The wide-field spectroscopic telescope (WST) will be an innovative 12-m class telescope with simultaneous operation of a large field-of-view (3 sq. degree) and high multiplex (30,000) multi-object spectrograph facility with both medium and high resolution modes (MOS), and a giant panoramic (3×3 sq. arcmin) integral field spectrograph (IFS). WST will achieve transformative results in most areas of astrophysics: e.g. the nature and expansion of the dark Universe, the formation of first stars and galaxies and their role in the cosmic reionisation, the study of the dark and baryonic material in the cosmic web, the baryon cycle in galaxies, the formation history of the Milky Way and dwarf galaxies in the Local Group, characterization of exoplanet hosts, and the characterization of transient phenomena, including electromagnetic counterparts of gravitational wave events.

This presentation will discuss current science, status and plans.

• Speaker: Prof Roland Bacon (CRAL, Lyon, FR and WST Collaboration Coordinator)
• Tuesday 01 July 2025, 11:30-12:30
• Venue: Martin Ryle Seminar Room, Kavli Building.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

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arXiv:2505.03737v2 Announce Type: replace Abstract: Weak gravitational lensing of the CMB has been established as a robust and powerful observable for precision cosmology. However, the impact of Galactic foregrounds, which has been studied less extensively than many other potential systematics, could in principle pose a problem for CMB lensing measurements. These foregrounds are inherently non-Gaussian and hence might mimic the characteristic signal that lensing estimators are designed to measure. We present an analysis that quantifies the level of contamination from Galactic dust in lensing measurements, focusing particularly on measurements with the Atacama Cosmology Telescope and the Simons Observatory. We employ a whole suite of foreground models and study the contamination of lensing measurements with both individual frequency channels and multifrequency combinations. We test the sensitivity of different estimators to the level of foreground non-Gaussianity, and the dependence on sky fraction and multipole range used. We find that Galactic foregrounds do not present a problem for the Atacama Cosmology Telescope experiment (the bias in the inferred CMB lensing power spectrum amplitude remains below $0.3\sigma$). For Simons Observatory, not all foreground models remain below this threshold. Although our results are conservative upper limits, they suggest that further work on characterizing dust biases and determining the impact of mitigation methods is well motivated, especially for the largest sky fractions.

arXiv:2506.13907v1 Announce Type: new Abstract: Supermassive black hole feedback is the currently favoured mechanism to regulate the star formation rate of galaxies and prevent the formation of ultra-massive galaxies ($M_\star>10^{12}M_\odot$). However, the mechanism through which the outflowing energy is transferred to the surrounding medium strongly varies from one galaxy evolution model to another, such that a unified model for AGN feedback does not currently exist. The hot atmospheres of galaxy groups are highly sensitive laboratories of the feedback process, as the injected black hole energy is comparable to the binding energy of halo gas particles. Here we report multi-wavelength observations of the fossil galaxy group SDSSTG 4436. The hot atmosphere of this system exhibits a highly relaxed morphology centred on the giant elliptical galaxy NGC~3298. The X-ray emission from the system features a compact core ($<$10 kpc) and a steep increase in the entropy and cooling time of the gas, with the cooling time reaching the age of the Universe $\sim15$ kpc from the centre of the galaxy. The observed entropy profile implies a total injected energy of $\sim1.5\times10^{61}$ ergs, which given the high level of relaxation could not have been injected by a recent merging event. Star formation in the central galaxy NGC~3298 is strongly quenched and its stellar population is very old ($\sim$10.6 Gyr). The currently detected radio jets have low power and are confined within the central compact core. All the available evidence implies that this system was affected by giant AGN outbursts which excessively heated the neighbouring gas and prevented the formation of a self-regulated feedback cycle. Our findings imply that AGN outbursts can be energetic enough to unbind gas particles and lead to the disruption of cool cores.

arXiv:2506.13852v1 Announce Type: new Abstract: JWST has revealed the apparent evolution of the black hole (BH)-stellar mass ($M_\mathrm{BH}$-$M_\rm{\ast}$) relation in the early Universe, while remaining consistent the BH-dynamical mass ($M_\mathrm{BH}$-$M_\mathrm{dyn}$) relation. We predict BH masses for $z>3$ galaxies in the high-resolution THESAN-ZOOM simulations by assuming the $M_\mathrm{BH}$-$M_\mathrm{dyn}$ relation is fundamental. Even without live BH modelling, our approach reproduces the JWST-observed $M_\mathrm{BH}$ distribution, including overmassive BHs relative to the local $M_\mathrm{BH}$-$M_\mathrm{\ast}$ relation. We find that $M_\mathrm{BH}/M_\mathrm{\ast}$ declines with $M_\mathrm{\ast}$, evolving from $\sim$0.1 at $M_\mathrm{\ast}=10^6\,\mathrm{M_\odot}$ to $\sim$0.01 at $M_\mathrm{\ast}=10^{10.5}\,\mathrm{M_\odot}$. This trend reflects the dark matter ($f_\mathrm{DM}$) and gas fractions ($f_\mathrm{gas}$), which decrease with $M_\mathrm{\ast}$ but show little redshift evolution down to $z=3$, resulting in small $M_\mathrm{\ast}/M_\mathrm{dyn}$ ratios and thus overmassive BHs in low-mass galaxies. We use $\texttt{Prospector}$-derived stellar masses and star-formation rates to infer $f_\mathrm{gas}$ across 48,022 galaxies in JADES at $3

Nucleosynthesis at the isotopic level: how chemical abundances enhance our understanding of globular clusters and dwarf galaxies

In the context of hierarchical galaxy assembly, both globular clusters and dwarf galaxies serve as indispensable probes of the formation of our Milky Way. The chemical composition of stars within these ancient structures plays a pivotal role in constraining their chemical enrichment history. To date, most studies have focused almost exclusively on elemental abundances, however, nucleosynthesis operates at the isotopic level. This talk will discuss how Mg isotope ratios shed light on both the accreted dwarf galaxy component of our Milky Way and the light element enhanced populations within globular clusters. This reveals contributions from supernova and low-mass stars that cannot be discerned through element abundances alone.

• Speaker: Madeleine McKenzie (Carnegie)
• Friday 20 June 2025, 11:30-12:30
• Venue: Ryle Seminar Room, KICC + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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arXiv:2506.12122v1 Announce Type: new Abstract: We present an extension of the pop-cosmos model for the evolving galaxy population up to redshift $z\sim6$. The model is trained on distributions of observed colors and magnitudes, from 26-band photometry of $\sim420,000$ galaxies in the COSMOS2020 catalog with Spitzer IRAC $\textit{Ch. 1}<26$. The generative model includes a flexible distribution over 16 stellar population synthesis (SPS) parameters, and a depth-dependent photometric uncertainty model, both represented using score-based diffusion models. We use the trained model to predict scaling relationships for the galaxy population, such as the stellar mass function, star-forming main sequence, and gas-phase and stellar metallicity vs. mass relations, demonstrating reasonable-to-excellent agreement with previously published results. We explore the connection between mid-infrared emission from active galactic nuclei (AGN) and star-formation rate, finding high AGN activity for galaxies above the star-forming main sequence at $1\lesssim z\lesssim 2$. Using the trained population model as a prior distribution, we perform inference of the redshifts and SPS parameters for 429,669 COSMOS2020 galaxies, including 39,588 with publicly available spectroscopic redshifts. The resulting redshift estimates exhibit minimal bias ($\text{median}[\Delta_z]=-8\times10^{-4}$), scatter ($\sigma_\text{MAD}=0.0132$), and outlier fraction ($6.19\%$) for the full $0