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Unveiling the ionising properties of galaxies at the Epoch of Reionisation with NIRCam

The Epoch of Reiniosation describes the cosmic period in which the Universe went from being dark and neutral, to being transparent to radiation. Understanding the first galaxies responsible for lighting up the Universe is of utmost importance for unveiling the mysteries of this epoch.

In this talk I will present work done through the use of deep NIR Cam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) to study the evolution of the ionising photon production efficiency, ξion, with redshift (3 < z < 9). When observing Lyman-alpha emitters (LAEs) and emission-line galaxies (ELGs), we find that low-mass galaxies with bursty star formation histories are more efficient in producing ionising radiation, and could represent the main drivers of reionisation. However, we find that the observed increase of ξion with redshift depends on the nature of the sample: the trends observed in LAEs and ELGs are less significant when a stellar-mass complete sample is used instead.

By combining these results we find that galaxies are likely the main drivers of reionisation, and that there is no crisis in the cosmic ionising budget when a stellar-mass complete sample is considered.

• Speaker: Dr. Charlotte Simmonds (Kavli Institute for Technology, University of Cambridge)
• Tuesday 04 June 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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Inside-out growth in the Early Universe: a core in a vigorously star-forming disc

In extragalactic astrophysics, the mechanisms governing morphological evolution and structural diversity among high-z galaxies represent a key area of active research. In this talk, I will present JADES -GS+53.18343-27.79097, a galaxy of complex morphology, which existed during one of the earliest stages of the universe at z=7.43 (i.e. within its first 700 million years).

With a stellar mass exceeding 10^8.6 solar masses, this star-forming galaxy exhibits a multi-component structure, comprising of a compact core with a half-light radius of 144 parsecs, a vigorous star-forming disc spanning 468 parsecs, and a distinct star-forming clump, each characterised by unique star-formation histories. The central stellar mass density of this high-z galaxy approaches that of the most massive elliptical galaxies observed today, despite its total stellar mass being around only a one-thousandth of theirs. The galaxy also appears to be a possible progenitor of the kind of redshift 2 ellipticals we have seen previously.

Furthermore, the radial profile of the specific star-formation rate of the galaxy shows a sharp increase towards the outskirts, suggesting the detection of inside-out growth in a high-z galaxy within the first billion years of the Universe’s existence.

• Speaker: William Baker (University of Cambridge)
• Tuesday 28 May 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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Title to be confirmed

Abstract not available

• Speaker: Zhong-Zhi Xianyu (Tsinghua U.)
• Friday 14 June 2024, 10:00-11:00
• Venue: CMS, Pav. B, MR9 (B0.09) .
• Series: Cosmology Lunch; organiser: Dr Dong-Gang Wang.

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Role of AGN in galaxy evolution in z~3-11 with Deep JWST spectroscopy

AGN feedback remains a vital path for the quenching of galaxies in theoretical models. With the recent discovery of quiescent galaxies at z>3, identification of typical moderate AGNs at high redshift became more vital than ever, in order to explain the ever-growing population of quiescent galaxies. As typical selection techniques such as X-ray and radio observations are not sensitive enough to detect typical AGN population at high redshifts (z>3), we need to rely on optical emission lines, not accessible to astronomers at these redshifts until the launch of JWST . However, typical selection techniques using optical emission lines (such as BPT diagram), fail to reliably select AGN due to low metallicities of galaxies at high redshift, hence the need to revisit AGN selection. In this talk, I will present the results from the JWST Advanced Galactic Survey (JADES) and its deep NIR Spec/MSA observations of 500 galaxies between z~3-11. I will describe the selection of AGN host galaxies at high-z using these emission lines, to reliably distinguish between star-forming and AGN host galaxies.Using this unique state-of-the-art dataset, I will present the first characterization of moderate luminosity AGN and their host galaxy properties (such as type-1/type-2 fractions, black-hole masses, star-formation rates, stellar mass, etc.) and compare them to AGN in the local Universe and at Cosmic Noon (z=1-3)

• Speaker: Jan Scholtz
• Wednesday 22 May 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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The nature of diffuse ionised gas in star-forming galaxies

It is thought that the diffuse ionised gas (DIG) is ionised via radiation leaking from HII regions, however photoionisation models struggle to replicate observed line ratio trends without introducing unconventional secondary sources of ionisation. I will present a new analysis of the DIG in star-forming galaxies with a high-resolution, isolated Milky Way-like simulation. I will show how the synthetic observations are able to match observed line ratio trends, and that these trends arise from an increasing temperature and hardening radiation field in the DIG . I will demonstrate that this is due to early stellar feedback clearing HII regions within ~5 Myr, unveiling a luminous population of stars with intrinsically hardened SEDs which ionise low-density gas on kiloparsec scales. The state of the DIG in star-forming galaxies is driven by recent star formation, not a secondary source of ionisation.

• Speaker: Will McClymont
• Wednesday 22 May 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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arXiv:2405.10881v1 Announce Type: new Abstract: We present a simulation-based cosmological analysis using a combination of Gaussian and non-Gaussian statistics of the weak lensing mass (convergence) maps from the first three years (Y3) of the Dark Energy Survey (DES). We implement: 1) second and third moments; 2) wavelet phase harmonics; 3) the scattering transform. Our analysis is fully based on simulations, spans a space of seven $\nu w$CDM cosmological parameters, and forward models the most relevant sources of systematics inherent in the data: masks, noise variations, clustering of the sources, intrinsic alignments, and shear and redshift calibration. We implement a neural network compression of the summary statistics, and we estimate the parameter posteriors using a simulation-based inference approach. Including and combining different non-Gaussian statistics is a powerful tool that strongly improves constraints over Gaussian statistics (in our case, the second moments); in particular, the Figure of Merit $\textrm{FoM}(S_8, \Omega_{\textrm{m}})$ is improved by 70 percent ($\Lambda$CDM) and 90 percent ($w$CDM). When all the summary statistics are combined, we achieve a 2 percent constraint on the amplitude of fluctuations parameter $S_8 \equiv \sigma_8 (\Omega_{\textrm{m}}/0.3)^{0.5}$, obtaining $S_8 = 0.794 \pm 0.017$ ($\Lambda$CDM) and $S_8 = 0.817 \pm 0.021$ ($w$CDM). The constraints from different statistics are shown to be internally consistent (with a $p$-value>0.1 for all combinations of statistics examined). We compare our results to other weak lensing results from the DES Y3 data, finding good consistency; we also compare with results from external datasets, such as \planck{} constraints from the Cosmic Microwave Background, finding statistical agreement, with discrepancies no greater than $

arXiv:2405.10866v1 Announce Type: new Abstract: Empirical correlations connecting starlight to galaxy dynamics (e.g., the fundamental plane (FP) of elliptical/quiescent galaxies and the Tully--Fisher relation of spiral/star-forming galaxies) provide cosmology-independent distance estimation and are central to local Universe cosmology. In this work, we introduce the mass hyperplane (MH), which is the stellar-to-dynamical mass relation $(M_\star/M_\mathrm{dyn})$ recast as a linear distance indicator. Building on recent FP studies, we show that both star-forming and quiescent galaxies follow the same empirical MH, then use this to measure the peculiar velocities (PVs) for a sample of 2496 galaxies at $z

Extremal black hole formation as a critical phenomenon

I will present a proof which shows that extremal black holes arise on the threshold of gravitational collapse. More precisely, I will present a construction of one-parameter families of smooth solutions to the Einstein-Maxwell-Vlasov system which interpolate between dispersion and collapse and for which the critical solution is an extremal black hole. This is joint work with Ryan Unger (Princeton).

• Speaker: Christoph Kehle, ETH Zürich
• Friday 24 May 2024, 13:00-14:00
• Venue: Potter room/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

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Nature, Published online: 17 May 2024; doi:10.1038/s41586-024-07494-x

Author Correction: A small and vigorous black hole in the early Universe

Some Disassembly Required

Planetary systems are shaped as much by destructive processes— N-body instabilities, catastrophic impacts, and atmospheric loss— as by accretionary ones. We examine the histories of violence written in: (a) the orbital architectures of super-Earths and sub-Neptunes; (b) the scattered light morphologies of debris disks; (c) chondritic meteorites and high-temperature minerals in comets; and (d) the chaotically variable light curves of disintegrating planets.

• Speaker: Eugene Chiang, Professor of Astronomy and Earth & Planetary Science, University of California, Berkeley
• Thursday 23 May 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: .

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New results about black hole feedback in galaxy clusters

Clusters of galaxies serve as excellent laboratories for exploring the physics of black hole feedback, illustrating how AGN -driven jets can deliver substantial energy to their surroundings via shock fronts, sound waves, and turbulence. These jets can also drive powerful molecular outflows and expel metals from galaxies. In this talk, I will review the current state of the field, focusing on how these powerful AGN -driven jets influence the properties of galaxy clusters over cosmic time. Additionally, I will present new observations of the giant multiphase nebula within the Perseus galaxy cluster and share insights into the pivotal role machine learning can—and will—play in advancing our understanding of galaxy clusters.

• Speaker: Julie Hlavacek-Larrondo, Université de Montréal
• Thursday 30 May 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: .

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arXiv:2312.04621v2 Announce Type: replace Abstract: Strongly-lensed supernovae are rare and valuable probes of cosmology and astrophysics. Upcoming wide-field time-domain surveys, such as the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), are expected to discover an order-of-magnitude more lensed supernovae than have previously been observed. In this work, we investigate the cosmological prospects of lensed type Ia supernovae (SNIa) in LSST by quantifying the expected annual number of detections, the impact of stellar microlensing, follow-up feasibility, and how to best separate lensed and unlensed SNIa. We simulate SNIa lensed by galaxies, using the current LSST baseline v3.0 cadence, and find an expected number of 44 lensed SNIa detections per year. Microlensing effects by stars in the lens galaxy are predicted to lower the lensed SNIa detections by $\sim 8 \%$. The lensed events can be separated from the unlensed ones by jointly considering their colours and peak magnitudes. We define a `gold sample' of $\sim 10$ lensed SNIa per year with time delay $> 10$ days, $> 5$ detections before light-curve peak, and sufficiently bright ($m_i

arXiv:2311.12926v2 Announce Type: replace Abstract: We construct an anti-halo void catalogue of $150$ voids with radii $R > 10\,h^{-1}\mathrm{\,Mpc}$ in the Local Super-Volume ($

Science, Volume 384, Issue 6697, Page 724-724, May 2024.

Glimpse of galactic merger, via James Webb telescope, may explain presence of monster black holes

A pair of black holes has been observed colliding in the ancient universe for the first time. The observations, by the James Webb Space Telescope, reveal a merger of two galaxies and the monster black holes at their centres when the universe was just 740m years old, about a 20th of its current age.

The discovery that massive mergers appear to have been common in the infant universe could help explain how supermassive black holes like the one at the heart of the Milky Way achieved such tremendous proportions.

Continue reading...

Astronomers have found supermassive black holes with masses of millions to billions times that of the Sun in most massive galaxies in the local Universe, including in our Milky Way galaxy. These black holes have likely had a major impact on the evolution of the galaxies they reside in. However, scientists still don’t fully understand how these objects grew to become so massive.

The finding of gargantuan black holes already in place in the first billion years after the Big Bang indicates that such growth must have happened very rapidly, and very early. Now, the James Webb Space Telescope is shedding new light on the growth of black holes in the early Universe.

The new Webb observations have provided evidence for an ongoing merger of two galaxies and their massive black holes when the Universe was just 740 million years old. The system is known as ZS7.

Massive black holes that are actively accreting matter have distinctive spectrographic features that allow astronomers to identify them. For very distant galaxies, like those in this study, these signatures are inaccessible from the ground and can only be seen with Webb.

“We found evidence for very dense gas with fast motions in the vicinity of the black hole, as well as hot and highly ionised gas illuminated by the energetic radiation typically produced by black holes in their accretion episodes,” said lead author Dr Hannah Übler of Cambridge’s Cavendish Laboratory and Kavli Institute for Cosmology. “Thanks to the unprecedented sharpness of its imaging capabilities, Webb also allowed our team to spatially separate the two black holes.”

The team found that one of the two black holes has a mass that is 50 million times the mass of the Sun. “The mass of the other black hole is likely similar, although it is much harder to measure because this second black hole is buried in dense gas,” said team member Professor Roberto Maiolino, also from the Kavli Institute.

“Our findings suggest that merging is an important route through which black holes can rapidly grow, even at cosmic dawn,” said Übler. “Together with other Webb findings of active, massive black holes in the distant Universe, our results also show that massive black holes have been shaping the evolution of galaxies from the very beginning.”

The team notes that once the two black holes merge, they will also generate gravitational waves. Events like this will be detectable with the next generation of gravitational wave observatories, such as the upcoming Laser Interferometer Space Antenna (LISA) mission, which was recently approved by the European Space Agency and will be the first space-based observatory dedicated to studying gravitational waves.

This discovery was from observations made as part of the Galaxy Assembly with NIRSpec Integral Field Spectroscopy programme. The team has recently been awarded a new Large Programme in Webb’s Cycle 3 of observations, to study in detail the relationship between massive black holes and their host galaxies in the first billion years. An important component of this programme will be to systematically search for and characterise black hole mergers. This effort will determine the rate at which black hole merging occurs at early cosmic epochs and will assess the role of merging in the early growth of black holes and the rate at which gravitational waves are produced from the dawn of time.

These results have been published in the Monthly Notices of the Royal Astronomical Society.

Reference:
Hannah Übler et al. ‘GA-NIFS: JWST discovers an offset AGN 740 million years after the big bang’ Monthly Notices of the Royal Astronomical Society (2024). DOI: 10.1093/mnras/stae943

Adapted from a press release by the European Space Agency.

An international team of astronomers, led by the University of Cambridge, has used the James Webb Space Telescope to find evidence for an ongoing merger of two galaxies and their massive black holes when the Universe was only 740 million years old. This marks the most distant detection of a black hole merger ever obtained and the first time that this phenomenon has been detected so early in the Universe.

Massive black holes have been shaping the evolution of galaxies from the very beginningHannah ÜblerESA/Webb, NASA, CSA, J. Dunlop, H. Übler, R. Maiolino, et. alThe environment of the galaxy system ZS7 from the JWST PRIMER programme as seen by Webb's NIRCam instrument

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Cosmology with the CMB: from Planck to SPT-3G

The observation of the Cosmic Microwave Background (CMB) is one of the most powerful probes of our universe. ESA ’s Planck satellite confirmed that the ΛCDM model works astonishingly well to describe the CMB anisotropies, measuring cosmological parameters with percent-level accuracy. Nevertheless, the Planck results reveal a number of outstanding inconsistencies that might hint at cracks in this very successful model. The most critical one is the Hubble tension, the difference between the expansion rate of the universe measured by the CMB and other early universe probes, versus the rate measured by Type Ia supernovae calibrated with Cepheids. In this talk I will present the current efforts to shed light on these problems using the South Pole Telescope. SPT is a ground-based CMB experiment which is observing the sky with its latest camera, SPT -3G. It is expected to provide ground-breaking CMB measurements over 25% of the sky. I will show SPT -3G early results, the several innovations we are introducing in the analysis pipeline for our upcoming second data release, and the expectations for the future.

• Speaker: Silvia Galli (Institut Astrophysique de Paris)
• Monday 20 May 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Fiona McCarthy.

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Phenomenology of axion-gauge field interactions in the early universe

In this talk, I will give a brief overview of my work on the phenomenology of axion-gauge interactions in the early universe. Couplings between axion-like particles (ALPs) and gauge fields arise naturally in UV-complete theories such as string theory. Moreover, their phenomenology is rich and potentially within reach of current or future experimental probes. For the aforementioned reasons there has been a considerable and systematic effort to uncover the phenomenology of such couplings and I will be providing a review of past results with a focus on couplings between axions and massless U(1) gauge fields as well as SU(2) gauge fields (chromo-natural inflation etc.). In the context of inflation, these models in particular produce strong gravitational waves, potentially observable with current of future interferometers or PTA experiments. Additionally, they predict strongly sourced scalar perturbations, scalar induced gravitational waves, primordial black holes and more. Finally, I will emphasize a regime of these models which is only recently beginning to be explored, namely the “strong backreaction” regime and give a detailed breakdown of the unique signatures of such a regime during infllation.

• Speaker: Alexandros Papageorgiou (IFT, Madrid)
• Tuesday 28 May 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Thomas Colas.

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The Extremes of Resolved Stellar Spectroscopy

The study of local star clusters and galaxies with existing spectroscopic instruments and techniques has reached the point of diminishing returns. Breakthroughs require new instruments or innovation in spectral analysis. I will describe the measurement of radial velocities and abundances of individual stars at the threshold of spectral resolution and signal-to-noise ratio. First, I will address measurements from Keck/DEIMOS and KCWI . I will discuss the “backsplash” galaxy Andromeda XVIII (at 1.33 Mpc!), neutron-capture abundances in Milky Way satellites, and the “fundamental” stellar mass-stellar metallicity relation of low-mass field galaxies. New spectrograph innovations, like the upgrade to DEIMOS and the Subaru Prime Focus Spectrograph, will lead stellar spectroscopy into the future.

• Speaker: Evan Kirby (Notre Dame)
• Friday 24 May 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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Diffusion meets Nested Sampling

Sampling techniques are a stalwart of reliable inference in the physical sciences, with the nested sampling paradigm emerging in the last decade(s) as a ubiquitous tool for model fitting and comparison. Parallel developments in the field of generative machine learning have enabled advances in many applications of sampling methods in scientific inference pipelines. This work explores the synergy of the latest developments in diffusion models and nested sampling. I will review the challenges of precise model comparison in high dimension, and explore how score based generative models can provide a solution. This work builds towards a public code that can apply out of the box to many established hard problems in fundamental physics, as well as providing potential to extend precise inference to problems that are intractable with classical methods. I will motivate some potential applications at the frontiers of inference that can be unlocked with these methods.

• Speaker: David Yallup (University of Cambridge)
• Tuesday 21 May 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: David Buscher.

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