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From a vantage point high in the Chilean Andes, cosmologists with the Simons Observatory have begun searching for evidence of what happened in the minuscule fraction of a second that followed the Big Bang. The observatory, which just completed its main construction phase, will make some of the most precise measurements...

arXiv:2406.05728v1 Announce Type: new Abstract: Through the chemodynamical characterisation of metal-poor stars, one can efficiently probe the early history of the Milky Way. We aim at decontaminating a sample of $\sim$ 3M giant stars with Gaia DR3 XP-based \textit{Pristine-Gaia} metallicities, to investigate a subset of very metal-poor stars ([Fe/H] 180 km s$^{-1}$ and $Z_{\text{max}}$

Modelling the impact of host galaxy dust on type Ia supernova distance measurements

Type Ia Supernovae (SNe Ia) are a critical tool in measuring the accelerating expansion of the universe. Recent efforts to improve these standard candles have focused on incorporating the effects of dust on distance measurements with SNe Ia. In this paper, we use the state-of-the-art Dark Energy Survey 5 year sample to evaluate two different families of dust models: empirical extinction models derived from SNe Ia data, and physical attenuation models from the spectra of galaxies. These empirically-derived extinction distributions are highly incompatible with the physical attenuation models from galactic spectral measurements. From these results, we conclude that SNe Ia must either preferentially select extreme ends of galactic dust distributions, or that the characterisation of dust along the SNe Ia line-of-sight is incompatible with that of galactic dust distributions. Additionally, we check the evolution of dust parameters with redshift, and find strong evidence that the environments of type Ia supernovae change with redshift.

• Speaker: Brodie Popovic
• Wednesday 05 June 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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Low luminosity AGN across cosmic time - a preliminary census

The origin and evolution of supermassive black holes as well as their interaction with their host galaxies still holds many unanswered questions. The launch of JWST was expected to shed more light on this domain by probing the low mass, low luminosity end of the active galactic nuclei (AGN) distribution – a regime missed by previous all sky surveys which were sensitive only to the brightest objects. However, the first year of results has revealed some peculiar properties of this low luminosity AGN population. Among the more notable ones being their offset compared to the local black hole mass – stellar mass relation and significant X-ray weakness. Here I will present two notable objects that exhibit these properties in the most extreme manner and discuss their implications on black hole formation accretion disk radiation models. In addition I will briefly discuss the sample of AGN found by the JADES survey.

• Speaker: Ignas Juodžbalis (University of Cambridge)
• Wednesday 05 June 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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Diving chaotic orbits in axisymmetric potentials

Chaotic orbits in axisymmetric systems have the capacity to come arbitrarily close to the centre of the potential – if this system hosts a massive black hole a close passage can lead to the orbiting body disrupting, causing high energy observable phenomena – in this talk i’ll show which kinds of orbit can manage this feat, how they do it, and the timescale over which we can expect an object to be disrupted

• Speaker: Zephyr Penoyre (Leiden Observatory)
• Wednesday 29 May 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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New frontiers in strongly lensed supernova studies with JWST and the Vera C. Rubin Observatory

Strongly lensed supernovae are excellent laboratories for measuring cosmological parameters and studying supernova astrophysics in the high-redshift universe. After reviewing some recent results from ground-based surveys on discoveries of Type Ia supernovae lensed by field galaxies, I will summarise results from two new SN discoveries from JWST : SN H0pe and SN Encore. I will present first constraints on the Hubble constant from a lensed Type Ia supernova and ongoing work on supernova progenitor evolution using SN Encore. Finally, I will conclude with detailed predictions for Vera C. Rubin Observatory’s Legacy Survey of Space and Time.

• Speaker: Suhail Dhawan
• Wednesday 29 May 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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Diving chaotic orbits in axisymmetric potentials

Chaotic orbits in axisymmetric systems have the capacity to come arbitrarily close to the centre of the potential – if this system hosts a massive black hole a close passage can lead to the orbiting body disrupting, causing high energy observable phenomena – in this talk i’ll show which kinds of orbit can manage this feat, how they do it, and the timescale over which we can expect an object to be disrupted

• Speaker: Leiden Observatory
• Wednesday 29 May 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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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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Prototyping a Sparse-Aperture, Segmented, Parabolic Primary Mirror Telescope for SUPERSHARP

The motivation for my research comes from the SUPERSHARP mission concept for large, unfolding, lightweight space telescopes which take advantage of unfolding segmented optics and a sparse aperture primary mirror to generate powerful observations while maintaining limited cost, mass, and volume requirements. The original motivation for the SUPERSHARP design comes from the ongoing search for life in the universe, but the technology has wider applications in both space and Earth observation. Prototyping of the optical system is integral to ensuring technological readiness of key aspects of the telescope design – in particular, the active control and maintenance of optics alignment. In this talk, I will present the work I have done designing and building a prototype of a sparse-aperture, segmented, parabolic primary mirror telescope using two mirror segments. I will also outline the immediate improvements and next steps required for the prototype to more accurately model an effective imaging system.

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

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Type Ia supernovae: Constraining thermonuclear explosion physics with machine learning

Type Ia supernovae are thermonuclear explosions of white dwarfs in binary systems. They play an important role in many areas of astrophysics, from providing chemical enrichment for galaxies to acting as cosmological distance probes. In spite of this, we still fundamentally do not know how or why some white dwarfs explode as thermonuclear supernovae. Multiple explosion mechanisms have been proposed, but the computational expense associated with developing realistic explosion simulations and the difficulty in observing key diagnostic signatures mean that providing robust constraints on the explosion physics is challenging. In this talk, I will provide a general overview of thermonuclear explosion physics and discuss the main explosion scenarios suggested in the literature. I will present my recent work focused on using machine learning to automatically fit spectral sequences of type Ia supernovae in a much more quantitative and efficient way than existing methods. With automated fitting we can test different explosion scenarios against observations and statistically determine which scenario provides the best overall agreement. As spectroscopic samples of supernovae continue to grow, automated fitting tools will become increasingly important to maximise the physical constraints that can be gained in a quantitative and consistent manner.

• Speaker: Mark Magee (University of Warwick)
• Wednesday 08 May 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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The cometary delivery of prebiotic feedstock molecules to the early-Earth and rocky exoplanets

The delivery of prebiotic feedstocks molecules, such as hydrogen cyanide (HCN), during cometary impacts may have significantly influenced prebiotic chemistry on the early Earth, motivated by the discovery of a rich diversity of CHN - and CHS -bearing molecules on solar system comets. Numerical experiments have demonstrated that HCN survival during cometary impacts is however only possible in oblique impacts at very low velocities. In this talk I will discuss the effects of stellar mass, and planetary architecture on minimum cometary impact velocities onto rocky exoplanets. Using both an analytical model and numerical N-body simulations, we show the lowest impact velocities occur for low-mass planets in tightly-packed planetary systems around high-mass (i.e., Solar-mass) stars, enabling the intact delivery of prebiotic feedstock molecules. I will finish by discussing a specific origins scenario, proposed to achieve favourable conditions for subsequent prebiotic chemistry, which invokes the arrival of a secondary impactor in the same location. We consider the atmospheric fragmentation of cometary impactors, and use the lunar crater record to quantitatively evaluate the likelihood of these `double impact’ scenarios on the early-Earth. These scenarios are found to be extremely unlikely settings for the initial stages of prebiotic chemistry, unless there was a particularly high impact rate on the early-Earth, and global environmental conditions conducive to successful cometary delivery.

• Speaker: Richard Anslow (University of Cambridge)
• Wednesday 08 May 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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Scientists from the Cambridge University have suggested that molecules vital to the development of life could have formed from a process known as graphitisation. Once verified in the laboratory, the finding could allow scientists to recreate plausible conditions for life's emergence. It has long been debated how the...

In a series of studies, a team of astronomers (including IoA postdoc Álvaro Ribas) has shed new light on the fascinating and complex process of planet formation. The stunning images, captured using the European Southern Observatory's Very Large Telescope (ESO’s VLT) in Chile, represent one of the largest ever surveys of...

Wading through the wealth of data from ESA’s Gaia mission , scientists have uncovered a ‘sleeping giant’. A large black hole, with a mass of nearly 33 times the mass of the Sun, was hiding in the constellation Aquila, less than 2000 light-years from Earth. This is the first time a black hole of stellar origin this big has...

In brief For the first time, a team of astronomers (including IoA astronomer Nic Walton) have spotted potential signs of a rainbow-like ‘glory effect’ on a planet outside our Solar System. Glory are colourful concentric rings of light that occur only under peculiar conditions. Data from ESA’s sensitive Characterising...

Primordial black holes in the dark matter halo of our Galaxy

If there are primordial black holes in the dark matter halo, they must collide with the Galactic neutron stars (NSs) and produce light black holes (LBHs), with masses below 1.4 M_Sun. This has observational consequences that may be checked by microlensing, by LIGO -Virgo-Kagra interferometers detecting gravitational waves from collisions of LBHs with NSs and BHs, and (possibly) by detecting LBHs in X-ray binaries and from pulsars statistics.

• Speaker: Prof. Marek Abramowicz
• Tuesday 19 March 2024, 14:00-15:00
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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A new convection scheme for exoplanet atmospheres

Convection is an essential process for transporting heat and moisture in planetary atmospheres. The standard Earth picture of moist convection rising from the surface is only one of a number of modes of convection. Notably, convection in atmospheres with a high condensible mass fraction (non-dilute atmospheres), or with a lighter background gas than the condensible species (e.g. water convection in a hydrogen dominated atmosphere) – acts very differently and can be much weaker or even shut down entirely in the latter case. Here I present a new mass-flux scheme which can capture these variations and simulate convection in a wide range of parameter space for use in 3D climate models. A validation using the case of Trappist-1 e is presented.

• Speaker: Edouard Barrier (University of Cambridge)
• Wednesday 13 March 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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Constraining physics and astrophysics with multifrequency CMB data

The CMB anisotropies are measured in several microwave frequency bands. Having this frequency information allows us to separate signals that are due to different sources. We can easily make maps that are sensitive to specific frequency combinations, and in this way isolate the contribution from the primary CMB (early-Universe) and various other CMB interactions such as the Sunyaev—Zel’dovich (SZ) effect (the scattering of the CMB from electrons in the late Universe). I will talk about constraints on the SZ effect from Planck data using a new frequency-separation code, pyilc, which we use to isolate the signal while removing other late-Universe biases, in particular the infrared emission from star-forming galaxies. I will also show an application to beyond standard model interactions between the CMB and a non-trivial dark sector, and how we can use the CMB to constrain beyond-standard-model particle physics.

• Speaker: Fiona McCarthy (DAMTP)
• Wednesday 13 March 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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The winds that help to form planets in the gaseous discs of early solar systems have been imaged for the first time by the James Webb Space Telescope (JWST) using the noble gases neon and argon. Planetary systems like our Solar System seem to contain more rocky objects than gas-rich ones. Around our sun, these include the...