[Astro] [CAPT] CAPT Weekly Bulletin (w/c 19-05-25)

Mon May 19 08:12:34 BST 2025

Monday 19th May at 3pm, A113 CAPT – Theoretical Physics Student Seminar
Noe Larousse

Vacuum bubbles and Penrose diagrams
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Tuesdays at 11am, CAPT Foyer – Astro Coffee

Tuesday 20th May at 11.30am, A113 CAPT – Astronomy Journal Club

Tuesday 20th May at 1pm, A113 CAPT – Particle Cosmology and Gravity Seminar
Diederick Roest (Groningen)

Hidden zeros in plane site: on the unity and covariance of Goldstone boson scattering amplitudes

We will provide a pedestrian introduction to the symmetries and scattering of Goldstone bosons, with main emphasis on Pions. Their amplitudes feature surprising aspects, such as the long-known Adler zero but also hidden zeros and factorisations, as found very recently. We will put forward a covariant formulation where their properties are manifest throughout and show an exact factorisation theorem. Finally, we comment on the unity with other Goldstone boson theories, such as DBI and the special Galileon.

Link to join: https://teams.microsoft.com/l/meetup-join/19%3ameeting_OGM3OTk5NzQtZWEwZS00ZmUyLTk3MGUtZjFhY2M5OTU2MjI1%40thread.v2/0?context=%7b%22Tid%22%3a%2267bda7ee-fd80-41ef-ac91-358418290a1e%22%2c%22Oid%22%3a%22f3250584-4b5f-48fa-a897-08e77f2246b7%22%7d
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Wednesday 21st May at 3.45pm, C4 Physics – Astronomy Weekly Seminar

Sugata Kaviraj (Hertfordshire)

Dwarf galaxies in deep-wide surveys: a new frontier in the study of galaxy evolution

Dwarf (M < 10^9.5 MSun) galaxies dominate the galaxy number density, making them critical to a complete understanding of galaxy evolution. However, typical dwarfs are not bright enough to be detectable, outside the very local Universe, in past large surveys like the SDSS, because they are too shallow. The dwarfs that do exist in such surveys have extreme star formation rates, which makes them anomalously blue and unrepresentative of dwarfs in general. New deep-wide surveys from the Hyper Suprime-Cam (HSC), LSST and Euclid will revolutionise our understanding of galaxy evolution, by offering unbiased statistical samples of dwarfs out to at least z∼0.4. We demonstrate the game-changing potential of such surveys, by exploring four key aspects of galaxy evolution in the dwarf regime (10^8 MSun < M < 10^9.5 MSun), using several thousand dwarfs in the HSC U/deep footprint in COSMOS: star formation, quenching, morphologies and AGN activity.

The fraction of red/quenched dwarfs in HSC U/Deep is around 40%, a factor of 8 higher than what is concluded using the SDSS. Red dwarfs reside in higher-density environments and closer to nodes, large-scale filaments and massive galaxies. However, the probability of dwarfs being red is most strongly correlated with the distance to the nearest massive galaxy. Dwarfs show three principal morphological types: early-type, late-type and a featureless class which lacks both the central concentrations found in early-types or any spiral structure. Dwarf early-types, unlike their massive counterparts, are likely to be shaped by secular processes (not interactions), while the featureless dwarfs are likely created by baryonic feedback. Finally, broadband variability studies (which will become a key tool for AGN detection in the LSST era) suggest that the incidence of AGN in dwarfs and massive galaxies may be similar, suggesting that AGN could be important in the dwarf regime, as they are in massive galaxies. Dwarfs represent a vast discovery space for new and future deep-wide surveys like Euclid and LSST which promises new insights into how galaxies form and evolve over cosmic time.
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Thursday 22nd  May at 1pm, A113 CAPT – Astronomy Lunch Talk

Jacob Campbell

Dark matter substructure detection using gravitational lensing and machine learning

Simulations have shown that dark matter not only forms as a large halo around galaxies, but also as a population of smaller subhaloes. The mass function of these subhaloes is dependent on the dark matter model used, therefore constraining this mass function can provide valuable insight into the nature of dark matter. Gravitational lensing provides a promising method for both detecting the presence of subhaloes as well as measuring their masses by searching for perturbations in Einstein rings. The upcoming surveys of Euclid and LSST are expected to provide ~100,000 observations of new lensed systems, therefore it is important to develop a method that allows us to quickly identify and determine the mass of subhaloes. In this talk, I will explore the prospect of using a machine learning based method for subhalo detection in preparation for these surveys, as well as looking at the limitations and potential issues that we expect to face.

Sara Santoni (Sapienza, University of Rome)

The Three Hundred project: estimating the dependence of cosmic filaments on galaxy clusters properties from 3D and 2D maps

Galaxy clusters reside in the densest areas of the universe and are intricately connected to larger structures through the filamentary network of the cosmic web. In this framework, matter flows from lower density areas to higher density ones. As a result, galaxy clusters are deeply influenced by the presence of cosmic filaments attached to them, which can be quantified by a parameter known as connectivity. We benefit from the extensive data set of The Three Hundred hydrodynamical simulation, which provides 324 simulated cosmological regions, centred on massive galaxy clusters. We extract the cosmic web in the outskirts of the massive galaxy clusters, focusing on filaments, from 3D gas density maps and 2D Compton-y, X-rays and optical mock-maps that mimic the properties of known instruments. We investigate the correlation between the presence of filaments and the main properties of galaxy clusters, such as their mass, dynamical state – expressed in terms of the degree of relaxation and hydrodynamical mass bias – and the filaments’ evolution with redshift. We study the projection effects in the cosmic web identification arising from 3D maps to 2D. Lastly, we compare the skeletons extracted from gas maps with those from mock y and X-rays maps.

Thursday 22nd May at 3pm, A113 CAPT – Particle Cosmology Journal Club

Fridays at 4pm, CAPT Foyer – CAPT Cakes
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VISITORS
PhD student Sara Santoni is visiting from Rome to from Mon - Fri to work with Meghan, Frazer, Ulli, and the rest of cosmic web group.

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If you have any events/visitors you would like included in next week’s bulletin, please let me know.

Best wishes

Ella

Ella Batchelor (she/her)
Administrator

School of Physics & Astronomy

University of Nottingham
A112a Centre for Astronomy & Particle Theory
University Park
Nottingham, NG7 2RD

+44 (0) 115 74 86778 |  nottingham.ac.uk<http://nottingham.ac.uk/>

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