[Astro] [CAPT] CAPT Weekly Bulletin (w/c: 10-12-24)

[Ella Batchelor]

Tuesdays at 11am, CAPT Foyer – Astro Coffee


Tuesday 10th December at 1pm, A113 CAPT – Particle Cosmology and Gravity Seminar

Bruno Alexandre (Imperial College London)
Higgs Mechanism for the Ashtekar Self-Dual Connection


We introduce the Higgs mechanism for the self-dual spin connection (also known as the Ashtekar connection), using the Plebanski formulation of gravity. We develop our formalism within the framework of the chiral action and derive the equations of motion of the theory. One particular test model is explored: since anisotropy is an intrinsic property of the theory, a modified version of the spatially flat Bianchi I model with two different scale factors is considered. We apply our formalism and derive the Friedmann equations which regulate the scale factors and the Higgs field. We also present a Proca-like term for the connection, which when reduced to minisuperspace with a positive Λ yields a De Sitter universe with an effective cosmological constant that depends on the mass of

the gauge fields. We finally investigate the effect of these mass terms on gravitational waves and find that the wave equation remains unchanged relatively to GR; however the Weyl tensor is scaled by a constant which depends on the mass of the connection components.

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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Thursday 12th December at 1pm, A113 CAPT – Astronomy Lunch Talk

Harry Stephenson (Lancaster)

Anisotropic Quenching in 𝒛∼𝟎.𝟒 clusters: AGN or Large Scale Structure?



The mechanisms that suppress star formation in cluster galaxies are numerous, and analysing their impact is crucial to understanding galaxy evolution. Recently, studies have shown that the quenching of satellite galaxies is dependent on their orientation angle to the brightest cluster galaxy (BCG), whereby galaxies along the BCG major axis have significantly reduced star formation compared to those that reside along the minor axis. This has been dubbed “anisotropic quenching” or “angular conformity”.

To probe this anisotropic quenching signal, we used Subaru data of Cluster Lensing And Supernovae survey with Hubble clusters to analyse the colour of ≈ 7,000 satellites, and passive galaxy fractions, at z = 0.2 – 0.5 as a function of their orientation angle from the BCG.

I will discuss our detection of an anisotropic quenching signal out to cluster-centric radii of 3R200 in both satellite colour and passive galaxy fraction against orientation angle that peaks along the major axis. The amplitude of this signal is the largest observed in studies of anisotropic quenching. We find a peak in the amplitude at ≈ 1.25R200 for both satellite colour and passive galaxy fraction. We also investigated if the increased quenching along the major axis is a reflection of the increased density of galaxies. We find that passive galaxy fractions are significantly higher along the major axis for fixed values of local density, suggesting another mechanism is preferentially acting along the major axis. We believe that this signal is caused by preprocessing in filaments that feed satellites into the cluster along the BCG major axis.



Thursday 12th December at 3pm, A113 CAPT – Particle Cosmology Journal Club
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Fridays at 4pm, CAPT Foyer – CAPT Cakes
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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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