Astrophysics Brown Bag Lunch Talk 9/26/2022: Speakers: Yonadav-Barry Ginat (Technion, Israel) And Emily Charles (University Of Surrey, UK)

Monday September 26, 2022 12:00 pm

In Person in Marlar and/or Virtual Brown Bag Lunch 
Monday September 26, 2022 at 12:00 Link Below
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Presentation in Marlar 37-252/37-272 for those wishing to attend in person


Yonadav-Barry Ginat, Technion, Israel at 12:05 (in person )

Relativistic effects on galaxy number counts and cosmological observers

Abstract: Light from galaxies across the Universe does not travel on straight lines, as it would in a perfect FLRW universe. This difference between perturbed and unperturbed photon geodesics is due to projection effects – relativistic corrections to the geodesic equation of the photons, along the cosmological observer’s past light-cone. The magnitude of these effects necessitates accounting for them in any measurement of large-scale structure, especially on large scales.
In this talk I will describe a fully relativistic, non-linear, covariant calculation of the galaxy over-density field, as well as the implications of a single observer’s viewpoint on measurements of galaxy clustering statistics, and in particular, on the monopole. I will present a decomposition of the observed galaxy over-density into gauge-invariant observables, each of which has a clear physical meaning. From there, I will move on to show that only differences of potential can be extracted from galaxy clustering data, in agreement with the equivalence principle. The decomposition is independent of the observer’s choice of background – be it the true, global FLRW background, or an inferred one, using the local inferred expansion rate.


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Emily Charles, University of Surrey, UK at 12:30 pm (virtual)

Andromeda 25 – a dwarf galaxy with a low central dark matter

Abstract:  The most successful model of the Universe to date is the Lambda Cold Dark Matter Model (LCDM). Theoretical predictions from LCDM on large scales closely match observational evidence.  However, on small scales (e.g. galactic scales) long-standing tensions between theory and observation exist. Dwarf galaxies are dark matter dominated systems, making them powerful probes for studying dark matter on small scales. Recently I have been focusing on Andromeda 25 (And 25), a dwarf satellite galaxy of M31. And 25 was previously identified in Collins et al (2013) as an outlier with little-to-no dark matter content.  However, this conclusion was heavily caveated due to the small sample size of only 26 stars. With the inclusion of new spectroscopic data, we more than doubled the sample size. In this talk, I will discuss the revised kinematic results of And 25 to find out if it truly is a dwarf galaxy with no dark matter component. I will then expand the discussion to include results from the dynamical mass modelling of And 25 to investigate its unusual dark matter profile and potential explanations for its low central dark matter density.


Event Contact

Josh Borrow