Testing gravity with relativistic effects in large-scale structure

Camille Bonvin

Université de Genève, Département de Physique Théorique and

Center for Astroparticle Physics

Testing gravity with relativistic effects in large-scale structure

Abstract: The distribution of galaxies is a power tool to test our cosmological model. In this talk I will discuss the different contributions that affect the observed distribution of galaxies. I will show that besides the standard density and redshift-space distortions, the number counts of galaxies is affected by gravitational lensing and relativistic effects. I will then discuss how one of these effects, called gravitational redshift, can be used to build new tests of gravity.

سه شنبه  28 دی 1400، ساعت 19:00

Tuesday 18 January 2022 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

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Luminous and Dark Matter in Massive Early-type Galaxies with Weak Gravitational Lensing‪ 

Maryam Tajalli

Leiden Observatory

Luminous and Dark Matter in Massive Early-type Galaxies with Weak Gravitational Lensing‪ 

 

Abstract: The stellar initial mass function (IMF) is one of the fundamental properties of stellar populations and detecting a variation, or lack thereof, of the IMF with galaxy properties can give us insight into the physics of star formation. However, determining the stellar IMF of massive galaxies is still one of the open problems in cosmology. Future space-based surveys will provide unprecedented weak lensing shape measurements on scales of a few tens of kpc, enabling us to probe the stellar masses of galaxies as well as the inner slope of the dark matter density profile.

In this talk, I will present forecasted constraints on the stellar IMF and stellar-to-halo mass relation of massive early-type galaxies from the future Euclid survey based on the Bayesian hierarchical inference formalism that we have developed. I will show that Euclid is expected to constrain the IMF normalization at the unprecedented level of ∼ 0.02 dex, allowing us to distinguish between a Salpeter and a Chabrier IMF. This is an important result and could lead to a solution to one of the open problems in cosmology, that is, whether the stellar IMF is a universal function or not.

 

یکشنبه 19 دی 1400، ساعت 19:00

Sunday 9 January 2022 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

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Void Galaxy Distribution: A Challenge for ΛCDM

‪Saeed Tavasoli

Physics Department, Kharazmi University

Void Galaxy Distribution: A Challenge for ΛCDM

Abstract: The under-dense regions of cosmic web provide powerful cosmological laboratories and have been widely used in recent years to extract cosmological information. Since these environments are in the linear regime, this makes them attractive to theoretical modeling and tests.

 On the other hand, the low frequency of galaxy mergers inside these regions makes them an ideal environment for the study of the environmental dependence of galaxy formation and evolution with the minimal impact from mergers.

In this talk I will discuss properties of void environments and how void-galaxy distribution could make a possible challenge with LCDM model.

یکشنبه 12 دی 1400، ساعت 19:00

Sunday 2 January 2022 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

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Weekly cosmology seminar

Sara Aliqolizadehsafari

Institute for Particle Physics and Astrophysics, ETH, Zurich

Separating Weak Gravitational Lensing and Galaxy Intrinsic Alignments in the Dark Energy Survey (DES)

Abstract: The assumption that galaxies’ orientations are randomly distributed in the universe is not sufficiently accurate when dealing with modern surveys and can lead to contamination of weak lensing measurements with a systematic bias called Intrinsic Alignment (IA).

This bias has to be dealt with properly so as to preserve the accuracy of recent weak lensing measurements. The alignment of elliptical galaxies, especially luminous red galaxies, with the local tidal field at large scales has been observed in recent years. At small scales, however, non-linearities can complicate this behavior. In this work, we have extracted the intrinsic alignment signal using two tomographic bins of DES Y1 source galaxies, 0.3<z<0.45 and 0.55<z<0.7, and the DES redMaGiC lens sample at 0.3<z<0.45. Our method is based on the fact that the measured lensing signal, ΔΣ, is the same for the two tomographic source bins since it depends only on the characteristics of the lens sample.

Statistically, the number of galaxies that contribute to the intrinsic alignment contamination signal is expected to reduce as the separation between lens and source sample increases. Error estimation is done via the Jackknife covariance method using 40 sub-samples. We have found IA signals using two different weighting schemes which both have a signal-to-noise ratio over 10. Finally, we have modeled the intrinsic alignment signal in the tidal alignment framework, using linear theory on large scales and a fully non-perturbative treatment of the one-halo scale. We have found that this model provides good agreement with the measured signal.

یکشنبه 5 دی 1400، ساعت 19:00

Sunday 26 December 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

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The Astrophysical Context of Gravitational Wave Events

Mohammad Safarzadeh

NASA-GSFC fellow

The Astrophysical Context of Gravitational Wave Events

Abstract: We live in an era of breakthrough discoveries in gravitational waves (GW) astronomy. Every month or so, such discoveries by LIGO/Virgo have been making headlines because these events’ nature has been far from the expectations. But why are we puzzled? And what is the road ahead for us to a deeper understanding? I discuss two of the puzzling events that LIGO has discovered: 1) The most massive binary black hole merger with masses above the pair-instability limit. After a deep dive into the physics of pair-instability supernova, I will discuss how a broader perspective on the host environment of binary black holes can hold the key to understanding the nature of such massive systems. 2) The most massive binary neutron star merger. I will present possible scenarios to explain why we have not detected such systems in the radio observations before and how the key to understanding these events might lie in the r-process enrichment in the early universe and magnetic field evolution of neutron stars. Through these two examples, I will conclude that the synergy of traditional electromagnetic-wave astronomy with gravitational wave astronomy is essential for gaining insights into the surprises that are being uncovered with these new observations.

 یکشنبه 28 آذر 1400، ساعت 19:00

Sunday 19 December 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

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The Rise and Fall of Star Formation in Galaxies

**لطفا  به   روز و  ساعت   نامتعارف سمینار توجه فرمایید**

Allison Man

Department of Physics & Astronomy, University of British Columbia

The Rise and Fall of Star Formation in Galaxies

 

Abstract: Star formation and supermassive black hole growth were most active at cosmic noon (z~2). Massive galaxies appear to experience accelerated growth at early cosmic times, and eventually quench their star formation and become more bulge-dominated. Exactly why these transformations take place is unclear. Mergers and active galactic nuclei feedback are often invoked as explanations, but a consensus is yet to be reached. I will discuss how multi-wavelength observations of stellar populations and multiphase gas of distant galaxies can shed new light on the complex problem of galaxy evolution.

 

دوشنبه 22 آذر 1400، ساعت 19:00

Monday 13 December 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

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Search for The Missing Pieces in Cosmology

Marzieh Farhang

Department of Physics, Shahid Beheshti University

Search for The Missing Pieces in Cosmology

Abstract: The LambdaCDM model has been extraordinarily successful in describing the observed cosmos. There are however hints that this picture is missing serious pieces. In this talk, we discuss the various systematic approaches for the exploration of the beyond LCDM world.

یکشنبه 14 آذر 1400، ساعت 19:00

Sunday 5 December 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

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Nuw Cosmology beyond the average from one-point statistics

Cora Uhlemann

School of Mathematics, Statistics and Physics, Newcastle University

Nuw Cosmology beyond the average from one-point statistics

Abstract: Nonlinear gravitational collapse shaped the cosmic web and created a plethora of different density environments – from voids through filaments to galaxy groups. To realise the full potential of galaxy surveys, we need to dissect different density environments that are lumped together in traditional two-point statistics. This is particularly important for detecting extensions of LCDM including massive neutrinos (Nu), dynamical dark energy (w) and modified gravity. I will show how to extract additional information from the mildly nonlinear one-point statistics of matter densities and associated galaxy survey observables. We showed that using the lensing PDF jointly with the 2pt correlation could improve parameter constraints on nuLCDM/wCDM models by 40% when combined with Planck. Recently, we demonstrated the strong discriminating power of the matter PDF for modified gravity finding an up to sixfold increase of the detection significance compared to the power spectrum alone.

 

یکشنبه 7 آذر 1400، ساعت 19:00

Sunday 28 November 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

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The radial acceleration relation in a LCDM universe

Aseem Paranjape

Inter-University Centre for Astronomy & Astrophysics (IUCAA)

 Pune, India

The radial acceleration relation in a LCDM universe

Abstract: I will discuss some recent analytical insights into the nature of the `radial acceleration relation’ (RAR) between total and baryonic centripetal acceleration profiles of central galaxies in the Lambda-cold dark matter (LCDM) framework. Specifically, there is an intimate connection between the RAR and the physics of quasi-adiabatic relaxation of dark matter in the presence of baryons in the galaxy’s parent halo. Using analytical approximations and a realistic LCDM mock galaxy catalog, we have explored the sensitivity of the RAR in different acceleration regimes to quasi-adiabatic relaxation physics, halo mass and concentration, and the abundance of diffuse gas in the halo outskirts. These results cleanly demonstrate how the mean RAR and its scatter emerge from the interplay of dark matter and baryons in the LCDM paradigm. Time permitting, I will also discuss some new results demonstrating that LCDM predicts a statistical `external field effect’ in which the shape of the RAR of any galaxy correlates with the gravitational acceleration due to mass external to the galaxy, without any violation of the strong equivalence principle.

 

یکشنبه 30 آبان 1400، ساعت 19:00

Sunday 21 November 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

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Warm inflation and string theory conjectures 

Vahid Kamali

Department of Physics, Bu-Ali Sina (Avicenna) University

Warm inflation and string theory conjectures 

 

Abstract: In early time cosmology, inflation is the most interesting scenario originating from effective field theory. It can answer some significant questions regarding hot big bang cosmology. Taking the linear perturbation theory into account, inflation can explain how large-scale structures form. In recent years, the field theory of inflation has been challenged by some conjectures motivated by string theory. As part of this talk, I will discuss a special scenario of inflation where the inflaton is coupled with light fields in a thermal bath. I will demonstrate how this model can be out of swampland.

 

یکشنبه 23 آبان 1400، ساعت 15:00

Sunday 14 November 2021 – 15:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

گزینه ورود به صورت مهمان – Enter as a Guest