همه‌ی نوشته‌های Mojahed Parsi Mood

The Hubble-constant crisis

The Hubble-constant crisis

Valerio Marra

Núcleo de Astrofísica e Cosmologia & Departamento de Física, Universidade Federal do Espírito Santo, Brazil

 INAF – Osservatorio Astronomico di Trieste, Italy.

IFPU – Institute for Fundamental Physics of the Universe, Italy.

 

Abstract:  The determination of the Hubble constant H0 – the present-day expansion rate of the universe – is one of the key goals of cosmology, for it impacts all measurements of cosmological properties. Determinations of H0 from Cosmic Microwave Background observations disagree with local determinations from calibrated supernovas Ia: this tension is now approaching the 5 sigma level. After reviewing the present status of cosmology, I will present recent work on model-independent determinations of H0 and their implications for cosmologies beyond LCDM.

سه شنبه 12 اسفند 1399، ساعت 13:30

Tuesday 2 March 2021 – 13:30 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

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

گزینه ورود به صورت مهمان – Enter as a Guest

Tracing the galaxy evolution and morphologies

Tracing the galaxy evolution and morphologies using the DM and Stellar halo from the cosmological hydrodynamical simulations of TNG

Razieh Emami

Institute for Theory and Computation

Harvard-Smithsonian Center for Astrophysics

Abstract:  One of the fundamental questions about the galaxy evolution is the redshift evolution of the galaxy morphology as traced by DM and stars. Tracking the galaxy morphology enables us to shed light about how the galaxies are evolved with time and also to connect the visible matter, traced by stars, with the invisible matter, DM. In this talk, we will use the next generation (TNG) of cosmological simulations and study the morphology of DM and stars in a sample of Milky Way like galaxies at zero redshift. We will also present how does the galaxy morphology vary with the time. It is intriguing to investigate how does the major mergers affect the galaxy morphology.

یکشنبه 3 اسفند 1399، ساعت 19:00

Sunday 21 February 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

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

گزینه ورود به صورت مهمان – Enter as a Guest

A conclusive test of the cold dark matter model

A conclusive test of the cold dark matter model

Carlos Frenk

Institute for Computational Cosmology, Durham University

 

Abstract:  The “Lambda cold dark matter” (LCDM) cosmological model is one of the great achievements in Physics of the past thirty years. Theoretical predictions formulated in the 1980s turned out to agree remarkably well with measurements, performed decades later, of the galaxy distribution and the temperature structure of the cosmic microwave background radiation. Yet, these successes do not inform us directly about the nature of the dark matter. Indeed, there are competing (and controversial) claims that the dark matter may have already been discovered, either through the annihilation of cold, or the decay of warm, dark matter particles. In astrophysics the identity of the dark matter manifests itself clearly on subgalactic scales, including the dwarf satellite galaxies of the Milky Way and especially less massive dark matter halos, too small to have made a galaxy.  I will discuss predictions from cosmological simulations assuming cold and warm (in the form of sterile neutrinos) dark matter, including for the properties of the very first halos that ever formed, and show how forthcoming astronomical observations can conclusively distinguish between the two.

 

یکشنبه 26 بهمن 1399، ساعت 19:00

Sunday 14 February 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

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

گزینه ورود به صورت مهمان – Enter as a Guest

Characterizing the non-linear evolution of dark energy models

Characterizing the non-linear evolution of dark energy models

Farbod Hassani

Institute of theoretical astrophysics of the University of Oslo

 

Abstract: Understanding the reason behind the observed accelerating expansion of the Universe is one of the most notable puzzles in modern cosmology, and conceivably in fundamental physics. In the upcoming years, near future surveys will probe structure formation with unprecedented precision and will put firm constraints on the cosmological parameters, including those that describe properties of dark energy. In light of this, during past years I mainly focused on precision cosmology by characterizing the non-linear evolution of cosmological components using N-body simulations. In this talk, first I will introduce gevolution and the idea of developing EFT-evolution N-body code, in which we consistently study the dark matter and dark energy structures up to non-linear scales. Then I will discuss the consequences of clustering dark energy on cosmological observables.

 یکشنبه 19 بهمن 1399، ساعت 19:00

Sunday 7 February 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

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

گزینه ورود به صورت مهمان – Enter as a Guest

کاربرد شبکه‌های عصبی و یادگیری ماشین در تحلیل داده‌های تابش زمینه کیهانی

Application of Neural Networks and Machine Learning in CMB data analysis

Farida Farsian

Alma Mater Studiorum – Università di Bologna

 

Abstract:  In the next decade, Primordial Gravitation Waves detection as a CMB B-mode polarization source will play an important role in leading the CMB experiments and constraining inflationary models. To reach this detection, CMB foregrounds seem to be the most challenging problem.

On the other hand, the application of Neural Networks and Machine Learning (ML) in general, as computational tools, expands exponentially in the scientific fields. With their unique computational power, these methods can become a very helpful implement in solving the computational challenges in Cosmology and specifically in the CMB field.

In this talk, at first, I will quickly review the ML methods and then introduce new applications of NNs in the CMB data analysis that we recently developed. We will see that the implemented methods gain advantages in terms of accuracy and efficiency compared to traditional methods.

یکشنبه 12 بهمن 1399، ساعت 19:00

Sunday 31 January 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

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

گزینه ورود به صورت مهمان – Enter as a Guest

Non-parametric modeling of data

Non-parametric modeling of data

Ahmad Mehrabi

Department of Physics, Bu-Ali Sina University

 

Abstract: Given a data set, one can assume a model with some free parameters and then use a parameter inference method to find the best values of parameters as well as their uncertainties.

The maximum likelihood estimator and Bayesian inference provide two important methods to infer free parameters. Fixing all parameters of a model might result in losing some features or predicting biased values in those parts in which the data set is poor. On the other hand, one might develop some non-parametric modeling to reconstruct all possible curves that are consistent with the data. In this talk, I will review some non-parametric modeling of data and then apply them to Hubble data to reconstructing the Hubble diagram. Finally, I will compare these methods and give some discussions. 

یکشنبه 5 بهمن 1399، ساعت 15:00

Sunday 24 January 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

The MOSDEF Survey

The MOSDEF Survey: Environmental dependence of the gas-phase metallicity of galaxies at 1.4≤ z ≤2.6

Nima Chartab

Department of Physics and Astronomy, University of California at Riverside

Abstract:  Using the near-IR spectroscopy of the MOSFIRE Deep Evolution Field (MOSDEF) survey, we investigate the role of the local environment in the gas-phase metallicity of galaxies. The local environment measurements are derived from accurate and uniformly calculated photometric redshifts with well-calibrated probability distributions. Based on rest-frame optical emission lines, [NII]λ6584 and Hα, we measure gas-phase oxygen abundance of 167 galaxies at 1.37≤z≤1.7 and 303 galaxies at 2.09≤z≤2.61, located in diverse environments. We find that at z∼1.5, the average metallicity of galaxies in overdensities with M∗∼10^ 9.8 M⊙,10^10.2 M⊙ and 10^10.8 M⊙ is higher relative to their field counterparts by 0.094±0.051, 0.068±0.028 and 0.052±0.043 dex, respectively.

 However, this metallicity enhancement does not exist at higher redshift, z∼2.3, where, compared to the field galaxies, we find 0.056±0.043, 0.056±0.028 and 0.096±0.034 dex lower metallicity for galaxies in overdense environments with M∗∼10^9.8M⊙,10^10.2 M⊙ and 10^10.7 M⊙, respectively. Our results suggest that, at 1.37≤ z ≤2.61, the variation of mass-metallicity relation with the local environment is small (<0.1dex), and reverses at z∼2. Our results support the hypothesis that, at the early stages of cluster formation, owing to efficient gas cooling, galaxies residing in overdensities host a higher fraction of pristine gas with prominent primordial gas accretion, which lowers their gas-phase metallicity compared to their coeval field galaxies. However, as the Universe evolves to lower redshifts (z≲2), shock-heated gas in overdensities cannot cool down efficiently, and galaxies become metal-rich rapidly due to the suppression of pristine gas inflow and re-accretion of metal-enriched outflows in overdensities.

 

یکشنبه 21 دی 1399، ساعت 19:00

Sunday 10 January 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

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

گزینه ورود به صورت مهمان – Enter as a Guest

سمینار هفتگی گروه کیهانشناسی

Measuring the stellar atmosphere parameters using follow-up polarimetry microlensing observations

Elahe Khalouei

Physics Department, Sharif University of Technology

 

Abstract:  We present an analysis of the potential follow-up polarimetry microlensing observation to study the stellar atmospheres of the distant stars. First, we produce synthetic microlensing events using the Galactic model, stellar population, and interstellar dust toward the Galactic Bulge. We simulate the polarization microlensing light curves and pass them through the instrument specifications of FOcal Reducer and low dispersion Spectrograph (FORS2) polarimeter at Very Large Telescope (VLT), and then analyze them. We find that the accuracy of the VLT telescope lets us constrain the atmosphere of cool RGB stars. Assuming detection of about 3000 microlensing events per year by the OGLE telescope, we expect to detect almost 20,~10,~8,  and 5 of polarization microlensig events for the four different criteria of being three consecutive polarimetry data points above the baseline with 1\sigma, 2\sigma, 3\sigma, and 4\sigma, respectively in the polarimetry light curves. We generalize the covariance matrix formulation and present the combination of polarimetry and photometry information that leads us to measure the scattering optical depth of the atmosphere and the inner radius of the stellar envelope of red giant stars. These two parameters could determine the dust opacity of the atmosphere of cool RGB source stars and the radius where dust can be formed.

یکشنبه 14 دی 1399، ساعت 15:00

Sunday 3 January 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

A hint from Hubble

A hint from Hubble: Does tension reveal the secrets of dark energy?

Abdolali Banihashemi

Physics Department of Shahid Beheshti University

 

Abstract: In this talk we will have a brief review on  tension and then we investigate, theoretically and observationally, a model in which dark energy emerges as a critical phenomenon.

   

یکشنبه 7 دی 1399، ساعت 15:00

Sunday 27 December 2020 – 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

Tehran Meeting on Cosmology at the Crossroads

Dear colleagues,

We are organizing the virtual “Tehran Meeting on Cosmology at the Crossroads” for 22nd-25th February 2021. In this meeting which is the third one in its series, the challenges in LCDM will be discussed. We would appreciate it if you can circulate it with those you think are interested and encourage them to participate and or have a presentation.

Best regards,

Shant Baghram on behalf of Organizers