سخنران: محسن شادمهری (دانشگاه گلستان)

تاریخ برگزاری رویداد: دوشنبه ۱۱ اسفند ماه ۱۳۹۹

Abstract:
The protoplanetary discs (PPDs) are known as sites of planet formation. Mass of a PPD mostly consists of gas, however, dust particles also exist with an abundance around one percent. While it was believed that magnetorotational instability (MRI) is responsible for the mass accretion in the PPDs, recent observational evidence and theoretical arguments indicate that probably wind-driven accretion is dominant at least in the inner disc region. Although this feature has raised intense investigations, a big challenge is how to propose a robust diagnostic to discriminate the dominant mechanism of the accretion in the PPDs. In this talk, I first review the major mechanisms that generate PPDs turbulence. The most recent observational diagnostics supporting the existence of efficient magnetically wind-driven accretion are discussed. We then explore the evolution of the PPDs in the presence of the magnetically driven winds and the resulting isochrones tracks in the accretion rate and disc mass plane are confronted with the observed PPDs. Evolutions of the disc quantities such as its total mass and its radius are studied for different levels of the magnetic wind strength. While previous studies based on the viscous disc model were able to obtain isochrones tracks more or less consistent with the observed PPDs, our more sophisticated disc model which incorporates magnetic winds can also give us isochrones tracks consistent with the observations. Our results thereby reinforce that role of the magnetic winds cannot be neglected in PPDs.

با حضور پروفسور کامران وفا (دانشگاه هاروارد)

تاریخ برگزاری رویداد: شنبه ۲ اسفند ماه ۱۳۹۹

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سخنران: شانت باغرام (دانشگاه صنعتی شریف، تهران)

تاریخ برگزاری رویداد: دوشنبه ۲۷ بهمن ماه ۱۳۹۹

Abstract:
Nowadays, precision cosmology is based on the standard model of LCDM. One of the main predictions of this model is the clustered web-like distribution of matter. This distribution is the result of the hierarchical structure formation based on dark matter halo mergers and accretions. In this talk, first I will discuss how the characteristics of the cosmic web, such as the distribution of the filaments and statistics of nearest neighbor can be used as cosmological probes. Then I will show how CMB lensing and the merger history of dark matter halo can be used as observational probes to distinguish cosmological models, specifically those who address the LCDM challenges.

سخنران: مرضیه فرهنگ (دانشگاه شهید بهشتی، تهران)

تاریخ برگزاری رویداد: دوشنبه ۲۲ دی ماه ۱۳۹۹

چکیده: موفقیت مدل لامبدا سی دی ام در توضیح گستره متنوعی از مشاهدات حیرت انگیز هست. اما تعدادی از مشاهدات اخیر این نظریه را به چالش کشیده اند. در این سخنرانی چالش های پیش روی لامبدا سی دی ام را مرور می کنیم و بعد به صورت مفصل تر به دو نمونه از این ناهنجاری ها می پردازیم:‌ لکه سرد در تابش زمینه کیهان و تنش هابل ابتدا به این می پردازیم که وجود یک لکه بزرگ سرد در نقشه تابش زمینه کیهان جه قدر قابل توجیه هست. آیا عوامل سرراهی می توانند این لکه را ایجاد کرده باشند و یا به نظریه ای فراتر از لامبدا سی دی ام نیاز هست؟ سپس به تنش هابل می پردازیم و به صورت خاص پیشنهاد می کنیم که یک گذار فاز گرانشی می تواند این تنش (و به صورت هم زمان چند تنش دیگر) را حل کند.

سخنران: محمد آخشیک (دانشگاه کنتیکت، آمریکا)

تاریخ برگزاری رویداد: دوشنبه ۱۵ دی ماه ۱۳۹۹

In this talk, I will first discuss the methodology behind the new code, 'requiem2d', a Bayesian framework that combines HST 2D grism spectroscopy with HST and Spitzer photometric data to constrain the spatially resolved stellar populations and measure age and star-formation rate gradients. This code is developed for the purpose of analyzing the REQUIEM^2D Galaxy Survey, a sample of 8 strongly lensed quiescent galaxies spanning redshifts of z = 1.6 − 2.9 and stellar masses of log M* = 10.4 − 11.5. After briefly reviewing the sample, I will discuss the results from our REQUIEM^2D pilot target, MRG-S0851, a gravitationally lensed quintuply imaged massive compact red galaxy at z=1.9. Using our recovered ages and SFHs from the joint spectrophotometric analysis, along with trajectories in the UVJ and FUVVJ color-color diagrams, I show that MRG-S0851 is consistent with an early forming, slow quenched galaxy that is going through a centrally-concentrated rejuvenation phase. I finally discuss that using MRG-S0851 as a prototype, ~1% of massive quiescent galaxies at 1
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