Samaneh Sarbaz

Department of Physics, Sharif University of Technology

Frequency shift in binary lensing system

Abstract: In the gravitational microlensing phenomenon, multiple responses are obtained for the parameters of the gravitational lens. There are many ways to solve this problem. One of the recent techniques proposed is by the use of source starlight spectroscopy, in which shifts in the absorption lines of the source star can be considered as the reason for the relative motion of the lens. In this research, our objective is to study the frequency shifts in binary lenses. Therefore, after reviewing the frequency shift in single gravitational lens systems, we will study this phenomenon in binary systems.

In binary lenses, which are mainly used to detect extrasolar planets, the problem of degeneracy is causing multiple responses, and we want to use this technique to detect extrasolar planets better than before.

 یکشنبه 3 مرداد 1400، ساعت 19:00

Sunday 25 July 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

Nonlinear astrophysical probes of gravity beyond General Relativity

David F. Mota

Institute of Theoretical Astrophysics, University of Oslo

Abstract:x Extending General Relativity by adding extra degrees of freedom is a popular approach to explain the accelerated expansion of the universe and to build high energy completions of the theory of gravity. The presence of such new degrees of freedom is, however, tightly constrained from observations and experiments. The viability of a given modified theory of gravity therefore strongly depends on the existence of screening mechanisms that suppresses the extra degrees of freedom in certain scales and regimes. I describe how one can use nonlinear structure formation to probe extensions to General Relativity, and will present a set of astrophysical observables that could give smoking guns of screening mechanism.

یکشنبه 27 تیر 1400، ساعت 19:00

Sunday 18 July 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

Mohammadreza Ayromlou

Max Planck Institute for Astrophysics

Galaxy formation with L-Galaxies: galaxy evolution meets large-scale structure

Abstract: I first describe the standard theory of galaxy formation and evolution and introduce different kinds of galaxy formation modeling, including semi-analytical models and hydrodynamical simulations.

I then introduce a local background environment (LBE) estimator to quantify environment locally for all galaxies within cosmological simulations. Analyzing the LBE properties, I show that there should be no boundary for dark matter haloes when modeling galaxy evolution. I use the time-evolving LBE of galaxies to develop a method to better account for environmental processes within the Munich semi-analytical model of galaxy formation, L-Galaxies. Using this new method, I remove the artificial halo boundary and extend environmental processes to all galaxies in the simulation. I recalibrate the updated model using a Markov Chain Monte Carlo (MCMC) method and a few observational constraints. By comparing our results to data on galaxy properties in different environments from different surveys (e.g. SDSS, HSC), I demonstrate that the updated model significantly improves the agreement with the observations. Overall, in the vicinity of massive dark matter haloes, the new model produces stronger environmental dependencies, better recovering observed trends with halocentric distance up to scales much beyond the halo virial radius. This is likely to influence the correlations between galaxies up to tens of Megaparsecs. This presentation is based on the following papers: arXiv 1903.01988, 2004.14390, 2011.05336

یکشنبه 20 تیر 1400، ساعت 19:00

Sunday 11 July 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

Mahya Sadaghiani

Physikalisches Institut, Universität zu Köln

Unveiling the properties of the clusters in the NGC6334 filamentary cloud, including the physics of shocked gas and accretion

Abstract: NGC6334 is a nearby high-mass star-forming complex that has been the target of multiple studies at different wavelengths. This filamentary cloud contains several massive protoclusters at different stages of evolution which are likely pinpointing sites of high mass star formation activity. In order to investigate the kinematics of the dense gas at the scales of the clusters (<1 pc), we conducted ALMA observations towards the two high-mass protoclusters NGC6334-I and NGC6334-I(N) embedded in the filamentary star-forming complex NGC6334, as well as the gas connecting them to the large-scale filament. The observations cover the spatial scales from 1800au to 0.25 pc and are sensitive to the 3 mm continuum emission and different molecular species. The intensity maps of dense gas tracers reveal a network of filamentary structures converging at the positions of these two clusters. The analysis of the velocity fields results in similar mass accretion rates for both clusters, suggesting that they are competing for the mass reservoir in the main filament.

The ALMA continuum map at 3 mm revealed a total of 142 cores in the observed region. The compact cores are grouped in four main clusters identified by machine learning algorithms.

The typical separations (4000-12000 au) together with the core masses (0.2-100 Msun) are in agreement with turbulent fragmentation at scales of 0.1 pc. We find that the CMF of the clusters show an excess of high-mass cores compared to the IMF, which can be due to effect of temperature and the unresolved multiplicity.

The evidence of mass-segregation is found in NGC6334-I and NGC6634-I(N) with locating the massive cores close to the center.

The accretion process via the filamentary network possibly generates slow shocks due to the transport of material. On the other side, a large population of star-forming cores can produce high-velocity shocks due to the outflows. The SiO emission map obtained with ALMA is an ideal tracer of shocked gas and exhibits a complex morphology with a broad variety of line profiles and a large number of overlapping emission features towards the clusters NGC6334-I and NGC6334-I(N). As an attempt to decompose the slow shocks from the high-velocity shocks, I took advantage of spectral decomposition and wavelet analysis. The spectral decomposition separates the two types of shocks based on the width of the SiO line profile. The complex wavelet analysis isolates the slow shocks based on the probability density function (PDF) of their wavelet coefficients. The decomposition analysis reveals that 30% of the shock energetics in the region are generated in slow shocks, while for the remaining 70%, outflows are responsible. The widespread emission generated by slow shocks dominates at scales >0.1 pc.

یکشنبه 13 تیر 1400، ساعت 19:00

Sunday 4 July 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

Sara Rezaei Khoshbakht

Chalmers University of Technology, Department of Space, Earth and Environment, Gothenburg, Sweden

Max Planck Institute for Astronomy (MPIA), Heidelberg, Germany.

3D mapping of dust in the Milky Way in the Gaia era

Abstract: The unprecedented astrometry from the Gaia mission provides us with an opportunity to study the solar neighbourhood in the finest details ever possible. Extracting the wealth of information in these data remains a challenge, however. We have developed a state-of-the-art, three-dimensional dust mapping technique using the Gaussian process that provides detailed 3D maps of the Milky Way. We obtain the 3D positions of stars from Gaia, and their individual extinction using 2MASS and WISE photometry, which are then used as the input for our model. Taking into account both distance and extinction uncertainties, together with the 3D spatial correlation between neighbouring points, we produce detailed 3D maps of the local molecular clouds, revealing the 3D shapes of individual clouds for the first time.

In this talk, I will start by introducing dust and why it is an important component of the interstellar medium, followed by some of the most recent literature works in the field. Then I will introduce you to our technique and its application to mapping both the Galactic-scale structures and the local molecular clouds. I will finish by showing some of our latest results towards Orion A and California molecular clouds that solved a long-standing mystery of their contrasting star formation rates.

یکشنبه 30خرداد 1400، ساعت 19:00

Sunday 20 June 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

Matteo Viel

SISSA-International School for Advanced Studies,

INFN, Sezione di Trieste,

INAF – Osservatorio Astronomico di Trieste,

IFPU, Institute for Fundamental Physics of the Universe

Hydrogen as a tracer of cosmic structures: fundamental physics and astrophysical aspects

Abstract: I will review the use of neutral hydrogen (HI) in the post reionization era as a tracer of the structure formation process. I will focus on atomic hydrogen both in absorption (IGM) and in emission (21cm intensity mapping). IGM is a probe of HI in volume, while intensity mapping is sensitive to the HI mass distribution. This combined information is thus highly complementary. The IGM, diffuse matter between galaxies (the so-called cosmic web) allows to measure the matter perturbations down to small scales and at high redshift. In recent years, baryonic acoustic oscillations have been detected at high redshift and unprecedented tight constraints on dark matter nature and neutrino mass have also been obtained, using IGM data (mainly from low resolution BOSS and high resolution quasar spectra from HIRES/Keck). On the other hand, emission at 21cm will probe is going to be an important probe that will also probe structure formation at high redshift. The IGM and intensity mapping can be used to address fundamental physical questions like the nature of dark matter, neutrino masses, possible extension of the standard cosmological model, and offer important clues on the cosmic cycle of baryons and the galaxy/IGM interplay.

سه شنبه 11خرداد 1400، ساعت 19:00

Tuesday 1 June 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

https://www.psi.ir/farsi.asp?page=bookrelease1

Zahra Sattari

Department of Physics and Astronomy, University of California, Riverside

Evidence for Gas-phase Metal Deficiency in Massive Protocluster Galaxies at z ~2.2

Abstract: We study the mass-metallicity relation for 19 members of a spectroscopically confirmed protocluster in the COSMOS field at z=2.2 (CC2.2) and compare it with that of 24 similarly selected field galaxies at the same redshift. Both samples are Hα emitting sources, chosen from the HiZELS narrowband survey, with metallicities derived from the N2 ([NII]λ6584/Hα) line ratio. For the mass-matched samples of protocluster and field galaxies, we find that protocluster galaxies with 10^9.9 M⊙ ≤ M* ≤ 10^10.9 M⊙ are metal deficient by 0.10 ± 0.04 dex (2.5σ significance) compared to their coeval field galaxies. This metal deficiency is absent for low-mass galaxies, M* < 10^9.9 M⊙. Moreover, relying on both spectral energy distributions derived and Hα (corrected for dust extinction based on M*) star formation rates (SFRs), we find no strong environmental dependence of the SFR-M* relation; however, we are not able to rule out the existence of small dependence due to inherent uncertainties in both SFR estimators. The existence of 2.5σ significant metal deficiency for massive protocluster galaxies favors a model in which funneling of the primordial cold gas through filaments dilutes the metal content of protoclusters at high redshifts (z≳2). At these redshifts, gas reservoirs in filaments are dense enough to cool down rapidly and fall into the potential well of the protocluster to lower the gas-phase metallicity of galaxies. Moreover, part of this metal deficiency could be originated from galaxy interactions that are more prevalent in dense environments.

یکشنبه 2 خرداد 1400، ساعت 19:00

Sunday 23 May 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