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

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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

Dear Colleagues, as you may know, a series of events are ongoing by the Astronomy Society of Iran. You can find the events on the web-page of the ASI

Please note that

* Friday   24 Ordibehesht / 14 May Professor Yousef Sobouti will be the guest of the program.

* Sunday 26 Ordibehesht / 16 May Professor Sohrab Rahvar will participate in a discussion on professional and amateur astronomy.

Also, there are two colloquiums in the Physics Departments of Tehran University and Sharif University as

*Nima Khosravi on “Cosmological tensions”- Saturday 25 Ordibehesht 1400 / 15 May 2021 @ 15:30 – UT – Please see the attachment.

*Shant Baghram on ” Cosmology’s century: Large scale structure of Dark Universe”-  Sunday 26 Ordibehesht 1400 / 16 May 2021 @ 13:30 – SUT – Please see the attachment.

Zeinab Kalantari

Department of Physics, Sharif University of Technology

Imprints of Gravitational Microlensing on the Light Curve of Gamma-Ray Bursts

Abstract: Gamma-ray bursts (GRBs) are one of the most luminous and prolific high-energy transients that have been observed since their discovery in 1963. The theoretical investigations of gravitational lensing of GRBs have been carried out in the past half-century. In this talk, I will briefly review of Gamma_Ray Bursts (GRBs) detections and GRBs progenitors. Next, I will give a general overview of gravitational microlensing and its observable signature on a GRB light curve for a point mass model of lens. Then, I will concentrate on the Autocorrelation method and its efficiency in finding microlensed candidates. Finally, I will highlight the results of our recent probe in the Fermi/GBM catalog and the estimation of the dark matter density parameter in the form of black holes in the Universe.

یکشنبه 26 اردیبهشت 1400، ساعت 15:00

Sunday 16 May 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

Martin Kunz

Department of Theoretical Physics and Center for Astroparticle Physics, University of Geneva

A brief introduction to Euclid and what we can learn from it 

Abstract: Euclid is an ESA medium class astronomy and astrophysics space mission. Euclid was selected by ESA in October 2011 and its launch is planned for 2022. Euclid will explore how the Universe evolved over the past 10 billion years to address questions related to fundamental physics and cosmology on the nature and properties of dark energy, dark matter and gravity. Euclid will also provide insightful information on the physics of the early universe and on the initial conditions which seed the formation of cosmic structure.

I will give a brief general overview of the Euclid satellite and its mission, and describe the main probes and how they observe the evolution of the Universe. Focusing particularly on dark energy models, I will then briefly review what we know now, and how Euclid will improve our knowledge.

یکشنبه 19 اردیبهشت 1400، ساعت 19:00

Sunday 9 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