سمینار این هفته را خانم نجمه شیخی از دانشکده فیزیک دنشگاه تحصیلات تکمیلی علوم پایه زنجان ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
کسر دوتایی ها و تفکیک جرمی در خوشه ی باز آلفا برساووش
The binary fraction and mass segregation in Alpha Persei open cluster
Abstract: We have obtained membership probabilities of stars within a field of :3ofrom the center of the open cluster Alpha Persei using proper motions and photometry from the PPMXL and Wide-field Infrared Survey Explorer catalogues. We have identified 810 possible stellar members of Alpha Persei. We derived the global and radial present day mass function of the cluster and found that they are well matched by two stage power law relations with different slopes at different radii. The global MF of Alpha Persei shows a turnover at 0.62Me with low and high mass slopes of αlow =0.50 ±0.09 and αhigh = 2.23 ±0.14, respectively. The high mass slope of the cluster increases from 2.01 inside 1o.10 to 2.63 outside 2o .2, whereas the mean stellar mass decreases from 0.95 to 0.57Mein the same regions, signifying clear evidence of mass segregation in the cluster. From performing a series of Monte Carlo simulations, we obtained a binary fraction of fbin= 34±12 per cent for stars with 0.70<m/Me<4.68. This is significantly larger than the observed binary fraction, indicating that this open cluster contains a large population of unresolved binaries. Finally, we corrected the MF slopes for the effect of unresolved binaries and found low and high mass slopes of αlow= 0.89 ± 0.11 and αhigh = 2.37 ± 0.09 and a total cluster mass of 352Me for Alpha Persei.
این سمینار در روز یکشنبه ۲۵ بهمن ۱۳۹۴، ساعت ۱۵ در اتاق ۵۱۷ در طبقهٔ پنجم دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار این هفته را آقای فربد حسنی از دانشکده فیزیک دانشگاه صنعتی شریف ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
Lensing as a probe of early universe physics
Abstract: The standard cosmological model ΛCDM describes the large-scale structure and early universe greatly well. However some hints of departures from ΛCDM exist in the present cosmological data in large scales as well as small scales. Of these, significant attention has been paid to various “anomalies” in measurements of the cosmic microwave background radiation. Observations of Planck collaboration indicate the persistence of the dipole modulation in the primordial power spectrum which first seen in WMAP data and it is found with local variance estimator. In the case, if the anomalies are not the statistical flukes It is worthwhile considering whether observations other than CMB might be able to address this question. In our recent work arXiv:1511.05534, we propose that the CMB lensing and also CMB lensing cross-correlation with galaxy lensing can be used as a unique probe for detection of these anomalies especially dipole modulation and constraining on their scale dependence.
In the first part of my talk I will review the CMB lensing and galaxy lensing theories. Then I will show how these observations would help us to probe the early universe physics.
این سمینار در روز یکشنبه ۱۸ بهمن ماه ۱۳۹۴، ساعت ۱۵ در اتاق ۵۱۷ در طبقهٔ پنجم دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار امروز را خانم فاطمه باقری از دانشکده فیزیک دانشگاه شریف و آقای امیر ملازاده از دانشکده فیزیک دانشگاه خوارزمی ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
Seminar 1: Too Big To Fail?
Seminar 2: Degeneracy between bias and Dark energy equation of state, is weak lensing a solution?
Seminar 1- Abstract: Over and over again, new observations come in that match the predictions of ΛCDM. But there are still a few anomalies that bug us, especially on relatively small (galaxy-sized) scales. One such anomaly is the “too big to fail” problem. In this talk, first, I will explain what this problem exactly is and then I will briefly review some solutions have been found to explain it so far.
Seminar 2-Abstract: The nature and the properties of Dark Energy are among the most significant unsolved problems in physics. We now know that Dark Energy accounts for about 70% of the energy density of the Universe and is causing the cosmic expansion to accelerate. But there exist only very few observational windows into the properties of this phenomenon. Measurements of the Integrated Sachs-Wolfe effect (ISW) provide a powerful method to probe Dark Energy, as this effect is sensitive to the time evolution of the gravitational potential sourced by Large Scale Structure. One interesting feature of several of the previous studies is that the cross correlation signal lies above the predicted value in the standard cosmological model (in which the Dark Energy is a Cosmological Constant). We could show a dark energy with redshift dependent equation of state ( w_0 + w_a*(1/(1+z)) ) is a good fit to data, but if we change our assumption about a “constant bias” and use a redshift dependent bias LambdaCDM is still a good fit too! Here is the question: Redshift dependent bias or varying with time equation of state. We think weak lensing can break this degeneracy!
این سمینار امروز یکشنبه ۱۱ بهمن ماه ۱۳۹۴، ساعت ۱۵ در اتاق ۵۱۷ در طبقه پنجم دانشکدهٔ فیزیک برگزار خواهد شد.
سمینارهای این هفته را آقایان نیما چرتاب و محمدرضا ایرملو از دانشکده فیزیک دانشگاه صنعتی شریف ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
Seminar 1: The Effective Field Theory of Cosmological Large Scale Structures
Seminar 2: Halo Merger Trees and Halo Assembly Time
Seminar 1- Abstract: Over the next decade, large scale structure (LSS) surveys will play an increasingly important role in the measurement of cosmological parameters and as a probe of initial conditions. The Effective Field Theory of LSS is an efficient approach to make precise analytical predictions on large scale structures. In this talk, I will explain how all of the complicated dynamics at the scales of galaxies and clusters could affect large scale matter perturbations. After reviewing the recently developed effective field theory of large scale structure, I will compare the matter power spectrum measured from the simulations with theoretical models (e.g. EFT of LSS and Halo Model).
Seminar 2-Abstract: A powerful method for computing the mass function of dark matter halos is provided by Excursion Set Theory (EST), where density perturbations evolve stochastically with the smoothing scale, and the problem of computing the probability of halo formation is mapped into the so-called first passage time problem in the presence of a barrier. While the full dynamical complexity of halo formation can only be revealed through N-body simulations, Excursion Set Theory provides a simple analytic framework for understanding various aspects of this complex process. With EST one can calculate Progenitor Mass Function, Plant Halo Merger Trees, Find Halo Assembly Time, Calculate the Bias and lots of other things. In this talk I will present some methods of Halo Merger Trees, Halo Assembly Time and Bias.
این سمینارها در روز یکشنبه ۲۷ دی ماه ۱۳۹۴، ساعت ۱۵ در کلاس فیزیک ۴ در طبقهٔ اول دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار این هفته را آقای علیرضا مولایی نژاد از پژوهشکده نجوم پژوهشگاه دانش‌های بنیادی (IPM) ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
Understanding the nature of Barred galaxies: From morphology to dynamics
Abstract: Barred galaxies represent a considerable fraction of the entire disc galaxy population. Bars could be considered as the key drivers of the internal secular evolution in disc galaxies by redistribution of the angular momentum and triggering of star formation, or changing the morphological structure of disk galaxies. In edge-on or highly inclined systems, bars are most easily recognized by boxy and peanut-shapes, and sometimes X-shape morphology formed by the stellar material above the disc plane. BP bulges specifically and bars in general produce distinct kinematic features that can be easily detected in galaxies. I will present our recent results of the study on the stellar kinematics and populations of a sample of intermediate inclined disk galaxies, obtained with the SAURON integral-field spectrograph on the 4.2m William Herschel Telescope. I will also discuss our approach to unveil hidden bars and inner disks on the basis of their kinematics and introduce a method to quantify the cylindrical rotation, as a common kinematics feature of barred galaxies. The results of this study allow us to establish the link between the stellar kinematics and populations of bulges and bars with their surrounding thin and thick disks, and relate them to the properties observed in disk galaxies.
این سمینار در روز یکشنبه ۲۰ دی ماه ۱۳۹۴، ساعت ۱۵ در کلاس فیزیک ۴ در طبقهٔ اول دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار فوق العاده این هفته را آقای بهنام جوانمردی از دانشکده نجوم دانشگاه بن ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
Finding dwarf galaxies with small telescopes
Abstract: In the framework of the standard model of cosmology, galaxies form in a hierarchical process. In this scenario, many substructures (or satellites) are expected to exist around massive (Milky Way-like) galaxies. The number, spatial distribution, and other properties of these satellite galaxies can be used to test different models of structure formation. Therefore, increasing the number of known dwarf satellite galaxies outside the Local Group is very crucial. We recently launched the Dwarf Galaxy Survey with Amateur Telescopes (DGSAT) project to use the ability of small telescopes for finding low surface brightness galaxies. In this talk, I will briefly highlight the importance of finding dwarf satellite galaxies and will present the first results of the DGSAT project (http://arxiv.org/abs/1511.04446) which is the discovery of 11 low surface brightness systems in the field of 6 nearby spiral galaxies.
این سمینار در روز شنبه ۱۲ دی ماه ۱۳۹۴، ساعت ۱۱ در اتاق ۵۱۷ در طبقهٔ پنجم دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار این هفته را آقای دکتر شهرام خسروی از دانشکده فیزیک دانشگاه خوارزمی ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
Dark Energy at Large Scales: Homogeneous or What?
Abstract: The Integrated Sachs Wolfe (ISW) cross correlation with the galaxy distribution in late time is a promising tool to constrain the dark energy properties. In this work we study the effect of dark energy clustering on the ISW-galaxy cross correlation. Indicating the fact that the bias parameter between the distribution of the galaxies and the underlying dark matter introduce a degeneracy and complications. We argue that as the time of the galaxy’s host halo formation is different from the observation time, we have to consider the evolution of the halo bias parameter. We indicate that any deviation from ΛCDM model will change the evolution of the bias as well. Also we show that the halo bias strongly depends on the sub-sample of galaxies which is chosen for cross correlation. We show that joint kernel of ISW effect and the galaxy distribution have the dominant effect on the observed signal, accordingly we can enhance the signal of a specific dark energy model by choosing an appropriate tracer. More specifically we compare the clustered dark energy models with two samples of galaxies. First is a sub-sample of galaxies from Sloan Digital chosen with the r-band magnitude 18<r<21 with a host dark matter halos of mass M∼1012M⊙ and formation redshift of z∼2.5. Secondly with the sub-sample of Luminous Red galaxies with a host dark matter halos of mass M∼1013M⊙ and formation redshift of z∼2.0. Using the evolved bias we improve the χ2 for the ΛCDM which it reconcile the ∼1-2σ tension of the ISW-galaxy signal and ΛCDM prediction. Finally we show how sub-samples change the bias parameter and will improve the constrains on dark energy clustering.
این سمینار در روز یکشنبه ۶ دی ماه ۱۳۹۴، ساعت ۱۵ در کلاس فیزیک ۴ در طبقه اول دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار مشترک ذرات و کیهانشناسی این هفته را آقای دکتر روح الله محمدی از موزه علوم و فناوری ایران ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
The generation of CMB B-mode polarization due to Compton scattering and any new interaction such as CMB -CNB interactions
Abstract: By approximately solving the first order of Quantum Boltzmann Equation for the density matrix of a photon ensemble, and time-evolution of Stokes parameters, we briefly show that how to add any new interaction in right side of Boltzmann equation. The magnetic-type of linear polarization, B-mode polarization, for the Cosmic Microwave Background cannot be generated by Compton scattering in the case of scalar mode of matter perturbations but this is possible to have B-mode in framework of the Compton scattering in the case of tensor mode of matter perturbations. For this reason, the ratio of tensor to scalar mode of matter perturbation, r-parameter, is estimated (at least for small $l$) by comparing the B-mode power spectrum with E-mode one $r\sim C_l^{BB}/C_l^{EE}$. We study the polarization of CMB specially B-mode polarization due to the weak interactions of Cosmic Neutrino Background (CNB) and CMB in additional to Compton scattering in both cases of scalar and tensor metric perturbations. In this framework, we show that B-mode polarization power spectrum $C_l^{BB}$ receives some contributions from the scalar and tensor modes which have significant effects on the value of r-parameter and also we show that B-mode polarization power spectrum can be used as indirectly detector for CNB which is very difficult to detect by using usual neutrino detectors.
این سمینار در روز سه شنبه ۱ دی ماه ۱۳۹۴، ساعت ۱۵ در تالار جناب (آمفی‌تئاتر دانشکده فیزیک) در زیرزمین دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار این هفته را خانم دکتر اکرم حسنی زنوز از دانشکده فیزیک دانشگاه تحصیلات تکمیلی علوم پایه زنجان ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
The Sizes of Globular Clusters as Tracers of Galactic Halo Potentials
Abstract: We present $N$-body simulations of globular clusters, exploring the effect of different galactic potentials on cluster sizes, $r_h$. For various galactocentric distances, $R_G$, we assess how cluster sizes change when we vary the virial mass and concentration of the host galaxy’s dark-matter halo. We show that sizes of GCs are determined by the local galactic mass density rather than the virial mass of the host galaxy. We find that clusters evolving in the inner haloes of less concentrated galaxies are significantly more extended than those evolving in more concentrated ones, while the sizes of those orbiting in the outer halo are almost independent of concentration. Adding a baryonic component to our galaxy models does not change these results much, since its effect is only significant in the very inner halo. Our simulations suggest that there is a relation between $r_h$ and $R_G$, which systematically depends on the physical parameters of the halo. Hence, observing such relations in individual galaxies can put a new observational constraint on dark-matter halo characteristics. However, by varying the halo mass in a wide range of $10^{9}\leq M_{vir}/\msun \leq10^{13}$, we find that the $r_h-R_G$ relationship will be nearly independent of halo mass, if one assumes $M_{vir}$ and $c_{vir}$ as two correlated parameters, as is suggested by cosmological simulations.
این سمینار در روز یکشنبه ۲۲ آذر ماه ۱۳۹۴، ساعت ۱۵ در کلاس فیزیک ۴ در طبقه اول دانشکدهٔ فیزیک برگزار خواهد شد.
