سمینار این هفته را خانم غزاله عرفانیانفر از دانشگاه فنی مونیخ (Excellence Cluster Universe) ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
اثر محیط در تغییر فعالیت ستاره زایی کهکشان ها
(Environmental dependence of star forming galaxies)
Abstract: The level of star formation (SF) activity in galaxy systems is known to be suppressed relative to the field. According to the well known morphology-density relation and the star formation rate-density relation, in the local Universe high density regions, like groups and clusters, host mostly early type galaxies with lower SF level than field (mostly late-type) galaxies. The environmental dependence of galaxy SF rate may change with redshift, as galaxies in systems undergo significant evolution. Why to study groups in this context? What emerges from recent results is that the largest contribution to the the star formation rate density of the Universe is provided by rather massive galaxies (10^10 -10^11Msun). Galaxy groups host 70% of massive galaxies at least up to redshift ~1. Thus, it is likely that, if SF rate quenching happens in high density regions, those must be galaxy groups. Thus, to obtain a complete census of the group galaxy population at stellar mass larger than 10^10 Msun and of their star formation activity up to redshift ~1, we create a statistical sample of X-ray selected groups up to z~1 in the major blank fields (AEGIS, COSMOS, CDFN and ECDFS) observed also by the infrared Herschel satellite. We observe a clear evolution in the level of star formation activity in galaxy groups. The total star formation activity in high redshift groups (0.5<z<1) is higher with respect to the low redshift (0.15<z<0.5) sample at any mass by 0.8±0.12 dex. We also analyse the dependence of environments on the position of galaxies in the star formation rate (SFR) versus stellar mass diagram. We distinguish lower halo mass environments based on the local galaxy density. We find that Main Sequence (MS) of star forming galaxies is not a linear relation and there is a flattening towards higher stellar masses ( Msun > 10^10.4Msun). The flattening exists in all environmental classes. All environments have almost the same MS at high redshifts (0.5<z<1.1) while group galaxies tend to deviate from the mean MS towards the region of quiescence with respect to other environments in low redshifts (0.15<z<0.5). Our results suggest group galaxies evolve in a much faster way with respect to galaxies in lower mass halos in terms of quenching of the SF activity.
این سمینار در روز یکشنبه ۱۲ بهمن ماه ۱۳۹۳، ساعت ۱۵ در کلاس فیزیک ۴ در طبقه اول دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار این هفته را آقای علیرضا اللهیاری از دانشکده فیزیک دانشگاه صنعتی شریف ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
تصحیحات نسبیتی در تشکیل ساختار های کیهانی
(Relativistic corrections in large scale structure formation)
Abstract: In this talk I will review recent results on linear relativistic effects in galaxy clustering. To this end, the photon geodesic in an inhomogeneous universe is solved without imposing any gauge condition. Various effects that perturb the redshift space are given. These results are then used in constructing volume perturbations for galaxy number counts. Then, I will talk about gauge choice in the relativistic bias relation and corrected power spectrum. Finally, I will mention if these effects can be observed.
این سمینار در روز یکشنبه ۲۸ دی ماه ۱۳۹۳، ساعت ۱۵ در کلاس فیزیک ۴ در طبقهٔ اول دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار این هفته را خانم دکتر صدیقه سجادیان از دانشکده فیزیک دانشگاه صنعتی شریف ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
آشکارسازی لکه‌های ستاره‌ای ازطریق رصد قطبش‌سنجی از رویدادهای ریزهمگرایی گرانشی در حین گذر سوختیک
(Detecting stellar spots through polarimetry observations of microlensing events in caustic-crossing)
Abstract:
A magnetic field over the surface of a star generates convective motions which cause a temperature contrast with the source surface temperature, so-called as a stellar spot. A stellar spot over the surface of a star makes polarization signal through two channels of Zeeman effect and breaking circular symmetry of the source surface brightness due to its temperature contrast. We assume that the source star of a microlensing event has a stellar spot. In that case, lensing can magnify the polarization signal due to the spotted source, often located at the galactic bulge, and even makes it be detected. In this talk, I first explain the characteristics of spot-induced perturbations in polarimetric microlensing during caustic-crossing of a binary lensing. Then, I estimate the efficiency for detecting these anomalies and the number of detectable signals due to stellar spots through polarimetric observations during caustic-crossing of binary lensing.
این سمینار در روز یکشنبه ۲۱ دی ماه ۱۳۹۳، ساعت ۱۵ در کلاس فیزیک ۴ در طبقهٔ اول دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار این هفته را خانم آزاده مرادی نژاد دیزگاه از دانشکده فیزیک نظری دانشگاه ژنو ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
محاسبه افت خیزهای پس زمینه فرابنفش ناشی از خوشه بندی اختروش ها
(Ultraviolet background fluctuations with clustered sources)
Abstract: Modeling helium reionization is challenging since a wide range of dynamical range is needed to account simultaneously for the scarcity and clustering of the sources and the physical properties of the low density intergalactic medium. Up to now several semi-analytic approaches have been developed that combine the analytical approaches with numerical simulations. Nevertheless several issues including the contribution of the quasar clustering to the variance of helium-ionizing fluctuations towards the end of the HeII reionization are still not settled. In this talk I will describe our analytical approach to this issue, which is based on the count-in-cells formalism. We demonstrate that an exact expression can be obtained if the clustering of the ionizing sources follows the hierarchical ansatz. In this case, quasar clustering contributes less than 30% to the variance of the intensity fluctuations for attenuation length less than 55 Mpc and the correlation length below 15 Mpc.
این سمینار در روز یکشنبه ۱۴ آذر ماه ۱۳۹۳، ساعت ۱۵ در کلاس فیزیک ۴ در طبقهٔ اول دانشکدهٔ فیزیک برگزار خواهد شد.
این هفته شاهد ادامه سمینار خانم دکتر مریم توکلی از پژوهشکده نجوم پژوهشگاه دانش‌های بنیادی خواهیم بود. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
بررسی کانال های مختلف در آشکارسازی غیرمستقیم ماده تاریک(II)
(Multichannel analysis in indirect dark matter detection (Part II))
Abstract: One of the most appealing dark matter candidates is the weakly interacting massive particle (WIMP). WIMPs can be indirectly detected via searching for the products of their pair annihilation which happen today in dark matter halos. The traces of WIMP annihilation might be seen in the spectra of cosmic rays (such as positrons and antiprotons), in the spectra of photons in a broad wavelength range as well as in WIMP-induced neutrino fluxes. However, in most of these detection channels and for most viable observational targets, the WIMP contribution is, in general, rather small compared with the component induced by more standard astrophysical sources. Evaluating the astrophysical background, we perform a multichannel analysis to derive constraints on dark matter properties. The constraints are given for a generic dark matter particle and a specific dark matter candidate, Wino. For every indirect detection probe, we explore the most relevant astrophysical uncertainty influencing the strength of the derived limits to examine the robustness of those limits.
این سمینار در روز یکشنبه ۷ دی ماه ۱۳۹۳، ساعت ۱۵ در کلاس فیزیک ۴ در طبقهٔ اول دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار این هفته را آقای دکتر مهدیار نوربالا از دانشکده فیزیک دانشگاه تهران ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
اندازه: چگونه در فضا زمان بینهایت شمارش کنیم! (II)
(The Measure: How to Count in an Infinite Spacetime – (Part II
Abstract:
I will begin with some facts about de Sitter space and how it’s affected by quantum tunneling. Then I’ll talk about examples of counting in the resulting spacetime.
این سمینار در روز یکشنبه ۲۳ آذر ماه ۱۳۹۳، ساعت ۱۵ در کلاس درس فیزیک ۴ در طبقهٔ اول دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار این هفته را آقای دکتر قاسم اکسیری فرد از دانشکده علوم دانشگاه خواجه نصیرالدین طوسی ارائه خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
درباره هندسه فضا زمان ناریمانی و الگوواره (پارادایم) تاریک اخترفیزیک و کیهان‌شناسی
(On Non-Riemannian space-time geometry and dark astronomical/cosmological paradigm)
Abstract: We study dynamical deviation from the Riemann space-time geometry and search for its possible implication on observational quantities. We construct a simple model composed of two scalars two gauge fields and the metric, and only one new fundamental constant beside the Newton’s constant such that it
1) is covariant,
2) Leads to simple second order equations of motion,
3) Is free of ghosts,
4) Dynamically coincides to the Einstein-Hilbert action for strong gravity,
5) Reproduces the Tully-Fisher relation without the need to introduce dark matter,
6) Correctly reproduces the weak gravitational lensing associated to dark matter halo.
We further comment on the cosmological solutions of the model and its capacity to account for at least a part of dark-energy too.
این سمینار در روز یکشنبه ۱۶ آذر ماه ۱۳۹۳، ساعت ۱۵ در کلاس فیزیک ۴ در طبقهٔ اول دانشکدهٔ فیزیک برگزار خواهد شد.
سمینار این هفته را آقای مهدی فیروزآبای از دانشکده فیزیک دانشگاه شهید بهشتی برگزار خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
ماده تاریک از منظر ذرات بنیادی
(Dark matter prospect as a particle)
Abstract: In this talk I will represent an overall review of dark matter behavior as relic particles of early universe. I will inform you about existing signals that motivate various interaction models to provide likely candidates for dark matter and their production scenarios. The scalar triplet model (arXiv:1408.0654) will be included as a sample.
این سمینار در روز یکشنبه ۲۵ آبان ۱۳۹۳، ساعت ۱۵ در کلاس فیزیک ۴ در طبقهٔ اول دانشکدهٔ فیزیک برگزار خواهد شد.
این هفته شاهد دفاع خانم حلیمه السادات میرآقایی جعفری از رساله دکتریشان خواهیم بود. ایشان رساله خود را با راهنمایی دکتر راهوار و دکتر خسروشاهی انجام داده‌اند. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:
گرمایش محیط میان کهکشانی در گروه های کهکشانی فسیل
(IGM Heating in Fossil Galaxy Groups)
Abstract: Fossil galaxy groups, famed to have undisturbed inter-galactic gas due to lack of recent groupscale mergers, are energetically and morphologically ideal environments to study the IGMheating. In this article, we study the role of active galactic nuclei in heating the IGM in asample of five fossil galaxy groups by employing their GMRT observations at 610 MHz and1.4 GHz. We find that only two of the dominant galaxies in fossil groups are associated withthe radio lobes. We evaluate the PdV work of the radio lobes and their corresponding heatingpower and compare to the X-ray emission loss within cooling radius. Our results show thatthe power due to mechanical heating is not sufficiently high to suppress the cooling. We alsoconsidered shock and vortex heating and conduction as alternative heating sources. The 1.4GHz and 610 MHz radio luminosities of fossil groups are compared to a sample of normalgalaxy groups for the same BGGs stellar mass and total group stellar mass quantified usingthe K-band luminosity. It appears that the fossil BGGs are under luminous at 1.4 GHz and610 MHz for a given BGG stellar mass, luminosity, in comparison to a general population ofthe groups. We also explore how the bolometric radio luminosity of fossil sample dependson clusters and groups characteristics. We find that fossil groups follow the strong cool coreclusters, from HILFUGCS sample, as far as the large scale characteristics of the groups aretaken into account, consistent with the relaxed and virialized nature of fossil galaxy groups.
این سمینار در روز یکشنبه ۱۸ آبان ماه ۱۳۹۳، ساعت ۱۵ در کلاس فیزیک ۴ در طبقهٔ اول دانشکدهٔ فیزیک برگزار خواهد شد.
