Abstract: Dark matter heating of gas clouds hundreds of parsecs from the Milky Way Galactic center provides us a powerful new test of dark matter interactions. To illustrate, the leading bound on nucleon scattering for 10-100 MeV mass dark matter can be derived using this method. Furthermore, millicharged dark matter models, including those proposed to match the recent EDGES 21 cm absorption anomaly can be constrained from gas cloud’s cooling rate. For Galactic center gas clouds, galactic fields’ magnetic deflection of electromagnetically charged dark matter is mitigated, because the magnetic fields around the Galactic center are poloidal, as opposed to being aligned parallel to the Milky Way disk.
Discovery of massive star formation quenching by nonthermal effects in the center of NGC 1097
فاطمه طباطبایی (پژوهشکده نجوم پژوهشگاه دانش های بنیادی IPM )
Abstract: Observations show that massive star formation quenches first at centers of galaxies. To understand quenching mechanisms, we investigate the thermal and nonthermal energy balance in the central kpc of NGC1097- a prototypical galaxy undergoing quenching- and present a systematic study of the nuclear star formation efficiency and its dependencies. This region is dominated by the nonthermal pressure from the magnetic field, cosmic rays, and turbulence. A comparison of the mass-to-magnetic flux ratio of the molecular clouds shows that most of them are magnetically critical or supported against gravitational collapse needed to form cores of massive stars. Moreover, the star formation efficiency of the clouds drops with the magnetic field strength. Such an anti-correlation holds with neither the turbulent nor the thermal pressure. Hence, a progressive built up of the magnetic field results in high-mass stars forming inefficiently, and it may be the cause of the low-mass stellar population in the bulges of galaxies.
فرشاد کمالی نژاد (دانشکده فیزیک دانشگاه صنعتی شریف)
Abstract: Large scale structure surveys are the major probes of cosmology in the next decade. Understanding the formation of structures in an expanding universe is the key to solve many open problems in cosmology. Linear perturbation theory is successful to explain the temperature fluctuations of the CMB when the perturbations are small. These fluctuations grow larger, perturbation theory at linear order breaks and the effects of nonlinearities become dominant. These nonlinearities are well described by applying the standard perturbation theory. In this talk, I study the effects of nonlinear growth of structure on the total matter power spectrum, and in the end, I prove that we can define a “linear point” which is robust against these nonlinear effects.
بهنام جوانمردی (پژوهشکده نجوم پژوهشگاه دانش های بنیادیIPM )
Abstract: The claims of van Dokkum et al. [1] that the dark matter content of the ultra diffuse galaxy NGC1052–DF2 is much less than expected (or even consistent with zero) has triggered a lot of excitements, but also serious debates, in the field. A galaxy without dark matter can potentially be a problem for alternative scenarios and modified gravity theories. In particular, van Dokkum et al. claimed that their measured properties of the NGC1052–DF2 is inconsistent with MOND. In a recently published paper [2], we showed they were wrong. In my talk, I will tell you the story of this exciting galaxy.
