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22/01/2018-26/01/2018

SHAO Astrophysics Colloquium

Speaker: Shiyin Shen (SHAO)

Time: Jan 25 (Thursday), 3pm

Location: Lecture hall, 3rd floor
Title: The dust along the line-of-sight to extra-galactic objects

Abstract:  All the extra-galactic objects we observed have been extincted and reddened by the inter-galactic(cosmic)  and  Galactic dust. There are  measurements of the Galactic dust from infrared emissions, while we know few about the cosmic dust. In this talk, I will introduce our statistical measurements on the Galactic and cosmic dust respectively. We probe the Galactic dust extinction and reddening from galaxy number counts and color distributions  based on the cosmological principle. While for cosmic dust, we take the advantages of the large Quasar sample of SDSS, and make a statistical  probe to redshift z~3. The implications of the cosmic dust to extra-galactic background light is further discussed.

Special Colloquium

Speaker: Hsi-Yu Schive (National Center for Supercomputing Applications, USA))

Time: Jan 22 (Monday), 3pm

Location: Lecture hall, 3rd floor
Title: Wave Dark Matter Predictions from GPU-accelerated Adaptive Mesh Refinement Simulations
Abstract: The conventional particle interpretation of cold dark matter (CDM) still lacks laboratory support and struggles to explain the basic properties of dwarf galaxies. This tension motivates wave dark matter (ψDM) composed of extremely light bosons (mψ~10-22 eV), which suppresses structure below the kpc scale by the uncertainty principle but retains the large-scale structure predicted by CDM. In the first part of this talk, I will present the first cosmological ψDM simulations that achieve an unprecedented high resolution capable of resolving dwarf galaxies. These simulations reveal that every ψDM halo has a prominent soliton core surrounded by fluctuating density granules. These predictions compare favorably with the observations of galaxy formation, the Lyman-alpha forest and reionization, and also help explain gravitational lensing flux anomalies. The second part of the talk focuses on GAMER, a GPU-accelerated adaptive mesh refinement (AMR) code. A rich set of physics modules is incorporated and which outperforms other widely-adopted AMR codes by one to two orders of magnitude. The code scales well to thousands of GPUs and achieves a uniform resolution as high as 10,2403 cells. I will present several ongoing astrophysical projects with GAMER that require substantially higher resolution than previously feasible, including turbulence cascade in galaxy cluster mergers, star formation in isolated disk galaxies, supermassive black hole accretion, and ψDM simulations.
 

Speaker: Fabo Feng (Univ. of Hertfordshire, UK)

Time: Jan 23 (Tuesday), 3pm

Location: room 1715, 17th floor

Title: Identification and exploration of a network of habitable worlds
Abstract: The past decade has seen the discovery of thousands of exoplanets, serious endeavor from Breakthrough Initialtives to launch a nano spacecraft for interstellar travel, and Gaia's precise measurements of positions and velocities for one billion stars. Based on these progresses, I simulate the motions of stars to identify a network of stellar encounters and to study their formation, evolution and interaction. From this stellar network, I identify a network of habitable worlds by detecting and characterizing Earth-like planets and studying their habitability. This habitable world network is studied numerically using network theory to explore optimal routes for interstellar travel and to solve the Fermi-Hart paradox in a robust way.

Speaker: Ke Wang (European Southern Observatory)

Time: Jan 25 (Thursday), 1:30 pm

Location: Lecture hall, 3rd floor
Title: The Dawn of Star Formation: revealing the initial conditions for massive star formation throughout the Milky Way

Abstract: Star formation sets the conditions for the formation of planets and origin of life. On large scales, massive stars drive the evolution of galaxies. The formation of massive stars is a fundamentally important yet unresolved problem in astrophysics. In particular, the initial conditions are not well known due to a lack of in-depth observations. This has led to different assumed initial conditions in debating theoretical models. Thanks to recent multi-wavelength surveys, it is finally feasible to make a Galaxy-wide census of massive clumps (precursors to high-mass star clusters) using high-resolution deep ALMA observations. I present our series studies on infrared dark clouds (IRDCs) that pioneered in characterizing the earliest stages during massive star formation. Built on these, I show how our carefully designed ALMA surveys of starless IRDCs and filaments can uncover deeply embedded core populations for robust cross comparison, and thereby can single out the truly initial conditions across the Galaxy. In the next 5-10 years, we expect that these combined efforts will give definitive answers to key questions in high-mass star formation, and motivate the next generation of star formation models.

Speaker: Kenneth Wong (National Astronomical Observatory of Japan)

Time: Jan 29 (Monday), 3pm

Location:  room 1715, 17th floor

Title: Studying the Dark Universe with Gravitational Lenses
Abstract: Strong gravitational lensing is a powerful probe of the mass distribution in the Universe.  Lensing is sensitive to the total mass distribution along the line of sight, making it a unique probe of dark matter in lensing galaxies.  However, strong lenses are quite rare and require deep wide-area imaging surveys to build up a statistical sample.  The Hyper-Suprime Cam survey is an ongoing multiband imaging survey using the Subaru Telescope that will cover 1400 deg^2 of the sky to a depth of r~26.  I present the current work of the HSC SSP strong lens working group, which is focused on searching for new lenses and leveraging these systems for studies of galaxy structure and cosmology.  The search methods and science cases being developed now for surveys such as the HSC SSP are necessary to prepare for the upcoming revolution in strong lensing from LSST and Euclid, which will discover orders of magnitude more lenses than are currently known.  Searches for lensed quasars are particularly valuable because they are variable and can be monitored to measure the "time delay" between the multiple images.  In particular, the time-delay distance from such a system is primarily sensitive to the Hubble constant (H0).  This method is independent of type Ia supernovae and CMB observations, and may shed light on the growing H0 discrepancy between local universe and CMB measurements.  I discuss the H0 Lenses In COSMOGRAIL’s Wellspring (H0LiCOW) project, which has measured H0 to ~3.8% precision for a flat Lambda CDM cosmology from three time-delay lenses. Our results are in moderate tension with the latest Planck results for a similar cosmology, hinting at possible new physics beyond the standard LCDM model and highlighting the importance of this independent probe.

Group meetings

Black hole Accretion and High-energy Astrophysics /Black Hole Feedback and Cosmic Ray Astrophysics Seminar

Location: 1608

Time: 14:00-16:00, Wednesday (Jan. 17th)

Speaker: Can Cui

Title: Polytropic transsonic galactic outflows in a dark matter halo with a central black hole

http://adsabs.harvard.edu/abs/2017MNRAS.470.2225I

Speaker: MaoChun Wu

Title: AGN jet feedback on a moving mesh:cocoon inflation, gas flows and turbulence

http://adsabs.harvard.edu/abs/2017MNRAS.472.4707B

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