SHAO Astrophysics Colloquia
Title: Probing Missing Baryons with X-ray Spectroscopy
Speaker: Wei Cui (Tsinghua & Purdue University)
Time: 3 PM, May 04th (Thursday)
Abstract:
The number of baryons produced in the Big Bang Nucleosynthesis (BBN) is fully accounted for at the redshift of about 1000, with observations and modeling of the cosmic microwave background. Most (if not all) of the BBN baryons are also found at redshifts above 2-4. In the present-day universe, however, only about half of the BBN baryons are detected, thus the global “missing baryon” problem. On smaller scales, observations have revealed that, while the measured baryon fraction of the richest clusters agrees with the cosmic average, it becomes increasingly smaller toward lower mass systems, so there is also a local “missing baryon” problem. Furthermore, about 80-90% of the metals in the universe seem to be “missing”, as far as observations are concerned. A single solution to all three problems may be that the “missing” baryons are hidden in a hot phase of IGM and/or CGM that is significantly enriched (with a metallicity of 0.2-0.3). Such gas has so far evaded observations, but may be detected through the emission or absorption lines of its highly ionized constituents at soft X-ray energies (< 1 keV). For that, an X-ray spectrometer of high throughput and high resolution would likely be required. I will describe the development of microcalorimeters for X-ray spectroscopy, and also briefly discuss the design of a satellite experiment that employs a microcalorimeter array to directly image the hot IGM/CGM. The
results would likely have significant implications on our understanding of structure formation and evolution.
Seminar talk
Title: Measuring and Modeling Variability in Quasars and Blazars
Speaker: Prof. Paul Wiita (The College of New Jersey)
Place: Middle conference room, 3rd floor, Tianwen Tower.
Time: May 3rd, 2pm (Wednesday)
Abstract: After a review of some of the key properties of quasars and blazars we will focus on the optical variability measurements made by the Kepler satellite over the past several years. These observations are unique in terms of their high cadence and nearly uninterrupted coverage over almost 4 years of a modest number of relatively bright extragalactic sources. Kepler data show that essentially red noise behavior extends over several decades in frequency. We have performed computations of the variability arising from turbulence in relativistic jets as well as some of the variations induced by changing Doppler factors produced by instabilities in propagating relativistic jets. We find that short time-scale variability can be produced by turbulence while longer time-scales could be explained in terms of bulk jet fluctuations. Combined, these models can describe an unprecedented 5 decades of temporal variability.
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(May 3rd)
Speaker: Prof. Fulai Guo
Title: Do AGN outflows quench or enhance star formation?
http://adsabs.harvard.edu/abs/2017arXiv170310782Z
Visitors
Name: Prof. Paul Wiita
Affiliation: The College of New Jersey, USA
Dates: 19/04/2017-12/05/2017
Host: Prof. Minfeng Gu
Office: 1519
