Happy New Year ! Our first Lunch Talk of 2019 will be given by Zhicheng He (何志成) at 10:40AM Thursday(Jan.3rd) in the 19th-floor Observatory Hall (天文台报告厅). The title of the talk will be “The properties of broad absorption line outflows based on a large sample of quasars”.

Dr. He is an associate research fellow of our department, and his work has been accepted to Nature Astronomy (arXiv:1812.08982) .

Here is the abstract:

Quasar outflows carry mass, momentum and energy into the surrounding environment, and have long been considered a potential key factor in regulating the growth of supermassive black holes and the evolution of their host galaxies. A crucial parameter for understanding the origin of these outflows and measuring their influence on their host galaxies is the distance (R) between the outflow gas and the galaxy center. While R has been measured in a number of individual galaxies, its distribution remains unknown. Here we report the distributions of R and the kinetic luminosities of quasars outflows, using the statistical properties of broad absorption line variability in a sample of 915 quasars from the Sloan Digital Sky Surveys. The mean and standard deviation of the distribution of R are 10^{1.4+\-0.5} parsecs. The typical outflow distance in this sample is tens of parsec, which is beyond the theoretically predicted location (0.01 ~ 0.1 parsecs) where the accretion disc line-driven wind is launched, but is smaller than the scales of most outflows that are derived using the excited state absorption lines. The typical value of the mass-flow rate is of tens to a hundred solar masses per year, or several times the accretion rate. The typical kinetic-to-bolometric luminosity ratio is a few per cent, indicating that outflows are energetic enough to influence the evolution of their host galaxies.

You are welcome to join the discussion. We will provide boxed food from the faculty canteen, and more details about signing up for boxed food are given below.

The previous reports and papers in Journal Club & Lunck Talk can be found in http://www.yulongcosmos.com/journal_club.html