Basic Science

New Finding on the Law of Star Formation and Regulation

A research team from the Purple Mountain Observatory, CAS, carried out a detailed analysis to examine the characteristics of the main sequence of star-forming galaxies 6 Gyr ago (z～0.7) using a large galaxy sample selected from CSOMOS survey, which contains multi-wavelength deep observations in the same sky area. Stacking technique together with physical models allow the team to quantify for the first time the distribution of star formation rate (SFR) of low-mass galaxies at the redshift examined. They found that the averaged specific SFR, i.e. the ratio of SFR over stellar mass (a measure of relative star formation intensity), is nearly identical for both high-mass and low-mass star-forming galaxies; the scatter of specific SFRs varies along the main sequence in the sense that the scatter is smaller for galaxies with lower stellar masses. This finding indicates that the physical processes regulating star formation tend to be similar in low-mass galaxies, but be more violent in massive galaxies. This is a new feature found for the so-called main sequence relationship and help to shed light on the physical mechanisms driving galaxy formation and evolution. This work was published in the Astrophysical Journal, led by PhD student Guo Kexin and her supervisor Dr. Zheng Xianzhong in collaboration with Dr. Fu Hai from the University of Iowa.

A New Breakthrough in Materials Research

Owing to the specific two-dimensional (2D) confinement of electron motion and the absence of interlayer perturbation, 2D semiconductors possess unique optoelectronic properties and have become a research hot-spot in recent years. Recently, Prof. Wang Jun at the Shanghai Institute of Optics and Fine Mechanics and his collaborators reported for the first time the outstanding ultra fast saturable absorption performance in 2D layered MoS2 nanomaterials in the near infrared wavelength band. The results have been published in American Chemical Society - Nano (ACS Nano, 7, 9260 (2013)). Realized that the sizable and thickness-dependent band gap offers the layered transition metal dichalcogenides, say, MoS2, MoSe2, WS2, etc., a huge potential in the development of photonic devices with high performance and unique functions, Dr. Wang and his co-workers successfully prepared 2D MoS2 dispersions with high-quality layered nanosheets using liquid-phase exfoliation technology, and showed that the ultra fast saturable absorption performance of the MoS2 nanosheets is more excellent than that of graphene for fs pulses in the near infrared region. The exciting results open up the door to 2D photonic nano-devices, such as optical switches, pulse shaping devices, mode-lockers, optical limiters, etc., capable of ultra fast response and broadband tunability.