The fourth element of galaxies

Ancient people believed that everything in the world is composed of four fundamental elements, including fire, air, earth, and water. The idea of four elements was a starting point of the successful history of modern chemistry.

Now a similar discussion is going on star-forming galaxies among astronomers. What are four fundamental parameters in galaxy?

In previous studies, three fundamental parameters were found, i.e., (i) metallicity (amount of elements heavier than Helium), (ii) stellar mass, and (iii) molecular gas mass. There three well correlate each other.

I, for the first time, found the forth fundamental parameter of star-forming galaxies based on Sloan Digital Sky Survey Data (Right figure). The forth fundamental parameter is (iv) surface density of stellar mass, which revealed the basic physics behind star formation and chemical enrichment of star-forming galaxies. This finding is also important when Gamma-Ray Burst host galaxies, i.e., galaxies where the bursts happened, are compared with normal star-forming galaxies to highlight special characteristics of the host galaxies.

This project is based on the following publication and wrtiting.

Hashimoto Tetsuya, Tomotsugu Goto, and Riseko Momose, 'Surface density: a new parameter in the fundamental metallicity relation of star-forming galaxies' , Monthly Notices of the Royal Astronomical Society, Volume 475, p.4424-4433. (2018)

Tetsuya Hashimoto, Tomotsugu Goto, Rieko Momose, 'The four fundamental parameters of star-forming galaxies' , astronomical Society of Japan, EUREKA, Oct, 2018.