Metals often refer to any element that is heavier than Hydrogen and Helium. The main reason is that most metals cannot be produced in the Big Bang Nucleosynthesis (BBN). Normally, Metals are the products of the nucleosynthesis process in stars. However, in the field of Interstellar Medium (ISM), metallicity is always equivalent to oxygen abundance,… Continue reading Inverted Metallicity Gradient of Extreme Emission Line Galaxies (1): Review