Tracing Star Formation Rate

1. From H$\alpha$ to SFR

• The young, massive stars emmit a large amount of UV photons, which ionize the surrounding gas and produce free eletrons.
• The H II ions recombine with free electrons and become excited hydrogen atoms.
• The excited hydrogen atoms will have a possibility to transit to the ground state and emit H$\alpha$ photons.
• If H$\alpha$ line is observed, the star formation rate (SFR) can be estimated.