Converting Halpha luminosities into SFRs

Understand

Star-formation rates (SFRs) of galaxies are commonly calculated by converting the measured Halpha luminosities (L_Halpha) into current SFRs.

• This conversion is based on a constant initial mass function (IMF) independent of the total SFR.
• As recently recognised the maximum stellar mass in a star cluster is limited by the embedded total cluster mass and, in addition, the maximum embedded star cluster mass is constrained by the current SFR.
• The combination of these two relations leads to an integrated galaxial initial stellar mass function (IGIMF, the IMF for the whole galaxy) which is steeper in the high mass regime than the constant canonical IMF, and is dependent on the SFR of the galaxy.