Star counts at high and intermediate galactic latitudes , in the visible and the near infrared , are used to determine the density law and the initial mass function of the thick disc population .
The combination of shallow fields dominated by stars at the turnoff with deep fields allows the determination of the thick disc mass function in the mass range 0.2-0.8M _ { \odot } .
Star counts are compared with simulations of a synthesis population model .
The fit is based on a maximum likelihood criterion .
The best fit model gives a scale height of 800 pc , a scale length of 2500 pc and a local density of 10 ^ { -3 } stars pc ^ { -3 } or 7.1 10 ^ { -4 } M _ { \odot } pc ^ { -3 } for Mv \leq 8 .
The IMF is found to follow a power law dN/dm \propto m ^ { -0.5 } .
This is the first determination of the thick disc mass function .