The mass surface density in the local disk and the chemical evolution of   the Galaxy
  We have studied the effect of adopting different values of the total baryonic mass surface density in the local disk at the present time in a model for the chemical evolution of the Galaxy. We have compared our model results with the G-dwarf metallicity distribution, the amounts of gas, stars, stellar remnants, infall rate and SN rate in the solar vicinity, and with the radial abundance gradients and gas distribution in the disk. This comparison strongly suggests that the value of the total baryonic mass surface density in the local disk which best fits the observational properties should lie in the range 50-75 Msun pc-2, and that values outside this range should be ruled out. 
D. Romano (1), F. Matteucci (2,1), P. Salucci (1), C. Chiappini (3)   ((1) SISSA/ISAS, Italy, (2) Dipartimento di Astronomia...