The Properties of Star-Forming Galaxies at z~2

We study the properties of star-forming galaxies at redshift z~2 anera in which a substantial fraction of the stellar mass in theuniverse formed. Using 114 near-IR spectra of the H-alpha and [N II]emission lines and model spectral energy distributions fit torest-frame UV through IR photometry we examine the galaxies' starformation properties dynamical masses and velocity dispersionsspatially resolved kinematics outflow properties and metallicitiesas a function of stellar mass and age. While the stellar masses ofthe galaxies in our sample vary by a factor of ~500 dynamical massesfrom H-alpha velocity dispersions and indirect estimates of gas massesimply that the variation of stellar mass is due as much to theevolution of the stellar population and the conversion of gas intostars as to intrinsic differences in the total masses of the galaxies.About 10% of the galaxies are apparently young starbursts with highgas fractions caught just as they have begun to convert large amountsof gas into stars. Using the [N II]/H-alpha ratio of compositespectra to estimate the average oxygen abundance we find a monotonicincrease in metallicity with stellar mass. From the estimated gasfractions we conclude that the observed mass-metallicity relation isprimarily driven by the increase in metallicity as gas is converted tostars. The picture that emerges is of galaxies with a broad range instellar population properties from young galaxies with ages of a fewtens of Myr stellar masses M~10^9 Msun and metallicities Z~ 1/3Zsun to massive objects with M*~10^11 Msun Z~Zsun and ages as oldas the universe allows. All however are rapidly star-forming powergalactic-scale outflows and have masses in gas and stars of at least~10^10 Msun in keeping with their likely role as the progenitors ofelliptical galaxies seen today.