The Rest‐Frame Optical Properties ofz ≃ 3 Galaxies

We present the results of a near-infrared imaging survey of z~3 Lyman BreakGalaxies (LBGs). The survey covers a total of 30 arcmin^2 and includes 118photometrically selected LBGs with K_s band measurements, 63 of which also haveJ band measurements, and 81 of which have spectroscopic redshifts. Using thedistribution of optical {\cal R} magnitudes from previous work and {\cal R}-K_scolors for this sub-sample, we compute the rest-frame optical luminosityfunction of LBGs. At the brightest magnitudes, where it is fairly wellconstrained, this luminosity function strikingly exceeds locally determinedoptical luminosity functions. The V-band luminosity density of only theobserved bright end of the z~3 LBG luminosity function already approaches thatof all stars in the local universe. For the 81 galaxies with measuredredshifts, we investigate the range of LBG stellar populations implied by thephotometry which generally spans the range 900--5500 AA in the rest-frame.While there are only weak constraints on the parameters for most of theindividual galaxies, there are strong trends in the sample as a whole. Aunified scenario which accounts for the observed trends in bright LBGs is onein which a relatively short period of very rapid star-formation (hundreds ofM_sun/yr) lasts for roughly 50--100 Myr, after which both the extinction andstar-formation rate are considerably reduced and stars are formed at a morequiescent, but still rapid, rate for at least a few hundred Myr. In our sample,a considerable fraction (~20%) of the LBGs have best-fit star-formation ages ~>1 Gyr, implied stellar masses of ~> 10^10 M_sun, and are still forming stars at\~30 M_sun/yr.Comment: 61 pages including 19 figures. Accepted for publication in Ap