Massive Lyman Break Galaxies at z~3 in the Spitzer Extragalactic First Look Survey

Abstract

We investigate the properties of 1088 Lyman Break Galaxies (LBGs) at z~3 selected from a ~2.63$deg2sub-regionoftheFirstLookSurveyfieldusingtheground-basedmulti-colordataandtheSpitzerSpaceTelescopemid-infrareddataat3--8and24um.Withthewideareaandthebroadwavelengthcoverage,wesamplealargenumberof‘‘rar{e}^{\prime \prime }u-banddropoutswhicharemassive(M\ast >10^{1}1Msun),allowingustoperformastatisticalanalysisofthesesubsetsofLBGsthathavenotbeenstudiedindetail.Opticallybright(R(AB)<24.5mag)LBGsdetectedinmid-infrared(S_{3.6um}>6uJy)resideatthemostmassiveanddustyendoftheLBGpopulation,withrelativelyhighandtight$M/L$ in rest-frame near-infrared. Most infrared-luminous LBGs (S_{24um} > 100 uJy) are dusty star-forming galaxies with star formation rates of 100--1000 Msun/yr, total infrared luminosity of > 10^12 Lsun. By constructing the UV luminosity function of massive LBGs, we estimate that the lower limit for the star formation rate density from LBGs more massive than 10^11 Msun at z~3 is > 3.3 x 10^-3 Msun/yr/Mpc^3, showing for the first time that the UV-bright population of massive galaxies alone contributes significantly to the global star formation rate density at z~3. When combined with the star formation rate densities at z < 2, our result reveals a steady increase in the contribution of massive galaxies to the global star formation from z=0 to z=3, providing strong support to the downsizing of galaxy formation.

15 pages, 13 figures. Accepted for publication in ApJ

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• High redshift galaxies in the ALHAMBRA survey: I. selection method and number counts based on redshift PDFs
• The quasar luminosity function at $z\sim 5$ via deep learning and Bayesian information criterion