A New Photometric Technique for the Joint Selection of Star-forming and Passive Galaxies at 1.4 <~ z <~ 2.5

摘要: A simple two-color selection based on B-, z-, and K-band photometry is proposed for culling galaxies at 1.4 z 2.5 in K-selected samples classifying them as star-forming or passive systems. The method calibrated the highly complete spectroscopic redshift database of K20 survey, verified with simulations tested other data sets. Requiring BzK = (z - K)AB (B z)AB > -0.2 allows us to select actively 1.4, independently their dust reddening. On hand, objects colors include passively evolving often spheroidal morphologies. Simple recipes estimate reddening, star formation rates (SFRs), masses BzK-selected are derived K < 20 galaxies. These have typical stellar ~1011 M☉ sky volume densities ~1 arcmin-2 ~10-4 Mpc-3, respectively. Based UV (reddening-corrected), X-ray, radio luminosities, turn out average SFR ≈ 200 yr-1 median reddening E(B V) ~ 0.4. This a factor 10 higher than that 1 dusty extremely red objects, 3 found 2 UV-selected galaxies, both similar limits. Besides missing appears miss some relevant fraction 20, hence (obscured) density this redshift. high SFRs add existing evidence these may be among precursors 0 early-type V/Vmax test suggests such population increasing number Theoretical models cannot reproduce simultaneously space 2. In view Spitzer Space Telescope observations, an analogous technique RJL complement identify massive 4.0. By selecting well (including strongly dust-reddened ones), color criteria should help completing census mass