THE ROLE OF MAJOR GAS-RICH MERGERS ON THE EVOLUTION OF GALAXIES FROM THE BLUE CLOUD TO THE RED SEQUENCE

With the aim of exploring the fast evolutionary path from the blue cloud of star-forming galaxies to the red sequence of quiescent galaxies in the local universe, we select a local advanced merging infrared luminous and ultraluminous galaxy (adv-merger (U)LIRGs) sample and perform careful dust extinction corrections to investigate their positions in the star formation rate-M-*, u-r, and NUV-r color-mass diagrams. The sample consists of 89 (U) LIRGs at the late merger stage, obtained from cross-correlating the Infrared Astronomical Satellite Point Source Catalog Redshift Survey and 1 Jy ULIRGs samples with the Sloan Digital Sky Survey DR7 database. Our results show that 74% +/- 5% of adv-merger (U) LIRGs are localized above the 1 sigma line of the local star-forming galaxy main sequence. We also find that all adv-merger (U) LIRGs are more massive than and as blue as the blue cloud galaxies after corrections for Galactic and internal dust extinctions, with 95% +/- 2% and 81% +/- 4% of them outside the blue cloud on the u-r and NUV-r color-mass diagrams, respectively. These results, combined with the short timescale for exhausting the molecular gas reservoir in adv-merger (U) LIRGs (3 x 10(7) to 3 x 10(8) years), imply that the adv-merger (U) LIRGs are likely at the starting point of the fast evolutionary track previously proposed by several groups. While the number density of adv-merger (U) LIRGs is only similar to 0.1% of the blue cloud star-forming galaxies in the local universe, this evolutionary track may play a more important role at high redshift.