The Spitzer  Matching Survey of the UltraVISTA Ultra-deep Stripes (SMUVS): The Evolution of Dusty and Nondusty Galaxies with Stellar Mass at z = 2–6

The Spitzer Matching Survey of the UltraVISTA Ultra-deep Stripes (SMUVS) has obtained the largest ultradeep Spitzer maps to date in a single field of the sky. We considered the sample of about 66,000 SMUVS sources at z = 2–6 to investigate the evolution of dusty and nondusty galaxies with stellar mass through the analysis of the galaxy stellar mass function (GSMF), extending previous analyses about one decade in stellar mass and up to z = 6. We further divide our nondusty galaxy sample with rest-frame optical colors to isolate red quiescent (“passive”) galaxies. At each redshift, we identify a characteristic stellar mass in the GSMF above which dusty galaxies dominate, or are at least as important as nondusty galaxies. Below that stellar mass, nondusty galaxies compose about 80% of all sources, at all redshifts except at z = 4–5. The percentage of dusty galaxies at z = 4–5 is unusually high: 30%–40% for {M}* ={10}9{--}{10}10.5 {M}ȯ and >80% at M * > 1011 M ⊙, which indicates that dust obscuration is of major importance in this cosmic period. The overall percentage of massive ({log}}10({M}* /{M}ȯ )> 10.6) galaxies that are quiescent increases with decreasing redshift, reaching >30% at z ∼ 2. Instead, the quiescent percentage among intermediate-mass galaxies (with {log}}10({M}* /{M}ȯ )=9.7{--}10.6) stays roughly constant at a ∼10% level. Our results indicate that massive and intermediate-mass galaxies clearly have different evolutionary paths in the young universe and are consistent with the scenario of galaxy downsizing.