THE INTRINSIC SCATTER ALONG THE MAIN SEQUENCE OF STAR-FORMING GALAXIES AT z ∼ 0.7

A sample of 12,614 star-forming galaxies (SFGs) with stellar mass >10(9.5) M-circle dot between 0.6 < z < 0.8 from COSMOS is selected to study the intrinsic scatter of the correlation between star formation rate (SFR) and stellar mass. We derive SFR from ultraviolet (UV) and infrared (IR) luminosities. A stacking technique is adopted to measure IR emission for galaxies undetected at 24 mu m. We confirm that the slope of the mass-SFR relation is close to unity. We examine the distributions of specific SFRs (SSFRs) in four equally spaced mass bins from 10(9.5) M-circle dot to 10(11.5) M-circle dot. Different models are used to constrain the scatter of SSFR for lower mass galaxies that are mostly undetected at 24 mu m. The SFR scatter is dominated by the scatter of UV luminosity and gradually that of IR luminosity at increasing stellar mass. We derive SSFR dispersions of 0.18, 0.21, 0.26, and 0.31 dex with a typical measurement uncertainty of less than or similar to 0.01 dex for the four mass bins. Interestingly, the scatter of the mass-SFR relation seems not constant in the sense that the scatter in SSFR is smaller for SFGs of stellar mass <10(10.5) M-circle dot. If confirmed, this suggests that the physical processes governing star formation become systematically less violent for less massive galaxies. The SSFR distribution for SFGs with intermediate mass 10(10)-10(10.)5 M-circle dot is characterized by a prominent excess of intense starbursts in comparison with other mass bins. We argue that this feature reflects that both violent (e.g., major/minor mergers) and quiescent processes are important in regulating star formation in this intermediate-mass regime.