No abstract

A sample of 12 614 star-forming galaxies (SFGs) with stellar mass >10 9.5 M 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 µm. 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 to 10 11.5 M . Different models are used to constrain the scatter of SSFR for lower mass galaxies that are mostly undetected at 24 µm. 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 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 . 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 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.

Four-phase (liquid water + hydrate + liquid hydrocarbon + vapor) equilibrium data are reported for structure II hydrates of methane + cyclohexane or cyclopentane and a ternary mixture gas (methane ) 91.96 mol %, ethane ) 5.13 mol %, propane ) 2.91 mol %) + cyclohexane in the pressure range (0.165 to 9.486) MPa and the temperature range (273.83 to 301.90) K. The equilibrium pressures of the experimental systems of methane + cyclohexane or cyclopentane are concededly lower than that of the system of pure methane at a given temperature. The presence of cyclohexane inhibits hydrate formation, rather than promoting it, at higher temperatures in the test system of the ternary mixture gas + cyclohexane.