The SAMI Galaxy Survey: spatially resolving the main sequence of star formation

Abstract

We present the ~800 star formation rate maps for the SAMI Galaxy Survey based\non H{\\alpha} emission maps, corrected for dust attenuation via the Balmer\ndecrement, that are included in the SAMI Public Data Release 1. We mask out\nspaxels contaminated by non-stellar emission using the [O III]/H{\\beta}, [N\nII]/H{\\alpha}, [S II]/H{\\alpha}, and [O I]/H{\\alpha} line ratios. Using these\nmaps, we examine the global and resolved star-forming main sequences of SAMI\ngalaxies as a function of morphology, environmental density, and stellar mass.\nGalaxies further below the star-forming main sequence are more likely to have\nflatter star formation profiles. Early-type galaxies split into two populations\nwith similar stellar masses and central stellar mass surface densities. The\nmain sequence population has centrally-concentrated star formation similar to\nlate-type galaxies, while galaxies >3{\\sigma} below the main sequence show\nsignificantly reduced star formation most strikingly in the nuclear regions.\nThe split populations support a two-step quenching mechanism, wherein halo mass\nfirst cuts off the gas supply and remaining gas continues to form stars until\nthe local stellar mass surface density can stabilize the reduced remaining fuel\nagainst further star formation. Across all morphologies, galaxies in denser\nenvironments show a decreased specific star formation rate from the outside in,\nsupporting an environmental cause for quenching, such as ram-pressure stripping\nor galaxy interactions.\n