The distribution of star formation in the SAMI Galaxy Survey: the implications for quenching mechanisms and galaxy evolution

The distribution of the star formation across galaxy disks is examined with integral field spectroscopy to determine if the distribution varies according to the so-called 'main sequence' locus of galaxies on the plane of integrated star-formation rate and galaxy mass. Integral field spectroscopy allows the construction of radial profiles of star formation in the disks of star forming galaxies. The profiles are here used in the testing of various mechanisms that have been proposed for galaxy quenching and evolution. A goal is to determine whether processes local to each galaxy (such as a central process) or global environmental factors such as strangulation are the prime drivers of quenching. A sample of star forming galaxies from the SAMI Galaxy Survey is used, noting that only galaxies with a majority of spaxels in the central area that are star forming are suitable for construction of a radial profile. Galaxies have been classified as main sequence, above-, and below main sequence based on their location in relation to the star formation main sequence ridgeline. The radial profiles of star formation indicate that central suppression of star formation occurs in 16-20 percent of galaxies on, above or below the main sequence. The radial profiles are generally consistent with coherent star formation, whereby whatever the quenching process is that drives reduced SFR, it acts in such a way that SF remains largely coherent across the galaxy body. Coherent star formation favors several proposed quenching mechanisms including strangulation or cosmic web detachment. Central suppression is not a signature of a quenching process, but is consistent with a central process such as the compaction scenario, and cyclic central star formation. This study has been unable to distinguish between quenching from the inside out such as the 'compaction' scenario, and strangulation as a primary quenching mechanism. A weak positive correlation between bulge size and central SF radial profile slope has been detected, however the results do not support a major role of bulges in the initiation of central suppression of star formation.