The SAMI Galaxy Survey: Spatially Resolving the Main Sequence of Star Formation

TL;DR

This study uses spatially resolved star formation maps from the SAMI Galaxy Survey to analyze how star formation varies within galaxies and how it relates to galaxy type, environment, and quenching mechanisms.

Contribution

It provides the first large-scale, spatially resolved analysis of star formation across diverse galaxy types and environments, revealing insights into quenching processes.

Findings

Galaxies below the main sequence have flatter star formation profiles.

Early-type galaxies split into two populations with different star formation characteristics.

Denser environments correlate with outside-in quenching of star formation.

Abstract

We present the ~800 star formation rate maps for the SAMI Galaxy Survey based on H{\alpha} emission maps, corrected for dust attenuation via the Balmer decrement, that are included in the SAMI Public Data Release 1. We mask out spaxels contaminated by non-stellar emission using the [O III]/H{\beta}, [N II]/H{\alpha}, [S II]/H{\alpha}, and [O I]/H{\alpha} line ratios. Using these maps, we examine the global and resolved star-forming main sequences of SAMI galaxies as a function of morphology, environmental density, and stellar mass. Galaxies further below the star-forming main sequence are more likely to have flatter star formation profiles. Early-type galaxies split into two populations with similar stellar masses and central stellar mass surface densities. The main sequence population has centrally-concentrated star formation similar to late-type galaxies, while galaxies >3{\sigma} below the main sequence show significantly reduced star formation most strikingly in the nuclear regions. The split populations support a two-step quenching mechanism, wherein halo mass first cuts off the gas supply and remaining gas continues to form stars until the local stellar mass surface density can stabilize the reduced remaining fuel against further star formation. Across all morphologies, galaxies in denser environments show a decreased specific star formation rate from the outside in, supporting an environmental cause for quenching, such as ram-pressure stripping or galaxy interactions.