On the Elevation and Suppression of Star Formation within Galaxies

Abstract

To understand star formation in galaxies, we investigate the star formation rate (SFR) surface density (Σ SFR ) profiles for galaxies, based on a well-defined sample of 976 star-forming MaNGA galaxies. We find that the typical Σ SFR profiles within 1.5R e of normal SF galaxies can be well described by an exponential function for different stellar mass intervals, while the sSFR profile shows positive gradients, especially for more massive SF galaxies. This is due to the more pronounced central cores or bulges rather than the onset of a "quenching" process. While galaxies that lie significantly above (or below) the star formation main sequence (SFMS) show overall an elevation (or suppression) of Σ SFR at all radii, this central elevation (or suppression) is more pronounced in more massive galaxies. The degree of central enhancement and suppression is quite symmetric, suggesting that both the elevation and suppression of star formation are following the same physical processes. Furthermore, we find that the dispersion in Σ SFR within and across the population is found to be tightly correlated with the inferred gas depletion time, whether based on the stellar surface mass density or the orbital dynamical time. This suggests that we are seeing the response of a simple gas-regulator system to variations in the accretion rate. This is explored using a heuristic model that can quantitatively explain the dependence of σ(Σ SFR ) on gas depletion timescale. Variations in accretion rate are progressively more damped out in regions of low star-formation efficiency leading to a reduced amplitude of variations in star-formation.

The Variability of the Star Formation Rate in Galaxies. I. Star Formation Histories Traced by EW(Hα) and EW(HδA)

“…This further supports the idea that the narrow SFMS is indeed the result of the quasi-steady state between the inflow, outflow and star formation (e.g. Schaye et al 2010;Bouché et al 2010;Lilly et al 2013;Tacchella et al 2016;Wang et al 2019).…”

“…The dispersion of the SFR 5Myr /SFR 800Myr at a given relative galactic radius and a given stellar mass decreases with the (indirectly inferred) gas depletion time: locations with short gas depletion time appear to undergo bigger variations in their star-formation rates on Gyr or less timescales. In Wang et al (2019) we showed that the dispersion in star-formation rate surface densities Σ SFR in the galaxy population appears to be inversely correlated with the inferred gas depletion timescale and interpreted this in terms of the dynamical response of a gas-regulator system to changes in the gas inflow rate. In this paper, we can now prove directly with SFR 5Myr /SFR 800Myr that these effects are indeed due to genuine temporal variations in the SFR of individual galaxies on timescales between 10 7 and 10 9 years rather than possibly reflecting intrinsic, non-temporal, differences between different galaxies.…”

Spatially resolved star formation and fuelling in galaxy interactions

“…Ellison et al 2018a;Hani et al 2020a). Wang et al (2019) find similar results with the same survey, but using the median SFR in stellar-mass bins (rather than the rSFMS) as reference. Morselli et al (2019) report similar bifurcations out to z = 1.2 using multiwavelength Hubble Space Telescope (HST) data selected from the GOODS+CANDELS campaign.…”

Inverse stellar population age gradients of post-starburst galaxies at z = 0.8 with LEGA-C

“…By definition, these mechanisms act gradually, thereby leaving a Q galaxy with roughly the same mass and size, and the same structure as the original SF galaxy. Most SF galaxies form in an inside-out fashion (Pezzulli et al 2015;Ellison et al 2018;Wang et al 2019), leading to negative age gradients. At the same time, chemical enrichment models predict negative or flat stellar metallicity gradients (with some inversion in the centre, see Schönrich & McMillan 2017).…”