Two currently debated problems in galaxy evolution, the fundamentally local or global nature of the main sequence of star formation and the evolution of the mass-size relation of star forming galaxies (SFGs), are shown to be intimately related to each other. As a preliminary step, a growth function g is defined, which quantifies the differential change in half-mass radius per unit increase in stellar mass (g = dlogR1\/2\/dlogM) due to star formation. A general derivation shows that g = K(sSFR)\/sSFR, meaning that g is proportional to the relative difference in specific star formation rate between the outer and inner half of a galaxy, with K a dimensionless structural factor for which handy expressions are provided. As an application, it is shown that galaxies obeying a fundamentally local main sequence also obey, to a good approximation, g n, where is the slope of the normalized local main sequence (|$sSFR ,, propto ,, Sigma _star ^{-gamma }$|) and n the Sersic index. An exact expression is also provided. Quantitatively, a fundamentally local main sequence is consistent with SFGs growing along a stationary mass-size relation, but inconsistent with the continuation at z = 0 of evolutionary laws derived at higher z. This demonstrates that either the main sequence is not fundamentally local, or the mass-size relation of SFGs has converged to an equilibrium state some finite time in the past, or both.<\/p>\n
The Author(s) 2021. Published by Oxford University Press on behalf of Royal Astronomical Society.<\/p>\n
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Implications of a spatially resolved main sequence for the size evolution of star forming galaxies - Oxford Academic<\/a><\/p>\n","protected":false},"excerpt":{"rendered":" Two currently debated problems in galaxy evolution, the fundamentally local or global nature of the main sequence of star formation and the evolution of the mass-size relation of star forming galaxies (SFGs), are shown to be intimately related to each other. As a preliminary step, a growth function g is defined, which quantifies the differential change in half-mass radius per unit increase in stellar mass (g = dlogR1\/2\/dlogM) due to star formation Continue reading