An analysis of the J-method from the perspective of the AGB evolution

Abstract

The JAGB method has been proposed as a distance indicator for Local Group galaxies. We investigate the populations of the J region in the (J-K,J) colour-magnitude plane of the Large and Small Magellanic Clouds (LMC and SMC), aiming to distinguish general features of the J luminosity function (JLF) from those sensitive to the stellar population of each galaxy. Using a population synthesis approach based on stellar evolution and dust formation modelling, we predict the distribution of stars within the J region and compare it with observations. Stars in this region are identified as recently formed C-stars that have not yet accumulated large amounts of carbon. Typically, 2--3 $M_\odot$ stars remain longer in the J region, while lower-mass stars evolve faster. The JLF of the LMC, peaked at the expected magnitudes for these stars, confirms this picture. In the SMC, the J flux distribution is shifted to higher magnitudes, indicating an older population with lower-mass progenitors.