The UK Infrared Telescope M33 monitoring project – III. Feedback from dusty stellar winds in the central square kiloparsec

Abstract

We have conducted a near-infrared monitoring campaign at the UK InfraRed\nTelescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main\naim was to identify stars in the very final stage of their evolution, and for\nwhich the luminosity is more directly related to the birth mass than the more\nnumerous less-evolved giant stars that continue to increase in luminosity. In\nthis third paper of the series, we measure the dust production and rates of\nmass loss by the pulsating Asymptotic Giant Branch (AGB) stars and red\nsupergiants. To this aim, we combined our time-averaged near-IR photometry with\nthe multi-epoch mid-IR photometry obtained with the Spitzer Space Telescope.\nThe mass-loss rates are seen to increase with increasing strength of pulsation\nand with increasing bolometric luminosity. Low-mass stars lose most of their\nmass through stellar winds, but even super-AGB stars and red supergiants lose\n$\\sim40$% of their mass via a dusty stellar wind. More than three-quarters of\nthe dust return is oxygenous. We construct a 2-D map of the mass-return rate,\nshowing a radial decline but also local enhancements due to agglomerations of\nmassive stars. We estimate a total mass-loss rate of 0.004--0.005 M$_\\odot$\nyr$^{-1}$ kpc$^{-2}$, increasing to $\\sim0.006$ M$_\\odot$ yr$^{-1}$ kpc$^{-2}$\nwhen accounting for eruptive mass loss (e.g., supernov{\\ae}); comparing this to\nthe current star formation rate of $\\sim0.03$ M$_\\odot$ yr$^{-1}$ kpc$^{-2}$ we\nconclude that star formation in the central region of M\\,33 can only be\nsustained if gas is accreted from further out in the disc or from\ncircum-galactic regions.\n