A Spitzer IRAC census of the asymptotic giant branch populations in local group dwarfs.: I.: WLM

We present Spitzer IRAC observations at 3.6 and 4.5 mu m along with optical data from the Local Group Galaxies Survey to investigate the evolved stellar population of the Local Group dwarf irregular galaxy WLM. These observations provide a nearly complete census of the AGB stars. We find that 39% of the infrared-detected AGB stars are not detected in the optical data, even though our 50% completeness limit is 3 mag fainter than the red giant branch tip. An additional 4% of the infrared-detected AGBs are misidentified in the optical, presumably due to reddening by circumstellar dust. We also compare our results with those of a narrowband optical carbon star survey of WLM and find the latter study sensitive to only 18% of the total AGB population. We detect objects with infrared fluxes consistent with them being mass-losing AGB stars and derive a present-day total mass-loss rate from the AGB stars of. M = (0.7-2.4); 10(-3) M-circle dot yr(-1). The distributions of mass-loss rates and bolometric luminosities of AGBs and red supergiants are very similar to those in the LMC and SMC, and the empirical maximum mass-loss rate observed in the LMC and SMC is in excellent agreement with our WLM data.