1997/09/25 by Andrew Gould, Gould, Andrew
Engineering · Physics and Astronomy · #Advanced optical system design #Calibration and Measurement Techniques #Photocathodes and Microchannel Plates #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9709263
5 pages. No figures
arxiv created 1997/09/25 · arxiv updated 2009/12/01
Zhao has proposed that the microlensing events observed toward the Large Magellanic Cloud (LMC) could be due to faint stars in a dwarf galaxy or tidal debris lying along the line of sight to the LMC. Zaritsky & Lin claim to have detected such a structure which, they believe, could account for most of the observed microlensing optical depth. Here I show that a large-area surface-brightness map made by de Vaucouleurs constrains any such structure to one of four possibilities. Either 1) it does not account for a significant fraction of the observed microlensing, 2) it covers the inner ~3 degrees of the LMC but does not extend beyond ~5 degrees from the LMC center, 3) it is smooth on scales of ~15 degrees in both transverse directions or 4) it has a stellar mass-to-light ratio which exceeds by a factor >10 that of known stellar populations. The second and third possibilities would not be expected to apply to tidal debris. The last merely rephrases the dark-matter problem in a new form.