A Tidally-Stripped Stellar Component of the Magellanic Bridge [GA]


Deep photometry of the Small Magellanic Cloud (SMC) stellar periphery (R=4 deg, 4.2 kpc) is used to study its line-of-sight depth with red clump (RC) stars. The RC luminosity function is affected little by young (<1 Gyr) blue-loop stars in these regions because their main-sequence counterparts are not observed in the color magnitude diagrams. The SMC’s eastern side is found to have a large line-of-sight depth (~23 kpc) while the western side has a much shallower depth (~10 kpc), consistent with previous photographic plate photometry results. We use a model SMC RC luminosity function to deconvolve the observed RC magnitudes and construct the density function in distance for our fields. Three of the eastern fields show a distance bimodality with one component at the “systemic” ~67 kpc SMC distance and a second component at ~55 kpc. Our data are not reproduced well by the various extant Magellanic Cloud and Stream simulations. However, the models predict that the known HI Magellanic Bridge (stretching from the SMC eastward towards the LMC) has a decreasing distance with angle from the SMC and should be seen in both the gaseous and stellar components. From comparison with these models we conclude that the most likely explanation for our newly identified ~55 kpc stellar structure in the eastern SMC is a stellar counterpart of the HI Magellanic Bridge that was tidally stripped from the SMC ~200 Myr ago during a close encounter with the LMC. This discovery has important implications for microlensing surveys of the SMC.

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Date added: Mon, 21 Oct 13