科研之友
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摘要
We present deep Ha imaging of three nearby dwarf galaxies, carefully selected to optimize observations with the Maryland-Magellan Tunable Filter (MMTF) on the Magellan 6.5 m telescope. An effective bandpass of similar to 13 angstrom is used, and the images reach 3 sigma flux limits of similar to 8 x 10(-18) erg s(-1) cm(-2), which is about an order of magnitude lower than standard narrowband observations obtained by the most recent generation of local H alpha galaxy surveys. The observations were originally motivated by the finding that the H alpha/FUV flux ratio of galaxies systematically declines as global galactic properties such as the star formation rate (SFR) and stellar mass decrease. The three dwarf galaxies selected for study have SFRs that, when calculated from their H alpha luminosities using standard conversion recipes, are similar to 50% of those based on the FUV. Follow-up studies of many of the potential causes for the trends in the H alpha/FUV flux ratio have been performed, but the possibility that previous observations have missed a non-negligible fraction of faint ionized emission in dwarf galaxies has not been investigated. The MMTF observations reveal both diffuse and structured H alpha emission (filaments, shells, possible single-star H II regions) spanning extents up to 2.5 times larger relative to previous observations. However, only up to an additional similar to 5% of H alpha flux is captured, which does not account for the trends in the H alpha/FUV ratio. Beyond investigation of the H alpha/FUV ratio, the impact of the newly detected extended flux on our understanding of star formation, the properties of H II regions, and the propagation of ionizing photons warrant further investigation.
- 出版日期2016-2-1
- 单位MIT
