科研之友
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摘要
We present MMT/Megacam imaging of the Leo IV dwarf galaxy in order to investigate its structure and star formation history, and to search for signs of association with the recently discovered Leo V satellite. Based on parameterized fits, we find that Leo IV is round, with is an element of < 0.23 (at the 68% confidence limit) and a half-light radius of r(h) similar or equal to 130 pc. Additionally, we perform a thorough search for extended structures in the plane of the sky and along the line of sight. We derive our surface brightness detection limit by implanting fake structures into our catalog with stellar populations identical to that of Leo IV. We show that we are sensitive to stream-like structures with surface brightness mu(r) less than or similar to 29.6 mag arcsec(-2), and at this limit we find no stellar bridge between Leo IV (out to a radius of similar to 0.5 kpc) and the recently discovered, nearby satellite Leo V. Using the color-magnitude fitting package StarFISH, we determine that Leo IV is consistent with a single age (similar to 14 Gyr), single metallicity ([Fe/H] similar to -2.3) stellar population, although we cannot rule out a significant spread in these values. We derive a luminosity of M(V) = -5.5 +/- 0.3. Studying both the spatial distribution and frequency of Leo IV's " blue plume" stars reveals evidence for a young (similar to 2 Gyr) stellar population which makes up similar to 2% of its stellar mass. This sprinkling of star formation, only detectable in this deep study, highlights the need for further imaging of the new Milky Way satellites along with theoretical work on the expected, detailed properties of these possible " reionization fossils."
- 出版日期2010-7-20
