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 \epsilon < 0.23 ( at the 68 % confidence limit ) and a half-light radius of r _ { h } \simeq 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 } \lesssim 29.6 mag arcsec ^ { -2 } , and at this limit , we find no stellar bridge between Leo IV ( out to a radius of \sim 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 ( \sim 14 Gyr ) , single metallicity ( [ Fe / H ] \sim - 2.3 ) stellar population , although we can not rule out a significant spread in these value .
We derive a luminosity of M _ { V } = -5.5 \pm 0.3 .
Studying both the spatial distribution and frequency of Leo IV ’ s ’ blue plume ’ stars reveals evidence for a young ( \sim 2 Gyr ) stellar population which makes up \sim 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 ’ .