A deeper look at Leo IV: Star formation history and extended structure

David J. Sand, Anil Seth, Edward W. Olszewski, Beth Willman, Dennis Zaritsky, Nitya Kallivayalil

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


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 ∈ < 0.23 (at the 68% confidence limit) and a half-light radius of rh 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 μr ≲ 29.6 mag arcsec∼2, and at this limit we find no stellar bridge between Leo IV (out to a radius of ∼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 (∼14 Gyr), single metallicity ([Fe/H] ∼ -2.3) stellar population, although we cannot rule out a significant spread in these values. We derive a luminosity of MV = -5.5 ± 0.3. Studying both the spatial distribution and frequency of Leo IV's "blue plume" stars reveals evidence for a young (∼2 Gyr) stellar population which makes up ∼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".

Original languageEnglish (US)
Pages (from-to)530-542
Number of pages13
JournalAstrophysical Journal
Issue number1
StatePublished - Jul 20 2010


  • Galaxies: dwarf
  • Local group

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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