Holmberg IX: The Youngest Nearby Galaxy

Details Holmberg IX: The Youngest Nearby Galaxy Holmberg IX: The Youngest Nearby Galaxy

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21112203g&link_type=abstract

American Astronomical Society, AAS Meeting #211, #122.03; Bulletin of the American Astronomical Society, Vol. 39, p.952

Astronomy and Astrophysics

Astronomy

Scientific paper

Stellar photometry from archival Hubble Space Telescope images taken with the Advanced Camera for Surveys are used to study the star formation history of Holmberg IX (Ho IX). This dwarf irregular companion to M81 (projected distance 11 kpc) appears to be an independent entity in terms of its stellar populations, HI distribution and HI kinematics. Taking advantage of the wide field of view of the ACS, we map the positions of younger stellar populations from the main sequence and blue/red loop stars, as well as the locations of older red giants. Stars with ages of <1; Gyr are concentrated in Ho IX, while most red giants show a smooth gradient across the region. This feature, in combination with red giant colors consistent with a metal-rich population, shows that most of these older stars are in the halo of M81. We demonstrate that Ho IX contains few if any red giants; the majority of its stars have ages of <200; Myr, consistent with them being associated with the last close encounter between M81 and its companions 200-300 Myr in the past. The star formation history of Ho IX is consistent with it being a tidal dwarf galaxy that formed due to interactions in the M81 group.

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