Open AccessThe stellar content of the isolated transition dwarf galaxy DDO210 ★
Author(s) -
McConnachie Alan W.,
Arimoto Nobuo,
Irwin Mike,
Tolstoy Eline
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.11053.x
Subject(s) - physics , astrophysics , red giant branch , astronomy , dwarf galaxy , stars , star formation , galaxy , asymptotic giant branch , population , stellar population , metallicity , red clump , dwarf spheroidal galaxy , giant star , stellar collision , star count , horizontal branch , stellar evolution , k type main sequence star , lenticular galaxy , t tauri star , demography , sociology
We use Subaru Suprime‐Cam and VLT FORS1 photometry of the dwarf galaxy DDO210 to study the global stellar content and structural properties of a transition‐type galaxy (with properties intermediate between dwarf irregular and dwarf spheroidal systems). This galaxy is sufficiently isolated that tidal interactions are not likely to have affected its evolution in any way. The colour–magnitude diagrams of DDO210 show a red giant branch (RGB) population (with an RGB bump), a bright asymptotic giant branch population, a red clump, young main‐sequence stars and blue‐loop stars. The youngest stars formed within the last 60 Myr and have a distinct radial distribution compared to the main population. Whereas the overall stellar spatial distribution and H i spatial distribution are concentric, the young stars are offset from the centre of DDO210 and are coincident with a ‘dent’ in the H i distribution. The implied recent star formation rate required to form the young population is significantly higher than the derived current star formation rate, by a factor of >10. Most of the stars in DDO210 are found in a red clump, and its mean I ‐band magnitude suggests that the majority of stars in DDO210 have an average age of 4 +2 −1 Gyr . Given this age, the colour of the RGB implies a mean metallicity of [Fe/H]≃−1.3 . By comparing the shape of the red clump with models for a variety of star formation histories, we estimate that an old (>10 Gyr) stellar population can contribute ∼20–30 per cent of the stars in DDO210 at most. The unusual star formation history of DDO210, its low‐mass estimate and its isolated nature, provide insight into how star formation proceeds in the lowest mass, unperturbed, dwarf galaxy haloes.