Open AccessResolving the mystery of the dwarf galaxy HIZSS003
Author(s) -
Begum Ayesha,
Chengalur Jayaram N.,
Karachentsev I. D.,
Sharina M. E.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society: letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.067
H-Index - 122
eISSN - 1745-3933
pISSN - 1745-3925
DOI - 10.1111/j.1745-3933.2005.00040.x
Subject(s) - physics , astrophysics , giant metrewave radio telescope , galaxy , irregular galaxy , galaxy rotation curve , dwarf galaxy , interacting galaxy , astronomy , satellite galaxy , barred spiral galaxy , metallicity , galaxy formation and evolution , radio galaxy
The nearby galaxy HIZSS003 was recently discovered during a blind H i survey of the Zone of Avoidance. Follow‐up Very Large Array (VLA) observations as well as optical and near‐infrared imaging and spectroscopy confirm that it is a low‐metallicity dwarf irregular galaxy. However, there are two puzzling aspects of these observations: (i) current star formation, as traced by Hα emission, is confined to a small region at the edge of the VLA H i image; and (ii) the metallicity of the older red giant branch stars is higher than that of the gas in the H ii region. We present high spatial and velocity resolution Giant Metrewave Radio Telescope observations which resolve these puzzles by showing that HIZSS003 is actually a galaxy pair and that the H ii region lies at the centre of a much smaller companion galaxy (HIZSS003B) to the main galaxy (HIZSS003A). The H i emission from these two galaxies overlaps in projection, but can be separated in velocity space. HIZSS003B has an H i mass of 2.6 × 10 6 M ⊙ , and a highly disturbed velocity field. Since the velocity field is disturbed, an accurate rotation curve cannot be derived; however, the dynamical mass indicated is ∼5 × 10 7 M ⊙ . For the bigger galaxy HIZSS003A we derive an H i mass of 1.4 × 10 7 M ⊙ . The velocity field of this galaxy is quite regular, and from its rotation curve we derive a total dynamical mass of ∼6.5 × 10 8 M ⊙ .