VII Zw 403: H I structure in a blue compact dwarf galaxy

Caroline E. Simpson, Deidre A. Hunter, Tyler E. Nordgren, E. Brinks, Bruce G. Elmegreen, Trisha Ashley, Roger Lynds, Vince J. McIntyre, Earl J. O'Neil, Goran Ostlin, David J. Westpfahl, Eric M. Wilcots

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We present optical (UBVJ), ultraviolet (FUV, NUV), and high-resolution atomic hydrogen (H I) observations of the nearby blue compact dwarf (BCD), VII Zw 403. We find that VII Zw 403 has a relatively high H I mass-to-light ratio for a BCD. The rotation velocity is nominally 10-15 km s(-1), but rises to similar to 20 km s(-1) after correction for the similar to 8-10 km s(-1) random motions present in the gas. The velocity field is complex, including a variation in the position angle of the major axis going from the northeast to the southwest parts of the galaxy. Our high-resolution Hi maps reveal structure in the central gas, including a large, low-density Hi depression or hole between the southern and northern halves of the galaxy, coincident with an unresolved X-ray source. Although interactions have been proposed as the triggering mechanism for the vigorous star formation occurring in BCDs, VII Zw 403 does not seem to have been tidally triggered by an external interaction, as we have found no nearby possible perturbers. It also does not appear to fall in the set of galaxies that exhibit a strong central mass density concentration, as its optical scale length is large in comparison to similar systems. However, there are some features that are compatible with an accretion event: optical/Hi axis misalignment, a change in position angle of the kinematic axis, and a complex velocity field.

Original languageEnglish
Article number82
Pages (from-to)-
Number of pages21
JournalThe Astronomical Journal
Issue number3
Publication statusPublished - Sept 2011


  • galaxies: individual (VII Zw 403)
  • galaxies: irregular
  • galaxies: ISM
  • galaxies: star formation


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