Samenvatting
I Zw 18 is a prototype blue compact dwarf (BCD) galaxy, characterized by
a strong starburst and extremely low metallicity (Z ~ 0.02
Z⊙). It has long been considered a candidate young galaxy
in the Local Universe, but recent studies have found that it contains
old stars. We analysed archival VLA observations of the 21 cm line and
found that the H i associated to the starburst region forms a compact
rapidly rotating disk. The H i column densities are very high, up to
~50-100 M⊙ pc-2 (~0.6-1.2 ×
1022 atoms cm-2). The rotation curve is flat with
a steep rise in the inner parts, indicating that there is a strong
central concentration of mass. Mass models with a dark matter halo show
that baryons may dominate the gravitational potential in the inner
regions. A radial inflow/outflow motion of ~15 km s-1 is also
present. I Zw 18 appears to be structurally different from typical dwarf
irregulars in terms of its gas distribution, stellar distribution, and
dynamics. It may be considered as a "miniature" high-surface-brightness
disk galaxy. These dynamical properties must be tightly related to the
starburst. They also shed new light on the question of the descendants
of BCDs. There is also extended H i emission towards the outlying
stellar complex I Zw 18 C and a ~13.5 kpc H i tail. An
interaction/merger between gas-rich dwarfs is the most likely
explanation of the starburst.
Originele taal-2 | English |
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Artikelnummer | A72 |
Aantal pagina's | 13 |
Tijdschrift | Astronomy & Astrophysics |
Volume | 537 |
DOI's | |
Status | Published - 11-jan.-2012 |