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Register a new userInflows and Outflows in the Dwarf Starburst Galaxy NGC 5253: High-Resolution HI Observations
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Added by
Henry A. (Chip) Kobulnicky
Publication date
2007
fields
Physics
and research's language is
English
Authors
Henry A. Kobulnicky
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VLA and Parkes 64 m radiotelescope 21-cm observations of the starburst dwarf galaxy NGC 5253 reveal a multi-component non-axisymmetric HI distribution. The component associated with the stellar body shows evidence for a small amount of rotational support aligned with the major axis, in agreement with optically measured kinematics and consistent with the small galaxian mass. Approximately 20-30% of the HI emission is associated with a second component, an HI plume extending along the optical minor axis to the southeast. We consider outflow, inflow, and tidal origins for this feature. Outflow appears improbable, inflow is a possibility, and tidal debris is most consistent with the observations. These observations also reveal a filamentary third component that includes an 800 pc diameter HI shell or bubble to the west of the nucleus, coinciding with an Halpha shell. The mass of HI in the shell may be as large as ~4x10^6 Msun. This large mass, coupled with the lack of expansion signatures in the neutral and ionized gas (v<30 km/s), suggests that this feature may be an example of a starburst-blown bubble stalled by interaction with a massive neutral envelope. Many other HI kinematic features closely resemble those seen in Halpha emission from the ionized gas, supporting the interpretation of neutral and ionized gas outflow at velocities of ~30 km/s. Comparison between extinction estimates from the Balmer emission-line decrement and the HI column densities suggest a gas-to-dust ratio 2-3 times the Galactic value in this low-metallicity (Z=1/4 Zsun) galaxy.
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There are few observational constraints on how the escape of ionizing photons from starburst galaxies depends on galactic parameters. Here, we report on the first major detection of an ionization cone in NGC 5253, a nearby starburst galaxy. This high-excitation feature is identified by mapping the emission-line ratios in the galaxy using [S III] lambda 9069, [S II] lambda 6716, and H_alpha narrow-band images from the Maryland-Magellan Tunable Filter at Las Campanas Observatory. The ionization cone appears optically thin, which is suggestive of the escape of ionizing photons. The cone morphology is narrow with an estimated solid angle covering just 3% of 4pi steradians, and the young, massive clusters of the nuclear starburst can easily generate the radiation required to ionize the cone. Although less likely, we cannot rule out the possibility of an obscured AGN source. An echelle spectrum along the minor axis shows complex kinematics that are consistent with outflow activity. The narrow morphology of the ionization cone supports the scenario that an orientation bias contributes to the difficulty in detecting Lyman continuum emission from starbursts and Lyman break galaxies.
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We present HI observations performed at the GMRT of the nearby dwarf galaxy NGC 1560. This Sd galaxy is well-known for a distinct wiggle in its rotation curve. Our new observations have twice the resolution of the previously published HI data. We derived the rotation curve by taking projection effects into account, and we verified the derived kinematics by creating model datacubes. This new rotation curve is similar to the previously published one: we confirm the presence of a clear wiggle. The main differences are in the innermost ~100 arcsec of the rotation curve, where we find slightly (<~ 5 km/s) higher velocities. Mass modelling of the rotation curve results in good fits using the core-dominated Burkert halo (which however does not reproduce the wiggle), bad fits using the a Navarro, Frenk & White halo, and good fits using MOND (Modified Newtonian Dynamics), which also reproduces the wiggle.
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