Journal Article

Ionized gas in the starburst core and halo of NGC 1140*

M. S. Westmoquette, J. S. Gallagher and L. de Poitiers

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 403, issue 4, pages 1719-1728
Published in print April 2010 | ISSN: 0035-8711
Published online April 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16283.x
Ionized gas in the starburst core and halo of NGC 1140*

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We present deep WIYN Hα SparsePak and DensePak spatially resolved optical spectroscopy of the dwarf irregular starburst galaxy NGC 1140. The different spatial resolutions and coverage of the two sets of observations have allowed us to investigate the properties and kinematics of the warm ionized gas within both the central regions of the galaxy and the inner halo. We find that the position angle (PA) of the Hα rotation axis for the main body of the galaxy is consistent with the H i rotation axis at PA =39°, but that the ionized gas in the central 20 × 20 arcsec2 (∼ 2 × 2 kpc2) is kinematically decoupled from the rest of the system, and rotates at a PA approximately perpendicular to that of the main body of the galaxy at +40°. We find no evidence of coherent large-scale galactic outflows. Instead, multiple narrow emission line components seen within a radius of ∼1–1.5 kpc, and high [S ii]/Hα ratios found beyond ∼2 kpc implying a strong contribution from shocks, suggest that the intense star formation is driving material outwards from the main star-forming zone in the form of a series of interacting superbubbles/shells.

A broad component [100 ≲ full width at half-maximum ≲ 230 km s−1] to the Hα line is identified throughout galaxy disc out to greater than 2 kpc. Based on recent work looking at the origins of this component, we conclude that it is produced in turbulent mixing layers on the surfaces of cool gas knots embedded within the interstellar medium, set up by the impact of the ionizing radiation and fast-flowing winds from young massive star clusters. Our data suggest a physical limit to the radius where the broad emission line component is significant, and we propose that this limit marks a significant transition point in the development of the galactic outflow, where turbulent motion becomes less dominant. This mirrors what has recently been found in another similar irregular starburst galaxy NGC 1569.

Keywords: ISM: jets and outflows; ISM: kinematics and dynamics; galaxies: individual: NGC 1140; galaxies: ISM; galaxies: starburst

Journal Article.  6229 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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