Dynamics of starbursting dwarf galaxies^⋆,⋆⋆

III. A H I study of 18 nearby objects

¹ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
e-mail: lelli@astro.rug.nl
² Department of Astronomy, Case Western Reserve University, 10090 Euclid Avenue, Cleveland, OH 44106, USA
e-mail: federico.lelli@case.edu
³ Department of Physics and Astronomy, University of Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy

Received: 12 September 2013
Accepted: 24 April 2014

Abstract

We investigate the dynamics of starbursting dwarf galaxies, using both new and archival H I  observations. We consider 18 nearby galaxies that have been resolved into single stars by HST observations, providing their star formation history and total stellar mass. We find that 9 objects have a regularly rotating H I  disk, 7 have a kinematically disturbed H I  disk, and 2 show unsettled H I  distributions. Two galaxies (NGC 5253 and UGC 6456) show a velocity gradient along the minor axis of the H I  disk, which we interpret as strong radial motions. For galaxies with a regularly rotating disk we derive rotation curves, while for galaxies with a kinematically disturbed disk, we estimate the rotation velocities in their outer parts. We derive baryonic fractions within about 3 optical scale lengths and find that, on average, baryons constitute at least 30% of the total mass. Despite the star formation having injected ~10⁵⁶ ergs in the ISM in the past ~500 Myr, these starbursting dwarfs have both baryonic and gas fractions similar to those of typical dwarf irregulars, suggesting that they did not eject a large amount of gas out of their potential wells.