The H i Kinematics and Distribution of Four Blue Compact Dwarf Galaxies

Abstract

We present VLA H i observations of the blue compact dwarf (BCD) galaxies NGC 2366, NGC 4861, VII Zw 403, and Haro 2. These galaxies span a range of BCD morphological types. The cometary-like BCDs NGC 2366 and NGC 4861 have regular rotational kinematics with a V = of 8.7 and 6.4, respectively. On the other hand, the velocity fields of the iE BCD VII Zw 403 and of the nE BCD Haro 2 lack regularity, and their rotational motion is around the major, not the minor, axis. The H i distribution is centrally peaked in VII Zw 403 and Haro 2, a general feature of all iE and nE-type BCDs, the most common ones. In contrast, cometary-type BCDs have multiple H i peaks that are scattered over the disk. The active regions of star formation are associated with regions of high H i column densities, with slight displacements between the H i and stellar peaks. NGC 2366 shows many H i minima , resulting from the disruptive influence of massive star formation and supernovae on the interstellar medium (ISM). In NGC 2366 and NGC 4861, there is a tendency for H i gas with a higher velocity dispersion to be associated with regions of lower H i column density. This anticorrelation can be understood in the context of a two-phase model of the ISM. In all BCDs, the radio continuum emission is associated with the star-forming regions and is predominantly thermal in nature. H i clouds with no optical counterparts have been found in the vicinity of NGC 4861 and Haro 2.