The HI Kinematics and Distribution of Four Blue Compact Dwarf Galaxies

Thuan, T. X. (UVa), Hibbard, J. E. (NRAO), & Levrier, F. (UVa & Ecole Normale Supérieure ), 2004, The Astronomical Journal, 128, 617 (pdf 3.2MB) (ADS)

We present VLA HI 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/sigma 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 HI 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. By contrast, cometary-type BCDs have multiple HI peaks which are scattered over the disk. The active regions of star formation are associated with regions of high HI column densities, with slight displacements between the HI and stellar peaks. NGC 2366 shows many HI holes, resulting from the disruptive influence of massive star formation and supernovae on the interstellar medium (ISM). In all BCDs, there is a tendency for HI gas with higher velocity dispersion to be associated with regions of lower HI column density. This anti-correlation 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. HI clouds with no optical counterparts have been found in the vicinity of NGC 4861 and Haro 2.

RIGHT: False color of integrated HI intensity of the four systems studied.

 The following list provides links to the color images for each of the systems (figures published in b/w).
Mosaics are 6-panel representations of the data, arranged in the following order:
Top Left: Digitized Sky Survey (DSS) with a deep stretch to show the extent of the galaxy.
Top Right: Digitized Sky Survey with a shallow stretch to show the star-forming regions.
Middle Left: Lower resolution total HI in contours over the DSS in greyscale.
Middle Right: Lower resolution total HI, but in greyscale.
Bottom Left: Higher resolution HI velocity field, in both contours and greyscale.
Bottom Right: Higher resolution HI velocity dispersion in greyscale, with total HI in contours.
are a blow-up of the area around the most active starforming regions in each system,
Left: High-resolution Radio continuum contours on Optical CCD image in false color.
Middle: High-resolution integrated HI contours on Optical CCD image in false color.
Right: High-resolution integrated HI contours on HI velocity dispersion false color
Channel Maps
are channel maps.

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Last modified: Fri Jul 30 17:37:04 EDT 2004