Do HI Companions to HII Galaxies Have Optical Counterparts?

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Session 48 -- Spiral, Dwarf and Irregular Galaxies
Display presentation, Wednesday, 1, 1994, 9:20-6:30

[48.03] Do HI Companions to HII Galaxies Have Optical Counterparts?

C.L. Taylor, E.D. Skillman (U. Minnesota), E. Brinks (NRAO)

Taylor, Brinks \& Skillman (1993; AJ 105, 128 and 1994; BAAS 25, 1342) mapped thirty dwarf galaxies undergoing bursts of star formation (HII galaxies) in the 21--cm line with the VLA. They discovered an HI rich companion population in the vicinity of these otherwise isolated galaxies. Of the thirty HII galaxies observed, eighteen have a total of twenty-two confirmed companions and two more have unconfirmed candidate companions. Ten had no companions within the primary beam of the VLA (30$^{\prime}$) and inside the velocity range covered ($\pm$ 250 km/s of each galaxy). The high detection rate of companions near HII galaxies suggests that interactions may have a role in instigating their bursts of star formation.

Seven of the companions have high surface brightness optical counterparts, easily seen in the POSS. A further three were detected in preliminary R band CCD follow--up observations, leaving eight undetected down to a limiting surface brightness of 23 magnitudes per square arcsecond. We will present new observations of these fields, which will push our limiting surface brightness down to 26 magnitudes per square arcsecond, in an effort to determine whether or not these objects are truly intergalactic HI clouds, or are extremely low surface brightness dwarf galaxies. If it can be shown that the companions have have no stars then the study of these galaxy--massed HI clouds will yield constraints on what conditions are necessary for star formation to take place.

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