ABSTRACT

Strong central starbursts occur most frequently in early-type disk galaxies, especially barred galaxies. We have taken U, B, R, I, and Ha images and long slit nuclear spectra of eight galaxies of type SO/SBO to Sa/SBa with bright central starbursts, selected on the basis of IRAS colors and fluxes. Four of the galaxies have circumnuclear ring-like distributions of hot stars and gas. Some or all of these four galaxies may be cases of barred galaxies with inner Lindblad resonances (ILRs), in which gas has been channelled into a ring at an ILR and compressed into star formation. Another galaxy is clearly interacting with a companion Seyfert galaxy. The strong interaction has apparently lead to the producion of the bright nuclear and near-nuclear emitting regions and the complex of fainter star-forming clumps and filaments surrounding them. Two of the remaining galaxies have compact nuclear starbursts. We conjecture that these galaxies may not have ILRs, so that gas perturbed by a bar potential or by a companion has accumulated at the nucleus instead of in a ring. The final galaxy appears to have a very bright off-center clump of star formation, conspicuous at all wavelengths. Although the possibility of a centered but dust-obscured burst is discussed, the apparent asymmetry may be real and in need of explanation.

INTRODUCTION

Strong central starbursts are occurring in a significant minority of S0 and early-type spiral galaxies. The IRAS survey data can be used reliably to find complete samples of these galaxies, since on-going bursts produce far infrared radiation that is warmer than that produced by disks.