E+A Galaxies and the Formation of Early‐Type Galaxies atz ∼ 0

We present HST/WFPC2 observations of the five bluest E+A galaxies (z~0.1) inthe Zabludoff et al. sample to study whether their detailed morphologies areconsistent with late-to-early type evolution and to determine what drives thatevolution. The morphologies of four galaxies are disturbed, indicating that agalaxy-galaxy merger is at least one mechanism that leads to the E+A phase.Two-dimensional image fitting shows that the E+As are generally bulge-dominatedsystems, even though at least two E+As may have underlying disks. In theFundamental Plane, E+As stand apart from the E/S0s mainly due to their higheffective surface brightness. Fading of the young stellar population and thecorresponding increase in their effective radii will cause these galaxies tomigrate toward the locus of E/S0s. E+As have profiles qualitatively like thoseof normal power-law early-type galaxies, but have higher surface brightnesses.This result provides the first direct evidence supporting the hypothesis thatpower-law ellipticals form via gas-rich mergers. In total, at least four E+Asare morphologically consistent with early-type galaxies. We detect compactsources, possibly young star clusters, associated with the galaxies. Thesesources are much brighter (M_R ~ -13) than Galactic globular clusters, haveluminosities consistent with the brightest clusters in nearby starburstgalaxies, and have blue colors consistent with the ages estimated from the E+Agalaxy spectra (several 10^8 yr). Further study of such young star clustercandidates might provide the elusive chronometer needed to break theage/burst-strength degeneracy for these post-merger galaxies.Comment: 30 pages, 11 figures, accepted for publication in Ap