Evidence for a merger in the peculiar virgo cluster Sa galaxy NGC 4424

We present R-band and H alpha images and H alpha long-slit spectroscopy of the peculiar Virgo cluster Sa galaxy NGC 4424. The broadband R image reveals banana-shaped isophotes, shell-like features, and other complex structure generally associated with mergers and significant accretion events. The only H alpha emission arises from a few bright H II complexes located within 500 pc of the nucleus and inside the bulge-dominated region. Although the main stellar body of NGC 4424 is highly elongated in projection, and the outer part of the galaxy has a disk-like exponential light profile, gas velocities are remarkably low in the central kpc, indicating strong non-circular motions or complex geometry for the inner gas. The peculiar properties are consistent with an intermediate mass ratio (0.1-0.5) merger making NGC 4424 one of the best cases among spiral galaxies in the nearby Virgo cluster for a significant and recent merger. The degree of morphological peculiarities suggest that the merger is recent, and we propose that the galaxy will become a small-bulge SO within similar to 1 Gyf. We discuss the possibility that the banana-shaped stellar distribution is the result of a merger-induced bending instability. (C) 1996 American Astronomical Society.