Deep Optical Imaging of the Bright Seyfert Galaxy NGC 5548: A Long, Very Low Surface Brightness Tail

Abstract

Deep Hubble Space Telescope Wide Field Camera (WFC-1) imaging of a region east of the V \ 13 3@ .7 mag Seyfert galaxy NGC 5548 in the F555W and F785LP bands, and deep ground-based V and I imaging, show a new extended, blue, low surface brightness structure, apparently a remnant of a tidal interaction associated with NGC 5548. If this straight, low surface brightness (V D 2728 mag arcsec~2) tidal tail is associated with NGC 5548, it extends at least 80 kpc from it and has an absolute magnitude of km s~1 Mpc~1). Previous imaging surveys of Seyfert galaxies would have M V B [16.4 (H 0 \ 65 missed such low surface brightness tails. Morphologically similar to some brighter tails seen in other interacting systems and in simulations of merging galaxies, this faint tail is a useful diagnostic of an earlier interaction and of the progenitors halo-to-disk mass ratios. Luminous ripples and a brighter tail wrapped around the galaxy are seen in the inner 110 kpc region. Unresolved blue objects in the long tail have the colors and absolute magnitudes of young globular clusters. Taken together, the two tails and other features suggest that two spirals merged less than B1 Gyr ago. The inner luminosity prole of NGC 5548 is a good t to a de Vaucouleurs prole with kpc. Recent simulations of merged r eff \ 5.8 galaxies with high-mass halos fail to form lasting tidal tails, suggesting that the NGC 5548 progenitor spirals had modest halo masses.