The tidal filament of NGC 4660

TL;DR

Deep imaging of NGC 4660 reveals a tidal filament indicating a recent wet merger, with evidence of star formation and possible tidal dwarf galaxy remnants, suggesting complex interaction history.

Contribution

First detection of a tidal filament around NGC 4660, providing insights into its recent merger history and star formation activity.

Findings

Discovery of a long, narrow tidal filament associated with NGC 4660.

Presence of bluer disk colors indicating recent star formation.

Identification of brighter concentrations resembling evolved tidal dwarf galaxies.

Abstract

NGC 4660, in the Virgo cluster, is a well-studied elliptical galaxy which has a strong disk component (D/T about 0.2-0.3). The central regions including the disk component have stellar populations with ages about 12-13 Gyr from SAURON studies. However we report the discovery of a long narrow tidal filament associated with the galaxy in deep co-added Schmidt plate images and deep CCD frames, implying that the galaxy has undergone a tidal interaction and merger within the last few Gyr. The relative narrowness of the filament implies a wet merger with at least one spiral galaxy involved, but the current state of the system has little evidence for this. However a 2-component photometric fit using GALFIT shows much bluer B-V colours for the disk component than for the elliptical component, which may represent a residual trace of enhanced star formation in the disk caused by the interaction 1-2 Gyr ago. There are brighter concentrations within the filament which resemble Tidal Dwarf Galaxies, although they are at least 40 times fainter. These may represent faint, evolved versions of these galaxies. A previously detected stripped satellite galaxy south of the nucleus is seen in our residual image and may imply that the filament is a tidal stream produced by perigalactic passages of this satellite.