NGG 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. parameters 2009), the filamentary connections between NGC 4410 A/B, C and D (Pérez-Grana et al. 2008) etc. Although such Schmidt plate/film studies have become almost obselete in modern astronomy, this discovery of the present, previously unsuspected, filament of NGC 4660 shows that they could still be put to productive uses.Here we report the discovery of the filament using the Schmidt data, and describe subsequent multiband CCD observations with the 2.1m telescope at the San Pedro Mártir Observatory, which provide colour information for this galaxy and further imaging of the -4filament. In Section 2 we provide a summary of the previous work on the galaxy NGC 4660, while in Section 3 we describe the observational data and their processing. Results of the photometry of NGC 4660 and of the filament are given in Section 4, and in Section 5 we discuss the age and the formation of the filament and give general conclusions.
Previous work on NGC 4660NGC 4660 (VCC 2000) has been studied in various ways, and has formed part of many samples of early-type galaxies over the years, on account of its proximity to us in the Virgo cluster and its incrusted disk component. It is located at RA = 12:44:32.0 Dec. = +11:11:26 (J2000), has a recessional velocity of 1083 km/s, and redshift of 0.003612 (NASA/IPAC Extragalactic Database). Although its classification in the SIMBAD database is E5, the Virgo Cluster Catalogue (Binggeli et al. 1985) gives a classification of E3/S0-1(3), which emphasises its transitionary nature.There have been a few previous photometric and structural studies of NGC 4660, though three of them have used the same observational dataset. We compare our photometric results with theirs in Section 4. Bender et al. (1988) carri...
