We present a case study of the tidal interaction between low mass, star-forming, galaxies initially found exploring the Sloan Digital Sky Survey (SDSS) images and further analyzed with SDSS spectroscopy and UV GALEX photometry. With a luminosity of M
$_{r}$ = $-$17.7 mag and exhibiting a prominent tidal filament, UGC 6741 appears as a scale down version of massive gas--rich interacting systems and mergers.The stellar disk of the smaller companion, UGC 6741_B, which is three times less massive, has likely been already destroyed. Both galaxies, which are connected by a 15 kpc long stellar bridge, have a similar oxygen abundance of 12+log(O/H)$sim$8.3. Several knots of star-forming regions are identified along the bridge, some with masses exceeding $sim$10$^{7}$ M$_{sun}$. The most compact of them, which are unresolved, may evolve into globular clusters or Ultra Compact Dwarf galaxies (UCDs). This would be the first time progenitors of such objects are detected in mergers involving dwarf galaxies. UGC 6741 has currently the color and star formation properties of Blue Compact Dwarf galaxies (BCDs). However the analysis of its surface photometry suggests that the galaxy lies within the scaling relations defined by early-type dwarf galaxies (dEs). Thus UGC 6741 appears as a promising system to study the possible transformation of BCDs into dEs, through possibly a merger episode. The frequency of such dwarf-dwarf mergers should now be explored.
We present a sample of dwarf galaxies that suffer ongoing disruption by the tidal force of nearby massive galaxies. Analysing structural and stellar population properties using the archival imaging and spectroscopic data from the Sloan Digital Sky Su
rvey (SDSS), we find that they are likely a `smoking gun example of the formation of early-type dwarf galaxies (dEs) in the galaxy group environment through the tidal stirring. Inner cores of these galaxies are fairly intact and the observed light profiles are well fitted with the Sersic functions, while the tidally stretched stellar halos are prominent in the outer parts. They are all located within the 50 kpc sky-projected distance from the center of host galaxies and no dwarf galaxies have relative line-of-sight velocity larger than 205 km/s to their hosts. We derive the Composite Stellar Population (CSP) properties these galaxies by fitting the SDSS optical spectra to a multiple-burst composite stellar population model. We find that these galaxies accumulate a significant fraction of stellar mass within the last 1 Gyr, while they contain a majority stellar population of intermediate age of 2 to 4 Gyr. With these evidences, we argue that tidal stirring, particularly through the galaxy-galaxy interaction, might have an important role in the formation and evolution of dEs in the group environment, where the influence of other gas stripping mechanism might be limited.
[Abridged] Using VLT/FORS2 spectroscopy, we have studied the properties of the central stellar populations of a sample of 38 nucleated early-type dwarf (dE) galaxies in the Virgo Cluster. We find that these galaxies do not exhibit the same average st
ellar population characteristics for different morphological subclasses. The nucleated galaxies without discs are older and more metal poor than the dEs with discs . The alpha-element abundance ratio appears consistent with the solar value for both morphological types. Besides a well-defined relation of metallicity and luminosity, we also find a clear anti-correlation between age and luminosity. More specifically, there appears to be a bimodality: brighter galaxies, including the discy ones, exhibit significantly younger ages than fainter dEs. Therefore, it appears less likely that fainter and brighter dEs have experienced the same evolutionary history, as the well-established trend of decreasing average stellar age when going from the most luminous ellipticals towards low-luminosity Es and bright dEs is broken here. The older and more metal-poor dEs could have had an early termination of star formation activity, possibly being primordial galaxies in the sense that they have formed along with the protocluster or experienced very early infall. By contrast, the younger and relatively metal-rich brighter dEs, most of which have discs, might have undergone structural transformation of infalling disc galaxies.
