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A unique isolated dwarf spheroidal galaxy KKR25

 Russian version

    We present a photometric and spectroscopic study of the unique isolated nearby galaxy KKR25. The isolated dwarf spheroidal (dSph) galaxy KKR25 was discovered by Karachentseva, Karachentsev & Richter (1999, A&AS, 135, 221) during the search of dwarf galaxies in the direction of the Local Void. In spite of its isolation KKR 25 has no gas and looks like a normal dwarf spheroidal system. This fact draws our attention, because we expect to find dSph galaxies in dense regions, like groups and clusters of galaxies. Obviously, that any kind of interaction with massive galaxy is not suitable to explain properties of KKR 25. This galaxy can play a crucial role in testing of different scenarios of dSph's formation.
    Long-slit spectroscopy was carried out using the Russian 6-m telescope of the integrated starlight and bright individual objects in the galaxy. We have discovered a planetary nebula in KKR25. This is the first known planetary nebula in a dwarf spheroidal galaxy outside the Local Group.
    We have constructed a model of the resolved stellar populations and measured the star formation rate and metallicity as function of time. The main star formation activity period occurred about 12.6 to 13.7 Gyr ago. About 60 per cent of the total stellar mass was formed during this event. There are indications of intermediate age star formation in KKR25 between 1 and 4 Gyr with no signficant signs of metal enrichment for these stars.
Published:
Makarov Dmitry, Makarova Lidia, Sharina Margarita, Uklein Roman, Tikhonov Anton, Guhathakurta Puragra, Kirby Evan, Terekhova Natalya 2012arXiv1206.5545M accepted to MNRAS.

Contact - Makarov D.I.

Fig.1. The map of galaxies in the SuperGalactic coordinates is centred on KKR 25. The left panel presents the projection of galaxies on the SuperGalactic plane, while the right panel shows the edge-on view on the 'pancake' of galaxies. The filled circle size is proportional to absolute magnitude of galaxies. Galaxies are coded by a colour from red for early types (T=-5) to blue for late types (T=10), according to morphological type in de Vaucouleur's numerical scale (de Vaucouleurs et al. 1991). The zero-velocity surface is shown by big blue circle around the Local Group. Distance to nearby structure is marked by dash-dotted lines with corresponding distance written on it. The brightest galaxies in the volume under consideration are Milky Way (WM), Andromeda galaxy (M31) and M81. They are signed on the figures. KK 230 is a closest galaxy to KKR 25. Three associations of dwarf galaxies (Tully et al. 2006) are shown on left panel. DDO 190 is the brightest member of 14+08 association. DDO 187 corresponds to 'Dregs' association and NGC 4214 to 14+07. The Local Void occupies the upper half of the right panel just above KKR 25.
Fig.2. HST WFPC2 image of KKR 25 in F814W band. The long slit positions are overplotted. The integrated spectrum of the stellar light was obtained in the slit position '0'. Fig.3. The colour-magnitude diagram based on HST/WFPC2 image of KKR 25. Extremely blue object 4 from our spectroscopic study is shown by open circle.