Journal Article

A unique isolated dwarf spheroidal galaxy at <i>D</i> = 1.9 Mpc

Dmitry Makarov, Lidia Makarova, Margarita Sharina, Roman Uklein, Anton Tikhonov, Puragra Guhathakurta, Evan Kirby and Natalya Terekhova

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 425, issue 1, pages 709-719
Published in print September 2012 | ISSN: 0035-8711
Published online September 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21581.x
A unique isolated dwarf spheroidal galaxy at D = 1.9 Mpc

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Abstract

We present a photometric and spectroscopic study of the unique isolated nearby dwarf spheroidal (dSph) galaxy KKR 25. The galaxy was resolved into stars with Hubble Space Telescope/Wide Field Planetary Camera 2 including old red giant branch and red clump. We have constructed a model of the resolved stellar populations and measured the star formation rate and metallicity as a function of time. The main star formation activity period occurred about 12.6–13.7 Gyr ago. These stars are mostly metal poor, with a mean metallicity [Fe/H] ∼ −1 to −1.6 dex. About 60 per cent of the total stellar mass was formed during this event. There are indications of intermediate-age star formation in KKR 25 between 1 and 4 Gyr with no significant signs of metal enrichment for these stars. 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 (PN) in KKR 25. This is the first known PN in a dSph galaxy outside the Local Group. We have measured its oxygen abundance 12 + log (O/H) = 7.60 ± 0.07 dex and a radial velocity Vh = −79 km s−1. We have analysed the stellar density distribution in the galaxy body. The galaxy has an exponential surface brightness profile with a central light depression. We discuss the evolutionary status of KKR 25, which belongs to a rare class of very isolated dwarf galaxies with spheroidal morphology.

Keywords: galaxies: distances and redshifts; galaxies: dwarf; galaxies: individual: KKR 25; galaxies: stellar content

Journal Article.  8009 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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