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Astron. Astrophys. 352, 363-370 (1999)


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The Sagittarius dwarf irregular galaxy (SagDIG): distance and star formation history *

I. Karachentsev 1, A. Aparicio 2 and L. Makarova 1

1 Special Astrophysical Observatory, Russian Academy of Sciences, N. Arkhyz, KChR, 357147, Russia
2 Instituto de Astrofísica de Canarias, 38200 La Laguna, Canary Islands, Spain

Received 7 May 1999 / Accepted 4 October 1999

Abstract

The distance, star formation history and global properties of the Local Group dIrr galaxy SagDIG are derived based on an [[FORMULA]] colour-magnitude diagram of [FORMULA] stars. A distance of [FORMULA] Mpc is obtained from the I magnitude of the TRGB. This corresponds to 1.17 Mpc to the barycenter of the Local Group and 1.34 to M 31, being DDO 210, at 0.35 Mpc, the nearest galaxy to SagDIG. The metallicity is estimated from the colour of the RGB to be [Fe/H] [FORMULA]. SagDIG is hence a probable member of the Local Group and a candidate for the lowest-metallicity star forming galaxy known.

The radial density profile of the galaxy has been obtained together with other integrated properties (magnitude, colour and central surface density). The galaxy density profile is fitted by an exponential law of scale length [FORMULA], corresponding to 140 pc.

The star formation history of SagDIG has been analysed, based on synthetic colour-magnitude diagrams. The galaxy is currently in a high star formation activity epoch, forming stars at a rate about 10 times greater than the average for its entire life. This is a common feature of galaxies classified as dIrrs.

Key words: galaxies: distances and redshifts – galaxies: dwarf – galaxies: individual: Sagittarius dwarf – galaxies: Local Group – galaxies: stellar content – galaxies: structure

* Based on observations made with the 2.5 m Nordic Optical Telescope operated on the island of La Palma by NOT S.A. in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias.

© European Southern Observatory (ESO) 1999

Online publication: December 2, 1999

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