The extended structure of the dwarf irregular galaxy Sagittarius^⋆,⋆⋆

¹ European Southern Observatory, Alonso de Cordova 3107, Vitacura Santiago, Chile
e-mail: gbeccari@eso.org
² INAF – Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna, Italy
³ Dipartimento di Astronomia - Università degli Studi di Bologna, Via Ranzani 1, 40127 Bologna, Italy
⁴ Department of Astronomy and Astrophysics, Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Macul, Santiago, Chile
⁵ Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁶ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
⁷ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio, Italy
⁸ Instituto de Astrofsica de Canarias, 38205 La Laguna, Tenerife, Spain

Received: 16 June 2014
Accepted: 6 August 2014

Abstract

We present a detailed study of the stellar and H i structure of the dwarf irregular galaxy Sagittarius. We use new deep and wide field photometry to trace the surface brightness profile of the galaxy out to ≃5.0′ (corresponding to ≃1600 pc) and down to μ_V ≃ 30.0 mag/arcsec², thus showing that the stellar body of the galaxy is much more extended than previously believed, and it is similarly (or more) extended than the overall H i distribution. The whole major-axis profile is consistent with a pure exponential, with a scale radius of ≃340 pc. The surface density maps reveal that the distribution of old and intermediate-age stars is smooth and remarkably flattened out to its edges, while the associated H i has a much rounder shape, is off-centred and presents multiple density maxima and a significant hole. No clear sign of systemic rotation is detectable in the complex H i velocity field. No metallicity gradient is detected in the old and intermediate age population of the galaxy, and we confirm that this population has a much more extended distribution than young stars (age ≲ 1 Gyr).