The AGB population in IC 1613 using JHK photometry ^⋆

¹ School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
e-mail: l.sibbons1@herts.ac.uk
² University of Cambridge, Institute of Astronomy, Madingley Rd, Cambridge CB3 OHA, UK

Received: 11 April 2014
Accepted: 12 September 2014

Abstract

Context. A member of the Local Group, IC 1613 is a gas rich irregular dwarf galaxy that appears to have formed stars continuously over the last 10 Gyr and is relatively independent of external influences from other galaxies.

Aims. This paper aims to study the spatial distribution of the asymptotic giant branch (AGB) population in IC 1613 and its metallicity.

Methods. Using WFCAM on UKIRT, high quality JHK photometry of an area of 0.8 deg² centered on IC 1613 was obtained. The data have been used to isolate the C- and M-type components of the AGB population and using their number ratio, C/M, a global mean metallicity has been derived. The metallicity and the tip of the red giant branch magnitude (TRGB) have been studied as a function of distance from the galactic centre and as a function of azimuthal angle.

Results. The TRGB has been found to be at K₀ = 18.25 ± 0.15 mag. The colour separation between the C- and M-type components of the AGB population has been located at (J − K)₀ = 1.15 ± 0.05 mag, giving a global C/M ratio of 0.52 ± 0.04 and from this an iron abundance of [Fe/H] = −1.26 ± 0.07 dex has been calculated.

Conclusions. The AGB population has been detected out to a radial distance of 4.5 kpc in the de-projected plane of the galaxy. The measured TRGB is consistent with previous measurements and no significant variation is detected in the TRGB or in metallicity either with galactocentric distance or azimuthal angle.