Letter to the Editor

The truncation of the stellar disc of NGC 6504

¹ Departamento de Física Teórica y del Cosmos, Universidad de Granada, Spain e-mail: estrella@ugr.es
² Instituto Carlos I. Física Teórica y Computacional, Universidad de Granada, Spain
³ Centro Astronómico Hispano Alemán, Almería, Spain

Received: 4 July 2007
Accepted: 19 July 2007

Abstract

Context.This is the first work reporting observations of the truncation of a stellar disc, in both the optical and the NIR spectral ranges. No galaxy has been observed at both wavelengths with the required depth. The optical radial profiles of spiral galaxy discs seem to suggest a double exponential behaviour, whilst NIR profiles seem to show a real truncation.

Aims.We study one galaxy with the best available resolution and detail, in both optical and NIR bands, with the same deprojection method and similar reduction procedures, to see if the different descriptions are real.

Methods.Optical observations (V band) were made with the William Herschel Telescope. NIR observations (J, H, K_s) were made with the CAIN infrared camera on the Carlos Sánchez Telescope in Tenerife (Spain). The deprojection method was that described in Florido et al. (2001, A&A, 378, 82; 2006a, A&A, 455, 467).

Results.NGC 6504 has a real truncation in both the optical and the NIR radial profiles. A double exponential does not fit the observed optical profile. The truncation radius is larger in the V band than in the NIR by ~10 arcsec, about 3 kpc (equivalent to about 10%). We examine the constraints of this observation in theoretical scenarios.