Stellar content of NGC 404 – The nearest S0 Galaxy

¹ Special Astrophysical Observatory, Russian Academy of Sciences, N. Arkhyz, KChR 369167, Russia
² Isaac Newton Institute of Chile, SAO Branch, Russia
³ Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain

Corresponding author: N. A. Tikhonov, dolly@sao.ru

Accepted: 6 December 2002

Abstract

We report band and band CCD stellar and surface photometry of the galaxy NGC 404 , taken with HST WFPC2 and the 2.5 m Nordic telescope. The colour-magnitude diagram for the stars in this galaxy is typical of that of spheroidal systems (i.e. it lacks luminous, young stars but contains a large number of Asymptotic Giant Branch (AGB) and Red Giant Branch (RGB) stars). The disk of the galaxy is mostly dominated by red giant stars while its bulge consists of both the AGB and RGB population. Using the distance indicator technique, based on the tip of the red giant branch (TRGB), we find a distance of  Mpc for this galaxy. Global photometric characteristic of this galaxy were then measured out to a radius of 3′, giving and . We find for the nucleus of NGC 404. The integral colour of the galaxy changes slightly along the radius, and its mean value is = 1.1. On the HST images situated at 9′ from the galaxy center there are many red giants. This means that the size of the disk of NGC 404 exceeds 20 kpc. The value of the mean metallicity of the red giants in the disk is .