The Metallicity Distribution in the Halo Stars of NGC 5128: Implications for Galaxy Formation

We have used the Hubble Space Telescope to obtain WFPC2 V, I photometry for stars in the halo of NGC 5128, the nearest giant elliptical galaxy. The resulting color-magnitude diagram (CMD) of this field, which lies ∼21 kpc from the center of the galaxy, contains more than 10,000 stars and reaches almost 3 mag down the red giant branch (RGB). From the sharply defined RGB tip at I = 24.1 ± 0.1 and MI(tip) = -4.1, we obtain a distance to NGC 5128 …