X iv : a st ro - p h / 04 06 27 3 v 1 1 0 Ju n 20 04 The Metallicity Distribution in the Outer Halo of M 33
نویسندگان
چکیده
We present the results of deep I and V-band photometry of the halo stars near the southeast minor axis of the Local Group spiral galaxy M33. An (I, V − I) color-magnitude diagram distinctly reveals the red giant branch stars at the bright end of the color-magnitude diagram. A luminosity function in the I-band which utilizes a background field to remove the contaminating effects of Galactic foreground stars and distant, unresolved galaxies reveals the presence of the tip of the red giant branch at (m − M) I = 20.70 ± 0.10. Assuming an absolute magnitude of the tip of the red giant branch of M I,T RGB = −4.1 ± 0.1 and a foreground reddening of E(V − I) = 0.054 ± 0.020, the distance modulus of M33 is determined to be (m − M) • = 24.72 ± 0.14 (880 ± 60 kpc). The metallicity distribution function derived by interpolating between evolutionary tracks of red giant branch models is dominated by a relatively metal poor stellar population, with a mean metallicity of [m/H] = −0.94 ± 0.04 or [Fe/H] = −1.24. We fit a leaky-box chemical enrichment model to the halo data, which shows that the halo is well represented by a single-component model with an effective yield of y ef f = 0.0024. The mean metallicity of a sample of globular clusters in the M33 halo ([Fe/H]= −1.3 ± 0.1) matches very closely the metallicity of the halo, but the cluster sample is too small to investigate other aspects of the metallicity distribution function of the clusters.
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