The Metallicity Distribution in the Outer Halo of M33

Abstract

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. Assuming an absolute magnitude of the tip of the red giant branch of M_{I,TRGB}=-4.1 and a foreground reddening of E(V-I)=0.054, the distance modulus of M33 is determined to be (m-M)=24.72 (880 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 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_{eff}=0.0024.

arXiv comment25 pages, 8 figures, 2 tables, accepted for publication in AJ, tentatively scheduled for July

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• The Stellar Populations of M33's Outer Regions IV: Inflow History and Chemical Evolution
• Halos of Spiral Galaxies. II. halo metallicity-luminosity relation
• AGB stars as tracers of metallicity and mean age across M33
• The Stellar Populations of M33's Outer Regions II: Deep ACS Imaging
• The Disk and Extraplanar Environment of NGC 247
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• The Stellar Halo Metallicity - Luminosity Relationship for Spiral Galaxies
• Stellar structures in the outer regions of M33
• The Outskrits of Spiral Galaxies: Evidence for Multiple Stellar Populations
• Fossil records of cosmic reionization in galactic stellar halos
• Stellar Populations in the Outer Disk and Halo of the Spiral Galaxy M101
• Discovery of an extended halo of metal-poor stars in the Andromeda spiral galaxy
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• A Distance Measurement to M33 Using Optical Photometry of Mira Variables
• The Astrophysical Distance Scale: V. A 2% Distance to the Local Group Spiral M33 via the JAGB Method, Tip of the Red Giant Branch, and Leavitt Law