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Date and Time of the Query: 2019-07-19 T20:03:31 PDT
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For refcode 2007ApJ...666..903H:
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2007ApJ...666..903H The Leo Elliptical NGC 3379: A Metal-Poor Halo Emerges William E. Harris, Gretchen L. H. Harris, Andrew C. Layden, and Elizabeth M. H. Wehner Abstract. We have used the ACS camera on HST to obtain (V, I) photometry for 5300 red giant stars in the halo of the dominant Leo group member NGC 3379, a galaxy usually regarded as a classic normal giant elliptical. We use this data to derive the metallicity distribution function (MDF) for its outer-halo field stars at a location centered 33 kpc from the galaxy center. In at least two ways the MDF is distinctly unlike all the other E galaxies for which similar data exist. First, the NGC 3379 MDF is extremely broad and flat, with many stars at every interval in [m/H]. Second, we see a metallicity gradient such that in ithe outermost parts of the field the low-metallicity stars ([m/H]<-0.7) begin to dominate and the higher metallicity stars are rapidly diminishing. We find that a distinct two-stage chemical evolution model is necessary to explain the MDF shape. Our target field is centered at a projected distance of 12R_e_, twice as far out in units of effective radius as in any of the other galaxies yet surveyed. If NGC 3379 is indeed representative of large E/S0 galaxies, we predict that other such galaxies will reveal diffuse low-metallicity subpopulations, but that photometry at radii r=~(10 -- 15)R_e_ will be necessary to get beyond the edge of the dominant metal-rich component. Key words: Galaxies: Elliptical and Lenticular, cD, Galaxies: Individual: NGC 3379
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