Population Gradients in Local Group Dwarf Spheroidals
Population Gradients in Local Group Dwarf Spheroidals Daniel Harbeck1, Eva K. Grebel1,11, Jon Holtzman2, Puragra Guhathakurta3, Wolfgang Brandner4,5, Doug Geisler6,11 , Ata Sarajedini7,11, Andrew Dolphin8, Denise Hurley-Keller9,10,11, Mario Mateo10,11 ABSTRACT We present a systematic and homogeneous analysis of population gradients for the Local Group dwarf spheroidals (dSphs) Carina, Sculptor, Sextans, Tucana, Andromeda I-III, V, and VI. For all of the Milky Way companions studied here we find significant population gradients. The same is true for the remote dSph Tucana located at the outskirts of the LG. Among the M 31 dSph companions only Andromeda I and VI show obvious gradients. In all cases where a HB morphology gradient is visible, the red HB stars are more centrally concentrated. The occurence of a HB morphological gradient shows a correlation with a morphology gradient in the red giant branch. It seems likely that metallicity is the driver of the gradients in Sextans, Sculptor, Tucana, and Andromeda VI, while age is an important factor in Carina. We find no evidence that the vicinity of a nearby massive spiral galaxy influences the formation of the population gradients. Subject headings: galaxies: dwarf – galaxies: structure – galaxies: stellar content – stars: abundances – stars: horizontal-branch – Local Group 1Max-Planck-Institut f¨ur Astronomie, K¨onigstuhl 17, D-69117 Heidelberg, Germany 2New Mexico State University, Department 4500, Box 30001, Las Cruces, NM 88003 arXiv:astro-ph/0109121v1 7 Sep 2001 3UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, CA 95064, USA 4University of Hawaii, Institute for Astronomy, 2680 Woodlawn Dr., Honolulu, HI 96822 5European Southern Observatory, Karl-Schwarzschild-Str.
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