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Prolate rotation and metallicity gradient in the transforming dwarf galaxy Phoenix

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posted on 04.01.2017, 15:28 by N. Kacharov, G. Battaglia, M. Rejkuba, A. A. Cole, R. Carrera, F. Fraternali, Mark I. Wilkinson, C. G. Gallart, M. Irwin, E. Tolstoy
Transition type dwarf galaxies are thought to be systems undergoing the process of transformation from a star-forming into a passively evolving dwarf, which makes them particularly suitable to study evolutionary processes driving the existence of different dwarf morphological types. Here we present results from a spectroscopic survey of ∼200 individual red giant branch stars in the Phoenix dwarf, the closest transition type with a comparable luminosity to “classical” dwarf galaxies. We measure a systemic heliocentric velocity Vhelio = −21.2 ± 1.0 km s−1. Our survey reveals the clear presence of prolate rotation, which is aligned with the peculiar spatial distribution of the youngest stars in Phoenix. We speculate that both features might have arisen from the same event, possibly an accretion of a smaller system. The evolved stellar population of Phoenix is relatively metal-poor (<[Fe/H] > = − 1.49 ± 0.04 dex) and shows a large metallicity spread (σ[Fe/H] = 0.51 ± 0.04 dex), with a pronounced metallicity gradient of −0.13 ± 0.01 dex per arcmin similar to luminous, passive dwarf galaxies. We also report a discovery of an extremely metal-poor star candidate in Phoenix and discuss the importance of correcting for spatial sampling when interpreting the chemical properties of galaxies with metallicity gradients. This study presents a major leap forward in our knowledge of the internal kinematics of the Phoenix transition type dwarf galaxy, and the first wide area spectroscopic survey of its metallicity properties.


This study was partially financially supported by a 2015 ESO DGDF grant. NK acknowledges financial support from IAC for a three-weeks visit to the institute. GB gratefully acknowledges support through a Marie- Curie action Intra European Fellowship, funded by the European Union Seventh Framework Program (FP7/2007-2013) under Grant agreement number PIEF-GA-2010-274151, as well as the financial support by the Spanish Ministry of Economy and Competitiveness (MINECO) under the Ramon y Cajal Programme (RYC-2012-11537). AC was supported by a fellowship from the Netherlands Research School for Astronomy (NOVA). This work made extensive use of the NASA Astrophysics Data System bibliographic services. This research used the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency.



Monthly Notices of the Royal Astronomical Society, 2016

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Monthly Notices of the Royal Astronomical Society


Oxford University Press (OUP), Royal Astronomical Society





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