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Prolate rotation and metallicity gradient in the transforming dwarf galaxy Phoenix

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Kacharov, N, Battaglia, G, Rejkuba, M, Cole, AA ORCID: 0000-0003-0303-3855, Carrera, R, Fraternali, F, Wilkinson, MI, Gallart, CG, Irwin, M and Tolstoy, E 2017 , 'Prolate rotation and metallicity gradient in the transforming dwarf galaxy Phoenix' , Monthly Notices of the Royal Astronomical Society, vol. 466, no. 2 , pp. 2006-2023 , doi: 10.1093/mnras/stw3188.

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Abstract

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 that 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 ( = −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 arcmin−1 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. A table containing the measured velocities, metallicities, and CaT equivalent widths of all spectroscopic targets is available online at the CDS.

Item Type: Article
Authors/Creators:Kacharov, N and Battaglia, G and Rejkuba, M and Cole, AA and Carrera, R and Fraternali, F and Wilkinson, MI and Gallart, CG and Irwin, M and Tolstoy, E
Keywords: galaxies: dwarf, galaxies: kinematics and dynamics, Local Group, galaxies: stellar content
Journal or Publication Title: Monthly Notices of the Royal Astronomical Society
Publisher: Blackwell Publishing Ltd
ISSN: 0035-8711
DOI / ID Number: 10.1093/mnras/stw3188
Copyright Information:

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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