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Prolate rotation and metallicity gradient in the transforming dwarf galaxy Phoenix

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posted on 2023-05-19, 03:13 authored by Kacharov, N, Battaglia, G, Rejkuba, M, Andrew ColeAndrew Cole, Carrera, R, Fraternali, F, Wilkinson, MI, Gallart, CG, Irwin, M, Tolstoy, E
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 (<[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 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.

History

Publication title

Monthly Notices of the Royal Astronomical Society

Volume

466

Pagination

2006-2023

ISSN

0035-8711

Department/School

School of Natural Sciences

Publisher

Blackwell Publishing Ltd

Place of publication

9600 Garsington Rd, Oxford, England, Oxon, Ox4 2Dg

Rights statement

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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  • Open

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Expanding knowledge in the physical sciences

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