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Star formation at the edge of the Local Group: a rising star formation history in the isolated galaxy WLM


Albers, SM and Weisz, DR and Cole, AA and Dolphin, AE and Skillman, ED and Williams, BF and Boylan-Kolchin, M and Bullock, JS and Dalcanton, JJ and Hopkins, PF and Leaman, R and McConnachie, AW and Vogelsberger, M and Wetzel, A, Star formation at the edge of the Local Group: a rising star formation history in the isolated galaxy WLM, Monthly Notices of the Royal Astronomical Society, 490, (4) pp. 5538-5550. ISSN 0035-8711 (2019) [Refereed Article]


Copyright Statement

Copyright 2019 The Author(s) This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2019. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

DOI: doi:10.1093/mnras/stz2903


We present the star formation history (SFH) of the isolated (D ∼ 970 kpc) Local Group dwarf galaxy Wolf–Lundmark–Melotte (WLM) measured from colour–magnitude diagrams (CMDs) constructed from deep Hubble Space Telescope imaging. Our observations include a central (⁠0.5𝑟) and outer field (⁠0.7𝑟⁠) that reach below the oldest main-sequence turn-off. WLM has no early dominant episode of star formation: 20 per cent of its stellar mass formed by ∼ 12.5 Gyr ago (⁠⁠𝑧 ∼ 5). It also has an SFR that rises to the present with 50 per cent of the stellar mass within the most recent 5 Gyr (𝑧 < 0.7). There is evidence of a strong age gradient: the mean age of the outer field is 5 Gyr older than the inner field despite being only 0.4 kpc apart. Some models suggest such steep gradients are associated with strong stellar feedback and dark-matter core creation. The SFHs of real isolated dwarf galaxies and those from the Feedback in Realistic Environment suite are in good agreement for M(⁠𝑧 = 0) ∼ 107–109M⊙, but in worse agreement at lower masses (⁠M*(𝑧 = 0) ∼ 105−107M⊙⁠). These differences may be explainable by systematics in the models (e.g. reionization model) and/or observations (HST field placement). We suggest that a coordinated effort to get deep CMDs between HST/JWST (crowded central fields) and WFIRST (wide-area halo coverage) is the optimal path for measuring global SFHs of isolated dwarf galaxies.⁠

Item Details

Item Type:Refereed Article
Keywords:Local Group, galaxies: dwarf, galaxies: evolution, Local Group, galaxies: stellar content
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Cosmology and extragalactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Cole, AA (Professor Andrew Cole)
ID Code:136006
Year Published:2019
Web of Science® Times Cited:11
Deposited By:Physics
Deposited On:2019-11-26
Last Modified:2020-06-02
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