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

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Albers, SM, Weisz, DR, Cole, AA ORCID: 0000-0003-0303-3855, Dolphin, AE, Skillman, ED, Williams, BF, Boylan-Kolchin, M, Bullock, JS, Dalcanton, JJ, Hopkins, PF, Leaman, R, McConnachie, AW, Vogelsberger, M and Wetzel, A 2019 , '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, vol. 490, no. 4 , 5538–5550 , doi: 10.1093/mnras/stz2903.

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Abstract

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society 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 (0.5 rh) and outer field (0.7 rh) 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) ∼ 105-107 M☉). 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 Type: Article
Authors/Creators: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
Keywords: Local Group, dwarf galaxies, galaxy evolution
Journal or Publication Title: Monthly Notices of the Royal Astronomical Society
Publisher: Blackwell Publishing Ltd
ISSN: 0035-8711
DOI / ID Number: 10.1093/mnras/stz2903
Copyright Information:

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.

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