McQuinn, K, Boyer, M, Mitchell, M, Skillman, E, Gehrz, R, Groenewegen, M, McDonald, I, Sloan, GC, van Loon, JT, Whitelock, P and Zijlstra, A (2017) DUSTiNGS III: Distribution of Intermediate-Age and Old Stellar Populations in Disks and Outer Extremities of Dwarf Galaxies. The Astrophysical Journal, 834 (1). ISSN 0004-637X

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We have traced the spatial distributions of intermediate-age and old stars in nine dwarf galaxies in the distant parts of the Local Group, using multi-epoch 3.6 and 4.5 μm data from the DUST in Nearby Galaxies with Spitzer (DUSTiNGS) survey. Using complementary optical imaging from the Hubble Space Telescope, we identify the tip of the red giant branch (TRGB) in the 3.6 μm photometry, separating thermally pulsating asymptotic giant branch stars from the larger red giant branch populations. Unlike the constant TRGB in the I band, at 3.6 μm, the TRGB magnitude varies by ~0.7 mag, making it unreliable as a distance indicator. The intermediate-age and old stars are well mixed in two-thirds of the sample, with no evidence of a gradient in the ratio of the intermediate-age to old stellar populations outside the central ~1'–2'. Variable AGB stars are detected in the outer extremities of the galaxies, indicating that chemical enrichment from these dust-producing stars may occur in the outer regions of galaxies with some frequency. Theories of structure formation in dwarf galaxies must account for the lack of radial gradients in intermediate-age populations and the presence of these stars in the outer extremities of dwarfs. Finally, we identify unique features in individual galaxies, such as extended tidal features in Sex A and Sag DIG and a central concentration of AGB stars in the inner regions of NGC 185 and NGC 147.

Item Type: Article
Uncontrolled Keywords: galaxies:dwarf; galaxies:evolution; galaxies:fundamental parameters; galaxies:photometry; galaxies:stellar content; Local Group
Subjects: Q Science > QB Astronomy
Divisions: Faculty of Natural Sciences > School of Physical and Geographical Sciences
Depositing User: Symplectic
Date Deposited: 20 Mar 2017 16:15
Last Modified: 02 Apr 2019 15:31

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