University of Oulu

Mihos, J., Durrell, P., Feldmeier, J., Harding, P., Watkins, A. (2018) Stellar Populations in the Outer Disk and Halo of the Spiral Galaxy M101. Astrophysical Journal, 862 (2), 99. doi:10.3847/1538-4357/aacd14

Stellar populations in the outer disk and halo of the spiral galaxy M101

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Author: Mihos, J. Christopher1; Durrell, Patrick R.2; Feldmeier, John J.2;
Organizations: 1Department of Astronomy, Case Western Reserve University
2Department of Physics and Astronomy, Youngstown State University
3University of Oulu, Astronomy Research Unit
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 5.3 MB)
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Language: English
Published: IOP Publishing, 2018
Publish Date: 2018-09-20


We use deep Hubble Space Telescope imaging in the outskirts of the nearby spiral M101 to study stellar populations in the galaxy’s outer disk and halo. Our Advanced Camera for Surveys (ACS) field lies \(17{\mbox{$.\mkern-7mu^\prime$}}6\) (36 kpc) from the center of M101 and targets the blue “NE Plume” of M101’s outer disk, while the parallel Wide Field Camera 3 (WFC3) field lies at a distance of \(23{\mbox{$.\mkern-7mu^\prime$}}3\) (47 kpc) to sample the galaxy’s stellar halo. The WFC3 halo field shows a well-defined red giant branch characterized by low metallicity ([M/H] = −1.7 ± 0.2), with no evidence of young stellar populations. In contrast, the ACS disk field shows multiple stellar populations, including a young main sequence, blue and red helium-burning stars, and old RGB and asymptotic giant branch (AGB) populations. The mean metallicity of these disk stars is quite low: [M/H] = −1.3 ± 0.2 for the RGB population, and −1.15 ± 0.2 for the younger helium-burning sequences. Of particular interest is a bunching of stars along the BHeB sequence, indicative of an evolving cohort of massive young stars. We show that the young stellar populations in this field are well-described by a decaying burst of star formation that peaked ~300–400 Myr ago, along with a more extended star formation history to produce the older RGB and AGB populations. These results confirm and extend the results from our previous deep surface photometry of M101’s outer disk, providing an important cross-check on stellar population studies using resolved stellar populations versus integrated light photometry. We discuss our results in the context of halo formation models and the interaction history of M101 and its companions.

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Series: Astrophysical journal
ISSN: 0004-637X
ISSN-E: 1538-4357
ISSN-L: 0004-637X
Volume: 862
Issue: 2
Article number: 99
DOI: 10.3847/1538-4357/aacd14
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: J.C.M., P.R.D., and J.J.F. were supported through funds provided by NASA through grant GO-13701 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.
Copyright information: © 2018. The American Astronomical Society. All rights reserved. Published in this repository with the kind permission of the publisher.