Stellar Mergers or Truly Young? Intermediate-age Stars on Highly Radial Orbits in the Milky Way’s Stellar Halo

Horta, Danny; Lu, Yuxi (Lucy); Ness, Melissa K.; Lisanti, Mariangela; Price-Whelan, Adrian M.

doi:10.3847/1538-4357/ad58de

Stellar Mergers or Truly Young? Intermediate-age Stars on Highly Radial Orbits in the Milky Way’s Stellar Halo

Journal Article · Fri Aug 16 00:00:00 EDT 2024 · The Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/ad58de· OSTI ID:2484151

^[1]; ^[2]; ^[3]; ^[4]; ^[5]

Flatiron Institute, New York, NY (United States); Princeton University
American Museum of Natural History, New York, NY (United States); Columbia University, New York, NY (United States)
Columbia University, New York, NY (United States); Australian National University, Canberra ACT (Australia)
Flatiron Institute, New York, NY (United States); Princeton University, NJ (United States)
Flatiron Institute, New York, NY (United States)

Reconstructing the mass assembly history of the Milky Way relies on obtaining detailed measurements of the properties of many stars in the galaxy, especially in the stellar halo. One of the most constraining quantities is stellar age, as it can shed light on the accretion time and quenching of star formation in merging satellites. However, obtaining reliable age estimates for large samples of halo stars is difficult. We report published ages of 120 subgiant halo stars with highly radial orbits that likely belong to the debris of the Gaia-Enceladus/Sausage (GES) galaxy. The majority of these halo stars are old, with an age distribution characterized by a median of 11.6 Gyr and a 16th (84th) percentile of 10.5 (12.7) Gyr. However, the distribution is skewed, with a tail of younger stars that span ages down to ~6–9 Gyr. All highly radial halo stars have chemical and kinematic/orbital quantities that associate them with the GES debris. Initial results suggest that these intermediate-age stars are not a product of mass transfer and/or stellar mergers, which can bias their age determination low. If this conclusion is upheld by upcoming spectrophotometric studies, then the presence of these stars will pose an important challenge for constraining the properties of the GES merger and the accretion history of the galaxy.

View Accepted Manuscript (DOE)

Research Organization:: Princeton University, NJ (United States)

Sponsoring Organization:: USDOE

Grant/Contract Number:: SC0007968

OSTI ID:: 2484151

Journal Information:: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 2 Vol. 971; ISSN 0004-637X

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: United States

Language:: English

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