The Ages of Galactic Bulge Stars with Realistic Uncertainties

Joyce, Meridith; Johnson, Christian I.; Marchetti, Tommaso; Rich, R. Michael; Simion, Iulia T.; Bourke, John

doi:10.3847/1538-4357/acb692

Cited by 22 publications

(4 citation statements)

References 89 publications

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“…However, Eri IIʼs formation epoch (∼13.5 Gyr) is older than the age of an EDE universe. Though multiple stellar models (and CMD fitting techniques) find a consistently old age for Eri II, additional uncertainties in stellar physics (e.g., convection) may also need to be considered in determining absolute ages (e.g., Chaboyer et al 1996Chaboyer et al , 2017O'Malley et al 2017;Joyce et al 2023). Alternatively, since virtually all known UFDs around the MW appear to be older than ∼13 Gyr (e.g., Weisz et al 2014a;Brown et al 2014;Sacchi et al 2021), it may indicate that physics-based solutions to the Hubble tension resulting in ages younger than ∼13 Gyr may not be consistent with all available measurements of the universeʼs age.…”

Section: The Age Of Eri II In a Cosmological Contextmentioning

confidence: 99%

On the Reionization-era Globular Cluster in the Low-mass Galaxy Eridanus II

Weisz

Savino

Dolphin

2023

ApJ

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Using color–magnitude diagrams from deep archival Hubble Space Telescope imaging, we self-consistently measure the star formation history of Eridanus II (Eri II), the lowest-mass galaxy (M ⋆(z = 0) ∼ 105 M ⊙) known to host a globular cluster (GC), and the age, mass, and metallicity of its GC. The GC (∼13.2 ± 0.4 Gyr, 〈[Fe/H]〉 = −2.75 ± 0.2 dex) and field (mean age ∼13.5 ± 0.3 Gyr, 〈[Fe/H]〉 = −2.6 ± 0.15 dex) have similar ages and metallicities. Both are reionization-era relics that formed before the peak of cosmic star and GC formation (z ∼ 2–4). The ancient star formation properties of Eri II are not extreme and appear similar to z = 0 dwarf galaxies. We find that the GC was ≲4 times more massive at birth than today and was ∼10% of the galaxy's stellar mass at birth. At formation, we estimate that the progenitor of Eri II and its GC had M UV ∼ −7 to −12, making it one of the most common type of galaxy in the early universe, though it is fainter than direct detection limits, absent gravitational lensing. Archaeological studies of GCs in nearby low-mass galaxies may be the only way to constrain GC formation in such low-mass systems. We discuss the strengths and limitations in comparing archaeological and high-redshift studies of cluster formation, including challenges stemming from the Hubble Tension, which introduces uncertainties into the mapping between age and redshift.

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Section: The Age Of Eri II In a Cosmological Contextmentioning

confidence: 99%

On the Reionization-era Globular Cluster in the Low-mass Galaxy Eridanus II

Weisz

Savino

Dolphin

2023

ApJ

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“…The isochrones were transformed from theoretical coordinates to the appropriate bandpasses using a combination of the Sloan Digital Sky Survey and PanSTARRS color transformation schemes. The α-element enhancement is accounted for following the procedure described in Joyce et al (2023). The shorter-wavelength passbands (e.g., u band) allow for the largest discrimination between isochrones with, e.g., different metallicities and ages, but shorter-wavelength passbands are also more sensitive to variations in reddening and extinction, as discussed above.…”

Section: Color-magnitude Diagrammentioning

confidence: 99%

The Milky Way Bulge Extra-tidal Star Survey: BH 261 (AL 3)

Kunder,

Prudil,

Covey

et al. 2023

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The Milky Way Bulge extra-tidal star survey is a spectroscopic survey with the goal of identifying stripped globular cluster stars from inner Galaxy clusters. In this way, an indication of the fraction of metal-poor bulge stars that originated from globular clusters can be determined. We observed and analyzed stars in and around BH 261, an understudied globular cluster in the bulge. From seven giants within the tidal radius of the cluster, we measured an average heliocentric radial velocity of 〈RV〉 = −61 ± 2.6 km s−1 with a radial velocity dispersion of 〈σ〉 = 6.1 ± 1.9 km s−1. The large velocity dispersion may have arisen from tidal heating in the cluster’s orbit about the Galactic center, or because BH 261 has a high dynamical mass as well as a high mass-to-light ratio. From spectra of five giants, we measure an average metallicity of 〈[Fe/H]〉 = −1.1 ± 0.2 dex. We also spectroscopically confirm an RR Lyrae star in BH 261, which yields a distance to the cluster of 7.1 ± 0.4 kpc. Stars with 3D velocities and metallicities consistent with BH 261 reaching to ∼0.°5 from the cluster are identified. A handful of these stars are also consistent with the spatial distribution of potential debris from models focusing on the most recent disruption of the cluster.

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“…As studies of the bulge/bar/inner galaxy increase, it has become appreciated that its star formation history may be more complex (Bensby et al 2017), and even reassessments of age (Joyce et al 2023) support an age range among the most metalrich stars. Johnson et al (2022) find a striking concentration of bulge/bar metal-rich stars in the Galactic plane.…”

Section: Introductionmentioning

confidence: 99%

Composition of Giants 1° North of the Galactic Center: Detailed Abundance Trends for 21 Elements Observed with IGRINS

Nandakumar,

Ryde,

Mace

et al. 2024

ApJ

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We report the first high-resolution, detailed abundances of 21 elements for giants in the Galactic bulge/bar within 1° of the Galactic plane, where high extinction has rendered such studies challenging. Our high-signal-to-noise-ratio and high-resolution, near-infrared spectra of seven M giants in the inner bulge, located at (l, b) = (0°, +1°), are observed using the IGRINS spectrograph. We report the first multichemical study of the inner Galactic bulge by investigating, relative to a robust new solar neighborhood sample, the abundance trends of 21 elements, including the relatively difficult to study heavy elements. The elements studied are: F, Mg, Si, S, Ca, Na, Al, K, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Ce, Nd, and Yb. We investigate bulge membership of all seven stars using distances and orbital simulations, and we find that the most metal-poor star may be a halo interloper. Our investigation also shows that the inner bulge as close as 1° north of the Galactic Center displays a similarity to the inner disk sequence, following the high-[α/Fe] envelope of the solar vicinity metal-rich population, though no firm conclusions for a different enrichment history are evident from this sample. We find a small fraction of metal-poor stars ([Fe/H] > −0.5), but most of our stars are mainly of supersolar metallicity. Fluorine is found to be enhanced at high metallicity compared to the solar neighborhood, but confirmation with a larger sample is required. We will apply this approach to explore the populations of the nuclear stellar disk and the nuclear star cluster.

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The Ages of Galactic Bulge Stars with Realistic Uncertainties

Cited by 22 publications

References 89 publications

On the Reionization-era Globular Cluster in the Low-mass Galaxy Eridanus II

On the Reionization-era Globular Cluster in the Low-mass Galaxy Eridanus II

The Milky Way Bulge Extra-tidal Star Survey: BH 261 (AL 3)

Composition of Giants 1° North of the Galactic Center: Detailed Abundance Trends for 21 Elements Observed with IGRINS

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