Metallicity Distribution Function of the Eridanus II Ultra-faint Dwarf Galaxy from Hubble Space Telescope Narrowband Imaging

Fu, Sal Wanying; Weisz, Daniel R.; Starkenburg, Else; Martín, Nicolás F.; Ji, Alexander P.; Patel, Ekta; Boylan-Kolchin, Michael; Côté, Patrick; Dolphin, Andrew E.; Longeard, Nicolas; Mateo, Mario; Sandford, Nathan R.

doi:10.3847/1538-4357/ac3665

Cited by 12 publications

(26 citation statements)

References 132 publications

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“…We find the mean metallicity of the field population to be 〈[Fe/H]〉 = −2.6 ± 0.15 dex, which is similar to RGB star metallicities (e.g., Li et al 2017;Fu et al 2022). If Eri II is αenhanced, the values of [Fe/H] may be a few tenths of a dex lower; BaSTI α-enhanced models were not available at the time of our analysis, however.…”

Section: Resultssupporting

confidence: 50%

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: Resultssupporting

confidence: 50%

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

Weisz

Savino

Dolphin

2023

ApJ

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“…The rationale for the two SW filters is described in §3.3. The LW filters are located near metallicity sensitive molecular features in the mid-IR, and they may be suitable for measuring photometric metallicities of metal-poor stars (e.g., Schlaufman & Casey 2014;Casey & Schlaufman 2015) similar to what is possible in the optical using, for example, the Calcium H&K lines (e.g., Starkenburg et al 2017b;Fu et al 2022). For NIRISS, we used the F090W and F150W filters.…”

Section: Draco IImentioning

confidence: 99%

“…The width of the lower MS is in excess of photometric noise. Metallicities derived from more luminous stars in Draco II suggest a spread of σ ∼ 0.5 dex (e.g., Li et al 2017;Longeard et al 2018;Fu et al 2022), which may contribute to this scatter. Background galaxies are also a source of contamination and likely contribute to the scatter, particularly at the faintest magnitudes.…”

Section: Draco IImentioning

confidence: 99%

“…The F150−F360M CMD (panel c) extends to a comparably low stellar mass as the SW CMD, albeit at lower SNR. The LW CMD (panel d) is much shallower; though the primary purpose of these filters is to explore their potential as photometric metallicity indicators akin to the Calcium H & K filters being used in the optical (e.g., Starkenburg et al 2017a;Longeard et al 2018;Fu et al 2022).…”

Section: Draco IImentioning

confidence: 99%

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The JWST Resolved Stellar Populations Early Release Science Program II. Survey Overview

Weisz¹,

McQuinn²,

Savino³

et al. 2023

Preprint

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We present the JWST Resolved Stellar Populations Early Release Science (ERS) science program. We obtained 27.5 hours of NIRCam and NIRISS imaging of three targets in the Local Group (Milky Way globular cluster M92, ultra-faint dwarf galaxy Draco II, star-forming dwarf galaxy WLM), which span factors of ∼ 10 5 in luminosity, ∼ 10 4 in distance, and ∼ 10 5 in surface brightness. We describe the survey strategy, scientific and technical goals, implementation details, present select NIRCam color-magnitude diagrams (CMDs), and validate the NIRCam exposure time calculator (ETC). Our CMDs are among the deepest in existence for each class of target. They touch the theoretical hydrogen burning limit in M92 (< 0.08 M ; SNR ∼ 5 at m F 090W ∼ 28.2; M F 090W ∼ +13.6), include the lowest-mass stars observed outside the Milky Way in Draco II (0.09 M ; SNR = 10 at m F 090W ∼ 29; M F 090W ∼ +12.1), and reach ∼ 1.5 magnitudes below the oldest main sequence turnoff in WLM (SNR = 10 at m F 090W ∼ 29.5; M F 090W ∼ +4.6). The PARSEC stellar models provide a good qualitative match to the NIRCam CMDs, though are ∼ 0.05 mag too blue compared to M92 F090W−F150W data. The NIRCam ETC (v2.0) matches the SNRs based on photon noise from DOLPHOT stellar photometry in uncrowded fields, but the ETC may not be accurate in more crowded fields, similar to what is known for HST. We release beta versions of DOLPHOT NIRCam and NIRISS modules to the community. Results from this ERS program will establish JWST as the premier instrument for resolved stellar populations studies for decades to come.

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“…Meanwhile, its star formation history (SFH) measured from deep broadband imaging is consistent with Eri II forming nearly all of its stellar mass (∼ 2 × 10 5 M ) in a short (< 500 Myr) burst over 13 Gyr ago, making it a true relic of the pre-reionization era (Simon et al 2021;Gallart et al 2021). Further, its orbit inferred from Gaia eDR3 proper motions and its current distance at ∼ 350 kpc place Eri II at first infall into the Milky Way (MW), indicating that it likely evolved in isolation and removing the need to account for ram pressure stripping or tidal interactions (Battaglia et al 2022;Fu et al 2022).…”

mentioning

confidence: 99%

Strong Outflows and Inefficient Star Formation in the Reionization-era Ultra-faint Dwarf Galaxy Eridanus II

Sandford¹,

Weinberg²,

Weisz³

et al. 2022

Preprint

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We present novel constraints on the underlying galaxy formation physics (e.g., mass loading factor, star formation history, metal retention) at z 7 for the low-mass (M * ∼ 10 5 M ) Local Group ultra-faint dwarf galaxy (UFD) Eridanus II (Eri II). Using a hierarchical Bayesian framework, we apply a one-zone chemical evolution model to Eri II's CaHK-based photometric metallicity distribution function (MDF; [Fe/H]) and find that the evolution of Eri II is well-characterized by a short, exponentially declining star-formation history (τ SFH = 0.39± 0.18 0.13 Gyr), a low star-formation efficiency (τ SFE = 27.56± 25.14 12.92 Gyr), and a large mass-loading factor (η = 194.53± 33.37 42.67 ). Our results are consistent with Eri II forming the majority of its stars before the end of reionization. The large mass-loading factor is consistent with strong outflows in Eri II and is in good agreement with theoretical predictions for momentum-driven galactic winds. It also results in the ejection of >90% of the metals produced in Eri II. We make predictions for the distribution of [Mg/Fe]-[Fe/H] in Eri II as well as the prevalence of ultra metal-poor stars, both of which can be tested by future chemical abundance measurements. Spectroscopic follow-up of the highest metallicity stars in Eri II ([Fe/H] > −2) will greatly improve model constraints. Our new framework can readily be applied to all UFDs throughout the Local Group, providing new insights in to the underlying physics governing the evolution of the faintest galaxies in the reionization-era.

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Metallicity Distribution Function of the Eridanus II Ultra-faint Dwarf Galaxy from Hubble Space Telescope Narrowband Imaging

Cited by 12 publications

References 132 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 JWST Resolved Stellar Populations Early Release Science Program II. Survey Overview

Strong Outflows and Inefficient Star Formation in the Reionization-era Ultra-faint Dwarf Galaxy Eridanus II

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