Star Formation Histories of Ultra-faint Dwarf Galaxies: Environmental Differences between Magellanic and Non-Magellanic Satellites?*

Sacchi, Elena; Richstein, Hannah; Kallivayalil, Nitya; Marel, Roeland P. van der; Libralato, Mattia; Zivick, Paul; Besla, Gurtina; Brown, Thomas M.; Choi, Yumi; Deason, Alis J.; Fritz, Tobias; Geha, Marla; Guhathakurta, Puragra; Jeon, Myoungwon; Kirby, Evan N.; Majewski, Steven R.; Patel, Ekta; Simon, Joshua D.; Sohn, Sangmo Tony; Tollerud, Erik; Wetzel, Andrew

doi:10.3847/2041-8213/ac2aa3

“…As discussed, HST observations of the Milky Way's ultra-faint dwarfs down to the oldest main-sequence turnoff reveal early, nearly synchronous star formation (Weisz et al 2014a;Brown et al 2014). There are hints that those ultra-faint dwarfs associated with the Magellanic Clouds had a slightly different star formation epoch than those of the Milky Way (Sacchi et al 2021) and probing further systems and environments is essential for confirming and extending these results. Prior to the advent of the James Webb Space Telescope, similar observations beyond the Local Group were prohibitive, but the Near Infrared Camera (NIRCam) enables such studies out to ∼2 Mpc (e.g., Weisz & Boylan-Kolchin 2019).…”

Section: Summary and Future Outlookmentioning

confidence: 84%

Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D ≈ 1.4 Mpc*

Sand

¹

,

Mutlu-Pakdil

²

,

Jones

³

et al. 2022

ApJL

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We report the discovery of Tucana B, an isolated ultra-faint dwarf galaxy at a distance of D = 1.4 Mpc. Tucana B was found during a search for ultra-faint satellite companions to the known dwarfs in the outskirts of the Local Group, although its sky position and distance indicate the nearest galaxy to be ∼500 kpc distant. Deep ground-based imaging resolves Tucana B into stars, and it displays a sparse red giant branch consistent with an old, metal-poor stellar population analogous to that seen in the ultra-faint dwarf galaxies of the Milky Way, albeit at fainter apparent magnitudes. Tucana B has a half-light radius of 80 ± 40 pc and an absolute magnitude of M V = − 6.9 − 0.6 + 0.5 mag ( L V = ( 5 − 2 + 4 ) × 10 4 L ⊙), which is again comparable to the Milky Way’s ultra-faint satellites. There is no evidence for a population of young stars, either in the optical color–magnitude diagram or in GALEX archival ultraviolet imaging, with the GALEX data indicating log ( SFR NUV / M ⊙ yr − 1 ) < − 5.4 for star formation on ≲100 Myr timescales. Given its isolation and physical properties, Tucana B may be a definitive example of an ultra-faint dwarf that has been quenched by reionization, providing strong confirmation of a key driver of galaxy formation and evolution at the lowest mass scales. It also signals a new era of ultra-faint dwarf galaxy discovery at the extreme edges of the Local Group.

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“…Muñoz et al (2018) re-analyse the data of Martin et al (2015) and find an absolute V-band magnitude of −4.60 ± 0.37 mag and a half-light radius of 1.65 ± 0.39 arcmin (64.3 ± 15.2 pc). An analysis of photometry from HST by Sacchi et al (2021) indicates that Hya II reached half of its cumulative star formation 13.21 ± 0.32 Gyr ago. Koposov et al (2015) discovered Gru 1 in public DES data, with an absolute V-band magnitude of −3.4 ± 0.3 mag and a half-light radius of 1.77 +0.85 −0.39 arcmin (62 +29.8 −13.6 pc), at a distance of 120 kpc.…”

Section: Samplementioning

confidence: 99%

The MUSE-Faint survey. III. No large dark-matter cores and no significant tidal stripping in ultra-faint dwarf galaxies

Zoutendijk¹,

Júlio²,

Brinchmann³

et al. 2021

Preprint

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Aims. The lowest-mass galaxies, ultra-faint dwarf galaxies, promise unparalleled constraints on how feedback regulates galaxy formation, and on the small-scale matter power spectrum. Their inner dark-matter densities can also be used to constrain dark-matter models and to determine the most promising targets for potential signals from dark-matter annihilation or decay. However, these goals are limited by the current large uncertainties on the properties of the dark-matter haloes that these galaxies inhabit. In this paper, we present 201 new stellar line-of-sight velocities from the MUSE-Faint survey for the faint and ultra-faint dwarf galaxies Antlia B, Leo T, Hydra II, and Grus 1. Combining these with literature data, we obtain the tightest constraints to date on their dark-matter halo masses and inner dark-matter densities. Methods. We use the Jeans equations implemented in CJAM to model the density profiles and constrain the presence of dark-matter cores and solitons (a prediction of fuzzy dark-matter models). Further modelling is done with GravSphere to test the influence of the choice of modelling tool. We calculate masses, concentrations, and circular velocities from the profiles, include results for Eridanus 2 from our previous work, and compare these properties to theoretical scaling relations, deriving constraints on tidal stripping in the process.Results. We find that dark-matter cores as large as those of more massive dwarf galaxies are ruled out for our galaxies (core radius r c < 66-95 pc at the 68% confidence level). We constrain the soliton radii to r sol < 13-112 pc (68% confidence level). We find that the galaxies are consistent with not having been significantly tidally stripped within their half-light radii. The virial masses and concentrations are sensitive to the choice of dynamical modelling tool: GravSphere produces results consistent with M 200 ∼ 10 9 M , as expected from models in which ultra-faint dwarf galaxies are re-ionization fossils, while CJAM prefers haloes that are less massive.

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“…As blue HB stars are typically considered to trace ancient stellar populations, this could imply Peg V was quenched very early compared to the other M31 dwarfs, making it a good candidate for a reionisation fossil (Bovill & Ricotti 2009). It is also more similar to the UFDs of the MW, all of which appear to have been quenched 10 Gyr ago (Brown et al 2014;Weisz et al 2014;Sacchi et al 2021) and possess blue HB features.…”

Section: Discussionmentioning

confidence: 99%

Pegasus V -- a newly discovered ultra-faint dwarf galaxy on the outskirts of Andromeda

Collins,

Charles,

Martínez-Delgado

et al. 2022

Preprint

0

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We report the discovery of an ultra-faint dwarf in the constellation of Pegasus. Pegasus V (Peg V) was initially identified in the public imaging data release of the DESI Legacy Imaging Surveys and confirmed with deep imaging from Gemini/GMOS-N. The colour-magnitude diagram shows a sparse red giant branch (RGB) population and a strong over-density of blue horizontal branch stars. We measure a distance to Peg V of 𝐷 = 692 +33 −31 kpc, making it a distant satellite of Andromeda with 𝑀 𝑉 = −6.3 ± 0.2 and a half-light radius of 𝑟 half = 89 ± 41 pc. It is located ∼ 260 kpc from Andromeda in the outskirts of its halo. The RGB is well-fit by a metal-poor isochrone with [Fe/H]= −3.2, suggesting it is very metal poor. This, combined with its blue horizontal branch could imply that it is a reionisation fossil. This is the first detection of an ultra-faint dwarf outside the deep Pan-Andromeda Archaeological Survey area, and points to a rich, faint satellite population in the outskirts of our nearest neighbour.

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Star Formation Histories of Ultra-faint Dwarf Galaxies: Environmental Differences between Magellanic and Non-Magellanic Satellites?*

Cited by 44 publications

References 49 publications

Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D ≈ 1.4 Mpc*

Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D ≈ 1.4 Mpc*

The MUSE-Faint survey. III. No large dark-matter cores and no significant tidal stripping in ultra-faint dwarf galaxies

Pegasus V -- a newly discovered ultra-faint dwarf galaxy on the outskirts of Andromeda

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