Triangulum II. Not Especially Dense After All*

Kirby, Evan N.; Cohen, Judith G.; Simon, Joshua D.; Guhathakurta, Puragra; Thygesen, A. O.; Duggan, G.

doi:10.3847/1538-4357/aa6570

Cited by 114 publications

(141 citation statements)

References 87 publications

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“…Data for Sag, Crater II, and Bootes are from Table 1 of H19, and data for Antlia are from Torrealba et al (2019). Vertical arrows indicate upper limits for Tucana III (data from Simon et al 2017), Triangulum II (Kirby et al 2017), Segue 2 (Kirby et al 2013), Grus (Walker et al 2016), and Hydra II (Kirby et al 2015). accounting for this would suffice to bring it on the anticorrelation of Figure 6. To this category, one may add Crater (cyan point; see Sect.…”

Section: A Tentative Classification Scheme For the Mw Dsphsmentioning

confidence: 99%

Orbital Evidences for Dark-matter-free Milky Way Dwarf Spheroidal Galaxies

Hammer

Yang

Arenou

et al. 2020

ApJ

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The nature of Milky Way dwarf spheroidals (MW dSphs) has been questioned, in particular whether they are dominated by dark matter (DM). Here we investigate an alternative scenario, for which tidal shocks are exerted by the MW to DM-free dSphs after a first infall of their gas-rich progenitors, and for which theoretical calculations have been verified by pure N-body simulations. Whether or not the dSphs are on their first infall cannot be resolved on the sole basis of their star formation history. In fact, gas removal may cause complex gravitational instabilities, and near-pericenter passages can give rise to tidal disruptive processes. Advanced precision with the Gaia satellite in determining both their past orbital motions and the MW velocity curve is however providing crucial results.First, tidal shocks explain why DM-free dSphs are found preferentially near their pericenter where they are in a destructive process, while their chance to be long-lived satellites is associated to a very low probability P∼ 2 ×10 −7 , which is at odds with the current DM-dominated dSph scenario. Second, most dSph binding energies are consistent with a first infall. Third, the MW tidal shocks that predict the observed dSph velocity dispersions are themselves predicted in amplitude by the most accurate MW velocity curve. Fourth, tidal shocks accurately predict the forces or accelerations exerted at half-light radius of dSphs, including the MW and the Magellanic System gravitational attractions.The above is suggestive of dSphs that are DM-free and tidally shocked near their pericenters, which may provoke a significant quake in our understanding of near-field cosmology.

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Section: A Tentative Classification Scheme For the Mw Dsphsmentioning

confidence: 99%

Orbital Evidences for Dark-matter-free Milky Way Dwarf Spheroidal Galaxies

Hammer

Yang

Arenou

et al. 2020

ApJ

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“…see Gregory et al 2019 comparison of FORS2 multislit versus FLAMES/GIRAFFE fibres observations of the Tucana dSph) but sometimes even when the same instrument and configuration mode is adopted (e.g. comparison of Keck/DEIMOS R ∼ 6500 observations of the Triangulum II system, Kirby et al 2017a). However, we have vali-dated our data-reduction and analysis procedure in multiple studies that included sub-samples of repeated exposures for the same stars, which yielded consistent results.…”

Section: Comparison With Kirby Et Al (2017)mentioning

confidence: 99%

Kinematic and metallicity properties of the Aquarius dwarf galaxy from FORS2 MXU spectroscopy

Hermosa-Muñoz

Taibi

Battaglia

et al. 2020

A&A

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Context. Dwarf galaxies found in isolation in the Local Group (LG) are unlikely to have interacted with the large LG spirals, and therefore environmental effects such as tidal and ram-pressure stripping should not be the main drivers of their evolution. Aims. We aim to provide insight into the internal mechanisms shaping LG dwarf galaxies by increasing our knowledge of the internal properties of isolated systems. Here we focus on the evolved stellar component of the Aquarius dwarf galaxy, whose kinematic and metallicity properties have only recently started to be explored. Methods. Spectroscopic data in the region of the near-infrared Ca II triplet lines has been obtained with FORS2 at the Very Large Telescope for 53 red giant branch (RGB) stars. These data are used to derive line-of-sight velocities and [Fe/H] of the individual RGB stars. Results. We have derived a systemic velocity of −142.2 +1.8 −1.8 km s −1 , in agreement with previous determinations from both the HI gas and stars. The internal kinematics of Aquarius appears to be best modelled by a combination of random motions (l.o.s. velocity dispersion of 10.3 +1.6 −1.3 km s −1 ) and linear rotation (with a gradient −5.0 +1.6 −1.9 km s −1 arcmin −1 ) along a P.A. = 139 +17 −27 deg, broadly consistent with the optical projected major axis. This rotation signal is significantly misaligned or even counter-rotating to that derived from the HI gas. We also find the tentative presence of a mild negative metallicity gradient and indications that the metal-rich stars have a colder velocity dispersion than the metalpoor ones. Conclusions. This work represents a significant improvement with respect to previous measurements of the RGB stars of Aquarius, as it doubles the number of member stars already studied in the literature. We speculate that the misaligned rotation between the HI gas and evolved stellar component might have been the result of recent accretion of HI gas, or re-accretion after gas-loss due to internal stellar feedback.

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“…The chemical evolution of Sr behaves differently among dwarf galaxies with different masses. Stars in several UFDs such as Canes Venatici I, II, Hercules, and Triangulum II are enhanced in [Sr/Ba] (François et al 2016;Kirby et al 2017). As shown in Section 4.2, 5.2% and 5.9% of stars have [Sr/Ba] > 1 in models B and D, respectively, reflecting the ejecta from ECSNe with Sr but no Ba (note that RMSs give [Sr/Ba] ≈ 1 at low metallicity).…”

Section: Enrichment Of Sr In Lg Dwarf Galaxiesmentioning

confidence: 99%

Enrichment of Strontium in Dwarf Galaxies

Hirai

Wanajo

Saitoh

2019

ApJ

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Light trans-iron elements such as Sr serve as the key to understanding the astrophysical sites of heavy elements. Spectroscopic studies of metal-poor stars have revealed large star-to-star scatters in the ratios of [Sr/Ba], which indicates that there are multiple sites for the production of Sr. Here we present the enrichment history of Sr by a series of the N -body/smoothed particle hydrodynamics simulations of a dwarf galaxy with a stellar mass of 3 × 10 6 M ⊙ . We show that binary neutron star mergers (NSMs) and asymptotic giant branch (AGB) stars contribute to the enrichment of Sr in the metallicity ranges [Fe/H] −3 and [Fe/H] −1, respectively. It appears insufficient, however, to explain the overall observational trends of Sr by considering only these sites. We find that the models including electron-capture supernovae (ECSNe) and rotating massive stars (RMSs), in addition to NSMs and AGBs, reasonably reproduce the enrichment histories of Sr in dwarf galaxies. The contributions of both ECSNe and NSMs make scatters of ≈ 0.2 dex in [Sr/Fe], [Sr/Ba], and [Sr/Zn] as can be seen for observed stars in the metallicity range [Fe/H] < −2. We also find that the mass range of ECSN progenitors should be substantially smaller than 1 M ⊙ (e.g., 0.1-0.2 M ⊙ ) to avoid over-prediction of [Sr/Ba] and [Sr/Zn] ratios. Our results demonstrate that NSMs, AGBs, ECSNe, and RMSs all play roles in the enrichment histories of Local Group dwarf galaxies, although more observational data are required to disentangle the relative contributions of these sources.

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Triangulum II. Not Especially Dense After All*

Cited by 114 publications

References 87 publications

Orbital Evidences for Dark-matter-free Milky Way Dwarf Spheroidal Galaxies

Orbital Evidences for Dark-matter-free Milky Way Dwarf Spheroidal Galaxies

Kinematic and metallicity properties of the Aquarius dwarf galaxy from FORS2 MXU spectroscopy

Enrichment of Strontium in Dwarf Galaxies

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