Kinematics of the Tucana Dwarf Galaxy: an unusually dense dwarf in the Local Group

Gregory, Alexandra L.; Collins, Michelle; Read, Justin I.; Irwin, M. J.; Ibata, Rodrigo; Martín, Nicolás F.; McConnachie, Alan W.; Weisz, Daniel R.

doi:10.1093/mnras/stz518

Cited by 26 publications

(27 citation statements)

References 66 publications

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“…The velocity anisotropy was well-recovered in all cases, except PlumCoreOm for which 1,000 tracers was insufficient to detect the radial anisotropy at large radii (Read et al 2021). In Gregory et al (2019), G S was tested on mock data for fewer tracers (20, 100 and 500 tracer stars). There, a similar bias towards low densities at large radii was reported.…”

Section: Data Availabilitymentioning

confidence: 99%

“…However, the code has a tendency to underestimate the density at large radii 𝑅 2𝑅 1/2 (Read et al , 2021. Furthermore, for small numbers of stars, or where the measurement error on each star is large, the binning method within the code can become biased (Gregory et al 2019;Zoutendijk et al 2021).…”

Section: Mass Modelling With G Smentioning

confidence: 99%

“…However, these findings were based on dynamics of only 32 member stars, meaning that detailed dynamical modelling of its halo could not be carried out. In this work, we reanalyse the mass for And XXI using dynamics for 77 member stars, modelling its radial dark matter density profile for the first time with an updated version of the G S Jeans code Read & Steger 2017;Read et al 2018;Gregory et al 2019;Genina et al 2019). We combine our dynamical analysis with the measured star formation history for this galaxy from Weisz et al (2019b) to determine whether its central density can be explained by dark matter heating driven by stellar feedback (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Andromeda XXI – a dwarf galaxy in a low-density dark matter halo

Collins

Read

Ibata

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Andromeda XXI (And XXI) has been proposed as a dwarf spheroidal galaxy with a central dark matter density that is lower than expected in the Standard Λ Cold Dark Matter (ΛCDM) cosmology. In this work, we present dynamical observations for 77 member stars in this system, more than doubling previous studies to determine whether this galaxy is truly a low density outlier. We measure a systemic velocity of vr = −363.4 ± 1.0 km s−1 and a velocity dispersion of $\sigma _v=6.1^{+1.0}_{-0.9}{\rm \, km\, s^{-1}}$, consistent with previous work and within 1σ of predictions made using the modified Newtonian dynamics framework. We also measure the metallicity of our member stars from their spectra, finding a mean value of [Fe/H] = −1.7 ± 0.1 dex. We model the dark matter density profile of And XXI using an improved version of GravSphere, finding a central density of $\rho _{\rm DM}({\rm 150 pc})=2.6_{-1.5}^{+2.4} \times 10^7 \, {\rm M_\odot \, kpc^{-3}}$ at 68% confidence, and a density at two half light radii of $\rho _{\rm DM}({\rm 1.75 kpc})=0.9_{-0.2}^{+0.3} \times 10^6 \, {\rm M_\odot \, kpc^{-3}}$ at 68% confidence. These are both a factor ∼3 − 5 lower than the densities expected from abundance matching in ΛCDM. We show that this cannot be explained by ‘dark matter heating’ since And XXI had too little star formation to significantly lower its inner dark matter density, while dark matter heating only acts on the profile inside the half light radius. However, And XXI’s low density can be accommodated within ΛCDM if it experienced extreme tidal stripping (losing $>95\%$ of its mass), or if it inhabits a low concentration halo on a plunging orbit that experienced repeated tidal shocks.

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Section: Data Availabilitymentioning

confidence: 99%

Section: Mass Modelling With G Smentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Andromeda XXI – a dwarf galaxy in a low-density dark matter halo

Collins

Read

Ibata

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…Although difficult to detect, these ultra-diffuse systems have the potential of yielding important clues to our understanding of dwarf galaxy formation. Indeed, the kinematics of their stars have proved challenging to interpret: some have extremely low velocity dispersion, hinting at very low dark matter densities (e.g., Crater II, And XIX, Collins et al 2013;Caldwell et al 2017), while others inhabit surprisingly dense haloes, according to the kinematical evidence (e.g., Draco, Tucana, Walker et al 2007;Gregory et al 2019). These diverse properties are mirrored by other UDGs outside the Local Group (LG), where some have been associated with massive dark haloes (van Dokkum et al 2016;Beasley et al 2016), whereas others have been found to contain little obvious evidence for dark matter (van Dokkum et al 2018).…”

Section: Introductionmentioning

confidence: 99%

The missing dwarf galaxies of the Local Group

Fattahi

Navarro

Frenk

2020

Monthly Notices of the Royal Astronomical Society

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We study the Local Group (LG) dwarf galaxy population using cosmological simulations of volumes selected to resemble the surroundings of the Milky Way (MW) and Andromeda (M31) galaxies. The simulations, from the APOSTLE project, indicate that the total mass within 3 Mpc of the pair's midpoint (M 3Mpc ) typically exceeds ∼ 3 times the sum of the virial masses of the two primaries and that the dwarf galaxy formation efficiency per unit mass is uniform throughout the volume. This suggests that MW and M31 satellites should make up fewer than one third of all LG dwarfs within 3 Mpc. This is consistent with the fraction (28 per cent) of galaxies with stellar mass M * > 10 7 M that are satellites. In addition, the total number of such galaxies (42) suggests, for the APOSTLE galaxy mass-halo mass relation, a total LG mass of M 3Mpc ∼ 10 13 M . At lower galaxy masses, however, the satellite fraction is substantially higher (42 per cent for M * > 10 5 M , or 42 out of 99). If this is due to incompleteness in the field sample, then ∼ 50 dwarf galaxies at least as massive as the Draco dwarf spheroidal are missing from our current LG field dwarf inventory. The incompleteness interpretation is supported by the pronounced flattening of the LG luminosity function below M * ∼ 10 7 M , and by the scarcity of low-surface brightness LG field galaxies: whereas ∼ 40 per cent of all M * > 10 5 M MW/M31 satellites have effective surface brightness below Σ eff = 26.5 m V /arcsec 2 , only 1 out of all field dwarfs does. The simulations indicate that most missing dwarfs should lie near the virial boundaries of the two LG primaries, and predict a trove of nearby dwarfs that await discovery by upcoming wide-field imaging surveys.

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“…Of the other SIDM models, vd100 model predicts the fewest subhaloes, with 90 per cent of CDM at 𝑀 sub ∼ 10 8 M and 75 per cent at 𝑀 sub ∼ 10 7 M . This demonstrates part of the way in which the vdSIDM model addresses the TBTF problem by predicting fewer subhaloes capable of hosting luminous galaxies, with the aforementioned mass range being synonymous with the dark matter halo mass of 'problematic' dwarf galaxies such as Tucana (Gregory et al 2019).…”

Section: The Subhalo Populationmentioning

confidence: 95%

The Onset of Gravothermal Core Collapse in Velocity Dependent Self-Interacting Dark Matter Subhaloes

Turner,

Lovell,

Zavala

et al. 2020

Preprint

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It has been proposed that gravothermal collapse due to dark matter self-interactions (i.e. selfinteracting dark matter, SIDM) can explain the observed diversity of the Milky Way (MW) satellites' central dynamical masses. We investigate the process behind this hypothesis using an 𝑁-body simulation of a MW-analogue halo with velocity dependent self-interacting dark matter (vdSIDM) in which the low velocity self-scattering cross-section, 𝜎 T /𝑚 x , reaches 100 cm 2 g −1 ; we dub this model the vd100 model. We compare the results of this simulation to simulations of the same halo that employ different dark models, including cold dark matter (CDM) and other, less extreme SIDM models. The masses of the vd100 haloes are very similar to their CDM counterparts, but the values of their maximum circular velocities, 𝑉 max , are significantly higher. We determine that these high 𝑉 max subhaloes were objects in the mass range [5 × 10 6 , 1 × 10 8 ] M at 𝑧 = 1 that undergo gravothermal core collapse. These collapsed haloes have density profiles that are described by single power laws down to the resolution limit of the simulation, and the inner slope of this density profile is approximately −3. Resolving the ever decreasing collapsed region is challenging, and tailored simulations will be required to model the runaway instability accurately at scales < 1 kpc.

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Kinematics of the Tucana Dwarf Galaxy: an unusually dense dwarf in the Local Group

Cited by 26 publications

References 66 publications

Andromeda XXI – a dwarf galaxy in a low-density dark matter halo

Andromeda XXI – a dwarf galaxy in a low-density dark matter halo

The missing dwarf galaxies of the Local Group

The Onset of Gravothermal Core Collapse in Velocity Dependent Self-Interacting Dark Matter Subhaloes

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