A METHOD FOR MEASURING (SLOPES OF) THE MASS PROFILES OF DWARF SPHEROIDAL GALAXIES

By M. Walker, J. Peñarrubia. 2011

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We introduce a method for measuring the slopes of mass profiles within dwarf spheroidal (dSph) galaxies directly from stellar spectroscopic data and without adopting a dark matter halo model. Our method combines two recent results: (1) spherically symmetric, equilibrium Jeans models imply that the product of half-light radius and (squared) stellar velocity dispersion provides an estimate of the mass enclosed within the half-light radius of a dSph stellar component, and (2) some dSphs have chemodynamically distinct stellar subcomponents that independently trace the same gravitational potential. We devise a statistical method that uses measurements of stellar positions, velocities, and spectral indices to distinguish two dSph stellar subcomponents and to estimate their individual half-light radii and velocity dispersions. For a dSph with two detected stellar subcomponents, we obtain estimates of masses enclosed at two discrete points in the same mass profile, immediately defining a slope. Applied to published spectroscopic data, our method distinguishes stellar subcomponents in the Fornax and Sculptor dSphs, for which we measure slopes Γ ≡ Δlog M/Δlog r = 2.61+0.43−0.37 and Γ = 2.95+0.51−0.39, respectively. These values are consistent with “cores” of constant density within the central few hundred parsecs of each galaxy and rule out “cuspy” Navarro–Frenk–White (NFW) profiles (dlog M/dlog r ⩽ 2 at all radii) with a significance ≳ 96% and ≳ 99%, respectively. Tests with synthetic data indicate that our method tends systematically to overestimate the mass of the inner stellar subcomponent to a greater degree than that of the outer stellar subcomponent, and therefore to underestimate the slope Γ (implying that the stated NFW exclusion levels are conservative).

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/e88086787b7a12234a6087a56f4535227bef67d3

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Citations in the corpus

Cosmological Simulations with Self-Interacting Dark Matter I: Constant Density Cores and Substructure (2012, methodology): “…modelings using stellar kinematics together with chemo-dynamiclly distinct stellar subcomponets of Milky Way dwarf spheroidal gaaxies suggest central densities of approximately∼ 0.1M⊙/pc3 (Strigari et al. 2008; Wolf et al. 2010; Walker & Peñarrubia2011; Amorisco & Evans 2012; Wolf & Bullock 2012).”
Too big to fail in the Local Group (2014, methodology): “For example, measurements of stellar kinematics in dSphs, utilizing both kinematically distinct populations (Walker & Peñarrubia 2011; Agnello & Evans 2012; Amorisco & Evans 2012; Amorisco, Agnello & Evans 2013) and treating the system as a single population (Jardel & Gebhardt 2012) indicate cored…”
THE COUPLING BETWEEN THE CORE/CUSP AND MISSING SATELLITE PROBLEMS (2012, background): “…significantly: the estimated mass profiles are consistent with homogeneous-density ’cores’ (Kuzio de Naray et al. 2008; Battaglia et al. 2008; de Blok 2010; Walker & Peñarrubia 2011; Amorisco & Evans 2012) and the satellite mass function is remarkably flat (Klypin et al. 1999; Moore et al. 1999).”
Dark matter cores all the way down (2015, background): “The situation for the gas-poor dSphs is more murky, with claims of cores (e.g. Battaglia et al. 2008; Walker & Peñarrubia 2011; Amorisco & Evans 2011; Agnello & Evans 2012); cusps (Richardson & Fairbairn 2014; Strigari et al. 2014, e.g.); and everything in between (e.g. Breddels & Helmi 2014;…”
Cusp-core transformations in dwarf galaxies: observational predictions (2012, background): “It is interesting to note, however, that the very latest dynamical models for Sculptor appear to favour a cored rather than cusped mass distribution (Battaglia et al. 2008; Walker & Peñarrubia 2011; Amorisco & Evans 2012).”
The SLUGGS Survey: kinematics for over 2500 globular clusters in 12 early-type galaxies (2012, result): “It will be interesting to test how a classic Jeans analysis that makes use of the different GC anisotropies found in this paper compares with recent studies that do not require assumptions on the dark matter halo (Walker & Peñarrubia 2011).”
Can feedback solve the too-big-to-fail problem? (2013, result): “Rather we find mild cusps, ρ ∝ r−α, with α & 0.5 – significantly steeper than those observed in dSphs by Walker & Peñarrubia (2011) and Amorisco & Evans (2012).”
Dark matter and fundamental physics with the Cherenkov Telescope Array (2012, background): “On the other hand, for systems of the size of dSphs, the possibility of centrally cored profiles has also been suggested [82,83,14].”
Globular clusters as the relics of regular star formation in ‘normal’ high-redshift galaxies (2015, background): “The disruption time-scale during the halo phase is chosen to bet5,evap ∼ 1011 yr, consistent with a galactocentric radius ofR = 2 kpc (cf. Mackey & Gilmore 2003) in the observed gravitational potential (Walker & Peñarrubia 2011).”
Extragalactic science, cosmology, and Galactic archaeology with the Subaru Prime Focus Spectrograph (2012, methodology): “Recently, Walker & Peñarrubia (2011) develop a method for measuring the slopes of mass profiles in the inner regions of dSphs and conclude that the Fornax and Sculptor dSphs have ‘cores’ of constant dark-matter density.”
LSST: From Science Drivers to Reference Design and Anticipated Data Products (2008, background): “• The measurement of the internal motions of Milky Way dwarf galaxies, thereby constraining their density profiles and possibly the nature of dark matter (e.g., Walker & Peñarrubia 2011).”
Dark matter cores and cusps: the case of multiple stellar populations in dwarf spheroidals (2011, methodology): “The modelling is then simpler than a Jeans analysis, but Walker & Peñarrubia (2011) argue that it is more robust.”
The Dynamical and Chemical Evolution of Dwarf Spheroidal Galaxies with GEAR (2009, background): “…(Blais-Ouellette et al. 2001; de Blok & Bosma 2002; Swaters et al. 2003; Gentile et al. 2004, 2005; Spekkens et al. 2005; de Blok 2005; de Blok et al. 2008; Spano et al. 2008; Walker & Peñarrubia 2011), including the recent and high resolution observations of the THINGS survey (Oh et al. 2011).”
ETHOS - an effective theory of structure formation: dark matter physics as a possible explanation of the small-scale CDM problems (2015, background): “…related diversity of dwarf rotation curves (Oman et al. 2015), (iii) the corecusp (CC) problem for low surface brightness galaxies (De Blok & McGaugh 1997), and dwarf galaxies (e.g. see Oh et al. 2011; Walker & Peñarrubia 2011), and (iv) the plane of satellites problem (Pawlowski et al. 2013).”
Small scale problems of the $\Lambda$CDM model: a short review (2016, background): “[314] claimed simulations in agreement with [206], injecting however 50% more energy from SNs.”