Comparison of simple mass estimators for slowly rotating elliptical galaxies

Lyskova, N.; Thomas, Jens; Churazov, E.; Tremaine, Scott; Naab, Thorsten

doi:10.1093/mnras/stv835

Cited by 5 publications

(11 citation statements)

References 36 publications

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“…Of course, real elliptical galaxies are never perfectly spherical, nor they have exactly M (r) ∝ r mass profile or constant anisotropy. Despite all these complications the above relation was shown to provide essentially unbiased masses of massive elliptical galaxies with the RMS scatter of ≃ 12% (see tests in Lyskova et al 2015).…”

Section: Description Of the Simple Methodsmentioning

confidence: 99%

Mass density slope of elliptical galaxies from strong lensing and resolved stellar kinematics

Lyskova

Churazov

Naab

2018

Monthly Notices of the Royal Astronomical Society

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We discuss constraints on the mass density distribution (parameterized as ρ ∝ r −γ ) in early-type galaxies provided by strong lensing and stellar kinematics data. The constraints come from mass measurements at two 'pinch' radii. One 'pinch' radius r 1 = 2.2R Einst is defined such that the Einstein (i.e. aperture) mass can be converted to the spherical mass almost independently of the mass-model. Another 'pinch' radius r 2 = R opt is chosen so that the dynamical mass, derived from the lineof-sight velocity dispersion, is least sensitive to the anisotropy of stellar orbits. We verified the performance of this approach on a sample of simulated elliptical galaxies and on a sample of 15 SLACS lens galaxies at 0.01 z 0.35, which have already been analysed in Barnabè et al. (2011) by the self-consistent joint lensing and kinematic code. For massive simulated galaxies the density slope γ is recovered with an accuracy of ∼ 13%, unless r 1 and r 2 happen to be close to each other. For SLACS galaxies, we found good overall agreement with the results of Barnabè et al. (2011) with a sample-averaged slope γ = 2.1 ± 0.05. While the two-pinch-radii approach has larger statistical uncertainties, it is much simpler and uses only few arithmetic operations with directly observable quantities.

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Section: Description Of the Simple Methodsmentioning

confidence: 99%

Mass density slope of elliptical galaxies from strong lensing and resolved stellar kinematics

Lyskova

Churazov

Naab

2018

Monthly Notices of the Royal Astronomical Society

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“…The half-light mass estimators that is based on have been verified to be robust in a wide range of systems and N-body simulations (Walker & Peñarrubia 2011;Kowalczyk et al 2013;Laporte, Walker & Peñarrubia 2013;Lyskova et al 2015;Campbell et al 2017;González-Samaniego et al 2017;Errani, Peñarrubia & Walker 2018). There has been a healthy discussion about the robustness of the estimator (Walker & Peñarrubia 2011;Kowalczyk et al 2013;Laporte et al 2013;Genina et al 2018).…”

Section: S I M P L E E S T I M Ato R S O F M a S S S L O P Ementioning

confidence: 99%

Multiple chemodynamic stellar populations of the Ursa Minor dwarf spheroidal galaxy

Pace

Kaplinghat

Kirby

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present a Bayesian method to identify multiple (chemodynamic) stellar populations in dwarf spheroidal galaxies (dSphs) using velocity, metallicity, and positional stellar data without the assumption of spherical symmetry. We apply this method to a new Keck/Deep Imaging Multi-Object Spectrograph (DEIMOS) spectroscopic survey of the Ursa Minor (UMi) dSph. We identify 892 likely members, making this the largest UMi sample with line-of-sight velocity and metallicity measurements. Our Bayesian method detects two distinct chemodynamic populations with high significance (in logarithmic Bayes factor, ln B ∼ 33). The metal-rich ([Fe/H] = −2.05 ± 0.03) population is kinematically colder (radial velocity dispersion of $\sigma _v=4.9_{-1.0}^{+0.8} \, \mathrm{km} \, \mathrm{s}^{-1}$) and more centrally concentrated than the metal-poor ($[{\rm Fe/H}]=-2.29_{-0.06}^{+0.05}$) and kinematically hotter population ($\sigma _v =11.5_{-0.8}^{+0.9}\, \mathrm{km} \, \mathrm{s}^{-1}$). Furthermore, we apply the same analysis to an independent Multiple Mirror Telescope (MMT)/Hectochelle data set and confirm the existence of two chemodynamic populations in UMi. In both data sets, the metal-rich population is significantly flattened (ϵ = 0.75 ± 0.03) and the metal-poor population is closer to spherical ($\epsilon =0.33_{-0.09}^{+0.12}$). Despite the presence of two populations, we are able to robustly estimate the slope of the dynamical mass profile. We found hints for prolate rotation of order ${\sim}2 \, \mathrm{km} \, \mathrm{s}^{-1}$ in the MMT data set, but further observations are required to verify this. The flattened metal-rich population invalidates assumptions built into simple dynamical mass estimators, so we computed new astrophysical dark matter annihilation (J) and decay profiles based on the rounder, hotter metal-poor population and inferred $\log _{10}{(J(0{^{\circ}_{.}}5)/{\rm GeV^{2} \, cm^{-5}})}\approx 19.1$ for the Keck data set. Our results paint a more complex picture of the evolution of UMi than previously discussed.

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“…The simple mass estimators have been tested on ideal spherically symmetric systems (Walker & Peñarrubia 2011), simulations of ideal dSphs in a static MW potential (Kowalczyk et al 2013), stellar distributions placed in subhaloes from dark matter only simulations (Laporte et al 2013a), and cosmological zoom simulations of isolated elliptical galaxies (Lyskova et al 2015). More recently, the first generation of simulations with enough resolution to model the satellite galaxies of the MW reliably, in a realistic cosmological setting, have become available (Grand et al 2016;Sawala et al 2016;Wetzel et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Knowing the unknowns: uncertainties in simple estimators of galactic dynamical masses

Campbell

Frenk

Jenkins

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The observed stellar kinematics of dispersion-supported galaxies are often used to measure dynamical masses. Recently, several analytical relationships between the stellar line-of-sight velocity dispersion, the projected (2D) or deprojected (3D) half-light radius, and the total mass enclosed within the half-light radius, relying on the spherical Jeans equation, have been proposed. Here, we make use of the APOSTLE cosmological hydrodynamical simulations of the Local Group to test the validity and accuracy of such mass estimators for both dispersion and rotation-supported galaxies, for field and satellite galaxies, and for galaxies of varying masses, shapes, and velocity dispersion anisotropies. We find that the mass estimators of Walker et al. and Wolf et al. are able to recover the masses of dispersion-dominated systems with little systematic bias, but with a 1σ scatter of 25 and 23 percent, respectively. The error on the estimated mass is dominated by the impact of the 3D shape of the stellar mass distribution, which is difficult to constrain observationally. This intrinsic scatter becomes the dominant source of uncertainty in the masses estimated for galaxies like the dwarf spheroidal (dSph) satellites of the Milky Way, where the observational errors in their sizes and velocity dispersions are small. Such scatter may also affect the inner density slopes of dSphs derived from multiple stellar populations, relaxing the significance with which Navarro-Frenk-White profiles may be excluded, depending on the degree to which the relevant properties of the different stellar populations are correlated. Finally, we derive a new optimal mass estimator that removes the residual biases and achieves a statistically significant reduction in the scatter to 20 percent overall for dispersion-dominated galaxies, allowing more precise and accurate mass estimates.

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Comparison of simple mass estimators for slowly rotating elliptical galaxies

Cited by 5 publications

References 36 publications

Mass density slope of elliptical galaxies from strong lensing and resolved stellar kinematics

Mass density slope of elliptical galaxies from strong lensing and resolved stellar kinematics

Multiple chemodynamic stellar populations of the Ursa Minor dwarf spheroidal galaxy

Knowing the unknowns: uncertainties in simple estimators of galactic dynamical masses

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