The Effect of Substructure on Mass Estimates of Galaxies

Yencho, Brian; Johnston, Kathryn V.; Bullock, James S.; Rhode, Katherine L.

doi:10.1086/502619

Cited by 20 publications

(26 citation statements)

References 53 publications

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“…Removing kinematic substructures lead to reduction in mass estimates and for our galaxy sample, the average over-estimation varies from ∼14 − 19 per cent, depending on velocity anisotropy. This agrees with the study of Yencho et al (2006) where the effect of substructure on mass estimate of galaxies was found to be ∼20 per cent. Keplerian potential Isothermal potential 720 821 1023 1400 1407 2768 3115 3377 3608 4278 4365 4374 4473 4486 4494 4526 4564 4649 4697 5846 7457 3607 The greatest fractional mass over-estimation is found in NGC 4526 (∼30 per cent).…”

Section: Quantifying the Effect Of Kinematic Substructures On Mass Essupporting

confidence: 93%

“…Our best-fit function is similar to those reported in Tortora et al (2014) determined at much more central radii of 0.5 and 1 R e . When constrained this way, α reflects the shallower (steeper) total mass density profiles for more ( arbitrary galaxy with MW-like stellar mass, consistent with the results for the MW potential in Yencho et al (2006) and Watkins et al (2010). Table 2 contains a summary of α adopted for the galaxies in this study, given their stellar mass.…”

Section: Tracer Mass Estimators (Tmes)supporting

confidence: 69%

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The SLUGGS survey: the mass distribution in early-type galaxies within five effective radii and beyond

Alabi

Forbes

Romanowsky

et al. 2016

Mon. Not. R. Astron. Soc.

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We study mass distributions within and beyond 5 effective radii (R e ) in 23 early-type galaxies from the SLUGGS survey, using their globular cluster (GC) kinematic data. The data are obtained with Keck/DEIMOS spectrograph, and consist of line-of-sight velocities for ∼3500 GCs, measured with a high precision of ∼15 km s −1 per GC and extending out to ∼13 R e . We obtain the mass distribution in each galaxy using the tracer mass estimator of Watkins et al. and account for kinematic substructures, rotation of the GC systems and galaxy flattening in our mass estimates.The observed scatter between our mass estimates and results from the literature is less than 0.2 dex. The dark matter fraction within 5 R e ( f DM ) increases from ∼0.6 to ∼0.8 for lowand high-mass galaxies, respectively, with some intermediate-mass galaxies (M * ∼10 11 M ) having low f DM ∼ 0.3, which appears at odds with predictions from simple galaxy models. We show that these results are independent of the adopted orbital anisotropy, stellar mass-tolight ratio, and the assumed slope of the gravitational potential. However, the low f DM in the ∼10 11 M galaxies agrees with the cosmological simulations of Wu et al. where the pristine dark matter distribution has been modified by baryons during the galaxy assembly process. We find hints that these M * ∼10 11 M galaxies with low f DM have very diffuse dark matter haloes, implying that they assembled late. Beyond 5 R e , the M/L gradients are steeper in the more massive galaxies and shallower in both low and intermediate mass galaxies.

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Section: Quantifying the Effect Of Kinematic Substructures On Mass Essupporting

confidence: 93%

Section: Tracer Mass Estimators (Tmes)supporting

confidence: 69%

The SLUGGS survey: the mass distribution in early-type galaxies within five effective radii and beyond

Alabi

Forbes

Romanowsky

et al. 2016

Mon. Not. R. Astron. Soc.

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“…On cluster scales, the impact of kinematic substructures on the inferred DM halo is negligible inside 2-3 virial radii (Falco et al 2014). Also on galactic scales, the kinematic substructures have been shown to affect the final results up to 20 per cent (Yencho et al 2006;Kafle et al 2012).…”

Section: Remarks On the Data Fittingmentioning

confidence: 99%

The SLUGGS survey: multipopulation dynamical modelling of the elliptical galaxy NGC 1407 from stars and globular clusters

Pota¹,

Romanowsky²,

Brodie³

et al. 2015

Monthly Notices of the Royal Astronomical Society

103

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We perform in-depth dynamical modelling of the luminous and dark matter (DM) content of the elliptical galaxy NGC 1407. Our strategy consists of solving the spherical Jeans equations for three independent dynamical tracers: stars, blue GCs and red GCs in a self-consistent manner. We adopt a maximum-likelihood Markov-Chain Monte Carlo fitting technique in the attempt to constrain the inner slope of the DM density profile (the cusp/core problem), and the stellar initial mass function (IMF) of the galaxy. We find the inner logarithmic slope of the DM density profiles to be γ = 0.6±0.4, which is consistent with either a DM cusp (γ = 1) or with a DM core (γ = 0). Our findings are consistent with a Salpeter IMF, and marginally consistent with a Kroupa IMF. We infer tangential orbits for the blue GCs, and radial anisotropy for red GCs and stars. The modelling results are consistent with the virial mass-concentration relation predicted by ΛCDM simulations. The virial mass of NGC 1407 is log M vir = 13.3 ± 0.2M ⊙ , whereas the stellar mass is log M * = 11.8 ± 0.1M ⊙ . The overall uncertainties on the mass of NGC 1407 are only 5 per cent at the projected stellar effective radius. We attribute the disagreement between our results and previous X-ray results to the gas not being in hydrostatic equilibrium in the central regions of the galaxy. The halo of NGC 1407 is found be DM dominated, with a dynamical mass-to-light ratio of M/L = 260 +174 −100 M ⊙ /L ⊙,B . However, this value can be larger up to a factor of 3 depending on the assumed prior on the DM scale radius.

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“…This has been shown through simulations of Milky Way-like ha-los, which suggest that even large samples of hundreds of outer halo stars may actually be on only a handful of independent orbits (Bullock & Johnston 2005). Assuming that orbits in a truly unrelaxed halo are randomized introduces a bias of ∼ 20% in mass estimates (Yencho et al 2006). Like satellite galaxies and halo stars, tidal streams can be used as tracers of the gravitational potential.…”

Section: Introductionmentioning

confidence: 95%

Milky Way Mass and Potential Recovery Using Tidal Streams in a Realistic Halo

Bonaca

Geha

Küpper

et al. 2014

ApJ

Self Cite

132

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We present a new method for determining the Galactic gravitational potential based on forward modeling of tidal stellar streams. We use this method to test the performance of smooth and static analytic potentials in representing realistic dark matter halos, which have substructure and are continually evolving by accretion. Our FAST-FORWARD method uses a Markov Chain Monte Carlo algorithm to compare, in 6D phase space, an "observed" stream to models created in trial analytic potentials. We analyze a large sample of streams evolved in the Via Lactea II (VL2) simulation, which represents a realistic Galactic halo potential. The recovered potential parameters are in agreement with the best fit to the global, present-day VL2 potential. However, merely assuming an analytic potential limits the dark matter halo mass measurement to an accuracy of 5 to 20%, depending on the choice of analytic parametrization. Collectively, mass estimates using streams from our sample reach this fundamental limit, but individually they can be highly biased. Individual streams can both under-and overestimate the mass, and the bias is progressively worse for those with smaller perigalacticons, motivating the search for tidal streams at galactocentric distances larger than 70 kpc. We estimate that the assumption of a static and smooth dark matter potential in modeling of the GD-1 and Pal5-like streams introduces an error of up to 50% in the Milky Way mass estimates.

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The Effect of Substructure on Mass Estimates of Galaxies

Cited by 20 publications

References 53 publications

The SLUGGS survey: the mass distribution in early-type galaxies within five effective radii and beyond

The SLUGGS survey: the mass distribution in early-type galaxies within five effective radii and beyond

The SLUGGS survey: multipopulation dynamical modelling of the elliptical galaxy NGC 1407 from stars and globular clusters

Milky Way Mass and Potential Recovery Using Tidal Streams in a Realistic Halo

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