Radial Alignment in Simulated Clusters

Pereira, M. J.; Bryan, Greg L.; Gill, Stuart

doi:10.1086/523830

Cited by 76 publications

(173 citation statements)

References 41 publications

(65 reference statements)

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“…The tidal torquing mechanism predicts stronger radial alignments at smaller fractions of the virial radius (except at radii where satellite galaxies are at the perihelion of elliptical orbits, Pereira et al 2008). Our uncertainties in Fig.…”

Section: Resultsmentioning

confidence: 71%

“…1 we show some model probability distributions for φ, with periodicity imposed. The short-dashed green line is a fit to the distribution found in the N -body simulations of Pereira et al (2008) while the solid red line is the best fit to our data as described in Section 4 below. The long-dashed blue line shows the uniform distribution.…”

Section: Position Anglementioning

confidence: 97%

“…This simple picture then predicts that satellite galaxies should be more radially aligned in more concentrated (i.e. typically lower mass) groups and that the degree of alignment should have an inverse relation to the angular speed of the galaxy thereby imparting a dependence on the distance from the potential centre (Kuhlen et al 2007;Pereira et al 2008;Pereira & Bryan 2010). This tidal torquing model for the radial alignments of satellite galaxies could be complicated by effects such as the tidal stripping of infalling satellites or the misalignments of stars and dark matter due to complex accretion and merger histories.…”

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confidence: 99%

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Galaxy And Mass Assembly (GAMA): galaxy radial alignments in GAMA groups

Schneider¹,

Cole²,

Frenk³

et al. 2013

Monthly Notices of the Royal Astronomical Society

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We constrain the distributions of projected radial alignment angles of satellite galaxy shapes within the Galaxy And Mass Assembly survey group catalogue. We identify the galaxy groups using spectroscopic redshifts and measure galaxy projected ellipticities from Sloan Digital Sky Survey imaging. With a sample of 3850 groups with 13655 satellite galaxies with high quality shape measurements, we find a less than 2-σ signal of radial alignments in the mean projected ellipticity components and the projected position angle when using galaxy shape estimates optimized for weak lensing measurements. Our radial alignment measurement increases to greater than 3-σ significance relative to the expectation for no alignments if we use 2-D Sérsic model fits to define galaxy orientations. Our weak measurement of radial alignments is in conflict with predictions from dark matter N -body simulations, which we interpret as evidence for large mis-alignments of baryons and dark matter in group and cluster satellites. Within our uncertainties, that are dominated by our small sample size, we find only weak and marginally significant trends of the radial alignment angle distributions on projected distance from the group centre, host halo mass, and redshift that could be consistent with a tidal torquing mechanism for radial alignments. Using our lensing optimized shape estimators, we estimate that intrinsic alignments of galaxy group members may contribute a systematic error to the mean differential projected surface mass density of groups inferred from weak lensing observations by −1 ± 20% at scales around 300 h −1 kpc from the group centre assuming a photometric redshift r.m.s. error of 10%, and given our group sample with median redshift of 0.17 and median virial masses ∼ 10 13 h −1 M .

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Section: Resultsmentioning

confidence: 71%

Section: Position Anglementioning

confidence: 97%

mentioning

confidence: 99%

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Galaxy And Mass Assembly (GAMA): galaxy radial alignments in GAMA groups

Schneider¹,

Cole²,

Frenk³

et al. 2013

Monthly Notices of the Royal Astronomical Society

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“…In both studies, the centroids, axis ratios and position angles of the cluster galaxies have been fixed to the observed light distributions. While studies such as the Sloan Lens ACS Survey indicate that light is generally a good tracer of mass for isolated galaxy lenses in the field (Koopmans et al 2006;Bolton et al 2008a,b), there can be misalignments especially for galaxies in dynamical environments such as in groups and clusters (e.g., Pereira et al 2008). If there are misalignments in the cluster galaxies in Abell 370 and Abell 611, then fixing these lens parameter values to the observed light distribution could lead to a bias in the determination of the halo size.…”

Section: Introductionmentioning

confidence: 99%

The halos of satellite galaxies: the companion of the massive elliptical lens SL2S J08544−0121

Suyu¹,

Halkola

2010

A&A

182

184

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Strong gravitational lensing by groups or clusters of galaxies provides a powerful technique to measure the dark matter properties of individual lens galaxies. We study in detail the mass distribution of the satellite lens galaxy in the group-scale lens SL2S J08544−0121 by modelling simultaneously the spatially extended surface brightness distribution of the source galaxy and the lens mass distribution using Markov chain Monte Carlo methods. In particular, we measure the dark matter halo size of the satellite lens galaxy to be 6.0 +2.9 −2.0 kpc with a fiducial velocity dispersion of 127 +21 −12 km s −1 . This is the first time the size of an individual galaxy halo in a galaxy group has been measured using strong gravitational lensing without assumptions of mass following light. We verify the robustness of our halo size measurement using mock data resembling our lens system. Our measurement of the halo size is compatible with the estimated tidal radius of the satellite galaxy, suggesting that halos of galaxies in groups experience significant tidal stripping, a process that has been previously observed on galaxies in clusters. Our mass model of the satellite galaxy is elliptical with its major axis misaligned with that of the light by ∼50 deg. The major axis of the total matter distribution is oriented more towards the centre of the host halo, exhibiting the radial alignment found in N-body simulations and observational studies of satellite galaxies. This misalignment between mass and light poses a significant challenge to modified Newtonian dynamics.

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“…Theoretically, Ciotti & Dutta (1994) studied the dynamical process of shape changing of an elliptical galaxy under the cluster's tidal field using N-body simulations, and showed an alignment tendency between the galaxies' major axes with the radial direction. Pereira et al (2008) found strong RA of dark matter substructures in a cluster halo in N-body simulations. Usami & Fujimoto (1997) studied a gaseous ellipsoid of uniform density orbiting in the logarithmic potential, and discussed the application of their result to the alignment of galaxies in rich clusters.…”

Section: Introductionmentioning

confidence: 88%

Radial alignment of elliptical galaxies by the tidal force of a cluster of galaxies

Zhang

et al. 2015

Monthly Notices of the Royal Astronomical Society

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Unlike the random radial orientation distribution of field elliptical galaxies, galaxies in a cluster are expected to point preferentially towards the center of the cluster, as a result of the cluster's tidal force on its member galaxies. In this work an analytic model is formulated to simulate this effect. The deformation time scale of a galaxy in a cluster is usually much shorter than the time scale of change of the tidal force; the dynamical process of the tidal interaction within the galaxy can thus be ignored. An equilibrium shape of a galaxy is then assumed to be the surface of equipotential, which is the sum of the self-gravitational potential of the galaxy and the tidal potential of the cluster at this location. We use a Monte-Carlo method to calculate the radial orientation distribution of these galaxies, by assuming the NFW mass profile of the cluster and the initial ellipticity of field galaxies. The radial angles show a single peak distribution centered at zero. The Monte-Carlo simulations also show that a shift of the reference center from the real cluster center weakens the anisotropy of the radial angle distribution. Therefore, the expected radial alignment cannot be revealed if the distribution of spatial position angle is used instead of that of radial angle. The observed radial orientations of elliptical galaxies in cluster Abell 2744 are consistent with the simulated distribution.

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Radial Alignment in Simulated Clusters

Cited by 76 publications

References 41 publications

Galaxy And Mass Assembly (GAMA): galaxy radial alignments in GAMA groups

Galaxy And Mass Assembly (GAMA): galaxy radial alignments in GAMA groups

The halos of satellite galaxies: the companion of the massive elliptical lens SL2S J08544−0121

Radial alignment of elliptical galaxies by the tidal force of a cluster of galaxies

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