The radial alignment of dark matter subhaloes: from simulations to observations

Knebe, Alexander; Yahagi, Hideki; Kase, Hiroyuki; Lewis, Geraint F.; Gibson, Brad K.

doi:10.1111/j.1745-3933.2008.00495.x

Cited by 24 publications

(28 citation statements)

References 44 publications

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“…7 are too large to detect a radius dependence in the position angle distributions. We note again however, that our observed radial alignments are much weaker than that found for the alignments of haloes in N -body simulations (Knebe et al 2008b). Our observed mean position angles are consistent at 2-σ with previous measurements using SDSS isophotal shapes (Pereira & Kuhn 2005;Faltenbacher et al 2007), which found equivalent values of φ ∼42-44 • with φ increasing with increasing group radius.…”

Section: Resultssupporting

confidence: 87%

“…Kuhlen et al (2007) and Knebe et al (2008b) showed that using only the inner 10-20% of the particles in a dark matter sub-halo, rather than all bound sub-halo particles, introduces significant scatter in the distribution of radial alignment angles that is more consistent with previous observations. Using N -body simulations with gas and star formation physics included, Knebe et al (2010) concluded that gas physics does not measurably affect the radial alignment angles of satellite galaxies relative to the orientations inferred from studying the parent dark matter sub-haloes alone.…”

supporting

confidence: 78%

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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: Resultssupporting

confidence: 87%

supporting

confidence: 78%

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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“…Furthermore, it has also been reported in the literature that the orientation of their shapes is not random and their major axis preferentially points towards their host centre (e.g. Kuhlen et al 2007; Faltenbacher et al 2008; Knebe et al 2008a,b; Pereira et al 2008). This ‘radial alignment’ is quantified by the (cosine of the) angle between the position vector of the subhalo d sat in the rest frame of its host halo and the major axis a sat of the actual subhalo (again, as determined via the eigenvectors of the standard moment of inertia tensor).…”

Section: Resultsmentioning

confidence: 92%

The impact of baryonic physics on the shape and radial alignment of substructures in cosmological dark matter haloes

Knebe¹,

Libeskind²,

Knollmann³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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We use two simulations performed within the Constrained Local UniversE Simulation (CLUES) project to study both the shape and radial alignment of (the dark matter component of) subhaloes; one of the simulations is a dark matter only model while the other run includes all the relevant gas physics and star formation recipes. We find that the involvement of gas physics does not have a statistically significant effect on either property – at least not for the most massive subhaloes considered in this study. However, we observe in both simulations including and excluding gas dynamics a (pronounced) evolution of the dark matter shapes of subhaloes as well as of the radial alignment signal since infall time. Further, this evolution is different when positioned in the central and outer regions of the host halo today; while subhaloes tend to become more aspherical in the central 50 per cent of their host’s virial radius, the radial alignment weakens in the central regime while strengthening in the outer parts. We confirm that this is due to tidal torquing and the fact that subhaloes at pericentre move too fast for the alignment signal to respond.

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“…Agustsson & Brainerd 2006;Kang et al 2007;Faltenbacher et al 2008;Knebe et al 2008;Okumura et al 2008). Since real galaxies are seen in projection, we project the dark matter distribution before diagonalizing the moment of inertia tensor.…”

Section: The Orientations Of Semi-analytic Galaxiesmentioning

confidence: 99%

Alignment between galaxies and large-scale structure

Faltenbacher

White

et al. 2009

Res. Astron. Astrophys.

166

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Based on the Sloan Digital Sky Survey DR6 (SDSS) and Millennium Simulation (MS) we investigate the alignment between galaxies and large-scale structure. For this purpose we develop two new statistical tools, namely the alignment correlation function and the cos(2θ)-statistic. The former is a two-dimensional extension of the traditional two-point correlation function and the latter is related to the ellipticity correlation function used for cosmic shear measurements. Both are based on the cross correlation between a sample of galaxies with orientations and a reference sample which represents the large-scale structure. We apply the new statistics to the SDSS galaxy catalog. The alignment correlation function reveals an overabundance of reference galaxies along the major axes of red, luminous (L L * ) galaxies out to projected separations of 60 h −1 Mpc. The signal increases with central galaxy luminosity. No alignment signal is detected for blue galaxies. The cos(2θ)-statistic yields very similar results. Starting from a MS semi-analytic galaxy catalog we assign an orientation to each red, luminous and central galaxy, based on that of the central region of the host halo (with size similar to that of the stellar galaxy). As an alternative we use the orientation of the host halo itself. We find a mean projected misalignment between a halo and its central region of ∼ 25• . The misalignment decreases slightly with increasing luminosity of the central galaxy. Using the orientations and luminosities of the semi-analytic galaxies we repeat our alignment analysis on mock surveys of the MS. Agreement with the SDSS results is good if the central orientations are used. Predictions using the halo orientations as proxies for central galaxy orientations overestimate the observed alignment by more than a factor of 2. Finally, the large volume of the MS allows us to generate a two-dimensional map of the alignment correlation function which shows the reference galaxy distribution to be flattened parallel to the orientations of red luminous galaxies with axis ratios of ∼ 0.5 and ∼ 0.75 for halo and central orientations, respectively. These ratios are almost independent of scale out to 60 h −1 Mpc.

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The radial alignment of dark matter subhaloes: from simulations to observations

Cited by 24 publications

References 44 publications

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

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

The impact of baryonic physics on the shape and radial alignment of substructures in cosmological dark matter haloes

Alignment between galaxies and large-scale structure

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