Galaxy Alignments: Observations and Impact on Cosmology

Kirk, D.; Brown, Michael L.; Hoekstra, Henk; Joachimi, Benjamin; Kitching, Thomas D.; Mandelbaum, Rachel; Sifón, Cristobál; Cacciato, Marcello; Choi, A.; Kiessling, Alina; Leonard, Adrienne; Rassat, A.; Schäfer, Björn Malte

doi:10.1007/s11214-015-0213-4

Cited by 166 publications

(160 citation statements)

References 268 publications

(508 reference statements)

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“…Typically, these alignments can be mitigated through modelling their effect on the power spectrum, or discounting galaxies which are expected to be most affected (such as close pairs on the sky or redder galaxies). An overiew of IA effects can be found in Joachimi et al (2015), Kiessling et al (2015) and Kirk et al (2015).…”

Section: Weak Lensing Systematicsmentioning

confidence: 99%

“…The first term is the cosmological signal that we are interested in, the following three terms are contaminating 'intrinsic alignment' terms (see Joachimi et al 2015;Kiessling et al 2015;Kirk et al 2015, for a recent review) and the final term is a systematics term (we have ignored terms correlating systematics with signals on the sky). Any contributions to these systematics terms which are uncorrelated between different experiments and wavebands will be suppressed by the crosscorrelation, greatly increasing the robustness of cosmological constraints.…”

Section: Introductionmentioning

confidence: 99%

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SKA weak lensing – I. Cosmological forecasts and the power of radio-optical cross-correlations

Harrison¹,

Camera²,

Zuntz³

et al. 2016

Mon. Not. R. Astron. Soc.

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We construct forecasts for cosmological parameter constraints from weak gravitational lensing surveys involving the Square Kilometre Array (SKA). Considering matter content, dark energy and modified gravity parameters, we show that the first phase of the SKA (SKA1) can be competitive with other Stage III experiments such as the Dark Energy Survey (DES) and that the full SKA (SKA2) can potentially form tighter constraints than Stage IV optical weak lensing experiments, such as those that will be conducted with LSST, WFIRST-AFTA or Euclid -like facilities. Using weak lensing alone, going from SKA1 to SKA2 represents improvements by factors of ∼ 10 in matter, ∼ 10 in dark energy and ∼ 5 in modified gravity parameters. We also show, for the first time, the powerful result that comparably tight constraints (within ∼ 5%) for both Stage III and Stage IV experiments, can be gained from cross-correlating shear maps between the optical and radio wavebands, a process which can also eliminate a number of potential sources of systematic errors which can otherwise limit the utility of weak lensing cosmology.

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Section: Weak Lensing Systematicsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

SKA weak lensing – I. Cosmological forecasts and the power of radio-optical cross-correlations

Harrison¹,

Camera²,

Zuntz³

et al. 2016

Mon. Not. R. Astron. Soc.

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“…During the processes leading to the formation of galaxies and their evolution, environmental effects such as tidal gravitational fields in the large-scale structure tend to align nearby galaxies. Furthermore, events such as galaxy mergers affect the relative alignments of both galaxies' shapes and angular momenta throughout their history (see Joachimi et al 2015;Kiessling et al 2015;Kirk et al 2015, for a recent review series). If we now focus on IAs only, the observed galaxy ellipticity is ǫ obs = γ + ǫ int , where ǫ int is the intrinsic ellipticity of a given galaxy.…”

Section: Intrinsic Alignmentsmentioning

confidence: 99%

SKA weak lensing – III. Added value of multiwavelength synergies for the mitigation of systematics

Camera

Harrison

Bonaldi

et al. 2016

Mon. Not. R. Astron. Soc.

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In this third paper of a series on radio weak lensing for cosmology with the Square Kilometre Array, we scrutinise synergies between cosmic shear measurements in the radio and optical/near-IR bands for mitigating systematic effects. We focus on three main classes of systematics: (i) experimental systematic errors in the observed shear; (ii) signal contamination by intrinsic alignments; and (iii) systematic effects due to an incorrect modelling of non-linear scales. First, we show that a comprehensive, multiwavelength analysis provides a self-calibration method for experimental systematic effects, only implying < 50% increment on the errors on cosmological parameters. We also illustrate how the cross-correlation between radio and optical/near-IR surveys alone is able to remove residual systematics with variance as large as 10 −5 , i.e. the same order of magnitude of the cosmological signal. This also opens the possibility of using such a cross-correlation as a means to detect unknown experimental systematics. Secondly, we demonstrate that, thanks to polarisation information, radio weak lensing surveys will be able to mitigate contamination by intrinsic alignments, in a way similar but fully complementary to available self-calibration methods based on position-shear correlations. Lastly, we illustrate how radio weak lensing experiments, reaching higher redshifts than those accessible to optical surveys, will probe dark energy and the growth of cosmic structures in régimes less contaminated by non-linearities in the matter perturbations. For instance, the higher-redshift bins of radio catalogues peak at z ≃ 0.8 − 1, whereas their optical/near-IR counterparts are limited to z 0.5 − 0.7. This translates into having a cosmological signal 2 to 5 times less contaminated by non-linear perturbations.

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“…Moreover, knowledge of intrinsic alignment properties of galaxies can be used to locate filaments of galaxies (Pimbblet 2005a;Rong et al 2016). Modelling of this alignment is needed in weak-lensing studies to quantify the intrinsic alignment bias (Joachimi et al 2011;Blazek et al 2015;Codis et al 2015a); see also Joachimi et al (2015), Kiessling et al (2015), and Kirk et al (2015) for an excellent overview of galaxy alignments.…”

Section: Introductionmentioning

confidence: 99%

Alignment of galaxies relative to their local environment in SDSS-DR8

Hirv

Pelt

Saar

et al. 2017

A&A

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Aims. We study the alignment of galaxies relative to their local environment in SDSS-DR8 and, using these data, we discuss evolution scenarios for different types of galaxies. Methods. We defined a vector field of the direction of anisotropy of the local environment of galaxies. We summed the unit direction vectors of all close neighbours of a given galaxy in a particular way to estimate this field. We found the alignment angles between the spin axes of disc galaxies, or the minor axes of elliptical galaxies, and the direction of anisotropy. The distributions of cosines of these angles are compared to the random distributions to analyse the alignment of galaxies. Results. Sab galaxies show perpendicular alignment relative to the direction of anisotropy in a sparse environment, for single galaxies and galaxies of low luminosity. Most of the parallel alignment of Scd galaxies comes from dense regions, from 2 . . . 3 member groups and from galaxies with low luminosity. The perpendicular alignment of S0 galaxies does not depend strongly on environmental density nor luminosity; it is detected for single and 2 . . . 3 member group galaxies, and for main galaxies of 4 . . . 10 member groups. The perpendicular alignment of elliptical galaxies is clearly detected for single galaxies and for members of ≤10 member groups; the alignment increases with environmental density and luminosity. Conclusions. We confirm the existence of fossil tidally induced alignment of Sab galaxies at low z. The alignment of Scd galaxies can be explained via the infall of matter to filaments. S0 galaxies may have encountered relatively massive mergers along the direction of anisotropy. Major mergers along this direction can explain the alignment of elliptical galaxies. Less massive, but repeated mergers are possibly responsible for the formation of elliptical galaxies in sparser areas and for less luminous elliptical galaxies.

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Galaxy Alignments: Observations and Impact on Cosmology

Cited by 166 publications

References 268 publications

SKA weak lensing – I. Cosmological forecasts and the power of radio-optical cross-correlations

SKA weak lensing – I. Cosmological forecasts and the power of radio-optical cross-correlations

SKA weak lensing – III. Added value of multiwavelength synergies for the mitigation of systematics

Alignment of galaxies relative to their local environment in SDSS-DR8

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