Lens galaxies in the Illustris simulation: power-law models and the bias of the Hubble constant from time delays

Xu, D.; Sluse, Dominique; Schneider, Peter; Springel, Volker; Vogelsberger, Mark; Nelson, Dylan; Hernquist, Lars

doi:10.1093/mnras/stv2708

Cited by 96 publications

(136 citation statements)

References 43 publications

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“…The total power-law slope also correlates with the in-situ formed stellar mass ratio and redshift, in line with previous simulation studies (Xu et al 2017;Remus et al 2017;Bellstedt et al 2018). Although a slightly negative total density slope/central velocity dispersion correlation and a shallower slope with time are in tension with observational trends, the uncertainties and systematics in observations may have obscured the true trends (Xu et al 2016(Xu et al , 2017Tagore et al 2018). In this work, we will hence investigate the redshift evolution of the density profiles of z = 0 ETG progenitors, and statistical ETG samples at higher redshifts selected based on their morphology.…”

Section: Introductionsupporting

confidence: 88%

Early-type galaxy density profiles from IllustrisTNG – II. Evolutionary trend of the total density profile

Wang

Vogelsberger

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We study the evolutionary trend of the total density profile of early-type galaxies (ETGs) in IllustrisTNG. To this end, we trace ETGs from z = 0 to z = 4 and measure the power-law slope γ of the total density profile for their main progenitors. We find that their γ steepen on average during z ∼ 4 − 2, then becoming shallower until z = 1, after which they remain almost constant, aside from a residual trend of becoming shallower towards z = 0. We also compare to a statistical sample of ETGs at different redshifts, selected based on their luminosity profiles and stellar masses. Due to different selection effects, the average slopes of the statistical samples follow a modified evolutionary trend. They monotonically decrease since z = 3, and after z ≈ 1, they remain nearly invariant with a mild increase towards z = 0. These evolutionary trends are mass-dependent for both samples, with low-mass galaxies having in general steeper slopes than their more massive counterparts. Galaxies that transitioned to ETGs more recently have steeper mean slopes as they tend to be smaller and more compact at any given redshift. By analyzing the impact of mergers and AGN feedback on the progenitors' evolution, we conjecture a multi-phase path leading to isothermality in ETGs: dissipation associated with rapid wet mergers tends to steepen γ from z = 4 to z = 2, whereas subsequent AGN feedback (especially in the kinetic mode) makes γ shallower again from z = 2 to z = 1. Afterwards, passive evolution from z = 1 to z = 0, mainly through gas-poor mergers, mildly decreases γ and maintains the overall mass distribution close to isothermal.

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Section: Introductionsupporting

confidence: 88%

Early-type galaxy density profiles from IllustrisTNG – II. Evolutionary trend of the total density profile

Wang

Vogelsberger

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…The bias on H0 is likely at the 0.6% level for the measurement of Suyu et al (2013) using RXJ1131; but the bias becomes more significant if the density profiles of individual lenses are less well constrained by the data, or if multiple lenses are combined. The bias may be larger in current datasets if degeneracies such as the source-position transformation (Schneider & Sluse 2014) mean that uncertainties of current measurements of η are underestimated (Xu et al 2016). Meng et al (2015) find that even with faint doubles where total magnitude of the arcs is ∼23, Euclid will be able to constrain the slope to 0.034 precision.…”

Section: Resultsmentioning

confidence: 95%

“…However the time-delays are proportional to λ, so the inferred time-delay distance is degenerate with the unknown value of the rescaling λ. This mass-sheet can be internal to the lens where the assumed density profile deviates from the true profile by a mass-sheet transformation within the Einstein ring (Xu et al 2016), or external to the lens where the outskirts of dark matter halos along the line-of-sight act like mass-sheets plus an external shear. The internal mass-sheet can in principle be broken with observations of the stellar kinematics, and whilst inference on the external mass-sheet can be made using observations of galaxies along the line of sight (Collett et al 2013;Greene et al 2013), such measurements are extremely challenging.…”

Section: Introductionmentioning

confidence: 99%

Observational selection biases in time-delay strong lensing and their impact on cosmography

Collett

Cunnington

2016

Mon. Not. R. Astron. Soc.

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Inferring cosmological parameters from time-delay strong lenses requires a significant investment of telescope time; it is therefore tempting to focus on the systems with the brightest sources, the highest image multiplicities and the widest image separations. We investigate if this selection bias can influence the properties of the lenses studied and the cosmological parameters that are inferred. Using a population of lenses with ellipsoidal powerlaw density profiles, we build a sample of double and quadruple image systems. Assuming reasonable thresholds on image separation and flux, based on current lens monitoring campaigns, we find that the typical density profile slopes of monitorable lenses are significantly shallower than the input ensemble. From a sample of quadruple image lenses we find that this selection function can introduce a 3.5% bias on the inferred time-delay distances if the ensemble of deflector properties is used as a prior for a cosmographical analysis. This bias remains at the 2.4% level when high resolution imaging of the quasar host is used to precisely infer the density profiles of individual lenses. We also investigate if the lines-of-sight for monitorable strong lenses are biased. After adding external convergence, κ, and shear to our lens population we find that the expectation value for κ is increased by 0.004 and 0.009 for doubles and quads respectively. κ is degenerate with the value of H 0 inferred from time delays; fortunately the shift in κ only induces a 0.9 (0.4) percent bias on H 0 for quads (doubles). We therefore conclude that whilst the properties of typical quasar lenses and their lines-of-sight do deviate from the global population, the total magnitude of this effect is likely a subdominant effect for current analyses, but has the potential to be a major systematic for samples of ∼25 or more lenses.

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“…As shown by Xu et al (2016), true profiles of realistic galaxies deviate from power-law distributions. In order to validate the robustness of the applied power-law assumption despite this fact, we first defined a curvature parameter for the 3-D enclosed mass distribution M (r) (defined by Eq.…”

Section: Robustness Of the Power-law Assumptionmentioning

confidence: 98%

The inner structure of early-type galaxies in the Illustris simulation

Springel

Sluse³

et al. 2017

Monthly Notices of the Royal Astronomical Society

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144

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Early-type galaxies provide unique tests for the predictions of the cold dark matter cosmology and the baryonic physics assumptions entering models for galaxy formation. In this work, we use the Illustris simulation to study correlations of three main properties of early-type galaxies, namely, the stellar orbital anisotropies, the central dark matter fractions and the central radial density slopes, as well as their redshift evolution since z = 1.0. We find that lower-mass galaxies or galaxies at higher redshift tend to be bluer in rest-frame colour, have higher central gas fractions, and feature more tangentially anisotropic orbits and steeper central density slopes than their higher-mass or lowerredshift counterparts, respectively. The projected central dark matter fraction within the effective radius shows a very mild mass dependence but positively correlates with galaxy effective radii due to the aperture effect. The central density slopes obtained by combining strong lensing measurements with single aperture kinematics are found to differ from the true density slopes. We identify systematic biases in this measurement to be due to two common modelling assumptions, isotropic stellar orbital distributions and power-law density profiles. We also compare the properties of early-type galaxies in Illustris to those from existing galaxy and strong lensing surveys, we find in general broad agreement but also some tension, which poses a potential challenge to the stellar formation and feedback models adopted by the simulation.

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Lens galaxies in the Illustris simulation: power-law models and the bias of the Hubble constant from time delays

Cited by 96 publications

References 43 publications

Early-type galaxy density profiles from IllustrisTNG – II. Evolutionary trend of the total density profile

Early-type galaxy density profiles from IllustrisTNG – II. Evolutionary trend of the total density profile

Observational selection biases in time-delay strong lensing and their impact on cosmography

The inner structure of early-type galaxies in the Illustris simulation

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