Weak gravitational lensing as a probe of large-scale structure and galaxy formation

The study of the relation between galaxies and their surrounding haloes of dark matter is a fundamental component to understand the evolution of the large-scale structure of the Universe. In this thesis, we investigate how galaxy-galaxy lensing, the distortion of the shapes of background galaxies around selected foreground lens galaxies, can help to elucidate this interplay together with complementary galaxy clustering measurements. Galaxy-galaxy lensing, on one hand, provides a direct estimate of the mass inside a given aperture and also its distribution, which allows for connecting certain classes of galaxies, chosen according to properties such as stellar mass and colour, to the mass and shape of the encompassing dark host structures. Galaxy clustering, on the other hand, describes the spatial distribution of galaxies and the combination of the two probes can be used to jointly constrain the cosmological parameters for the matter fraction Ωm and the amplitude of the matter fluctuations σ8. This thesis is split into three parts addressing three outstanding challenges each for small-scale galaxy-galaxy lensing to act as a competitive probe for current and future large-scale structure surveys. In Chapter 3 (Renneby et al., 2018), we investigate how a cosmological rescaling algorithm, which fast and cost-efficiently maps particle and halo distributions from one N-body simulation to another one with a different set of cosmological parameters, can be adapted to accurately predict galaxy-galaxy lensing profiles and quantify the induced errors. The subsequent Chapter 4 (Renneby et al., prepa) deals with verifying that both lensing and clustering probes yield consistent predictions in semi-analytical models of galaxy formation (SAMs) and hydrodynamical simulations. To conclude in Chapter 5 (Renneby et al., prepb), we examine the main systematic effect on lensing profiles, namely the imprint of baryonic processes, using a range of hydrodynamical simulations. The major findings are the following: In Chapter 3 we establish that an N-body simulation with a set of parameters (Ωm, σ8) can be used to emulate the lensing profiles for central galaxies with no further restriction in a different background cosmology with two principal biases in halo concentrations Δc and the positions of the halo splashback radii Δrsp. These biases can be predicted well with the concentration-mass-redshift relations presented in Ludlow et al. (2016) and the splashback radius-mass-redshift relations from Diemer et al. (2017). To continue, we discover that lensing and clustering observations in Chapter 4 point towards a consistent picture for the feedback prescriptions. The hydrodynamical IllustrisTNG simulation suite is in agreement with current constraints from the KiDS+GAMA surveys for stellar mass only selected samples as well as locally brightest galaxies (LBGs) in SDSS. For the Munich SAM L-Galaxies, constraints from LBG lensing and general clustering demand a weaker radio-mode AGN feedback and shorter dynamical friction merger time than the default setup in the latest model from Henriques et al. (2015). Still, this comparison also highlights difficulties in the two modelling frameworks to accurately predict the signal for intermediate mass red galaxies below < 10^11 Msun, where the observations suggest lower host halo masses for quenched satellite galaxies. This calls for improved environmental quenching and merging mechanisms in galaxy groups and clusters. Finally, we retrieve a similar baryonic imprint as previously established in the literature for specific lens samples (e.g. Leauthaud et al., 2017) with suppressions of 10 − 20% for 0.1 < r h−1 Mpc < 1 and show that it is generalisable to a large range of stellar masses and for central galaxies in groups. Despite their different galaxy formation recipes, the Eagle and IllustrisTNG simulations produce similar lensing profile descriptions consistent with observations. The considerable gas ejection of the AGN feedback implementation in the Illustris simulation puts it at the extreme end in terms of the extent of the suppression up to r ~ 5 − 6 h−1 Mpc whereas its successor IllustrisTNG achieves mass convergence at r ~ 1 − 2 h−1 Mpc. These radii are largely independent of the stellar mass of the samples, with a slightly larger impact for group class haloes where the AGN feedback is most efficient, and there is little redshift evolution to z = 1. We attempt to parameterise the effect using the baryonic correction model of Schneider & Teyssier (2015) for group and cluster-size haloes in the TNG300 simulation. We find that the model captures the main deformation features but that further work is required for it to properly adjust the gravity-only mass profiles

The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey::N-body Mock Challenge for the eBOSS Emission Line Galaxy Sample

21 pages, 7 figures and 9 tables, A summary of all SDSS BAO and RSD measurements with accompanying legacy figures can be found at https://www.sdss.org/science/final-bao-and-rsd-measurements/ . The full cosmological interpretation of these measurements can be found at https://www.sdss.org/science/cosmology-results-from-eboss/ . Comments are welcomeInternational audienceCosmological growth can be measured in the redshift space clustering of galaxies targeted by spectroscopic surveys. Accurate prediction of clustering of galaxies will require understanding galaxy physics which is a very hard and highly non-linear problem. Approximate models of redshift space distortion (RSD) take a perturbative approach to solve the evolution of dark matter and galaxies in the universe. In this paper we focus on eBOSS emission line galaxies (ELGs) which live in intermediate mass haloes. We create a series of mock catalogues using haloes from the Multidark and {\sc Outer Rim} dark matter only N-body simulations. Our mock catalogues include various effects inspired by baryonic physics such as assembly bias and the characteristics of satellite galaxies kinematics, dynamics and statistics deviating from dark matter particles. We analyse these mocks using the TNS RSD model in Fourier space and the CLPT in configuration space. We conclude that these two RSD models provide an unbiased measurement of redshift space distortion within the statistical error of our mocks. We obtain the conservative theoretical systematic uncertainty of $3.3\%$, $1.8\%$ and $1.5\%$ in $f\sigma_8$, $\alpha_{\parallel}$ and $\alpha_{\bot}$ respectively for the TNS and CLPT models. We note that the estimated theoretical systematic error is an order of magnitude smaller than the statistical error of the eBOSS ELG sample and hence are negligible for the purpose of the current eBOSS ELG analysis

Comparing galaxy formation in the L-GALAXIES semi-analytical model and the IllustrisTNG simulations

We perform a comparison, object by object and statistically, between the Munich semi-analytical model, L-GALAXIES, and the IllustrisTNG hydrodynamical simulations. By running L-GALAXIES on the IllustrisTNG dark matter-only merger trees, we identify the same galaxies in the two models. This allows us to compare the stellar mass, star formation rate, and gas content of galaxies, as well as the baryonic content of subhaloes and haloes in the two models. We find that both the stellar mass functions and the stellar masses of individual galaxies agree to better than ∼0.2dex. On the other hand, specific star formation rates and gas contents can differ more substantially. At z = 0, the transition between low-mass star-forming galaxies and high-mass quenched galaxies occurs at a stellar mass scale ∼0.5dex lower in IllustrisTNG than that in L-GALAXIES. IllustrisTNG also produces substantially more quenched galaxies at higher redshifts. Both models predict a halo baryon fraction close to the cosmic value for clusters, but IllustrisTNG predicts lower baryon fractions in group environments. These differences are primarily due to differences in modelling feedback from stars and supermassive black holes. The gas content and star formation rates of galaxies in and around clusters and groups differ substantially, with IllustrisTNG satellites less star forming and less gas rich. We show that environmental processes such as ram-pressure stripping are stronger and operate to larger distances and for a broader host mass range in IllustrisTNG. We suggest that the treatment of galaxy evolution in the semi-analytic model needs to be improved by prescriptions that capture local environmental effects more accurately

Joint galaxy-galaxy lensing and clustering constraints on galaxy formation

We compare predictions for galaxy–galaxy lensing profiles and clustering from the Henriques et al. public version of the Munich semi-analytical model (SAM) of galaxy formation and the IllustrisTNG suite, primarily TNG300, with observations from KiDS + GAMA and SDSS-DR7 using four different selection functions for the lenses (stellar mass, stellar mass and group membership, stellar mass and isolation criteria, and stellar mass and colour). We find that this version of the SAM does not agree well with the current data for stellar mass-only lenses with M∗ >1011M⊙⁠. By decreasing the merger time for satellite galaxies as well as reducing the radio-mode active galactic nucleus accretion efficiency in the SAM, we obtain better agreement, both for the lensing and the clustering, at the high-mass end. We show that the new model is consistent with the signals for central galaxies presented in Velliscig et al. Turning to the hydrodynamical simulation, TNG300 produces good lensing predictions, both for stellar mass-only (χ2 = 1.81 compared to χ2 = 7.79 for the SAM) and locally brightest galaxy samples (χ2 = 3.80 compared to χ2 = 5.01). With added dust corrections to the colours it matches the SDSS clustering signal well for red low-mass galaxies. We find that both the SAMs and TNG300 predict ∼50 per cent excessive lensing signals for intermediate-mass red galaxies with 10.2 10M*[M⊙] −1Mpc⁠, which require further theoretical development

Joint galaxy–galaxy lensing and clustering constraints on galaxy formation

© 2020 The Author(s) We compare predictions for galaxy-galaxy lensing profiles and clustering from the Henriques et al. public version of the Munich semi-analytical model (SAM) of galaxy formation and the IllustrisTNG suite, primarily TNG300, with observations from KiDS + GAMA and SDSS-DR7 using four different selection functions for the lenses (stellar mass, stellar mass and group membership, stellar mass and isolation criteria, and stellar mass and colour). We find that this version of the SAM does not agree well with the current data for stellar mass-only lenses with M∗ > 1011 M. By decreasing the merger time for satellite galaxies as well as reducing the radio-mode active galactic nucleus accretion efficiency in the SAM, we obtain better agreement, both for the lensing and the clustering, at the high-mass end. We show that the new model is consistent with the signals for central galaxies presented in Velliscig et al. Turning to the hydrodynamical simulation, TNG300 produces good lensing predictions, both for stellar mass-only (χ2 = 1.81 compared to χ2 = 7.79 for the SAM) and locally brightest galaxy samples (χ2 = 3.80 compared to χ2 = 5.01). With added dust corrections to the colours it matches the SDSS clustering signal well for red low-mass galaxies. We find that both the SAMs and TNG300 predict ∼ 50 per cent excessive lensing signals for intermediate-mass red galaxies with 10.2 < log10M∗[M] < 11.2 at r ≈ 0.6 h−1 Mpc, which require further theoretical development