Disk dominated galaxies retain their shapes below $z = 1.0$
Abstract:
The high abundance of disk galaxies without a large central bulge challenges predictions of current hydrodynamic simulations of galaxy formation. We aim to shed light on the formation of these objects by studying the redshift and mass dependence of their 3D shape distribution in the COSMOS galaxy survey. This distribution is inferred from the observed distribution of 2D shapes, using a reconstruction method which we test using hydrodynamic simulations. We find a moderate bias for the inferred average disk circularity and relative thickness with respect to the disk radius, but a large bias on the dispersion of these quantities. Applying the 3D shape reconstruction method on COSMOS data, we find no significant dependence of the inferred 3D shape distribution on redshift. The relative disk thickness shows a significant mass dependence which can be accounted for by the scaling of disk radius with galaxy mass. We conclude that the shapes of disk dominated galaxies are overall not subject to disruptive merging or feedback events below redshift $z=1.0$. This favours a scenario where these disks form early and subsequently undergo a tranquil evolution in isolation. In addition, our study shows that the observed 2D shapes of disk dominated galaxies can be well fitted using an ellipsoidal model for the galaxy 3D morphology combined with a Gaussian model for the 3D axes ratio distribution, confirming findings from similar work reported in the literature. Such an approach allows to build realistic mock catalogs with intrinsic galaxy shapes that will be essential for the study of intrinsic galaxy alignment as a contaminant of weak lensing surveys.Early-type galaxy spin evolution in the Horizon-AGN simulation
The Astrophysical Journal University of Chicago Press
Abstract:
Using the Horizon-AGN simulation data, we study the relative role of mergers and environmental effects in shaping the spin of early-type galaxies (ETGs) after $z \simeq 1$. We follow the spin evolution of 10,037 color-selected ETGs more massive than 10$^{10} \rm \, M_{\odot}$ that are divided into four groups: cluster centrals (3%), cluster satellites (33%), group centrals (5%), and field ETGs (59%). We find a strong mass dependence of the slow rotator fraction, $f_{\rm SR}$, and the mean spin of massive ETGs. Although we do not find a clear environmental dependence of $f_{\rm SR}$, a weak trend is seen in the mean value of spin parameter driven by the satellite ETGs as they gradually lose their spin as their environment becomes denser. Galaxy mergers appear to be the main cause of total spin changes in 94% of central ETGs of halos with $M_{vir} > 10^{12.5}\rm M_{\odot}$, but only 22% of satellite and field ETGs. We find that non-merger induced tidal perturbations better correlate with the galaxy spin-down in satellite ETGs than mergers. Given that the majority of ETGs are not central in dense environments, we conclude that non-merger tidal perturbation effects played a key role in the spin evolution of ETGs observed in the local ($z < 1$) universe.Enhanced constraints on large-scale structure from secondary CMB anisotropies
Abstract:
The large-scale structure of the Universe encodes invaluable information about the fundamental cosmological parameters, the physics of structure formation, and the thermodynamic history of the Universe. In this thesis, we explore how secondary anisotropies of the Cosmic Microwave Background (CMB), particularly the thermal Sunyaev-Zeldovich (tSZ) effect and CMB lensing, can improve constraints on the large-scale structure. We develop a framework to cross-correlate tSZ maps from the Planck satellite with the distribution of galaxies at low redshift using tomographic bins with data from the 2MASS Photometric Redshift catalogue and WISE x SuperCOSMOS. These cross-correlations enable precise measurements of the bias-weighted gas pressure, β¨πPeβ©, and the hydrostatic mass bias parameter, 1βbH,Β as a function of redshift.This thesis is primarily based on two complementary studies employing galaxy clustering (πΏπ Γ πΏπ), galaxy-tSZ cross-correlations (πΏπ Γ y), and galaxy-CMB lensing cross-correlations (πΏπ Γ K) to constrain cosmological and thermodynamic parameters across six redshift bins (π§ β [0.1, 0.6]).
In the first study, we use a combination of πΏπ Γ πΏπΒ and πΏπΒ Γ y to improve constraints on the thermal history of the Universe. We achieve ~6 \% precision on 1-bH across the six redshift bins, finding consistency with previous results and no evidence for significant redshift dependence. Our best-fit value of 1βπH = 0.75 Β± 0.03 aligns well with joint analyses of Planck cluster counts and CMB anisotropies calibrated with CMB lensing. Additionally, our constraints on β¨πππβ©, accurate to ~10% per bin, represent the most precise measurements to date, providing a robust test of baryonic feedback and models of energy injection.
The second study incorporatess πΏπ Γ KΒ to enhance our tomographic analysis of structure growth and gas thermodynamics. Using CMB lensing as an additional tracer of large-scale structure, we constrain the amplitude of fluctuations of the matter power spectrum, π8, to 6% across all redshift bins, the hydrostatic mass bias, 1 - bH to ~ 18 %, the bias-weighted average electron pressure, β¨πππβ©, to ~12%, the thermal energy density, Ξ©thΒ to ~ 10%, as well as TAGN, a single parameter quantifying the intensive thermodynamic properties of haloes. We perform multiple robustness checks to verify the stability of our models, and we report broad agreement with previous results in the literature.
This work builds on the use of secondary CMB anisotropies as a probe of non-linear physics, and of the interplay between dark matter and baryonic matter in haloes. We incorporate novel methods for combining tSZ data with other probes, in an attempt to refine models of halo bias and constrain π8. The inclusion of πΏπ Γ K helps to break degeneracies between key parameters of the theoretical framework used. Hence, we highlight the importance of secondary CMB anisotropies as a complementary tool for understanding the large-scale structure, offering new insights into the thermal evolution of the Universe, as well as the growth of structure.
Euclid preparation. TBD. The effect of linear redshift-space distortions in photometric galaxy clustering and its cross-correlation with cosmic shear
Submitted in A&A
Abstract:
Cosmological surveys planned for the current decade will provide us with unparalleled observations of the distribution of galaxies on cosmic scales, by means of which we can probe the underlying large-scale structure (LSS) of the Universe. This will allow us to test the concordance cosmological model and its extensions. However, precision pushes us to high levels of accuracy in the theoretical modelling of the LSS observables, in order not to introduce biases in the estimation of cosmological parameters. In particular, effects such as redshift-space distortions (RSD) can become relevant in the computation of harmonic-space power spectra even for the clustering of the photometrically selected galaxies, as it has been previously shown in literature studies. In this work, we investigate the contribution of linear RSD, as formulated in the Limber approximation by arXiv:1902.07226, in forecast cosmological analyses with the photometric galaxy sample of the Euclid survey, in order to assess their impact and quantify the bias on the measurement of cosmological parameters that neglecting such an effect would cause. We perform this task by producing mock power spectra for photometric galaxy clustering and weak lensing, as expected to be obtained from the Euclid survey. We then use a Markov chain Monte Carlo approach to obtain the posterior distributions of cosmological parameters from such simulated observations. We find that neglecting the linear RSD leads to significant biases both when using galaxy correlations alone and when these are combined with cosmic shear, in the so-called 3Γ2pt approach. Such biases can be as large as 5Ο-equivalent when assuming an underlying ΞCDM cosmology. When extending the cosmological model to include the equation-of-state parameters of dark energy, we find that the extension parameters can be shifted by more than 1Ο.