95 research outputs found
Precision Cosmology with Weak Gravitational Lensing
In recent years, cosmological science has developed a highly predictive model for the universe on large scales that is in quantitative agreement with a wide range of astronomical observations. While the number and diversity of successes of this model provide great confidence that our general picture of cosmology is correct, numerous puzzles remain. In this dissertation, I analyze the potential of planned and near future galaxy surveys to provide new understanding of several unanswered questions in cosmology, and address some of the leading challenges to this observational program. In particular, I study an emerging technique called cosmic shear, the weak gravitational lensing produced by large scale structure. I focus on developing strategies to optimally use the cosmic shear signal observed in galaxy imaging surveys to uncover the physics of dark energy and the early universe.
In chapter 1 I give an overview of a few unsolved mysteries in cosmology and I motivate weak lensing as a cosmological probe. I discuss the use of weak lensing as a test of general relativity in chapter 2 and assess the threat to such tests presented by our uncertainty in the physics of galaxy formation. Interpreting the cosmic shear signal requires knowledge of the redshift distribution of the lensed galaxies. This redshift distribution will be significantly uncertain since it must be determined photometrically. In chapter 3 I investigate the influence of photometric redshift errors on our ability to constrain dark energy models with weak lensing. The ability to study dark energy with cosmic shear is also limited by the imprecision in our understanding of the physics of gravitational collapse. In chapter 4 I present the stringent calibration requirements on this source of uncertainty. I study the potential of weak lensing to resolve a debate over a long-standing anomaly in CMB measurements in chapter 5. Finally, in chapter 6 I summarize my findings and conclude with a brief discussion of my outlook on the future of weak lensing studies of cosmology
Clustering Constraints on the Relative Sizes of Central and Satellite Galaxies
We empirically constrain how galaxy size relates to halo virial radius using
new measurements of the size- and stellar mass-dependent clustering of galaxies
in the Sloan Digital Sky Survey. We find that small galaxies cluster much more
strongly than large galaxies of the same stellar mass. The magnitude of this
clustering difference increases on small scales, and decreases with increasing
stellar mass. Using Halotools to forward model the observations, we test an
empirical model in which present-day galaxy size is proportional to the size of
the virial radius at the time the halo reached its maximum mass. This simple
model reproduces the observed size-dependence of galaxy clustering in striking
detail. The success of this model provides strong support for the conclusion
that satellite galaxies have smaller sizes relative to central galaxies of the
same halo mass. Our findings indicate that satellite size is set prior to the
time of infall, and that a remarkably simple, linear size--virial radius
relation emerges from the complex physics regulating galaxy size. We make
quantitative predictions for future measurements of galaxy-galaxy lensing,
including dependence upon size, scale, and stellar mass, and provide a scaling
relation of the ratio of mean sizes of satellites and central galaxies as a
function of their halo mass that can be used to calibrate hydrodynamical
simulations and semi-analytic models.Comment: 12 pages plus an appendix. Submitted to MNRAS. Figure 5 shows that a
simple empirical model, with R50 = 0.01Rvir, can accurately reproduce new
measurements of size-dependent clustering of SDSS galaxies. Figure 9 shows
predictions for the size-dependence of future lensing measurements. Figure 10
provides a diagnostic for hydro sims and SAM
Probing Satellite Quenching With Galaxy Clustering
Satellites within simulated massive clusters are significantly spatially
correlated with each other, even when those satellites are not gravitationally
bound to each other. This correlation is produced by satellites that entered
their hosts relatively recently, and is undetectable for satellites that have
resided in their hosts for multiple dynamical timescales. Therefore, a
measurement of clustering statistics of cluster satellites may be used to
determine the typical accretion redshifts of those satellites into their
observed hosts. We argue that such measurements may be used to determine the
fraction of satellite galaxies that were quenched by their current hosts,
thereby discriminating among models for quenching of star formation in
satellite galaxies.Comment: 7 page
Physical Correlations of the Scatter between Galaxy Mass, Stellar Content, and Halo Mass
We use the UniverseMachine to analyze the source of scatter between the
central galaxy mass, the total stellar mass in the halo, and the dark matter
halo mass. We also propose a new halo mass estimator, the cen+N mass: the sum
of the stellar mass of the central and the N most massive satellites. We show
that, when real space positions are perfectly known, the cen+N mass has scatter
competitive with that of richness-based estimators. However, in redshift space,
the cen+N mass suffers less from projection effects in the UniverseMachine
model. The cen+N mass is therefore a viable low scatter halo mass estimator,
and should be considered an important tool to constrain cosmology with upcoming
spectroscopic data from DESI. We analyze the scatter in stellar mass at fixed
halo mass and show that the total stellar mass in a halo is uncorrelated with
secondary halo properties, but that the central stellar mass is a function of
both halo mass and halo age. This is because central galaxies in older halos
have had more time to grow via accretion. If the UniverseMachine model is
correct, accurate galaxy-halo modeling of mass selected samples therefore needs
to consider halo age in addition to mass.Comment: 13 pages, 11 figures, submitted to MNRA
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