40 research outputs found
Dipolar Modulation of Large-Scale Structure.
For the last two decades, we have seen a drastic development of modern cosmology based on various observations such as the cosmic microwave background (CMB), type Ia supernovae, and baryonic acoustic oscillations (BAO). These observational evidences have led us to a great deal of consensus on the cosmological model so-called LCDM and tight constraints on cosmological parameters consisting the model.
On the other hand, the advancement in cosmology relies on the cosmological principle: the universe is isotropic and homogeneous on large scales. Testing these fundamental assumptions is crucial and will soon become possible given the planned observations ahead.
Dipolar modulation is the largest angular anisotropy of the sky, which is quantified by its direction and amplitude. We measured a huge dipolar modulation in CMB, which mainly originated from our solar system’s motion relative to CMB rest frame. However, we have not yet acquired consistent measurements of dipolar modulations in large-scale structure (LSS), as they require large sky coverage and a number of well-identified objects.
In this thesis, we explore measurement of dipolar modulation in number counts of LSS objects as a test of statistical isotropy. This thesis is based on two papers that were published in peer-reviewed journals. In Chapter 2 [Yoon et al., 2014], we measured a dipolar modulation in number counts of WISE matched with 2MASS sources. In Chapter 3 [Yoon & Huterer, 2015], we investigated requirements for detection of kinematic dipole in future surveys.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133440/1/mijin_1.pd
Citizen Engagement in Smart City Planning: The Case of Living Labs in South Korea
The smart city is recognized as a new city model for inclusive urban planning. Many local governments are making smart city plans to develop new policies that manage urban issues in South Korea. They identify issues through citizen surveys and decide which issues should be managed with priority. Some governments test developed policies based on citizen engagement. Most local governments use the living labs to encourage citizen engagement in smart city plans since these are public spaces where planners engage citizens to develop innovative and inclusive ideas. This study conducted a content analysis of smart city plans of local government. We analyzed the various approaches to the living lab and examined the stage of the planning process it is utilized in. Additionally, we identified the barrier to the living lab by interviewing people who participated in the smart city plan. According to the analysis, a barrier to citizen engagement exists in smart city plans; most citizen engagement is only used when planners develop ideas for setting visions and goals. It implies that citizen engagement occurs at a limited level in smart city plans and may cause planning to be less inclusive. We suggest that citizen engagement should be considered in the whole planning process to improve the inclusiveness of smart city plans and encourage sustainable citizen engagement
Minimising the impact of scale-dependent galaxy bias on the joint cosmological analysis of large scale structures
We present a mitigation strategy to reduce the impact of non-linear galaxy
bias on the joint `pt' cosmological analysis of weak lensing and
galaxy surveys. The -statistics that we adopt are based on Complete
Orthogonal Sets of E/B Integrals (COSEBIs). As such they are designed to
minimise the contributions to the observable from the smallest physical scales
where models are highly uncertain. We demonstrate that -statistics carry
the same constraining power as the standard two-point galaxy clustering and
galaxy-galaxy lensing statistics, but are significantly less sensitive to
scale-dependent galaxy bias. Using two galaxy bias models, motivated by
halo-model fits to data and simulations, we quantify the error in a standard pt analysis where constant galaxy bias is assumed. Even when adopting
conservative angular scale cuts, that degrade the overall cosmological
parameter constraints, we find of order biases for Stage III surveys
on the cosmological parameter .
This arises from a leakage of the smallest physical scales to all angular
scales in the standard two-point correlation functions. In contrast, when
analysing -statistics under the same approximation of constant galaxy
bias, we show that the bias on the recovered value for can be decreased
by a factor of , with less conservative scale cuts. Given the
challenges in determining accurate galaxy bias models in the highly non-linear
regime, we argue that pt analyses should move towards new
statistics that are less sensitive to the smallest physical scales.Comment: 14 pages, 13 figures, accepted to be published in MNRA
Improvement of Aerosol Optical Depth Retrieval over Hong Kong from a Geostationary Meteorological Satellite Using Critical Reflectance with Background Optical Depth Correction
Despite continuous efforts to retrieve aerosol optical depth (AOD) using a conventional 5-channelmeteorological imager in geostationary orbit, the accuracy in urban areas has been poorer than other areas primarily due to complex urban surface properties and mixed aerosol types from different emission sources. The two largest error sources in aerosol retrieval have been aerosol type selection and surface reflectance. In selecting the aerosol type from a single visible channel, the season-dependent aerosol optical properties were adopted from longterm measurements of Aerosol Robotic Network (AERONET) sun-photometers. With the aerosol optical properties obtained fromthe AERONET inversion data, look-up tableswere calculated by using a radiative transfer code: the Second Simulation of the Satellite Signal in the Solar Spectrum (6S). Surface reflectance was estimated using the clear sky composite method, awidely used technique for geostationary retrievals. Over East Asia, the AOD retrieved from the Meteorological Imager showed good agreement, although the values were affected by cloud contamination errors. However, the conventional retrieval of the AOD over Hong Kong was largely underestimated due to the lack of information on the aerosol type and surface properties. To detect spatial and temporal variation of aerosol type over the area, the critical reflectance method, a technique to retrieve single scattering albedo (SSA), was applied. Additionally, the background aerosol effect was corrected to improve the accuracy of the surface reflectance over Hong Kong. The AOD retrieved froma modified algorithmwas compared to the collocated data measured by AERONET in Hong Kong. The comparison showed that the new aerosol type selection using the critical reflectance and the corrected surface reflectance significantly improved the accuracy of AODs in Hong Kong areas,with a correlation coefficient increase from0.65 to 0.76 and a regression line change from MI [basic algorithm] = 0.41AERONET + 0.16 to MI [new algorithm] = 0.70AERONET + 0.01
KiDS-Legacy calibration: unifying shear and redshift calibration with the SKiLLS multi-band image simulations
We present SKiLLS, a suite of multi-band image simulations for the weak
lensing analysis of the complete Kilo-Degree Survey (KiDS), dubbed KiDS-Legacy
analysis. The resulting catalogues enable joint shear and redshift calibration,
enhancing the realism and hence accuracy over previous efforts. To create a
large volume of simulated galaxies with faithful properties and to a sufficient
depth, we integrated cosmological simulations with high-quality imaging
observations. We also improved the realism of simulated images by allowing the
point spread function (PSF) to differ between CCD images, including stellar
density variations and varying noise levels between pointings. Using realistic
variable shear fields, we accounted for the impact of blended systems at
different redshifts. Although the overall correction is minor, we found a clear
redshift-bias correlation in the blending-only variable shear simulations,
indicating the non-trivial impact of this higher-order blending effect. We also
explored the impact of the PSF modelling errors and found a small yet
noticeable effect on the shear bias. Finally, we conducted a series of
sensitivity tests, including changing the input galaxy properties. We conclude
that our fiducial shape measurement algorithm, lensfit, is robust within the
requirements of lensing analyses with KiDS. As for future weak lensing surveys
with tighter requirements, we suggest further investments in understanding the
impact of blends at different redshifts, improving the PSF modelling algorithm
and developing the shape measurement method to be less sensitive to the galaxy
properties.Comment: 28 pages, 31 figures, 2 tables, minor revisions to match the final
accepted versio
Discovery of a Radio Relic in the Massive Merging Cluster SPT-CL 2023-5535 from the ASKAP-EMU PILOT SURVEY
The ASKAP-EMU survey is a deep wide-field radio continuum survey designed to
cover the entire southern sky and a significant fraction of the northern sky up
to . Here, we report a discovery of a radio relic in the merging
cluster SPT-CL 2023-5535 at z=0.23 from the ASKAP-EMU pilot 300 sq. deg survey
(800-1088 MHz). The deep high-resolution data reveal a Mpc-scale radio
halo elongated in the east-west direction, coincident with the intracluster
gas. The radio relic is located at the western edge of this radio halo
stretched Mpc in the north-south orientation. The integrated spectral
index of the radio relic within the narrow bandwidth is . Our weak-lensing
analysis shows that the system is massive () and composed of at least three subclusters. We suggest a scenario,
wherein the radio features arise from the collision between the eastern and
middle subclusters. Our discovery illustrates the effectiveness of the
ASKAP-EMU survey in detecting diffuse emissions in galaxy clusters and when
completed, the survey will greatly increase the number of merging cluster
detections with diffuse radio emissions.Comment: Accepted to Ap