• 천문학회보
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• 제42권2호
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• pp.54.3-55
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• 2017

The Deep Lens Survey (DLS), a precursor to the Large Synoptic Survey Telescope (LSST), is a 20 deg2 survey carried out with NOAO's Blanco and Mayalltelescopes. DLS is unique in its depth reaching down to ~27th mags in BVRz bands. This enables a broad redshift baseline and is optimal for investigating cosmological evolution of the large scale structure. Galaxy-galaxylensing is a powerful tool to estimate averaged matter distribution around lensgalaxies by measuring shape distortions of background galaxies. The signal from galaxy-galaxy lensing is sensitive not only to galaxy halo properties, but also to cosmological environment at large scales. In this study, we measure galaxy-galaxy lensing and galaxy clustering, which together put strong constraints on the cosmological parameters. We obtain significant galaxy-galaxy lensing signals out to ~20 Mpc while tightly controlling systematics. The B-mode signals are consistent with zero. Our lens-source flip test indicates that minimal systematic errors are present in DLS photometric redshifts. Shear calibration is performed using high-fidelity galaxy image simulations. We demonstrate that the overall shape of the galaxy-galaxy lensing signal is well described by the halo model comprised of central and non-central halo contributions. Finally, we present our preliminary constraints on the matter density and the normalization parameters.

• 천문학회보
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• 제43권1호
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• pp.35.1-35.1
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• 2018

Shock waves have been observed in the outskirts of galaxy clusters. They are commonly interpreted as being driven by mergers of sub-clumps, so are called "merger shocks". We here report a study of the properties of merger shocks in merging galaxy clusters with cosmological hydrodynamic simulations. As a representative case, we describe the case where sub-clusters with mass ratio ~ 2 go through an almost head-on, binary-like merger. Because of the turbulent nature of hierarchical clustering, shock surfaces are not uniform, but composed of parts with different Mach numbers. As merger shocks expand from the core to the outskirts, the average Mach number, < $M_s$ >, increases. The shocks propagating along the merger axis could be observed as X-ray shocks and/or radio relics. The kinetic energy through the shocks peaks at ~ 1 Gyr after shock launching, or at ~ 1 - 2 Mpc from the core. The most energetic shocks are found to have the kinetic-energy weighted Mach number, < $M_s$ > $_{\phi}{\simeq}2-3$, and the CR-energy weighted Mach number, < $M_s$ > $_{CR}{\simeq}3-4$. We then discuss the observational implications of our results.

• 천문학회보
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• 제44권1호
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• pp.56.3-56.3
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• 2019

We are currently living in the era of the wide field cosmological surveys, either spectroscopic such as Dark Energy Spectrograph Instrument or photometric such as the Dark Energy Survey or the Large Synoptic Survey Telescope. By analyzing the distribution of matter clustering, we can use the growth of structure, in combination with measurements of the expansion of the Universe, to understand dark energy or to test different models of gravity. But we also live in the era of multi-tracer or multi-messenger astrophysics. In particular, during the next decades radio surveys will map the matter distribution at higher redshifts. Like in optical surveys, there are radio imaging surveys such as continuum radio surveys such as the ongoing EMU or spectroscopic by measuring the hydrogen 21cm line. However, we can also use intensity mapping as a low resolution spectroscopic technique in which we use the intensity given by the emission from neutral hydrogen from patches of the sky, at different redshifts. By cross-correlating this maps with galaxy catalogues we can improve our constraints on cosmological parameters and to understand better how neutral hydrogen populates different types of galaxies and haloes. Creating realistic mock intensity mapping catalogues is necessary to optimize the future analysis of data. I will present the mock neutral hydrogen catalogues that we are developing, using the Horizon run 4 simulations, to cross-correlate with mock galaxy catalogues from low redshift surveys and I will show the preliminary results from the first mock catalogues.

• 천문학회보
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• 제45권1호
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• pp.68.3-69
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• 2020

We develop a series of N-body data challenges, functional to the final analysis of the extended Baryon Oscillation Spectroscopic Survey (eBOSS) Data Release 16 (DR16) galaxy sample, primarily based on high-fidelity catalogs constructed from the Outer Rim simulation. We generate synthetic galaxy mocks by populating Outer Rim halos with a variety of halo occupation distribution (HOD) schemes of increasing complexity, spanning different redshift intervals. We then assess the performance of three complementary redshift space distortion (RSD) models in configuration and Fourier space, adopted for the analysis of the complete DR16 eBOSS sample of Luminous Red Galaxies (LRGs). We find that all the methods are mutually consistent, with comparable systematic errors on the Alcock-Paczynski parameters and the growth of structure, and robust to different HOD prescriptions - thus validating the robustness of the models and the pipelines used for the baryon acoustic oscillation (BAO) and full shape clustering analysis. Our study is relevant for the final eBOSS DR16 'consensus cosmology', as the systematic error budget is informed by testing the results of analyses against these high-resolution mocks. In addition, it is also useful for future large-volume surveys, since similar mock-making techniques and systematic corrections can be readily extended to model for instance the DESI galaxy sample.

• 천문학회보
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• 제45권1호
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• pp.38.2-38.2
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• 2020

Horizon Run 5 (HR5) is a cosmological hydrodynamical simulation which captures the properties of the Universe on a Gpc scale while achieving a resolution of 1 kpc. This enormous dynamic range allows us to simultaneously capture the physics of the cosmic web on very large scales and account for the formation and evolution of dwarf galaxies on much smaller scales. Inside the simulation box. we zoom-in on a high-resolution cuboid region with a volume of 1049 × 114 × 114 Mpc3. The subgrid physics chosen to model galaxy formation includes radiative heating/cooling, reionization, star formation, supernova feedback, chemical evolution tracking the enrichment of oxygen and iron, the growth of supermassive black holes and feedback from active galactic nuclei (AGN) in the form of a dual jet-heating mode. For this simulation we implemented a hybrid MPI-OpenMP version of the RAMSES code, specifically targeted for modern many-core many thread parallel architectures. For the post-processing, we extended the Friends-of-Friend (FoF) algorithm and developed a new galaxy finder to analyse the large outputs of HR5. The simulation successfully reproduces many observations, such as the cosmic star formation history, connectivity of galaxy distribution and stellar mass functions. The simulation also indicates that hydrodynamical effects on small scales impact galaxy clustering up to very large scales near and beyond the baryonic acoustic oscillation (BAO) scale. Hence, caution should be taken when using that scale as a cosmic standard ruler: one needs to carefully understand the corresponding biases. The simulation is expected to be an invaluable asset for the interpretation of upcoming deep surveys of the Universe.

• 천문학논총
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• 제30권1호
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• pp.11-16
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• 2015

First light galaxies have predictable linear clustering, and are expected to produce fluctuations with a characteristic spatial power spectrum, which peaks at an angular scale of ~ 10 arcminutes and in the $1-2{\mu}m$ spectral regions. The Cosmic Infrared Background ExpeRiment 2 (CIBER2) is a dedicated sounding rocket mission for measuring the fluctuations in the extragalactic infrared background light, following up the previous successful measurements of CIBER1. With a 28.5 cm telescope accompanied with three arms of camera barrels and a dual broadband filter on each H2RG (${\lambda}_c=2.5{\mu}m$) array, CIBER2 can measure 6 bands of wide field ($1.1{\times}2.2$ degrees) up to 3 AB magnitudes deeper than CIBER1. This project is leaded by California Institute of Technology/Jet Propulsion Laboratory, collaborating internationally with Institute of Space and Astronautical Science in Japan, Korea Astronomy and Space Science Institute, Korea Basic Science Institute, and Seoul National University. The Korean team is in charge of 1) one H2RG scientific array, 2) ground station hardware and software, 3) telescope lenses, and 4) flight and test bed electronics fabrication. In this paper, we describe the detailed activities of the Korean participation as well as the current status of the CIBER2 project.