• 천문학회지
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• 제29권spc1호
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• pp.85-86
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• 1996

The imaging spectroscopic observations of the Magellanic irregular galaxy NGC 4449 were made to show the detailed kinematic structure of the galaxy. Many filamentary structures and Several bubble-like structures are recognized in a 3D data cube of H$\alpha$ emission line. Velocity field shows the kpc-scale mosaic structure and counter- rotation of ionized gas.

• 천문학논총
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• 제30권2호
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• pp.367-369
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• 2015

The FastSound project is a galaxy redshift survey using Subaru/FMOS to detect $H{\alpha}$ emitting galaxies at z ~ 1:3, for the purpose of probing the origin of the accelerated expansion of the universe. The survey has detected ~4,000 galaxy redshifts in a total area of $30deg^2$, and detected the redshift space distortion at this redshift range for the first time. The redshift space distortion (RSD) signal will be used to derive a measurement of the growth rate of large scale structure, which will provide a test for modified gravity as a possible origin of accelerated cosmic explansion. Here we present an overview and the current status of the project.

• 천문학회보
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• 제43권2호
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• pp.40.3-40.3
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• 2018

This dissertation presents the results on two-dimensional Redshift space distortion (hereafter RSD) analyses of the large-scale structure of the universe using spectroscopic data and on improvement of modeling of the RSD effect. RSD is an effect caused by galaxies' peculiar velocity on their clustering feature in observation along the line of sight and is thus intimately connected to the growth rate of the structure in the universe, from which we can test the origin of cosmic acceleration and Einstein's theory of gravity at cosmic scales in the end. However, there are several challenges in modeling precise and accurate RSD effect, such as non-linearities and the existence of an exotic component, e.g. massive neutrino. As part of endeavors for modeling more precise and accurate galaxy clustering in redshift space, this dissertation includes a series of works for this issue. (More detailed descriptions were omitted.)

• Journal of Astronomy and Space Sciences
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• 제40권1호
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• pp.29-33
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• 2023

An unexplained acceleration on the order of 10^-8 cm s^-2, which is close to cH, where c is the speed of light and H is the Hubble constant, is detected in gravitationally bound systems of different scales, from the solar system to clusters of galaxies. We found that any test body located inside a fractal structure with fractal dimension D = 2 experiences acceleration of the same order and confirmed the previous work that photons propagating through this structure decrease the frequency owing to gravitational redshift. The acceleration can be directed against the movement of the test body. The fractal distribution of the matter should be at scales of at least hundreds of megaparsecs to a few gigaparsecs for the existence of this acceleration.

• 천문학회지
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• 제37권4호
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• pp.211-216
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• 2004

We present the results of an H I aperture synthesis mosaic of the Large Magellanic Cloud (LMC), made by combining data from 1344 separate pointing centers using the Australia Telescope Compact' Array (ATCA) and the Parkes multibeam receiver. The resolution of the mosaiced images is 50" (<15 pc, using a distance to the LMC of 55kpc). This mosaic, with a spatial resolution .15 times higher than that which had been previously obtained, emphasises the turbulent and fractal structure of the ISM on the small scale, resulting from the dynamical feedback of the star formation processes with the ISM. We also have done a widefield panoramic survey of H$\alpha$ emission from the Magellanic Clouds with an imager mounted on the 16-inch telescope at Siding Spring Observatory. This survey produced H$\alpha$ images which are equal to the ATCA survey in area coverage and resolution. This survey allows us to produce a continuum-subtracted image of the entire LMC. In contrast with its appearance in the H$\alpha$ image, the LMC is remarkably symmetric in H I on the largest scales, with the bulk of the H I residing in a disk of diameter 8. $^{\circ}4$ (7.3 kpc) and a spiral structure is clearly seen. The structure of the neutral atomic ISM in the LMC is dominated by H I filaments combined with numerous shells and holes.

• 천문학회보
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• 제40권2호
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• pp.32.3-33
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• 2015

There exist scaling relations that link the mass of supermassive black holes with both the velocity dispersion and the mass of the central stellar cusp of their host galaxies. This implies that these two components grow in tandem. Feedback from actively accreting supermassive black holes (AGN), in the form of multi-phase gas outflows, has been argued to be the agent of this co-evolution. Here we employ the powerful GMOS integral field spectroscopy unit on the 8.2m Gemini-North telescope to investigate ionized gas outflows of luminous Type 2 AGN in the local Universe (z<0.1). Our sample of 6 galaxies is drawn from the Sloan Digital Sky Survey (SDSS) and was selected based on their [OIII] dust-corrected luminosity (>1042 erg/s) and signatures of outflows in the [OIII] line profile of their spatially integrated SDSS spectra. These are arguably the best candidates to explore AGN feedback in action since they are < 1% of a large local type 2 AGN SDSS sample selected based on their [OIII] kinematics. We combine a careful spectral decomposition of the [OIII] and $H{\alpha}$ line profiles with spatial information on ~0.5kpc scales to understand the outflow kinematics and energetics in these objects. We find clear evidence for strong outflows in [OIII] and occasionally $H{\alpha}$ that are clearly driven by the ionizing radiation of the AGN. We kinematically and spatially decompose outflowing and rotating ionized gas components. We find [OIII] to be a better tracer of AGN outflows, while $H{\alpha}$ appears to be strongly affected by both stellar rotation and outflows induced by ongoing star formation. The observed kinematics and spatial distribution of the ionized gas imply a large opening angle for the outflow. Finally, we find the projected outflow velocity to decrease as a function of distance, while its dispersion shows a more complex structure with a potentially initially increasing trend (out to 0.5-1kpc distances).

• 천문학회보
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• 제38권2호
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• pp.39.1-39.1
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• 2013

We use high-resolution hydrodynamic simulations to study nonlinear gas responses to imposed non-axisymmetric stellar potentials in barred-spiral galaxies. The gas is assumed to be infinitesimally thin, isothermal, and unmagnetized. We consider various spiral-arm models with differing strength and pattern speed, while fixing the bar parameters. We find that the extent and shapes of spiral shocks as well as the related mass drift depend rather sensitively on the pattern speed. In models where the arm pattern is rotating more slowly than the bar, the gaseous arms extend from the bar ends all the way to the outer boundary, with a pitch angle slightly smaller than that of the stellar counterpart. The arms drive mass inflows at a rate of ${\sim}0.5-2.5M{\odot}/yr$ to the bar region to which the shock dissipation, external torque, and self-gravitational torque contribute about 50%, 40%, and 10%, respectively. About 85% of the inflowing mass is added to bar substructures such as an inner ring, dust lanes, and a nuclear ring. while the remaining 15% encircles the bar region. On the other hand, models where the arms corotate with the bar exhibit mass outflows, rather than inflows, over most of the arm region. In these models, spiral shocks are much more tightly wound than the stellar arms and cease to exist in the region where $M{\bot}/sinp*{\geq}25-40$, where $M{\bot}$ denotes the Mach number of a rotating gas perpendicular to the arms with pitch angle p*. We demonstrate that the distributions of line-of-sight velocities and densities can be a useful diagnostic tool to distinguish if the arms and bar corotate or not.

• 천문학논총
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• 제32권1호
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• pp.11-15
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• 2017

We present the AKARI far-infrared (FIR) all-sky maps and describe its characteristics, calibration accuracy and scientific capabilities. The AKARI FIR survey has covered 97% of the whole sky in four photometric bands, which cover continuously 50-180 micron with band central wavelengths of 65, 90, 140, and 160 microns. The data have been publicly released in 2014 (Doi et al., 2015) with improved data quality that have been achieved since the last internal data release (Doi et al., 2012). The accuracy of the absolute intensity is ${\leq}10%$ for the brighter regions. Quantitative analysis of the relative intensity accuracy and its dependence upon spatial scan numbers has been carried out. The data for the first time reveal the whole sky distribution of interstellar matter with arcminute-scale spatial resolutions at the peak of dust continuum emission, enabling us to investigate large-scale distribution of interstellar medium in great detail. The filamentary structure covering the whole sky is well traced by the all-sky maps. We describe advantages of the AKARI FIR all-sky maps for the study of interstellar matter comparing to other observational data.

• 천문학회지
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• 제48권5호
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• pp.285-298
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• 2015

Active Galactic Nuclei (AGN) with bright radio jets offer the opportunity to study the structure of and physical conditions in relativistic outflows. For such studies, multi-frequency polarimetric very long baseline interferometric (VLBI) observations are important as they directly probe particle densities, magnetic field geometries, and several other parameters. We present results from first-epoch data obtained by the Korean VLBI Network (KVN) within the frame of the Plasma Physics of Active Galactic Nuclei (PAGaN) project. We observed seven radio-bright nearby AGN at frequencies of 22, 43, 86, and 129 GHz in dual polarization mode. Our observations constrain apparent brightness temperatures of jet components and radio cores in our sample to > 10^8.01 K and > 10^9.86 K, respectively. Degrees of linear polarization m_L are relatively low overall: less than 10%. This indicates suppression of polarization by strong turbulence in the jets. We found an exceptionally high degree of polarization in a jet component of BL Lac at 43 GHz, with m_L ~ 40%. Assuming a transverse shock front propagating downstream along the jet, the shock front being almost parallel to the line of sight can explain the high degree of polarization.

• 천문학회보
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• 제41권1호
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• pp.39.4-40
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• 2016

We aim to investigate formation of satellite sub-galactic structures around isolated dwarf galaxies using cosmological hydrodynamic zoom simulations. For this, we modify a cosmological hydrodynamic code, GADGET-3, in a way that includes gas cooling down to T~10K, gas heating by universal reionization when z < 8.9, UV shielding for high density regions of $n_{shield}$ > $0.014cm^{-3}$, star formation in the dense regions ($n_H$ > $100cm^{-3}$), and supernova feedback. To get good statistics, we perform three different simulations for different target galaxies of the same mass of ${\sim}10^{10}M_{sun}$. Each simulation starts in a cubic box of a side length of 1Mpc/h with 17 million particles from z = 49. The mass of dark matter (DM) and gas particle is $M_{DM}=4.1{\times}10^3M_{sun}$ and $M_{gas}=7.9{\times}10^2M_{sun}$, respectively, thus each satellite sub-galactic structure can be resolved with more than hundreds or thousands particles. We analyze total 90 sub-galactic structures that have formed outside of the main halos but infall the main halos. We found that 1) mini halos that interact more with the other mini halos tend to accrete the more mass, 2) mini halos that interact more before the reionization tend to form more stars, 3) mini halos with the more interaction tend to approach closer to the galactic center and have the lower orbital circularity, 4) survivals even in the strong tidal fields evolve baryon dominated system, such as globular clusters.