• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.31.2-31.2
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• 2017

The central regions of barred-spiral galaxies contain interesting gaseous structures such as dust lanes and nuclear rings with intense star formation. While our previous studies were useful in understanding the formation of these structures star formation history, they were limited to 2D isothermal galaxies in which the stellar disk and halo are modeled by fixed gravitational potentials. To study the effects of bar growth as well as the vertical dimension, we use the mesh-free hydrodynamic code named GIZMO and run 3D simulations by treating the stellar disk and halo as being live. We find that the new 3D models form the gaseous features similarly to the previous 2D models, although the detailed formation processes are quite different. For example, a ring has a large radius when it first forms and shrinks over time in the previous 2D models. In the 3D live-potential models, however, a ring forms small and grows in size with time. We present the results of the new simulations and discuss them in comparison with the previous 2D results.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.35.2-35.2
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• 2018

Magnetic fields in clusters of galaxies play a critical role in shaping up the intracluster medium. Their existence has been established through observations of synchrotron emission, especially from radio relics and halos, as well as observations of rotation measure. In the so-called Sausage relic, which is one of Mpc-size giant radio relics detected in the outskirts of merging clusters, for instance, the magnetic fields are believed to have a few ${\mu}G$ strength and a Mpc scale. The observed magnetic fields are conjectured to be produced by the process of small-scale turbulence dynamo. To investigate the dynamo origin, we simulate the development of turbulence and the follow-up amplification of magnetic fields in galaxy clusters using a three-dimensional magnetohydrodynamical(MHD) code. Turbulence is induced in highly stratified backgrounds expected in clusters, and driven sporadically mimicking major mergers. We here present preliminary results, aiming to answer whether the turbulence dynamo scenario can explain observed magnetic fields in clusters of galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.49.2-49.2
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• 2019

Clusters of galaxies shape up through a series of hierarchical mergers. It is believed that major mergers lead to cluster-wide shock waves, which are manifested as radio relics. The 1RXS J0603.0+4213 and CIZA J2242.8+5301 clusters, for instance, contain Mpc-size giant radio relics in the outskirts. Synchrotron emission from these radio relics reveals the presence of relativistic electrons and the magnetic fields of a few ${\mu}G$ strength. The presence of such magnetic fields in the ICM has been explained by the so-called small-scale turbulent dynamo. To get quantitative measures for magnetic fields in clusters of galaxies, we investigate the development of turbulence and the follow-up amplification of magnetic fields through three-dimensional numerical magnetohydrodynamical (MHD) simulations. The turbulence is induced in highly stratified cluster media, and driven sporadically by major mergers. We here present the results, aiming to answer whether the turbulence dynamo scenario can explain the observed strength and scale of magnetic fields in clusters. Also, we discuss whether the observed properties of giant radio relics can be reproduced in our simulations.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.52.3-53
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• 2018

We compare vertical profiles of the extraplanar $H{\alpha}$ emission to those of the UV emission for 38 nearby edge-on late-type galaxies. It is found that detection of the "diffuse" extraplanar dust (eDust), traced by the vertically extended, scattered UV starlight, always coincides with the presence of the extraplanar $H{\alpha}$ emission. A strong correlation between the scale heights of the extraplanar $H{\alpha}$ and UV emissions is also found; the scale height at $H{\alpha}$ is found to be ~0.74 of the scale height at FUV. Our results may indicate the multiphase nature of the diffuse ionized gas and dust in the galactic halos. The existence of eDust in galaxies where the extraplanar $H{\alpha}$ emission is detected suggests that a larger portion of the extraplanar $H{\alpha}$ emission than that predicted in previous studies may be caused by $H{\alpha}$ photons that originate from H II regions in the galactic plane and are subsequently scattered by the eDust. This possibility raise an advantage in studying the extraplanar diffuse ionized gas. We also find that the scale heights of the extraplanar emissions normalized to the galaxy size correlate well with the star formation rate surface density of the galaxies. The properties of eDust in our galaxies is on a continuation line of that found through previous observations of the extraplanar polycyclic aromatic hydrocarbons emission in more active galaxies known to have galactic winds.

• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.597-600
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• 2004

A substantial number of processes have been suggested as possible contributors to the extragalactic $\gamma$-ray background (EGRB). Yet another contribution to this background will be emission produced in hadronic interactions of cosmic-ray protons with the cluster thermal gas; this class of cosmic rays (CRs) has been shown to be responsible for the EUV emission in the Coma Cluster of galaxies. In this paper we assume the CRs in the Coma Cluster is prototypic of all clusters and derive the contribution to the EGRB from all clusters over time. We examine two different possibilities for the scaling of the CR flux with cluster size: the number density of the CRs scale with the number density of the thermal plasma, and alternatively, the energy density of the CRs scale with the energy density of the plasma. We find that in all scenarios the EGRB produced by this process is sufficiently low that it will not be observable in comparison with other mechanisms that are likely to produce an EGRB.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.46.2-46.2
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• 2012

The black hole mass-stellar velocity dispersion ($M_{BH}-{\sigma}_*$) relation observed in the present-day universe has motivated numerous studies on the black hole-galaxy co-evolution. It is crucial to define the$M_{BH}-{\sigma}_*$ local active galaxies since cosmic evolution of the correlations is calibrated based on the local relation. However, stellar velocity dispersion is difficult to measure in active galaxies due to much higher AGN continuum than stellar pseudo-continuum, resulting in a small sample with reliable velocity dispersion measurements for studying the AGN $M_{BH}-{\sigma}_*$ relation. To increase the sample size and improve the measurements, we obtained high S/N near-IR spectra for 3 local AGNs, i.e., NGC 3227, Akn 120, 3C 390.3, for which reverberation black hole masses are measured, using the TripleSpec at the Palomar 5-m Telescope. By investigating aperture effect and correcting for rotation component, we determine the luminosity-weighted ${\sigma}_*$, based on the spatially resolved kinematics and compare them with optical measurements from literature. Combining our new measurements with literature data, we present an improved $M_{BH}-{\sigma}_*$ relation for the enlarged sample of reverberation-mapped AGNs.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.46.3-46.3
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• 2017

We investigate the changes of galaxy spin orientation in dense environments using hydrodynamical cosmological zoom-in simulations for 17 galaxy clusters. This study reveals that the spin axes of satellite galaxies become more unstable when the satellites have lower initial $V/{\sigma}$, orbits with smaller pericenter distance, and higher merger rates after infall into the model clusters. The satellite galaxies involved in mergers after infall experience twice larger angular changes of spin axes than those without mergers. We also find that perturbation exerted by environments or neighboring galaxies strongly correlates with the stability of spin orientation and final $V/{\sigma}$. On the other hand, the size or stellar mass density of the satellites are not significantly affected by mergers or perturbation in cluster environments.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.76.3-76.3
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• 2017

We compare vertical profiles of the extraplanar $H{\alpha}$ emission to those of FUV and NUV emission for 39 nearby edge-on galaxies to investigate the origin of the extraplanar $H{\alpha}$ emission. A strong correlation between scale heights of the extraplanar $H{\alpha}$ and UV emissions is found. This may indicate that the diffuse extraplanar $H{\alpha}$ emission either co-exists with the extraplanar dust or originates from the similar mechanism as the diffuse extraplanar UV emission such as scattering of $H{\alpha}$ photons at diffuse extraplanar dust. The scale heights of the extraplanar $H{\alpha}$ and UV emissions are also compared with size, star formation rate, and star formation rate surface density of the host galaxies to figure out what is the most important parameter associated with the extraplanar emission.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.117.2-117.2
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• 2011

We probe 12CO J=2-1 and 13CO J=1-0 properties of a Virgo disk galaxy, NGC 4402 which is located near the cluster center. Our goal is to study the impact of intra cluster medium (ICM) on the molecular gas of a galaxy in the cluster environment. It has been believed that cluster galaxies are deficient in atomic hydrogen gas (HI gas) compared to their field counterparts and now there is much evidence that low density ISM can be easily removed by ram pressure caused by ICM wind. Meanwhile, no significant molecular gas deficiency of the cluster galaxy population has been found yet they show overall lower star formation rate than galaxies in the field, and it is still controversy whether dense ISM can be also stripped by the ICM wind or not. NGC 4402 with truncated HI disk($D_{HI}/D_{opt}$ ~ 0.75 and only 36%of HI gas compare to field galaxies of a similar size) and a disturbed gas morphology, appears to have strong ongoing ram pressure. Using high resolution 12 and 13CO data of NGC 4402 from a Sub Millimeter Array (SMA), we probe the molecular gas properties under strong ICM pressure. We discuss how its star formation activity and hence the global color of NGC4402 would be changed in the future.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.113.1-113.1
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• 2011

The Leo ring in the M96 group is unique in its morphology and size among the intergalactic gas features found in nearby universe. Its ring-like structure of 200 kpc on diameter appears to be orbiting around the M105-NGC 3384 pair with $1.67{\times}109\;M{\odot}$ of HI gas. While the origin of the ring - whether it is primordial or tidally stripped - is yet unclear, the optical and gas properties of dwarf galaxies associated with the gas ring help us to understand the formation process of this large scale intergalactic HI cloud. At the first step, we present the optical catalog of dwarf galaxy candidates in the Leo ring using deep optical images with MegaCam on the CFHT. Image convolution method is used in order to detect very faint dwarf galaxies. Comparing the ALFALFA HI data from the literature, we have identified that 4 dwarf candidates coexist with HI clumps. There are also 27 HI dwarfs with no optical counterpart and 12 optical dwarfs with no HI clump. In this work, we probe the optical and global gas properties of these dwarfs.