• Journal of the Korean Vacuum Society
• /
• v.12 no.2
• /
• pp.105-111
• /
• 2003

In order to find out whether a reflectron can be used as a mass selector in the gas cluster experiment, computer simulation are performed using the SIMION’ program. flight paths of energetic particles in the reflectron does not depend on their mass but energy. In the case of $(CO_2)n $ gas cluster, however, the position of clusters just after passing through the reflectron are spacially distributed with respect to the mass. The reason that the masses spacially distributes is the E/m ratio of clusters is constant, and it is the key reason that a reflectron can be used as a mass selector. Mass resolution does not depend on the cluster size and incident angle of clusters, and it is proportional to the incident position of clusters. This means that mass resolution can be enhanced by resizing the dimension of a reflectron. Therefore, it is concluded that a reflectron can be used as a mass selector with excellent mass resolution in the gas cluster experiment.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.1
• /
• pp.62.2-62.2
• /
• 2011

It is well known that the cluster environment can change the atomic gas properties of galaxies through tidal interactions and/or by the hot cluster medium. Meanwhile, the molecular gas is expected to be less vulnerable to its surroundings due to its higher density, and no obvious influence of the environment on the molecular gas properties had been found among cluster spirals until recently. However, in a recent study by Fumagalli et al. (2009) of a sub-sample of Virgo spirals, it has been suggested that HI deficient galaxies can be also CO deficient. In order to further investigate if the HI deficiency indeed can result in the deficiency in molecular gas content, we compare the global CO and HI gas properties of Virgo spirals with those of galaxies in the Ursa Major cluster and the Pisces cluster, much lower density environments than Virgo. We discuss possible consequences of molecular gas deficiency in star formation activity of spiral galaxies in high density environment.

• The Bulletin of The Korean Astronomical Society
• /
• v.45 no.1
• /
• pp.30.2-31
• /
• 2020

We present the properties of circumnuclear gas associated with the AGN located in the center of Abell 1644-South. A1644-S is the main cluster in a merging system, which is also known for gas sloshing in its core as seen in X-ray. The X-ray emission of A1644-S shows a rapidly declining profile, indicating the presence of cooling gas flow. This flow of cool gas may fuel the supermassive black hole embedded in the brightest cluster galaxy, leading to the activation of the central AGN. Indeed, we find a parsec-scale bipolar jet feature in the center of A1644-S in our recent KaVA observation, which implies that its central AGN is likely to have been (re)powered quite recently. In order to verify the hypothesis that cooling gas flow in the cluster core can (re)activate the central AGN, we probe the cold gas properties of the central 1 kpc region of A1644-S using the archival VLA and ALMA data. Based on the spatially resolved morphology and kinematics of HI and CO gas, we challenge to identify inflow/outflow gas streams and clumps. We study the role of circumnuclear cool gas in fueling the centrally located cluster AGN in the cool-core environment. We also discuss how the feedback due to the (re)powered AGN affects the surrounding medium.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.1
• /
• pp.41.1-41.1
• /
• 2012

Interactions between the galactic interstellar medium (ISM) and the intra cluster medium (ICM) are believed to be one of the main processes affecting galaxy evolution in cluster environments. The aim of our research is to study the molecular gas properties of a galaxy under the ICM pressure in the cluster environment. It has been well known 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 is being removed by ram pressure due to 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 puzzling how the star formation could decrease without stripping of dense molecular gas. To address this issue, we probe the detailed molecular gas properties of NGC 4402, located near the cluster center, as part of a study of four spiral galaxies in the Virgo Cluster. NGC 4402 is well known undergoing ram pressure stripping with a 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. Comparing the high resolution 12CO and 13CO data of NGC 4402 from the Sub Millimeter Array (SMA) with existing other wavelength data, we probe the spatial distribution and a physical condition of molecular gas under strong ICM pressure. We discuss the star formation activity might have been altered and hence how the global color of NGC4402 would change in the future.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.76.1-76.1
• /
• 2017

In cluster environments, most of the galaxies are found to be red and dead, but the origin of these passive galaxies is not yet clearly understood. Using a set of cosmological hydrodynamic zoom-in simulations, we study gas depletion process in and outside clusters. Our results are consistent with previous studies showing rapid stripping of a galactic cold gas reservoir during the first infall to the cluster center. Moreover, we found a fraction of galaxies that were already in the gas deficient state before reaching the cluster (i.e., pre-processed galaxies) is non-negligible. These findings lead to the idea that a complete understanding of passive galaxy population in clusters can not be achieved without a detailed understanding of gas stripping process in group size halos prior to the cluster infall.

• Journal of the Korean Institute of Gas
• /
• v.7 no.1 s.18
• /
• pp.41-46
• /
• 2003

The Phase and temperature changes of large clusters formed in a free jet expansion of acetylene in 14atm and 233K has been studied. The cluster has been treated as a sphere composed of many shells. A mean diameter of 4.88 microns was obtained by modeling the experimental cooling curve of clusters based on evaporation and heat conduction theory.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.2
• /
• pp.117.2-117.2
• /
• 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
• /
• v.38 no.1
• /
• pp.33.1-33.1
• /
• 2013

Galaxies undergo various processes in the cluster environment, which could affect their evolution. In particular, ram pressure due to intracluster medium (ICM) can effectively remove HI gas, which is a relatively diffuse form of interstellar medium (ISM). On the other hand, molecular gas is not expected to get easily stripped as atomic gas since it is denser and sitting well within the stellar disk in a deeper potential well. However, cluster galaxies are found to be redder and more passive in star formation activity compared to their field counterpart. This implies that molecular gas may also get affected somehow in dense environments. In this work, we investigate molecular gas properties of a sample of galaxies undergoing HI stripping due to the ICM. We present the 12/13 CO (2-1) data of four spiral galaxies in the Virgo cluster at different ram pressure stripping stages, obtained using the Sub Millimeter Array (SMA). CO morphology of the sample appears to be highly asymmetric and disturbed. Using the ratio of different lines, we probe the molecular gas temperature in different regions. We find higher gas temperature than the range normally found among field galaxies. We discuss how these distinct molecular gas properties may affect star formation and hence the evolution of the cluster galaxy population.

• The Bulletin of The Korean Astronomical Society
• /
• v.45 no.1
• /
• pp.61.1-61.1
• /
• 2020

We examine the HI gas kinematics and distribution of galaxy pairs in group or cluster environment from high-resolution Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pilot observations. We use 22 well-resolved galaxies in the Hydra cluster of which 4 galaxies are visually identified as pairs and others are isolated ones. We perform profile decomposition of HI velocity profiles of the galaxies using a new tool, BAYGAUD which enables us to separate a line-of-sight velocity profile into an optimal number of Gaussian components based on Bayesian MCMC techniques. All the HI velocity profiles of the galaxies are decomposed into kinematically cold or warm gas components with their velocity dispersion, 4~8 km/s or > 8 km/s, respectively. We derive the mass fraction of the kinematically cold gas with respect to the total HI gas mass, f = log10(M_cold / M_HI), of the galaxies and correlate them with their dynamical mass. The cold gas reservoir of the paired galaxies in the Hydra cluster is found to be relatively higher than that of the isolated ones which show a negative correlation with the dynamical mass in general.

• The Bulletin of The Korean Astronomical Society
• /
• v.43 no.1
• /
• pp.33.2-34
• /
• 2018

Galaxies associated with massive groups/clusters are normally gas deficient in contrast to field galaxies. HI observations on such galaxies have revealed signs of violent gas stripping, the direct evidence of the environmental effect. At the same time, the notable number of passive galaxies at the cluster outskirts indicates the presence of pre-processing that makes galaxies gas-poor before entering clusters. We investigate the possible channels for the production of the gas deficient galaxies using the state-of-the-art cosmological hydrodynamic zoom-in simulations of 16 clusters (Choi&Yi). We find cluster effect and pre-processing together play an important role in producing the gas-poor galaxies and in both cases gas loss qualitatively agrees with the ram pressure stripping description. Among the currently gas-poor cluster galaxies, 34% are pre-processed before the cluster infall. They are mainly satellites that have undergone ram pressure stripping in group halos. 43% deplete quickly after arriving at cluster during their first approach to the center. Some of them are group halo satellites low in the gas at the infall compared to galaxies directly coming from the field. 24% retain gas even after their first pericentric pass mainly because they are falling into low mass clusters and/or they have a circular orbit that minimizes the ram pressure effect. This study highlights the importance of the past history of galaxies, especially in group halos, before joining the current cluster when understanding the excess of passive galaxies in clusters.