• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.465-467
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• 2015

We presents a study of interactions between galaxies in the low-redshift group known as the NGC 4065 group. Imaging data were taken using the 2.4 meter telescope at the Thai National Observatory (TNO) for B, V and $R_c$ broadband filters and [$S\small{II}$] and Red-continuum narrowband filters. There are 21 galaxies in our sample. The results show that most early type galaxies (ETGs) with equivalent width EW($H{\alpha}$) < $10{\AA}$ are gas-deficient galaxies, while late type galaxies (LTGs) show more EW($H{\alpha}$) and are bluer than the ETGs. This means that star formation activity in the LTGs could be triggered by tidal interactions between galaxy members due to dense environmental effects in the compact group.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.46.1-46.1
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• 2017

Late-type galaxies falling into a cluster would evolve being influenced by the interactions with both the cluster and the nearby cluster member galaxies. Most numerical studies, however, tend to focus on the effects of the former with little work done on those of the later. We thus perform numerical study on the evolution of a late-type galaxy falling radially toward the cluster center interacting with neighbouring early-type galaxies, using N-body, hydrodynamical simulations. Based on the information about the typical galaxy encounters obtained by using the galaxy catalog of Coma cluster, we run the simulations for the cases where a Milky Way Galaxy-like late-type galaxy, flying either edge-on or face-on, experiences six consecutive collisions with twice more massive early-type galaxies having hot gas in their halos. Our simulations show that the evolution of the late-type galaxy can be significantly affected by the high-speed multiple collisions with the early-type galaxies, such as on the cold gas content and the star formation activity, particularly through the hydrodynamic interactions between the cold disk and the hot gas halos. By comparing our simulation results with those of others, we claim that the role of the galaxy-galaxy interactions on the evolution of late-type galaxies in clusters could be comparable with that of the galaxy-cluster interactions, depending on the dynamical history.

• Journal of The Korean Astronomical Society
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• v.54 no.2
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• pp.71-88
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• 2021

We use N-body/hydrodynamic simulations to study the evolution of the spin of a Milky Way-like galaxy through interactions. We perform a controlled experiment of co-planar galaxy-galaxy encounters and study the evolution of disk spins of interacting galaxies. Specifically, we consider cases where the late-type target galaxy encounters an equally massive companion galaxy, which has either a late or an early-type morphology, with a closest approach distance of about 50 kpc, in prograde or retrograde sense. By examining the time change of the circular velocity of the disk material of the target galaxy from each case, we find that the target galaxy tends to lose the spin through prograde collisions but hardly through retrograde collisions, regardless of the companion galaxy type. The decrease of the spin results mainly from the deflection of the orbit of the disk material by tidal disruption. Although there is some disk material which gains the circular velocity through hydrodynamic as well as gravitational interactions or by transferring material from the companion galaxy, it turns out that the amount of the material is generally insufficient to increase the overall galactic spin under the conditions we set. We find that the spin angular momentum of the target galaxy disk decreases by 15-20% after a prograde collision. We conclude that the accumulated effects of galaxy-galaxy interactions will play an important role in determining the total angular momentum of late-type galaxies.

• Journal of The Korean Astronomical Society
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• v.49 no.6
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• pp.239-253
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• 2016

We determined the warp parameters of 192 warped galaxies which are selected from 340 edge-on galaxies using color images as well as r-band isophotal maps. We derive the local background density (${\Sigma}_n$) to examine the dependence of the warp amplitudes on the galaxy environment. We find a clear trend that strongly warped galaxies are likely to be found in high density regions where tidal interactions are supposed to be frequent. However, the correlation between ${\alpha}_{\omega}$ and ${\Sigma}_n$ is too weak for weakly warped galaxies (${\alpha}_{\omega}$ < $4^{\circ}$) and the cumulative distributions of weakly warped galaxies are not significantly different from those of galaxies with no detectable warps. This suggests that tidal interactions do not play a decisive role in the formation of weak warps.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.47.3-48
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• 2015

We present environmental effects on the galaxy evolution in the Virgo cluster focusing on intracluster medium - interstellar medium (ICM-ISM) interactions and gravitational interactions. We identify signatures of these environmental effects for 21 massive late-type galaxies based on the visual inspection of high resolution HI data from VLA Imaging of Virgo spirals in Atomic gas (VIVA) survey comparing with multi-wavelength data. We classify galaxies into three subgroups showing different environmental effects. First and second groups includes galaxies influenced by ongoing/active and past ram pressure stripping effect, respectively. Third group consists of galaxies undergoing gravitational interactions. Additionally, we define neighbor galaxies for each VIVA galaxies utilizing kinematic data from Extended Virgo Cluster Catalog. Assuming that neighbor galaxies share similar levels of environmental effects with host VIVA galaxies, we investigate environmental effects on galaxy properties in different subgroups using SDSS optical and GALEX ultraviolet photometric data. We find that dwarf neighbor galaxies in first and second groups show rapid quenching of their star formation (SF), while massive counterparts are still in SF activity. On the other hand, most third group galaxies show hints of SF activity regardless of their mass. We conclude that SF and evolution of galaxy in the cluster environment is closely linked to ICM-ISM interactions and dwarf galaxies seem to be more sensitive to this effect compared to massive counterparts.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.469-471
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• 2015

How galaxies are affected by their neighboring galaxies during galaxy-galaxy interactions is a long-standing question. We investigate the role of neighbors in galaxy pairs based on the SDSS data release 7 and the KIAS value-added galaxy catalog. Three groups of galaxies are identified: (a) galaxies with an early-type neighbor, (b) with a late-type neighbor, and (c) isolated ones with no neighbor. We compare their UV + optical colors and $H{\alpha}$ emission as indicators of the recent star-formation rate (SFR). Given that galaxies show systematic differences in SFR as functions of morphology, luminosity, and large-scale environments, we construct a control sample in which the galaxies have the same conditions (in terms of morphology, luminosity, and large-scale environment) except for the neighbor's properties (i.e., morphology, mass, and distance). The results are as follows. (1) Galaxies with a late-type companion demonstrate more enhanced SFR than those with an early-type companion. (2) Galaxies with an early-type neighbor show NUV- and u-band derived SFRs that are even lower than that of isolated galaxies, while they have similar or slightly higher $H{\alpha}$-based SFR compared to isolated ones.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.495-497
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• 2015

Galaxies can be "pre-processed" in the low-density outskirts by ambient medium in the filaments or tidal interactions with other galaxies while falling into the cluster. In order to probe how early on and by which mechanisms galaxies can be affected before they enter high-density cluster environments, we are carrying out an atomic hydrogen ($H\small{I}$) imaging study of a sample of galaxies selected from three filamentary structures around the Virgo cluster. Our sample consists of 14 late-type galaxies, which are potentially interacting with their surroundings. The $H\small{I}$ observations have been done using the Westerbork Synthesis Radio Telescope, the Giant Metrewave Radio Telescope, and the Jansky Very Large Array with column density sensitivity of ${\approx}3-5{\times}10^{19}cm^{-2}$ in $3{\sigma}$ per channel, which is low enough to detect faint $H\small{I}$ features in the outer disks of galaxies. In this work, we present the Hi data of two galaxies that were observed with GMRT. We examine the $H\small{I}$ morphology and kinematics to find the evidence for gas-gas and/or tidal interactions, and discuss which mechanism(s) could be responsible for pre-processing in these cases.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.70.1-70.1
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• 2012

We investigate 53 late-type galaxies in Virgo to get better understanding galaxy evolution driven by environmental effects in the cluster. The goal is to study how galaxies are strongly affected gravitationally by their surroundings and/or how interstellar medium (ISM) of galaxies changes through the interaction with intracluster medium (ICM). To quantify these, a variety of diagnostic methods have been introduced. Our diagnostics have two different perspectives. First, we have carefully examined the morphological and kinematical properties of individual galaxies using high resolution HI images and compared with multi-wavelength data. Based on the visual inspection, we have identified signatures of the interactions with other galaxies or the ICM. Second, we have quantified influence of local environments of individual galaxies using X-ray data and optical catalog of the cluster. By combining all the diagnostics, we have identified the environmental effect(s) at work on individual galaxies. We also probe the environmental processes as a function of the cluster centric distance. Various gravitational interactions are found throughout the cluster, while the ICM-ISM interaction is mainly dominant near the cluster center. However, we find some evidence that galaxies start losing their gas already in the low density outskirts of the cluster.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.233-233
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• 2012

I review the dependence of galaxy properties on environmental parameters such as the local density, nearest neighbor distance and morphology. We find that a galaxy with an early- or late-type nearest companion within its virial radius tends to be an early or late type, respectively. The morphology of galaxies located in high density regions tends to be the same as that of the ones in low density regions if their luminosity and the nearest neighbor environment are the same. This strongly supports that galaxy morphology and luminosity evolution have been driven mainly by galaxy-galaxy interactions, and the background density affected morphology and luminosity only through the frequency of interactions.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.31.3-32
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• 2021

We quantify the relative role of galaxy environment and bar presence on AGN triggering in face-on spiral galaxies using a volume-limited sample with 0.02 < z < 0.055, Mr < 19.5, and σ > 70 km s-1 selected from Sloan Digital Sky Survey (SDSS) Data Release 7. To separate their possible entangled effects, we divide the sample into bar and non-bar samples, and each sample is further divided into three environment cases of isolated galaxies, interacting galaxies with a pair, and cluster galaxies. The isolated case is used as a control sample. For these six cases, we measure AGN fractions at a fixed central star formation rate and central velocity dispersion, σ. We demonstrate that the internal process of the bar-induced gas inflow is more efficient in AGN triggering than the external mechanism of the galaxy interactions in groups and cluster outskirts. The significant effects of bar instability and galaxy environments are found in galaxies with a relatively less massive bulge. We conclude that from the perspective of AGN-galaxy coevolution, a massive black hole is one of the key drivers of spiral galaxy evolution. If it is not met, a bar instability helps the evolution, and in the absence of bars, galaxy interactions/mergers become important. In other words, in the presence of a massive central engine, the role of the two gas inflow mechanisms is reduced or almost disappears. We also find that bars in massive galaxies are very decisive in increasing AGN fractions when the host galaxies are inside clusters.