• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.69.3-70
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• 2016

We study the orbital histories of Virgo galaxies undergoing different HI gas stripping stages using phase-space diagrams. Based on the HI properties of galaxies, we find that location of galaxies is in good agreement with ram-pressure stripping predicted by numerical simulations with different infall time. For example, galaxies experiencing active gas stripping are mostly found in the first infall region showing high velocity with respect to the cluster center. Meanwhile, most galaxies that are likely to have lost gas a while ago are found in the cluster outskirts with low orbital velocities. We also discuss the cases where observational properties of galaxies and their locations in the phase-space do not well agree. In addition, we probe the phase-space of filaments and subgroups around or within Virgo. Our results strongly suggest that substructures can play important roles in galaxy evolution while galaxies are falling to the cluster.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.423-427
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• 2015

Recognition of the role of radio galaxies in the universe has been increasing in recent years. Their colossal energy output over huge volumes is now widely believed to play a key role not only in the formation of galaxies and their supermassive black holes, but also in the evolution of clusters of galaxies and, possibly, the cosmic web itself. In this regard, we need to understand the inflation of radio bubbles in the hot gas atmospheres of clusters and the importance of the role that radio galaxies play in the overall energy budget of the intracluster medium. Here, we present results from X-ray and radio band observations of the hot gas atmospheres of powerful, nearby radio galaxies in poor clusters.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.189-191
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• 2017

We performed systematic observations of the H $\small{I}$ $Br{\alpha}$ line ($4.05{\mu}m$) in 51 nearby (z<0.3) ultraluminous infrared galaxies (ULIRGs), using AKARI near-infrared spectroscopy. The $Br{\alpha}$ line is predicted to be the brightest among the H ${\small{I}}$ recombination lines in ULIRGs with visual extinction higher than 15 mag. We detected the $Br{\alpha}$ line in 33 ULIRGs. In these galaxies, the relative contribution of starburst to the total infrared luminosity ($L_{IR}$) is estimated on the basis of the ratio of the $Br{\alpha}$ line luminosity ($L_{Br{\alpha}}$) to $L_{IR}$. The mean $L_{Br{\alpha}}/L_{IR}$ ratio in LINERs or Seyferts is significantly lower (~50%) than that in H $\small{II}$ galaxies. This result indicates that active galactic nuclei contribute significantly (~50%) to $L_{IR}$ in LINERs, as well as Seyferts. We also estimate the absolute contribution of starburst to $L_{IR}$ using the ratio of star formation rates (SFRs) derived from $L_{Br{\alpha}}$ ($SFR_{Br{\alpha}}$) and those needed to explain $L_{IR}$ ($SFR_{IR}$). The mean $SFR_{Br{\alpha}}/SFR_{IR}$ ratio is only 0.33 even in H $\small{II}$ galaxies, where starburst is supposed to dominate the luminosity. We attribute this apparently low $SFR_{Br{\alpha}}/SFR_{IR}$ ratio to the absorption of ionizing photons by dust within H $\small{II}$ regions.

• Journal of The Korean Astronomical Society
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• v.55 no.2
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• pp.37-57
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• 2022

Using I-band images of 35 nearby (z < 0.1) type 1 active galactic nuclei (AGNs) obtained with Hubble Space Telescope, selected from the 70-month Swift-BAT X-ray source catalog, we investigate the photometric properties of the host galaxies. With a careful treatment of the point-spread function (PSF) model and imaging decomposition, we robustly measure the I-band brightness and the effective radius of bulges in our sample. Along with black hole (BH) mass estimates from single-epoch spectroscopic data, we present the relation between BH mass and I-band bulge luminosity (M_BH-M_I,bul relation) of our sample AGNs. We find that our sample lies offset from the M_BH-M_I,bul relation of inactive galaxies by 0.4 dex, i.e., at a given bulge luminosity, the BH mass of our sample is systematically smaller than that of inactive galaxies. We also demonstrate that the zero point offset in the M_BH-M_I,bul relation with respect to inactive galaxies is correlated with the Eddington ratio. Based on the Kormendy relation, we find that the mean surface brightness of ellipticals and classical bulges in our sample is comparable to that of normal galaxies, revealing that bulge brightness is not enhanced in our sample. As a result, we conclude that the deviation in the M_BH-M_I,bul relation from inactive galaxies is possibly because the scaling factor in the virial BH mass estimator depends on the Eddington ratio.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.357-360
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• 2012

This paper presents $H{\alpha}$ emission line detections for four galaxies at z > 3.5 made with AKARI as part of the FUHYU mission program. These are the highest-redshift $H{\alpha}$ detections to date in star-forming galaxies. AKARI's unique near-infrared spectroscopic capability has made these detections possible. For two of these galaxies, this represents the first evidence of their redshifts and confirms their physical association with a companion radio galaxy. The star formation rates (SFRs) estimated from the $H{\alpha}$ lines under-predict the SFRs estimated from their far-infrared luminosities by a factor of ~ 2 - 3. We have also detected broad $H{\alpha}$ components in the two radio galaxies which indicate the presence of quasars.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.313-315
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• 2017

We present physical properties of $24{\mu}m$ galaxies detected by AKARI and Spitzer and their evolution between redshifts 0.4 < z < 2. Using multi-wavelength data from X-ray to radio observations in NEP Deep Field (for AKARI) and Subaru/XMM-Newton Deep Field (for Spitzer), we derive photometric redshift, stellar mass, star-formation rate (SFR), dust extinction magnitude and rest-frame luminosities/colors of the $24{\mu}m$ galaxies from photometric SED fitting. We infer the SFRs from rest-frame ultraviolet luminosity and total infrared luminosity calibrated against Herschel photometric data. For both survey fields, we obtain complete samples with stellar mass of > $10^{10}M_{\odot}$ and SFR of > $30M_{\odot}/yr$ up to z = 2. We find that specific SFRs evolves with redshift at all stellar masses in NON-power-law galaxies (non-PLGs) as star-formation dominant luminous infrared galaxies (LIRGs). The correlations between specific SFR and stellar mass in the Spitzer and AKARI galaxy samples are well consistent with trends of the main sequence galaxies. We also discuss nature of PLGs and their evolution.

• Journal of the Korean earth science society
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• v.36 no.5
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• pp.427-436
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• 2015

We classified Abell clusters using the magnitude differences between two or three bright member galaxies and investigated how such classification was correlated with the properties of brightest cluster galaxies (BCGs). S-type BCGs being clearly brighter than the rest of the member galaxies were likely to be red, luminous, and evolved as early type galaxies. On the other hand, T-type BCGs being not dominant at all were less luminous than early type galaxies. A small fraction of BCGs was currently forming stars, and all of the star-forming BCGs were T-type BCGs. Active galactic nuclei were most frequent for S-type BCGs. Through these quantitative analyses of the BCG properties, we discussed the possible scenario of BCG formation and the differences between S-type and T-type of BCGs.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.299-300
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• 2012

We investigate the relation between star formation activity and PAH $3.3{\mu}m$ emission. Our targets are mid-infrared-excess galaxies selected from the AKARI all-sky survey point source catalog. We performed AKARI near-infrared spectroscopy for them. As a result, we obtained $2.5-5{\mu}m$spectra of 79 galaxies, and selected 35 star-forming galaxies out of them. Comparing the PAH $3.3{\mu}m$ luminosities with the infrared luminosities, we find a linear correlation between them. However, by adding the results from literatures for luminous infrared galaxies and ultra-luminous infrared galaxies that are more luminous than our sample, the ratio of the PAH to the infrared luminosity is found to decrease towards the luminous end.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.44.2-44.2
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• 2013

The local environmental effects on the active galactic nucleus(AGN) activity has been studied by many authors, but there is still controversy. We performed statistical analysis for nearby(0.01 < z < 0.05) volume limited(Mr < -19) sample via visual inspection based on Sloan Digital Sky Survey Data Release7. We visually inspect around 50,000 galaxy images to find peculiar objects which show not only ongoing merging features and tidal features, but also post merging features like shell or ring structures. We found that the frequency of AGN host galaxies is at least 2 times higher among peculiar galaxies than non-peculiar galaxies, and this trend is still visible when galaxy properties such as color or stellar mass are fixed. Furthermore, L[OIII] of peculiar galaxies is found to be more increased than those of normal galaxies. The majority of the most luminous AGN hosts show peculiar feature, which indicates that the luminous AGN galaxies may be the result of the local environmental effects. In addition, the enhancement of L[OIII] in peculiar galaxies is more significant for bluer galaxies, which implies that AGN activity is enhanced effectively when gas is available. In order to ensure our results, we also checked it for a smaller subsample with 2 magnitude deeper monochromatic images provided by SDSS Stripe82 database, and found consistent results. Overall, the results of this study tell us that the local environment of galaxies affects the frequency as well as the strength of AGN activity.

• Journal of Astronomy and Space Sciences
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• v.39 no.2
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• pp.43-50
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• 2022

The unified scheme of Seyfert galaxies hypothesizes that the observed differences between the two categories of Seyfert galaxies, type 1 (Sy1) and type 2 (Sy2) are merely due to the difference in the orientation of the toroidal shape of the obscuring material in the active galactic nuclei. We used in this paper, a sample consisting of 120 Seyfert galaxies at 1.40 × 10⁹ Hz in radio, 2.52 × 10¹⁷ Hz in X-ray and 2.52 × 10²³ Hz in γ-ray luminosities observed by the Fermi Large Area Telescope (Fermi-LAT) in order to test the unified scheme of radio-quiet Seyfert galaxies. Our main results are as follows: (i) We found that the distributions of multiwave luminosities (L_radio, L_X-ray, and L_γ-ray) of Sy1 and Sy2 are completely overlapped with up to a factor of 4. The principal component analysis result reveals that Sy1 and Sy2 also occupy the same parameter spaces, which agrees with the notion that Sy1 and Sy2 are the same class objects. A Kolmogorov-Smirnov test performed on the sub-samples indicates that the null hypothesis (both are from the same population) cannot be rejected with chance probability p ~ 0 and separation distance K = 0.013. This result supports the fact that there is no statistical difference between the properties of Sy1 and Sy2 (ii) We found that the coefficient of the best-fit linear regression equation between the common properties of Sy1 and Sy2 is significant (r > 0.50) which plausibly implies that Sy1 and Sy2 are the same type of objects observed at different viewing angle.