• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.281-284
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• 2012

We utilize AKARI's slitless spectroscopic capability to detect the $3.3{\mu}m$ polycyclic aromatic hydrocarbons (PAHs) emission and measure star formation (SF) activity for various AKARI programs. First, we obtain $2{\sim}5{\mu}m$ spectra of 20 flux-limited galaxies with mixed SED classes in order to calibrate the $3.3{\mu}m$ PAH luminosity ($L_{PAH3.3}$) as a star formation rate (SFR) indicator. We find that $L_{PAH3.3}$ correlates with $L_{IR}$ as well as with the $6.2{\mu}m$ PAH luminosity ($L_{PAH6.2}$). The correlations does not depend on SED classes. We find that ULIRGs deviate from the correlation between PAH luminosities and $L_{IR}$, while they do not for the correlation between PAH luminosities. We suggest possible effects to cause this deviation. On the other hand, how AGN activity is linked to SB activity is one of the most intriguing questions. While it is suggested that AGN luminosity of quasars correlates with starburst (SB) luminosity, it is still unclear how AGN activity is connected to SF activity based on host galaxy properties. We are measuring SFRs for the LQSONG sample consisting of reverberation mapped AGNs and PG-QSOs. This is an extension of the ASCSG program by which we investigated the connection between SB and AGN activities for Seyferts type 1s at z ~ 0.36. While we found no strong correlation between $L_{PAH3.3}$ and AGN luminosity for these Seyferts 1s, $L_{PAH3.3}$ measured from the central part of galaxies correlates with AGN luminosity, implying that SB and AGN activities are directly connected in the nuclear region.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.291-292
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• 2012

We select infrared-luminous galaxies by cross-matching the SDSS spectroscopic sample of galaxies with the WISE all-sky survey catalog. Based on photometric data points covering from SDSS u-band to WISE $22{\mu}m$, their spectral energy distributions (SEDs) are separated into AGN, elliptical, spiral, and irregular galaxy components. The derived luminosities of spiral galaxy and AGN are well correlated with $H{\alpha}$ and [OIII] line luminosities, respectively. Most galaxies are dominated by young stellar populations even for optical AGNs, but at least 10% of optical non-AGNs appear to harbor buried AGNs. The AGN contribution increases dramatically with the total luminosity. These results show that the SED decomposition is successful and is useful to understand the true nature of dusty galaxies.

• Publications of The Korean Astronomical Society
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• v.7 no.1
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• pp.63-69
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• 1992

We have systematically investigated the X-ray spectra of normal galaxies, by using the Imaging Proportional Counter (IPC) data in the Einstein data base. We employed the X-ray color-color plot as well as the standard model fitting method which requires higher signal to noise ratio. We discuss X-ray emission mechanisms in terms of their spectral properties and the signature of cooling flows which are most likely present in X-ray bright early type galaxies. On the average, fits to absorbed thermal spectra show that the X-ray emission temperature of spirals is higher than that of ellipticals. This is consistent with our understanding that accreting binaries are a major X-ray source in spirals, while extended gaseous halos are present in ellipticals. The emission temperature becomes lower with increasing X-ray to optical luminosity ratio in E and S0 galaxies. This result is what we would expect if the emission of X-ray faint early type galaxies consists of a large evolved stellar component, while the gaseous emission becomes dominant in X-ray brighter galaxies. We also find a cool, self-absorbed core in some early type galaxies, which directly indicates the presence of cooling flows in such galaxies.

• Journal of The Korean Astronomical Society
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• v.23 no.1
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• pp.43-62
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• 1990

We present (U-B) and (U-V) radial color distributions of 103 galaxies based on the UBV multiaperture photometry compiled by Longo, de Vaucouleurs, and Corwin (1983). About half of the galaxies show radial negative color gradients (i. e., bluer at the outer parts of the galaxies). E and SO galaxies have similar color gradients. and there appears to be no correlation between the size of color gradients in these galaxies and their luminosity, but the luminous spiral galaxies tend to have steeper color gradients. The metallicity gradients of elliptical galaxies derived from the (U-V) color gradients agree with those from the magnesium gradients within the errors.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.32.2-32.2
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• 2018

We present the structural parameters of ~ 910 dwarf elliptical-like galaxies in the local universe ($z{\lesssim}0.01$) derived from the r-band images of the Sloan Digital SKy Survey (SDSS). We examine the dependence of structural parameters on the morphological types (dS0, dE, dEbc, dSph, and dEblue) and the environment. There is not much difference in the structural parameters among the five subtypes but the mean surface brightness within the effective radius (<${\mu}e$>) of dSph galaxies is clearly different from that of other subtypes. The frequency of disk features such as spiral arm, bar, lens, and rings strongly depends on the morphology of dwarf elliptical-like galaxies with no disk features in dSph galaxies. The absence of disk features and the low surface brightness of dSph galaxies are thought to be closely related to their low mass which leads to different evolution from other subtypes of dwarf elliptical-like galaxies. Density Environments Using IMSNG.

• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.149-158
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• 2003

Deep surveys at mid-infared through submillimeter wavelengths indicate that a substantial fraction of the total luminosity output from galaxies at high redshift (z > 1) emerges at wavelengths 30 - 300${\mu}m$. In addition, much of the star formation and AGN activity associated with galaxy building at these epochs appears to reside in a class of luminous infrared galaxies (LIGs), often so heavily enshrouded in dust that they appear as 'blank-fields' in deep optical/UV surveys. Here we present an update on the state of our current knowledge of the cosmic evolution of LIGs from z = 0 to z $\~$ 4 based on the most recent data obtained from ongoing ground-based redshift surveys of sources detected in ISO and SCUBA deep fields. A scenario for the origin and evolution of LIGs in the local Universe (z < 0.3), based on results from multiwavelength observations of several large complete samples of luminous IRAS galaxies, is then discussed.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.77.1-77.1
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• 2019

We present the results of the merger fraction evolution for galaxies in NEP-Wide field depending on star formation mode and redshift. We select the galaxies which have AKARI 9 ㎛ detections as a sample for large number of galaxies. We use multi-wavelength data from GALEX to Herschel, and Subaru HSC i-band images for analysis. We classify the merger galaxies with using Gini and M20, which are non-parametric calculated by statmorph code. We obtain the total infrared luminosity from the SED modeling with using one band, AKARI 9 ㎛. We find that the merger fractions of galaxies in all different star formation mode increase as the redshift increases. However, with fixed mass range of 10.5 < log(M🞵) < 11.5, the merger fractions of starbursts significantly increase as the redshift increases compared to those of main sequence and quiescent galaxies. We discuss the implications of these results in this poster.

• Journal of The Korean Astronomical Society
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• v.39 no.3
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• pp.57-71
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• 2006

We investigated the structural parameters of a sample of 30 dwarf galaxies(15 dEs and 15 dS0s) in the Virgo Cluster using i-band images from the Sloan Digital Sky Survey Data Release 4. Among 28 galaxies for which surface brightness profiles were derived from ellipse fittings, 23 galaxies had a single component that was adequately described by a generalized $S\acute{e}rsic$ function with a shape parameter ranging from n=0.5 to 2, while 5 galaxies(2 dEs and 3 dS0s) had bulge and disk components that were fitted by a generalized $S\acute{e}rsic$ function and an exponential function, respectively. Since the majority of dwarf galaxies in the present sample had a single component, it seems likely that genuine dS0 galaxies that have disk and bulge components are quite rare in the Virgo Cluster. The similarity in structural parameters of genuine dS0 galaxies in the Virgo Cluster with those of Magellanic-type galaxies implies that the progenitors of dwarf lenticular galaxies in the Virgo Cluster were most likely Magellanic-type galaxies if dS0s are harassed late-type spirals.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.257-261
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• 2017

We built a $8{\mu}m$ selected sample of galaxies in the NEP-AKARI field by defining 4 redshift bins with the four AKARI bands at 11, 15, 18 and 24 microns (0.15 < z < 0.49, 0.75 < z < 1.34, 1.34 < z < 1.7 and 1.7 < z < 2.05). Our sample contains 4079 sources, 599 are securely detected with Herschel/PACS. Also adding ultraviolet (UV) data from GALEX, we fit the spectral energy distributions using the physically motivated code CIGALE to extract the star formation rate, stellar mass, dust attenuation and the AGN contribution to the total infrared luminosity ($L_{IR}$). We discuss the impact of the adopted attenuation curve and that of the wavelength coverage to estimate these physical parameters. We focus on galaxies with a luminosity close the characteristic $L^*_{IR}$ in the different redshift bins to study the evolution with redshift of the dust attenuation in these galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.35.2-35.2
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• 2016

We present a census of AGN-driven gas outflows based on the kinematics of ionized gas and stars, using a large sample of ~11,000 emission line galaxies at z < 0.3, selected from SDSS. First, a broad correlation between gas and stellar velocity dispersions indicates that the bulge gravitational potential plays a main role in determining the ionized gas kinematics. However, the velocity dispersion of the [OIII] emission line is larger than stellar velocity dispersion by a factor of 1.3-1.4, suggesting that the non-gravitational (non-virial) component, i.e., outflows, is almost comparable to the gravitational component. Second, gas-to-stellar velocity dispersion ratio increases with both AGN luminosity and Eddington ratio, suggesting that non-gravitational kinematics are clearly linked to AGN accretion. The distribution in the [OIII] velocity - velocity dispersion diagram dramatically expands toward large values with increasing AGN luminosity, implying that the launching velocity of gas outflows increases with AGN luminosity. Third, the fraction of AGNs with a signature of the non-gravitational kinematics, steeply increases with AGN luminosity and Eddington ratio, while the majority of luminous AGNs presents the non-gravitational kinematics in the [OIII] profile. These results suggest that ionized gas outflows are prevalent among type 2 AGNs. On the other hand, we find no strong trend of the [OIII] kinematics with radio luminosity, once we remove the effect of the bulge gravitational potential, indicating that ionized gas outflows are not directly related to radio activity for the majority of type 2 AGNs. We will discuss the implication of these results for AGN feedback in the local universe.