• Journal of The Korean Astronomical Society
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• v.38 no.3
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• pp.339-344
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• 2005

We present analysis results of the energy spectra of MCG-2-58-22 associated with occasional flares which appear in a long-term X-ray light curve. We measure an intrinsic power-law slope of this object to be ${\Gamma}=1.74{\pm}0.02$ in the energy range of ${\sim}1-5keV$ and find that this slope is little affected by flares. We confirm that there exists a broad excess emission above 5 keV to the power-law continuum. The excess emission is less variable compared with a flux variation of flare and tends to be relatively weak during flares. A soft X-ray spectrum is also found to change, implying the presence of a variable soft component. We discuss the implications of these spectral variations.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.30.4-31
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• 2021

We will present a scenario of the presence of a second AGN in a nearby Seyfert galaxy, NGC 1068. Using VLT/MUSE IFU data, we investigated the complex kinematics of ionized gas in the central region of NGC 1068. Interestingly, at a distance of 180 pc to the northeast from the nucleus of NGC 1068, we detected a kinematical signature of the launching point of AGN gas outflows, which suggests that there would be a second AGN. We will also discuss another supporting evidence of the second AGN based on previous spectropolarimetric results.

• Publications of The Korean Astronomical Society
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• v.25 no.3
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• pp.77-82
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• 2010

Recent results from large surveys of the local universe show that the galaxy-black hole connection is linked to host morphology at a fundamental level and that there are two fundamentally different modes of black hole growth. The fraction of early-type galaxies with actively growing black holes, and therefore the AGN duty cycle, declines significantly with increasing black hole mass. Late-type galaxies exhibit the opposite trend: the fraction of actively growing black holes increases with black hole mass. Issues of AGN selection bias and prospects for near-future efforts with high redshift data are discussed.

• Journal of the Korean earth science society
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• v.27 no.5
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• pp.569-578
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• 2006

The distribution and kinematic information of the continuum, $H{\alpha},\;H{\beta}$, [O III], & [N II] images based on spectroscopic data secured with the OASIS at the Hawaii CFHT 3.6m telescope have been analyzed to study the physical characteristics of NGC 5728. The three bright regions-northwestern knot, southeastern knot, and the nucleus-exist within a $15"{\times}12"$ sky area which seem to indicate gas flows along the northwestern or western direction from the nucleus. We find that the center of a 10" diameter ring is at the northwestern knot, not at the galactic center. To further analyze the formation mechanism of such a ring, the kinematics of the nucleus and knot have been studied and the central structure of the Active Galactic Nuclei has been investigated by comparing various emission images.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.439-442
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• 2015

We observed multiple CO transition lines and the HCN(1-0) line at ~ 1" (~ 34 pc) or higher resolution toward the Seyfert 2 nucleus of M51 using the IRAM Plateau de Bure Interferometer (PdBI) and the Submillimeter Array (SMA). All the images show very similar overall molecular gas distribution; there are two discrete clouds at the eastern and western sides of the nucleus, and the western cloud exhibits an elongated distribution and velocity gradient along the radio jet. In addition, high HCN(1-0)/CO(1-0) brightness temperature ratios of about unity have been observed, especially along the radio jet, similar to those observed in shocked molecular gas in our Galaxy. This strongly indicates that the molecular gas along the jet is shocked, that the radio jet and the molecular gas are interacting, and the jet is entraining both diffuse (CO) and dense (HCN) molecular gas outwards from the circumnuclear region. This is the first clear imaging of the outflowing molecular gas entrained by the AGN jet, and showing the detailed physical status of outflowing molecular gas. Since a relatively high HCN(1-0)/CO(1-0) ratio has been observed in the high velocity wing of ultraluminous infrared galaxies, it can also be explained by a similar mechanism to those we describe here.

• Journal of Astronomy and Space Sciences
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• v.22 no.3
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• pp.187-196
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• 2005

From the line ratios of Si III] 1892 to C III] 1909 (Feibelman & Aller 1987), we estimated the BLR electron densities and their changes of Seyfert 1 galaxy NGC 7469 using IUE spectra observed from June 11 to July 29, 1996 (Wanders et al. 1997). We separated blended Si III] and C III] lines using the STARLINK/DIPSO and measured their fluxes within the error of $12.4\%\;and\;6.6\%,$ respectively. Electron density fluctuated from $10^{9.69}\;to\;10^{10.93}$ during about two month period, i.e. 17.3 times density variation within 50 days. We also derived time delays from UV emission line variations .elative to the continuum $(at\;1315{\AA}):$ 2 days for C IV, 4 days for C III], 8 days for Si III]. This suggests that their stratified UV line emission regions are at 0.002 pc, 0.004 pc and 0.006 pc, respectively, from the central region. Based on the BLR sizes and their rotation velocities deduced from the line profiles, we estimate the central black hole mass as about $10^6M_{\odot}$

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.257-258
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• 2012

With AKARI, we carried out near-infrared spectroscopy of the nearby barred spiral galaxy, NGC 1097, categorized as Seyfert 1 with a circumnuclear starburst ring. Our observations mapped the galactic center region. As a result, we obtain the spatial distributions of the polycyclic aromatic hydrocarbon $3.3{\mu}m$ and the aliphatic hydrocarbon $3.4-3.6{\mu}m$ emission. The former is detected from all the observed regions and the latter is enhanced near the bar connecting the ring with the nucleus. In addition, we detect absorption features due to $H_2O$ ice and CO/SiO at the ring and the galactic center, while we detect the hydrogen recombination line $Br{\alpha}$ only from the ring. Hence the observed spectra change dramatically within the central 1 kpc region.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.36.2-36.2
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• 2019

Fe II emission is a prominent and ubiquitous feature in the spectra of broad-line Active Galactic Nuclei (AGN) by producing a pseudo-continuum from UV to optical with complex and strong blends of the numerous emission lines themselves, other emission lines, and continuum. Since theoretical modeling of such intricate Fe II emission is very difficult and still far from able to reproduce observed data in detail, an empirical iron emission template, derived from observations of a narrow-line Seyfert 1 galaxy, is an essential and practical tool to obtain accurate measurements of all the emission lines and continuum in AGN spectra. However, the existing iron templates, based on the single prototypical strong Fe II emitter I Zw 1, are suffering from inadequate S/N and non-simultaneous, inconsistent data with limited wavelength coverage, which consequently limit the accuracy of all the spectral measurements. To overcome the limitations and construct an improved iron template with wide spectral coverage, high-quality UV and optical spectra for the new and better identified template galaxy, Mrk 493, were successfully obtained from our HST STIS program (GO-14744). We will show the preliminary results for multicomponent spectral decomposition of the data and template construction with application tests to various AGN spectra and comparison with previous templates.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.271-274
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• 2012

We present the result of systematic AKARI IRC infrared $2.5-5{\mu}m$ spectroscopy of >100 nearby luminous infrared galaxies, to investigate the energetic roles of starbursts and optically-elusive buried AGNs. Based on (1) the equivalent widths of the $3.3{\mu}m$ PAH emission features, (2) the optical depths of absorption features, and (3) continuum slopes, we can disentangle emission from starbursts and AGNs. We find that the energetic importance of buried AGNs increases with increasing galaxy infrared luminosities, suggesting that the AGN-starburst connections (and thereby possible AGN feedback to host galaxies) are luminosity dependent.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.46.1-46.1
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• 2013

WIth high accretion rate and low black hole mass, narrow line seyfert 1 galaxies (NLS1s) are an interesting sub-class of AGNs. To investigate whether NLS1s follow the same M-${\sigma}*$ relation as other AGNs, we selected a sample of 110 NLS1s at relatively low redshift z < 0.1 from SDSS DR7 by constraining the FWHM of Ha broad component, and determined their black hole masses. We measured stellar velocity dispersion of 65 objects which showed strong enough stellar lines in the SDSS spectra, while we adopted the ${\sigma}*$ measurements of 45 objects from Xiao et al. 2011. We find that NLS1s follow the M-${\sigma}*$ relation of active and inactive galaxies while there is a dependency due to the galaxy inclination, which probably cause rotational broadening of stellar absorption lines.