• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.74.2-74.2
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• 2012

Metallicity is an important tracer of star formation in galaxy evolution. Based on the flux ratios of broad emission lines, AGN metallicity has shown a correlation with AGN luminosity. However, it is not clear what physical parameter drives the observed correlation. Using a sample 69 Palomar-Green QSOs at low-z (z<0.5), we determine BLR gas metallicity from emission line flux ratios, i.e., N V1240/C IV1549, (Si IV1398+O IV1402)/C IV1549 and N V1240/He II1640 based on the UV spectra from the HST and IUE archives. We compare BLR gas metallicity with various AGN properties, i.e., black hole mass, AGN luminosity and Eddington ratio, in order to investigate physical connection between metal enrichment and AGN activity. In contrast to high-z QSOs, which show the correlation between metallicity and black hole mass, we find that the metallicity of low-z QSOs correlates with Eddington ratio, but not with black hole mass, suggesting that metallicity enrichment mechanism is different between low-z and high-z.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.36.1-36.1
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• 2019

We present the observed relationship between Eddington ratio (${\lambda}Edd$) and optical narrow-emission-line ratio ([NII] ${\lambda}6583/H{\alpha}$) of X-ray-selected unobscured active galactic nuclei (AGN) at 0.6 < z < 1.7 using 27 near-infrared spectra from the Fiber Multi-Object Spectrograph mounted on the Subaru telescope along with 26 additional sources from the literature. We show that the ${\lambda}Edd$ and [NII] ${\lambda}6583/H{\alpha}$ ratio at 0.6 < z < 1.7 exhibits a similar distribution of ${\lambda}Edd$-[NII] ${\lambda}6583/H{\alpha}$ anti-correlation that has been found for local ( = 0.036), hard X-ray selected AGN. The observed anti-correlation suggests that [N II] ${\lambda}6583/H{\alpha}$ optical narrow-line ratio in the AGN host galaxy may carry important information about the accretion state of the central supermassive black hole, suggesting the observational hint of consistent relationship from local to z ~ 1.7. Further study is necessary to determine whether the ${\lambda}Edd$-[N II] ${\lambda}6583/H{\alpha}$ correlation in high-redshift still holds at ${\log}{\lambda}Edd$ < -2 compared to local AGN.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.44.1-44.1
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• 2013

We present the preliminary results from 86 GHz GMVA observations on 2 AGN - 0954+658 and 0716+714. The observation was taken with the Global mm-VLBI Array in Oct. 2010, with dual polarization mode. The aim of the observation is to produce the polarization maps of the sources, with the Stokes parameters - I, Q, U and V. The final results will be used for estimating the strength of the intrinsic magnetic field and the geometries of AGN jets.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.451-452
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• 2015

We performed statistical analysis for a nearby (0.01 < z < 0.05) volume limited ($M_r$ < -19) sample of galaxies via visual inspection and the definition of galaxy pair systems based on the Sloan Digital Sky Survey Data Release 7 in order to confirm the effects of galaxy interaction on AGN activities. We found that local environmental effects such as galaxy interaction have an influence on the enhancement of the frequency and the strength of the AGN activity. This article is the summary of the paper which will be submitted soon.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.75.1-75.1
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• 2015

Environments (field, galaxy groups, and galaxy clusters) can affect galaxy evolution due to galaxy interaction which is controlled by different galaxy number densities and velocity dispersions. Since the galaxy interaction or merger triggers both star formation and AGN, AGN fraction can be used to understand the effect of environment. We detected X-ray AGN fraction in a nearby galaxy cluster, Abell 133, using Chandra X-ray image and optical spectra. We found ~600 X-ray point sources in the field of Abell 133 using the 2.8 Msec exposure Chandra images. We determined 3 cluster members based on the redshifts derived from optical spectra obtained from Magellan IMACS observation. The AGN fraction in Abell 133 is similar to that of other environments, i.e., COSMOS and CDFS. We will discuss the results by comparing Abell 133 with other environments.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.50.1-50.1
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• 2012

As a tracer of star formation history, metallicity provides crucial information for understanding galaxy evolution. In the case AGN, gas metallicity is often derived from the flux ratio of UV emission lines, i.e., NV1240 and CIV1549. To investigate the dependence of metallicity on AGN luminosity, black hole mass, and accretion rate, we measure NV1240 and CIV1549 line fluxes and derive gas metallicity of a sample of 73 local Seyfert 1 galaxies and QSOs, using archival UV spectra obtained with the HST and IUE. In this work, we will present the metallicity of local AGN and its relation with AGN properties.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.32.2-32.2
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• 2010

Red dusty Active Galactic Nuclei (AGNs) are suspected to mid-stage between ULIRG and AGN phase. As well as, they are suspected that they have more than 50% of AGN population. To understand character of red AGN, Black Hole (BH) mass of red AGN is a key property and haven't measured by existing method such as reverberation mapping and single epoch method. So we still don't know their character and properties clearly. To estimate properties of red AGNs escape from effect of dust-obscuration, we have obtained Near InfraRed (NIR) spectra of 31 reverberation mapped AGNs and 49 Palomar-Green(PG) Quasi-Stellar Object (QSO) using the infrared camera (IRC) for AKARI with unique wavelength range 2.5-$5.0{\mu}m$. From this spectra, we measured the FWHM and luminosity of brackett ${\alpha}$, ${\beta}$ at 4.0, 2.6 micron meter for deriving new BH mass estimators based on the properties of Brackett line emission.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.46.1-46.1
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• 2014

In understanding "cooling flow" problem and the galaxy-SMBH co-evolution, AGN feedback is considered as one of the most important phenomena. Among various AGN feedback phenomena, X-ray cavities are particularly useful for studying AGN feedback over 10 kpc scales, as the origin of X-ray cavities is believed to be related to radio jet from AGN. For a comprehensive study of X-ray cavities, we collect all available diffuse X-ray data of galaxies in various galaxy environments, ranging from field galaxies to galaxy clusters, using the Chandra X-ray data archive. As a result we build up a sample of 87 targets showing enough X-ray photons to perform the analysis. Using modeling and unsharp masking techniques, we detected X-ray cavities and measured their physical properties (i.e., cavity size) for the 49 targets. Here, we present X-ray cavity properties and discuss environmental effects.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.477-479
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• 2015

By probing nuclear regions and the overall properties of AGN hosts as a function of their environments, we aim to observationally examine how AGN activities are related to their surroundings. We have selected a representative sample of AGN hosts in the Virgo cluster. The selected galaxies are located in a range of density regions showing various morphologies in 1.4 GHz continuum emission. High-resolution observations with the Korean VLBI Network (KVN) allow us to access the inner region of the AGN without suffering from dust extinction and synchrotron self-absorption. Since a number of our targets are too weak to be detected at K-band (22 GHz) within their coherence time, we applied phase referencing to calibrate fast atmospheric phase fluctuations.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.49.1-49.1
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• 2011

Utilizing single-epoch spectra and the empirical relation between the size of the broad-line region and AGN continuum luminosity, the so-called single-epoch method has been widely used for estimating AGN black hole masses. However, the systematic uncertainties and the potential biases of this method are not well examined. Taking the full advantage of the high-quality homogeneous spectra from the Lick AGN Monitoring Project (LAMP), we investigate in detail the uncertainties of single-epoch mass estimates by comparing with the reverberation-mapping results. We find that the uncertainty due to AGN variability is less than 0.1 dex, while there is a systematic offset between single-epoch masses and reverberation masses. Particularly, narrow-line Seyfert 1 galaxies show that the Hbeta line widths measured from single-epoch (or mean) spectra are systematically larger than those from rms spectra, indicating a potential bias of single-epoch masses. We will present the detailed measurement method, the test of virial assumption, and the systematic uncertainties.