• Journal of Astronomy and Space Sciences
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• 제20권3호
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• pp.163-174
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• 2003

The motion of 3C 120 Jet relative to the core is reasonably uniform and the VLBI scale jet connects outwards to a VLA ~ 100kpc scale. We measured the jet width variation from the center and found some indication of a power law which indicates the jet expands roughly with a constant opening angle and a constant flow velocity, $V_{f}{\cong}c$, from subparsec scales to ~ 100 kpc. With such a constant flow velocity and based on other physical parameters deduced from observed emission characteristics of the jet, we have established an equipartition jet model which might accommodate the basic parameters of the jet on subparsec scales, with which one can fit the radio intensities over all the scale of the jet even to ~100 kpc.

• 천문학회보
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• 제37권1호
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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.

• 천문학회보
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• 제35권2호
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• pp.34.2-34.2
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• 2010

The 3C84 (NGC 1275), one of Seyfert 2 galaxy, is an interesting object with its peculiar sub-mas structure. We found that the inner jet (r < 2.5mas) of 3C84 seemed to even changed its position angle and flux over one and a half years based on the result of global 86GHz VLBI survey (Lee et al. 2008). In order to confirm the 'precession' of jet, we observed the object in 4 epochs May07, Oct.07, May08 and Oct.08 with the GMVA (Global mm-VLBI Array) at 3mm (86.25GHz) and the each observation time is about 14 hours. Here we present observation and preliminary result of Oct.07 and May08 epochs.

• 천문학회지
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• 제41권2호
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• pp.17-22
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• 2008

We present an analysis of the soft X-ray emission of MRK 841 to investigate its long-term variation. The light variation of MRK 841 for three different energy bands of soft, medium, and hard values were studied. The maximum variability with a factor of 5 for about two years was confirmed at all three different bands. The light curves exhibit a gradual variation of brightness. In addition to a gradual variation, the short- term or micro variation was also confirmed with a factor of about two for all three different bands. The light variation of each band did not exhibit a correlation between them, but the flare event is strongest in the soft band. The hardness ratio for hard and soft bands shows irregular variation but there was no correlation between them. It was confirmed that there is a gradual decrease of the photon index. Results of our analysis are discussed within the framework of the accretion disk phenomenon.

• 천문학논총
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• 제30권2호
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• pp.531-533
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• 2015

We have investigated the long term variability of the intensities of the broad-line region emission lines in the UV spectra of Seyfert I galaxy NGC 5548 from 1973-1996. We have obtained the following results: 1) a high level correlation between the intensities of emission lines as well as between intensities of emission lines and continuum fluxes was discovered. With increasing wavelength the correlation in both cases becomes weaker, 2) the relationship between the intensity of emission lines and the flux radiation in the continuum can be expressed by a power law function with coefficients of ${\alpha}{\approx}0.8-1.1$ for different lines. When the difference between the wavelengths of spectral lines and the continuum is increased, the value of the power function decreases, and 3) it was found that the magnitude of the variability of the line intensities are weaker than the range of variability of the continuum fluxes. The magnitude of the variability of the line intensities and the continuum fluxes increase at longer wavelengths.

• 천문학논총
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• 제27권4호
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• pp.335-338
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• 2012

We present the $18{\mu}m$ luminosity function (LF) of galaxies at 0.006 < z < 0.8 (the average redshift is ~ 0.04) using the AKARI mid-infrared All-Sky Survey catalogue. We have selected 243 galaxies at $18{\mu}m$ from the Sloan Digital Sky Survey (SDSS) spectroscopic region. These galaxies then have been classified into five types; Seyfert 1 galaxies (Sy1, including quasars), Seyfert 2 galaxies (Sy2), low ionization narrow emission line galaxies (LINER), galaxies that are likely to contain both star formation and Active Galactic Nuclei (AGN) activities (composites), and star forming galaxies (SF) using optical emission lines such as the line width of $H{\alpha}$ or the emission line ratios of [OIII]/$H{\beta}$ and [NII]/$H{\alpha}$. As a result of constructing the LF of Sy1 and Sy2, we found the following results; (i) the number density ratio of Sy2 to Sy1 is $1.64{\pm}0.37$, larger than the results obtained from optical LF and (ii) the fraction of Sy2 in the entire AGN population may decrease with $18{\mu}m$ luminosity. These results suggest that most of the AGNs in the local universe are obscured by dust and the torus structure probably depends on the mid-infrared luminosity.

• 천문학회보
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• 제40권1호
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• pp.73.1-73.1
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• 2015

Isolated galaxies in low-density regions are significant in the sense that they are least affected by the hierarchical pattern of galaxy growth and interactions with perturbers at least for the last few Gyr. To form a comprehensive picture of the star formation history of isolated galaxies, we construct a catalog of isolated galaxies and their comparison sample in relatively denser environments. The galaxies are drawn from SDSS DR7 in the redshift range of 0.025 < z < 0.044. We performed visual inspection and classified their morphology following the Hubble classification scheme. We have investigated the color-magnitude diagram and found elliptical and unbarred spiral galaxies in isolated systems are relatively fainter and bluer than those in denser regions. For the spectroscopic study, we make use of the OSSY catalog (Oh et al. 2011). Our analysis on the absorption-line properties based on the comparison with stellar population models suggests that isolated elliptical galaxies are likely to be younger and metal poorer, while isolated Sc-type galaxies seem to have older luminosity-weighted ages, than their high-density counterpart. In addition, according to the BPT diagnostics, early-type galaxies among isolated galaxies are rather evenly classified into star forming, composite, Seyfert and LINER, whereas their comparisons are mainly populated in the LINER region. On the other hand, late-type galaxies do not show any prominent difference. We discuss the evolutionary histories of isolated galaxies in the context of the standard ${\Lambda}CDM$ cosmology.

• 천문학회보
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• 제42권2호
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• pp.77.1-77.1
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• 2017

We present the preliminary results from our intensive monitoring campaign for measuring continuum and line variability of a low-mass Seyfert galaxy, NGC 4395, which host a smallest known AGN black hole in the reverberation mapping studies. We performed consecutive photometric observations during 5 nights in April 2017. Various telescopes in the world, including BOAO 1.8-m, NYSC 1-m, MDM 2.4-m, 1.3-m, etc, were dedicated for this campaign. Preliminary results show that the tentative time lag can be determined, which is approximately order of 1-2 hours.

• 천문학회지
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• 제36권2호
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• pp.73-73
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• 2003

Proof correction to the equation in the third paragraph of the DISCUSSION AND CONCLUSION has not been carried faithfully to the published version of the paper. The corrected equation should read ${\approx}10^{-3}\;M_8^4/^3(N_{\ast}/10^6\;pc^{-3})({\sigma}/300 km\;s^{-l})^{-l}(r/r_t)\;yr^{-1}$, where Ms is the mass of the SMBH in units of $10^8\;M_{\bigodot}$, $\sigma$ is the virial velocity of the stars, $r_t$ is the tidal radius of the SMBH. This estimates the frequency that a star would pass within a sphere with the radius r from the SMBH, rather than the frequency of the tidal disruption event. Therefore, it increases with the mass of the SMBH. However, the loss cone effect should also be taken into account, which reduces the actual event rate. Here, we adopted a factor of one hundred to consider the deficiency from the isotrophic rate. The authors sincerely regret this error.

• 천문학회보
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• 제36권1호
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• pp.55.1-55.1
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• 2011

We investigate dynamical evolution of gas in barred galaxies using a high-resolution, grid-based hydrodynamic simulations on two-dimensional cylindrical geometry. Non-axisymmetric gravitational potential of the bar is represented by the Ferrers ellipsoids independent of time. Previous studies on this subject used either particle approaches or treated the bar potential in an incorrect way. The gaseous medium is assumed to be infinitesimally-thin, isothermal, unmagnetized, and initially uniform. To study the effects of various environments on the gas evolution, we vary the gas sound speed as well as the mass of a SMBH located at the center of a galaxy. An introduction of the bar potential produces bar substructure including a pair of dust lane shocks, a nuclear ring, and nuclear spirals. The sound speed affects the position and strength of the bar substructure significantly. As the sound speed increases, the dust lane shocks tend to move closer to the bar major axis, resulting in a smaller-size nuclear ring at the galactocentric radius of about 1 kpc. Nuclear spirals that develop inside a nuclear ring can persist only when either sound speed is low or in the presence of a SMBH; they would otherwise be destroyed by the ring material with eccentric orbits. The mass inflow rates of gas toward the galactic center is also found to be proportional to the sound speed. We find that the sound speed should be 15 km/s or larger if the mass inflow rate is to explain nuclear activities in Seyfert galaxies.