• Journal of The Korean Astronomical Society
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• v.47 no.5
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• pp.167-178
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• 2014

We search for misclassified type 1 AGNs among type 2 AGNs identified with emission line flux ratios, and investigate the properties of the sample. Using 4 113 local type 2 AGNs at 0.02 < z < 0.05 selected from Sloan Digital Sky Survey Data Release 7, we detected a broad component of the $H{\alpha}$ line with a Full-Width at Half-Maximum (FWHM) ranging from 1 700 to $19090km\;s^{-1}$ for 142 objects, based on the spectral decomposition and visual inspection. The fraction of the misclassified type 1 AGNs among type 2 AGN sample is ~3.5%, implying that a large number of missing type 1 AGN population may exist. The misclassified type 1 AGNs have relatively low luminosity with a mean broad $H{\alpha}$ luminosity, log $L_{H\alpha}=40.50{\pm}0.35\;erg\;s^{-1}$, while black hole mass of the sample is comparable to that of the local black hole population, with a mean black hole mass, log $M_{BH}=6.94{\pm}0.51\;M_{\odot}$. The mean Eddington ratio of the sample is log $L_{bol}/L_{Edd}=-2.00{\pm}0.40$, indicating that black hole activity is relatively weak, hence, AGN continuum is too weak to change the host galaxy color. We find that the O III lines show significant velocity offsets, presumably due to outflows in the narrow-line region, while the velocity offset of the narrow component of the $H{\alpha}$ line is not prominent, consistent with the ionized gas kinematics of general type 1 AGN population.

• New Physics: Sae Mulli
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• v.68 no.11
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• pp.1262-1267
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• 2018

We introduce a new method to construct wormholes without adopting exotic matters in Einstein-Born-Infeld gravity with a negative cosmological constant. Contrary to the conventional method, the throat of the wormhole is located at the point where the metric solutions are joined smoothly. Thus, exotic matters are not needed to sustain the throat. We consider the behavior of a minimally coupled scalar field to study the stability of the new wormhole. If we define the quasinormal mode of the scalar field as the purely ingoing flux at the throat of the wormhole, the stability of wormhole can be discussed in analogy with the argument that we use for the stability of a black hole. Because an analytic solution can not be found, we suggest a formalism to find quasinormal modes numerically. The crucial difference from the black hole case is that the coefficient of the second-order derivative term of the radial equation is expanded from n = -1, which is contrary to the black hole case where it is expanded from n = 0.

• 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.19 no.1
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• pp.11-16
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• 2004

In this review article the famous 'jet equation' in a Minkowski magnetosphere around the compact objects will be fully derived for the pedagogical purposes.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.75.1-75.1
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• 2012

Narrow-Line Seyfert 1 galaxies are arguably the most important AGN subclass in investigating the origin of the black hole mass-galaxy stellar velocity dispersion (MBH-${\sigma}$) relation because of their high accretion rates close to the Eddington limit. Currently, it is still under discussion whether NLS1s are off from the local MBH-${\sigma}$ relation. We select a sample of 325 NLS1 at relatively low redshift (z<0.1) from the SDSS DR7 by constraining FWHM of $H{\beta}$ in the range of 800-2,200 km/s. Among them, we measured stellar velocity dispersion of 40 objects which show strong stellar absorption lines, e.g. Mg b triplet(${\sim}5175{\AA}$), Fe($5270{\AA}$). In contrast, the other 285 objects show too weak stellar absorption lines to measure velocity dispersion. Using the sample of 40 objects with stellar velocity dispersion measurements, we investigate whether NLS1s follow the same MBH-${\sigma}$ relation as normal galaxies and broad line AGNs. We also test the reliability of the width of narrow lines as a surrogate of stellar velocity dispersion by comparing directly measured stellar velocity dispersion with ${\sigma}$ inferred from [O III], [N II], [S II] line widths, respectively. We will discuss the connection between AGN activity in NLS1s and galaxy evolution based on these results.

• Journal of The Korean Astronomical Society
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• v.55 no.4
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• pp.131-138
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• 2022

We report the discovery of four quasars with M₁₄₅₀ ≳ -25.0 mag at z ~ 5 and supermassive black hole mass measurement for one of the quasars. They were selected as promising high-redshift quasar candidates via deep learning and Bayesian information criterion, which are expected to be effective in discriminating quasars from the late-type stars and high-redshift galaxies. The candidates were observed by the Double Spectrograph on the Palomar 200-inch Hale Telescope. They show clear Lyα breaks at about 7000-8000 Å, indicating they are quasars at 4.7 < z < 5.6. For HSC J233107-001014, we measure the mass of its supermassive black hole (SMBH) using its C _IV λ1549 emission line. The SMBH mass and Eddington ratio of the quasar are found to be ~10⁸ M_⊙ and ~0.6, respectively. This suggests that this quasar possibly harbors a fast growing SMBH near the Eddington limit despite its faintness (L_Bol < 10⁴⁶ erg s^-1). Our 100% quasar identification rate supports high efficiency of our deep learning and Bayesian information criterion selection method, which can be applied to future surveys to increase high-redshift quasar sample.

• Journal of The Korean Astronomical Society
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• v.35 no.3
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• pp.123-130
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• 2002

An elliptical accretion disk may be formed by tidally disrupted debris of a flying-by star in an active galactic nucleus (AGN) or by tidal perturbation due to a companion in a binary black hole system. We investigate the iron K$\alpha$ line profiles expecting from a geometrically thin, relativistic, elliptical disk in terms of model parameters, and find that a broad and skewed line profile can be reproduced well. Its shape is variable to the model parameters, such as, the emissivity power-law index, the ellipticity of the disk, and the major axis orientation of the elliptical accretion disk. We suggest that our results may be useful to search for such an elliptical disk and consequently the tidal disruption event.

• Journal of The Korean Astronomical Society
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• v.48 no.3
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• pp.203-206
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• 2015

The masses of supermassive black holes in active galactic nuclei (AGN) can be derived spectroscopically via virial mass estimators based on selected broad optical/ultraviolet emission lines. These estimates commonly use the line width as a proxy for the gas speed and the monochromatic continuum luminosity, λL_λ, as a proxy for the radius of the broad line region. However, if the size of the broad line region scales with the bolometric AGN luminosity rather than λL_λ, mass estimates based on different emission lines will show a systematic discrepancy which is a function of the color of the AGN continuum. This has actually been observed in mass estimates based on Hα/Hβ and C_IV lines, indicating that AGN broad line regions indeed scale with bolometric luminosity. Given that this effect seems to have been overlooked as yet, currently used single-epoch mass estimates are likely to be biased.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.62.1-62.1
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• 2020

We present a scaling relation between black hole (BH) mass and bulge luminosity for 35 nearby (z<0.1) type 1 active galaxies, selected from the 70-month Swift-BAT X-ray source catalog. Thanks to the unbiased selection and proximity of the parent sample, our sample is suitable to study the physical connection between central black holes and host galaxies. We use the F814W images obtained with the Advanced Camera for Surveys on Hubble Space Telescope, to perform the imaging decomposition with GALFIT. With a careful treatment on the PSF model, we measure the I-band bulge brightness robustly. In combination with the BH mass estimated from a single-epoch spectroscopic data, we present the correlation between BH mass and bulge luminosity of the target AGNs. We demonstrate that our sample marginally lies off from the M(BH)-L(bulge) relation of inactive galaxies. We discuss possible physical origins of this discrepancy. Finally, we present how the relation depends on the photometric properties of AGNs and host galaxies, which may provide an useful insight on the co-evolution between BHs and host galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.67.1-67.1
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• 2012

Shocks are evolved when the relativistic jets in active galactic nuclei (AGNs), black hole binaries, supernova remnants (SNR) and gamma-ray bursts (GRBs) interact with the surrounding medium. The high energy particles are believed to be accelerated by the diffusive shock acceleration and the strong magnetic field is generated by Weibel instability in the shock. When ultrarelativistic electrons with strong magnetic field cool by the synchrotron emission, the radiation is observed in gamma-ray burst and the near-equipartitioned magnetic field in the external shock delays the afterglow emission. In this paper, we performed the 3D particle-in-cell (PIC) simulations to understand the characteristics of these relativistic shock and particle acceleration. Forward and reverse shocks are shaped while the unmagnetized injecting jet interacts with the unmagnetized ambient medium. Both upstream and downstream become thermalized and the particle accelerations are shown in each transition region of the shock structures.