Optically Adaptive System for Imaging Spectroscopy (OASIS) 3D data of the Canada-France-Hawaii Telescope in the central 10''.48''.3 (2.92.3 kpc2) region of the Seyfert 2 galaxy NGC 1358 were analyzed. Emission line maps for H at 6563 Å and H at 4861 Å were obtained from the OASIS spectra in the 4800-5500 and 6220-6990 Å wavelength regions. Density distribution, as indicated by the H/H flux ratio, is 105.5 cm3 at the center and 104.4-106.0 cm3 surrounding the center. An elliptical region with a density of 105.5-105.8 cm-3 (perpendicular to the bar's position angle, PA) was discovered at symmetrical locations approximately 1.2-2.0 arcsec and 1.1-1.9 arcsec south east (SE) and north west (NW), respectively, of the center along the bar (PA=130o) axis. A lower-density region (appearing as a void) also existed between the center and this symmetrical structure. The high F(H)/F(H) flux ratio values and the distribution of line widths suggest a region with high-density neutral hydrogen gas. The H flux image and linewidth, and F(H)/F(H) flux ratio image maps suggest presence of a substructure associated with a supermassive black hole at the galactic center, as well as independent structures with relatively strong fluxes in the SE and NW regions. The SE structure is delineated as one substantial substructure, whereas the NW substructure appears broken, or is potentially two separate structures, due to dust shielding. The regions have an independent boundary layer with a density exceeding 106.0cm3 toward the center, likely resulting from collision of the structure flowing along the bar with the Inner Lindblad resonance zone.

It has been suggested that only the most luminous AGNs (L ≳ 1045 erg/s) are triggered by galaxy mergers, while less luminous AGNs (L ~ 1043 erg/s) are driven by other internal processes. The lack of merging features in low luminosity AGN host galaxies has been a primary argument against the idea of merger triggering of low luminosity AGNs. But a merger, especially a rather minor one, might still have played an important role in low luminosity AGNs, as minor merging features at low luminosities are more difficult to identify than major merging features. Using SNUCAM on the 1.5 m telescope at Maidanak observatory, we obtained deep optical images of NGC 7743, a barred spiral galaxy classified as a Seyfert 2 AGN with a low bolometric luminosity of 5 X 1042 erg/s. Surprisingly, we discovered a merging feature around the galaxy, which indicates past merging activity in the galaxy. This example indicates that the merging fraction of low luminosity AGNs may be much higher than previously thought, hinting at the importance of galaxy mergers even in low luminosity AGNs.

We investigated the circumnuclear region of the Seyfert 2 galaxy NGC 5728, using the CFHT 3.6 m OASIS [S ΙΙ], [O ΙΙΙ] & Hβ, spectral images complemented with the IUE spectra. The physical condition of the circumnuclear zone has been derived: the gas density (indicated by [S ΙΙ]6716/31 ratio) around the C core is generally similar to that around the NW core, i.e., ~ 500 cm-3. However, there appears to be evidence of a higher density shell in front of the NW core, ~ 104 cm -3 at -250 km s-1. The IUE Si ΙΙΙ]1892/C ΙΙΙ]1909 ratio implies a possible presence of a broad emission region of gas densities of ~1010 cm-3. The SE cone and surrounding area show several prominent features, while the NW cone does not show any particular structure: we identified three prominent blobs in the SE cone and one possible candidate in the NW cone. The outflow activities exist within the relatively large conic opening angle. We discussed the possibility of inflow or outflow activities of blobs found in the circumnuclear region of NGC 5728. The gas around two cores, two cones, and several blobs, is likely to be excited by the AGN hot source(s).

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 Γ =1.74 ± 0.02 in the energy range of ~ 1 -5 keV 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.

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 ≈ 10 -3 M 8 4/3(N*/10 6 pc-3)(σ/300 km s-l)-l(r/rt) yr-1, where Ms is the mass of the SMBH in units of 10 8 M⊙, σ is the virial velocity of the stars, rt 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.

We have studied the long-term X-ray light curve (2-10 keV) of the luminous Seyfert 1 galaxy MCG-2-58-22 by compiling data, from various X-ray satellites, which together cover more than 20 years. We have found two distinct types of time variations in the light curve. One is a gradual and secular decrease of the X-ray flux, and the other is the episodic increase of X-ray flux (or flare) by a factor of 2-4 compared with the level expected from the secular variation. We detected 3 such flares in total; a representative duration for the flares is ~2 years, with intervening quiescent intervals lasting ~6-8 years. We discuss a few possible origins for these variabilities. Though a standard disk instability theory may explain the displayed time variability in the X-ray light curve, the subsequent accretions of stellar debris, from a tidal disruption event caused by a supermassive black hole in MCG-2-58-22, cannot be ruled out as an alternative explanation.

We report results from an analysis of the X-ray archival data on MCG-2-58-22 obtained with Ginga, ROSAT and ASCA. By analyzing both short- and long-term light curves, we find clear time variations, ranging widely from, ~10 3 s to more than several years, in the X-ray energy range 0.1 - 10 keV. In addition, a flare is detected in 1991, overlaid on a gradual, secular flux decrease from 1979 to 1993; this flare has a time scale of about 1 year, and the X-ray flux increased by at least a factor of 3. The implications of these observational results are discussed in terms of accretion flow dynamics near a supermassive black hole.