Variability in the Nucleus of NGC 1068

The near-infrared output of the nucleus of NGC 1068 increased by a factor of two over the 18 years between 1976 and 1994 and has recently started to decline. It is not clear whether this event has been the response of an extended dusty region to a single outburst in the central engine or is the result of a continuous change in its XUV output. The integrated energy of the event amounts to well over 1052 erg and thus cannot be due to a single supernova. The variable part of the infrared flux from NGC 1068, observed through an aperture of constant diameter, is found to have a constant spectral shape. Comparison with similar data from other Seyfert galaxies shows that the variable infrared component in NGC 1068 is reddened by about 20 mag in Av if the emission mechanism is similar in all cases. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evidence for Absorption in NGC 1068

We present evidence that interstellar absorption is responsible for producing much of the complex morphology seen in the inner few arcseconds of NGC 1068. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamics of the Nuclear Outflow in NGC 1068

A short survey is presented of dynamical (and thermodynamical) issues relevant to outflows in Seyfert galaxies like NGC 1068. Numerical simulations incorporating both realistic radiative heating and cooling, and angular momentum, show that the fraction of injected gas which escapes in a wind is very sensitive to both the injection pressure and the gas's angular momentum. Radiation pressure acting through a variety of atomic opacity processes may also be important. This revised version was published online in July 2006 with corrections to the Cover Date.     

The optical variability of the Seyfert galaxies NGC 4051 and NGC 1068

The optical (BV) monitoring data for the Seyfert galaxies NGC 4051 and NGC 1068 are presented in this paper. NGC 4051 showed a variation of 0.43 mag in 21 minutes in B band from its bright nucleus, and the nucleus of NGC 1068 exhibited a variability of 0.46 mag in B band in a timescale of 1.8 hours. These results argued that the optical emission from the nuclei of the two Seyfert galaxies could be dominated by the nonthermal radiation. The data in this paper, however, are only marginal evidence on the rapid optical variability of these two Seyferts, and further monitoring is needed to confirm this type of variability.     

Clumpy Structure and Polarization in NGC 1068

The polarization map from the HST archival data of the imaging polarimetry for NGC 1068 is analyzed. In the HST images, the central few arcsecond region seems to consist of several clumps, and if we extract the polarization of the clumps separately, the viewing angle of each clump can be determined. This enables us to have a three-dimensional view of this central region. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Nuclear Stellar Cluster in NGC 1068

We present new near-infrared integral field spectroscopy and adaptive optics imaging of the nucleus of NGC 1068. Using the stellar CO absorption features in the H and K bands, we have identified a moderately extincted stellar core centered on the nuclear position and of intrinsic size ~50 pc. We show that this nuclear stellar core is probably 5-16 × 108 years in age and contributes at least 7% of the total nuclear luminosity of ~1 × 1011 L⊙. This revised version was published online in July 2006 with corrections to the Cover Date.     

X-ray Spectroscopy of the Scattered Emission in NGC 1068

We discuss the iron K line complex in NGC 1068. The line complex basically consists of three components, as previously reported. A new analysis of the ASCA data shows that cold reflection appears to dominate the observed X-ray emission above 4 keV based on the detection of ‘Compton shoulder’, a weak red wing of the 6.4 keV fluorescence iron K line, and a very flat continuum. The other two weaker lines at higher energies can be identified with FeXXV and FeXXVI and suggest an highly ionized X-ray mirror as well, although the line energies are systematically lower than those expected from the resonant lines, consistent with a redshift by 1.5%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Origin of the Coronal Line Emission in NGC1068

We present recent observations of several near infrared emission lines of highly ionized (IP ? 100eV) species in NGC1068 which appear to be emitted predominantly within the NE ionization cone; peak at ? 30pc from the nucleus and are blueshifted by ? 300 km s-1 relative to the systemic velocity. The blueshift is the same as that observed for the better known Fe coronal lines in the visible and the absence of red-shifted components in the less extincted infrared lines suggests that any emission in the counter-cone to the SW is intrinsically faint rather than heavily obscured. Following a review of the possible ionization mechanisms and comparison of the line ratios with recent models we conclude that the coronal emission arises predominantly in outflowing gas photoionized by the EUV continuum of the AGN.     

Ultraviolet Lines and Gas Composition in NGC 1068

Recent ultraviolet and X-ray observations suggest that the Fe/O ratio in the NLR gas in NGC 1068 is abnormally high. The X-ray analysis, which is presented elsewhere, suggests a large Fe/H and the data shown and discussed here, in particular the extremely weak O III] λ1663 line, argue for small O/N and O/C. Models to support this claim are shown and discussed. They include improved reddening estimates, dusty and dust-free calculations, and abnormal abundances. The anomalous composition makes NGC 1068 unique among Seyfert galaxies and an unusual laboratory for investigating metal enrichment and depletion.     

X-Ray Excitation of Molecular Hydrogen and [Fe II] Emission in NGC 1068

NGC 1068 is a source of luminous emission in the near-infrared lines of molecular hydrogen and [Fe II]. Although these emission lines are commonly attributed to shocks, I show that in NGC 1068 it is quite plausible that they arise in the X-Ray Dissociation Region (XDR) produced by X-ray irradiation of the gas in the disk by the powerful active nucleus. This mechanism naturally produces the observed size scale of the H2 emission. I will also briefly discuss the implications of the observations of the pure rotation lines of H2 with ISO (Lutz, this workshop).     

Stellar Velocity Field in the Central Region of NGC 1068

We present the velocity field of the stars in the central 25″ × 22″ of NGC 1068 derived from 2-D spectroscopy of the Ca II triplet. A preliminary analysis provides evidence for two distinct stellar systems in the centre of NGC 1068. In the outer regions (say r > 10″), the mean stellar velocity field seems coupled to those of the ionized and molecular gas, indicating aproximately regular rotation with the kinematic minor axis at PA ~ 0°. However, in the inner region, the stars are rotating, whereas the ionized gas is outflowing in the NE-SW direction probably due to the effects of the nuclear activity, and the molecular gas is responding to the bar potential. This revised version was published online in July 2006 with corrections to the Cover Date.     

A new quasar identified in the vicinity of NGC1068

An X-ray source close to the classical Seyfert galaxy NGC 1068 is identified as a quasar with a redshift of 0.63. The very high surface density of quasars around NGC 1068 suggests that the quasars may be physically associated with this active galaxy.     

NGC 1333/IRA6-9 区域中的致密分子云核

利用紫金山天文台青海站的13．7m毫米波望远镜,对NGC1333／IRAS6－9附近的一个10．3'X10'和6．8'X8'的恒星形成区,进行了13CO（1－0）和C18O（1－0）的成图观测,发现了多个新的分子云核和沿SSV12－IRASS方向的13CO（1－O）双极外向流．本文给出了每个云核的观测特性和物理参数．分析了这一区域的云核分布和速度场结构．详细讨论了该区域的云核分布、双极外向流和群集的年轻天体、红外源以及HH天体的关系．     

The circumnuclear X-ray reflectors in NGC 1068 and the Circinus galaxy

The ASCA and BeppoSAX spectra of the Circinus galaxy and NGC 1068 are analysed and compared with photoionization models based on cloudy . In the case of Circinus, a single, mildly ionized reflector can account for the line spectrum, while in NGC 1068 at least three different reflectors (with different ionization states) are needed. We suggest that the reflector in Circinus and the low ionized one in NGC 1068 are the inner and visible part of the material responsible for the X-ray absorption. With this assumption, we estimate for the inner radius of the absorber a value of 0.2 pc for Circinus and of a few parsecs for NGC 1068.     

A Direct Image of the Inner Torus of NGC 1068

We present the first VLBI observations of the compact source S1 in the radio jet of NGC 1068. Roughly 1 pc in length and 0.2 pc wide, S1 resolves into clumps aligned perpendicular to the local radio jet axis. The radio continuum emission arises from a hot (Te ~ 106 K), dense (ne ~ 106 cm-3) plasma, and the source of the radio emission is either thermal free-free emission or Thomson-reflected synchrotron emission. The clouds comprising S1 are opaque to soft X-radiation, and we therefore propose that S1 is the inner, ionized region, or ‘hot zone,’ of the obscuring medium surrounding the active nucleus. The covering fraction of the hot zone is small, Cf ⋦ 10%. Since the covering fraction of the dusty, obscuring medium is probably much larger, the obscuring disk must either flare or warp outside of the hot zone. That the radio jet and hot zone axes are perpendicular also suggests that the hot zone may be considered to trace the outermost extent of the accretion disk. This revised version was published online in July 2006 with corrections to the Cover Date.