Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userVLTI/VINCI observations of the nucleus of NGC 1068 using the adaptive optics system MACAO
110
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present the first near-infrared K-band long-baseline interferometric measurement of the prototype Seyfert 2 galaxy NGC 1068 with resolution lambda/B ~ 10 mas obtained with the Very Large Telescope Interferometer (VLTI) and the two 8.2m Unit Telescopes UT2 and UT3. The adaptive optics system MACAO was employed to deliver wavefront-corrected beams to the K-band commissioning instrument VINCI. A squared visibility amplitude of 16.3 +/- 4.3 % was measured for NGC 1068 at a sky-projected baseline length of 45.8 m and azimuth angle 44.9 deg. This value corresponds to a FWHM of the K-band intensity distribution of 5.0 +/- 0.5 mas (0.4 +/- 0.04 pc) at the distance of NGC 1068) if it consists of a single Gaussian component. Taking into account K-band speckle interferometry observations (Wittkowski et al. 1998; Weinberger et al. 1999; Weigelt et al. 2004), we favor a multi-component model for the intensity distribution where a part of the flux originates from scales clearly smaller than about 5 mas (<0.4 pc), and another part of the flux from larger scales. The K-band emission from the small (< 5 mas) scales might arise from substructure of the dusty nuclear torus, or directly from the central accretion flow viewed through only moderate extinction.
rate research
Read More
Context. The putative tori surrounding the accretion disks of active galactic nuclei (AGNs) play a fundamental role in the unification scheme of AGNs. Infrared long-baseline interferometry allows us to study the inner dust distribution in AGNs with unprecedented spatial resolution over a wide infrared wavelength range. Aims. Near- and mid-infrared interferometry is used to investigate the milli-arcsecond-scale dust distribution in the type 1.5 Seyfert nucleus of NGC 3783. Methods. We observed NGC 3783 with the VLTI/AMBER instrument in the K-band and compared our observations with models. Results. From the K-band observations, we derive a ring-fit torus radius of 0.74 +/- 0.23 mas or 0.16 +/- 0.05 pc. We compare this size with infrared interferometric observations of other AGNs and UV/optical-infrared reverberation measurements. For the interpretation of our observations, we simultaneously model our near- and mid-infrared visibilities and the SED with a temperature/density-gradient model including an additional inner hot 1400 K ring component.
We present diffraction-limited near-IR images in J, H and K of the nucleus of NGC 1068, obtained with the Adaptive Optics system {Pueo} at CFHT. The achieved resolution (0.12) reveals several components, particularly prominent on the [J-K] image: a) an unresolved, conspicuous core (size < 9 pc); b) an elongated structure at P.A. ~102 deg, beginning to show up at radius ~ 15 pc; c) a S-shaped structure with radial extent ~ 20 pc, including a bar-like central elongation at P.A. ~ 15 deg and two short spiral arms. The K core is at the location of the putative central engine (radio source S1) : the core is likely the emission from the hot inner walls of the dust/molecular torus. The extremely red colors of the central 0.2, [J-K]=7.0, [H-K]=3.8, lead to an extinction Av > 25. The elongated structure at P.A.~ 102 deg may trace the presence of cooler dust within and around the torus. This interpretation is supported by two facts : a) the elongated structure is perpendicular to the local radio jet originating at S1; b) its direction follows exactly that of the disk of ionized gas recently found with the VLBA. The S-shaped feature suggests an extremely compact barred spiral structure, that would be the innermost of a series of nested spiral structures, as predicted by simulations. This is supported by the inner stellar distribution - deduced from the J image - which clearly follows an exponential disk with a 19 pc scale-length, precisely that expected from the rotation of a bar.
We present J and K imaging linear polarimetric adaptive optics observations of NGC 1068 using MMT-Pol on the 6.5-m MMT. These observations allow us to study the torus from a magnetohydrodynamical (MHD) framework. In a 0.5 (30 pc) aperture at K, we find that polarisation arising from the passage of radiation from the inner edge of the torus through magnetically aligned dust grains in the clumps is the dominant polarisation mechanism, with an intrinsic polarisation of 7.0%$pm$2.2%. This result yields a torus magnetic field strength in the range of 4$-$82 mG through paramagnetic alignment, and 139$^{+11}_{-20}$ mG through the Chandrasekhar-Fermi method. The measured position angle (P.A.) of polarisation at K$$ is found to be similar to the P.A. of the obscuring dusty component at few parsec scales using infrared interferometric techniques. We show that the constant component of the magnetic field is responsible for the alignment of the dust grains, and aligned with the torus axis onto the plane of the sky. Adopting this magnetic field configuration and the physical conditions of the clumps in the MHD outflow wind model, we estimate a mass outflow rate $le$0.17 M$_{odot}$ yr$^{-1}$ at 0.4 pc from the central engine for those clumps showing near-infrared dichroism. The models used were able to create the torus in a timescale of $geq$10$^{5}$ yr with a rotational velocity of $leq$1228 km s$^{-1}$ at 0.4 pc. We conclude that the evolution, morphology and kinematics of the torus in NGC 1068 can be explained within a MHD framework.
We present K-band commissioning observations of the Mira star prototype o Cet obtained at the ESO Very Large Telescope Interferometer (VLTI) with the VINCI instrument and two siderostats. The observations were carried out between 2001 October and December, in 2002 January and December, and in 2003 January. Rosseland angular radii are derived from the measured visibilities by fitting theoretical visibility functions obtained from center-to-limb intensity variations (CLVs) of Mira star models (Bessel et al. 1996, Hofmann et al. 1998, Tej et al. 2003). Using the derived Rosseland angular radii and the SEDs reconstructed from available photometric and spectrophotometric data, we find effective temperatures ranging from T_eff=3192 +/- 200 K at phase phi=0.13 to 2918 +/- 183 K at phi=0.26. Comparison of these Rosseland radii, effective temperatures, and the shape of the observed visibility functions with model predictions suggests that o Cet is a fundamental mode pulsator. Furthermore, we investigated the variation of visibility function and diameter with phase. The Rosseland angular diameter of o Cet increased from 28.9 +/- 0.3 mas (corresponding to a Rosseland radius of 332 +/- 38 R_sun for a distance of D=107 +/- 12 pc) at phi=0.13 to 34.9 +/- 0.4 mas (402 +/- 46 R_sun) at phi=0.4. The error of the Rosseland linear radius almost entirely results from the error of the parallax, since the error of the angular diameter is only approximately 1 %.
Spectra of the archetypal Type II Seyfert galaxy NGC 1068 in a narrow wavelength interval near 3.7 microns have revealed a weak absorption feature due to two lines of the molecular ion H3+. The observed wavelength of the feature corresponds to velocity of -70 km/s relative to the systemic velocity of the galaxy, implying an outward flow from the nucleus along the line of sight. The absorption by H3+ along with the previously known broad hydrocarbon absorption at 3.4~microns probably are formed in diffuse gas that is in close proximity to the continuum source, i.e. within a few tens of parsecs of the central engine. Based on that conclusion and the measured H3+ absorption velocity and with the assumption of a spherically symmetric wind we estimate a rate of mass outflow from the AGN of ~1 Msun/yr.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
