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Register a new userThe Central Region of the Nearby Seyfert 2 Galaxy NGC 4945 : A Pair of Spirals
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NGC 4945 is a Seyfert 2 galaxy at a distance of 3.82 Mpc. Its relative proximity has permitted a detailed SMA study of the circumnuclear molecular gas in a galaxy exhibiting an AGN. Based on an analysis of the high-resolution velocity field of the central region (20 X 20, 1 = 19 pc), we demonstrate that the S-shaped structure of the isovelocity contours is well reproduced by the numerical results of a two dimensional hydrodynamical simulation. In particular, the velocity structure is represented by the bending produced by a shock along the spiral density waves, which are excited at the outer-inner Lindblad resonance by a fast rotating bar. The simulated density map reveals a pair of tightly wound spirals in the center which pass through most of the ring-like (claimed to be a circumnuclear starburst ring by other authors) high intensity region in the observations as well as intersect several Pa$alpha$ emission line knots located outside the ring-like region. The calculated mass inflow rate at a scale of 50 pc is about three times the inferred mass accretion rate of the AGN of NGC 4945. We find that self-gravity of the gas is important and should be included in our model for NGC 4945. The model is compared with the gas orbit model discussed in Lim et al. (2009), and it is shown that the hydrodynamic model provides a better match to the observed position-velocity diagram and, hence, provides a more reliable prediction of the outer inner Lindblad resonance position.
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We present mid infrared (MIR) spectra of the Seyfert 2 (Sy 2) galaxy NGC 1808, obtained with the Geminis Thermal-Region Camera Spectrograph (T-ReCS) at a spatial resolution of 26 pc. The high spatial resolution allowed us to detect bright polycyclic aromatic hydrocarbons (PAHs) emissions at 8.6micron and 11.3micron in the galaxy centre (26 pc) up to a radius of 70 pc from the nucleus. The spectra also present [Ne ii]12.8micron ionic lines, and H2 S(2)12.27micron molecular gas line. We found that the PAHs profiles are similar to Peeterss A class, with the line peak shifted towards the blue. The differences in the PAH line profiles also suggests that the molecules in the region located 26 pc NE of the nucleus are more in the neutral than in the ionised state, while at 26 pc SW of the nucleus, the molecules are mainly in ionised state. After removal of the underlying galaxy contribution, the nuclear spectrum can be represented by a Nenkovas clumpy torus model, indicating that the nucleus of NGC 1808 hosts a dusty toroidal structure with an angular cloud distribution of sigma = 70degree, observers view angle i = 90degree, and an outer radius of R0 = 0.55 pc. The derived column density along the line of sight is NH = 1.5 x 10^24 cm-2, which is sufficient to block the hard radiation from the active nucleus, and would explain the presence of PAH molecules near to the NGC 1808s active nucleus.
The AGN NGC 2110 presents a peculiar case among the Seyfert 2 galaxies, as it displays also features of radio-loud objects and is classified as FR-I radio galaxy. Here we analyse simultaneous INTEGRAL and Swift data taken in 2008 and 2009. We reconstruct the spectral energy distribution in order to provide further insight. The combined X-ray spectrum is well represented by an absorbed cut-off power law model plus soft excess. Combining all available data, the spectrum appears flat (photon index 1.25 +- 0.04) with the high-energy cut-off being at 82 +- 9 keV. The intrinsic absorption is moderate (NH = 4E22 1/cm**2), the iron K-alpha line is weak (EW = 114 eV), and no reflection component is detected in the INTEGRAL spectrum. The data indicate that the X-ray spectrum is moderately variable both in flux and spectral shape. The 2008 spectrum is slightly steeper (photon index 1.5, Ec = 90 keV) with the source being brighter, and flatter in 2009 (photon index 1.4, Ec = 120 keV) in the lower flux state. The spectral energy distribution gives a bolometric luminosity of L = 2E44 erg/sec. NGC 2110 appears to be a borderline object between radio loud narrow line Seyfert 1 and radio quiet Seyfert 2. Its spectral energy distribution might indeed be dominated by non-thermal emission arising from the jet.
Using the method of integral-field (3D) spectroscopy, we have investigated the kinematics and distribution of the gas and stars at the center of the early-type spiral galaxy with a medium scale bar NGC 7177 as well as the change in the mean age of the stellar population along the radius. A classical picture of radial gas inflow to the galactic center along the shock fronts delineated by dust concentration at the leading edges of the bar has been revealed. The gas inflow is observed down to a radius R = 1.5 -- 2, where the gas flows at the inner Lindblad resonance concentrate in an azimuthally highly inhomogeneous nuclear star formation ring. The bar in NGC 7177 is shown to be thick in z coordinate; basically, it has already turned into a pseudo-bulge as a result of secular dynamical evolution. The mean stellar age inside the star formation ring, in the galactic nucleus, is old, ~10 Gyr. Outside, at a distance R = 6 - 8 from the nucleus, the mean age of the stellar population is ~2 Gyr. If we agree that the bar in NGC 7177 is old, then, obviously, the star formation ring has migrated radially inward in the last 1-2 Gyr, in accordance with the predictions of some dynamical models.
We report far-infrared (FIR) imaging of the Seyfert 2 galaxy NGC 3081 in the range 70-500 micron, obtained with an unprecedented angular resolution, using the Herschel Space Observatory instruments PACS and SPIRE. The 11 kpc (~70 arcsec) diameter star-forming ring of the galaxy appears resolved up to 250 micron. We extracted infrared (1.6-500 micron) nuclear fluxes, that is active nucleus-dominated fluxes, and fitted them with clumpy torus models, which successfully reproduce the FIR emission with small torus sizes. Adding the FIR data to the near- and mid-infrared spectral energy distribution (SED) results in a torus radial extent of Ro=4(+2/-1) pc, as well as in a flat radial distribution of the clouds (i.e. the q parameter). At wavelengths beyond 200 micron, cold dust emission at T=28+/-1 K from the circumnuclear star-forming ring of 2.3 kpc (~15 arcsec) in diameter starts making a contribution to the nuclear emission. The dust in the outer parts of the galaxy is heated by the interstellar radiation field (19+/-3 K).
We use the full broad-band XMM-Newton EPIC data to examine the X-ray spectrum of the nearby Seyfert 2 galaxy NGC 1068, previously shown to be complex with the X-ray continuum being a sum of components reflected/scattered from cold (neutral) and warm (ionised) matter, together with associated emission line spectra. We quantify the neutral and ionised reflectors in terms of the luminosity of the hidden nucleus. Both are relatively weak, a result we interpret on the Unified Seyfert Model by a near side-on view to the putative torus, reducing the visibility of the illuminated inner surface of the torus (the cold reflector), and part of the ionised outflow. A high inclination in NGC 1068 also provides a natural explanation for the large (Compton-thick) absorbing column in the line-of-sight to the nucleus. The emission line fluxes are consistent with the strength of the neutral and ionised continuum components, supporting the robustness of the spectral model.
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