A B S T R A C TWe present contemporary optical and infrared spectroscopic observations of the type IIn SN 1998S covering the period between 3 and 127 days after discovery. During the first week the spectra are characterized by prominent broad H, He and C iiiaN iii emission lines with narrow peaks, superimposed on a very blue continuum T , 24 000 KX In the following two weeks the C iiiaN iii emission vanished, together with the broad emission components of the H and He lines. Broad, blueshifted absorption components appeared in the spectra. The temperature of the continuum also dropped to ,14 000 K. By the end of the first month the spectrum comprised broad, blueshifted absorptions in H, He, Si ii, Fe ii and Sc ii. By day 44, broad emission components in H and He reappeared in the spectra. These persisted to as late as days ,100±130Y becoming increasingly asymmetric. We agree with Leonard et al. that the broad emission lines indicate interaction between the ejecta and circumstellar material (CSM) emitted by the progenitor. We also agree that the progenitor of SN 1998S appears to have gone through at least two phases of mass-loss, giving rise to two CSM zones. Examination of the spectra indicates that the inner zone extended to #90 au, while the outer CSM extended from 185 au to over 1800 au.We also present high-resolution spectra obtained at days 17 and 36. These spectra exhibit narrow P Cygni H i and He i lines superimposed on shallower, broader absorption components. Narrow lines of [N ii], [O iii], [Ne iii] and [Fe iii] are also seen. We attribute the narrow lines to recombination and heating following ionization of the outer CSM shell by the UV/X-ray flash at shock breakout. Using these lines, we show that the outer CSM had a velocity of 40±50 km s 21 X Assuming a constant velocity, we can infer that the outer CSM wind commenced more than 170 years ago, and ceased about 20 years ago, while the inner CSM wind may have commenced less than 9 years ago. During the era of the outer CSM wind the outflow from the progenitor was high ± at least ,2 Â 10 25 M ( yr 21 X This corresponds to a mass-loss of at least ,0.003 M ( , suggesting a massive progenitor. The shallower, broader absorption is of width ,350 km s 21 , and may have arisen from a component of the outer CSM shell produced when the progenitor was going through a later q 2001 RAS

We used the CLUMPY torus models and a Bayesian approach to fit the infrared spectral energy distributions (SEDs) and ground-based high-angular resolution mid-infrared spectroscopy of 13 nearby Seyfert galaxies. This allowed us to put tight constraints on torus model parameters such as the viewing angle i, the radial thickness of the torus Y , the angular size of the cloud distribution σ torus , and the average number of clouds along radial equatorial rays N 0 . We found that the viewing angle i is not the only parameter controlling the classification of a galaxy into a type 1 or a type 2. In principle type 2s could be viewed at any viewing angle i as long as there is one cloud along the line of sight. A more relevant quantity for clumpy media is the probability for an AGN photon to escape unabsorbed. In our sample, type 1s have relatively high escape probabilities, P esc ∼ 12 − 44%, while type 2s, as expected, tend to have very low escape probabilities. Our fits also confirmed that the tori of Seyfert galaxies are compact with torus model radii in the range 1-6 pc. The scaling of the models to the data also provided the AGN bolometric luminosities L bol (AGN), which were found to be in good agreement with estimates from the literature. When we combined our sample of Seyfert galaxies with a sample of PG quasars from the literature to span a range of L bol (AGN) ∼ 10 43 − 10 47 erg s −1 , we found plausible evidence of the receding torus. That is, there is a tendency for the torus geometrical covering factor to be lower (f 2 ∼ 0.1 − 0.3) at high AGN luminosities than at low AGN luminosities (f 2 ∼ 0.9 − 1 at ∼ 10 43−44 erg s −1 ). This is because at low AGN luminosities the tori appear to have wider angular sizes (larger σ torus ) and more clouds along radial equatorial rays. We cannot, however rule out the possibility that this is due to contamination by extended dust structures not associated with the dusty torus at low AGN luminosities, since most of these in our sample are hosted in highly inclined galaxies.

Recent theoretical and observational works indicate the presence of a correlation between the star formation rate (SFR) and the active galactic nuclei (AGN) luminosity (and, therefore, the black hole accretion rate,Ṁ BH ) of Seyfert galaxies. This suggests a physical connection between the gas forming stars on kpc scales and the gas on sub-pc scales that is feeding the black hole. We compiled the largest sample of Seyfert galaxies to date with high angular resolution (∼ 0.4 − 0.8 ′′ ) mid-infrared (8-13 µm) spectroscopy. The sample includes 29 Seyfert galaxies drawn from the AGN Revised Shapley-Ames catalogue. At a median distance of 33 Mpc, our data allow us to probe nuclear regions on scales of ∼ 65 pc (median value). We found no general evidence of suppression of the 11.3 µm polycyclic aromatic hydrocarbon (PAH) emission in the vicinity of these AGN, and used this feature as a proxy for the SFR. We detected the 11.3 µm PAH feature in the nuclear spectra of 45% of our sample. The derived nuclear SFRs are, on average, five times lower than those measured in circumnuclear regions of 600 pc in size (median value). However, the projected nuclear SFR densities (median value of 22 M ⊙ yr −1 kpc −2 ) are a factor of 20 higher than those measured on circumnuclear scales. This indicates that the SF activity per unit area in the central ∼ 65 pc of Seyfert galaxies is much higher than at larger distances from their nuclei. We studied the connection between the nuclear SFR anḋ M BH and showed that numerical simulations reproduce fairly well our observed relation.

We present subarcsecond resolution mid-infrared (mid-IR) photometry in the wavelength range from 8 to 20 μm of 18 Seyfert galaxies, reporting high spatial resolution nuclear fluxes for the entire sample. We construct spectral energy distributions (SEDs) that the active galactic nucleus (AGN) dominates, relatively uncontaminated by starlight, adding near-IR measurements from the literature at similar angular resolution. We find that the IR SEDs of intermediate-type Seyferts are flatter and present higher 10 to 18 μm ratios than those of Seyfert 2 galaxies. We fit the individual SEDs with clumpy dusty torus models using the in-house-developed BayesClumpy tool. We find that the clumpy models reproduce the high spatial resolution measurements. Regardless of the Seyfert type, even with high spatial resolution data, near-to mid-IR SED fitting poorly constrains the radial extent of the torus. For the Seyfert 2 galaxies, we find that edge-on geometries are more probable than face-on views, with a number of clouds along equatorial rays of N 0 = 5-15. The 10 μm silicate feature is generally modeled in shallow absorption. For the intermediate-type Seyferts, N 0 and the inclination angle of the torus are lower than those of the Seyfert 2 nuclei, with the silicate feature appearing in weak emission or absent. The columns of material responsible for the X-ray absorption are larger than those inferred from the model fits for most of the galaxies, which is consistent with X-ray absorbing gas being located within the dust sublimation radius, whereas the mid-IR flux arises from an area farther from the accretion disk. The fits yield both the bolometric luminosity of the intrinsic AGN and the torus-integrated luminosity, from which we derive the reprocessing efficiency of the torus. In the models, the outer radial extent of the torus scales with the AGN luminosity, and we find the tori to be confined to scales less than 5 pc.

We present spatially-resolved, near-diffraction-limited 10 µm spectra of the nucleus of the Seyfert 2 galaxy NGC 1068, obtained with Michelle, the mid-IR imager and spectrometer on the 8.1 m Gemini North telescope. The spectra cover the nucleus and the central 6.0 ′′ × 0.4 ′′ of the ionization cones at a spatial resolution of approximately 0.4 ′′ (≈30 parsecs). The spectra extracted in 0.4 ′′ steps along the slit reveal striking variations in continuum slope, silicate feature profile and depth, and fine structure line fluxes on subarcsecond scales, illustrating in unprecedented detail the complexity of the circumnuclear regions of this galaxy at mid-IR wavelengths. A comparison of photometry in various apertures reveals two distinct components: a compact (radius < 15 pc), bright source within the central 0.4 ′′ × 0.4 ′′ and extended, lower brightness emission. We identify the compact source with the AGN obscuring torus, and the diffuse component with the AGN-heated dust in the ionization cones. While the torus emission dominates the flux observed in the near-IR, the mid-IR flux measured with apertures larger than about 1 ′′ is dominated instead by the dust emission from the ionization cones; in spite of its higher brightness, the torus contributes less than 30% of the 11.6 µm flux contained in the central 1.2 ′′ region. Many previous attempts to determine the torus spectral energy distribution are thus likely to be significantly affected by contamination from the extended emission. The observed spectrum of the compact source is compared with clumpy torus models, the first detailed comparison of such models with observational data. The models require most of the mid-IR emitting clouds to be located within a few parsecs of the central engine, in good agreement with recent mid-IR interferometric observations. We also present a UKIRT/CGS4 5 µm spectrum covering the R(0) -R(4) lines of the fundamental vibration-rotation band of 12 CO. None of these lines was detected, and we discuss these non-detections in terms of the filling factor and composition of the nuclear clouds.Recently, progress has been made towards overcoming some of these problems. For instance, using a model in which the dust is contained in discrete clouds, thought to be necessary to ensure dust survival in the harsh AGN environment, Nenkova et al. (2002) were able to construct SEDs broad enough to match typical observed SEDs. In these models, the silicate absorption feature was visible in an edge-on view of the torus but the emission could be greatly weakened in a face-on view. By biasing the grain size distribution to large sizes, van Bemmel & Dullemond (2003) were able to suppress the silicate emission feature, although their models tend to predict larger torus inner radii (≥10 pc) than recent observational limits (see below). Schartmann et al. (2005) were also able to suppress the silicate emission and fit the mean type 1 SED by introducing different sublimation radii for large and small grains. Given advances such as these, torus models will bene...