Results 1 - 10 of 14
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[en] An all-sky 12 micron flux-limited sample of active galaxies was selected from the IRAS Point Source Catalog. Most of the sample galaxies are in existing catalogs, and 99 percent have measured redshifts. The 12-micron and the far-infrared luminosity functions of active and normal galaxies are derived using IRAS co-added data. A total of 22 percent of the sample galaxies harbor active nuclei. The sample consists almost equally of Seyfert 1, Seyfert 2, and LINER nuclei. The derived luminosity fuctions for Seyfert 1 and Seyfert 2 galaxies are indistinguishable from those of the optically selected CfA sample. Thus, 12 micron selection is the most efficient available technique for finding complete active galaxy samples. 28 refs
[en] The results of a NIR photometric monitoring of the BL Lac object OJ 287 are presented. The standard JHK photometry shows variability of maximum amplitude of about 0.7 mag over the entire observing period of 23 months and about 0.3 mag on time intervals as short as about 3 hr. No spectral variability has been found. A fast monitoring performed in the H band, with a sampling period of about 4 min, provides evidence that variations can occur in this object on time scales of over 4 min and with an rms amplitude of 6-7 percent. These variations show slow increasing and fast decreasing trends, but no clear indication of periodicity is apparent. 30 refs
[en] The line fluxes of the far-infrared fine-structure ionic and atomic transitions in the narrow-line regions (NLRs) of active galaxies are predicted using a standard photoionization model. Using the observed H β flux of the Seyfert 2 galaxy NGC 1068, and assuming the standard conditions in active galaxies NLRs, it appears that [CII] 158μm, [OI] 63μm, [NIII] 57μm, [NII] 122μm and [OIII] 88μm and 52μm are all detectable at high resolution (R=104) with the Long Wavelength Spectrometer (LWS) on board of the next ESA satellite ISO
[en] We present here the preliminary results on the most important far-infrared fine-structure lines in the partially ionized regions around Herbig Ae/Be stars. Although a very simple chemistry is assumed, our model, balancing the main contributions to heating and cooling on a grid of spherical zones, allows an estimate of the line fluxes. The results are compared with the sensitivity of the Long Wavelength Spectrometer (LWS) on board of the future ESA satellite ISO
[en] A statistical analysis of the IRAS data for young stellar objects associated with mass outflows (Herbig-Haro objects and molecular outflows) is presented. Systematic differences are found between the observed far-infrared behaviour and that predicted by the models describing the main accretion phase during the formation of low-mass stars. We suggest that the low-mass outflow sources are at a later evolutionary stage and not truly protostellar. The IRAS colours of the young objects cannot in general be used to infer the presence of circumstellar discs, which could be responsible for the collimation of the associated molecular outflows, although the data are not in conflict with this idea. The IRAS data permit the derivation of relatively accurate bolometric luminosities, which span over six orders of magnitude for the driving sources of the molecular outflows. From the observed luminosity function the mass function is derived, which is not significantly different from the initial mass function for the stars in the solar neighbourhood, suggesting that heavy mass loss has been an important phase during the formation of stars at all times in the history of the Galaxy. (author)
[en] Far-infrared observations of the QSO 0241+62 taken around 1983 September are reported. They include detailed IRAS observations and maps of the region. The exact spectral turnover point in the optical-IR region is determined. Simple model-fitting using the established synchrotron self-Compton mechanism convincingly links the X-ray and the IR emission. The infrared colours, however, differ from published IRAS results for other quasars. (author)
[en] We present new images of Arp 220 from the Atacama Large Millimeter/submillimeter Array with the highest combination of frequency (691 GHz) and resolution (0.''36 × 0.''20) ever obtained for this prototypical ultraluminous infrared galaxy. The western nucleus is revealed to contain warm (200 K) dust that is optically thick (τ434 μm = 5.3), while the eastern nucleus is cooler (80 K) and somewhat less opaque (τ434 μm = 1.7). We derive full width at half-maximum diameters of 76 × ≤ 70 pc and 123 × 79 pc for the western and eastern nucleus, respectively. The two nuclei combined account for (83−38+65 (calibration) −34+0 (systematic))% of the total infrared luminosity of Arp 220. The luminosity surface density of the western nucleus (log (σT4)=14.3±0.2−0.7+0 in units of L ☉ kpc–2) appears sufficiently high to require the presence of an active galactic nucleus (AGN) or a ''hot starburst'', although the exact value depends sensitively on the brightness distribution adopted for the source. Although the role of any central AGN remains open, the inferred mean gas column densities of (0.6-1.8) × 1025 cm–2 mean that any AGN in Arp 220 must be Compton-thick
[en] A general re-thinking of the interaction of matter with radiation in terms of cooperative phenomena and emergent properties may turn out to be necessary, together with a reflection concerning the set of the elementary processes involved and their possible representations. From a foundational point of view, this provides a stimulus to reconsider the bases of the current approaches with a critical mind. In this paper are presented the basically features of this approach, leading to the realization of a CA model for a microscopic treatment of matter-radiation interaction in terms of the local elementary processes of interaction. In the following section it is presented a survey of the characteristics of modern integrated optics devices, and then in sect. 3 some of the problems affecting their design, which have represented the starting point of our reflections. In sect. 4 it has been described the CA approach. A comparison between the two approaches from a general point of view is worked out in sect. 5. The ability of CA models to provide in general a previously not-grasped insight into the matter light interaction will be tested in two different fields of application, namely: i) in modelling semiconductor laser sources; ii) in describing the propagation of an electromagnetic field in solution of proteins. The application of the CA approach to the first specific case of study is reported in sect. 6. It shall be seen in particular how this approach permits, in this case, to reobtain the characteristic curves, and to follow the optical damage dynamics of a semiconductor laser diode, this latter being an issue currently out of reach with standard modelling approaches. Furthermore, it shall be given a brief sketch of how the model can be extended to take into account phase-dependent effects, i.e. to simulate a Fabry-Perot resonator. A model comprising the features of the semiconductor laser and of the Fabry-Perot resonator provides the possibility to tackle the simulation of realistically complex active devices. Finally, a CA model will be proposed for the cooperative effects in phase-locked arrays of Vertical Cavity Surface Emitting Lasers (VCSELs) when provides predictions of near-field and far-field emission patterns. In sect. 7 it shall be seen how the CA approach permits, also in a case of biological interest in the field of cell morphogenesis, to investigate the role of the intracellular electromagnetic field in cytoskeleton structure formation through the simulation of the propagation of an electromagnetic field in a solution of proteins. The ensuing CA model results from a refinement of the previous semiconductor laser model obtained by means of the introduction of the effects of the ponderomotive force and of thermally induced random hydrodynamic flows present in cytoplasm. It will be seen how the simulation of the whole process of interaction allows to follow the formation and dynamics of the filamentary structures comprising cytoskeleton, and how it enables to make the non-linearity of the solution emerge from the effects of the ponderomotive force acting on biomolecules. Since the proposed approach has proved to be successful, it seems reasonable to extend it to the case of more complex systems and physical processes, that are currently out of reach in standard approaches, such as four-wave mixing elementary processes in laser-plasma interaction, lasers with optical feedback and to other situations that are of interest even out of the strict field of physics such as the competition among biological species in ecosystems. A survey of these possible extensions is presented in sect. 8 together with the conclusions
[en] We report the detection and successful modeling of the unusual 9.7 μm Si-O stretching silicate emission feature in the type 1 (i.e., face-on) LINER nucleus of M81. Using the Infrared Spectrograph (IRS) instrument on Spitzer, we determine the feature in the central 230 pc of M81 to be in strong emission, with a peak at ∼10.5 μm. This feature is strikingly different in character from the absorption feature of the galactic interstellar medium, and from the silicate absorption or weak emission features typical of galaxies with active star formation. We successfully model the high signal-to-noise ratio IRS spectra with porous silicate dust using laboratory-acquired mineral spectra. We find that the most probable fit uses micron-sized, porous grains of amorphous silicate and amorphous carbon. In addition to silicate dust, there is weak polycyclic aromatic hydrocarbon (PAH) emission present (particularly at 11.3 μm, arising from the C-H out-of-plane bending vibration of relatively large PAHs of ∼500-1000 C atoms) whose character reflects the low-excitation active galactic nucleus environment, with some evidence that small PAHs of ∼100-200 C atoms (responsible for the 7.7 μm C-C stretching band) in the immediate vicinity of the nucleus have been preferentially destroyed. Analysis of the infrared fine structure lines confirms the LINER character of the M81 nucleus. Four of the infrared H2 rotational lines are detected and fit to an excitation temperature of T ∼ 800 K. Spectral maps of the central 230 pc in the [Ne II] 12.8 μm line, the H2 17 μm line, and the 11.3 μm PAH C-H bending feature reveal arc- or spiral-like structures extending from the core. We also report on epochal photometric and spectroscopic observations of M81, whose nuclear intensity varies in time across the spectrum due to what is thought to be inefficient, sub-Eddington accretion onto its central black hole. We find that, contrary to the implications of earlier photometry, the nucleus has not varied over a period of two years at these infrared wavelengths to a precision of about 1%.
[en] We present new Herschel-SPIRE imaging spectroscopy (194-671 μm) of the bright starburst galaxy M82. Covering the CO ladder from J = 4 → 3 to J = 13 → 12, spectra were obtained at multiple positions for a fully sampled ∼3 × 3 arcmin map, including a longer exposure at the central position. We present measurements of 12CO, 13CO, [C I], [N II], HCN, and HCO+ in emission, along with OH+, H2O+, and HF in absorption and H2O in both emission and absorption, with discussion. We use a radiative transfer code and Bayesian likelihood analysis to model the temperature, density, column density, and filling factor of multiple components of molecular gas traced by 12CO and 13CO, adding further evidence to the high-J lines tracing a much warmer (∼500 K), less massive component than the low-J lines. The addition of 13CO (and [C I]) is new and indicates that [C I] may be tracing different gas than 12CO. No temperature/density gradients can be inferred from the map, indicating that the single-pointing spectrum is descriptive of the bulk properties of the galaxy. At such a high temperature, cooling is dominated by molecular hydrogen. Photon-dominated region (PDR) models require higher densities than those indicated by our Bayesian likelihood analysis in order to explain the high-J CO line ratios, though cosmic-ray-enhanced PDR models can do a better job reproducing the emission at lower densities. Shocks and turbulent heating are likely required to explain the bright high-J emission.