371 research outputs found

    Seyfert Activity and Nuclear Star Formation in the Circinus Galaxy

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    We present high angular resolution (0".15-0".5) near infrared images and spectroscopy of the Circinus galaxy, the closest Seyfert 2 galaxy known. The data reveal a non-stellar nuclear source at 2.2 microns. The coronal line region and the hot molecular gas emission extend for 20-50 pc in the ionization cone. The data do not show evidence for a point-like concentration of dark mass; we set an upper limit of 4*10^6 Mo to the mass of a putative black hole. We find evidence for a young nuclear stellar population, with typical ages between 4*10^7 and 1.5*10^8 yrs. The luminosity of the starburst inside a few hundred pc is comparable to the intrinsic luminosity of the Seyfert nucleus, and the two of them together account for most of the observed bolometric luminosity of the galaxy. Within the central 12 pc the starburst has an age of about 7*10^7 yrs and radiates about 2% of the luminosity of the active nucleus. We discuss the implications of these results for models that have been proposed for the starburst-AGN connection.Comment: 44 pages, Latex (including 11 Figures), Color Figures 1, 2 and 4 are available at http://www.arcetri.astro.it/~maiolino/ , ApJ in pres

    Infrared 3D Observations of Nearby Active Galaxies

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    We present multi-wavelength imaging observations of three nearby and famous active galaxies obtained with NICMOS, ISOCAM and the MPE near-IR integral field spectrometer. The data reveal a variety of features and properties that are missed in optical studies and in traditional IR monodimensional spectroscopy.Comment: 6 pages, to appear in "Imaging the Universe in Three Dimensions: Astrophysics with Advanced Multi-Wavelength Imaging Devices", eds. W. van Breugel and J. Bland-Hawthorn, needs pasp3D.st

    Near-Infrared-Spectroscopy with Extremely Large Telescopes: Integral-Field- versus Multi-Object-Instruments

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    Integral-field-spectroscopy and multi-object-spectroscopy provide the high multiplex gain required for efficient use of the upcoming generation of extremely large telescopes. We present instrument developments and designs for both concepts, and how these designs can be applied to cryogenic near-infrared instrumentation. Specifically, the fiber-based concept stands out the possibility to expand it to any number of image points, and its modularity predestines it to become the new concept for multi-field-spectroscopy. Which of the three concepts --- integral-field-, multi-object-, or multi-field-spectroscopy --- is best suited for the largest telescopes is discussed considering the size of the objects and their density on the sky.Comment: 8 pages, 4 figures (converted to bitmap), to appear in the proceedings of the Workshop on Extremely Large Telescopes, Sweden, June 1-2, 1999, uses spie.sty (V0.91) and spiebib.bst (V0.91

    A new era of spectroscopy: SINFONI, NIR integral field spectroscopy at the diffraction limit of an 8m telescope

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    SINFONI, the SINgle Faint Object Near-infrared Investigation, is an instrument for the Very Large Telescope (VLT), which will start its operation mid 2002 and allow for the first time near infrared (NIR) integral field spectroscopy at the diffraction limit of an 8-m telescope. SINFONI is the combination of two state-of-the art instruments, the integral field spectrometer SPIFFI, built by the Max-Planck-Institut fuer extraterrestrische Physik (MPE), and the adaptive optics (AO) system MACAO, built by the European Southern Observatory (ESO). It will allow a unique type of observations by delivering simultaneously high spatial resolution (pixel sizes 0.025arcsec to 0.25arcsec) and a moderate spectral resolution (R~2000 to R~4500), where the higher spectral resolution mode will allow for software OH suppression. This opens new prospects for astronomy.Comment: 9 pages, 4 figures, to appear in SPIE proceedings "Astronomical Telescopes and Instrumentation 2000". More recent sensitivity estimates are available at http://www.mpe.mpg.de/www_ir/ir_instruments/sinfoni/spiffi.ht

    Stellar dynamics observations of a double nucleus in M 83

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    We report on the discovery of a double nucleus in M 83, based on measurements of the line of sight velocity distribution of stars observed at near infrared wavelengths with the VLT ISAAC spectrograph. We observe two peaks separated by 2.7" in the velocity dispersion profile of light from late-type stars measured along a slit 0.6" wide, centered on the peak of K band emission and with P.A. 51.7 degrees. The first peak coincides with the peak of the K band light distribution, widely assumed to be the galaxy nucleus. The second peak, of almost equal strength, almost coincides with the center of symmetry of the outer isophotes of the galaxy. The secondary peak location has little K band emission, and appears to be significantly extincted, even at near infrared wavelengths. It also lies along a mid-infrared bar, previously identified by Gallais et al. (1991) and shows strong hydrogen recombination emission at 1.875 microns. If we interpret the observed stellar velocity dispersion as coming from a virialized system, the two nuclei would each contain an enclosed mass of 13.2 x 10^6 M_sun within a radius of 5.4pc. These could either be massive star clusters, or supermassive dark objects.Comment: 8 pages, 4 figures, Accepted for publication in A&A Letter

    The Central Region of M83

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    We combine VLT/ISAAC NIR spectroscopy with archival HST/WFPC2 and HST/NICMOS imaging to study the central 20"x20" of M83. Our NIR indices for clusters in the circumnuclear star-burst region are inconsistent with simple instantaneous burst models. However, models of a single burst dispersed over a duration of 6 Myrs fit the data well and provide the clearest evidence yet of an age gradient along the star forming arc, with the youngest clusters nearest the north-east dust lane. The long slit kinematics show no evidence to support previous claims of a second hidden mass concentration, although we do observe changes in molecular gas velocity consistent with the presence of a shock at the edge of the dust lane.Comment: Accepted for publication in MNRAS. 24 pages, 11 figure

    ALFA & 3D: integral field spectroscopy with adaptive optics

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    One of the most important techniques for astrophysics with adaptive optics is the ability to do spectroscopy at diffraction limited scales. The extreme difficulty of positioning a faint target accurately on a very narrow slit can be avoided by using an integral field unit, which provides the added benefit of full spatial coverage. During 1998, working with ALFA and the 3D integral field spectrometer, we demonstrated the validity of this technique by extracting and distinguishing spectra from binary stars separated by only 0.26". The combination of ALFA & 3D is also ideally suited to imaging distant galaxies or the nuclei of nearby ones, as its field of view can be changed between 1.2"x1.2" and 4"x4", depending on the pixel scale chosen. In this contribution we present new results both on galactic targets, namely young stellar objects, as well as extra-galactic objects including a Seyfert and a starburst nucleus.Comment: SPIE meeting 4007 on Adaptive Optical Systems Technology, March 200

    Nuclear Dynamics and Star Formation of AGN

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    We are using adaptive optics on Keck and the VLT to probe the dynamics and star formation in Seyfert and QSO nuclei, obtaining spatial resolutions better than 0.1" in the H- and K-bands. The dynamics are traced via the 2.12um H_2 1-0S(1) line, while the stellar cluster is traced through the CO 2-0 and 6-3 absorption bandheads at 2.29um and 1.62um respectively. Matching disk models to the H_2 rotation curves allows us to study nuclear rings, bars, and warps; and to constrain the mass of the central black hole. The spatial extent and equivalent width of the stellar absorption permits us to estimate the mass of stars in the nucleus and their contribution to the emission. Here we report on new data for I Zwicky 1, Markarian 231, and NGC 7469.Comment: 6 page contribution to 'Science with Adaptive Optics

    The Discovery of Quasisoft and Supersoft Sources in External Galaxies

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    We apply a uniform procedure to select very soft sources from point sources observed by Chandra in 4 galaxies. This sample includes one elliptical galaxy (NGC 4967), 2 face-on spirals (M101 and M83), and an interacting galaxy (M51). We have found very soft X-ray sources (VSSs) in every galaxy. Some of these fit the criteria for canonical supersoft sources (SSSs), while others are somewhat harder. These latter have characteristic values of kT < 300 eV; we refer to them as quasisoft sources (QSSs). We found a combined total of 149 VSSs in the 4 galaxies we considered; 77 were SSSs and 72 were QSSs. (See the paper for the original long abstract)Comment: 20 pages, 6 figures. Accepted for publication in Ap

    An explicit self-duality

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    We provide an exposition of the canonical self-duality associated to a presentation of a finite, flat, complete intersection over a Noetherian ring, following work of Scheja and Storch
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