437 research outputs found
Seyfert Activity and Nuclear Star Formation in the Circinus Galaxy
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
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
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
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
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
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
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
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
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
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