Prof. Niranjan Thatte

Abstract:

We have imaged a compact stellar cluster, with a characteristic size of 50 pc, toward the nucleus of NGC 1068, using near IR imaging spectroscopy of stellar absorption features in the H and K bands. The near IR stellar light is attributed to a population of late type stars, with an average spectral type of M0. Based on light-to-mass ratio measurements, we derive an upper limit for the age of the nuclear cluster of 4 x 10(9) years. The stellar cluster contributes a non-negligible fraction of the total nuclear bolometric luminosity, a value of 5% being a very conservative lower limit. The compact stellar distribution identifies the dynamical center of the galaxy as being coincident with the peak of the It band emission. The morphology of the excited molecular gas, revealed by mapping the H-2 S(1) line at 2.12 mu m, shows a molecular ring with a radius of similar to 100 pc. Millimeter interferometric imaging in the CO J = 2 --> 1 transition at 1.3 mm shows the ring to be rotating with velocities of similar to 100 km s(-1).

Abstract:

We present new near-infrared integral field spectroscopy and adaptive optics imaging of the nucleus of NGC 1068. Using the stellar CO absorption features in the H and K bands, we have identified a moderately extincted stellar core centered on the nuclear position and of intrinsic size similar to 50 pc. We show that this nuclear stellar core is probably 5-16 x 10(8) years in age and contributes at least 7% of the total nuclear luminosity of similar to 1 x 10(11) L..

Abstract:

3D, the new MPE NIR imaging spectrometer, provides us with a unique opportunity to probe in detail the structure of the stars, ionized gas, and hot molecular gas in the very centers of AGN. The instrument delivers data cubes with 16×160.5″ pixels which are 256 spectral channels deep. Thus, in a single observation we are able to obtain data on the entire K-Band over an 8″×8″ field of view, with a spectral resolution of R = λ/Δλ = 1000. In this paper we detail the working principles behind the instrument, and show first results from observations of the inner regions of the Seyfert 1 galaxy NGC 7469 made at the Calar Alto observatory. Copyright ©1996 Elsevier Science Ltd.

Abstract:

The new MPE near infrared imaging spectrometer 3D represents a new generation of astronomical instrumentation. It is based on a 2562 NICMOS-3 Rockwell array and can simultaneously obtain 256 H- or K-band spectra at R= 1100 or 2100 from a square 16×16 pixel field on the sky. Typical pixel scales are 0.3″/pixel or 0.5″/pixel. 3D is a combination of a novel image slicer and a liquid nitrogen cooled long slit spectrometer. It includes high definition on-axis lens optics, a high efficiency directly ruled KRS-5 grism as well as a cold closed-loop piezo-driven tilt mirror allowing full spectral sampling. The instrument efficiency including detector is 15%. Combining the advantages of imaging and spectroscopy increases the observing efficiency on key astronomical objects (e.g. galactic nuclei) by such a large factor over existing grating or Fabry-Perot spectrometers that subarcsecond near-IR spectroscopy of faint Seyferts, starbursts, quasars, or distant galaxy clusters becomes feasible for the first time with 4m-class telescopes. As a portable instrument 3D has already been successfully deployed on several 2 and 4m-class telescopes.

Abstract:

Near-infrared imaging spectroscopy at spatial resolutions of 0.5 arc sec can already be achieved by combining the spatial and spectral resolution of an IR-imaging spectrometer with a first-oreder adaptive-optics system and accurate autoguider. This development makes high-resolution near-IR imaging spectroscopy possible for astronomy.