Prof. Niranjan Thatte

Abstract:

Over the past decade, it has become clear that interaction induced formation of compact young star clusters is a ubiquitous pheonomenon, and the understanding of this process is thought to also shed light on galaxy evolution in general, because these young clusters are widely believed to be the progenitors of a part of the globular cluster systems seen in local elliptical galaxies. We have observed the prototypical merger NGC 4038/4039 using near-infrared broad- and narrow band imaging, integral field spectroscopy and medium and high resolution spectroscopy. We find that all of the bright star clusters are young (< 20 Myrs), but the "overlap region" hosts the youngest clusters (similar to5 Myrs), while the nuclear starbursts started similar to100 Myrs ago. Photometric and dynamical masses range from 10(5) to a few x 10(6)M(circle dot). However, mass-to-light ratios vary from cluster to cluster and suggest differences in the contribution of low-mass stars. While clusters with a deficiency in low-mass stars are likely to evaporate before they are a Hubble time old, those with a high mass-to-light-ratio could represent young globulars.

Abstract:

SPIFFI is the near-infrared integral-field spectrometer for the VLT. Assisted by the SINFONI adaptive optics module, the instrument will be offered to the astronomical community in 2004. We outline the scientific rationale for infrared integral-field spectroscopy at the VLT, and specifically for the enhancement of SPIFFI with a larger detector and higher spectral resolution gratings. We give examples of a broad variety of astronomical research which will gain specifically from the high angular and spectral resolution provided by SPIFFI, including studies of high red-shift galaxies, merging galaxies, starburst galaxies, superstar clusters, galactic nuclei, extra-solar planets, and circum-stellar discs.

Abstract:

Progress in understanding the embedded stars in LkHa225 has been hampered by their variability, making it hard to compare data taken at different times, and by the limited resolution of the available data, which cannot probe the small scales between the two stars. In an attempt to overcome these difficulties, we present new near-infrared data on this object taken using the ALFA adaptive optics system with the MPE 3D integral field spectrometer and the near-infrared camera Omega-Cass. The stars themselves have K-band spectra which are dominated by warm dust emission, analagous to class I-II for low mass YSOs, suggesting that the stars are in a phase where they are still accreting matter. On the other hand, the ridge of continuum emission between them is rather bluer, suggestive of extincted and/or scattered stellar light rather than direct dust emission. The compactness of the CO emission seen toward each star argues for accretion disks (which can also account for much of the K-band veiling) rather than a neutral wind. In contrast to other YSOs with CO emission, LkHa225 has no detectable Br_gamma emission. Additionally there is no H_2 detected on the northern star, although we do confirm that the strongest H_2 emission is on the southern star, where we find it is excited primarily by thermal mechanisms. A second knot of H_2 is observed to its northeast, with a velocity shift of -75kms and a higher fraction of non-thermal emission. This is discussed with reference to the H2O maser, the molecular outflow, and [S II] emission observed between the stars.

Abstract:

We report new results on the stellar kinematics and the mass distribution of the galaxy NGC 3115 based on NIR integral field spectroscopic data. Investigations using long slit spectroscopic data have yielded strong evidence for the presence of a massive dark object of ca. 10(9) solar masses. NGC 3115 therefore appears to be a prominent candidate for hosting a black hole in its center. We demonstrate that with integral field spectroscopy the rotation and velocity dispersion can be much better constrained by sampling in both spatial dimensions. This yields revised and more secure results.

Abstract:

Knowledge of the pattern speed in a barred galaxy is an important prerequisite for determining the radii of its dynamical resonances. Once identified, these can in turn be used to constrain models for nuclear fueling and secular evolution. Here, we present measurements of the pattern speeds in two barred galaxies-one direct (in NGC 1068, using the Tremaine-Weinberg method in the near infrared) and one indirect (in NGC 7479, using a fit to three-dimensional molecular emission-line data). We find good evidence that a configuration of dynamically decoupled "bars within bars" is present in each system.