Prof. Niranjan Thatte

Abstract:

SPIFFI is the near-infrared integral field spectrograph of the SINFONI VLT instrument. SPIFFI uses an image slicer with plane mirrors as its integral field unit. The integral field unit consists of two stacks of mirrors, each with 32 mirrors, rearranging a two-dimensional field-of-view of 32 x 32 pixels into a one-dimensional pseudo slit, which is fed into a long-slit spectrograph. The image slicer is constructed solely, from Zerodur and is operated at a cryogenic temperature of 77 Kelvin. Only optical contacting is used for the assembly of the individual slicer mirrors and the image slicer on its base-plate. The special slicer mount holds the image slicer stress-free and compensates for the different thermal coefficients of expansion of the Zerodur image slicer and the Aluminium mount. Tests at room and cryogenic temperatures show the performance of the image slicer, the durability of the optical contacting technique, and the accuracy of the slicer mount.

Abstract:

With the advent of efficient near-IR spectrometers on 10m-class telescopes, exploiting the new generation of low readout noise, large format detectors, OH avoidance and sub-arcsecond seeing, 1-2.4mum spectroscopy can now be exploited for detailed galaxy dynamics and for studies of high-z galaxies. In the following we present the results of three recent IR spectroscopy studies on the dynamics of ULIRG mergers, on super star clusters in the Antennae, and on the properties of the rotation curves of zsimilar to1 disk galaxies, carried out with ISAAC on the VLT, and NIRSPEC on the Keck.

Abstract:

Using ISAAC on VLT-ANTU and UVES on VLT-KUEYEN we have begun a program to measure stellar velocity dispersions of young star clusters in merging and interacting galaxies. In this contribution, we present results for clusters in two interacting galaxies - NGC 4038/39 and NGC 1487. Combining the measured velocity dispersions with sizes of the clusters estimated from Hubble Space Telescope imaging data resulted in the first determinations of dynamical masses of stellar clusters in galaxy mergers. Due to the faintness of the clusters and the high spectral resolution required, these results could only be obtained in with 10m class telescopes. Our results suggest that masses, sizes and concentrations of the light distributions are comparable to those of globular clusters, supporting the idea that part of the globular cluster population in elliptical galaxies is formed as a result of a merger event between to gas-rich spiral galaxies. However, the initial mass function (IMF) of the stars in the clusters seems to vary with environment: In some regions (dust-rich?), the IMF is more biased towards low-mass stars than in other (dust-poor) regions. There is a long-standing and substantial controversy in the literature whether or not their exists a "universal IMF". Our results for clusters in merging galaxies support the notion that the IMF depends on the birth environment of the cluster or perhaps some other variable. The relative content of low mass stars also influences the survival probability of stellar clusters. For their masses and light concentrations, some of the clusters have sufficiently shallow IMFs that it is likely that they will dissolve within a Hubble time, while for others, the IMF is sufficiently steep that they are likely to survive but undergo significant mass loss during their evolution.

Abstract:

We report the first results from a study of the internal kinematics, based on spatially resolved H_alpha velocity profiles, of three galaxies at redshift z~0.6 and one at redshift z~0.8, detected by ISOCAM in the Hubble Deep Field South. The kinematics are derived from high resolution near-infrared VLT spectroscopy. One of the galaxies is a massive spiral which possesses a very large rotational velocity of 460 km/s and contains a mass of 10^12 M_solar (within 20 kpc), significantly higher than the dynamical masses measured in most other local and high redshift spirals. Two of the galaxies comprise a counter-rotating interacting system, while the fourth is also a large spiral. The observed galaxies are representative examples of the morphologies encountered among ISOCAM galaxies. The mass-to-light (M /L_bol) ratios of ISOCAM galaxies lie between those of local luminous IR galaxies and massive spirals. We measure an offset of 1.6+/-0.3 mag in the rest frame B-band and of 0.7+/-0.3 mag in the rest frame I-band when we compare the four ISOCAM galaxies to the local Tully-Fisher B and I-band relations. We conclude that the large IR luminosity of the ISOCAM population results from a combination of large mass and efficient triggering of star formation. Since ISOCAM galaxies contribute significantly to the Cosmic Infrared Background our results imply that a relatively small number of very massive and IR luminous objects contribute significantly to the IR background and star formation activity near z~0.7.