Prof. Niranjan Thatte

Abstract:

We present results from integral field spectroscopy of the narrow line region of NGC 1068, carried out with the MPE 3D near infrared imaging spectrometer. A map and velocity field of the [Fe II] fine structure line at 1.64mum is presented. The kinematics of the [Fe II] emission, which arises in partially ionized zones, shows red shifted emission in the north eastern cone of the NLR, and blue shifted emission in the south west, reversed relative to high ionization species such as [Si VI] or [0 111]. We propose a model geometry of the narrow line region which is consistent with existing data and explains the observed [Fe II] kinematics.

Abstract:

The SINFONI integral field spectrometer for the VLT will provide near-infrared spatially resolved spectra at spatial resolutions close to the diffraction limit of the telescope (0." 05 at 2 pm). 1024 spectra can be simultaneously obtained, covering a 32x32 pixel field of view with similar to 100% filling factor. The spectral resolution is R similar to 4500, corresponding to a kinematic resolution of 67 km s(-1). SINFONI is ideally suited to study stellar kinematics in the nuclear regions of normal spiral galaxies, using the near-infrared H and K band CO stellar absorption features. Integral field data from SINFONI will provide high-resolution two-dimensional maps of nuclear velocity dispersion and rotation, which in turn will constrain the anisotropy parameter and yield robust estimates of the central dark mass.

Abstract:

The large populations of young star clusters observed in interacting galaxies like NGC4038 4039 ("The Antennae") are widely believed to be the progenitors of part of the globular cluster systems seen in local elliptical galaxies. For a comprehensive study of the young clusters in the Antennae we have obtained near infrared broad and narrow band images (SOFI on the NTT). integral field spectroscopy (MPE-3D at the AAT) and medium and high resolution spectroscopy (ISAAC VLT-UT1 and UVES VLT-UT2). We find that all of the bright star clusters are young (< 20 Myr), with the interaction region hosting the youngest clusters (similar to 5 Myr). The nuclear starbursts are older (similar to 65 Myr), but also show snore recent star formation activity. Age variations on small spatial scales are seen throughout the merger. Cluster masses range from 10(5) to a few x 10(6) M-circle dot. A comparison between dynamically determined masses and those estimated from photometry in combination with starburst models suggests variations in the IMF from cluster to cluster.

Abstract:

We performed near infrared integral field spectroscopy of several star clusters and the nuclei of the prototypical merger NGC 4038/39 ("The Antennae"). Near infrared (NIR) images covered both galaxies. The collision of the two gas-rich spiral galaxies has triggered a starburst obvious from a large number of young star clusters. ISO data suggest that the most active star formation occurs in the region where the two galaxy disks overlap. A significant fraction of the total bolometric luminosity of the system is produced there. Since this region is heavily extincted in the optical, the investigation was made in the NIR. Using Brgamma emission and CO absorption features as age indicators, we derive the ages and mass estimates of the star clusters from a comparison with stellar synthesis models. Extinction is calculated from the Brgamma/Halpha ratio. The young, bright star clusters have ages ranging from 4-12 Myrs, while the nuclear starbursts are much older (50-80 Myrs). The overlap region hosts most of the youngest star clusters below similar to8 Myrs, while the northwestern region is dominated by star clusters in the age range between 8 and 12 Myrs. Several regions, including the northern nucleus, show evidence for sequential star formation on small spatial scales (<100pc).

Abstract:

Integral field spectroscopy in the K-band (1.9-2.4um) was performed on four IR-bright star clusters and the two nuclei in NGC 4038/4039 (``The Antennae''). Two of the clusters are located in the overlap region of the two galaxies, and together comprise ~25% of the total 15um and ~10% of the total 4.8 GHz emission from this pair of merging galaxies. The other two clusters, each of them spatially resolved into two components, are located in the northern galaxy, one in the western and one in the eastern loop of blue clusters. Comparing our analysis of Brgamma, CO band-heads, He I (2.058um), Halpha (from archival HST data), and V-K colors with stellar population synthesis models indicates that the clusters are extincted (A_V ~ 0.7 - 4.3 mags) and young, displaying a significant age spread (4-13 Myrs). The starbursts in the nuclei are much older (65 Myrs), with the nucleus of NGC 4038 displaying a region of recent star formation northward of its K-band peak. Using our derived age estimates and assuming the parameters of the IMF (Salpeter slope, upper mass cut-off of 100 M_sun, Miller-Scalo between 1 M_sun and 0.1 M_sun), we find that the clusters have masses between 0.5 and 5 * 10^6M_sun.