N. Thatte

The Dark Mass Concentration in the Central Parsec of the Milky Way

We report ~1 resolution K-band (2 μm) imaging spectroscopy of the central parsec of our Galaxy. The derived radial velocities for 223 early- and late-type stars probe the nuclear mass distribution to spatial scales of 0.1 pc. We find a statistically very significant increase of projected stellar velocity dispersion from about 55 km s−1 at p ~ 5 pc to 180 km s−1 at p ~ 0.1 pc. The stars are also rotating about the dynamic center. The late-type stars follow general Galactic rotation, while the early-type stars show counter-rotation. Fitting simultaneously the observed projected surface densities and velocity dispersions, we derive the intrinsic volume densities and radial velocity dispersions as a function of distance from the dynamic center for both types of stars. We then derive the mass distribution between 0.1 and 5 pc from the Jeans equation assuming an isotropic velocity field. Our analysis requires a compact central dark mass of 2.5 − 3.2 × 106 M☉ at 6 − 8 σ significance. The dark mass has a density of 109 M☉ pc−3 or greater and a mass to 2 μm luminosity of ≥ 100. The increase in mass-to-luminosity ratio can be reduced but not eliminated even if extreme anisotropic velocity destributions are considered. The dark mass cannot be a cluster of solar mass remnants (such as neutron stars). It is either a compact cluster of 10–20 M☉ black holes or a single massive black hole.

The Nuclear Cluster of the Milky Way: Star Formation and Velocity Dispersion in the Central 0.5 Parsec

We report the first results of an extensive new study of the Galactic center stellar cluster. The central parsec is powered by a cluster of about two dozen luminous and helium-rich blue supergiants/Wolf-Rayet stars (Teff ~ 20,000-30,000 K) with ZAMS masses up to ~100 M☉. The most likely scenario for the formation of the massive stars is a small star formation burst between 3 × 106 and 7 × 106 years ago. In this scenario the Galactic center is presently in a short-lived, post-main-sequence wind phase. In addition, there is evidence for another star formation event about 108 years ago, as well as for recently formed massive stars that may have been transported into the central core along with orbiting gas streamers. The radial velocity dispersion of 35 early- and late-type stars with distances of 1-12 from Sgr A* is 154 ± 19 km s-1. Our new results strongly favor the existence of a central dark mass of ~3 × 106 M☉ (density ≥ 108.5 M☉ pc-3, M/L ≥ 10 M☉/L☉) within 0.14 pc of the dynamic center.

THE BERKELEY-ILLINOIS-MARYLAND-ASSOCIATION MILLIMETER ARRAY

We describe the characteristics of the BIMA millimeter wave array at Hat Creek, California. The array is an aperture synthesis instrument consisting of 9 6-meter diameter antennas which may be deployed in three differenet configurations, with spacings ranging from 7 meters up to 1.3 km. At an observing frequency of 100 GHz these configurations yield maps with angular resolutions of 5, 2, and 0.4, over a 2 field. Larger fields may be mapped by using multiple pointings. For all but the oldest telescopes, the surface accuracy is ≤ 30 microns rms, and the aperture efficiency is 77% at 100 GHz. Background emission from antenna losses and spillover is very low, about 5 K after subtraction of the cosmic Bv(2.7K). Each antenna contains a single dewar which accommodates up to four separate receivers. SIS mixers are cooled to 3.2 K with novel Gifford-McMahon cycle refrigerators. Both the upper and lower sidebands of the first local oscillator are received and separated, providing two bands extending from 70-900 MHz on each side of the first local oscillator. The correlation spectrometer covers a bandwidth of up to 800 MHz, and provides up to 2048 channels for each antenna pair. There are four independently tunable spectral windows (in each sideband), allowing simultaneous observations of several different spectral lines. The spectral resolution ranges from 6 kHz to 3 MHz. For a single 8 hour track in one configuration, the sensitivity is approximately 1 mJy/beam in the 800 MHz wide continuum. Measurements of atmospheric phase fluctuations as functions of both time and baseline have been made; these indicate that routine imaging at angular resolutions of less than 1 at 100 GHz is possible only if self-calibration or some other means of phase correction can be applied. Examples of a few recent results are included. We note that 30% of the observing time on the array is granted to visitors.

ROGUE - the Rapid Off-axis GUider Experiment

Near infrared imaging spectroscopy at spatial resolutions of 0.5 arc seconds will fundamentally change our understanding of active galactic nuclei. This long desired capability has been achieved for the first time by the latest generation of MPE instruments, ROGUE and 3D. ROGUE, the rapid off-axis guider experiment, is a low order adaptive optics system performing tip-tilt correction in the near infrared using natural guide stars. Three-dimensional is the MPE near infrared imaging spectrometer capable of simultaneous imaging and spectroscopy of the entire H and K atmospheric windows. ROGUE is capable of tip-tilt correction at 40 Hz in a 4 arc-minute diameter isokinetic patch using natural guide stars as faint as 18th magnitude. We discuss the design of the instrument, present the first astronomical results, and outline future efforts to incorporate variable image scales.

Near-Infrared Imaging Spectroscopy of IRAS FSC 10214+4724: Evidence for a Starburst Region around an Active Galactic Nucleus at z = 2.3

We report 1 imaging spectroscopy of the 1.95-2.4 μm wavelength region in the z = 2.284 galaxy IRAS FSC 10214+4724. We find that the rest-frame Hα and [N II] emission have different spatial extents. We also detect broad (ΔvFWZP ≈ 3500 km s-1) Hα emission. FSC 10214 is a very luminous gravitationally lensed galaxy, which intrinsically contains both a type 1 active galactic nucleus and a more extended star-forming disk. The AGN and circumnuclear star formation both contribute significantly to the total luminosity of ~1013 L☉.

3D: a new generation imaging spectrometer

MPE has developed 3D, a new type of a highly sensitive near- infrared integral field spectrometer. It has been designed to multiplex spectral as well as spatial information thus obtaining a full data cube in a single integration. At a spectral resolution between 1000 and 2000 and a field of view of 16 by 16 pixels, optimized for subarcsecond spatial resolution imaging spectroscopy, it has a much higher efficiency compared to conventional techniques. Outfitting one of the VLTs with a near-IR 3D type instrument will provide a powerful tool for diffraction-limited integral field spectroscopic research, in particular on faint high-z galaxies in the early universe. The basic design, recent upgrades as well as plans for a possible VLT-3D instrument are presented.

3D - a new generation imaging spectrometer

3D, the next generation near-IR spectrometer developed at the MPE, offers, in a single integration, the opportunity to image an 8 x 8 field with a pixel scale of 0.5 or 0.3 across the entire K- or H-band simultaneously at a spectral resolution of R equals 1000 or R equals 2000 (K). Combining the advantages of imaging and spectroscopy increases the observing efficiency on small extended objects (e.g., galactic nuclei) by such a large factor over existing grating or Fabry-Perot spectrometers that subarcsecond near-IR spectroscopy on faint Seyferts, starbursts, quasars, or distant galaxies clusters becomes feasible for the first time on 4 m class telescopes. 3D, including a NICMOS III FPA at 25 e-/single read, has been successfully operated at telescopes such as the 4.2 m WHT, 3.5 m Calar Alto, and 2.2 m La Silla. An additional tip-tilt seeing corrector for 3D called ROGUE correcting on up to 18th mag stars at 4 m-class-telescopes was successfully commissioned in the summer of 1994. The optical and electronic design of 3D as well as recent results are presented.

3D: A new tool for probing the stars and ISM in AGN

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 NGC7469 made at the Calar Alto observatory.

Near-IR Imaging Spectroscopy of CD Galaxy NGC1275

H and K band imaging spectroscopy of the central 12″ (4.2 kpc ) of NGC1275 using the Max-Planck-Institut fur extraterrestrische Physik imaging spectrometer “3D” maps the gas density and temperature in the core and separates the contribution of Seyfert emission to the core light.

Automated tuning of the Berkeley-Illinois-Maryland array receivers

The Berkeley Illinois Maryland Association (BIMA) array consists of 6 antennas, each 6 meters in diameter, operating at a wavelength of 3 mm. The telescope control is fully automated, allowing round-the-clock observing with little or no supervision. The array can also be controlled from a remote site. One of the major challenges of automated operation is the ability to tune multiple receivers to the desired operating frequency in a reliable manner. The large tuning range required at millimeter wavelengths (85 to 115 GHz), the nonlinear response of the microwave cavities and oscillator phase lock problems have been stumbling blocks for remote receiver tuning. At BIMA, we have developed an automated system capable of tuning all the receivers to any observing frequency within a few minutes. The system uses a Sun workstation in conjunction with dedicated hardware to control the receivers. Large disparities between receiver characteristics are handled in an efficient manner through the use of lookup tables. We describe the system design in detail, and discuss the problems encountered along with appropriate solutions. The generation of lookup tables in the laboratory is also presented.