Galaxy formation and evolution

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:

THE most distant astronomical objects observed are quasars at redshifts of z ≃ 4.9 (ref. 1), corresponding to a time when the Universe was less than a billion years old. This leaves little time during which the quasars and their host galaxies could form. In principle, the evolutionary state of the host galaxies can be probed by determining how many stars have formed, but this task is not straightforward because light from the quasar itself overwhelms any accompanying starlight. High-redshift radio galaxies-the likely progenitors of luminous elliptical galaxies-provide better targets for such studies, as optical emissions from their active nuclei are observed to be faint. Here we report the discovery of a radio galaxy (6C0140 + 326) at z = 4.41 which shows no evidence for either a stellar continuum or an unobscured quasar nucleus. We conclude that the galaxy associated with the radio source is neither fully formed nor obviously in the process of forming stars. This implies that at least some giant elliptical galaxies are still immature at z ≃ 4.5, and that if the intense bursts of star formation thought to produce the bulk of their stellar populations occur during the radio-bright phase, these star-forming regions are obscured by dust and gas.

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.

Abstract:

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 (ΔνFWZP ≈ 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⊙. © 1996. The American Astronomical Society. All rights reserved.

Abstract:

We describe the characteristics of the BIMA millimeter wave array at Hat Creek, CA. The array is an aperture synthesis instrument consisting of nine 6 m diameter antennas which may be deployed in three different configurations, with spacings ranging from 7 m 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 μm 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 B v(2.1 K). 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-hr 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.