Showing papers by "George H. Rieke published in 1995"

Luminous Quasars in Luminous Early-Type Host Galaxies

Abstract: Some recent observations of nearby quasars with Hubble Space Telescope (HST) have apparently failed to detect host galaxies. We review the HST observations as well as near-infrared ground-based observations of the same objects. We find that the quasar hosts can be detected in the HST data if they are smoothed sufficiently to reveal low surface brightness. The smooth hosts are very difficult to detect with HST but are more easily visible in the deeper, ground-based IR images. The V - H colors obtained by combining the HST and IR data are compatible with normal galaxy colors at the redshifts of the quasars. This behavior can be explained if the hosts are massive early-type galaxies. All together, HST images have been reported for 15 luminous quasars, ~13 of which have smooth early-type hosts. This kind of galaxy therefore appears to be the most common host for a luminous quasar.

Luminous Quasars in Luminous Early-Type Host Galaxies

Abstract: Some recent observations of nearby quasars with HST have apparently failed to detect host galaxies. We review the HST observations as well as near infrared ground-based observations of the same objects. We find that the quasar hosts can be detected in the HST data if they are smoothed sufficiently to reveal low surface brightness. The smooth hosts are very difficult to detect with HST but are more easily visible in the deeper, ground-based IR images. The V-H colors obtained by combining the HST and IR data are compatible with normal galaxy colors at the redshifts of the quasars. This behavior can be explained if the hosts are massive early-type galaxies. All together, HST images have been reported for 15 luminous quasars, approximately 13 of which have smooth early-type hosts. This kind of galaxy therefore appears to be the most common host for a luminous quasar.

Test results for the SIRTF far-infrared array module

Abstract: We present initial test results for far-infrared arrays built at the University of Arizona using Ge:Ga photoconductors and low temperature readouts operating at a temperature of 2 K. We also present separate test results for the Hughes CRC-696 multiplexer used in this program. The two array configurations considered are a 1 X 32 based on an older heated readout concept and a new 4 X 32 module that takes advantage of the benefits of having a true cryogenic readout. Based on these results, performance meeting the SIRTF goal of background-limited imaging can be expected for the 32 X 32 array under construction.

Construction of the large-format far-infrared array for SIRTF

Abstract: We report on the design, modeling, and construction of far-infrared focal plane array modules for the Space Infrared Telescope Facility (SIRTF). The modules consist of 4 X 32 detector elements, readout electronics, and interconnections. The modules, which are of Z- plane architecture, may be stacked to produce imaging arrays of at least 32 X 32 format. These arrays are the largest available operating in the wavelength range 50 - 120 micrometers . The design takes advantage of the Hughes CRC-696 readout which was specifically developed for use with far-infrared photoconductive detectors. Since the readouts have excellent performance at temperatures below 2 K, a simplified construction concept using the proven interconnection methods of wire boding and multilayer ceramic boards are used. We report on additional design considerations such as minimization of parasitic capacitance at the input node and accommodation of thermal annealing of the detectors.

Detection Limits in the Far Infrared

Abstract: The advent of far infrared arrays will change fundamentally the means of analyzing observations in this spectral region. Sources much fainter than traditional “confusion limits” will be extracted from images by using computer algorithms similar to CLEAN or DAOPHOT. We have conducted numerical experiments to evaluate these techniques and show that they will permit long integrations (∼10,000 sec at 60 μm, ∼200 sec at 100 μm) to achieve nearly photon-background-limited performance and hence very deep detection limits. The dominant noise sources—photon noise, confusion by distant galaxies, and confusion by IR cirrus — scale with nearly the same power of the telescope aperture. As a result, the integration times required to reach confusion limits are nearly aperture-independent.

Compact and versatile far-infrared imager for SIRTF

Abstract: We present the design for the multiband imaging photometer for SIRTF (MIPS). MIPS is a versatile instrument that provides diffraction-limited imaging at 30 micrometers , 70 micrometers , and 160 micrometers . MIPS also provides low resolution (5%) spectroscopy in the 50 - 100 micrometers wavelength range to allow the determination of far-infrared spectral energy distributions. The 70 micrometers array can also be used in a special high resolution mode that supports image reconstruction techniques for improved angular resolution. The one cryogenic mechanism on MIPS is a scanning mirror based on a space-qualified design used on the Infrared Space Observatory. We describe modifications to the scan mechanism to optimize it for use at very long wavelengths.

IRIS: a high-resolution midinfrared spectrometer for the upgraded 6.5-meter Multiple Mirror Telescope

Abstract: In mid-1996, the Multiple Mirror Telescope (MMT) will be upgraded from its current configuration of six 1.8-meter primary mirrors to house a single 6.5-meter primary. To exploit the dramatic increase in collecting area and spatial resolution, as well as the high infrared quality of the observing site, we have designed a new spectrometer that will cover the thermal infrared (4 to 25 micrometer) at high spectral and spatial resolution. The design is based on the new generation of Si:As BIB detectors with 256 by 256 formats, which represent a substantial advance in array size at these wavelengths. The design consists entirely of reflecting optics, and is arranged to deliver diffraction-limited resolution longwards of 8 micrometers. A maximum spectral resolving power of R equals 15,000 is provided by an echelle grating. A lower resolution grating or a plane mirror for two-dimensional imaging may be substituted for the echelle.