We describe observations of aromatic features at 7.7 and 11.3 μm in AGNs of three types, including PG, 2MASS, and 3CR objects. The feature has been demonstrated to originate predominantly from star formation. Based on the aromatic-derived star-forming luminosity, we find that the far-IR emission of AGNs can be dominated by either star formation or nuclear emission; the average contribution from star formation is around 25% at 70 and 160 μm. The star-forming infrared luminosity functions of the three types of AGNs are flatter than those of field galaxies, implying that nuclear activity and star formation tend to be enhanced together. The star-forming luminosity function is also a function of the strength of nuclear activity from normal galaxies to the bright quasars, with luminosity functions becoming flatter for more intense nuclear activity. Different types of AGNs show different distributions in the level of star formation activity, with 2MASS > PG > 3CR star formation rates.

The reddened, highly polarized QSO 2MASX J1049334+5837501 (2M 1049+5837) shows a strong IR dust signature with a spectral energy distribution peaked at similar to 20 mu m and a luminosity of similar to 10(11) L circle dot, but the active nucleus is outshone at optical wavelengths by the host galaxy. Remarkable variations with wavelength in the degree and position angle of polarization require two primary sources of scattered flux from the active nucleus. These are: ( 1) a reddened component with P >= 8% that we identify with material near the axis of a presumed obscuring dust torus in the context of orientation-dependent unification schemes for active galactic nuclei (AGNs); and ( 2) a faint, very blue source that is only important at lambda less than or similar to 4500 angstrom. The latter component is only revealed because of its extremely high polarization ( P = 20%-30%) and the fact that flux from the nucleus and the scattering lobes is nearly completely extinguished in this spectral region. High-resolution images show extensions approximately orthogonal to the two position angles of polarization. Consideration of these characteristics suggests refinements to the standard, first-order picture offered by the unified scheme for AGNs. Namely, that there can be multiple scattered sight lines within some AGNs, and that it is possible that the "polar scattering lobes'' can provide sufficient scattering optical depth that the emergent nuclear spectrum is highly reddened. These deviations are useful in explaining the existence of highly polarized, red, type 1 AGNs that form a significant fraction of the QSOs found in near-IR surveys. Importantly, the utility of the type 1/type 2 spectral signature as an indicator of orientation becomes less effective as the dust covering factor increases and nuclear radiation is more effectively scattered into all sight lines.

I came to the attention of astronomers through inventing the low temperature bolometer at Texas Instruments. I was quickly drawn into pioneering infrared (IR) astronomy. I soon transferred to the National Radio Astronomy Observatory and then to the University of Arizona to make astronomy my focus. Parallel programs were getting under way at the California Institute of Technology, Cornell, the Universities of Minnesota and of California, San Diego. Although our methods were crude, discoveries were easy and exciting. I was involved in many of them because I could supply good detectors and invented a number of new techniques. Eventually, I supplied detector systems and instruments through founding of a small company. By the early 1970s, systematic IR astronomy was under way on many important problems that are still active research topics. This rapid success led to investments in large new telescopes and in the IRAS survey satellite.

The National Aeronautics and Space Administration's Spitzer Space Telescope (formerly the Space Infrared Telescope Facility) is the fourth and final facility in the Great Observatories Program, joining Hubble Space Telescope (1990), the Compton Gamma-Ray Observatory (1991-2000), and the Chandra X-Ray Observatory (1999). Spitzer, with a sensitivity that is almost three orders of magnitude greater than that of any previous ground-based and space-based infrared observatory, is expected to revolutionize our understanding of the creation of the universe, the formation and evolution of primitive galaxies, the origin of stars and planets, and the chemical evolution of the universe. This review presents a brief overview of the scientific objectives and history of infrared astronomy. We discuss Spitzer's expected role in infrared astronomy for the new millennium. We describe pertinent details of the design, construction, launch, in-orbit checkout, and operations of the observatory and summarize some science highlights from the first two and a half years of Spitzer operations. More information about Spitzer can be found at http://spitzer.caltech.edu/.

Observations at 70 microns with the Spitzer Space Telescope have detected several stellar systems within 65 pc of the Sun. Of 18 presumably young systems detected in this study, as many as 15 have 70-micron emission in excess of that expected from their stellar photospheres. Five of the systems with excesses are members of the Tucanae Association. The 70-micron excesses range from a factor of ~2 to nearly 30 times the expected photospheric emission from these stars. In contrast to the 70-micron properties of these systems, there is evidence for an emission excess at 24 microns for only HD 3003, confirming previous results for this star. The lack of a strong 24-micron excess in most of these systems suggests that the circumstellar dust producing the IR excesses is relatively cool (T_dust < 150 K) and that there is little IR-emitting material within the inner few AU of the primary stars. Many of these systems lie close enough to Earth that the distribution of the dust producing the IR excesses might be imaged in scattered light at optical and near-IR wavelengths.

We describe observations of 9.7 μm silicate features in 97 AGNs, exhibiting a wide range of AGN types and of X-ray extinction toward the central nuclei. We find that the strength of the silicate feature correlates with the H I column density estimated from fitting the X-ray data, such that low H I columns correspond to silicate emission, while high columns correspond to silicate absorption. The behavior is generally consistent with unification models in which the large diversity in AGN properties is caused by viewing-angle-dependent obscuration of the nucleus. Radio-loud AGNs and radio-quiet quasars follow roughly the correlation between H I columns and the strength of the silicate feature defined by Seyfert galaxies. The agreement among AGN types suggests a high-level unification with similar characteristics for the structure of the obscuring material. We demonstrate the implications for unification models qualitatively with a conceptual disk model. The model includes an inner accretion disk (<0.1 pc in radius), a middle disk (0.1-10 pc in radius) with a dense diffuse component and with embedded denser clouds, and an outer clumpy disk (10-300 pc in radius).

Spitzer Space Telescope infrared measurements are presented for 24 members of the TW Hya association (TWA). High signal-to-noise ratio 24 μm photometry is presented for all these stars, including 20 stars that were not detected by IRAS. Among these 20 stars, only a single object, TWA 7, shows excess emission at 24 μm at the level of only 40% above the star's photosphere. TWA 7 also exhibits a strong 70 μm excess that is a factor of 40 brighter than the stellar photosphere at this wavelength. At 70 μm, an excess of similar magnitude is detected for TWA 13, although no 24 μm excess was detected for this binary. For the 18 stars that failed to show measurable IR excesses, the sensitivity of the current 70 μm observations does not rule out substantial cool excesses at levels 10-40 times above their stellar continua. Measurements of two T Tauri stars, TW Hya and Hen 6-300, confirm that their spectacular IR spectral energy distributions (SEDs) do not turn over even by 160 μm, consistent with the expectation for their active accretion disks. In contrast, the Spitzer data for the luminous planetary debris systems in the TWA, HD 98800B and HR 4796A, are consistent with single-temperature blackbody SEDs and agree with previous IR, submillimeter, and millimeter measurements. The major new result of this study is the dramatic bimodal distribution found for the association in the form of excess emission at a wavelength of 24 μm, indicating negligible amounts of warm (≳100 K) dust and debris around 20 of 24 stars in this group of very young stars. This bimodal distribution is especially striking given that the four stars in the association with strong IR excesses are ≳100 times brighter at 24 μm than their photospheres. Clearly, two terrestrial planetary systems, HD 98800B and HR 4796A, exist in some form. In addition, there are at least two active accreting objects, TW Hya and Hen 6-300, that may still be forming planetesimals. The remaining stars may possess significant amounts of cold dust, as in TWA 7 and 13, that have yet to be found.

The Multiband Imaging Photometer for Spitzer (MIPS) provides long wavelength capability for the mission, in imaging bands at 24, 70, and 160 microns and measurements of spectral energy distributions between 52 and 100 microns at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The Si:As BIB 24 micron array has excellent photometric properties, and measurements with rms relative errors of 1% or better can be obtained. The two longer wavelength arrays use Ge:Ga detectors with poor photometric stability. However, the use of 1.) a scan mirror to modulate the signals rapidly on these arrays, 2.) a system of on-board stimulators used for a relative calibration approximately every two minutes, and 3.) specialized reduction software result in good photometry with these arrays also, with rms relative errors of less than 10%.

Observations of Markarian 231 at 1.1 μm taken with NICMOS on the Hubble Space Telescope are described. The brightness of the object in the near‐infrared, and the inherent short‐term stability of the NICMOS optical and instrumental system, enables the application of special observational and analysis techniques that effectively increase high spatial resolution. By these means, we set an upper limit on the size of the core of the active galactic nucleus at 8 mas, corresponding to a radial projected distance of ∼3 pc from the center of Markarian 231.

We present new data for the Planetary Debris System in the multiple star system HD 98800.

In mid 1975 a representative group of IR, astronomers met, at NASA's request, to recommend a strategy for infrared astronomy in space. Wisely, the mission that would be known as SIRTF (Spitzer) was delayed until a small satellite (ultimately to be known as IRAS) could be launched to survey the infrared sky, and simultaneously, to develop and prove out the enabling technologies that would be needed to make truly significant scientific progress. Fred Gillett and colleagues set to work on the project only to find that the Netherlands was a bit ahead of NASA. The two countries formed a joint project that they called the InfraRed Astronomical Satellite, or IRAS. Fred made many contributions to the design of the pioneering IRAS hardware. As a result, Fred was instrumental in fixing hardware problems that stood in the way of the launch. Finally, in early 1983, IRAS was launched with great success, and Fred, along with George Aumann, volunteered to guide the real-time orbit-by-orbit calibration of the all-sky survey in each of the four wavelength bands. When Fred and George found that one of their primary standard stars, Vega, was far too bright at 25, 60, and 100 microns, it was clear that something was seriously amiss, either with the hardware, the software, or perhaps with Vega itself (Aumann, et al., 1984). Before the Vega discovery was made public, Fred devised observations that proved that Vega alone produced the observed far IR excess, not invisible companions or more distant objects. They also proved that the other calibration stars are free of excess IR emission and are not extended. Thus, it became clear that this most profound discovery of IRAS would soon be followed by many more examples.As the 20th anniversary of the launch of IRAS approaches, the astronomy world eagerly anticipates the launch of SIRTF (Spitzer) into its orbit around the Sun. Detailed plans are now in place to explore many young stars with SIRTF and to follow up in great detail the various planetary debris systems that are now known, suspected or yet to be found. Fred understood clearly that SIRTF would be needed to solve many of the mysteries associated with the formation of planetary systems and the debris systems within which they form. A time line of significant events is presented to chronicle Red's contributions to his own science, to IRAS and to SIRTF.

The Multiband Imaging Photometer for Spitzer (MIPS) provides long-wavelength capability for the mission in imaging bands at 24, 70, and 160 μm and measurements of spectral energy distributions between 52 and 100 μm at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point-spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The 24 μm array has excellent photometric properties, and measurements with rms relative errors of about 1% can be obtained. The two longer-wavelength arrays use detectors with poor photometric stability, but a system of onboard stimulators used for relative calibration, combined with a unique data pipeline, produce good photometry with rms relative errors of less than 10%.

The Multiband Imaging Photometer for SIRTF (MIPS) will be one of the three instruments on the Space Infrared Telescope Facility (SIRTF). MIPS will produce images at 24 (128x128 pixels), 70 (32x32 pixels), and 160 (2x20 pixels) microns using Si:As (24 micron) and Ge:Ga (70 and 160 microns) based detectors. The reduction and calibration of the Ge:Ga images present special challenges due to the nature of the bulk photoconductive detectors. The observing strategy of MIPS has been specifically designed to make the reduction and calibration of the Ge:Ga images quite robust and is different from that employed by the Infrared Space Observatory (ISO). The observations are carried out in the fast not the slow time domain, i.e. sources do not stay on the same detector pixels between exposures (3, 4, or 10 seconds). In addition, all data are taken with a high degree of redundancy and a flat field is taken every 2 minutes. The repeatability of this flat field is better than 1%. Worst case source flux repeatability of 10-15% has also been demonstrated. The general outline of the Ge:Ga data reduction and calibration will be presented. This includes continuing characterization work in the laboratory with flight-like arrays which allows for the ongoing study of the behavior of Ge:Ga detectors.

Pioneer of infrared astronomy from the ground and in space.

We present near-infrared images obtained with the Hubble Space Telescope NICMOS camera for a sample of nine luminous [LIGs: LIR(8–1000 μm) ≥ 1011 L⊙] and 15 ultraluminous (ULIGS: LIR ≥ 1012 L⊙) infrared galaxies. The sample includes representative systems classified as warm (f25 μm/f60 μm > 0.2) and cold (f25 μm/f60 μm ≤ 0.2) based on the mid-infrared colors and systems with nuclear emission lines classified as H II (i.e., starburst), QSO, Seyfert, and LINER. The morphologies of the sample galaxies are diverse and provide further support for the idea that they are created by the collision or interactions of spiral galaxies. Although no new nuclei are seen in the NICMOS images, the NICMOS images do reveal new spiral structures, bridges, and circumnuclear star clusters. The colors and the luminosities of the observed clusters are consistent with them being young (107–108 yr), formed as a result of galactic interactions, and having masses much greater than those of Galactic globular clusters. In NGC 6090 and VV 114, they are preferentially situated along the area of overlap of the two galactic disks. With the exception of IR 17208-0018, all of the ULIGs have at least one compact (2.2 μm FWHM ≤ 200 pc) nucleus. Analysis of the near-infrared colors (i.e., m1.1–1.6 vs. m1.6–2.2) derived from 1.″1 diameter apertures suggests that the warm galaxies have near-infrared colors consistent with QSO+hot dust emission and the cold galaxies, as a group, have near-infrared colors consistent with reddened starlight. In addition, the cold ULIG UGC 5101 (and possibly three others) have near-infrared colors suggesting additional active galactic nucleus–like near-infrared components in their nuclei. In a 2 kpc diameter aperture measurement, the global colors of all of the cold galaxies except UGC 5101 are consistent with starlight with a few magnitudes of visual extinction. The general dichotomy of the near-infrared properties of the warm and the cold galaxies are further supported by the light distributions: seven of the eight warm galaxies have unresolved nuclear emission that contributes significantly (i.e., ≥30%–40%) to the total near-infrared luminosity. The smooth, more extended light observed in all of the galaxies is most likely composed of giant and supergiant stars, but evidence at longer wavelengths suggests that these stars contribute little to the high 8–1000 μm luminosity of these galaxies. Finally, light profiles of nine of the 24 systems were fitted well by an r1/4 law (and not so well by an exponential disk profile). Whether these star systems eventually become massive central bulges or giant elliptical galaxies will depend on how efficiently the present ISM is converted into stars.

Spectral energy distributions (SEDs) from 0.4 to 4.7 mu m are presented for the two principal stellar components of HD 98800, A and B. The third major component, an extensive planetary debris system (PDS), emits greater than 20% of the luminosity of star B in a blackbody SED at 164 +/- 5 K extending from mid-IR to millimeter wavelengths. At 0.95 mu m, a preliminary upper limit of less than 0.06 is obtained for the ratio of reflected light to the total from star B. This result limits the albedo of the PDS to less than 0.3. Values are presented for the temperature, luminosity, and radius of each major systemic component. Remarkable similarities are found between the PDS and the interplanetary debris system around the Sun as it could have appeared a few million years after its formation.