松原 英雄

We present the observations of the reflection nebulae IC4954 and IC4955 region with the Infrared Camera (IRC) and the Far-Infrared Surveyor (FIS) on board the infrared astronomical satellite AKARI during its performance verification phase. We obtained 7 band images from 7 to 160um with higher spatial resolution and higher sensitivities than previous observations. The mid-infrared color of the S9W (9um) and L18W (18um) bands shows a systematic variation around the exciting sources. The spatial variation in the mid-infrared color suggests that the star-formation in IC4954/4955 is progressing from south-west to north-east. The FIS data also clearly resolve two nebulae for the first time in the far-infrared. The FIS 4-band data from 65um to 160um allow us to correctly estimate the total infrared luminosity from the region, which is about one sixth of the energy emitted from the existing stellar sources. Five candidates for young stellar objects have been detected as point sources for the first time in the 11um image. They are located in the red S9W to L18W color regions, suggesting that current star-formation has been triggered by previous star-formation activities. A wide area map of the size of about 1 x 1 (deg^2) around the IC4954/4955 region was created from the AKARI mid-infrared all-sky survey data. Together with the HI 21cm data, it suggests a large hollow structure of a degree scale, on whose edge the IC4954/4955 region has been created, indicating star formation over three generations in largely different spatial scales.

We present the spatially resolved observations of IRAS sources from the Japanese infrared astronomy satellite AKARI All-Sky Survey during the performance verification (PV) phase of the mission. We extracted reliable point sources matched with IRAS point source catalogue. By comparing IRAS and AKARI fluxes, we found that the flux measurements of some IRAS sources could have been over or underestimated and affected by the local background rather than the global background. We also found possible candidates for new AKARI sources and confirmed that AKARI observations resolved IRAS sources into multiple sources. All-Sky Survey observations are expected to verify the accuracies of IRAS flux measurements and to find new extragalactic point sources.

We report initial results of far-infrared observations of the Lockman hole with Far-Infrared Surveyor (FIS) onboard the AKARI infrared satellite. On the basis of slow scan observations of a 0.6 deg x 1.2 deg contiguous area, we obtained source number counts at 65, 90 and 140 um down to 77, 26 and 194 mJy (3 sigma), respectively. The counts at 65 and 140 um show good agreement with the Spitzer results. However, our 90 um counts are clearly lower than the predicted counts by recent evolutionary models that fit the Spitzer counts in all the MIPS bands. Our 90 um counts above 26 mJy account for about 7% of the cosmic background. These results provide strong constraints on the evolutionary scenario and suggest that the current models may require modifications.

We report the detection of an H-alpha emission line in the low resolution spectrum of a quasar, RX J1759.4+6638, at a redshift of 4.3 with the InfraRed Camera (IRC) onboard the AKARI. This is the first spectroscopic detection of an H-alpha emission line in a quasar beyond z=4. The overall spectral energy distribution (SED) of RX J1759.4+6638 in the near- and mid-infrared wavelengths agrees with a median SED of the nearby quasars and the flux ratio of F(Ly-alpha)/F(H-alpha) is consistent with those of previous reports for lower-redshift quasars.

We report preliminary results of AKARI observations of two globular clusters, NGC104 and NGC362. Imaging data covering areas of about 10x10 arcmin^2 centered on the two clusters have been obtained with InfraRed Camera (IRC) at 2.4, 3.2, 4.1, 7.0, 9.0, 11.0, 15.0, 18.0 and 24.0 mu. We used F11/F2 and F24/F7 flux ratios as diagnostics of circumstellar dust emission. Dust emissions are mainly detected from variable stars obviously on the asymptotic giant branch, but some variable stars that reside below the tip of the first-ascending giant branch also show dust emissions. We found eight red sources with F24/F7 ratio greater than unity in NGC362. Six out of the eight have no 2MASS counterparts. However, we found no such source in NGC104.

The Cosmic Far-Infrared Background (CFIRB) contains information about the number and distribution of contributing sources and thus gives us an important key to understand the evolution of galaxies. Using a confusion study to set a fundamental limit to the observations, we investigate the potential to explore the CFIRB with AKARI/FIS deep observations. The Far-Infrared Surveyor (FIS) is one of the focal-plane instruments on the AKARI (formerly known as ASTRO-F) satellite, which was launched in early 2006. Based upon source distribution models assuming three different cosmological evolutionary scenarios (no evolution, weak evolution, and strong evolution), an extensive model for diffuse emission from infrared cirrus, and instrumental noise estimates, we present a comprehensive analysis for the determination of the confusion levels for deep far-infrared observations. We use our derived sensitivities to suggest the best observational strategy for the AKARI/FIS mission to detect the CFIRB fluctuations. If the source distribution follows the evolutionary models, observations will be mostly limited by source confusion. We find that we will be able to detect the CFIRB fluctuations and that these will in turn provide information to discriminate between the evolutionary scenarios of galaxies in most low-to-medium cirrus regions.

We present the properties of 11 $\mu$m selected sources detected in the early data of the North Ecliptic Pole Deep (NEP-Deep) Survey of AKARI. The data set covers 6 wavelength bands from 2.5 to 11 $\mu$m, with the exposure time of 10 ~ 20 minutes. This field lies within the CFHT survey with four filter bands ($g', r', i',z'), enabling us to establish nearly continuous spectral energy distributions (SEDs) for wavelengths ranging from 0.4 to 11 $\mu$m. The main sample studied here consists of 71 sources whose 11 $\mu$m AB magnitudes are equal to or brighter than 18.5 (251 $\mu$Jy), which is complete to more than 90%. The 11 $\mu$m band has an advantage of sampling star forming galaxies with low to medium redshifts since the prominent PAH feature shifts into this band. As expected, we find that the majority (~68%) of 11 $\mu$m bright sources are star forming galaxies at 0.2 < z < 0.7 with $L_{IR} ~ 10^{10}$ -- $10^{12} L_{\odot}$ based on the detailed modelling of SEDs. We also find four AGNs lying at various redshifts in the main sample. In addition, we discuss a few sources which have non-typical SEDs of the main sample, including a brown dwarf candidate, a steep power-law source, flat spectrum object, and an early-type galaxy at moderate redshift.

We present a five (u*,g',r',i',z') band optical photometry catalog of the sources in the North Ecliptic Pole (NEP) region based on deep observations made with MegaCam at CFHT. The source catalog covers about 2 square degree area centered at the NEP and reaches depths of about 26 mag for u*, g', r' bands, about 25 mag for i' band, and about 24 mag for z' band (4 sigma detection over an 1 arcsec aperture). The total number of cataloged sources brighter than r'= 23 mag is about 56,000 including both point sources and extended sources. From the investigation of photometric properties using the color-magnitude diagrams and color-color diagrams, we have found that the colors of extended sources are mostly (u*-r') < 3.0 and (g'-z') > 0.5. This can be used to separate the extended sources from the point sources reliably, even for the faint source domain where typical morphological classification schemes hardly work efficiently. We have derived an empirical color-redshift relation of the red sequence galaxies using the Sloan Digital Sky Survey data. By applying this relation to our photometry catalog and searching for any spatial overdensities, we have found two galaxy clusters and one nearby galaxy group.

We present the J- and Ks-band galaxy counts and galaxy colors covering 750 square arcminutes in the deep AKARI North Ecliptic Pole (NEP) field, using the FLoridA Multi-object Imaging Near-ir Grism Observational Spectrometer (FLAMINGOS) on the Kitt Peak National Observatory (KPNO) 2.1m telescope. The limiting magnitudes with a signal-to-noise ratio of three in the deepest regions are 21.85 and 20.15 in the J- and Ks-bands respectively in the Vega magnitude system. The J- and Ks-band galaxy counts in the AKARI NEP field are broadly in good agreement with those of other results in the literature, however we find some indication of a change in the galaxy number count slope at J~19.5 and over the magnitude range 18.0 < Ks < 19.5. We interpret this feature as a change in the dominant population at these magnitudes because we also find an associated change in the B - Ks color distribution at these magnitudes where the number of blue samples in the magnitude range 18.5 < Ks < 19.5 is significantly larger than that of Ks < 17.5.

SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is a Japanese astronomical infrared satellite project with a 3.5-m telescope. The target year for launch is 2017. The telescope is cooled down to 4.5 K in space by a combination of newly-developed mechanical coolers with an efficient radiative cooling system at the L2 point. The SPICA telescope has requirements for its total weight to be lighter than 700 kg and for the imaging performance to be diffraction-limited at 5 μm at 4.5 K. Material for the SPICA telescope mirrors is silicon carbide (SiC). Among various types of SiC, primary candidates comprise normally-sintered SiC, reaction-sintered SiC, and carbon-fiber- reinforced SiC; the latter two have been being developed in Japan. This paper reports the current design and status of the SPICA telescope along with our recent activities on the cryogenic optical testing of SiC and C/SiC composite mirrors, including the development of an innovative support mechanism for cryogenic mirrors, which are based on lessons learned from a SiC 70 cm telescope onboard the previous Japanese infrared astronomical mission AKARI.

We investigate the segregation of the extragalactic population via colour criteria to produce an efficient and inexpensive methodology to select specific source populations as a function of far-infrared flux. Combining galaxy evolution scenarios and a detailed spectral library of galaxies, we produce simulated catalogues incorporating segregation of the extragalactic population into component types (normal, star-forming, AGN) via colour cuts. As a practical application we apply our criteria to the deepest survey to be undertaken in the far-infrared with the AKARI (formerly ASTRO-F) satellite. Using the far-infrared wavebands of the Far-Infrared Surveyor (FIS, one of the focal-plane instruments on AKARI) we successfully segregate the normal, starburst and ULIRG populations. We also show that with additional MIR imaging from AKARI's Infrared Camera (IRC), significant contamination and/or degeneracy can be further decreased and show a particular example of the separation of cool normal galaxies and cold ULIRG sources. We conclude that our criteria provide an efficient means of selecting source populations (including rare luminous objects) and produce colour-segregated source counts without the requirement of time intensive ground-based follow up to differentiate between the general galaxy population. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

The AKARI (formerly known as ASTRO-F) mission is the first Japanese satellite dedicated for large area surveys in the infrared (Murakami et al. 2004). AKARI was launched successfully on February 22nd 2006 (JST) from JAXA's Uchinoura Space Centre, Japan. AKARI is now orbiting around the Earth in a Sun-synchronous polar orbit at the altitude of 700 km. The 68.5 cm aperture telescope and scientific instruments are cooled to 6K by liquid Helium and mechanical coolers. The expected liquid Helium holding time is now found to be at least one year after the successful aperture lid-opening on 2006 April 13th (JST). AKARI will perform the most advanced all-sky survey in 6 mid- to far-infrared wavebands since the preceding IRAS mission over 2 decades ago. Deep imaging and spectroscopic surveys near the ecliptic poles with pointed observations are also on-going in 13 wavelength bands at 2-160 m (see Table 1, details are given in Matsuhara et al. 2006). AKARI is a perfect complement to Spitzer in respect of its wide sky area and wavelength coverage. Two unique aspects of the pointing deep surveys with AKARI are: many imaging bands including the wavelength gap of Spitzer (8-24 m), and the slitless spectroscopic capability (Ohyama et al. in this proceeding). Not only the All-Sky Survey but also the deep pointing surveys near the ecliptic poles over ∼15 deg in total will be particularly well suited to construct the luminosity functions of the infrared galaxies, to evaluate their clustering nature, and also to discover rare, exotic objects at various redshifts out to z ∼ 3. AKARI is also capable of detecting and measuring the spectrum and the fluctuations of the cosmic infrared background. The in-orbit sensitivity and spatial resolution of the surveys are found to be sufficient to achive the scientific goals listed above. © 2007 International Astronomical Union. 2

An all-sky survey in two mid-infrared bands covering wavelengths from 6 to 12 and 14 to 26 mu m, with a spatial resolution of similar to 9 ''.4-10 '', will be performed with the Infrared Camera (IRC) on board the ASTRO-F infrared astronomical satellite. The expected detection limit for point sources is 80-130 mJy (5 sigma). The all-sky survey will provide data with a detection limit and a spatial resolution an order of magnitude deeper and higher, respectively, than those of the Infrared Astronomical Satellite survey. The IRC is optimally designed for deep imaging in staring observations. It employs 256 x 256 Si: As IBC infrared focal plane arrays for the two mid-infrared channels. In order to make observations with the IRC during the scanning observations for the all-sky survey, a new method of operation for the arrays has been developed - "scan mode" operation. In the scan mode, only 256 pixels in a single row aligned in the cross-scan direction on the array are used as the scan detector, and they are sampled every 44 ms. Special care has been taken to stabilize the temperature of the array in scan mode, which enables the user to achieve a low readout noise, comparable to that in the imaging mode (20-30 e(-)). The accuracy of the position determination and the flux measurement for point sources is examined both in computer simulations and laboratory tests with the flight model camera and moving artificial point sources. In this paper we present the scan mode operation of the array, the results of the computer simulation and the laboratory performance test, and the expected performance of the IRC all-sky survey observations.

We present concepts for the background-limited infrared-submillimeter spectrograph (BLISS) for the Japanese SPICA mission to launch early next decade. SPICA will be a 3.5-meter telescope cooled to below 5 K, and offers the potential for far-IR observations limited only by the zodiacal dust emission. BLISS will provide moderate-resolution (R 1000) spectroscopy at this background limit throughout the 40-600 μm band. With sensitivities below 10 Wm in modest integrations, BLISS-SPICA will enable the first survey spectroscopy of the redshift 0.5 to 5 galaxies which produce the far-IR background. Both WaFIRS waveguide grating spectrometers, and new compact cross-dispersed echelle grating designs are under consideration. Detectors must have sensitivities around 3 × 10 W / √Hz and have good efficiency. The most promising near-term approaches to cover the full band are transition-edge bolometers cooled to ∼50 mK with an adiabatic demagnetization refrigerator. -20 2 -20

By exploiting the far-infrared (FIR) and radio correlation, we have performed a likelihood-ratio analysis to identify optical counterparts to the FIR sources that have been found in an area of similar to 0.9 deg(2) during the Infrared Space Observatory (ISO) deep FIR survey in the Lockman Hole. New ground-based observations have been conducted to build up the catalogs of radio and optical objects, which include a deep Very Large Array (VLA) observation at 1.4 GHz, optical R- and I-band imaging with the Subaru 8 m and University of Hawaii 2.2 m telescopes, and optical spectroscopy with the Keck II 10 m and WIYN 3.5 m telescopes. This work is based on FIR samples consisting of 116 and 20 sources selected with the criteria of F-C(90 mu m) &gt;= 43 mJy and F-C(170 mu m) &gt;= 102 mJy, respectively, where F-C is the bias-corrected flux. Using the likelihood ratio analysis and the associated reliability, 44 FIR sources have been identified with radio sources. Optical confirmation of the 44 FIR/radio associations was then conducted using accurate radio positions. Redshifts have been obtained for 29 out of the 44 identified sources. One hyperluminous infrared galaxy (HyLIRG) with L-FIR &gt; 10(13) L-. and four ultraluminous infrared galaxies (ULIRGs) with L-FIR = 10(12)-10(13) L-. are identified in our sample, while the remaining 24 FIR galaxies have L-FIR &lt; 10(12) L-.. The space density of the FIR sources at z = 0.3-0.6 is 4.6 x 10(-5) Mpc(-3), which is 460 times larger than the local value, implying a rapid evolution of the ULIRG population. Most ISO FIR sources have L(1.4 GHz)/L(90 mu m) similar to the star-forming galaxies Arp 220 and M82, indicating that star formation is the dominant mechanism for their FIR and radio luminosity. At least seven of our FIR sources show evidence for the presence of an active galactic nucleus (AGN) in optical emission lines, radio continuum excess, or X-ray activity. Three out of five (60%) of the ULIRGs/HyLIRGs are AGN galaxies, suggesting that the AGN fraction among the ULIRG/HyLIRG population may not change significantly between z similar to 0.5 and the present epoch. Five of the seven AGN galaxies are within the ROSAT X-ray survey field, and two are within the XMM-Newton survey fields. X-ray emission has been detected in only one source, 1EX030, which is optically classified as a quasar. The nondetection in the XMM-Newton 2 - 10 keV band suggests a very thick absorption column density of 3 x 10(24) cm(-2) or A(V) similar to 1200 mag obscuring the central source of the two AGN galaxies. Several sources have an extreme FIR luminosity relative to the optical R band, L(90 mu m)/ L(R) &gt; 500, which is rare even among the local ULIRG population. While source confusion or blending might offer an explanation in some cases, these observations may represent a new population of galaxies with an extreme amount of star formation in an undeveloped stellar system, i.e., formation of bulges or young elliptical galaxies.

ASTRO-F is the first Japanese satellite mission dedicated for large area surveys in the infrared. The 69cm aperture telescope and scientific instruments are cooled to 6K by liquid Helium and mechanical coolers. During the expected mission life of more than 500 days, ASTRO-F will make the most advanced all-sky survey in the mid- to far-infrared since the Infrared astronomical Satellite (IRAS). The survey will be made in 6 wavebands and will include the first all sky survey at >100-160(mu)m. Deep imaging and spectroscopic surveys with pointed observations will also be carried out in 13 wavelength bands from 2-160(mu)m. ASTRO-F should detect more than a half million galaxies tracing the large-scale structure of the Universe out to redshifts of unity, detecting rare, exotic extraordinarily luminous objects at high redshift, numerous brown dwarfs, Vega-like stars, protostars, and will reveal the large-scale structure of nearby galactic star forming regions. ASTRO-F is a perfect complement to Spitzer Space Telescope in respect of its wide sky and wavelength coverage. Approximately 30 percent of pointed observations will be allocated to an open-time opportunity. Updated pre-flight ensitivities as well as the observation plan including the large-area surveys are described.

We have started PISCES project; a panoramic imaging and spectroscopic survey of distant clusters on Subaru. It exploits the unique wide-field imaging capability of Suprime-Cam, which provides a 34' x 27' field of view corresponding to a physical area of 16 x 13 Mpc(2) at z similar to 1. We plan to target 15 clusters at 0.4 less than or similar to z less than or similar to 1.3. We report on our first results concerning the inner structures and large-scale structures of two distant clusters at z = 0.55 and 0.83 together with the earlier results on a z = 0.41 cluster. The photometric redshift technique has been applied to multi-color data in order to remove most of the foreground/background galaxies so as to isolate the cluster member candidates. We have found large-scale filamentary structures around the clusters, extending out to > 5 Mpc from the cores, as well as complex inner structures. The galaxy distributions in the inner regions of the clusters look similar to the X-ray intensity maps, suggesting tha. most of the optical structures trace physically bound systems. We also compared the structures of the three clusters with those of model clusters in a numerical simulation (N-body + semi-analytic model) by parameterising the shapes of the iso-density contours of galaxies, and found a broad agreement. Our results that cluster-scale assembly takes place along filaments during hierarchical clustering need to be confirmed spectroscopically in the near future.

The MIR-L is the mid-IR (12-26 μm) instrument for Japanese infrared astronomical satellite, the ASTRO-F. The instrument has 2 observing modes: a wide field imaging mode with a field of view of 10.7 × 10.2 arcmin 2 and a low resolution spectroscopic mode with a spectral resolution R -λ/Δλ about 20. The spectroscopic mode provides with not only slit-spectroscopy for extended sources but also slitless-spectroscopy for point sources. We describe here the design, manufacturing, and performance evaluation of the cryogenic optical system of the MIR-L. The concept of the optical system design is to realize wide field observations with a compact size. The instrument employs a refractive optics of 5 lenses (CsI - CsI - KRS-5 - Csl - KRS-5) with a 256 × 256 pixel Si:As IBC array detector, 3 filters, and 2 grisms. The refractive indices of CsI and KRS-5 at the operating temperature of about 6 K have ambiguities because of the difficulty of the measurements. We therefore designed the MIR-L optics with tolerances for the uncertainties of the indices. Since both CsI and KRS-5 have the fragility and the large thermal expansion, we designed a specialized mounting architecture to prevent from making damages and/or decentrations of the lenses at cryogenic temperatures under the serious vibration during the launch. As a result, the optical system of the MIR-L has passed both vibration and thermal cycle tests without damage and performance degradation, and achieved diffraction limited performance over its full wavelength range at the operating temperature.

The ASTRO-F is an on-going infrared satellite mission covering 2-200 μm infrared wavelengths. Not only the all-sky survey in the mid-IR and far-IR, but also deep pointing observations are planned especially at 2-26 μm. In this paper, we focus on the near-infrared (NIR) channel of the infrared camera (IRC) on board ASTRO-F, and describe its design, and results of the imaging mode performance evaluation as a single component. The NIR consists of 4 lenses (Silicon - Silicon - Germanium - Silicon) with a 412 × 512 In:Sb detector. Three broad-band filters, and two spectroscopic elements are installed covering 2-5 μm wavelengths. Since the ASTRO-F telescope and the focal plane are cooled to 6 K, the evaluation of adjustment of the focus and the end-to-end test of the whole NIR camera assembly have to be done at cryogenic temperature. As a result of measurements, we found that the transverse magnification and distortion are well matched with the specification value (1 versus 1.017 and 1 %), while the chromatic aberration, point spread function, and encircled energy are slightly degraded from the specification (300 μm from 88 μm, >1pixel from ∼1pixel, 80 % encircled energy radius >1pixel from ∼1pixel). However, with these three measured values, in-flight simulations show the same quality as specification without degradation. In addition to the image quality, we also verified the ghost image generated from the optical element (1 % energy fraction to the original image) and the slightly narrowed field of view (10' × 9.5' from 10' × 10'). For the responsivity, the NIR shows expected response. Totally, the NIR imaging mode shows satisfactory results for the expected in-flight performance.

The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission is the third Japanese astronomical infrared satellite project of a 3.5m cooled telescope optimized for mid- to far-infrared observations, following the Infrared Telescope in Space (IRTS) and the ASTRO-F missions. It will employ mechanical coolers and an efficient radiative cooling system, which allow us to have a cooled (4.5K) telescope of the aperture much larger than previous missions in space. The SPICA will attack a number of key problems in present-day astrophysics, ranging from the origin of the universe to the formation of planetary systems, owing to its high spatial resolution and unprecedented sensitivity in the mid- to far-infrared. The large aperture size for cryogenically use is, however, a great challenge and demands substantial technology developments for the telescope system. We adopt monolithic mirror design in the baseline model because of the technical feasibility and reliability. We set the optical performance requirement as being diffraction limited at 5μm at the operating temperature of 4.5K. The total weight attributed to the telescope system is 700kg, which requires a very light 3.5m primary mirror together with the mirror support structure. At present we are working on two candidate materials for the SPICA telescope: silicon carbide (SiC) and carbon-fiber reinforced silicon carbide (C/SiC). This presentation gives a general overview of the SPICA mission and reports the current design and status of the SPICA telescope system, including recent progress of the development of C/SiC mirrors.

MIR-L is a 12-26mum channel of Infrared Camera(IRC) onboard ASTRO-F. The camera employs a refractive optics which consists of 5 lenses (CsI - CsI - KRS-5 - CsI - KRS-5) and a large format Si:As IBC array detector (256 x 256 pixels). The design concept is to realize a wide field of view with a compact size. It has 2 observing modes: a wide field imaging with a field of view of 10.7 x 10.2arcmin(2) or a pixel resolution of 2.5 x 2.4arcsec(2) /pixel in 3 bands (12.5-18mum, 14-26mum, 22-26mum), and low resolution spectroscopy with a spectral resolution R = gimel/Deltagimel similar to 40 in 2 bands (11-19mum,18-26mum). It also has a small slit to adapt for spectroscopic observations of extended sources. We describe the current design of the optics and the mounting architecture of MIR-L and evaluation of the optical performance at cryogenic temperatures.

The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission is a Japanese astronomical infrared satellite project optimized for mid-to far-infrared observations. It will be launched at ambient temperature and cooled down on orbit by mechanical coolers on board with an efficient radiative cooling system, which allow us to have a 3.5m cooled (4.5 K) telescope in space. SPICA will answer a number of important problems in present-day astronomy, ranging from the star-formation history of the universe to the formation of planets, owing to its high spatial-resolution and unprecedented sensitivity in the mid- to far-infrared. The large aperture mirror for cryogenically use in space, however, demands a challenging development for the telescope system. A single-aperture design of the primary mirror will be adopted for the SPICA telescope rather than deployable mirror designs to avoid further complexity and ensure the feasibility. The number of actuators for the primary mirror, if needed, will be minimized. Silicon carbide and carbon-fiber reinforced silicon carbide are extensively investigated at present as the prime candidate materials for the SPICA primary mirror This presentation reports the current status of the SPICA telescope system development.

The Infrared Camera (IRC) is one of the focal-plane instruments on board the Japanese infrared astronomical space mission ASTRO-F. It will make wide-field deep imaging and low-resolution spectroscopic observations over a wide spectral range in the near- to mid-infrared (2-26μm) in the pointed observation mode of the ASTRO-F. The IRC will also be operated in the survey mode and make an all-sky survey at mid-infrared wavelengths. It comprises three channels. The NIR channel (2-5μm) employs a 512×412 InSb array, whereas both the MIR-S (5-12μm) and the MIR-L (12-26μm) channels use 256×256 Si:As impurity band conduction (IBC) arrays. The three channels will be operated simultaneously. All the channels have 10' × 10' fields of view with nearly diffraction-limited spatial resolutions. The NIR and MIR-S share the same field of view, while the MIR-L will observe the sky about 25' away from the NIR/MIR-S field of view. The IRC will give us deep insights into the formation and evolution of galaxies, the properties of brown dwarfs, the evolution of planetary disks, the process of star-formation, the properties of the interstellar medium under various physical environments, as well as the nature and evolution of solar system objects. This paper summarizes the latest laboratory measurements as well as the expected performance of the IRC.

An all-sky survey in two mid-infrared bands which cover wavelengths of 5-12mum and 12-26mum with a spatial resolution of similar to9" will be performed with the Infrared Camera (IRC) on board the ASTRO-F infrared astronomical satellite. The expected detection limits for point sources are few tens mJy. The all-sky survey will provide with the data of detection limits more than one order of magnitude deeper and of spatial resolutions an order of magnitude higher than those of the Infrared Astronomical Satellite (IRAS) survey.The IRC is optimally designed for deep imaging in pointing observations. It employs 256 x 256 Si:As IBC infrared focal plane arrays (FPA) for the two mid-infrared channels. In order to make observations with the IRC during the survey mode of the ASTRO-F, a new operation method for the arrays has been developed - the scan mode operation. In the scan mode, only 256 pixels in a single row aligned in the cross-scan direction on the array are used as the scan detector and sampled every 44ms. Special cares have been made to stabilize the temperature of the array in the scan mode, which enables to achieve a low readout noise compatible with that of the imaging mode (similar to30 e(-)). The flux calibration method in the scan mode observation is also investigated. Performance of the scan mode observations has been examined in computer simulations as well as in laboratory simulations by using the flight model camera and moving artificial point sources. In this paper we present the scan mode operation method of the array, results of laboratory performance tests, results of the computer simulation, and expected performance of the IRC all-sky survey observations.

The SPICA (Space Infrared Telescope for Cosmology and Astrophysics), which is a Japanese astronomical infrared satellite project with a 3.5-m telescope, is scheduled for launch in early 2010s. The telescope is cooled down to 4.5 K in space by a combination of mechanical coolers with an efficient radiative cooling system. The SPICA telescope has requirements for its total weight to be lighter than 700 kg and for the imaging performance to be diffraction-limited at 5 μm at 4.5 K. Two candidate materials, silicon carbide (SiC) and carbon-fiber-reinforced SiC (C/SiC composite), are currently under investigation for the primary mirror. A monolithic mirror design will be adopted in both cases because of the technical feasibility and reliability. This paper reports the current design and status of the SPICA telescope together with some of our recent results on laboratory cryogenic tests for the SiC and C/SiC composite mirrors.

We discuss the nature of faint 6.7um galaxies detected with the mid-infrared camera ISOCAM on board the Infrared Space Observatory (ISO). The 23 hour integration on the Hawaii Deep Field SSA13 has provided a sample of 65 sources down to 6uJy at 6.7um. For 57 sources, optical or near-infrared counterparts were found with a statistical method. All four Chandra sources, three SCUBA sources, and one VLA/FIRST source in this field were detected at 6.7um with high significance. Using their optical to mid-infrared colors, we divided the 6.7um sample into three categories: low redshift galaxies with past histories of rapid star formation, high redshift ancestors of these, and other star forming galaxies. Rapidly star forming systems at high redshifts dominate the faintest end. Spectroscopically calibrated photometric redshifts were derived from fits to a limited set of template SEDs. They show a high redshift tail in their distribution with faint (<30uJy) galaxies at z>1. The 6.7um galaxies tend to have brighter K magnitudes and redder I-K colors than the blue dwarf population at intermediate redshifts. Stellar masses of the 6.7um galaxies were estimated from their rest-frame near-infrared luminosities. Massive galaxies (M_star~10e11M_sun) were found in the redshift range of z=0.2-3. Epoch dependent stellar mass functions indicate a decline of massive galaxies' comoving space densities with redshift. Even with such a decrease, the contributions of the 6.7um galaxies to the stellar mass density in the universe are found to be comparable to those expected from UV bright galaxies detected in deep optical surveys.

We report on the extensive tests to characterize the performance of the infrared detector arrays for the Infrared Camera (IRC) on board the next Japanese infrared astronomical satellite, ASTRO-F. The ASTRO-F will be launched early 2004 and the IRC is one of the focal plane instruments to make observations in 2-26 mum. For the near-infrared observations of 2-5mum, a 512x412 InSb array will be employed, while two 256x256 Si:As arrays will be used for the observations of 5-26mum in the IRC. Both arrays are manufactured by Raytheon IRO.To maximize the advantage of the cooled telescope and extremely low background radiation conditions in space, the dark current and readout noise must be minimized.. The heat dissipation of the arrays also has to be minimized. To meet these requirements and achieve the best performance of the arrays, we optimized the array driving clocks, the bias voltage, and the supply currents, and evaluated the temperature dependence of the performance. In particular, we found that the voltage between the gate and source of the FET of the, multiplexer SBRC-189 had a strong dependence on temperature. This effect becomes a dominant source for the noise unless the temperature is kept within 20mK. We have achieved the readout noises of about 30e(-) and 40e(-) with the correlated double sampling for the flight model readout circuits of the InSb and Si:As arrays, respectively. These noises ensure that the background-limited performance can be achieved for the observations of IRC in the 4-26mum range in the current observing scheme.In addition, we are now planning to make scan mode observations with IRC. We have developed a new operation way of the arrays to achieve the stable response and low readout noise in the scanning operation for, the first time.The IRC is now installed in the flight model cryostat and the first end-to-end test has just been completed. We report on the expected performance of the IRC together with the array test results.

The infrared camera(IRC) onboard ASTRO-F is designed for wide-field imaging and spectroscopic observations at near- and mid-infrared wavelengths. The IRC consists of three channels; NIR, MIR-S and MIR-L, each of which covers wavelengths of 2-5, 5-12 and 12-26 micron, respectively. All channels adopt compact refractive optical designs. Large format array detectors (InSb 512x412 and Si:As IBC 256x256) are employed. Each channel has 10x10 arcmin wide FOV with diffraction-limited angular resolution of the 67cm telescope of ASTRO-F at wavelengths over 5 micron. A 6-position filter wheel is placed at the aperture stop in each channel, and has three band-pass filters, two grisms/prisms and a mask for dark current measurements. The 5 sigma sensitivity of one pointed observation is estimated to be 2, 11 and 62 micro-Jy at 4, 9, 20 micron bands, respectively. Because ASTRO-F is a low-earth orbiting satellite, the observing duration of each pointing is limited to 500 seconds. In addition to pointed observations, we plan to perform mid-infrared scanning observation. Fabrications of the flight-model of NIR, MIR-S, and the warm electronics have been mostly completed, while that of MIR-L is underway. The performance evaluation of the IRC in the first end-to-end test (including the satellite system) is presented.

We introduce a Japanese future plan of the IR space astrometry(JASMINE-project). JASMINE is an infrared(K-band) scanning astrometric satellite. JASMINE(I and/or II-project) is planned to be launched between 2013 and 2015 and will measure parallaxes, positions and proper motions with the precision of 10 microarcsec at K=12-14mag. JASMINE can observe about a few hundred million stars belonging to the disk and the bulge components of our Galaxy, which are hidden by the interstellar dust extinction in optical bands. Furthermore JASMINE will also measure the photometries of stars in K, J and H-bands. The main objective of JASMINE is to study the fundamental structure and evolution of the disk and the bulge components of the Milky Way Galaxy. Furthermore its important objective is to investigate stellar physics.

The design and the current development status of the Infrared Camera (IRC) onboard ASTRO-F is described. The IRC is designed for wide field imaging and slit-less spectroscopic observations at near- and mid-infrared wavelengths. The IRC consists of three channels, NIR, MIR-S and MIR-L, which cover wavelengths of 2-5, 5-12 and 12-26 micron, respectively. All of them consist of refractive optics. State-of-the-art large format array detectors are placed at the focal plane. Each channel has 10 x 10 arcmin wide field-of-view with diffraction-limited spatial resolution of 70 cm aperture of ASTRO-F telescope at wavelengths over 5 micron. We plan to have more than 7000 pointing observations dedicated for the IRC. The observational time of each pointing is limited to 500 seconds because of its low earth sun-synchronous polar orbit. The 5 sigma sensitivity of one pointing observation is estimated to be 2, 30 and 120 micro-Jy at 5, 9, 20 micron bands, respectively. Fabrication of the prototype model has been completed, and the performance tests are underway. (C) 2002 Published by Elsevier Science Ltd on behalf of COSPAR.

The spectral characteristics of the diffuse galactic mid- and far infrared emission at λ = 10 - 60 μm are investigated using the IRTS and IRAS data. We estimate the grain temperature, total far-infrared intensity (FIR) and radiation density from the emission of the large grains at λ > 100 μm, assuming that the spectrum has a single temperature Planck function with a λ emissivity law. We found that the spectral energy distribution of the diffuse galactic emission at wavelengths from 10 μm to 1 mm changed as a function of the dust temperature. In addition, we found clear correlation for the intensity of emissions at 12, 25, and 60 μm. The 12 μm intensity is proportional to FIR, and the ratios of the 25 and 60 μm intensities to FIR are proportional to the strength of the interstellar radiation field. These correlations are consistent with those found in the data of seven H II regions with various physical conditions. This suggests that the emitters of the emission at 12-60 μm are well mixed with large grains radiating at wavelength greater than 100 μm and implies that the ratio of the mass of these emitters to the mass of the large grains is constant in interstellar space. We conclude that the 12 μm emission is largely due to unidentified infrared features and that the 25 and 60 μm emission arises from very small grains transiently heated by multiple-photon © 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved. -2

The Far-Infrared Line Mapper (FILM) onboard the Infrared Telescope in Space (IRTS) made a survey for the far-infrared [C II] 158 μm line emission with high sensitivity and moderate spatial resolution. We have found that diffuse [C II] line emission extends to high Galactic latitude regions. The [C II] line intensity at |b| ∼ 60° ranges from 2 × 10 to 1.5 × 10 erg cm s sr . Comparisons of the distribution of the [C II] line emission with those of the H I column density and far-infrared radiation show some correlations, but the [C II] line emission differs from the far-IR and HI emission at high Galactic latitudes. These differences suggest that the [C II] line primarily comes from ionized gas in the high-latitude regions. The intensities of the [C II] line emission on the southern side (b < 0°) of the Galactic plane are systematically larger than those on the northern side (b > 0°). We infer from this difference that there is a displacement of the Sun with respect to the center of interstellar medium from which the [C II] line comes. When an exponential distribution is assumed for the [C II] emitting gas, it is expected that the Sun is located at the distance of about 17% of the scale height above the center of the gas. This is consistent with the previously reported displacement of the Sun from the Galactic plane. -7 -6 -2 -1 -1

We study the sensitivities of space infrared interferometers. We formulate the signal-to-noise ratios of infrared images obtained by aperture synthesis in the presence of source shot noise, background shot noise and detector read noise. We consider the case in which n beams are pairwise combined at n(n-1)/2 detectors, and the case in which all the n beams are combined at a single detector. We apply the results to future missions, Terrestrial Planet Finder and Darwin. We also discuss the potential of a far-infrared interferometer for a deep galaxy survey.

We present the results of ground-based imaging spectroscopy of the [Ne II] 12.8 mu m line emitted from the ultracompact (UC) H II regions W51d, G45.12 +/- 0.13, G35.20 - 1.74, and Monoceros R2, with 2" spatial resolution. We found that the overall distribution of the [Ne II] emission is generally in good agreement with the radio (5 or 15 GHz) VLA distribution for each source. The Ne+ abundance ([Ne+/ H+]) distributions are also derived from the [Ne II] and the radio maps. As for G45.12 + 0.13 and W51d, the Ne+ abundance decreases steeply from the outer part of the map toward the radio peak. On the other hand, the Ne+ abundance distributions of G35.20-1.74 and Mon R2 appear rather uniform. These results can be interpreted by the variation of ionizing structures of neon, which is determined primarily by the spectral type of the ionizing stars. We have evaluated the effective temperature of the ionizing star by comparing the Ne+ abundance averaged over the whole observed region with that calculated by H II region models based on recent non-LTE stellar atmosphere models: 39,100(-500)(+1100) K (O7.5 V-O8 V) for W51d; 37,200(-700)(+1000) K (O8 V-O8.5 V) for G45.12 + 0.13; 35,00-37,600(-600)(+1500) K (O8 V-O9 V) for G35.20-1.74; and less than or equal to 34,000 K (less than or equal to B0 V) for Mon R2. These effective temperatures are consistent with those inferred from the observed Ne+ abundance distributions.

We present a conceptual design of a future infrared astronomical satellite: the HII/L2 mission. Its telescope is to be launched at ambient temperature (warm launch) and is to be cooled to 4.5 K by effective radiative cooling and mechanical cryogenic coolers. The warm launch design reduces the total weight dramatically. A 3.5 m class telescope can be put into a halo orbit around S-E L2 by the Japanese H-IIA launching vehicle. This mission focuses on high-resolution mid-to far-infrared observations with unprecedented sensitivity. The target launch year is 2010. © 2000 COSPAR. Published by Elsevier Science Ltd.

We present a conceptual design of the infrared astronomical mission HII/L2, which incorporates a large, cooled telescope. We propose to cool a 3.5 m class telescope down to 4.5 K only by moderate mechanical cryogenic coolers with the help of effective radiative cooling. The Japanese H-IIA launching vehicle can put this 3.5 m telescope mission into a halo orbit around S-E L2. The cooled, large telescope makes the HII/L2 mission optimum for high-resolution mid- to far-infrared observations with unprecedented sensitivity. The target launch year is 2010.

We present a Grief description of an on-going Japanese infrared astronomical telescope mission in space: Infrared Imaging Surveyor (IRIS), as well as that of a future mission, a 3m class cooled telescope to be put into a halo orbit around the Sun-Earth L2 point by the Japanese H-IIA rocket(the HII/L2 mission). The IRIS is a 70cm cooled telescope dedicated to an infrared sky survey at 2 - 200 mu m. The HII/L2 mission is an ideal observatory-type platform to make follow-up observations to the IRIS survey mission. The mission is optimized for mid-infrared and far-infrared deep imaging and spectroscopic observations, thus will be complementary with NGST and FIRST. The target launch year is 2010.

The design overview and current development status of the Infrared Camera (IRC) onboard the Japanese infrared space mission, ASTRO-F (commonly called as the Infrared Imaging Surveyor; IRIS), are presented. The IRC is one of the focal plane instruments of ASTRO-F and will make imaging and low-resolution spectroscopy observations in the wide spectral range of the near- to mid-infrared of 2-26 μm. ASTRO-F will be brought into an IRAS-type sun-synchronous polar orbit. The IRC will be operated in the pointing mode, in which the telescope will be pointed at a fixed target position on the sky for about 10 minutes. The pointed observation may be scheduled up to three times per orbit. The IRC has three channels: NIR (2-5 μm), MIR-S (5-12 μm) and MIR-L (12-26 μm). All of the three channels use refractive optics. Each channel has a field-of-view of 10′×10′ with nearly diffraction-limited spatial resolution. The NIR and MIR-S channels simultaneously observe the same field on the sky, while the MIR-L observes the sky about 20′ away from the NIR/MIR-S position. State-of-the-art large format array detectors manufactured by Raytheon/IRCoE are employed for the IRC. The NIR channel uses a 512×412 InSb array, and 256×256 Si:As IBC arrays are used for the MIR channels. Fabrication of the proto-model has been completed and the preliminary performance test is under way.

Basic design and current development status of IRC; Infrared camera onboard the IRIS (Infrared Imaging Surveyor) is presented. IRC employs state-of-the-art large-format IR arrays for imaging and low-resolution spectroscopy at wavelength 2-25 μm. IRC consists of 3 cameras; NIR (2-5 μm), MIR-S (5-12 μm), and MIR-L (12-25 μm). These 3 channels simultaneously observe different fields (10′×10′ FOV each) of the sky, with diffraction-limited spatial resolution.

We present a conceptual design of a future Japanese infrared astronomical sateffite: the fflI/L2 mission. We propose a warm launch cooled telescope; the telescope is to be launched at ambient temperature and is to be cooled in orbit to 4.5K by a modest cryogenic cooler with the help of radiative cooling. Since liquid helium and hence a heavy vacuum vessel are no longer required, the warm launch design reduces the weight of the sateffite dramatically. We propose to launch this sateffite into a halo orbit around S-E L2, one of the Sun-Earth Lagrangian liberation points. The S-E L2 is an ideal orbit for infrared astronomy, since (1) radiative cooling can become very effective, and (2) long-integration observations become possible. A 3.5 m class telescope can be put into a halo orbit around S-E L2 by the Japanese H-hA launching vehicle. This mission focuses on high-resolution mid-to far-infrared observations with unprecedented sensitivity, since the large aperture reduces confusion noise and the cooled optics suppresses instrumental background radiation. The fflh/L2 mission is an ideal observatory-type platform to make follow-up observations to the ASTRO-F/IIUS survey mission. The target launch year is 2010.

We report the results of a rocket-borne observation of [C II] 158\micron line and far-infrared continuum emission at 152.5\micron toward the high latitude molecular clouds in Ursa Major. We also present the results of a follow-up observation of the millimeter ^{12}CO J=1-0 line over a selected region observed by the rocket-borne experiment. We have discovered three small CO cloudlets from the follow-up ^{12}CO observations. We show that these molecular cloudlets, as well as the MBM clouds(MBM 27/28/29/30), are not gravitationally bound. Magnetic pressure and turbulent pressure dominate the dynamic balance of the clouds. After removing the HI-correlated and background contributions, we find that the [C II] emission peak is displaced from the 152.5\micron and CO peaks, while the 152.5\micron continuum emission is spatially correlated with the CO emission. We interpret this behavior by attributing the origin of [C II] emission to the photodissociation regions around the molecular clouds illuminated by the local UV radiation field. We also find that the ratio of the molecular hydrogen column density to velocity-integrated CO intensity is 1.19+-0.29x10^{20} cm^{-2} (K kms^{-1})^{-1} from the FIR continuum and the CO data. The average [C II] /FIR intensity ratio over the MBM clouds is 0.0071, which is close to the all sky average of 0.0082 reported by the FIRAS on the COBE satellite. The average [C II]/CO ratio over the same regions is 420, which is significantly lower than that of molecular clouds in the Galactic plane.

We made two sets of spectroscopic observations of fundamental rotation-vibration absorption spectra around 4.6 mu m of gas-phase CO toward the objects near the Galactic center and toward the Infrared Quintuplet near the Radio Are. The first set of observations was made with moderate resolution and clearly showed many absorption Lines at different rotation quantum numbers. The second set of observations was made with high resolution for each line and revealed various velocity components at each transition. On the basis of these observations, we determined column densities and temperatures of clouds in lines of sight. The two sets of observations showed consistent results and imply that that the mass of molecular clouds previously derived on the basis of the radio CO observations was significantly overestimated toward the Galactic center.

The far-infrared line mapper (FILM) is a far-infrared spectrometer and in one of four focal plane instruments of the infrared telescope in space (IRTS), FILM was designed for wide area intensity mapping of far-infrared emission from interstellar gas and dust in the galaxy. The targets are the [CII] 158 micrometer line of the ionized carbon, the [OI] 63 micrometer line of the oxygen atom, and the continuum emission at 155 and 160 micrometer from the interstellar dust grain. A cylindrically concave varied line-space grating and a linear array of stressed Ge:Ga were successfully developed and allowed us to make a compact spectrometer compatible to severe limitations of the small cryogenic telescope. The IRTS, onboard the space flyer unit (SFU), was launched by a HII rocket on March 18, 1995 and was recovered by a STS on January 13, 1996. The FILM worked very well during four weeks allocated for the IRTS observation and produced a lot of valuable data. The sensitivity and the spatial resolution for the [CII] line are an order of magnitude better than the previous work.

We report the design and testing of a compact system of baffles for cooled infrared telescopes. The baffle system consists of a reflecting forebaffle and a black aftbaffle and provides a high level of rejection of emission from off-axis sources. The firebaffle reflects radiation incident at angles greater than 40 degrees off axis out of the telescope, thereby reducing the aperture heat load. The black aftbaffle absorbs radiation scattered or diffracted by the forebaffle, as well as radiation from sources within 40 degrees off axis. We describe ground-based measurements at lambda = 0.9 mu m of the baffle system at ambient temperature and rocketborne measurements at far-infrared wavelengths of the baffle system at similar to 3 K. The effective emissivity of the cooled forebaffle was measured to be 7 x 10(-3). The system has been successfully used in rocketborne measurements of the diffuse infrared background and will be used in the Infrared Telescope in Space.

The Infrared Telescope in Space (IRTS) is a cryogenically cooled small infrared telescope that will fly aboard the small space platform Space Flyer Unit. It will survey approximately 10% of the sky with a relatively wide beam during its 20 day mission. Four focal-plane instruments will make simultaneous observations of the sky at wavelengths ranging from 1 to 1000 μm,. The IRTS will provide significant information on cosmology, interstellar matter, late-type stars, and interplanetary dust. This paper describes the instrumentation and mission.

We have developed a Far-Infrared Line Mapper (FILM) as one of the four focal plane instruments on the Infrared Telescope in Space (IRTS). The FILM is a grating spectrometer designed to simultaneously measure [C II] 158 μm and [O I] 63 μm line intensities and continuum emission near the [C II] line with spatial resolution of 8 arcmin. Very high sensitivity and accuracy are achieved by using stressed and unstressed Ge: Ga detectors at 1.8 K with a helium cooled telescope and by using a spectral scanner to distinguish the line emission from the continuum emission. Line intensities of the [C II] and the [O I] will be mapped over 10% of the sky with much higher sensitivity than the previous survey measurements.

Using the balloon-borne infrared telescope (BIRT) incorporated with a liquid-helium-cooled double-channel Fabry-Perot spectrometer, intensities and velocity profiles of [C II] 158 μm and [O I] 63 μm fine-structure lines have been observed in the Galactic center region within |l| ≦ 0°.7. Intense [C II] line emission has been detected ubiquitously in almost all of the observed points. The distribution of the [ C II] intensity shows a central peak at Sgr A West together with two prominent peaks at Δ1 = ± 0°.6, which correspond to Sgr B1 (not Sgr B2) and Sgr C, respectively. The intensity distribution resembles but is not identical to, that of far-infrared emission. The velocity profiles of the [C II] line are resolved and can be deconvolved into multiple components, many of which can be traced to the features observed by molecular lines. The [O I] 63 μm line has been detected at Sgr A West and at some other points. The [O I] 63 μm/[C II] 158 μm ratios are always less than 3 in the beam of 3′.7. These observed results can be explained as the emission generated in photodissociation regions formed in the molecular clouds complexes illuminated by intense UV radiation field in the Galactic center regions. However, contribution from ELD region is possibly present and cannot be ruled out.

We give a detailed description of the design and flight performance of an instrument onboard the S-52015 rocket of the Institute of Space and Astronautical Science. The instrument, consisting of a near-infrared spectrometer and a far-infrared photometer at the focus of a 10 cm liquid-helium cooled telescope, was designed to observe both the brightness and distribution of diffuse emission with high sensitivity. The rocket was successfully launched and the instrument observed near-infrared and far-infrared continuum emission, as well as [C(II)] 157.7 mum line emission from regions at high Galactic latitude. We also give a brief description of the design and performance of an onboard attitude control system.

Interstellar [CII] and [OI] lines have been observed by the Balloon-Borne Infrared Telescope (BIRT) in corporation with a Fabry-Perot spectrometer. Two balloon flights were successfully made from Palestine, Texas in May/June 1988. With a new method of "frequency switching", diffuse [CII] line emission was efficiently detected and mapped in extended regions around HII/molecular cloud complexes and in a wide area of the Galactic plane. It has been shown that the [CII] emission is very strong and ubiquitously distributed in interstellar space in the Galaxy. © 1992.

A stressed Ge:Ga photoconductor array with three elements applied to the Infrared Telescope in Space satellite was fabricated and tested in experiments at 2.0 K in very low-photon-influx conditions (˜ 10 photons/s). Stress was applied to three Ge:Ga detectors in a series by a stable and compact stressing apparatus by using cone-disk springs. The cutoff wavelength was ˜ 180 μm. Responsivity was ˜ 100 A/W, and the product of quantum efficiency and photoconductive gain, t)G, was ˜ 1 with a chopping frequency of 2 Hz. The noise equivalent power was < 5 x HT W/Hz when low-noise transimpedance amplifiers were used. A slow transient response and a nonlinear response that was dependent on the background photon influx were observed in the experiments. The latter showed that the -ȠG had a time constant tc that was proportional to N . © 1992 Optical Society of America. 5 18 1/2 -1/2 ph