The Mid-Infrared Instrument (MIRI) is one of four science instruments to be flown aboard the James Webb Space Telescope (JWST). MIRI operates from 5 to 28.5 microns and provides a suite of versatile capabilities including imaging, low resolution spectroscopy (LRS), medium-resolution spectroscopy (MRS) via an integral field unit, and coronagraphy. The MIRI pipeline consists of three stages: 1) Raw to Slope Images, 2) Calibrated Slope Images, and 3) Multiple Exposures Combined. The pipeline is designed to provide well-calibrated, high level data products that maximize the scientific return from the instrument.

We present the stellar calibrator sample and the conversion from instrumental to physical units for the 24 micron channel of the Multiband Imaging Photometer for Spitzer (MIPS). The primary calibrators are A stars, and the calibration factor based on those stars is 4.54*10^{-2} MJy sr^{-1} (DN/s)^{-1}, with a nominal uncertainty of 2%. We discuss the data-reduction procedures required to attain this accuracy; without these procdures, the calibration factor obtained using the automated pipeline at the Spitzer Science Center is 1.6% +/- 0.6% lower. We extend this work to predict 24 micron flux densities for a sample of 238 stars which covers a larger range of flux densities and spectral types. We present a total of 348 measurements of 141 stars at 24 micron. This sample covers a factor of ~460 in 24 micron flux density, from 8.6 mJy up to 4.0 Jy. We show that the calibration is linear over that range with respect to target flux and background level. The calibration is based on observations made using 3-second exposures; a preliminary analysis shows that the calibration factor may be 1% and 2% lower for 10- and 30-second exposures, respectively. We also demonstrate that the calibration is very stable: over the course of the mission, repeated measurements of our routine calibrator, HD 159330, show a root-mean-square scatter of only 0.4%. Finally, we show that the point spread function (PSF) is well measured and allows us to calibrate extended sources accurately; Infrared Astronomy Satellite (IRAS) and MIPS measurements of a sample of nearby galaxies are identical within the uncertainties.

The images from the Multi-band Imaging Photometer for Spitzer (MIPS) instrument on the Spitzer Space Telescope are distorted by a few percent from a regular sky grid, and vary slightly from one exposure to the next due to the motion of' the scan mirror. We used the Code V optical models for Spitzer/MIPS to estimate the distortions present in the images from the three MIPS detectors. Based on the Code V results, we developed an algorithm to represent these distortions as polynomials with coefficients represented as FITS header keywords (the SIP convention). We present the method of correcting the MIPS images for distortions, the results of Code V testing, and the comparisons with on-orbit data.

We report the discovery of a debris system associated with the ~30 Myr old G3/5V star HD 12039 using Spitzer Space Telescope observations from 3.6-160 μm. An observed infrared excess (LIR/L* = 1 × 10-4) above the expected photosphere for λ ≳ 14 μm is fit by thermally emitting material with a color temperature of T ~ 110 K, warmer than the majority of debris disks identified to date around Sun-like stars. The object is not detected at 70 μm with a 3 σ upper limit 6 times the expected photospheric flux. The spectrum of the infrared excess can be explained by warm, optically thin material comprised of blackbody-like grains of size ≳7 μm that reside in a belt orbiting the star at 4-6 AU. An alternate model dominated by smaller grains, near the blowout size a ~ 0.5 μm, located at 30-40 AU is also possible but requires the dust to have been produced recently, since such small grains will be expelled from the system by radiation pressure in approximately a few times 102 yr.

We present 70 and 160 μm observations from the Spitzer extragalactic First Look Survey (xFLS). The data reduction techniques and the methods for producing co-added mosaics and source catalogs are discussed. Currently, 26% of the 70 μm sample and 49% of the 160 μm–selected sources have redshifts. The majority of sources with redshifts are star-forming galaxies at z < 0.5, while about 5% have infrared colors consistent with active galactic nuclei. The observed infrared colors agree with the spectral energy distributions (SEDs) of local galaxies previously determined from IRAS and Infrared Space Observatory data. The average 160 μm/70 μm color temperature for the dust is Td ≃ 30 ± 5 K, and the average 70 μm/24 μm spectral index is α ≃ 2.4 ± 0.4. The observed infrared-to-radio correlation varies with redshift as expected out to z ∼ 1 based on the SEDs of local galaxies. The xFLS number counts at 70 and 160 μm are consistent within uncertainties with the models of galaxy evolution, but there are indications that the current models may require slight modifications. Deeper 70 μm observations are needed to constrain the models, and redshifts for the faint sources are required to measure the evolution of the infrared luminosity function.

NASA's Spitzer Space Telescope (formerly known as the Space Infrared Telescope Facility SIRTF) is now on normal science operation and open to the international community. One of the Guaranteed Time Observer programs consists in a series of surveys using the two imaging instruments on Spitzer: MIPS (observing at 24, 70, and 160 microns) and IRAC (3.6, 4.5, 5.6 and 8 microns). The program includes observations to various depths, from wide field shallow, to very deep confusion limited surveys. We are also conducting a series of supporting programs (including also data from the spectrograph on Spitzer, IRS) to help interpret what we see in the deep surveys, e.g., the characterization of the spectral energy distributions of about 150 QSOs, and an extensive study of low-metallicity nearby star-forming galaxies. GTC first light is scheduled when the first well-established results from our Cosmological Surveys program will be released, offering us an incomparable facility to perform spectroscopic and photometric follow-ups of mid- and far-infrared selected sources. Moreover, the combination of the GTC, Spitzer and the Large Millimeter Telescope (LMT) facilities will allow us to study the galaxy populations in the Universe with a sensitivity and a coverage of the electromagnetic spectrum that have no precedents until today.

We analyze a sample of ~2600 Spitzer MIPS 24 μm sources brighter than ~80 μJy and located in the Chandra Deep Field-South to characterize the evolution of the comoving infrared (IR) energy density of the universe up to z ~ 1. Using published ancillary optical data, we first obtain a nearly complete redshift determination for the 24 μm objects associated with R ≲ 24 mag counterparts at z ≲ 1. These sources represent ~55%-60% of the total MIPS 24 μm population with f24 μm ≳ 80 μJy, the rest of the sample likely lying at higher redshifts. We then determine an estimate of their total IR luminosities using various libraries of IR spectral energy distributions. We find that the 24 μm population at 0.5 ≲ z ≲ 1 is dominated by "luminous infrared galaxies" (i.e., 1011 L☉ ≤ LIR ≤ 1012 L☉), the counterparts of which appear to be also luminous at optical wavelengths and tend to be more massive than the majority of optically selected galaxies. A significant number of fainter sources (5 × 1010 L☉ ≲ LIR ≤ 1011 L☉) are also detected at similar distances. We finally derive 15 μm and total IR luminosity functions (LFs) up to z ~ 1. In agreement with the previous results from the Infrared Space Observatory (ISO) and SCUBA and as expected from the MIPS source number counts, we find very strong evolution of the contribution of the IR-selected population with look-back time. Pure evolution in density is firmly excluded by the data, but we find considerable degeneracy between strict evolution in luminosity and a combination of increases in both density and luminosity [L ∝ (1 + z), ϕ ∝ (1 + z)]. A significant steepening of the faint-end slope of the IR luminosity function is also unlikely, as it would overproduce the faint 24 μm source number counts. Our results imply that the comoving IR energy density of the universe evolves as (1 + z)3.9±0.4 up to z ~ 1 and that galaxies luminous in the infrared (i.e., LIR ≥ 1011 L☉) are responsible for 70% ± 15% of this energy density at z ~ 1. Taking into account the contribution of the UV luminosity evolving as (1 + z)~2.5, we infer that these IR-luminous sources dominate the star-forming activity beyond z ~ 0.7. The uncertainties affecting these conclusions are largely dominated by the errors in the k-corrections used to convert 24 μm fluxes into luminosities.

We describe the data reduction algorithms for the Multiband Imaging Photometer for Spitzer (MIPS). These algorithms were based on extensive preflight testing and modeling of the Si:As (24 μm) and Ge:Ga (70 and 160 μm) arrays in MIPS and have been refined based on initial flight data. The behaviors we describe are typical of state‐of‐the‐art infrared focal planes operated in the low backgrounds of space. The Ge arrays are bulk photoconductors and therefore show a variety of artifacts that must be removed to calibrate the data. The Si array, while better behaved than the Ge arrays, does show a handful of artifacts that must also be removed to calibrate the data. The data reduction to remove these effects is divided into three parts. The first part converts the nondestructively read data ramps into slopes while removing artifacts with time constants of the order of the exposure time. The second part calibrates the slope measurements while removing artifacts with time constants longer than the exposure time. The third part uses the redundancy inherent in the MIPS observing modes to improve the artifact removal iteratively. For each of these steps, we illustrate the relevant laboratory experiments or theoretical arguments, along with the mathematical approaches taken to calibrate the data. Finally, we describe how these preflight algorithms have performed on actual flight data.

We present the discovery of debris systems around three Sun-like stars based on observations performed with the Spitzer Space Telescope as part of a Legacy Science Program, "The Formation and Evolution of Planetary Systems" (FEPS). We also confirm the presence of debris around two other stars. All the stars exhibit infrared emission in excess of the expected photospheres in the 70 μm band but are consistent with photospheric emission at ≤33 μm. This restricts the maximum temperature of debris in equilibrium with the stellar radiation to T < 70 K. We find that these sources are relatively old in the FEPS sample, in the age range 0.7-3 Gyr. On the basis of models of the spectral energy distributions, we suggest that these debris systems represent materials generated by collisions of planetesimal belts. We speculate on the nature of these systems through comparisons to our own Kuiper Belt, and on the possible presence of planet(s) responsible for stirring the system and ultimately releasing dust through collisions. We further report observations of a nearby star HD 13974 (d = 11 pc) that are indistinguishable from a bare photosphere at both 24 and 70 μm. The observations place strong upper limits on the presence of any cold dust in this nearby system (LIR/L⋆ < 10-5.2).

We present Spitzer 70μm and 160μm observations of the Spitzer extragalactic First Look Survey (xFLS). The data reduction techniques and the methods for producing co-added mosaics and source catalogs are discussed. Currently, 26% of the 70μm sample and 49% of the 160μm-selected sources have redshifts. The majority of sources with redshifts are star-forming galaxies at z < 0.5, while about 5% have infrared colors consistent with AGN. The observed infrared colors agree with the spectral energy distribution (SEDs) of local galaxies previously determined from IRAS and ISO data. The average 160μm/70μm color temperature for the dust is Td ≃ 30 ± 5K, and the average 70μm/24μm spectral index is α ≃ 2.4 ± 0.4. The observed infrared to radio correlation varies with redshift as expected out to z ∼ 1 based on the SEDs of local galaxies. The xFLS number counts at 70μm and 160μm are consistent within uncertainties with the models of galaxy evolution, but there are indications that the current models may require slight modifications. Deeper 70μm observations are needed to constrain the models, and redshifts for the faint sources are required to measure the evolution of the infrared luminosity function. Subject headings: galaxies: evolution — galaxies: starburst — infrared: galaxies

We investigate extremely red objects (EROs) using near- and mid-infrared observations in five passbands (3.6 to 24 μm) obtained from the Spitzer Space Telescope, and deep ground-based R and K imaging. The great sensitivity of the Infrared Array Camera (IRAC) camera allows us to detect 64 EROs (a surface density of 2.90 ± 0.36 arcmin-2; [3.6]AB < 23.7) in only 12 minutes of IRAC exposure time, by means of an R - [3.6] color cut (analogous to the traditional red R - K cut). A pure infrared K - [3.6] red cut detects a somewhat different population and may be more effective at selecting z > 1.3 EROs. We find ∼17% of all galaxies detected by IRAC at 3.6 or 4.5 μm to be EROs. These percentages rise to about 40% at 5.8 μm, and about 60% at 8.0 μm. We utilize the spectral bump at 1.6 μm to divide the EROs into broad redshift slices using only near-infrared colors (2.2/3.6/4.5 μm). We conclude that two-thirds of all EROs lie at redshift z > 1.3. Detections at 24 μm imply that at least 11% of 0.6 < z < 1.3 EROs and at least 22% of z > 1.3 EROs are dusty star-forming galaxies.

Galaxy source counts in the infrared provide strong constraints on the evolution of the bolometric energy output from distant galaxy populations. We present the results from deep 24 mum imaging from Spitzer surveys, which include approximate to5 x 10(4) sources to an 80% completeness of similar or equal to 60 muJy. The 24 mum counts rapidly rise at near-Euclidean rates down to 5 mJy, increase with a super-Euclidean rate between 0.4 and 4 mJy, and converge below similar to 0.3 mJy. The 24 mum counts exceed expectations from nonevolving models by a factor of greater than or similar to10 at S-nu similar to 0.1 mJy. The peak in the differential number counts corresponds to a population of faint sources that is not expected from predictions based on 15 mum counts from the Infrared Space Observatory. We argue that this implies the existence of a previously undetected population of infrared-luminous galaxies at z similar to 1-3. Integrating the counts to 60 muJy, we derive a lower limit on the 24 mum background intensity of 1.9 +/- 0.6 nW m(-2) sr(-1) of which the majority (similar to60%) stems from sources fainter than 0.4 mJy. Extrapolating to fainter flux densities, sources below 60 muJy contribute 0.8(-0.4)(+0.9) nW m(-2) sr(-1) to the background, which provides an estimate of the total 24 mum background of 2.7(-0.7)(+1.1) nW m(-2) sr(-1).

Well-resolved infrared observations of nearby galaxies are of fundamental importance to the study of the processes that affect galactic evolution. In this paper we report on the first imaging results from the Spitzer Infrared Nearby Galaxies Survey ( SINGS) using observations of the Sb galaxy NGC 7331. We present images of NGC 7331 over a large range of wavelengths that allow us to compare the distributions of gas, stars, and dust in unprecedented detail. As an example of the types of information that the full SINGS will provide, we use three methods to determine that the interstellar medium mass in the ring of NGC 7331 is similar to5 x 10(9) M-circle dot. We also present the first images showing emission from small hot (similar to1000 K) dust grains, but we show that these dust grains contribute only a small fraction of the integrated 4.5 mum emission from NGC 7331.

We investigate Extremely Red Objects (EROs) using nearand mid-infrared observations in five passbands (3.6 to 24μm) obtained from the Spitzer Space Telescope, and deep ground-based R and K imaging. The great sensitivity of the IRAC camera allows us to detect 64 EROs (a surface density of 2.90 ± 0.36 arcmin ; [3.6]AB < 23.7) in only 12 minutes of IRAC exposure time, by means of an R − [3.6] color cut (analogous to the traditional red R − K cut). A pure infrared K − [3.6] red cut detects a somewhat different population and may be more effective at selecting z > 1.3 EROs. We find ∼ 17% of all galaxies detected by IRAC at 3.6 or 4.5μm to be EROs. These percentages rise to about 40% at 5.8μm, and about 60% at 8.0μm. We utilize the spectral bump at 1.6μm to divide the EROs into broad redshift slices using only near-infrared colors (2.2/3.6/4.5μm). We conclude that two-thirds of all EROs lie at redshift z > 1.3. Detections at 24μm imply that at least 11% of 0.6 < z < 1.3 EROs and at least 22% of z > 1.3 EROs are dusty star-forming galaxies. Subject headings: cosmology: observations — galaxies: photometry — galaxies: evolution — galaxies: starburst — infrared: galaxies Spitzer Science Center, California Institute of Technology, 220-6, Pasadena, CA 91125; gillian@ipac.caltech.edu Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 Steward Observatory, University of Arizona, Tucson, AZ 85721 Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, U.K. Institut d’Astrophysique Spatiale, bat 121, Universiteé Paris Sud, F-91405 Orsay Cedex, France Department of Astrophysics, Oxford University, Keble Road, Oxford, OX1 3RH, U.K. Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 96720

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%.

We examine the 24 µm to X-ray color of 157 X-ray–selected AGN as a function of X-ray obscuration and optical classification in the Chandra Deep Field South. The sample consists of the Chandra hard–band detections with 2–8 keV flux > 10 −15 erg s −1 cm −2. A deep 24 µm mosaic obtained with Spitzer provides mid–infrared fluxes for the sample. Since obscured AGN locally have higher 24 µm/2–8 keV ratios than unobscured AGN, and since X-ray background models predict a large population of obscured AGN, we expect to find many X-ray–hard, IR–bright AGN. Instead, we find that the 24 µm to X-ray flux ratio does not depend on X-ray hardness in the full sample, nor does it differ between narrow– line and broad–line AGN. We identify 5 nearly Compton–thick AGN, and find they have similar 24 µm to X-ray flux ratios compared to the full sample. We consider AGN in the narrow redshift spikes at z ∼ 0.7; for these AGN, there is some evidence that the flux ratio increases with X-ray hardness. The redshift slice also shows an odd trend, which is also prominent in the full sample: a group of X-ray–hard AGN with very low 24 µm to X-ray flux ratios.

We present observations of the star formation region NGC 7129 taken with the Multiband Imaging Photometer for Spitzer (MIPS). A significant population of sources, likely pre-main-sequence members of the young stellar cluster, are revealed outside the central photoionization region. Combining Infrared Array Camera (IRAC) and ground-based near-infrared images, we have obtained colors and spectral energy distributions for some 60 objects. The [3.6]-[4.5] versus [8]-[24] color-color plane shows sources clustered at several different loci, which roughly correspond to the archetypal evolutionary sequence Class 0, I, II, and III. We obtain preliminary classifications for 36 objects and find significant numbers of both Class I and II objects. Most of the pre-main-sequence candidates are associated with the densest part of the molecular cloud surrounding the photoionization region, indicating active star formation over a broad area outside the central cluster. We discuss three Class II candidates that exhibit evidence of inner disk clearing, which would be some of the youngest known examples of a transition from accretion to optically thin quiescent disks.

We use the source counts measured with the Multiband Imaging Photometer for Spitzer (MIPS) at 24, 70, and 160 microns to determine the 5-sigma confusion limits due to extragalactic sources: 56 micro-Jy, 3.2 and 40 mJy at 24, 70 and 160 microns, respectively. We also make predictions for confusion limits for a number of proposed far infrared missions of larger aperture (3.5 to 10m diameter).