Over the past months, the MIRI Commissioning Team has been privy to some gorgeous images that we are glad to share with the public, now that all commissioning data has been released. While I am responsible for reducing and color-combining these images (and I am sure others will do a much better job at it), if published anywhere, please make sure to credit the entire "Team MIRI".
While beautiful to look at, these images were taken to commission the instrument for scientific use. Below, I give a short summary for each observation.
This is an image of a Seyfert 2 galaxy with an active center. The nucleus is quite bright at 5.6 microns, therefore produces the now familiar diffraction pattern and the MIRI curciform. Lots of background galaxies also visible, which are not present in the HST image.
The observations were carried out to test the latency of the imaging detector. To quote for the program abstract:
"The MIRI detectors can exhibit image persistence in images taken after bright sources are observed. The magnitude of the persistence is a function of flux of the source of origin as well as the time spent observing that source. This latent behaviour has been characterised during ground testing, but will need to be checked during commissioning to verify that the memory effect seen after a source has been observed on the detector, is as expected.
This CAR activity is designed to imprint an image on the imager and MRS detectors and analyse its decay (if any) for up to 25 minutes. This is felt to be sufficient to detect any large-scale changes from the on-ground behaviour. We repeat this test for a low and high background case to investigate the impact (F560W and F2100W)."
There are also 25.5 micron images available, but I only reduced the F560W images.
A shockingly beautiful planetary nebula (much like the one shown in the press release). The core of the nebula is quite small (0.2 ly radius), but is surrounded by an enormous halo (radius of 3.7 ly). The nebula is quite far, over 3000 ly from us! The central star died roughly a 1000 years ago. There are theories that the central star may have been a binary, but the MIRI image does not show this (unlike for the southern ring nebula ERO image).
The observations were carried out to study how well annealing removes latent images. To quote the program abstract:
"The purpose of the functional test is to demonstrate the ability to perform detector anneals and to assess how well they eliminate pixel effects. During the procedure, the detector heaters are turned on, one at a time, until the anneal tempertaure set point is reached, and then the detector is allowed to cool to its nominal operating temperature. The rise and return of the tempertaure is monitored in real-time to ensure it meets requirements. The standard anneals test includes full frame unbinned images before the anneal, and when the 3 detectors have been annealed a series of full frame unbinned images are taken to monitor the background and noise levels as the detectors recover (the data will be analysed off-line). The first section will be repeated at regular intervals through the commissioning period (and into normal operations), to assess how frequently the detector anneals are required.
The tuning of anneal settings will only be performed for the initial anneals test. This requires realtime commanding for the anneals (alllowing the settings to be chosen), and OSS/APT for the exposures. The settings determined from this will be transferred to OSS/APT for subsequent 'standard' anneals. The first standard anneal will still use real time commanding, as this is expected to be scheduled very soon after the initial anneals test.
MIRI should be cold and stable, detector operating temperatures optimised and stable, MIRI-002 executed successfully, and 'table 7' loaded for MIRI-focussed telemetry. The CCC is closed.
The first two standard anneals will use dark exposures to monitor the recovery. The third and fourth will use a very bright target to produce saturation, allowing the removal of latent images to the characterised. The fifth and final instance will use a normal brightness target, to provide important information on how quickly the photometry recovers after an anneal has been done."
A relatively empty region of the Large Magellanic cloud was imaged using ALL MIRI imaging filters to generate "sky" flat field images. The method was somewhat unique, dubbed the "thousand points of light", where the variation of each stellar source as they were dithered was used to measure the low-frequency component of the flat field. Aligning the images shows what MIRI is capable of in all of its filters and the production of some really nice color images (make sure to zoom in on the full resolution image).
To quote the program abstract:
"This measurement gives data the sky flat low spatial frequency component, and mask fading by the “thousand-points-of-light” technique. With this technique the overlapping regions will give the flat information. The highly overlapping mosaic gives the low spatial frequencly flat information, while the dither positions enhance the medium freq components and also the coverage of the detector. This data gives also information about cosmetics found on the detector, and also an acceptable SNR (~50-200 depending on the filter) pixel flat can be calculated using this data. The pixel flat will be compared with ground data for trending and also further improve calibration product. The correct sky flat will be measured for the first time with this measurement. Therefore acceptable SNR is necessary to calculate initial calibration product for the pipeline. The fading of the entrance mask is slightly different for the telescope background in comparison with the fading of stars. Also, this flat component is filter dependent, therefore all filters are to be measured.
This LMC field was chosen to avoid quick saturation at the shortest wavelengths by >4mJy stars. The field has only one 3.2 mJy star @ 5.6um, what gives 6 groups before 80% hard saturation. The limit for the longest wavelegths is the telescope background."
This relatively empty image was taken of a field within Corona Borealis, with the goal of studying the sky background variation as a function of telescope pointing. As always RED galaxies everywhere!
To quote the program abstract:
"This CAR aims at characterising variations in the telescope background emission spectrum observed by the MIRI imager. We will measure the observatory thermal background in the MIRI imager’s filters at two different attitude configurations: slew-to-cold and slew-to-hot. The aim is to bound the extreme cases for the thermal background emission spectrum which will be seen by MIRI during science operations.
There are already Goddard-led Comissioning Activites that include tests at hot/cold attitudes. CAR-752 and CAR-808 will keep the telescope at hot and cold attitudes for 4 and 14 days, respectively. The proposal is to run the two parts of this MIRI CAR after the telescope has moved to the hot (slew-to-hot) and cold (slew-to-cold) position. The current version of the CAR proposes four different targets. Two are in the region of the North and South Ecliptic Pole, respectively, and are alternatives to be used in the slew-to-hot observations. The other two lie close to an ecliptic latitute of about 45 degress with respect to the North Ecliptic Pole, and have been selected for the slew-to-cold observations. All four targets are regions of the sky that do not have any obvious sources in the WISE 3-bands combined image (similar wavelength coverage to MIRI).
To trace the SED of the background measured by MIRI we will use a suite of different filters. Each of the selected filters probes a regime where a different observatory component (tower, sunshield, OTE) is expected to dominate. For instance, at 12 microns the sunshield emisson, that represents one of the main contributors to the thermal background seen by MIRI, begins to contribute. We are also adding the 7.7 microns filter, to measure a wavelength region that will not have significant contributions from the thermal emission, but rather from the zodiacal light. Once the set of filters has been used, we propose repeating the observation at 12.8 microns, to measure any potential relaxation in the sunshield emission. The observing sequence will then be:
F770W, F1280W, F1500W, F1800W, F2100W, F2550W and again F1280W.
A 2x2 mosaic with 50% overlap in the F1800W filter will allow us to evaluate the presence of spatial structure in the thermal emission at longer wavelengths, and to correlate it with the measurements in all other filters. It will also provide enough coverage and redundancy to apply background matching techniques to the data. Each mosaic tile/individual pointing uses a 3-points dither pattern per filter."
MIRI was not the driving instrument for this program, rather used in parallel mode with NIRISS. While NIRISS was observing a small emission-line nebula in the LMC, MIRI was taking parallel data at various wavelengths to verify that the NIRISS spectra remained within its FOV.
Serendipitously, MIRI imaged a Mass Losing Asymptotic-Giant-Branch star. In the MIRI image you can see the dust trail the star is leaving behind (at least I am pretty sure that that is what we see). Oh, and obviously, background galaxies. They are everywhere.
To quote the program abstract:
" The wavelength dispersion solution of the GR150C and GR150R grisms of the WFSS mode will be measured at the center of the NIRISS FOV by observing an emission line source as a wavelength calibrator. Subarray exposures are also included to ensure that non-saturated direct images of the target are captured. Care should be taken to ensure that both the direct image and the 1st-order spectral traces remain within the FOV. Coordinated parallel exposures with MIRI are also included to validate this capability."
This program provided a set of images taken using the F770W filter of a field within the LMC. The PAH features are breathtaking! These images were taken on April 12/13, yielding first light images with MIRI! Amazingly, one of the fields were also imaged at F560W, yielding an opportunity to also make a color-combo MIRI image with our first-light observations. As you can imagine, seeing this in April was a joyful moment for the team.
The goals of this program were quite simple. Quoting from the program proposal:
"This proposal is to achieve better than 1 arcsec absolute pointing for MIRI during OTE commissioning. It is the implemention of OTE-34.
1. Determine the geometric distortion and plate scale of the MIRI Imager and MRS and their alignment relative to FGS1 and FGS2. 2. The SOC PRD's "MIRI_SIAF.xml" are to be updated based upon these observations. 3. These observations will also provide an estimate of possible vignetting across the MIRI FOV."
This program observed 8 different backgrounds to determine the contribution of stray light for various NIRCam and MIRI filters. Of these, one was the Galactic Center. This is possibly my favorite MIRI Commissioning image. Next to the GC, low background, 1.2 minimum zodi, and moderate background regions were also observed. All of them show interesting features.
The Galactic Center is obviously dust heavy. Separating the 7.7 and 10-12.8 mu regions is difficult, but possible. A PAH filament a the edge of the imaging region is an interesting feature.
The Low Background and the 1.2 Minimum Zodi images highlight some really red galaxies! Notice the two spirals that are only visible at 10 microns in the 1.2 Minimum Zodi image!
The PAH features are really evident in the moderate background region image.
As noted, the point of this dataset was to measure the level of stray light in the detectors. To quote from the program abstract:
"The pointed stray light observations will use multiple near-IR and mid-IR filters covering the spectral response of NIRCam and MIRI at 8 sky pointings. We also propose to characterize the background and straylight from 0.6 to 5.3 micron over the NIRSpec field of view by means of MOS observations at 3 pointings, and NIRISS imaging and grism observations at 3-5 sky pointings. The listed points (Table 1) correspond to the modeled sky pointings, one corresponds with the 1.2 min Zodi ‘Benchmark’ location, three correspond to deep field locations (or low background pointings if deep field are unavailable during commissioning), Continuous viewing zones and 3 pointings which explore stressing cases in the background model,
1) when the galactic center is observed face-on, 2) when moderate backgrounds in Zodiacal and non-Zodiacal backgrounds are observed, and 3) when Zodiacal light is at maximum with a minimum in-field contribution.
Not all pointings may be available at all times, so alternate pointings may be used."
This image was taken as part of the optical system checkout, following MIMF (muli-instrument, multi-field) alignment. As you can see, the PSFs are sharp for MIRI, so the OTE alignment went well. This may be less interesting than the other images, but it is still a nice image, so I wanted to include it, especially as it helps to understand the various instrument and system checkouts that were executed during commissinoning.
If this image is familiar, it is because you have seen it, although not exactly like this. Part of this image, the 7.7 micron filter part, was used in the famous PR image that shows the telescope field-of-view with all instruments. Not publicly known, 5.6 micron filter image was also taken, thereby allowing a color combination to be made. The resulting image is beautiful. I kept the small Lyot field in the top corner, as there is a nice small spiral galaxy in it. Enjoy!