---------------------------------------------- Checklist for IRS/SINGS validation on NGC 7331 ---------------------------------------------- Summary ------- -Critical Tests: The IRS data for NGC 7331 meet all of the critical IRS tests for the SINGS project: data accountability and integrity; pointing; sensitivity; and LL background. SH and LH cubes have not yet been created, so the ultimate centering of the high res cubes cannot yet be determined. However, the SH map appears to be centered based on the relative emission strength of the emission in the various high res pointings; for LH there is strong line emission in several pointings so the centering issue will remain unclear until we build an actual cube. The validation data emphasize the power of SL; the SINGS project would benefit from larger (2x) SL maps. The time can be obtained mostly from the time savings garnered by the fact that LL is wider and longer than reported in the original SOM--our LL maps now require fewer slit-perpendicular and slit-parallel steps to cover the same area. -Non-critical Tests: Cubism is progressing nicely. We can make excellent SL and LL cubes. SH and LH cubes are next on the docket. There are some minor issues that need to be resolved; they are listed in the Appendix. The preliminary wavelength calibration looks promising. Some of work is pending calibration files from the SSC. Preliminary cross-instrument and cross-observatory flux calibration work has been carried out. SL and ISOCAM data agree within a factor of two. There are no major fringing or stray light issues to stop SINGS from proceeding. use ======================================================================== Appendix for IRS/SINGS validation on NGC 7331 ============== Critical Tests ============== The following assessments are critical for further acquisition of IRS/SINGS data to continue as currently specified by the AORs. (1) Data Accountability and Integrity - Compare requested and expected number of raw DCEs and processed BCDs, mask files, extracted spectra, and ancillary data files. (did we receive all the expected files?) RESPONSE: We received all of the expected and necessary data. - Were there any corrupted data that will prevent our completion of any of the critical analysis tasks listed below (#2-4)? If so, do we need a re-transmission of data from JPL or the spacecraft? If data were corrupted on board (due to CR's, instrument anomalies, etc.) do we need to re-observe all or part of NGC 7331? RESPONSE: The data were not corrupted so as to prevent validation. - Were there significant saturated spectra that make validation of the data or data-taking strategy impossible? Has stray light from the peak-up arrays severly contaminated the SL2 spectra (see also #8, below)? RESPONSE: The data were not saturated so as to prevent validation, and peak-up stray light was not severe enough to prevent validation. (2) Pointing - Compare requested and reconstructed pointing for all IRS DCEs. * Is the center of the map consistent with the nucleus or HII region? Are there global offsets beyond the reported pointing accuracies of SIRTF and the IRS? These could indicate a problem with the pointing for NGC 7331 or the pointing reconstruction at the SSC. RESPONSE: The SL and LL maps created with Cubism nicely show that we are centered on the nucleus. SH and LH cubes have not yet been constructed There is no global offset beyond the reported pointing accuracy. * Are the positional offsets consistent with those requested over the entire map? This should be evaluated between slit positions and also between map legs. Requested positions are indicated by header keywords (RA,DEC,PA)_RQST in the BCDs. Reconstructed positions, based upon the current Observer, are indicated by header keywords (RA,DEC,PA)_FOV and (RA,DEC,PA)_SLT in the BCD (bcd_fp.fits files). RESPONSE: The issue of commanded vs expected positions is fine, as evidenced by the structure of the contructed map of the ring. (3) Sensitivity (and mapping redundancy) - Do the reported sensitivities of all four modules fall within the tolerances of the existing program? This can be answered without reference to NGC 7331 data. RESPONSE: The sensitivities of our data, and the signal-to-noise achieved for each IRS module, are generally in line with our expectations. (Show figure) SH: 3sigma: 2e-18 W/m^2 Goal: 5e-18 W/m^2 SOM: 2e-18 W/m^2 0.42e-17 W/m^2 for 30x2=60s + 4x redundancy S/N: 6 and 7 for [Ne III] and [Ne II] LH: 3sigma: 5e-18 W/m^2 Goal: 5e-18 W/m^2 SOM: 5e-18 W/m^2 1e-17 W/m^2 for 60s @ 34um + 4x redundancy S/N: 10 and 25 for [SIII] and [SiII] SL: 3sigma: 0.4-4 mJy for off-source ("background") Goal: 3 mJy SOM: 0.4/1.3 mJy 0.6/1.8 for 60/14s extranuc/nuc + 2x redund S/N: 5 to 20 ranging from nuc to interarm continuum LL: 3sigma: 1-4 MJy/sr Goal: 1-2 MJy/sr SOM: 1-8 MJy/sr 2-16 MJy/sr for 30s + 4x redundancy S/N: - Do our validation data suggest a deviation from the reported values which would compromise the program and/or force a revision in data-taking strategy (see #4 and #7, below)? RESPONSE: No. - If pointing and offsets were as commanded (see above), and the instrument response is as expected, is there adequate redundancy and slit overlap in our nominal data-taking strategy to ensure high S/N cubes and maps? This is particularly important for the SL spectral maps. RESPONSE: The validation data emphasize the power of SL; the SINGS project would benefit from larger (2x) SL maps. The time can be obtained mostly from the time savings garnered by the fact that LL is wider and longer than reported in the original SOM--our LL maps now require fewer slit-perpendicular and slit-parallel steps to cover the same area. (4) Removal of Slit Backgrounds [less critical than 1-3, above] - To what extent can data in the "wings" of the LL spectral maps be used to assess and remove the local backgrounds? Are the LL flanking fields spatially flat? Do we need to revise our data- taking plan to include real off-galaxy spectra? RESPONSE: The LL emission from NGC 7331 drops off fast enough radially, such that our LL map is large enough to get a good estimate of local backgrounds. ================== Non-Critical Tests ================== IRS/SINGS data can continue being taken, and non-critical issues will be addressed concurrently. (5) Cubism Functionality - Verify that CUBISM can read all the BCDs, extract the necessary header information and assemble the cubes. * Are there any artifacts in the cubes or extracted maps which cannot be explained via data-taking (e.g. stepping) anomalies addressed above? RESPONSE: There are unmasked and/or uncorrected hot pixels in all modules' data. This will probably not warrant a change of observing strategy. * Can anomalies in the cubes or maps be removed by modifying CUBISM in a reasonable amount of time -- without affecting our delivery schedule? RESPONSE: Yes. * Is the pointing information for each BCD accounted for correctly, such that multiple epochs of data will not pose problems? RESPONSE: Incorrect reconstructed positions are a minor (and hopefully temporary) inconvenience, preventing us from testing map astrometry refinement using the reconstructions. * Are there any irregularities in the regions of order overlap? If so, are these indicative of a problem in cubism, or the IRS pipeline products - e.g. flat fielding or stray light removal, (see #8, below). Can the overlapping scan legs be "seamlessly" combined to produce a map? RESPONSE: SH shows continuum oscillations in multi-order spectra. There are flat-field residuals in the high res BCDs that may be related. * Are the delivered uncertainty images useful for weighting and rejecting data from the extremities of the order/slit? RESPONSE: Valid uncertainty images are not yet produced by the IRS pipeline for testing. * Is there a significant difference in the maps when using the reconstructed vs. the requested offsets? RESPONSE: We can't perform reconstructed map builds because of the keyword errors. (6) Calibration Products - Are all requisite calibration products available in the correct formats? These include wavelength and order position solutions, permanent mask files, and flux calibration files/keywords. RESPONSE: There a few outstanding issues with calibration files. There are problems with LL's WAVSAMP, etc., and SL cubes are based on ground- based calibrations known to be wrong, etc. We haven't evaluated the high-res calibration data yet. - Does the calibration match pre-launch expectations? If not, will significant deviations require changes to the established cube-building algorithms? RESPONSE: Wavelength calibration hasn't been tested at all, but presumably the IRS team has looked into it. However, we have looked at the fitted central wavelengths to several lines in HighRes maps, and the results are encouraging. Accounting for a redshift of 816 km/s, we find: ------------------------------------------------- line rest expected observed diff obs-exp lam/R um um um % um um ------------------------------------------------- SIII 33.482 33.573 33.535 0.10 -0.038 0.056 SiII 34.815 34.910 34.906 0.01 -0.004 0.058 NeII 12.814 12.849 12.853 0.03 0.004 0.021 NeIII 15.555 15.597 15.605 0.05 0.008 0.026 ------------------------------------------------- LL seems to have inaccurate positions on the array for both orders, but we need to confirm this before we send it to SSC (they may not care anyway). (7) IRS - IRAC - MIPS cross-calibration - Verify calibration consistency through direct comparison to ISO maps. RESPONSE: We have carried out such an analysis, but beware the caveats: -The maps of the archive in LW8 (10.7-12.0um) and LW9 (14.0-16.0um) suffer from a flat-field artefact superposed right onto the nucleus, so we did not use them in the comparison. -The apertures used for 1D spectrum extraction from the IRS data are very small, smaller than the angular resolution of the ISOCAM maps. It's simply meaningless to do such a comparison. We tried to replace the large PSFs in the ISOCAM maps with gaussians of the appropriate width, but it's clearly not a rigorous solution. -The IRS photometric aperture positioning is not known with enough accuracy. -Subtraction of the zodiacal emission was based estimates from Spot. LW2 band (5-8.5 microns, corresponds to SL2) : aperture = 3.6" x 5.4" ISOCAM flux between 10.7 and 14.9 mJy (depending on exact aperture position, correction for flux dilution or not). IRS flux = at least 1.87 times the ISOCAM flux. This may be because the aperture is way too small, but the shape of the SL2 spectrum is not credible (weird slope and no 7.7 micron PAH, whereas PAHs jump out in SL1). LW3 band (12-18 microns, corresponds to SH) : aperture = 4.6" x 11.5" ISOCAM flux between 16.5 and 19.5 mJy. IRS flux = at maximum 0.35 times the ISOCAM flux. Anyway it's meaningless to measure the continuum in the high-resolution modules. Shape of the spectrum not credible (trough at 14-16 microns, with negative fluxes (masked out for flux measurement), other weird things). LW6 band (7.0 - 8.5 microns, corresponds to SL2) : aperture = 3.6" x 5.4" ISOCAM flux between 11.1 and 15.3 mJy. IRS flux = at least 1.59 times the ISOCAM flux. LW7 band (8.5 - 10.7 microns, corresponds to SL1) : aperture = 3.6" x 5.4" ISOCAM flux between 7.4 and 13.4 mJy. IRS flux = at least 1.18 times the ISOCAM flux. The spectrum looks decent until 14 microns. - Generate maps over relevant IRAC and MIPS filter bandpasses and compare to IRAC and MIPS data directly after extracting to the same projected aperture. This will require co-ordination with IRAC/MIPS groups. Is there a systematic offset in one of the derived products that is indicative of a change in sensitivity or an effect not documented by the IRAC, MIPS or IRS teams during IOC or SV? RESPONSE: This has not been done. - Do the IRS flanking peak-up fields sample backgrounds match what we derive from the slit perimeter fields (see #4, above)? Use SPOT visualization to verify peak-up and slit perimeter overlap. RESPONSE: This has not been done. (8) IRS Pipeline - Is fringing adequately removed by the pipeline flat-fielding? RESPONSE: Without a rigorous analysis, it appears that the pipeline processing will be sufficient. However, we need to build high-res cubes before this issue can be properly addressed. Fortunately, we can already tell that this will not be a show-stopper. - Are Peak-Up stray light and high-res crosstalk removal modules functioning well enough to use corrected BCD products as inputs to cubism? RESPONSE: Yes. The BCD products are OK for cubism. This is not a critical issue for validation. We are seeing some scattered light in the peakup arrays, but this is not an issue for validation and is not really a problem for SINGS. At the 5% level it would prevent people from taking the PU images in a spectral map and getting a "bonus" image which is well calibrated, but only if they were mapping a bright source.