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Proposal for SINGS MIPS-SED Observations

Proposal for SINGS MIPS-SED Observations. `Compromise’ is our Motto Daniela, Chad, Danny, and George H. Supporting document from Chad can be found at: http://sings.stsci.edu/teamarea/reports/reports.htm#tech. Background.

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Proposal for SINGS MIPS-SED Observations

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  1. Proposalfor SINGS MIPS-SED Observations `Compromise’ is our Motto Daniela, Chad, Danny, and George H. Supporting document from Chad can be found at: http://sings.stsci.edu/teamarea/reports/reports.htm#tech

  2. Background The less-than-perfect performance of MIPS-SED dictates that some compromises need to be identified to conduct the MIPS-SED portion of the SINGS project. A thorough analysis done by Chad, using as reference the IRAS 60 mm high-resolution images of the SINGS galaxies, suggests that with the original observing strategy of reaching S/N>=5 at ½ R25 in 240 sec exposure per point (as in the proposal), we can only observe 23 galaxies out of 75. If we relax the ½ R25 requirement, and accept that we will only reach S/N>=5 at 1/3 R25, we can observe 39 galaxies with the default strategy.

  3. Background (cont’d) The basic parameter space (morphology, LIR/Lopt, F60/F100, LIR, and SFR) covered by the MIPS-SED-`observable’ samples with these two options (1/3 R25 or ½ R25) are compared against the original SINGS sample in the next Table and plots. The Table and three pages of plots compare the following three sets: • The original sample of 75 galaxies. • The sample of galaxies for which MIPS-SED can reach S/N>=5 in 240 seconds per point at a distance from the galaxy’s center of 1/3 R25. • The sample of galaxies for which MIPS-SED can reach S/N>=5 in 240 seconds per point at a distance from the galaxy’s center of 1/2 R25; this is the original proposal’s requirement. The plots and table actually include those galaxies for which the required S/N is reached within 255 seconds per point (rather than 240 seconds).

  4. Original Sample MIPS SED at 1/3 R25 MIPS SED at ½ R25

  5. Original Sample MIPS SED at 1/3 R25 MIPS SED at ½ R25

  6. Original Sample MIPS SED at 1/3 R25 MIPS SED at ½ R25

  7. Problems • In either case, cool-dust/IR-weak galaxies are lost from the MIPS-SED sample (blue box in the first set of plots). The vast majority of these are the Irregular galaxies, that are disproportionately selected out, as only 3 out of 17 are retained with the above selection criteria. • Whatever the selection criterion, some important galaxies, e.g., M81, NGC1705, NGC2915, NGC4826, are lost from the MIPS-SED sample. • If we were to go for the original proposal’s requirement (S/N=5 at ½ R25), we would lose even more important galaxies, e.g. NGC7331, NGC4536, NGC4736, NGC1097, NGC3621, NGC4569 to name a few.

  8. Necessary Compromises • There are two basic compromises we need to accept up-front in order to construct a scientifically meaninful MIPS-SED program with the available time: • Assume that S/N=5 at ½ R25 is infeasible with the established MIPS-SED performance, and accept the new requirement of reaching S/N=5 at 1/3 R25; going out to 1/3 R25 will still provide us with plenty of important data and information, as a significant fraction of our galaxies have R25> 3’-5’, but we will lose the external regions of galaxies; • Relax the sample’s observational `uniformity’ in favor of preserving representation of the SINGS baseline parameter space; some galaxies (20) will have `tailored’ observing strategy to increase the total `observable’ sample to 59.

  9. Proposed Strategy (due entirely to Chad’s hard work) • 39 galaxies will be observed with the baseline observing strategy of 240 sec per point + the 10 added raster points [see Chad’s memo also for list of galaxies]; • 5 galaxies will be observed with 360 sec per point: ngc855, ngc1705, ngc3031, ngc4826, ngc4625; • 10 galaxies observed with 1 pointing only (240 sec), as the IRAS images show very concentrated IR emission: ngc3198, ngc6822, ngc2841, ngc4594, ngc925, ngc5033, ngc1512, ngc1291, ic2574, ngc1316; • 5 galaxies compact but fainter than point 3, and observable with 1 extra cycle (360 sec) and 1 pointing: ngc2915, ngc5474, ngc4450, ngc24, HoII. • The total is 59 galaxies in 68 hours.

  10. Strategy (2) The proposed program will use 68 of the ~73 hours allocated to MIPS-SED; the remaining time may be kept in reserve for `surprise’ targets that although currently `below the cut’ (I.e., not detected by IRAS/HIRES) may reveal unexpected emission in the MIPS images (e.g.., highly concentrated knot(s) of emission). The galaxies that are not making the cut are: IC4710, ngc4725, ngc4552, ngc4125, ddo053, ngc4236, ddo165, m81dwb, ngc584, ddo154, ngc3190, ngc1404, HoIX, HoI, ngc5866, m81dwa. These do not show measurable flux in the IRAS HIRES images. The next three pages compare the parameter space coverage of the MIPS-SED `optimized’ sample of 59 galaxies with the original SINGS sample. Most of the parameter space coverage is preserved in the `optimized’ sample.

  11. Original Sample Optimized Sample

  12. Original Sample Optimized Sample

  13. Original Sample Optimized Sample

  14. Observing Timeline/Priorities • It is also desirable to follow a tailored observing timeline for the optimized sample. In particular, it is proposed: • To release the galaxies in subgroups 1 and 2 (of the Proposed Strategy) for observation with MIPS-SED immediately following the validation observations (see next slide); these are the `bright’ galaxies in our optimized sample and should not present problems. • To defer MIPS-SED observations of the galaxies in subgroups 3 and 4 until we get and evaluate the MIPS images for these galaxies. These are the `faint’ galaxies in our optimized sample, and a conservative approach is advisable.

  15. Validation Observations for MIPS-SED • The validation observations should contain two galaxies: 1 of the intermediate-brightness galaxies in subgroup 1 to verify the observing strategy; and 1 of the brightest in our sample to check for potential saturation problems/work-arounds. • The two proposed galaxies are: • NGC7331 (intermediate brightness, visibility: end-May/begin-July): this is our generic validation galaxy, and has already all the other SPITZER data available; these data will be used to compare MIPS-SED actual results with expected results (sanity check); • NGC7552 (one of the brightest, visibility: mid-June/begin-Aug): this galaxy has a relatively small R25, and fairly gently declining luminosity profile up to ½ R25. Will offer the best check of saturation problems if present, while at the same time not using a large amount of observing time.

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