5.1 Overview of the Program

In this section, we summarize the steps followed to design the deep imaging MIPS program. This will serve both as a one-stop resource for those requiring only an overview of how to do such a program, and also as a roadmap of where to find more detailed information later in this chapter.

• Target Selection: This program is tied to a complementary IRAC program, developed in the previous chapter (§4). We use the same targets as were selected for that program. See §4.2 for further details.

• Background Estimate: We use Spot to obtain a background estimate at each of the target positions. In general, the background is characterized qualitatively by three levels (low, medium and high), and for these targets, the IR background in the MIPS wavelength regime is low/medium. See §5.2.

• Exposure Time Estimate: Equipped with the background characterization above, we look at the MIPS sensitivities for low, medium and high backgrounds, respectively. This enables an estimate of the required exposure time to reach a desired signal-to-noise ratio for point source detection.

  For MIPS, the 1-sigma confusion limit is $\simeq 1 \; {\rm mJy}$ at 70 microns and $\simeq 15 \; {\rm mJy}$ at 160 microns (Xu et al., 2001, ApJ, 562, 179; Franceschini et al., 2002, astro-ph/0202463; Dole et al., 2002, ApJ, 585, 617).

  For the 70 micron array, the low background sensitivity is approximately $1.2 \; {\rm mJy}$ $(1\sigma)$ in 500s for the default pixel scale. Similarly, for the 160 micron array, the low background sensitivity is approximately $3 \; {\rm mJy}$ $(1\sigma)$ in 500s. Hence, adopting a goal of imaging to the confusion limits in these passbands, we will require $\simeq 500 \; {\rm sec}$ at 70 microns, and $\simeq 20 \; {\rm sec}$ at 160 microns.

  At 24 microns, and finite observation times, the confusion limit is effectively never reached in regions of low background. In 500 seconds, with low/medium background, the $1\sigma$ sensitivity is $\simeq 20 \; \mu{\rm Jy}$. See §5.3.

• Filling out the MIPS Photometry/Super Resolution Imaging AOT: See §5.4 for details, and Figures 5.8 and 5.9 for screen captures of the completed AOTs.
  • For the 24 micron array, we select the large field size, with a minimal offset to the sky field; this, in effect, doubles our exposure time at the target position, and covers a $\sim$5 arcminute square FOV, with 24 exposures per pointing; see §5.4.1. We use an exposure time of 30 seconds, and one cycle. This yields 375.4 s on each of the science and sky fields, which are the same, and so an effective total exposure time of 751 s on our target field; see §5.4.2.

  • For the 70 micron array, we select the default pixel scale and small field of view, and use a Fixed Cluster-offsets target, observe the offsets only, with offsets $(0,80^{\prime\prime})$, and $(0,-80^{\prime\prime})$ in array coordinates. This again covers a $\sim$5 arcminute square FOV, with 10 exposures per cycle on the target; see §5.4.1. We use an exposure time of 10 seconds, and 5 cycles. This yields 545 seconds on target; see §5.4.2.

  • For the 160 micron array, we select the large field of view. This also covers a $\sim$5 arcminute square FOV, with one exposure per cycle on the target; see §5.4.1. We use a exposure time of 10 seconds, and 4 cycles. This yields 41.9 seconds on target; see §5.4.2.

• Duration: The total duration for this and the IRAC program developed in the last chapter is 22 hours. See §5.5.

• Constraints: In order to constrain the MIPS and IRAC observations to have the same (or similar) PA, we place a group-within constraint so that the IRAC and MIPS observations occur within 14 days of each other. See §5.6.

• Visualization: We visualize the observations as an overlay of the MIPS arrays on Digital Sky Survey and IRAS images of the clusters; see Figures 5.4, 5.7 and 5.5 .