5. Deep Imaging of Five Galaxy Clusters at 24 - 160 microns using MIPS

In the previous chapter, we described the procedure to develop a deep, small area, imaging campaign using IRAC, covering the 3.6 - 8.0 micron range. In this chapter, we describe a complementary project to image the same regions of sky, in the 24 - 160 micron wavelength range, using the Multiband Imaging Photometer for Spitzer (MIPS).

MIPS is designed to provide the Spitzer Space Telescope with diffraction limited imaging capability, with noise performance limited by natural sources, over the wavelength range from 20 to 180 microns. The instrument utilizes three detector arrays. These arrays provide photometric bands centered at 24, 70, and 160 microns respectively and a low-resolution spectroscopy mode covering 55 to 95 microns.

The MIPS Photometry and Super Resolution Mode allows accurate photometric measurements of sources using multiple and precise sampling of the 24, 70, and 160 micron MIPS bands employing a sequence of inertially fixed pointing positions. Super Resolution is enabled through precise fractional pixel pointing offsets in the standard dither patterns, and by the optional fine pixel scale optical path to the 70 micron array.

The 24 micron array enjoys a $5\hbox{$.\!\!^{\prime}$}4 \times 5\hbox{$.\!\!^{\prime}$}4$ field of view ( $128 \times 128 \; {\rm pixels}$, with $2\hbox{$.\!\!^{\prime\prime}$}55 \; {\rm per \; pixel}$). The 70 micron array large field has an instantaneous field of view of $\simeq 5\hbox{$.\!\!^{\prime}$}2 \times 2\hbox{$.\!\!^{\prime}$}6$ $(\simeq 32 \times 16 \; {\rm pixels}, \; 9\hbox{$.\!\!^{\prime\prime}$}98 \; {\rm per \; pixel})$, not including the noisy side B of the 70 micron array (see SOM, § 8.1.2.1), while the 160 micron band has an effective, unfilled field of $0\hbox{$.\!\!^{\prime}$}5 \times 5\hbox{$.\!\!^{\prime}$}3$ ( $2 \times 20 \; {\rm pixels}$, $16\hbox{$.\!\!^{\prime\prime}$}0 \; {\rm per \; pixel}$) that has a $0\hbox{$.\!\!^{\prime}$}25$ gap down the middle. In practice, scan mirror motions are used to fully sample the PSF at 160 microns.

The scan mirror can also deflect the beam to provide two alternate functions for the 70 micron array. In one position, a different set of re-imaging optics provides a higher magnification, with a field of $2\hbox{$.\!\!^{\prime}$}7 \times 1\hbox{$.\!\!^{\prime}$}35$; the improved pixel sampling will be used to achieve ``super resolution'' (i.e., to exceed the traditional Rayleigh criterion of resolution) through data processing. The pixel scale is $5\hbox{$.\!\!^{\prime\prime}$}20 \; {\rm per \; pixel}$ in super resolution mode (compared with $9\hbox{$.\!\!^{\prime\prime}$}98 \; {\rm per \; pixel}$ in default mode). In another position, the beam is sent to the low resolution spectrometer (SED mode). The observer can choose to observe in one, two, or all three bands.