COSMOS-Web: MIRI Data Reduction and Number Counts at 7.7 <i>μ</i>m Using JWST

Abstract The COSMOS-Web survey is the largest JWST Cycle 1 General Observer program, covering a contiguous ∼0.54 deg 2 area with NIRCam imaging in four broadband filters and a noncontiguous ∼0.2 deg 2 with parallel MIRI imaging in a single broadband filter, F770W. Here we present a comprehensive overview of the MIRI imaging observations, the data reduction procedure, the COSMOS-Web MIRI photometric catalog, and the first data release including the entire COSMOS-Web MIRI coverage. Data reduction primarily relies on the JWST Science Calibration Pipeline, supplemented by custom background subtraction to mitigate prominent instrumental artifacts and sky background within the MIRI images. We reach 5 σ (point source) limiting depths ( m F770W ∼ 25.51 based on r ∼ 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>″</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 3 circular apertures) that are significantly better than initial expectations. Using the images provided in this release, we construct a photometric catalog and compare the F770W flux densities to the Spitzer/IRAC CH4 measurements from the COSMOS2020 catalog (for CH4 detections with signal-to-noise ratio S/N &gt; 5). We find that these are in reasonable agreement with a small median offset of &lt;0.05 mag. We also derive robust 7.7 μ m number counts spanning five orders of magnitude in flux (∼0.2–2300 μ Jy)—making COSMOS-Web the only JWST survey to date to sample such a large flux range—which are in good agreement with estimates from other JWST and IRAC surveys.