Galaxy source counts at 7.7 $\mu$m, 10 $\mu$m and 15 $\mu$m with the James Webb Space Telescope

TL;DR

This paper presents deep mid-infrared galaxy counts from JWST's early observations, revealing unprecedented sensitivity and confirming models of faint infrared sources aligned with cosmic star formation history.

Contribution

First mid-infrared galaxy counts from JWST's early data, extending sensitivity by 100 times and validating evolutionary models of faint infrared sources.

Findings

Number counts reach 0.32-2.0 μJy, much deeper than previous telescopes.

Extrapolated models match observed counts, confirming understanding of faint IR sources.

Deep counts reveal PAH emission features and support cosmic star formation history.

Abstract

We present mid-infrared galaxy number counts based on the Early Release Observations obtained by the James Webb Space Telescope (JWST) at 7.7-, 10- and 15-$\mu$m (F770W, F1000W and F1500W, respectively) bands of the Mid-Infrared Instrument (MIRI). Due to the superior sensitivity of JWST, the 80 percent completeness limits reach 0.32, 0.79 and 2.0 $\mu$Jy in F770W, F1000W and F1500W filters, respectively, i.e., $\sim$100 times deeper than previous space infrared telescopes such as Spitzer or AKARI. The number counts reach much deeper than the broad bump around $0.05\sim0.5$ mJy due to polycyclic aromatic hydrocarbon (PAH) emissions. An extrapolation towards fainter flux from the evolutionary models in the literature agrees amazingly well with the new data, where the extrapolated faint-end of infrared luminosity functions combined with the cosmic star-formation history to higher redshifts can reproduce the deeper number counts by JWST. Our understanding of the faint infrared sources has been confirmed by the observed data due to the superb sensitivity of JWST.