  We present the analysis of the stellar population and star formation history
of 181 MIRI selected galaxies at redshift 0-3.5 in the massive galaxy cluster
field SMACS J0723.3-7327, commonly referred to as SMACS0723, using the James
Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI). We combine the data
with the JWST Near Infrared Camera (NIRCam) catalogue, in conjunction with the
Hubble Space Telescope (HST) WFC3/IR and ACS imaging. We find that the MIRI
bands capture PAH features and dust emission, significantly enhancing the
accuracy of photometric redshift and measurements of the physical properties of
these galaxies. The median photo-z's of galaxies with MIRI data are found to
have a small 0.1% difference from spectroscopic redshifts and reducing the
error by 20 percent. With MIRI data included in SED fits, we find that the
measured stellar masses are unchanged, while the star formation rate is
systematically lower by 0.1 dex. We also fit the median SED of active galactic
nuclei (AGN) and star forming galaxies (SFG) separately. MIRI data provides
tighter constraints on the AGN contribution, reducing the typical AGN
contributions by ~14 percent. In addition, we also compare the median SED
obtained with and without MIRI, and we find that including MIRI data yields
steeper optical and UV slopes, indicating bluer colours, lower dust
attenuation, and younger stellar populations. In the future, MIRI/MRS will
enhance our understanding by providing more detailed spectral information and
allowing for the study of specific emission features and diagnostics associated
with AGN.
