MIRI Deep Imaging Survey of the HUDF

The HUDF is one of the most observed extragalactic fields, with extensive multi-wavelength coverage, where (before JWST) galaxies up to z~7 have been confirmed, and at z>10 suggested, from HST photometry. We aim to characterise the galaxy population in HUDF at 5.6um, enabling studies such as: the rest frame NIR morphologies for galaxies at z<4.6, probing mature stellar populations and emission lines in z>6 sources, intrinsically red and dusty galaxies, and active galactic nuclei (AGN) and their host galaxies at intermediate redshifts.

We have reduced the MIRI data using the official JWST pipeline, augmented by in-house custom scripts. We measure the noise characteristics of the resulting image. Galaxy photometry has been obtained, and photometric redshifts have been estimated for sources with available multi wavelength photometry (and compared to spectroscopic redshifts when available).

Over the deepest part of our image the 5 sigma point source limit is 28.65mag AB (12.6nJy), ~0.35mag better than predicted by the JWST exposure time calculator. We find ~2500 sources, the overwhelming majority of which are distant galaxies, but note that spurious sources likely remain at faint magnitudes due to imperfect cosmic ray rejection in the JWST pipeline. More than 500 galaxies with available spectroscopic redshifts, up to z~11 have been identified, the majority of which are at z<6.

More than 1000 galaxies have reliable photometric redshift estimates, of which ~25 are at 6<z<12. The point spread function in the F560W filter has a FWHM of ~0.2 arcsec (corresponding to 1.4kpc at z=4), allowing the near infrared rest frame morphologies and stellar mass distributions to be resolved for z<4.5. Moreover, >100 objects with very red Near Infrared Camera (NIRCam) vs MIRI (3.6-5.6um>1mag) colours have been found, indicating dusty or old stellar populations at high redshifts.

We conclude that MIDIS surpasses preflight expectations and that deep MIRI imaging has great potential for characterizing the galaxy population from cosmic noon to dawn.