The universe as seen by JWST/MIRI

The recently commissioned James Webb Space Telescope (JWST) is already revolutionizing our view of the universe, for instance by finding more very high redshift galaxies than pre-launch estimates and peeking deeper into the dusty star-forming clouds in the Milky Way and nearby galaxies, resolving the structure of their interstellar medium (ISM).

Of the instruments on JWST, the Mid-Infra Red Instrument (MIRI) is unique in probing wavelengths beyond 5 microns, and unlike other JWST instruments, MIRI was built by a consortium of European (MIRI-EC) and US research institutes, and with Swedish participation (supported by SNSA and KAW). In return for the investments, MIRI-EC were awarded 450 hours of guaranteed time observations on JWST.

One of the largest time investments of the MIRI-EC GTO was deep imaging of the Hubble Ultra Deep Field at 5.6 microns, and medium resolution spectroscopy (MRS) of individual high redshift (z) galaxies and quasars.

The 5.6 micron observations have successfully identified Ha-alpha emitters at z>7, optical restframe emission at z>7, morphologies of galaxies at z»1-7, and discovered MIRI extremely red objects; whereas the MRS spectroscopy has probed the ionized ISM kinematics, star-formation and dust properties of several high-z objects.The 5.6 micron imaging will be followed up in cycle 3 with 7.7 and 10 micron imaging of the same field through MIDIS-Red, the first open time Swedish led large program on JWST, opening up exciting science opportunities, e.g. to find z>9 high-z Ha emitters, quantify the star formation history of galaxies in the epoch of reionisation, and study the co evolution of galaxies and active galactic nuclei (AGN) at cosmic noon (z= 1 to 4).

In addition, a cycle 3 medium size program led by our MIRI-EC collaborator, will provide 7.7 and 10 micron imaging of two strong lensing galaxy clusters, allowing the science themes for MIDIS-Red to explored over a larger area.In parallel to the MIRI imaging, MIDIS-Red will observe a parallel field with NIRCam, obtaining some of the deepest images of the universe as yet (32 magnitude), and allow for finding galaxy candidates at z=12-20.

The MIRI-EC GTO MRS observations of high-z galaxies will continue into Cy 3.

In addition we will obtain MIRI Low Resolution Spectroscopy (LRS) of a dusty z=2 galaxy detected with ALMA, and also test the capabilities of LRS in a slitless survey mode. Moreover, we will observe some low-z galaxies regarded as analogues of galaxies that reionised the universe.

Through a MIRI+NIRSPEC team collaboration we will observe the 1-28 micron spectrum of the ultra metal-poor dwarf SBS0335-05; as well as open time MIRI/MRS observations of 4 galaxies from the Low z Lyman Continuum Survey; to explore the inter stellar medium and AGN presence in such galaxies.

Finally we will complete a combined JWST+HST study of IZw18, the most metal-poor blue compact dwarf galaxy that can be resolved into individual stars. This galaxy hosts many hot stars emitting hard ionising photons.

With JWST we have identified the red luminous stars, and by adding UV observations from HST, we will get a complete census of the young population, to address questions related to stellar evolution, the origin of HeII emission, and the extinction law at ultra-low metallicity, relevant for galaxies at cosmic dawn.The project builds on the successful implementation of the MIRI-EC GTO and the expertise gathered with MIRI over many years.