Another ghostly spiral galaxy revealed by JWST

The famous American baseball player once said, “You can observe a lot of things just by looking.” This is certainly the case of the JWST, which has just published its latest “cobweb” image of a distant galaxy. He “looked” at IC 5332 using the on-board Mid-Infrared Instrument (MIRI). In the process, he observed dramatic details that are difficult to see in visible light.

IC 5332 is just under 30 million light years away and a bit larger than the Milky Way. It is a relatively dim galaxy, and a favorite of amateur astronomers. A quick glance shows it quietly forming stars in various parts of its arms. There is also a lot of dust in IC 5332. A Hubble Space Telescope image reveals piles of hot young stars and a nice spiral structure, but JWST and MIRI were able to see past the dust and show us a skeletal structure very tangled.

A look at the ghostly bones of IC 5332 with JWST

The Webb view of IC 5332 is one of many observations that will examine the structures of galaxies. We see the galaxy here unlike a Hubble view taken a few years ago. The Hubble image is part of a survey of galaxies called “High Angular Resolution Physics in the Neighboring Galaxy-HST” (PHANGS-HST). The idea is to use Hubble images and ALMA (Atacama Large Millimeter Array) data to create a dataset mapping the connections between young stars and cold molecular gas in different galactic environments. The Hubble image of this galaxy shows bright young stars (blue) and dark regions that appear to separate the spiral arms.

HST image of IC 5332 to compare to JWST image
The winding spiral structure of the galaxy IC 5332 as seen by NASA/ESA’s Hubble Space Telescope. Hubble’s Wide Field Camera 3 (WFC3) separates the arms of the galaxy from the dark specks of dust in between, which block ultraviolet and visible light to which Hubble is sensitive. Younger and older stars can be differentiated by their colors, showing how they are distributed in the galaxy. JWST’s MIRI image (above) offers a very different view, instead highlighting patterns of gas propagation in the galaxy. ESA/Webb, NASA & CSA, J. Lee and the PHANGS-JWST and PHANGS-HST teams

Data and imagery from JWST show more of a continuous tangle of structures that echo the shape of the spiral arms. The very different views of the galaxy are due to the presence of dusty regions. Note that different stars are visible in the two images. This is because some stars shine brighter in different wavelengths. The brightest in the infrared and ultraviolet are more hidden by dust and therefore less visible on the HST image. With its ability to see infrared more easily, the JWST MIRI instrument gives us a glimpse into the “bones” of the galaxy.

What bones can tell us

Both JWST and HST collect data on one of the most fascinating processes in galaxies: star birth. To understand this, astronomers examine stars, star clusters, associations, and star birth regions in galaxies. This is what PHANGS-HST does. The idea is to create a catalog of over 100,000 molecular clusters, associations and clouds. Eventually, this data will help them understand star formation times, the amount of gas in a given galaxy, the evolution of star-forming clouds, and even the structure of the galaxy itself.

JWST takes inspiration from PHANGS-HST data to focus on selected galaxies in the infrared to give a multi-wavelength view of their activities. The MIRI instrument is particularly well suited to scrutinize the dusty environment of the IC 5332. It is a supercooled instrument sensitive to a range of light between 5 and 28 microns in the mid-infrared part of the electromagnetic spectrum. This gives him a perfect window into the skeleton of this beautiful galaxy.

For more information

Webb’s frozen instrument reveals complex structures