Another Ghostly Spiral Galaxy Revealed by JWST

The famous American baseball player once said, “You can observe a lot just by watching.” That’s certainly true of the JWST, which just released its latest “spider-web” image of a distant galaxy. It “watched” IC 5332 using the onboard Mid-InfraRed Instrument (MIRI). In the process it observed spectacular details not easily seen in visible light.

IC 5332 is just under 30 million light-years away and a bit bigger than the Milky Way. It’s a relatively dim galaxy, and a favorite of amateur stargazers. A quick look shows that it’s quietly forming stars in various parts of its arms. There’s also a great deal of dust in IC 5332. A Hubble Space Telescope image reveals scads of hot young stars and a lovely spiral structure, but JWST and MIRI were able to see past the dust and show us a very tangled skeletal structure.

Peeking at the Ghostly Bones of IC 5332 with JWST

The Webb view of IC 5332 is one of many observations that will look at galaxy structures. We see the galaxy here in contrast to to a Hubble view taken a few years ago. Hubble’s image is part of a survey of galaxies called “Physics at High Angular Resolution in Nearby Galaxy-HST” (PHANGS-HST). The idea is to use Hubble images and Atacama Large Millimeter Array (ALMA) data to build a dataset charting connections between young stars and cold molecular gas in different galaxy environments. Hubble’s image of this galaxy shows bright young stars (blue) and dark regions that seem 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 the NASA/ESA Hubble Space Telescope. Hubble’s Wide Field Camera 3 (WFC3) separates the arms of the galaxy from dark patches of dust in between, which block out the ultraviolet and visible light Hubble is sensitive to. Younger and older stars can be differentiated by their colors, showing how they are distributed throughout the galaxy. JWST’s MIRI image (above) provides a very different view, instead highlighting the patterns of gas spread throughout the galaxy. ESA/Webb, NASA & CSA, J. Lee and the PHANGS-JWST and PHANGS-HST Teams

Data and imaging from JWST shows more of a continual tangle of structures that echo the shape of the spiral arms. The very different views of the galaxy is due to the presence of dusty regions. Note that different stars are visible in the two images. That’s because some stars shine more brightly in different wavelengths. Those brightest in infrared and ultraviolet are more hidden by the dust and thus not as easily seen in the HST image. With its ability to see infrared more easily, the JWST MIRI instrument gives us a look at the “bones” of the galaxy.

What the Bones Can Tell Us

Both JWST and HST gather data about one of the most fascinating processes in galaxies: star birth. To understand it, astronomers look at stars, star clusters, associations, and starbirth regions in galaxies. That’s what PHANGS-HST is doing. The idea is create a catalog of more than 100,000 clusters, associations and molecular clouds. Eventually, that 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 is drawing from the 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 peer through the dusty environment of IC 5332. It’s a supercooled instrument sensitive to a range of light between 5 and 28 microns in the mid-infrared part of the electromagnetic spectrum. That gives it a perfect window into the skeleton of this beautiful galaxy.

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