Dwarf galaxy NGC 4449 is the star of the show in The James Webb Space Telescopethe latest cosmic portrait.
NGC 4449, located 12.5 million light-years away in the constellation Canes Venatici, the hunting dogs, has much in common with our own The Large Magellanic Cloud (LMC), a satellite galaxy orbiting it Milky Way. Both are small and irregular in shape, and each has a distinct bar running down the middle. However, while the LMC has one extreme region of star formation, which is the 30 Doradus region, known as the Tarantula NebulaNGC 4449 has improved star-forming speeds along its entire length and width. In fact, so many stars are forming that NGC 4449 is described as undergoing a “starburst”.
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Starbursts occur when the molecular hydrogen that fills a galaxy is stirred up by a gravitational interaction or collision with another galaxy. NGC 4449 is part of the M94 group of about two dozen galaxies, so it has several neighbors to interact with.
Indeed, in 2012, a collaboration of professionals and amateurs led by David Martinez-Delgado of the Max Planck Institute of Astronomy in Germany and involving the work of several prominent amateur astrophotographers, as well as observations with the Subaru 8-meter telescope on Mauna Kea in Hawaii, found evidence for just such an interaction. The team resolved the stream of stars ejected from a smaller galaxy that perished by being engulfed by NGC 4449.
Although the small galaxy was torn apart by the larger NGC 4449, it did not go quietly. Gravitational tidal forces from being so close to NGC 4449 created turbulence in the molecular gas across NGC 4449, causing large pockets to gravitationally collapse and form numerous young star clusters. Among other things, these star clusters can be seen in JWST’s latest image, which was constructed by combining data from its Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI). Working at different wavelengths of infrared radiation (0.6 microns to 5 microns and 5 microns to 28 microns), they reveal different types of features in the galaxy.
The near-infrared view of NGC 4449 looks significantly different from the mid-infrared view. It is important to note that all colors are false colors that represent infrared wavelengths.
NIRCam shows a striking star bar full of newly born clusters of hot stars, amid a background of older stars whose combined light shows up as a diffuse blue glow. Ringing the bright center are tendrils of dust that mark star-forming regions of molecular gas ionized by the radiation of newborn stars that reside in clusters. These clusters are represented by compact blue regions embedded in the gas.
The MIRI image shows the dusty skeleton of NGC 4449 following the bar, but it also appears to be more densely concentrated around the bar than the material seen by NIRCam.
There are polycyclic aromatic hydrocarbons, abbreviated as PAH, in the dust marked with orange-red color. These carbon-based molecules are the building blocks of interstellar dust grains and play a key role in cosmic chemistry and the spread of organic material throughout the galaxy. Bright yellow regions are sites of active star formation, and bright blue spots signal the galaxy’s myriad sparkling stellar bodies.
Together, the NIRCam and MIRI data provide a beautiful snapshot of the galaxy going through a turbulent phase that will shape it for billions of years to come.
NGC 4449 is a sample of what may one day happen in the LMC if it interacts with its sibling, Small Magellanic Cloud, or even our own Milky Way, have become too large. NGC 4449 is also a modern version of the small galaxies that JWST also finds existed in the early universe. These early dwarf galaxies were the building blocks of the larger galaxies we see today and, through their own starbursts, contributed significant proportion of ionization energy must be brought cosmic dark ages even. As such, NGC 4449 is a unique window into the past and future of galactic evolution.