Webb detects active star formation in a dwarf galaxy

A close view of the central area of a dwarf galaxy
A close-up view of the central region of a dwarf galaxy. A huge number of stars fill the galaxy as tiny glowing dots. They are brightest around the glowing core of the galaxy. Thick clouds of gas and dust billow across the scene, curling like moving flames. They glow in warm colours according to their location: orange around the galaxy's core and around the glowing star clusters in the lower left, and dark red elsewhere. Credit: ESA/Webb, NASA & CSA, A. Adamo (Stockholm University) and the FEAST JWST team

A new image from the James Webb Space Telescope shows the dwarf galaxy NGC 4449. This galaxy, also known as Caldwell 21, is located about 12.5 million light-years away in the constellation of the Hounds. It is part of the M94 group of galaxies, which lies close to the Local Group, which contains our Milky Way.

A billion years of star formation

NGC 4449 has been forming stars for several billion years, but it is currently undergoing a period of star formation at a much higher rate than in the past. This extremely explosive and intense star formation activity is called an outburst, and so NGC 4449 is known as a flaring galaxy.

In fact, at the current rate of star formation, the gas reserves that fuel star production will only last for a billion years. Usually, starbursts occur in the central parts of galaxies, but NGC 4449 shows more widespread star formation activity, and the youngest stars are observed both in the core and in the streams surrounding the galaxy. It is likely that the current large-scale outbreak was caused by an interaction or merger with a smaller satellite. Thus, astronomers believe that the star formation of NGC 4449 was influenced by the interaction with several of its neighbors.

NGC 4449 is reminiscent of primordial star-forming galaxies that grew by merging and accreting smaller star systems. Since NGC 4449 is close enough to observe in detail, it is an ideal laboratory for astronomers to study what may have been happening during the formation and evolution of galaxies in the early Universe.

What the image conveys

This new image uses data from two Webb instruments:

  • MIRI is a mid-infrared instrument;
  • NIRCam is a near-infrared camera.

Infrared observations reveal the galaxy’s creeping tendrils of gas, dust, and stars. Bright blue spots show countless individual stars, while bright yellow areas intertwined throughout the galaxy indicate concentrations of active stellar nurseries where new stars are forming.

The orange-red areas indicate the distribution of a type of carbon-based compound known as polycyclic aromatic hydrocarbons (PAHs) – the MIRI F770W filter is particularly well suited to imaging these important molecules. The bright red spots correspond to areas rich in hydrogen that has been ionized by the radiation from the newly formed stars.

The diffuse blue light gradient around the central region shows the distribution of old stars. Compact light blue regions in the red ionized gas, mostly concentrated in the outer region of the galaxy, show the distribution of young star clusters.

NGC 4449 was discovered by Webb as part of a series of observations called Feedback in Emerging Extragalactic Star Clusters, or FEAST (PI: A. Adamo).


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