New dwarf galaxy identified in James Webb Space Telescope image

A team of astronomers, led by Arizona State University Assistant Research Scientist Tim Carleton, has discovered a dwarf galaxy that appeared in James Webb Space Telescope imaging that wasn’t the primary observation target.

Galaxies are bound together by gravity and made up of stars and planets, with vast clouds of dust and gas as well as dark matter. Dwarf galaxies are the most abundant galaxies in the universe, and are by definition small with low luminosity. They have fewer than 100 million stars, while the Milky Way, for example, has nearly 200 billion stars.

Recent dwarf galaxy observations of the abundance of “ultra-diffuse galaxies” beyond the reach of previous large spectroscopic surveys suggest that our understanding of the dwarf galaxy population may be incomplete.

In a newly published study, Carleton and the team were initially looking at a cluster of galaxies as part of the JWST Prime Extragalactic Areas for Reionization and Lensing Science (PEARLS) project.

The dwarf galaxy, PEARLSDG, happened to appear in some of the team’s JWST imaging. It wasn’t the target at all—just a bit off from the main observation field, in the area of space where they weren’t expecting to see anything.

Their results have been published in the Astrophysical Journal Letters.

PEARLSDG did not have the usual characteristics of a dwarf galaxy one would expect to see. It isn’t interacting with a nearby galaxy, but it also isn’t forming new stars. As it turns out, it is an interesting case of an isolated quiescent galaxy.

“These types of isolated quiescent dwarf galaxies haven’t really been seen before except for relatively few cases. They are not really expected to exist given our current understanding of galaxy evolution, so the fact that we see this object helps us improve our theories for galaxy formation,” said Carleton. “Generally, dwarf galaxies that are out there by themselves are continuing to form new stars.”

Until now, astronomers’ understanding of galaxy evolution showed an isolated galaxy that continued to form young stars or it would interact with a more massive companion galaxy. This theory didn’t apply to PEARLSDG, which presents as an old stellar population, not forming new stars as well as keeping to itself.

In a further surprise, individual stars can be observed in the team’s JWST images. These stars are brighter in JWST wavelengths; it is one of the farthest galaxies that we can see these stars with this level of detail. The brightness of these stars allows astronomers to be able to measure its distance—98 million light-years.

Top: the JWST of the PEARLSDG galaxy (blue = F090W + F150W, green = F200W + 0.5 × F277W, red = 0.5 × F277W+F356W+F444W). Bottom: DECALS grz image of the sky immediately surrounding PEARLSDG. Both images are aligned such that north is up and east is left. PEARLSDG is identified with the cyan box, and the green squares show the area covered by NIRCam imaging. Also shown are two of the closest (in-projection) nearby massive galaxies (identified in red circles). Credit: The Astrophysical Journal Letters (2024). DOI: 10.3847/2041-8213/ad1b56

For this study, Carleton—who is an assistant research scientist at the Beus Center for Cosmic Foundations in the School of Earth and Space Exploration at ASU—and the team used a wide range of data.

This includes imaging data from JWST’s Near-InfraRed Camera (NIRCam); spectroscopic data from the DeVeney Optical Spectrograph on the Lowell Discovery Telescope in Flagstaff, Arizona; archival imaging from NASA’s Galex and Spitzer space telescopes; and ground-based imaging from the Sloan Digital Sky Survey and the Dark Energy Camera Legacy Survey.

Source: Arizona State University

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