JWST uncovers massive grand-design spiral galaxy in early universe

Indian astronomers report the detection of a new grand-design galaxy with the James Webb Space Telescope (JWST). The newfound galaxy, which received designation A2744-GDSp-z4, is relatively large and massive. The finding was detailed in a paper published Dec. 6 on the pre-print server arXiv.

Grand-design spiral galaxies are characterized by their prominent, well-defined arms, which circle outwards from a clear core. It is assumed that the arms in such galaxies are actually overdense regions of the disk which trigger star formation as incoming material is compressed in that region.

It is still not well understood when and how spiral galaxies first emerged in the early universe and such galaxies are generally rare at high redshifts. To date, only a few individual spirals have been found at a redshift higher than 3.0.

Now, a team of astronomers led by Rashi Jain of the National Center for Radio Astrophysics in India, reports the finding of a new high-redshift spiral using JWST. The new galaxy is of the grand-design subtype and was identified at a redshift of 4.03.

“In this paper, we present the discovery, in the Abell 2744 cluster field, of a two-armed, grand-design spiral galaxy, with a redshift of z ∼4, when the universe was only ∼1.5 billion years old. Since this is a grand-design spiral (GDSp) galaxy lying in the A2744 field at z ∼4, we designate it as A2744-GDSp-z4,” the researchers explained.

A2744-GDSp-z4 was first recognized as an unusual galaxy and its further inspection found that it shows a grand-design spiral pattern with two well-formed spiral arms. The galaxy also showcases a bright central bulge and a large extended disk—about 32,000 light years in diameter.

According to the paper, A2744-GDSp-z4 has a stellar mass of around 14 billion solar masses and has a star-formation rate at a level of 57.6 solar masses per year. The mass-weighted age of the galaxy was derived to be 228 million years.

The astronomers calculated that the onset of star formation in A2744-GDSp-z4 occurred approximately 839 million years after the Big Bang. Therefore, this means that A2744-GDSp-z4 assembled a mass of 10 billion solar masses in a few hundred million years and the age of the universe at the galaxy’s redshift was only about 1.5 billion years.

The authors of the paper underlined that these findings challenge the current hierarchical models of galaxy formation and leave many questions open.

“How did A2744-GDSp-z4 acquire such a large disk in such a short time? How and when did the grand-design spiral arms emerge? These questions could be answered by investigating the dynamical state of this galaxy with future JWST/NIRSpec IFU observations,” the scientists wrote.

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