JWST detects a giant and compact resting galaxy

JWST color image of JWST-ER1. Credit: Van Dokkum et al., 2023.

Astronomers have reported the discovery of a new galaxy using the James Webb Space Telescope (JWST) as part of the JWST COSMOS-Web survey. The discovered object, named JWST-ER1, is a large, compact galaxy that has stopped forming stars. The results are detailed in a paper published September 14 on the preprint server arXiv. A team of astronomers led by Peter van Dokkum of Yale University reports the discovery of a new galaxy, designated JWST-ER1. The object was identified by JWST’s Near Infrared Camera (NIRCam) as part of an ongoing survey of one million galaxies called COSMOS-Web.

One of the most notable features of JWST-ER1 is the so-called Einstein ring, a phenomenon in which light appears in the ring due to gravitational lensing. NIRCam observations show that JWST-ER1 consists of a compact primordial galaxy and an Einstein ring (JWST-ER1r). This galaxy has a redshift of 1.94, a radius of approximately 21,500 light years, and an estimated mass of 650 billion solar masses. The results show that it is 1.9 billion years old and has a low star formation rate, about 4 times the mass of the Sun per year. As for the JWST-ER1r ring, astronomers found that it was formed by a background galaxy with an optical shift of 2.98.

The study also shows that JWST-ER1 is almost perfectly round, with no obvious star-forming regions, tidal tails or other features detected in the NIRCam images. The paper’s authors recommend further observations of JWST-ER1 to determine whether nearby galaxies or structures could contribute to its mass, and to test whether JWST-ER1 has must be the central progenitor galaxy of the cluster or not.

source: https://dx.doi.org/10.48550/arxiv.2309.07969