Astronomers have recently unveiled a novel galaxy’s existence, using the groundbreaking James Webb Space Telescope (JWST) as part of the expansive JWST COSMOS-Web survey. This newfound celestial object, known as JWST-ER1, stands out as a massive and compact quiescent galaxy. These exciting findings were published in a paper on September 14, available on the arXiv pre-print server.
Massive galaxies that ceased star formation, often referred to as massive quiescent galaxies, hold the potential to provide insights into the evolution of giant elliptical galaxies. These galaxies formed stars early in their history and rapidly amassed their stellar mass, making them crucial in our quest to comprehend the intricate process of galaxy evolution.
Led by Pieter van Dokkum from Yale University, a team of astronomers has now identified this intriguing new galaxy, JWST-ER1. The James Webb Space Telescope’s Near Infrared Camera (NIRCam) played a pivotal role in this discovery as part of the ongoing COSMOS-Web project, aiming to survey up to one million galaxies. One of JWST-ER1’s most remarkable features is the captivating Einstein ring phenomenon, where light forms a ring shape due to gravitational lensing.
The researchers explained, “The galaxy and its ring were identified in JWST NIRCam observations in the context of the COSMOS-Web project, a public wide-area survey using the F115W, F150W, F277W, and F444W filters.”
The NIRCam observations revealed that JWST-ER1 consists of a compact early-type galaxy (JWST-ER1g) and a complete Einstein ring (JWST-ER1r) with two prominent red concentrations. The center of the ring has a measured diameter of approximately 1.54 arcseconds.
This newfound galaxy resides at a redshift of 1.94, boasting a radius of around 21,500 light years and an estimated mass of 650 billion solar masses. These results indicate an age of 1.9 billion years and a low star-formation rate, amounting to four solar masses per year. Thus, JWST-ER1 emerges as a massive and tranquil galaxy, sharing similarities with other quiescent galaxies at similar redshifts.
Regarding the fascinating ring, JWST-ER1r, astronomers have determined that it originates from a background galaxy at a photometric redshift of 2.98. It joins the ranks of numerous known Einstein rings, although most of them are incomplete.
The study also noted that JWST-ER1 exhibits a nearly perfect round shape, devoid of obvious star-forming regions, tidal tails, or other irregularities as seen in NIRCam imaging.
In conclusion, the paper’s authors propose further observations of JWST-ER1 to explore whether nearby galaxies or structures along its line of sight could contribute to its mass. Additionally, they aim to investigate whether JWST-ER1 could be the central galaxy of a progenitor cluster.