Webb Discovers High-Redshift Einstein Ring Challenging previous theories

This 1′ × 1′ section of the COSMOS-Web mosaic is centered on JWST-ER1, revealing the object's seemingly isolated environment. While it could potentially belong to a group, it is notably distant from the central regions of a densely populated galaxy cluster. Credit: NASA et. al.

Sep 18, 2023 - In a groundbreaking discovery, astronomers using the James Webb Space Telescope (JWST) have stumbled upon a celestial wonder: a distant, enigmatic galaxy known as JWST-ER1. This massive, quiescent galaxy, located at a redshift of z = 2, has astounded researchers with its unusual properties and offers new insights into the mysteries of galaxy formation and evolution.

A Cosmic Surprise at High Redshifts - For years, astronomers have been intrigued by the cosmos' hidden secrets, and one of the most intriguing findings from the Hubble Space Telescope (HST) was the existence of compact, massive galaxies at a redshift of z ∼ 2, roughly 10 billion years in the past. These galaxies, surprisingly compact with half-light radii measuring just 1-2 kiloparsecs, have challenged our understanding of how galaxies form and evolve.

Meet JWST-ER1 - Enter JWST-ER1, a cosmic marvel that has caught the eye of scientists. This celestial object was discovered during the COSMOS-Web survey, a public project utilizing the JWST's NIRCam instrument to explore the universe. JWST-ER1 is composed of two components: a compact early-type galaxy (JWST-ER1g) and a complete Einstein ring (JWST-ER1r) with a remarkable diameter of 1.54 arcseconds. The ring's mesmerizing appearance is the result of a background galaxy situated at a photometric redshift of z = 2.98.

A Glimpse into Cosmic History - What makes JWST-ER1 truly exceptional is its ability to provide a direct measurement of the mass of the "pristine" core of a massive galaxy. This measurement was obtained before the stellar population underwent mixing and dilution during the 10 billion years of galaxy evolution between z = 2 and z = 0.

Massive Findings - Researchers have calculated that the lensing mass (Mlens) within a radius of 6.6 kiloparsecs is approximately 6.5 × 10^11 solar masses (M⊙). In contrast, the stellar mass within the same radius (Mstars) is estimated to be approximately 1.1 × 10^11 M⊙ for a Chabrier initial mass function (IMF). Dark matter's contribution (Mdm) within the Einstein ring is also determined to be approximately 2.6 × 10^11 M⊙.

The Mystery of Missing Mass - The discovery has left astronomers with a tantalizing mystery: a significant discrepancy exists between the lensing mass and the observed stellar mass of JWST-ER1g. The lensing mass is nearly six times higher than the stellar mass. Scientists are now exploring various theories to explain this missing mass.

Unveiling Potential Contributors - Possible explanations for the missing mass include the presence of gas, but this scenario would lead to a starburst, which is not observed in JWST-ER1. Dark matter is another consideration, but it only accounts for part of the discrepancy. A compelling alternative theory is that the initial mass function (IMF) of JWST-ER1g is bottom-heavy, meaning a larger proportion of low-mass stars contributes to the overall mass.

The IMF Puzzle - Astronomers are delving into the intriguing concept that JWST-ER1g's IMF may be steeper than the Chabrier IMF, potentially resembling a Salpeter IMF or even a "super-Salpeter" IMF with a slope of -2.7. Adjusting the IMF could reconcile the lensing mass with the observed stellar mass and provide crucial insights into the galaxy's history.

Consistency with Cosmic Neighbors - This IMF hypothesis aligns with findings from other massive galaxies at high redshifts, where the central regions are believed to possess steeper IMFs. The universe is slowly revealing its secrets, and JWST-ER1 could be the key to understanding the complex interplay of stars, dark matter, and galaxy formation.

Future Cosmic Voyages - Exciting prospects lie ahead as astronomers plan future observations, particularly with JWST's NIRSpec instrument. These observations could yield velocity dispersion measurements and unlock more secrets about the IMF and dark matter distribution within JWST-ER1. As the cosmic journey continues, our understanding of the universe's past and future is bound to deepen, one discovery at a time.

Stay tuned for more cosmic revelations as the James Webb Space Telescope continues to explore the mysteries of our universe.

Source - ARXIV