JWST finds distant galaxy with “impossible” light signature

Ever since its launch, JWST has revealed the cosmos in unprecedented light.

This region of space, viewed first iconically by Hubble and later by JWST, shows an animation that switches between the two. Both images still have fundamental limitations, as they were acquired from within our inner Solar System, where the presence of zodiacal light influences the noise floor of our instruments, and cannot easily be removed. The extra presence of point-like red objects in JWST images, also known as “little red dots,” has finally been explained, but other puzzles still remain.

The widespread discovery of early, bright, ubiquitous galaxies puzzled many.

This tiny fraction of the JADES survey area, taken with JWST’s NIRCam instrument, showcases relatively nearby galaxies in detail, galaxies at intermediate distances that appear grouped together, and even ultra-distant galaxies that may be interacting or forming stars, despite their faint nature and red appearance. Even though we’ve been performing JWST science for over two years, we are only beginning to probe the full richness of the cosmos with JWST.

Years of research was needed before we understood why they were so numerous.

The galaxies that are members of the identified proto-cluster A2744z7p9OD are shown here, outlined atop their positions in the JWST view of galaxy cluster Abell 2744. At just 650 million years after the Big Bang, it’s the oldest proto-cluster of galaxies ever identified. This is early, but is consistent with simulations of when the earliest proto-clusters should emerge from the most initially overdense regions.

However, a new mystery has just arisen with detailed measurements of a new, ultra-distant galaxy.

In between the two large, prominent foreground galaxies shown here, JWST has imaged a faint red object that was originally identified as an ultra-distant galaxy candidate: JADES-GS-z13-1-LA. After a spectroscopic study was performed, this galaxy has been confirmed to be at a redshift of between z=13.01 and z=13.05, placing its age as coming from when the Universe was only between 325 and 330 million years old.

Known as JADES-GS-z13-1-LA, it appears typical of very distant galaxies in many ways.

The region of space that contains galaxy JADES-GS-z13-1-LA has been photometrically imaged in a whopping 19 different JWST filters. In the 9 shortest-wavelength filters, the galaxy itself is completely invisible, failing to show up above the noise floor: evidence that its light is being blocked by intervening matter. However, at longer wavelengths, JWST’s unique capabilities reveal it, suggesting its ultra-distant nature.

It’s invisible at shorter wavelengths, and then bright at longer wavelengths: where unique JWST’s capabilities shine.

Preliminary total system throughput for each NIRCam filter, including contributions from the JWST Optical Telescope Element (OTE), NIRCam optical train, dichroics, filters, and detector quantum efficiency (QE). Throughput refers to photon-to-electron conversion efficiency. By using a series of JWST filters extending to much longer wavelengths than Hubble’s limit (between 1.6 and 2.0 microns), JWST can reveal details that are completely invisible to Hubble. The more filters that are leveraged in a single image, the greater the amount of details and features that can be revealed.

But this galaxy, the 5th most distant ever, has a surprise: a bright hydrogen emission line.

The spectrum taken by JWST’s NIRSpec instrument of galaxy JADES-GS-z13-1-LA, which clearly shows not only the “Lyman break” feature at the 1.7 micron mark in terms of observed wavelength, but an enormous “peak” to the right of the break: evidence for the Lyman-alpha hydrogen emission line. This is the most distant such emission line by over 200 million years.

The Lyman-α line, the brightest emission line of all, shines brilliantly in spectroscopic studies.

The spectrum of galaxy RXJ2129-z8HeII, showing the signature of ionized helium, some hydrogen lines, and the very strong doubly-ionized oxygen line at 500.8 nanometers. JWST has been able to detect several emission lines very far back in cosmic history, but JADES-GS-z13-1-LA is the only galaxy to possess the Lyman-alpha emission line earlier than a redshift of z=9. This is not presently explained.

This is the earliest distant galaxy to display such a line: by over 200 million years.

A variety of spectral features can be teased out of the NIRSpec/PRISM spectra of JADES-GS-z13-1-LA. The enormous emission line at ~1.7 microns is due to Lyman-alpha, but elsewhere, carbon, helium, oxygen, and carbon lines can all be seen as well. The enormous hydrogen emission line is unique to this object; no other JWST-imaged object from the first ~500 million years of cosmic history has one.

We presently have no explanation for how this could occur; all that light should be blocked.

For the first 550 million years of the Universe, neutral, light-blocking atoms persist in the space between galaxies, continuing what’s known as the cosmic dark ages. While that material persists, starlight is largely absorbed, and cannot penetrate through this “fog.” Once the last of that neutral matter becomes reionized, starlight can propagate freely through the Universe, marking the end of the reionization epoch.

The Universe remains filled with neutral, light-blocking atoms for nearly 1 billion years after the Big Bang.

Past a certain distance, before a certain time (about 1 billion years), or farther than a redshift (z) of 6, the Universe still has neutral gas in it, which blocks-and-absorbs light. These galactic spectra show the effect as a drop-to-zero in flux to the left of the big (Lyman-series) bump for all the galaxies past a certain redshift, but not for any of the ones at lower redshift. This physical effect is known as the Gunn-Peterson trough, and will block the brightest light produced by the earliest stars and galaxies. No signatures of the Lyman-alpha emission line, except for JADES-GS-z13-1-LA, has ever been seen past a redshift of ~z=9.

That gas is only ionized gradually: after enough cumulative ultraviolet starlight has been generated.

For the first 550 million years of the Universe, neutral, light-blocking atoms persist ubiquitously in the space between galaxies, continuing what’s known as the cosmic dark ages. Once the last of that neutral matter becomes reionized, starlight can propagate freely through the Universe, marking the end of the reionization epoch. In some locations, reionization happens earlier than average, but this should never happen as early as JADES-GS-z13-1-LA has been observed.

So how is this emission line coming through from so early on?

At the start of the hot Big Bang, the Universe was rapidly expanding and filled with high-energy, very densely packed, ultra-relativistic quanta. An early stage of radiation domination gave way to several later stages where radiation was sub-dominant, but still remained, while matter then clumped and collapsed into gas clouds, stars, star clusters, galaxies, and even richer structures over time, all while the space between those bound structures continues expanding. When stars form, the heat from them can not only ionize the surrounding matter, but the motions and high temperatures of the ionized material can boost and broaden their resultant emission lines.

Perhaps, tantalizingly, thermal or kinetic effects “boost” its energy.

The strong Lyman-alpha emission line from galaxy JADES-GS-z13-1-LA shows a significant amount of broadening, which could be due to thermal (very hot gas/plasma) effects and/or kinetic (fast motion) effects, but how that light escapes and travels through the intergalactic medium is not well-understood.

Otherwise, astronomers shall remain in the dark.

Dark, dusty molecular clouds, like Barnard 59, part of the Pipe Nebula, appear prominent as they block out the light from background objects: stars, heated gas, and light-reflecting material. In the young Universe, prior to an age of ~550 million years, a large fraction of atoms were not ionized, and so should be very efficient at blocking the light even from hot, newly-formed stars. Why a galaxy like JADES-GS-z13-1-LA has a bright hydrogen emission line is currently a puzzle for astronomy.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.