Over the past two years, scientists have used the NASA’s James Webb Space Telescope (also called Webb or JWST) to explore what astronomers call the Cosmic Dawn: the period of the first few hundred million years after the big Bang where the first galaxies were born.
These galaxies provide vital information about the ways gas, stars and black holes changed when the universe was very young.
In October 2023 and January 2024, an international team of astronomers used Webb to observe galaxies as part of the program JWST Advanced Deep Extragalactic Survey (JADES). Using Webb’s NIRSpec (near-infrared spectrograph), obtained a spectrum of an unprecedented galaxy observed only two hundred and ninety million years after the Big Bang. This corresponds to a redshift of about 14, which is a measure of how much a galaxy’s light is stretched due to the expansion of the universe.
Stefano Carniani from the Scuola Normale Superiore of Pisa, Italy, already Kevin Hainline from the University of Arizona in Tucson, Arizona, told NASA more about how this source was found and what its unique properties tell us about galaxy formation.
“Webb’s instruments were designed to find and understand the earliest galaxies, and in the first year of observations as part of JWST’s Advanced Deep Extragalactic Survey (JADES), we found many hundreds of candidate galaxies from the first 650 million years after the Big Bang. In early 2023, we discovered a galaxy in our data that had strong evidence of being above a redshift of 14, which was very exciting, but there were some properties of the source that made us wary. The source was surprisingly bright, which we wouldn’t expect from such a distant galaxy, and it was very close to another galaxy, so the two appeared to be part of a larger object. When we observed the source again in October 2023 as part of the JADES Origins Field, new imaging data obtained with Webb’s narrower NIRCam (near-infrared camera) filters further pointed toward the high redshift hypothesis. We knew we needed a spectrum, since anything we learned would be of immense scientific importance, whether as a new milestone in Webb’s investigation of the early universe or as a confusing oddball from a middle-aged galaxy..
“In January 2024, NIRSpec observed this galaxy, JADES-GS-z14-0, for almost ten hours, and when the spectrum was first processed, there was unequivocal evidence that the galaxy was indeed at a redshift of 14.32 , breaking the previous most-distant galaxy record (z = 13.2 from JADES-GS-z13-0). Seeing this spectrum was incredibly exciting for the entire team, given the mystery surrounding the source. This discovery was not only a new distance record for our team; The most important aspect of JADES-GS-z14-0 was that at this distance we know that this galaxy must be intrinsically very luminous. From the images, it is discovered that the source is more than 1,600 light years in diameter, demonstrating that the light we see is mainly coming from young stars and not from emissions near a growing supermassive black hole. So much starlight implies that the galaxy is several hundred million times the mass of the Sun! This begs the question: How can nature create such a large, massive and bright galaxy in less than 300 million years?
“The data reveal other important aspects of this amazing galaxy. We see that the color of the galaxy is not as blue as it could be, indicating that some of the light is reddened by dust, even at these very early times. JADES researcher Jake Helton of Steward Observatory and the University of Arizona also identified that JADES-GS-z14-0 was detected at longer wavelengths with Webb’s MIRI (Mid-Infrared Instrument), a notable achievement considering its distance. The MIRI observation covers wavelengths of light that were emitted in the visible light range, which are redshifted outside the reach of Webb’s near-infrared instruments. Jake’s analysis indicates that the source brightness implied by the MIRI observation is above what would be extrapolated from measurements by the other Webb instruments, indicating the presence of strong emissions of ionized gas in the galaxy in the form of bright emission lines of hydrogen and oxygen. “The presence of oxygen at such an early stage in the life of this galaxy is a surprise and suggests that multiple generations of very massive stars had already lived their lives before we observed the galaxy.”
“All of these observations, taken together, tell us that JADES-GS-z14-0 is not like the types of galaxies that theoretical models and computer simulations have predicted would exist in the early universe. Given the observed brightness of the source, we can predict how it might grow over cosmic time, and so far we have not found any suitable analogues of the hundreds of other high-redshift galaxies we have observed in our study. Given the relatively small region of sky we searched to find JADES-GS-z14-0, its discovery has profound implications for the expected number of bright galaxies we see in the early universe, as discussed in another concurrent JADES study (Robertson et al. al. al., recently accepted). Astronomers are likely to find many such luminous galaxies, possibly even in earlier times, over the next decade with Webb.
We are delighted to see the extraordinary diversity of galaxies that existed in Cosmic Dawn!“
This entry was published in News on 08 Jun 2024 by Francisco Martín León
