Combining data from different telescopes is one of the best ways to get a fuller picture of far-off objects. Because telescopes such as Hubble (visible light), the James Webb Space Telescope (infrared), and the Atacama Large Millimeter Array (radio) each collect data in different wavelengths, they are able to capture distinct features of objects like galaxies that other telescopes cannot observe. A new paper by a large group of authors, headed by Andreas Faisst of Caltech, presented at the American Astronomical Society Meeting last week and published in The Astrophysical Journal Supplement tracks eighteen early galaxies in as broad of a spectrum as those instruments can collect, and most significantly found that they seem to “grow up” faster than expected.
What does it mean for a galaxy to “grow up?” One definition could be in its collection of metals. In astrophysics, “metals” simply means any material other than hydrogen and helium that must be formed through fusion in a star. They’re the building blocks of planetary systems and even life as we know it, which is where the famous saying that “we’re all made of star-stuff” came from. However, early galaxies, like the ones in this survey, were thought to be relatively metal-poor, given that they existed in a time (12.5 billion years ago) when stars hadn’t had long to form metal in the first place.
They also found that there wasn’t a significant increase in the metallicity of galaxies between galaxies of this “Post-Reionization” epoch (1-1.5 billion years after the Big Bang) and those of the “Cosmic Noon” epoch of the universe that happened directly after this one. Astronomers will have to rethink models of how quickly these early galaxies upcycled the hydrogen and helium gas they were originally made out of into carbon and oxygen.
Fraser explains Little Red Dots and what they mean.That wasn’t the only feature of these galaxies that was interesting, though. They appear to host a collection of Active Galactic Nuclei (AGN) that are actively feeding on gas and dust, and had previously been undiscovered. AGNs are the regions around black holes at the center of galaxies that are actively accreting matter, and JWST has found so many of them in the early universe astronomers are starting to think they might be almost ubiquitous in typical star-forming galaxies during the Post-Reionization epoch.
Part of the reason these galaxies were selected for this survey is because they did not originally have obvious AGNs, making them easier to monitor in other wavelengths. Finding more of these supermassive black holes, even in galaxies that don’t exhibit all of their spectral signatures, also helps explain the Little Red Dots the JWST has been seeing scattered all over the early universe. This paper adds further evidence that those are, in fact, AGNs, and that they seem to be actively accreting more material.
Another interesting finding put forward in the paper is that the star formation is “bursty”. It seems that early galaxies are either in the process of creating lots of stars, or hardly creating any at all. Different star formation rates can be tracked using different indicators, such as the H-alpha line, which tracks star formation within the last 10 million years, or ultraviolet/infrared spectra, which track star formation within the last 100 million years. A discrepancy between those two indicators shows astronomers how intermittent star formation can be in these galaxies.
Video from SciTech Daily about the maturity level of galaxies. Credit - SciTech Daily YouTube ChannelThis paper was accompanied by another one, published in The Astrophysical Journal, that describes some of the findings in more detail. It also is the first in what promises to be a series looking at everything from the rotation of the galaxies to gradients of the number of metals present in them. Looking at a wide variety of spectra will be key to understanding those insights too. And as we get even more powerful telescopes, there’s undoubtedly going to be even more we can explore that far back in time.
Learn More:
Caltech - Young Galaxies Grow Up So Fast
A.L. Faisst et al. - The ALPINE-CRISTAL-JWST Survey: JWST/IFU Optical Observations for 18 Main-sequence Galaxies at z = 4–6
UT - Astronomers Spot "First Stars" Billions of Years After They Were Supposed to Die
UT - Webb Observations Shed New Light on Cosmic Reionization
