One of the most exciting developments in astronomy today is the way that advanced arrays and techniques are letting astronomers see farther back in time to the earliest periods of the Universe. In so doing, astronomers hope to get a closer at the earliest galaxies to learn more about how and when they first emerged – which can tell us a great deal more about their subsequent evolution.
This was the purpose of the ALMA Large Program to INvestigate C+ at Early times (ALPINE), a multiwavelength survey that examined galaxies that were around when the Universe was less than 1.5 billion years old. With funding provided by NASA and the European Southern Observatory (ESO), the ALPINE collaboration analyzed this data and learned some interesting things about the early evolution of galaxies.
The ALPINE collaboration was led by Andreas Faisst, a staff scientist at Caltech’s Infrared Processing and Analysis Center (IPAC), and includes members from the Space Telescope Science Institute (STSI), the Max Planck Institute for Astronomy (MPIA), the Niels Bohr Institute, the Cosmic Dawn Center, the Kavli Institute for the Physics and Mathematics of the Universe, NASA’s Jet Propulsion Laboratory, and multiple universities and institutes.
Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the ALPINE survey observed 118 remote galaxies over the course of 70 hours to learn more about their gas and dust distribution. Based on their redshift, these galaxies were estimated to be close to 12 billion years old, meaning they existed just 1 to 1.5 billion years after the Big Bang.
One of the key functions of this survey was to use ALMA to spot the emission line of C+ atoms, a positively charged form of carbon that is created when ultraviolet light from newborn stars interacts with clouds dust. By measuring the signature of this atom in galaxies, astronomers can see how the galaxies are rotating.
If the gas containing C+ atoms is spinning away from us, the light shifts towards the red end of the spectrum; if it is spinning towards us, it is shifted towards the blue end of the spectrum (aka. redshift/blueshift). As Faisst explained in a recent Caltech press release, this made the ALPINE survey unprecedented.
“This is the first multi-wavelength study from ultraviolet to radio waves of distant galaxies that existed between 1 billion and 1.5 billion years after the Big Bang,” he said. Based on the data they observed, the ALPINE team was able to create a catalog of these galaxies’ rotational speeds as well as other features – like their gas density and the number of new stars forming within them.
The ALMA data was then combined with measurements from other previous observations, including the W. M. Keck Observatory in Hawaii and NASA’s Hubble and Spitzer space telescopes. What they found was that 15% of the galaxies observed had perfectly-smooth and orderly rotations (which is expected of spiral galaxies) while the others had a mangled rotation and appeared to be in the process of merging.
As Faisst explains, this was a rather unexpected find for galaxies that existed this early in the Universe:
“We are finding nicely ordered rotating galaxies at this very early and quite turbulent stage of our universe. That means they must have formed by a smooth process of gathering gas and haven’t collided with other galaxies yet, as many of the other galaxies have.”
However, the authors indicate that the objects they observed may not be spiral galaxies after all, but rotating disks with clumps of material. As such, future observations involving next-generation space-based telescopes will be needed before anything definitive can be said. This will include the James Webb Space Telescope (JWST) which will pinpoint the detailed structure of these galaxies.
“How do galaxies grow so much so fast? What are the internal processes that let them grow so quickly?” said Faisst. “These are questions that ALPINE is helping us answer. And with the upcoming launch of NASA’s James Webb Space Telescope, we will be able to follow-up on these galaxies to learn even more.”
Beyond the JWST, a number of ground-based and space-based telescopes will become operational in the coming years. With their superior resolution, sensitivity, and more advanced optics, astronomers expect to be able to push the limits of what is observable in our Universe. From that, the pressing questions of how the first galaxies formed and evolved (and other cosmological mysteries) will finally be answered.
Further Reading: Caltech