An international team of scientists has created the most extensive and accurate three-dimensional map of excited hydrogen light in the early universe, based on data from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). Simultaneously, the HETDEX collaboration has publicly released its full dataset of over half a petabyte, covering a period 9 to 12 billion years ago. The research, which maps Lyman-alpha radiation emitted by hydrogen, provides a new method for observing galaxies and intergalactic gas during an era of peak star formation known as "cosmic noon."
Methodology: Line Intensity Mapping
The map was generated using a technique called Line Intensity Mapping. This approach measures the combined light from specific elements, such as hydrogen, across large regions of the sky rather than observing individual objects in detail. Scientists compare this method to viewing a scene through a smudged window, capturing all light rather than focusing only on the brightest points.
Hydrogen, the universe's most abundant element, emits Lyman-alpha light—a specific ultraviolet wavelength—when its atoms are energized by radiation from young, hot stars.
By charting the distribution and concentration of this light, researchers can trace both bright galaxies and the diffuse gas connecting them, creating a map that resembles a heat map of illumination across the cosmic web.
HETDEX Survey and Data
The HETDEX survey was conducted from 2017 to 2024 using the Hobby-Eberly Telescope at the McDonald Observatory in Texas. The survey collected over 600 million spectra across a sky area equivalent to approximately 2,000 full moons. The primary goal of the project is to map over one million bright galaxies to study the expansion history of the universe and the nature of dark energy.
The newly released dataset includes:
- 431,000 three-dimensional data cubes, each covering about 1/30th the size of the full Moon, primarily in regions around the Big Dipper and Orion
- A catalog of over 1 million distant galaxies, 500,000 nearby star-forming galaxies, 18,000 supermassive black holes, and 150,000 stars
The survey was untargeted, meaning it observed all objects within its field of view without pre-selecting specific targets. Researchers used a small fraction (approximately 5%) of the collected data to create the Lyman-alpha map, utilizing the substantial light present in regions between bright galaxies.
Key Findings
The map reveals previously unobserved structures, including fainter galaxies and immense intergalactic gas clouds that emit Lyman-alpha radiation. Previous studies had limited information on the locations of these objects. The map covers a period approximately 9 to 11 billion years ago, a time when star formation was at its most vigorous and galaxies were actively assembling.
This technique marks the first use of Line Intensity Mapping for charting Lyman-alpha emissions with such extensive data and precision.
Data Accessibility and Tools
The full dataset, which exceeds half a petabyte of raw and processed observations, is publicly accessible via hetdex.org. Features of the data release include:
- Custom subsets of data downloadable based on sky location
- High-performance cloud-based supercomputing resources available through UT Austin's Texas Advanced Computing Center
- Tutorials and tools for analysis
- AI software used in data processing to remove contamination from satellites and meteors
- Participation of over 24,000 citizen scientists through the Dark Energy Explorers program to confirm galaxy candidates
Future Research
The next phase of research will focus on improving noise-reduction techniques to separate desired signals from contaminants, including foreground galaxies, detector noise, analysis artifacts, scattered light sources, and Earth's atmospheric interference. This will allow for the use of fainter sources and lower-mass objects as tracers of cosmic evolution. Researchers anticipate that future surveys may rely more on intensity mapping to reveal the complete cosmic framework.
Collaboration
HETDEX is a joint project of Pennsylvania State University, the University of Texas at Austin, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen. The research describing the Lyman-alpha map and the data release was published in The Astrophysical Journal.