W. M. Keck Observatory Achieves First Light with New Instrument

W. M. Keck Observatory press release

W. M. Keck Observatory overnight captured the very first successful science data from its newest, cutting-edge instrument, the Keck Cosmic Web Imager (KCWI).

KCWI First Light Image
KCWI’s first look at the cosmos involved a spectral image of an exquisitely dense core of an ancient astronomical relic, showcasing the highest spectral resolving power and spatial resolution of the instrument. Credit W. M. Keck Observatory
KCWI captures three-dimensional data, as opposed to the traditional two-dimensional image or spectrum of conventional instruments. In a single observation, it records an image of the object at multiple wavelengths allowing scientists to explore both the spatial dimension (as in an image) and the spectral dimension (or color) of an object.

“I’m thrilled to see this new instrument,” said Keck Observatory Director Hilton Lewis. “It takes years to design and build these very sophisticated instruments. KCWI is a superb example of the application of the most advanced technology to enable the hardest science. I believe it has the potential to transform the science that we do, and continue to keep Keck Observatory right at the forefront of astronomical research.”

KCWI is extremely sensitive, specifically designed to capture high-resolution spectra of ultra-faint celestial bodies with unprecedented detail. It is able to differentiate even the slightest changes in spectral color with a great degree of accuracy.

This powerful capability is key for astronomers because a highly-detailed spectral image allows them to identify a cosmic object’s characteristics, including its temperature, motion, density, mass, distance, chemical composition, and more.

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Scientists Build First Map of Hidden Universe

W. M. Keck Observatory press release

A team led by astronomers from the Max Planck Institute for Astronomy has created the first three-dimensional map of the ‘adolescent’ Universe, just 3 billion years after the Big Bang. This map, built from data collected from the W. M. Keck Observatory, is millions of light-years across and provides a tantalizing glimpse of large structures in the ‘cosmic web’ – the backbone of cosmic structure.

The Cosmic Web
3D map of the cosmic web at a distance of 10.8 billion light years. Credit: Casey Stark (UC Berkeley) AND Khee-Gan Lee (MPIA)
On the largest scales, matter in the Universe is arranged in a vast network of filamentary structures known as the ‘cosmic web’, its tangled strands spanning hundreds of millions of light-years. Dark matter, which emits no light, forms the backbone of this web, which is also suffused with primordial hydrogen gas left over from the Big Bang. Galaxies like our own Milky Way are embedded inside this web, but fill only a tiny fraction of its volume.

Now a team of astronomers led by Khee-Gan Lee, a post-doc at the Max Planck Institute for Astronomy, has created a map of hydrogen absorption revealing a three-dimensional section of the universe 11 billions light years away – the first time the cosmic web has been mapped at such a vast distance. Since observing to such immense distances is also looking back in time, the map reveals the early stages of cosmic structure formation when the Universe was only a quarter of its current age, during an era when the galaxies were undergoing a major ‘growth spurt’.

The map was created by using faint background galaxies as light sources, against which gas could be seen by the characteristic absorption features of hydrogen. The wavelengths of each hydrogen feature showed the presence of gas at a specific distance from us. Combining all of the measurements across the entire field of view allowed the team a tantalizing glimpse of giant filamentary structures extending across millions of light-years, and paves the way for more extensive studies that will reveal not only the structure of the cosmic web, but also details of its function – the ways that pristine gas is funneled along the web into galaxies, providing the raw material for the formation of galaxies, stars, and planets.

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Cosmic Web Imager Coming to Keck

Caltech press release

Caltech astronomers have taken unprecedented images of the intergalactic medium (IGM)—the diffuse gas that connects galaxies throughout the universe—with the Cosmic Web Imager, an instrument designed and built at Caltech. Until now, the structure of the IGM has mostly been a matter for theoretical speculation. However, with observations from the Cosmic Web Imager, deployed on the Hale 200-inch telescope at Palomar Observatory, astronomers are obtaining our first three-dimensional pictures of the IGM. The Cosmic Web Imager will make possible a new understanding of galactic and intergalactic dynamics, and it has already detected one possible spiral-galaxy-in-the-making that is three times the size of our Milky Way.

Lyman Alpha Blob
Comparison of Lyman alpha blob observed with Cosmic Web Imager and a simulation of the cosmic web based on theoretical predictions.
Credit: Christopher Martin, Robert Hurt
The Cosmic Web Imager was conceived and developed by Caltech professor of physics Christopher Martin. “I’ve been thinking about the intergalactic medium since I was a graduate student,” says Martin. “Not only does it comprise most of the normal matter in the universe, it is also the medium in which galaxies form and grow.”

Since the late 1980s and early 1990s, theoreticians have predicted that primordial gas from the Big Bang is not spread uniformly throughout space, but is instead distributed in channels that span galaxies and flow between them. This “cosmic web”—the IGM—is a network of smaller and larger filaments crisscrossing one another across the vastness of space and back through time to an era when galaxies were first forming and stars were being produced at a rapid rate.

Martin describes the diffuse gas of the IGM as “dim matter,” to distinguish it from the bright matter of stars and galaxies, and the dark matter and energy that compose most of the universe. Though you might not think so on a bright sunny day or even a starlit night, fully 96 percent of the mass and energy in the universe is dark energy and dark matter (first inferred by Caltech’s Fritz Zwicky in the 1930s), whose existence we know of only due to its effects on the remaining 4 percent that we can see: normal matter. Of this 4 percent that is normal matter, only one-quarter is made up of stars and galaxies, the bright objects that light our night sky. The remainder, which amounts to only about 3 percent of everything in the universe, is the IGM.

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UCSC Scientists Capture First Cosmic Web Filaments at Keck Observatory

W. M. Keck Observatory press release

Astronomers have discovered a distant quasar illuminating a vast nebula of diffuse gas, revealing for the first time part of the network of filaments thought to connect galaxies in a cosmic web. Researchers at the University of California, Santa Cruz, led the study, published January 19 in the journal, Nature.

Cosmic Web Filament
This deep image shows the nebula (cyan) extending across 2 million light-years that was discovered around the bright quasar UM287 (at the center of the image). Credit: S. Cantalupo, UCSC
Using the 10-meter Keck I telescope at the W. M. Keck Observatory in Hawaii, the researchers detected a very large, luminous nebula of gas extending about 2 million light-years across intergalactic space.

“This is a very exceptional object: it’s huge, at least twice as large as any nebula detected before, and it extends well beyond the galactic environment of the quasar,” said Sebastiano Cantalupo, first author of the paper and a postdoctoral fellow at UC Santa Cruz.

The standard cosmological model of structure formation in the universe predicts that galaxies are embedded in a cosmic web of matter, most of which (about 84 percent) is invisible dark matter. This web is seen in the results from computer simulations of the evolution of structure in the universe, which show the distribution of dark matter on large scales, including the dark matter halos in which galaxies form and the cosmic web of filaments that connect them. Gravity causes ordinary matter to follow the distribution of dark matter, so filaments of diffuse, ionized gas are expected to trace a pattern similar to that seen in dark matter simulations.

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