Baby Galaxy Spotted Still Connected to Cosmic Web

First Posted: Aug 06, 2015 10:06 AM EDT

Astronomers have discovered a giant, swirling disk of gas that represents a galaxy being born. The forming galaxy is actively being fed cool primordial gas that traces back to the Big Bang.

"This is the first smoking-gun evidence for how galaxies form," said Christopher Martin, one of the researchers, in a news release. "Even as simulations and theoretical work have increasingly stressed the importance of cold flows, observational evidence of their role in galaxy formation has been lacking."

The newly discovered protogalactic disk is about 400,000 light-years across, which is about four times larger in diameter than our Milky Way. It's located in a system that's dominated by two quasars, which help illuminate the cosmic web filament feeding gas into the protogalaxy.

The researchers examined the forming galaxy with a series of spectral images that combined to form a multiwavelength map of a patch of sky around the two quasars. This data revealed areas where gas is emitting in the Lyman-alpha line, and indicated the velocities with which the gas is moving.

"The images plainly show that there is a rotating disk-you can see that one side is moving closer to us and the other is moving away," said Martin. "And you can also see that there's a filament that extends beyond the disk."

The new findings are the first ever evidence to support the cold-flow model. This model suggests that relatively cool gas, delivered by filaments, streams directly into protogalaxies. There, it can condense to form stars.

"That's a direct prediction of the cold-flow model, and this is exactly what we see-an extended dis with lots of angular momentum that we can measure," said Martin.

The findings are published in the journal Nature.

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