Astronomers using the Palomar Cosmic Web Imager have discovered a giant protogalaxy 10 billion light-years away, and found that it is connected to a filament of the intergalactic medium.
Using the Cosmic Web Imager (CWI) to study a system with two quasars 10 billion light-years away, the astronomers have unveiled a protogalaxy being fed cool gas by a filament of the cosmic web. The quasar UM 287 is the larger object at right; the newly-discovered protogalaxy is above and to the left of UM 287. This picture combines a visible light image of the system with CWI data; a filament of the cosmic web can be seen funneling cold gas onto the protogalaxy. Image credit: Chris Martin / PCWI / Caltech.
The protogalaxy is about 400,000 light-years across, about four times larger in diameter than our own Milky Way Galaxy.
It is situated in a system dominated by two quasars, the closest of which, UM 287, is positioned so that its emission is beamed like a flashlight, helping to illuminate the cosmic web filament feeding gas into the spiraling protogalaxy.
Last year, Dr Sebastiano Cantalupo of ETH Zurich in Switzerland and co-authors announced the discovery of what they thought was a large filament next to UM 287. The feature was brighter than it should have been if indeed it was only a filament. It seemed that there must be something else there.
In September 2014, the astronomers decided to follow up with observations of the system with the Cosmic Web Imager (CWI) at Palomar Observatory.
As an integral field spectrograph, CWI allowed the team to collect images around UM 287 at hundreds of different wavelengths simultaneously, revealing details of the system’s composition, mass distribution, and velocity.
The scientists focused on a range of wavelengths around an emission line in the UV known as the Lyman-alpha line. They collected a series of spectral images that combined to form a multiwavelength map of a patch of sky around the two quasars.
The data delineated areas where gas is emitting in the Lyman-alpha line, and indicated the velocities with which this gas is moving with respect to the center of the system.
“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. And you can also see that there’s a filament that extends beyond the disk,” said Prof Christopher Martin of the Cahill Center for Astrophysics at the California Institute of Technology, a team member and lead author of a paper published in the journal Nature.
The measurements indicate that the disk is rotating at a rate of about 400 km per second, somewhat faster than the Milky Way’s rate of rotation.
“The filament has a more or less constant velocity. It is basically funneling gas into the disk at a fixed rate. Once the gas merges with the disk inside the dark-matter halo, it is pulled around by the rotating gas and dark matter in the halo,” said co-author Dr Matt Matuszewski, also from the Cahill Center for Astrophysics.
According to the scientists, their discovery provides the strongest support yet for the so-called cold-flow model of galaxy formation, which holds that in the early Universe, relatively cool gas funneled down from the cosmic web directly into galaxies, fueling rapid star formation.
“This is the first smoking-gun evidence for how galaxies form,” Prof Martin said.
“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 scientists have already identified two additional disks that appear to be receiving gas directly from filaments of the cosmic web in the same way.
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D. Christopher Martin et al. A giant protogalactic disk linked to the cosmic web. Nature, published online August 05, 2015; doi: 10.1038/nature14616
