Ancient Galaxies Fed On Gas, Not Collisions

The Sombrero Galaxy. Credit: ESO/P. Barthe

The traditional picture of galaxy growth is not pretty. In fact, it’s a kind of cosmic cannibalism: two galaxies are caught in ominous tango, eventually melding together in a fiery collision, thus spurring on an intense but short-lived bout of star formation. Now, new research suggests that most galaxies in the early Universe increased their stellar populations in a considerably less violent way, simply by burning through their own gas over long periods of time.

The research was conducted by a group of astronomers at NASA’s Spitzer Science Center in Pasadena, California. The team used the Spitzer Space Telescope to peer at 70 distant galaxies that flourished when the Universe was only 1-2 billion years old. The spectra of 70% of these galaxies showed an abundance of H alpha, an excited form of hydrogen gas that is prevalent in busy star-forming regions. Today, only one out of every thousand galaxies carries such an abundance of H alpha; in fact, the team estimates that star formation in the early Universe outpaced that of today by a factor of 100!

This split view shows how a normal spiral galaxy around our local universe (left) might have looked back in the distant universe, when astronomers think galaxies would have been filled with larger populations of hot, bright stars (right). Image credit: NASA/JPL-Caltech/STScI

Not only did these early galaxies crank out stars much faster than their modern-day counterparts, but they created much larger stars as well. By grazing on their own stores of gas, galaxies from this epoch routinely formed stars up to 100 solar masses in size.

These impressive bouts of star formation occurred over the course of hundreds of millions of years. The extremely long time scales involved suggest that while they probably played a minor role, galaxy mergers were not the main precursor to star formation in the Universe’s younger years. “This type of galactic cannibalism was rare,” said Ranga-Ram Chary, a member of the team. “Instead, we are seeing evidence for a mechanism of galaxy growth in which a typical galaxy fed itself through a steady stream of gas, making stars at a much faster rate than previously thought.” Even on cosmic scales, it would seem that slow and steady really does win the race.

Source: JPL

Tagged as: Cosmology, galaxies, H Alpha, Spitzer, Spitzer Space Telescope, star formation

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3D Galaxies – Coming Straight On For You

As we’ve recently learned, the ATLAS3D project was able to study 260 individual galaxies and do some very amazing things. By imaging in both red and blue shift, astronomers were able to take stellar measurements and give us a clear picture of galaxy rotation. But looking at a computer generated image gives a picture just like you reading the text in this article – no dimension. By superimposing the velocity of the stars over the plane of the image, a new breakthrough in simulation can be made. And it’s coming straight on for you…

We understand images of grand spirals and their sweeping arms. We marvel at photos of dust-lanes in those far off distant island universes. Even the motley elliptical galaxy gives us a sense of shape. But what would happen if we could take a different angle at what we see? How would galaxy mergers affect rotation? When galaxies collide, it sparks new starbirth… But how would it look?

“Young galaxies seem to have lots of gas that hasn’t yet been turned into burning stars — and they spin fast, so they look like the poster-child galaxy with spiral arms and dust lanes.” says the ATLAS team. “By telling us how fast stars in a galaxy rotate around their galaxy’s centre, the ATLAS3D result changes our understanding of galaxies and how they evolve over time.”

By studying these new images and techniques, astronomers will be able to tell us more about galaxies that have survived a crash and lived to spin. It could very well be that mergers of this type don’t affect orderly rotation and overall symmetry. The ATLAS3D team has already prepared computer simulations and performed more telescope observations to test this idea. And it’s coming straight on… Straight on for you.

Original Story Source: University of Toronto. Animation: NASA/SAO/CXC/D.Berry Images: X-ray: NASA/CXC/UMass/D.Wang et al., UV: NASA/GSFC/UIT, Optical: NASA/HST/D.Wang et al.

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