Exposing the Nature of Cosmic Liaisons

Oct 16, 2007
Exposing the Nature of Cosmic Liaisons
Risa Wechsler has developed a new tool for measuring how galaxy interactions, such as that which drew out the trail of stars in the Tadpole Galaxy (pictured here), affect the rate of star formation.

Risa Wechsler of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) and her collaborators have devised a powerful technique to study how interactions between galaxies affect star formation. Their results shed light on the fundamental processes that drive galactic evolution.

In the early universe, the rate of star formation was higher than it is today. Galaxies frequently collided and coalesced with one another, spawning a profusion of new stars with each encounter. Although such prolific events are now relatively infrequent, less spectacular galactic interactions continue to forge stars and shape galaxies. Observational studies suggest that even these interactions increase the rate of star formation, but there is little consensus on the frequency and magnitude of such events.

"To study this, you need to observe pairs of galaxies, which have either just interacted or are about to interact, and determine whether their star formation rate is higher or lower than similar galaxies that haven't interacted," said Wechsler, who collaborated with researchers from the Center for Cosmology at the University of California in Irvine and the University of Chicago. Although the idea is straightforward, its execution is problematic. Galaxy interactions are highly complex and dynamic, and observation yields a mere snapshot of the unfolding events.

One complication is that the majority of galaxies exist in groups, where frequent interactions may have exhausted a galaxy's star-forming resources. In such crowded environments, it is difficult to discern the immediate effects of an isolated interaction. According to Wechsler, "it's very hard from observations alone to figure out how to control for this."

To overcome this technical hurdle, Wechsler used a cosmological simulation of dark matter and galaxies. “The simulation allowed us to see statistically how galaxies are connected to their environment. This enabled us to estimate the bias of pairs [toward group environments], and then to try to define selection criteria that would give us isolated pairs and appropriate controls." The criteria also controlled for galaxy age and brightness, thus optimizing their comparability.

Elizabeth Barton, Wechsler's collaborator from UCI, then used these criteria to analyze a subset of the 2dF astronomical survey. The analysis revealed that 14% of the galaxies in close pairs exhibited star formation rates boosted by at least a factor of 5, and on average a factor of 30. "This is the first clean estimate of triggered star formation from a large galaxy sample," Wechsler noted. "Our selection criteria allow us to constrain how the star formation rate changes in interactions, and will help us figure out how star formation contributes to galaxy evolution."

Source: by Elizabeth Buchen, SLAC

Explore further: Thermonuclear X-ray bursts on neutron stars set speed record

add to favorites email to friend print save as pdf

Related Stories

China's Alibaba plans IPO for week of September 8

14 hours ago

Chinese e-commerce giant Alibaba plans to hold its initial public offering on the US stock market the week of September 8, the Wall Street Journal reported Saturday, citing a person familiar with the matter.

Tablet sales slow as PCs find footing

15 hours ago

Tablets won't eclipse personal computers as fast as once thought, according to studies by market tracker International Data Corporation (IDC).

Startups offer banking for smartphone users

15 hours ago

The latest banks are small enough to fit in the palm of your hand. Startups, such as Moven and Simple, offer banking that's designed specifically for smartphones, enabling users to track their spending on the go. Some things ...

Recommended for you

How can we find tiny particles in exoplanet atmospheres?

Aug 29, 2014

It may seem like magic, but astronomers have worked out a scheme that will allow them to detect and measure particles ten times smaller than the width of a human hair, even at many light-years distance.  ...

Spitzer telescope witnesses asteroid smashup

Aug 28, 2014

(Phys.org) —NASA's Spitzer Space Telescope has spotted an eruption of dust around a young star, possibly the result of a smashup between large asteroids. This type of collision can eventually lead to the ...

Witnessing the early growth of a giant

Aug 27, 2014

Astronomers have uncovered for the first time the earliest stages of a massive galaxy forming in the young Universe. The discovery was made possible through combining observations from the NASA/ESA Hubble ...

User comments : 0