Dense Gas in Ultraluminous Infrared Galaxies

Jan 15, 2010
An optical image of the luminous infrared galaxy system NGC 6240, which is actually a system of interacting galaxies. New research on this and similar galaxies suggests that the particularly efficient star formation underway largely originates in regions of very dense gas. Credit: Hubble Space Telescope

(PhysOrg.com) -- Ultraluminous infrared galaxies have luminosities that exceed a trillion suns.

(For comparison, the Milky Way's is only that of about ten billion suns.) Extreme infrared activity is known to be associated with interacting galaxies, and indeed shows that many ultraluminous systems are in collision. The physical mechanism(s) that actually power the luminosity, however, are still not understood. Might the same process(es) be underway at a low level in our galaxy?

One of the primary sources of global energy production in galaxies is star formation, and ultraluminous galaxies show all the diagnostic signs of having vigorous star formation.

In a new paper by CfA astronomer Desika Narayanan and six colleagues, the case is made that this activity is the result of a higher proportion of dense clouds of gas in these objects, and that these clumps are probably the result of the collision. The conclusion counters earlier arguments that X-rays from the nuclear are responsible by chemically enhancing the gas with molecules that facilitate .

The astronomers reached their conclusions by analyzing a set of thirty-four nearby, infrared luminous galaxies in the emitted light of three key molecules: CO, ionized HCO, and HCN. These species are sensitive probes of total gas densities ranging from about one thousand molecules per cubic centimeter to nearly one hundred million per cubic centimeter.

The team compared the brightness of the molecular emission from each species to the overall galaxy luminosity, and found a strong correlation in the sense that the brighter the lines, the higher the luminosity.

This result had been well known before, and seemed sensible since new stars form out of the gas. New in the study is the authors' finding that denser gas makes stars at a faster rate: the three species in this study, for example, sample gas that spans a factor of about one million in stellar production rates. The new research convincingly shows that other suggested mechanisms, for example enhanced chemical abundances, are less important. In addition, the paper provides a welcome, relatively comprehensive study of gas densities in luminous .

Explore further: Magnetar discovered close to supernova remnant Kesteven 79

More information: www.cfa.harvard.edu/~dnarayan/website/research.htm

Related Stories

The Energy Sources of Ultraluminous Galaxies

Nov 27, 2009

(PhysOrg.com) -- Ultraluminous infrared galaxies ((ULIRGs) are galaxies whose luminosity exceeds that of a trillion suns; for comparison, the Milky Way galaxy has a typical (and much more modest) luminosity ...

Baby booms and birth control in space

Sep 25, 2007

Stars in galaxies are a bit similar to people: during the first phase of their existence they grow rapidly, after which a stellar birth control occurs in most galaxies. Thanks to new observations from Dutch ...

A Black Hole in Medusa's Hair

Mar 11, 2009

This composite image of the Medusa galaxy (also known as NGC 4194) shows X-ray data from NASA's Chandra X-ray Observatory in blue and optical light from the Hubble Space Telescope in orange. Located above ...

Hubble Eyes Star Birth in the Extreme

Jun 13, 2006

Staring into the crowded, dusty core of two merging galaxies, NASA's Hubble Space Telescope has uncovered a region where star formation has gone wild.

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 ...

User comments : 0