January 19, 2013
Astronomers Track Ionization Source For Nearby Starburst Galaxy
redOrbit Staff & Wire Reports - Your Universe Online
Shockwaves originating from the central starburst region of galaxy Messier 82 (M82) are most likely the source of bright clouds within a “cap” of gas clouds located some 40,000 light years away, astronomers have discovered.
Kyoto University´s Dr. Kazuya Matsubayshi and an international team of colleagues observed the nearby starburst galaxy, which is located approximately 12 million light-years away in the constellation Ursa Major, using instruments mounted on the Subaru Telescope at the National Astronomical Observatory of Japan.
By capturing an image using the telescope´s Faint Object Camera and Spectrograph (FOCAS) device, the astronomers found that outflows of gas from M82 collided with the gas cloud cap, and that the supersonic speed disturbances emanating from the galaxy´s central starburst region ionized the gas clouds within the gap.
Their discoveries “provide important clues about the wind's power,” the Observatory explained in a statement Friday.
In starburst galaxies, the central regions tend to be regions of immense star formation, the researchers explained. Thousands of massive stars several times heavier than the Sun are born there, and when they die, they explode as supernovae and heat the gases surrounding them to temperatures in excess of a million degrees.
The hot gas then escapes the galaxy as galactic winds that are so powerful that they could factor into the evolution of galaxies and of the inter-galactic medium, the astronomers added. Thus far, however, it has been difficult to establish just how powerful they actually are, because they tend to be diffused and hard to analyze.
“Nevertheless, it is possible to precisely estimate their energy level by measuring how far the galactic winds reach,” the Observatory said. That´s exactly what Dr. Matsubayshi´s team sought to do by studying M82, which is one of the starburst galaxies closest to Earth and also home to large-scale galactic winds known as “superwinds.”
M82´s cap is home to gas clouds some 40,000 light years away from its galactic disk, leading the researchers to seek out the cap´s ionization source to find out why those gas clouds were so far away. They believed that the ionization sources of the galaxy´s cap were either ultraviolet (UV) photons from massive stars within M82´s starburst regions, or shockwaves caused by the collision of its galactic winds with gas clouds inside the cap.
"Because we can estimate the intensity of ultraviolet photons from the starburst regions and the pressure of the galactic winds from past observational data, the morphology and H-alpha intensity,” — or, in other words, the intensity of one of the emission lines from hydrogen atoms — “of the cap region will reveal the answer,” the researchers said.
Using the Subaru Telescope, they were able to capture images of continuum and H-alpha emissions from the cap. If the ionization source was the UV photons, the H-alpha emission should have been one-tenth as strong as was recorded, they explained.
For that reason, “the team concluded that shockwaves from M 82's galactic winds ionized the gas clouds in the cap,” the Observatory said. “This suggests that the galactic winds travel and have direct impacts on inter-galactic gas at least 40,000 light years away from the galactic disk.”