* Astronomy

A composite radio-optical image shows five new clouds of hydrogen gas discovered using the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT). The spiral galaxy M81 and its satellite, M82, are seen in visible light (white); intergalactic hydrogen gas revealed by the GBT is shown in red; and additional hydrogen gas earlier detected by the Very Large Array is shown in green.


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Credit: Chynoweth et al., NRAO/AUI/NSF, Digital Sky Survey.

The M81 Group of galaxies, 11.8 million light-years from Earth, are interacting gravitationally with each other, as shown clearly by the gas streaming among them. The newly-discovered gas clouds, each containing from 14 to 57 million times the mass of our Sun, are similar to gas clouds also found near our own Milky Way Galaxy. Astronomers analysing these M81 Group clouds conclude that they are likely remnants of earlier interactions among the galaxies and that this indicates that their analogs near the Milky Way had a similar origin.
The research team is: Katie Chynoweth, a graduate student at Vanderbilt University; Glen Langston of the National Radio Astronomy Observatory (NRAO); Min Yun of the University of Massachusetts; Felix J. Lockman of NRAO; Kate Rubin of Lick Observatory; and Sarah Scoles of Cornell University. The astronomers presented their findings to the American Astronomical Society's meeting in Austin, Texas.

Source National Radio Astronomy Observatory.

Title: Molecular clouds in the centre of M81
Authors: V. Casasola, F. Combes, D. Bettoni, G. Galletta

We investigate the molecular gas content and the excitation and fragmentation properties in the central region of the spiral galaxy Messier 81 in both the ^{12}CO(1-0) and ^{12}CO(2-1) transitions. We have recently observed the two transitions of CO in the M~81 centre with A, B, and HERA receivers of the IRAM 30-m telescope. We find no CO emission in the inner ~ 300 pc and a weak molecular gas clump structure at a distance of around 460 pc from the nucleus. Observations of the first two CO transitions allowed us to compute the line ratio, and the average I_{21}/I_{10} ratio is 0.68 for the M~81 centre. This low value, atypical both of the galactic nuclei of spiral galaxies and of interacting systems, is probably associated to diffuse gas with molecular hydrogen density that is not high enough to excite the CO molecules. After analysing the clumping properties of the molecular gas in detail, we identify very massive giant molecular associations (GMAs) in CO(2-1) emission with masses of  ~ 10^5 solar masses and diameters of  ~ 250 pc. The deduced N(H_{2})/I_{CO} ratio for the individually resolved GMAs, assumed to be virialised, is a factor of  ~ 15 higher than the standard Galactic value, showing - as suspected - that the X ratio departs significantly from the mean for galaxies with an unusual physics of the molecular gas.

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Credit NASA

The sharpest image ever taken of the large "grand design" spiral galaxy M81 is being released today at the American Astronomical Society Meeting in Honolulu, Hawaii. A spiral-shaped system of stars, dust, and gas clouds, the galaxy's arms wind all the way down into the nucleus. Though the galaxy is located 11.6 million light-years away, the Hubble Space Telescope's view is so sharp that it can resolve individual stars, along with open star clusters, globular star clusters, and even glowing regions of fluorescent gas. The Hubble data was taken with the Advanced Camera for Surveys in 2004 through 2006. The colour composite was assembled from images taken in blue, visible, and infrared light.

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Position (J2000):     R.A. 09h 55m 33s Dec. +69° 03' 55"