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Post Info TOPIC: Messier 81


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Title: Discovery of New Dwarf Galaxies in the M81 Group
Authors: Kristin Chiboucas, Igor D. Karachentsev, R. Brent Tully

An order of magnitude more dwarf galaxies are expected to inhabit the Local Group, based on currently accepted galaxy formation models, than have been observed. This discrepancy has been noted in environments ranging from the field to rich clusters. However, no complete census of dwarf galaxies exist in any environment. The discovery of the smallest and faintest dwarfs is hampered by the limitations in detecting such faint and low surface brightness galaxies. An even greater difficulty is establishing distances to or group/cluster membership for such faint galaxies. The M81 group provides an almost unique opportunity for establishing membership for galaxies in a low density region complete to magnitudes as faint as M_{r'} = -10. With a distance modulus of 27.8, the tip of the red giant branch just resolves in ground-based surveys. We have surveyed a 65 square degree region around M81 with the CFHT/MegaCam. From these images we have detected 22 new dwarf galaxy candidates. Photometric, morphological, and structural properties are presented for the candidates. The group luminosity function has a faint end slope characterized by the parameter alpha = -1.28+/-0.06. We discuss implications of this dwarf galaxy population on cosmological models.

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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.

M81
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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.


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Holmberg IX.kmz

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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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Title: Molecular gas and star formation in M81
Authors: V. Casasola, F. Combes, G. Galletta, D. Bettoni

We present IRAM 30m observations of the central 1.6 kpc of the spiral M81 galaxy. The molecular gas appears weak and with an unusual excitation physics. We discuss a possible link between low CO emission and weak FUV surface brightness.

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m81_29may07
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Credit NASA


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The new image shows young, hot stars only a few million years old in the galaxy's spiral arms, as well as others that formed in a burst of activity about 600 million years ago.
It also reveals greenish areas of current star formation, where the gas around infant stars is glowing, or fluorescing, due to the ultraviolet light absorbed from the stars.
The current burst of star formation may have been triggered by an event 300 million years ago, when the galaxy passed close to two neighbouring galaxies - NGC 3077 and M82. Their gravity could have stirred up gas in M81, encouraging it to condense into stars.

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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"


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Bright Spiral Galaxy M81 in Ultraviolet from Galex
In a new Galaxy Evolution Explorer ultraviolet image, the magnificent M81 spiral galaxy is shown at the centre. The orbiting observatory spies the galaxy's "sizzling young starlets" as wisps of bluish-white swirling around a central golden glow. The tints of gold at M81's centre come from a "senior citizen" population of smouldering stars.
The large fluffy bluish-white material to the left of M81 is a neighbouring galaxy called Holmberg IX. This galaxy is practically invisible to the naked human eye. However, it is illuminated brilliantly in GALEX's wide ultraviolet eyes. Its ultraviolet colours show that it is actively forming young stars. The bluish-white fuzz in the space surrounding M81 and Holmberg IX is new star formation triggered by gravitational interactions between the two galaxies.
M81 and Holberg IX are located approximately 12 million light-years away in the northern constellation Ursa Major.

m81_big
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Image Credit: NASA/JPL-Caltech/J. Huchra (Harvard-Smithsonian CfA)

Position(2000): RA: 09:55.6 (h:m) DEC: +69:04(deg:m)

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