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Pinwheel Galaxy
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M101_INTs.jpg
This fantastic image of the Pinwheel Galaxy was obtained using the Wide Field Camera on the Isaac Newton Telescope. Its a three-colour composite made from data collected through the filters Sloan g, r+H and i. Credit: R. Barrena and D. Lpez (IAC). [ JPEG | TIFF | PDF (with text) ].

The Pinwheel Galaxy, also known as Messier 101 or NGC 5457, is a grand-design spiral galaxy located at a distance of about 27 million light-years from Earth. It is nearly twice the size of our Milky Way.

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RE: M101
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With a diameter of about 170,000 light years, the galaxy Messier 101 (M101) is a swirling spiral of stars, gas, and dust whose diameter is nearly twice that of our Milky Way Galaxy. Its orientation allows telescopes to see the spiral structure of the galaxy face-on, giving inspiration for its nickname of the Pinwheel Galaxy. M101 is found in the Ursa Major constellation and is at a distance of about 25 million light years from Earth.

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The Pinwheel galaxy is gussied up in infrared light in a new picture from NASA's Spitzer Space Telescope.
The fluffy-looking galaxy, officially named Messier 101, is dominated by a mishmash of spiral arms. In Spitzer's new view, in which infrared light is colour coded, the galaxy sports a swirling blue centre and a unique, coral-red outer ring.
A new paper appearing July 20 in the Astrophysical Journal explains why this outer ring stands out. According to the authors, the red colour highlights a zone where organic molecules called polycyclic aromatic hydrocarbons, which are present throughout most of the galaxy, suddenly disappear.

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AKARI: New Model of Galaxy Evolution May Be Necessary
AKARI has been observing galaxies in the far distant Universe to address one of the most important questions in modern astronomy: how did the galaxies evolve into their current form? The AKARI data shows that the number of galaxies increases rapidly as they appear fainter, and so indicates that the galaxies have merged. However, they do not seem to evolve as drastically as inferred by previous observations. As AKARI's are the most sensitive observations ever made at these wavelengths, this result suggests that a new galaxy evolution model may be necessary.

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The Pinwheel Galaxy, one of two identified with the appelation "pinwheel," with clear spiral structure in the arms, as seen through the Astrochannels 14" telescope and video camera.



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The oxygen abundance in the inner HII regions
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Title: The oxygen abundance in the inner HII regions of M101. Implications for the calibration of strong-line metallicity indicators
Authors: Fabio Bresolin

I present deep spectroscopy of four HII regions in the inner, metal-rich zone of the spiral galaxy M101 obtained with the LRIS spectrograph at the Keck telescope. From the analysis of the collisionally excited lines in two of the target HII regions, H1013 and H493, I have obtained oxygen abundances 12+log(O/H)=8.52 and 12+log(O/H)=8.74, respectively. These measurements extend the determination of the oxygen abundance gradient of M101 via the direct method to only 3 kpc from the centre. The intensity of the CII 4267 line in H1013 leads to a carbon abundance 12+log(C/H)=8.66, corresponding to nearly twice the solar value. From a comparison of the continuum temperature derived from the Balmer discontinuity, T(Bac)=5000 K, and the line temperature derived from (OIII)4363/5007, T(OIII)=7700 K, an average temperature T0=5500 K and a mean square temperature fluctuation t=0.06 have been derived. Accounting for the spatial inhomogeneity in temperature raises the oxygen abundance obtained from the oxygen auroral lines to 12+log(O/H)=8.93. These findings are discussed in the context of the calibration of strong-line metallicity indicators, in particular of the upper branch of R23. There is no evidence for the strong abundance biases arising from temperature gradients predicted theoretically for metal-rich HII regions.

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M101
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This Hubble Space Telescope image of the face-on spiral galaxy Messier 101 (NGC 4547, The Pinwheel Galaxy), is the largest and most detailed photo of a spiral galaxy that has ever been released from Hubble.
The galaxys portrait is actually composed of 51 individual exposures taken with Hubble's Advanced Camera for Surveys and the Wide Field and Planetary Camera 2 in March 1994, September 1994, June 1999, November 2002, and January 2003. The newly composed image also includes elements from images from ground-based photos.


Expand (112kb, 800 x 625)
Expand (997kb, 1280x1024)
Position (2000): R.A. 14h 03m 13s Dec. +54 20' 53"

The final composite image measures 16,000 by 12,000 pixels.

The Hubble archived observations that went into assembling this image were originally acquired for a range of Hubble projects: determining the expansion rate of the universe, studying the formation of star clusters in the giant star birth regions, finding the stars responsible for intense X-ray emission, and discovering blue supergiant stars.

The giant spiral disk of stars, dust, and gas is 170,000 light-years across or nearly twice the diameter of our galaxy, the Milky Way. M101 is estimated to contain at least one trillion stars. Approximately 100 billion of these stars could be like our Sun in terms of temperature and lifetime. It dominates a small group of galaxies, with some of its neighbours such as NGC5474 showing tidal effects of M101.

The magnitude 7.9 galaxy's spiral arms are sprinkled with large regions of star-forming nebulae. These nebulae are areas of intense star formation within giant molecular hydrogen clouds. Brilliant young clusters of hot, blue, newborn stars trace out the spiral arms. The disk of M101 is so thin that Hubble easily sees many more distant galaxies lying behind the galaxy.
M101 (also nicknamed the Pinwheel Galaxy) lies in the northern circumpolar constellation, Ursa Major (The Great Bear), at a distance of 25 million light-years from Earth. Therefore, we are seeing the galaxy as it looked 25 million years ago when the light we're receiving from it now was emitted by its stars at the beginning of Earth's Miocene Period, when mammals flourished and the Mastodon first appeared on Earth. The galaxy fills a region in the sky equal to one-fifth the area of the full moon.

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