Astr212, Spring 2005: M100, Chris Beaumont

Calvin Observatory

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M100: A Grand Design Spiral Galaxy

Galaxies are social objects. Even a brief survey the sky will reveal that they reside in groups, called galaxy clusters. The nearest such ensemble is the Virgo Cluster, of which M100 is a prominent member. Lying 58.7 million light years distant, M100 is 26 kly in diameter, about 80 percent the size of our own Milky Way Galaxy. A thoughtful study of both this image and others of M100 can reveal much about the nature of galaxies in general.

The most immediate and striking feature of this galaxy is its majestic spiral structure. Because of its easily identifiable arms, it is classified as a Grand-Design spiral galaxy. The display is especially inspiring because the galaxy is oriented in such a way that we see it nearly face on (By contrast, spiral galaxy M104 of the Virgo Cluster is seen nearly edge on, a dramatic difference).

The most dominant source of light in the galaxy is the core (called the galactic bulge). The region is incredibly bright and yellow. The light is produced by a strong concentration of globular clusters surrounding a central black hole. Extending out of the bulge are the dominant spiral arms. A careful look at the spiral arms reveals that they are composed of three layers. The innermost layer is marked by dark lanes of dust. This material (mostly Hydrogen gas) is being compressed as it enters into the spiral. As it passes through the arm, the hydrogen is compressed enough for new stars to form. The energy given off by these new stars ionizes the surrounding Hydrogen cloud, causing it to glow red. Beyond this red layer is the outer blue layer. By the time the newly formed stars leave the arms, the most massive and energetic members have run out of stellar fuel and have exploded. Without this energy source, the hydrogen gas cools, and we see the blue light given off by the remaining stars. There is also a knotty structure to the arms, indicating regions of concentrated star formation. The full picture reveals at least 5 other galaxies in the same field of view. Many of these are Dwarf Ellipticals or Lenticular Galaxies in the Virgo Cluster. This field is a microcosm for galactic distribution in general; spiral galaxies are much less common than smaller Elliptical and Lenticular galaxies.

Text and image made by student Chris Beaumont. Read more about M100 in his Astr212 project.

Observation Details
Coordinates	RA (J2000) 12h 22m 55.2s	Dec (J2000) 15° 49' 23"	This is in the constellation Virgo. North is up and East is to the left.
Scale	The image is 16.4 by 12.5 arcminutes, which is 280,000 by 210,000 lightyears at the distance of M100 (60 million lightyears)
Filter	Clear	B	V	R
Exposure time per filter	12 x 300s	13 x 300s	7 x 300s	7 x 300s
Dates of observation	2005 Mar 1 2005 Mar 8	2005 Feb 8 2005 April 5	2005 Feb 8 2005 March 7 2005 April 5	2005 Feb 8 2005 March 7 2005 April 5
Processing details:	All images were taken with the 16 inch telescope at the Calvin Rehoboth Robotic Observatory. Data in each of the red, blue, visual (green) and clear filters were calibrated using dark, bias, and flat fields to remove systematic artifacts from thermal noise, optical effects of the telescope, and digital artifacts. All the images from each filter were then aligned and combined with MaxIM’s Sigma Clip algorithm to improve the signal/noise ratio. An unsharp mask was applied to the clear image, which had the best S/N. Next, the combined image from each filter was combined with the others to produce a color picture. Color balance was selected so as to make a majority of background stars appear white. Next, a non-linear transform was applied to the image to enhance the fainter regions without overexposing the bulge. Finally, the color saturation was boosted to 120% and bad pixels were removed using MaxIM’s bad pixel processing tool.

Content updated 5/19/05