Messier 51 (NGC 5194)

Observatory / Course Archives / ASTR 212 Spring 2019 / Van Wyhe

Messier 51 or NGC 5194 a famous spiral galaxy found in the constellation Canes Venatici about 23 million light years away from Earth. Know by many as the Whirlpool Galaxy because of its incredible spiral pattern. It was first noted to have a spiral nature to it in 1845 by William Parsons. But at the time it was believe to be a nebula. It continued to be called a nebula until Edwin Hubble proved spiral nebulae were actually distinct galaxies. Even though it was thought to be a nebula in 1845, it is still credited as the first observed spiral galaxy.

Due to the distinct spiral arms and the second smaller galaxy, Messier 51 has become one of the most recognized spiral galaxy. While looking at the galaxy in the image above, a few colors should be noted. The first and faintest is the pink sections near the arms. These areas are emission nebulae. The pink coloring is caused by ionized gases emitting light. Then comes the more distinct structure the blue sections. The blue areas are known as reflection nebulae. The color of the reflection nebulae come from a similar phenomenon as the sky being blue. In other words, the reflection nebulae scatter the nearby star’s light causing a wavelength of light in the blue spectrum. The fact that both of these nebulae are seen means that there is star formation occurring there. The next structure of note is the darker and empty looking streaks along the arms. These structures are known as absorption nebulae. They are much cooler gasses that absorb star light as opposed to the other nebulae. Finally, one must notice the two bright yellow cores. The yellow coloring indicates an older star population and a lack of star formation. A unique thing about Messier 51 is that it consists of two galaxies. The main one being named M51a and the smaller one M51b. M51b is connected to M51a by what looks like a faint bridge. These galaxies will one day fully merge but that will take a while.

M51a has a major diameter of roughly 40500 lightyears and a minor diameter of approximately 38000 lightyears. This was calculated from the image above. Using its known distance away and angular size shown in the image, the major and minor diameter was calculated. Then using these values, the inclination angle could be determined. It was determined to be at roughly a 20-degree inclination.

“The Spitzer image is a four-color composite of invisible light, showing emissions from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8.0 microns (red). These wavelengths are roughly 10 times longer than those seen by the human eye. The visible light image comes from the Kitt Peak National Observatory 2.1m telescope, and has the same orientation and size as the Spitzer infrared image, measuring 9.9 by 13.7 arcminutes (north up). Also a four-color composite, the visible light image shows emissions from 0.4 to 0.7 microns, including the H-alpha nebular feature (red in the image).” https://www.messier-objects.com/messier-51-whirlpool-galaxy/

When looking at the image taken by the Spitzer Space Telescope, the temperature gradient con be seen much clearer; specifically, when looking at M51b. It should be noted that the blue color represents the smallest wavelength which corresponds to the hottest temperature. Another interesting thing that the Spitzer shows is the connection between the two galaxies. It appears red which means a relatively cooler gas that still emits in the infrared which proposes that there is star formation that occurs here.

References:

Messier 51: Whirlpool Galaxy. Messier Objects, 3 June 2015, www.messier-objects.com/messier-51-whirlpool-galaxy/.

Whirlpool Galaxy. Wikipedia, en.wikipedia.org/wiki/Whirlpool_Galaxy.

Kennicutt,Robert C.,,Jr, et al. Star Formation in NGC 5194 (M51a). II. the Spatially-Resolved Star Formation Law. Ithaca: Cornell University Library, arXiv.org, 2007. ProQuest.

Watkins, Aaron E., et al. Discovery of a Vast Ionized Gas Cloud in the M51 System. Ithaca: Cornell University Library, arXiv.org, 2018. ProQuest..

Right Ascension (J2000)	13:30
Declination (J2000)	47:12:00
Filters used	B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter	B (180s x 28), V(240 x 5), and R(180s x 3); C (60s x 7)
Image dimension	1092x736 pixels; 23.8x16.1 arcminutes
Date/time observed	March 18. 2019

Data reduction was done through the MaxIm. The biases and darks were stacked to create a master bias and a master dark image. Then using the master bias and dark images, the raw flats for each filter were calibrated. Then master flats for each filter was created. These flats were then stacked in order to create a color image. This color image did not look accuarte to what it should be. In order to fix this we balanced the colors to make ot look more realistic. The final color balance settings used in the image above were R: 2.5; V: 2.8;  B:18.