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Galaxy NGC 4656
Elizabeth Stranzenbach

NGC 4656

 

Introduction

Galaxies are huge groups of stars that are pulled together by their gravitational pull on each other. They swirl around in the galactic center and usually form a disk around the core. They can form beautiful spiral arms too.

This galaxy named NGC 4656 is also referred to as the Hockey stick galaxy (so says NOAO). It is a distant galaxy: about 8 Megaparsecs away (about 27 million light years). It is very blue. This galaxy is about 24 kiloparsecs across (about 78,000 light years). Our galaxy, the Milky way, is about 100,000 light years across. It is classified as SB(s)m pec. This means that it is a peculiar barred spiral merger without a ring.

This galaxy is unusually blue. Most galaxies are not this blue. The galaxy is viewed edge on. It has an irregular part at the top of the spiral.  This is because NGC 4656 is the end state of a merger of two galaxies. This merging causes the galaxies to influence each other gravitationally causing their shapes to become irregular. The irregular part at the top of the image is probably the core of the other galaxy that merged with it. At the bottom is a tidal tail caused by the gravitational effects of the merging process.   

 

Multiwavelength comparison

NGC 4656 at 70 micron

Figure 1: This image of NGC 4656 is from 70um, a far infrared wavelength. The regions that are highlighted in this wavelength are the core of the spiral and the irregular top of the spiral. The far infrared emission is caused by dust grains being warmed by the UV of hot stars in the cores of the two merging galaxies. This warmed dust indicates star formation in the highlighted regions. This image was taken by the Spitzer MIPS telescope.

 

 

 

NGC 4656 at 20cmFigure 2: This image of NGC 4656 is from 21cm, the radio wavelength emission line. This emission is caused by HI clouds, which are clouds of neutral hydrogen gas. This usually indicates the thin disk but there is no disk in this image. The two dots in the center that are close to each other are NGC 4656. The others are not part of NGC 4656. These dots correspond to the leftover cores of the two merged galaxies. The dots are showing what is left of the disks of those galaxies. This image was taken by the VLA telescope.

 

 

References:

"Hockey Stick Galaxy NGC 4656." National Optical Astronomy Observatory. Accessed 18 Apr. 2013. <http://www.noao.edu/image_gallery/html/im1111.html>.

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Right Ascension (J2000) 12:43:58.10
Declination (J2000) +32:10:11.0
Filters used

8 images in blue(B), 2 in red(R), 6 in clear(C), and 4 in green(V)

Exposure time per filter 5x60 seconds in C, 300 seconds in BVR
Date observed

March 29, 2013 (CVR)
April 12, 2013 (B)

Data analysis: NGC 4656 is a very distant and blue galaxy so I had to use mainly the blue filter. I collected 8 images in the blue filter on April 12. On March 29 I collected 2 images in the red filter, 6 in the clear filter, and 4 in the V filter. For color combine I used the settings for Red: 1, Green(V): 1.5, and Blue: 25. For brightness/contrast, I set the Permanent Stretch Type to Gamma 0.6. The values I used for the Minimum was 2480 and 3500 for the Maximum. I did not need to adjust the color saturation with this galaxy.

 

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