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NGC 4565 "Needle Galaxy"
Evan Jensen


Galaxies are massive and filled with gasses, stars, and dust. The one which we call our home is the Milky Way.  Galaxies themselves are however very unique and each has its own properties and or features that make it special in its own way. This of course led to the development of a system to tell them apart and classify them into groups that were more manageable. The galaxy I was observing is referred to as a spiral galaxy, however it has also earned the nickname "Needle Galaxy". This is due to the fact that from our point of observation the thin side-on view looks like a needle. This galaxy was discovered by Sir William Herschel in 1785. It is located over 50 million light years away in the constellation Coma Berenices and is about 30 kpc in diameter. It is classified as a SA(s)b galaxy, meaning it is a spiral galaxy with no bar , no ring, and its spiral arms are moderately loose. Some fun facts about this galaxy are it is even more luminous then the Andromeda galaxy and has even more globular clusters in it then out very own Milky Way galaxy.

In this image you can see what appears to be a very bright edge on spiral galaxy. The core of this galaxy is very luminous and the dust lane can be seen more visibly. Another very striking aspect of this image is the difference in color in the dust lane. Also this feature is what gave the galaxy its nickname, due to its very needle like appearance.

Other wavelengths:

NGC4565 in Infrared

Figure 1: Infrared of NGC 4565. Spitzer Space Telescope. 24 micron Mid- Far infrared








NGC4565 in Ultraviolet

Figure 2: GALEX The Galaxy Evolution Explorer. Ultraviolet Spectrum (two ultraviolet bands, Far UV (FUV) 1350-1780Å and Near UV (NUV) 1770 -2730Å). Spatial resolution 4.3 and 5.3 arcseconds respectively.

This image is actually two different spectral images stacked on top of one another. One of which is Far Ultraviolet and the other Near-Ultraviolet. Each is denoted by either yellow (far) or blue (near). Blue is from very hot massive stars (Far Ultraviolet); yellow is in (Near Ultraviolet) for stars that are not quite as hot. What this ends up telling us is that the slightly older stars in this galaxy are all mainly located near its center, while a lot of the newer and hotter OB stars are located along its outer edges.

In-depth Calculation:

NGC 4565 cross section

For my in-depth calculation I wished to look into the most prominent component of this galaxy which is its dust lane. Firstly, to determine the optical opacity of the dust lane, I took a graphical cross section of the galaxy's core and dust lane.  As we can see, the dip in the intensity values is where the dust lane is located on the image, and where there is a spike is the very bright core. Next I determined where an analogous portion of the galaxy is to where the dust lane is located. I did this by measuring the pixel count between the center (pixel 84) and the dust lane and determining a point on the other side of the core equal distance away.  With these points of reference, I could then determine the difference in the relative intensity at these points.  The negative natural log of the ratio of the equal distance intensity over the dust lane intensity gives the dust lane optical depth. In this case the value was 2.33, which corresponds to a dust lane that is optically thick. This can be used to determine the column density of this dust lane, using the formula

where tau is the optical depth and sigma is the dust cross section (10^-9 cm ^2 ). The column density of our dust lane is 2.33 X 10^9 cm^2, which refers to the number of dust grains per unit area integrated along a path, which in this case is the dust lane, or in other words how dense our dust lane is and its extinction potential.


Elmegreen, Debra. Galaxies and Galactic Structure. Upper Saddle River: Printice Hall PTR, 1998.

Kutner, Marc L. Astronomy: A Physical Perspective, 2nd ed. Cambridge: Cambridge University Press, 2003.

Massey, Robert, Anita Heward, and Klaus Jaeger. Public to get access to spectacular infrared images of galaxies. Accessed 29 Apr. 2013. <>.

Nemiroff, Robert and Jerry Bonnell. "The Sombrero Galaxy from Hubble" Astronomy Picture of the Day. 2010 February 11. Accessed 29 Apr 2013. <>

"Chapter 2 - GALEX Science Surveys." GALEX Galaxy Evolution Explorer . NASA, 13 Feb. 2010. Accessed 29 Apr. 2013. <>.

"GALEX Image: Ultraviolet Atlas of Nearby Galaxies Poster." GALEX Galaxy Evolution Explorer . Accessed 29 Apr. 2013. <>.

"NGC 4565 ." Wikipedia. Accessed 2 May 2013. <>.

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) 12:36:20
Declination (J2000) +25:59:16
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 5x60 seconds in C, 5x300 seconds in BVR
Date observed

March 21, 2013 (CBVR)

To get this image we took five 300 sec exposures of green, blue, red and five 60 sec of clear filters. Then I calibrated each image using bias, flat, and dark files. After that I averaged out each filter individually. Then I stacked each of those together to get one composite image for each filter. Then I combined the filters together to get one full filter image. Then I refined the brightness scale, removed bleeding stars, and fixed the color saturations.



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