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NGC 3624

NGC 3628 is a beautiful edge on spiral galaxy that is nestled within the constellation Leo. This galaxy was first discovered by William Herschel in 1784 and is best known by its edge on orientation and glorious dust extinction. NGC 3628 belongs to a small group of galaxies known as the Leo triplet which includes M65 and M66. These galaxies are in relatively close proximity and are causing tidal effects on one another. As seen in the image below, NGC 3628 has a long tail that is believed to have been created by galactic interactions. More evidence for galactic interaction is the opposing orbit of gas and stars.

NGC 3624 Tidal Tail

The first image above shows NGC 3628 possesses a very distinct dust extinction pattern as well as a glowing yellow bulge in the center. The yellow color of this bulge suggests that the central bulge of the galaxy is comprised of low-mass stars and stars that are farther along in their evolution. NGC 3628 is also a galaxy classified to be a starburst galaxy or a low level active galactic nucleus (AGN). This suggest that NGC 3628 is a high energy galaxy at the core. Under X-ray inspection the galaxy appears to have high levels of X-ray radiation emitting from its core. These levels of X-ray emission are typically common with quasars. Meaning that NGC 3628’s light is being produced by stars and a quasar. The extinction caused by the dust suggest that there is little light emitting gas located throughout the major axis of the galaxy.

NGC 3628 is located approximately 35 million light years away. This provides an angular size of 13.1 arc minutes which corresponds to a physical size of 133,000 light years along its major axis. The Milky Way galaxy by comparison is 100,000 light years in diameter, which is approximately 75% the size of NGC 3628.

The dust lane that is aligned with the major axis of the galaxy provides an excellent extinction pattern.

Center Extinction Profile

When this extinction pattern is analyzed it provides the graph shown below. This graph includes two lines, the dotted line represents the measured the light profile through the minor axis of NGC 3628, while the solid line represents a calculated value for the light profile if there was no extinction.

Measured vs. Calculated Pixel Intensity

The graph above provides the required information to solve for the optical depth and the column density.

Column Density

This graph shows the calculated column density as a function of the postion along the minor axis of NGC 3628. From this graph, it is seen that the density of the dust lane increases drastically as the center of the galaxy's dust lane approaches. This is to be expected. As the dust lane density increases the extinction of the light that passes through it increases and shows up as dark spots in the image. The peaks in dust density correspond directly with the dark spots on the image.


Arp et al. "NGC 3628: Ejection activity associated with quasars." Astronomy & Astrophysics. 391: 833-840. 2002. <>

Saurdiff, Glen, Joan Simpson, F. Haase, S. Peterson, and K. Garmany. "NGC 3628." National Optical Astronomy Observatory. Aura, 27 Mar. 20144. Web. 4 May 2015. <>..

Sinha, Sayontan. "NGC 3628: Sarah's Galaxy." Anne's Astronomy News. Ed. Sayontan Sinha. N.p., 2013. Web. 2 May 2015.

Wikipedia, "NGC 3628".

Right Ascension (J2000) 11:20:16
Declination (J2000) +13:35:24
Filters used B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter V, R (300s x 7); B (300s x 6), C (300s x 4)
Image dimension 1092x736 pixels; 23.8x16.1 arcminutes
Date/time observed March 28, 2015, 3:50 UT

In order to generate this image a variety of steps were taken. Each image for every filter was calibrated. This calibration was done with respect to a bias, dark, and flat image. After the calibration was compete each image from their respective filter were aligned using "auto-star matching" under the alignment tab and combined using "sigma clip" "16-bit Int". The combined single filter images were then combined using a color combine of "LRGB". These images were aligned using "auto-star align". The color balance was the adjusted to red 1, green 1.4, and blue 6.1 with the luminace set to 5%. Image refinement and pixel correction were then completed to remove noise in the image. Finally, saturation level was adjusted to emphasis detail in the dust lane while not over saturating the image.



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