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Astronomical Observatory: Cool Images

Astr212 Galaxy Projects, Spring 2007

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Sunflower Galaxy (M63, NGC 5055), Achyut Shrestha

M63
Fig.1: The Sunflower Galaxy (Telescope: Optical Guidance Systems, 16 inch)

M63, the Sunflower Galaxy, also catalogued as NGC 5055, was discovered by Pierre Méchain in 1779. It is a spiral galaxy like our own Milky way galaxy; however it has its own distinguishing features. The distance to this galaxy from us is 37 million light years. The diameter of the galaxy in the photo above is about 10 kpc which is five times smaller compared to Milky Way disk. The Sunflower Galaxy is visible in the north sky which can be seen using a small telescope in the constellation of Canes Venaciti. It has bulge in the center wrapped within the spiral arms and a surrounding halo.

The blue color of this galaxy (fig. 1) is due to a greater fraction of massive main-sequence stars. This color indicates that there are many young stars forming in the spiral arms. The visible part of the spectrum is heavily affected by the dust which absorbs and scatters the optical light.

Fig. 2 and fig. 3 are the images of M63 in near Infrared and ultraviolet respectively. The near infrared image shows a smoother pattern. More stars are visible since the near infrared part of spectrum passes through the dust while the other parts of the spectrum are blocked by the dust clouds. So the older stars are more prominent in this image than in other images. On the other hand, in the ultraviolet part of the spectrum more new stars can be seen. These are newly formed young stars and seem to make spiral pattern. The star formation usually takes place in the spiral arms since the density is more here than any other parts of the galaxy.

M63 Infrared
Fig. 2: M63 in near IR (Telescope:2MASS1.3m)
M63 Ultraviolet
Fig. 3: M63 in Ultraviolet (Telescope: GALEX)

M63 is classified as SA(rs)bc type spiral galaxy. 'S' denotes that it is a spiral galaxy while ‘bc’ is the sub-division which means it has a somewhere between medium and small bulge, less tightly spaced spiral arms and somewhat clumpy. Some spiral galaxies have spiral arms starting at center while some spiral galaxies have a ring and spiral arms start from the ring. This particular galaxy has been classified as ambiguous ('rs'), it is hard to see any ring formation around the nucleus in the above images. This galaxy has no bar, as indicated by 'A', running through the bulge. The disk orbital velocity is around 100 km/s for this type of galaxy. 

M63 Light Profile
Fig. 4: Light profile graph

The light profile graph, which is a plot of radius versus the natural log of brightness, shows a curving pattern as seen in fig. 2. The brightness of the galaxy decreases as you move from the center to the edge of the galaxy. There are few bumps along the straight line which are the spiral arms of the galaxy. The scale length of M63 is 1.7 kpc (±0.022). Typically, more than 75% of the total blue light of a spiral galaxy comes from the disk. When this galaxy is observed, it makes an angle to the plane of the sky, which is known as inclination angle and is about 49°. Galaxies with inclinations of 90° are called edge-on where as galaxies with 0° inclinations are called face-on.

M63 shows no distinct pattern in its shape. It seems to have multiple spiral arms but none of them are clearly distinguishable. The appearance of this galaxy looks less organized which says this is a flocculent spiral. When a spiral galaxy has a well defined pattern, it is termed grand design spiral. The spiral structure in M63 may be because of a series of temporary patterns. The differential rotation, i.e. regions that are adjacent at one point in time do not necessarily maintain that configuration, of the galaxy causes star regions to be drawn into a spiral. This is more obvious in the image taken in ultraviolet part of the spectrum. Newly formed stars seem to make the spiral arms pattern. While the spiral arms seem to appear and disappear at random in the other two images.

Data Reduction

The images taken in different filters were calibrated using bias, flat and dark images. After calibration, the images were aligned and median combined for each type of filter. Then the best images from each filter were color combined to get the final image (fig.1 ). The output color values were 17 for red, 8 for green and 120 for blue under LRGB. Clear filter was assigned to luminosity while green filter was assigned to visible. The saturation was intensified and gamma value of 0.5 used for the stretch. Image analysis was done using Maxim.

References:
Messier 63
<http://www.seds.org/Messier/m/m063.html>.

APOD, Robert Nemiroff (MTU) & Jerry Bonnell(USRA).
<http://antwrp.gsfc.nasa.gov/apod/ap000627.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.
<http://nedwww.ipac.caltech.edu/cgi-bin/nph-imgdata?objid=58776&objname=MESSIER%20063>

Right Ascension (J2000) 13:16:09
Declination (J2000) +41:59:25
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 15x60 seconds in C, 12x300 seconds in B, 3x300 seconds in V, 3x120 seconds in R
Date observed

March 16 , 2007 (C)
March 17 , 2007 (CBVR)

 

 

 

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