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Barred Spiral Galaxy Messier 109 (NGC 3992)
Andrew Peoples

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Spiral Galaxy M109

Messier 109 (also known as NGC 3992) is a Barred-Spiral Galaxy, same type as our Milky Way, and was discovered by Pierre Méchain in 1781. Messier 109 resides about 75 million light-years away from our Sun. That’s 30 times farther than our cosmic neighbor the Andromeda Galaxy. Messier 109 is also approximately 60,000 light-years in diameter, making it about 3/5 the size of our own Galaxy.

Messier 109 is categorized as an "SB(rs)bc" type galaxy. This means it is a barred-spiral galaxy (“SB”), with borderline rings (“rs”), a relatively small central bulge and loose, textured, arms (“bc”).

When viewing the night sky Messier 109 is located in the constellation Ursa Major, a.k.a. “The Big Dipper” (see below). It lies next to the star Phecda, which constitutes the lower left corner of the Dipper’s “bowl”.

Ursa Major constellation chart

Image from PP3-Celestial Chart Generation (Torsten Bronger), via Wikipedia

The small purple smudge near the upper left corner of the image below is UGC 6969, an irregular galaxy that is the brightest of M109's three small satellite galaxies.


Light, Colors, and Images:

When we look closely at the image of this galaxy we can see that different parts of the galaxy's structure give off different intensities and colors of light. These variations can reveal quite a bit of information about what is happening within a galaxy or even what is happening in the space between us and it. When we look at a much higher resolution image of Messier 109 we can also see several long brown patches within the galactic disk. These are residual dust clouds most likely left over by a galactic collision or merger somewhere in M109's past. These clouds are often created when diffuse gas clouds get compressed by gravitational density waves forming long feathery streaks of undissipated gas. These clouds are one of the possible sources of the raw materials needed to produce new stars. Once the cloud reaches a certain density the dust and gas clumps up to the point where there is enough mass compressed together to sustain the nuclear fusion of hydrogen atoms; the 'engine' of a star.

M109 higher resolution optical image

Image credit: Dale Swanson/Adam Block/NOAO/AURA/NSF , labels added.

The bright blue or purple regions in the spiral arms indicate regions of recent star production where new hot stars are being born. This blue color is given off by the large number high-mass, blue stars in the area. Conveniently, the color of a star has a direct correlation to its temperature. Blue stars are generally hotter and red stars are generally cooler. What this also means is that blue stars, because of their higher temperature, burn much faster and therefore don't last nearly as long. If a region has a high concentration of these stars, like the regions in this galaxy, then that's a good indication that they were formed nearby. The overall purple hue is from the mixture blue light from young stars and red light coming from gaseous HII regions. HII regions are clouds of hydrogen gas that have been mostly ionized by stars newly formed within their midst. The red light, known as H-alpha radiation, given off is a side-effect of the ionization-recombination-ionization cycle Hydrogen undergoes when exposed to UV radiation from the new stars. These regions are essentially gigantic star nurseries and are therefore an important part in studying how a galaxy evolves and matures throughout its lifespan.

Not all light is visible:

Astronomical objects give off light/electromagnetic-radiation all across the spectrum. This is extremely useful to us because some objects or features are invisible at some wavelengths but are very vivid at others. For example dust is largely opaque at shorter wavelengths (visible and UV) but it allows light through at longer wavelengths (Infrared, Microwave, Radio, etc). Below are two pictures of M109 taken in the radio part of the spectrum. The left image was taken in red light; the right image was taken in near infrared light where dust is more transparent. From the data within these images we are able to see that around the central bar and inner arms there is very little difference between the two images. This means that there is very little light lost due to dust extinction around the galactic center.

NGC3992 in red lightNGC 3992 in infrared light

Left: Red image of the inner region of NGC3992, shown in isophotal false color to highlight the structures. Image from Wilke et al: "The spiral structure extends up to the outer parts of the disk. The image was obtained using the 3.5m MPIA telescope at Calar Alto (Spain)"

Right: Similar image in near infrared (J band). Image from Wilke et al: "Observations were performed using the MAGICcamera mounted at the 2.2m-MPIA-telescope at Calar Alto (Spain)."


Creating Artificial Gas Cloud Rotation Curves using M109 as a standard model:

In May, 2000 K. Wilke, C. Möllenhoff, and M. Matthias concluded their study of the galaxies NGC 3992 (a.k.a. Messier 109) and NGC 7479. Later that same month they submitted their results to Astronomy & Astrophysics, a well known and respected scientific journal. The goal of their research was to develop new, more accurate, artificial rotation curves with which they would be able to better predict the rotations of HII gas regions within galaxies. They chose NGC 3992 and NGC 7479 as their test beds for developing their models. Below are three images. The left one is an image of M109 in the infrared part of the spectrum. The center is a picture of the model they developed to negate the effects of the galactic disk, bulge, and bar on their calculations of HII rotations. The right image shows the residuals left over when the model is subtracted from the left image, showing how well their new rotation curves fit the actual data. Though they admitted that even more accurate curves could be made with Near-Infared images of higher spatial resolution.

J band imageModelJ-band residuals

Image and caption from Wilke et al: "Left: J-band image of NGC3992 (scale: 0.67''/pixel), Center: 2D three-component model of the observed luminosity distribution, Right: residuals remaining after subtraction of the model from the original image."

Data Reduction:

The image of Messier 109 at the top of this page is actually a synthesis of several individual pictures taken using different filters and at slightly different times. Over 2 hours of telescope time was available for each galaxy, which was divided between the four different filter types. In this case because the telescope is much less sensitive in the blue part of the spectrum the most amount of time was spend using the Blue(B) filter. Before combining the images various sources of 'noise', such as dark, flat, and bias calibrations as well as other imperfections such as 'bleeding' were removed. Finally all the pictures were combined together into one image covering the entire visible spectrum. This image was then further enhanced by setting the color balance: Red=1, Green=1.5, and Blue = 7 and adjusting the Gamma and Saturation values.

More Astronomical Data: (from Wilke et al)

Mb (corrected Blue magnitude)

Blue luminosity vs. Sun's luminosity
Total Mass vs. Sun's Mass

Calvin-Rehoboth Observations:

Right Ascension (J2000) 11:57:36.0
Declination (J2000) +53:22:28
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 12x300 seconds in B, 10x300 seconds in C, 2x300s each in V, R
Date observed

March 2 and March 4, 2011


Bottema, R. and M. A. W. Verheijen. "Dark and luminous matter in the NGC 3992 group of galaxies". Astronomy and Astrophysics (2002), 388, 793. <>

Bronger, Torsten. "PP3 - Celestial Chart Generation". Accessed May 1, 2011. <> Image via Wikipedia .

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

“Messier 101-110” Astronomy Central. Accessed 25 April, 2011. <>

Wilke, K. , C. Möllenhoff, and M. Matthias. "Mass distribution and kinematics of the barred galaxies NGC3992 and NGC7479", Astronomy and Astrophysics (2000), 361, 507. <>

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.



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