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"The Box" NGC 4169 Galaxy Group
Joseph Garbini

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NGC 4169 Galaxy Group "The Box" NGC 4169 Galaxy Group "The Box"

The NGC 4169 galaxy group, also known as "The Box" galaxy group, includes four galaxies: NGC 4169, 4173, 4174, and 4175. Galaxies such as these are often located in small "Galaxy Groups," where several galaxies are located within the same region in space. Most galaxies in the universe are located in these types of Galaxy Groups. Our own galaxy, the Milky Way, is a member of a Galaxy Group that includes three large spiral galaxies and several irregular, elliptical, and dwarf galaxies. In "The Box" Galaxy Group, there are only 4 main galaxies that are visible. Three of these galaxies are close in proximity to each other at about 55 Mpc distance from Earth, with the fourth galaxy located a great deal closer at 9.7 Mpc (NGC 4173). For reference, one (1) Mpc is about the equivalent to the distance between our galaxy (Milky Way) with the Andromeda galaxy.

Galaxy Distance (Mpc) Linear Diameter (Kpc) Galaxy Class Galaxy Location (image)
NGC 4169 53.2 24.0 SO Right
NGC 4173 9.7 10.0 SBd Top
NGC 4174 56.8 13.0 SO Bottom
NGC 4175 56.4 29.0 Sbc Left

Distances to galaxies NGC 4169, 4174, and 4175 are determined using redshift of the galaxy and expansion of the universe, as the distances have not yet been measured independently. NGC 4173 is much closer, and the distance has been determined.

These four galaxies are unique because of the perspective at which they appear to us in the sky. These four galaxies make a nice box shape, thus the name "The Box" for the local Galaxy Group of these galaxies. Each of these individual galaxies is unique in its own way, with several different shapes, sizes, and colors noted between each galaxy. Different properties between these galaxies may indicate different histories and variables that effect each galaxy differently. Three of these galaxies are also close enough to each other in order to be having some sort of interaction between them, and further research into these galaxies may reveal an interesting and exciting future for this local galaxy group.

Colors and Structures:

Each of these four galaxies in the local galaxy group have a unique color and set of astrophysical properties that makes it different from the other galaxies in the group. While the official classifications of the galaxies indicate some of the structure and processes involved, there is much more to be seen by simply observing the galaxy in the optical image.

NGC 4169- This galaxy is officially classified by NED (NASA Extragalactic Database) as an SO galaxy. The classification of SO means that the galaxy is lenticular in shape, smooth and without clumps of stars throughout, and has a relatively large bulge in the center of the galaxy. All of this is observed in the optical image, especially the bright and relatively large bulge located right in the center of the galaxy. Due to the size and brightness of this galaxy compared to its neighboring galaxies, this galaxy is usually chosen to represent the group as the "NGC 4169 Galaxy Group." The center of this galaxy is probably a location of dense star structure. Since this galaxy is larger than the surrounding galaxies in the group, it is possible that other smaller galaxies have collided and combined with NGC 4169 in the past. The colliding galaxies must have been small in size, however, as there is no evidence of a large collision between this galaxy and another galaxy. The color of this galaxy is similar to that of the two other galaxies in close proximity to it (NGC 4174, NGC 4175).

NGC 4173- This galaxy is the faintest of the large four galaxies represented in the group, even though it is the closest galaxy in this group to our own. Officially classified by NED as an SBd galaxy, this galaxy is a barred spiral with a small bulge, loose arms, and clumpiness represented in the structure. The bar of this galaxy can be seen as a bright region located near the center of the galaxy, which extends at an angle from bottom to top of the galaxy. Because of the angle of this region, it must be a bar structure, rather than an arm or the galactic center. NGC 4173 also shows a large arm or tail region on one side of the galaxy, which is very loose and unaccompanied by a sister arm on the other side of the galaxy. The faintness of this galaxy may be due to the presence of large amounts of dust within the galaxy. The faintness may simply be due to the fact that this galaxy is much smaller in size compared to the other galaxies in the group. The blue colors represented in the image are due to the formation of new stars in the galaxy that are emitting bright blue light. NGC 4173 is moving slowly away from our galaxy, so the blue colors in the image are not attributed to redshift/blueshift. This galaxy is unique in its angle to us, making interpretation of its structure difficult to determine at some points.

NGC 4174- This galaxy is the smallest apparent galaxy in the local group, with a NED classification of SO. This small galaxy is similar in structure and brightness to the NGC 4169 galaxy, only at a much smaller size. NGC 4174 is classified the same as NGC 4169, but is much more narrow and elongated in its lenticular shape. This galaxy has a banded formation across the center of its elongated shape, with the galaxy's brightness getting progressively fainter from the central East-to-West line in each direction. This galaxy shows little evidence of other structures involving gas and dust.

NGC 4175- The final galaxy in this galaxy group is classified by NED as an Sbc galaxy, with loose arms, a small bulge, and the presence of clumpy areas. While similar to the other two neighboring galaxies in the cluster, this galaxy shows some unique structures that indicate the presence of much gas and dust within the galaxy. A large dust band appears to be located in the galaxy that runs right through the galactic center, making the core duller and less apparent than the other SO galaxies. Compared to the size of the central bulge of this galaxy, NGC 4175 also has very long and loose arms, as seen in the image. Again, this galaxy is similar in color to NGC 4169, most likely due to the same reasons. The darkness of the core of this galaxy is due to the presence of dust, making this galaxy a darker and duller shade than its neighbors.


Multi-wavelength Comparison:

NGC 4169 group in ultraviolet Ultraviolet image from GALEX (via WikiSky).







The UV (Ultraviolet) image of the local galaxy group shows some unique properties of the individual galaxies. The UV wavelength reveals areas of new star formation, as only new stars are bright enough to emit UV light.

NGC 4169- The UV image shows almost equal brightness throughout, with a faint and small bulge in the center. The optical image may be extremely bright due to older stars located in the center bulge of the galaxy. Either way, this image reveals structures in the UV that are not observed in optical, indicating a uniformity in star formation throughout the galaxy rather than a concentrated formation in the center.

NGC 4173- In comparison to the other galaxies in this image, NGC 4173 is brighter. This is because the galaxy is much closer than the other three galaxies. The UV image of this galaxy appears very clumpy, with many small clusters appearing throughout the galaxy. This structure indicates the presence of small bunches of star formation, which is different from the relative uniformity of the optical image. The dullness in the center where the bright bar structure appears in optical wavelengths may be dulled out due to dust, or may indicate an absence of star formation in the bar. Less formation in the bar region would make sense, since bars of galaxies generally have less gas than other regions. Higher brightness in the arm/tail region of the galaxy may indicate the lack of presence of dust, or a region of greater star formation.

NGC 4174- This galaxy appears similar in UV and optical, with the presence of the bright central bulge and bright centrally elongated disk throughout. This image is very smooth, indicates relatively uniform star formation in a region that is smaller than the galaxy's boundaries present in the optical image.

NGC 4175- This galaxy shows the complete absence of a bright core, possibly due to the already known presence of dust within the galaxy.

NGC 4169 in near infrared K(Near Infrared) Wavelength image of NGC 4169, 4174, 4175 from 2MASS







This image, taken in the Near Infrared (K) wavelength, shows some interesting structure in the three lower galaxies not apparent in the UV or optical wavelengths. While similar to that of the other images, this image shows relatively large bulges in the center of the galaxies. This is particularly important for the NGC 4175 galaxy on the left, because this bright center was not visible in other wavelengths due to the presence of dust. The relatively similar structure in this image shows that the assumptions made about the optical and UV wavelength images are correct, and that these three galaxies are smooth, lenticular, and contain relatively large bulges compared to the size of the galaxy. With this image, however, there may be a need to reclassify the NGC 4175 galaxy, since its bulge is obviously larger than was apparent earlier.

Distances Between the Galaxies:

The three galaxies that are the closest to one another (NGC 4169, 4174, 4175) have various spacing between them. Because of their proximity to one another, further research may discover some interaction between these galaxies.

Using the distance from our galaxy to these galaxies, as well as the pixel difference between the galactic centers on the optical image, a distance between each of these three galaxies can be determined. These pixel differences between galactic centers were first converted into arcseconds, then into radians (1 radian = 206265 arcseconds). Distances between the galaxies were then determined using the known distances from these galaxies to the Milky Way.

Results of Distances between Galaxies in NGC 4169 Galaxy Group:

Between: And: Distance (kpc)
NGC4169 NGC4174 35
NGC4174 NGC4175 20
NGC4175 NGC4169 39


UV Image taken from GALEX Satellite, using SKY-MAP.

Skrutskie, M.F. , R.M. Cutri, R. Stiening, M.D. Weinberg, S. Schneider, J.M. Carpenter, C. Beichman, R. Capps, T. Chester, J. Elias, J. Huchra, J. Liebert, C. Lonsdale, D.G. Monet, S. Price, P. Seitzer, T. Jarrett, J.D. Kirkpatrick, J. Gizis, E. Howard, T. Evans, J. Fowler, L. Fullmer, R. Hurt, R. Light, E.L. Kopan, K.A. Marsh, H.L. McCallon, R. Tam, S. Van Dyk, and S. Wheelock, "The Two Micron All Sky Survey (2MASS)" 2006, Astronomical Journal 131, 1163.

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.

Image Details:

Right Ascension (J2000) 12h 12m 12s
Declination (J2000) +29°10'00"
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter

300s (B) (9 Exposures)
300s (V) (6 Exposures)
300s (R) (6 Exposures)
180s (C) (29 Exposures)

Date observed

February 8, 2011 (CBVR)
March 1, March 2, March 4, 2011 (CBVR)

Description of Data Reduction:

The majority of the work on this project was performed using MaxIm DL 5 on Microsoft Windows Vista.

Data for this project was taken from the Calvin-Rehoboth telescope in Rehoboth, New Mexico using a high efficiency CCD camera. The data was saved as FITS (Flexible Image Transport System) in original format, and modified using the MaxIm DL 5 software.

After the first set of data provided an image, further observations were made using the telescope and a higher quality image was created using the same process.

First, the data was visually sorted to remove any images containing artifacts (unwanted streaks through image from airplanes, etc.) Bias, Dark, and Flat images were then selected based on their proximity in collection date, telescope temperature, and time of exposure. Calibration data was taken in expose times of .2 seconds (Bias), 180 seconds (Dark), and .75 seconds (Flat). All data, including the three calibration images, were then calibrated and combined into one image. Combining was performed using "Auto-star matching" in the program. The image was then adjusted for color. The color balances used were; 1 (Red), 1.5 (Green), 7.5 (Blue). Finally, the brightness of the image was adjusted to show different properties of the galaxies, and saved as JPEG images. Two variations of the same image were chosen to represent the different structures in the galaxies, since one image showed a better quality image of the NGC 4173 galaxy, and the other image showed a better quality image of the structure in the galaxies further away (NGC 4169, 4174, 4175).






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