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Galaxy NGC 3079
Sam Van Kooten

NGC 3079

NGC 3079 is a spiral galaxy 16 Mpc (52 million light years) away, 20 times further than the nearest spiral galaxy, and 30 kpc (98,000 light years) wide, about the size of the Milky Way. The galaxy has a high inclination, meaning we see it edge-on rather than face-on, so that the galaxy's spiral arms aren't easily visible from Earth. To the right of NGC 3079 is a small companion galaxy, MCG +09-17-009. This galaxy is 18 Mpc (59 million light years) away and 3.7 kpc (12,000 light years) wide.

The bulk of the disk of NGC 3079 is blue-tinged, meaning the disk is an active site for star formation. Both hot blue stars and cold red stars are produced, but the blue stars are so much larger and brighter that they dominate the color of the disk. The large, hot, blue stars burn through their fuel much more quickly than the small, cool, red stars, so in regions where stars are no longer being formed, the blue stars will go supernova and not be replaced, making regions with no star formation appear red or yellow. We see that in the yellow core of NGC 3079. Wrapping around this core is a slight, dark line. This is a dust lane, blocking light from behind it. Note that the brightest source of blue light is right next to this dust lane, illustrating how high dust concentration and star formation go hand-in-hand in spiral arms: dust flows into one side of a spiral arm and clumps up to form stars, which flow out the other side of the spiral arm.

NGC 3079 has a classification of SB(s)c edge-on. SB means the galaxy is a spiral galaxy with a bar connecting the spiral arms at the core. (This bar is not visible in my image.) (s) means the arms spiral all the way into the core; some galaxies have arms that join into a ring around the core. c means the spiral arms are rather loosely-wound and that the central bulge is less prominent. edge-on indicates we see the galaxy from the side of the disk, rather than face-on.

False-color Hubble ImageIn this false-color image from the Hubble Space Telescope, multiple dust lanes and many clumps of active, Hα-emitting star formation can be seen in NGC 3079. The picture also shows giant pillars of Hα gas, rising from the galaxy's core at over 6 million kilometers per hour. These pillars outline a giant bubble of gas also rising from the core. The gas comes from the material that floats between stars in every galaxy, called the interstellar medium, and is likely being pushed up by "wind" from a flurry of new stars in the galaxy's core. This wind is streams of subatomic particles ejected by these stars that has pushed this 3000-light-year-wide pocket of the interstellar medium a few thousand light years above the galaxy's disk. Of course, what goes up must come down, and the gas in this bubble will eventually spread out and rain back down on the galaxy, possibly contributing to star formation throughout its disk.


Hubble Image with overlayed Chandra Xray dataThis image overlays Chandra X-ray data in blue on the Hubble image. These X-rays come from hot gas which measures ten million degrees Celsius, as opposed to the gas pillars in the optical image, which are only ten thousand degrees. The way two types of gas pillars, very hot and kind-of hot, appear in the same places suggest they were both caused by the same interstellar wind from rapid star formation in the core. This wind would also be responsible for heating the X-ray-emitting gas.



VLBA Radio dataOn its left, this image shows X-ray data (black contours) once again overlaid on Hubble's Hα data (color contours). The outline of the bubble is clearly visible. The right frame magnifies the core of the galaxy. The green contours show 8 GHz data measured by the VLBI, emitted when charged particles in a hot gas curve along strong magnetic field lines. The colored dots show water masers, which are clouds of water vapor which emit at 22 GHz when excited by radiation from nearby stars. The colors of the dots indicate their Doppler velocities, meaning red dots are moving away from us relative to the galaxy and blue dots are moving toward us. Astronomers have used these data to model the core of the galaxy, also shown in the image. Their model includes a clumpy disk of gas, whose cross-section is shown in the image and which may have active star formation and be orbiting a supermassive black hole. The red and teal inside parts of the disk are using the same Doppler velocity color coding as the masers. This disk is aligned with the galactic disk. The model also includes significant outflows from the disk, shown in yellow, which extend to the galaxy's large bubble. The 8 GHz sources labeled A, B, and C in the image likely indicate jets of material, which can be seen in the model and are likely driven by material falling into the central black hole.


This rotating animation (full-screen view) displays the radio model of NGC 3079's core in 3D. Shown is the thick, flared disk in blue with its inside color-coded for observed Doppler shift, the expanding clouds of material with embedded jets in yellow, and surrounding clumpy interstellar medium in magenta.


In González et al., 2009, a group of astronomers analyze UV spectral data from NGC 3079 taken by the GALEX satellite. These emissions indicate recent star formation, occurring over no more than 100 million years. The observed spectra are not what is expected for clumps of young stars, suggesting significant extinction from dust. They chose fifteen points along the length of NGC 3079 and modeled the measured spectra by writing flux as proportional to wavelength raised to some power β. Their β values went as high as 1 for the reddest areas and as low as -2 in the bluest areas, while a value of -2.6 is expected for spectra unaffected by dust extinction. Roughly speaking, NGC 3079's UV spectrum is redder in the center and bluer at the edges. This suggests increased dust extinction near the core and therefore more dust near the core, and the authors hope to use more data in other wavelengths to confirm this.

NGC3079 5 GHz dataMiddelberg et al., 2007 used archival data from 1985 to 2005 to trace sources of radio emissions near the core of NGC 3079. Shown at right is 5 GHz data from 2005. The radio sources are the same as those shown in the model above. Two discrete decelerations were observed of sources A and B which coincided with increases in radio brightness. They explain that the radio sources moving out from the core indicate the presence of two jets (like those shown in the radio model above), while their deceleration and brightening suggest matter in these jets collided with dense clouds of interstellar medium, becoming slower and denser themselves. This model of jets ejecting from the core into a clumpy medium would explain the observed superbubble (and another one on the opposite side of the disk) as being a result of the jets slowing and widening. Sources E and F in the image are explained as material from the jet that has been deflected by collisions with interstellar medium.


 

References:

Gonzalez, D.R. et al. "GALEX UV Spectroscopy of Extended Objects: The Case of NGC 3079." 2009. New Quests in Stellar Astrophysics. II. 109.

Kondratko, P, L Greenhill, and J Moran. "Evidence for a Geometrically Thick Self-Gravitating Accretion Disk in NGC 3079." 2005. The Astrophysical Journal 618, 618.

Kondratko, P, L Greenhill, and J Moran. "Thick, Flared, and Disorganized Accretion Disk in NGC 3079." . National Radio Astronomy Observatory, Accessed 29 Apr. 2013. <http://www.vlba.nrao.edu/imgmonth/NGC3079/>.

Middelberg, E, I Agudo, A L Roy, and T P Krichbaum. "Jet-cloud collisions in the jet of the Seyfert galaxy NGC3079." 2007. Monthy Notices of the Royal Astronomical Society 377, 731.

Nemiroff, Robert and Jerry Bonnell. "The Bubbling Cauldron of NGC 3079." Astronomy Picture of the Day. 2004 October 16. Accessed 28 April 2013. <http://apod.nasa.gov/apod/ap041016.html>

"NGC 3079: Superwind Sculpts Filamentary Features." Chandra X-Ray Observatory Photo Album. NASA, 20 Feb. 2009. Web. 29 Apr. 2013. <http://chandra.harvard.edu/photo/2003/ngc3079/>.

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) 10:01:58
Declination (J2000) +55:40:47
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 7x5 minutes in C, 7x5 in B, 7x2.5 minutes in V, 5x2.5 minutes in R
Date observed March 22 & 24, 2013

Once the images were taken, they were calibrated with appropriate bias, dark and flat images. The images in each filter were combined separately and debloomed. These final color images were aligned and combined with a R:V:B ratio of approximately 1:1.5:5. A logarithmic screen stretch was applied, using a minimum count of 45 and a maximum of 162. Colors were then saturated 500% for pixels with values over 70. Finally, bad pixels (hidden until the screen stretching and saturation) were removed and the borders of the image were cropped off.

 

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