Astr212 Galaxy Projects, Spring 2005

NGC4449: an Irregular Galaxy, Jeff Olivero

NGC4449 is a irregular galaxy with many regions of star formation. This galaxy is not located in the Virgo cluster like many Messier galaxies but is located in the Canes Venatici constellation. NGC4449 is 9.8 million light years away and has a magnitude of 9.4. It was discovered back in 1788 by Sir William Herschel. Herschel started searching for nebulae and star clusters after getting a copy of the Messier catalog. He worked with an 18.7 inch reflector and catalogued a total of 2500 objects including Uranus.

The boxy shape of NGC4449 and the gaseous regions around it resemble a smaller version of the Large Magellanic Cloud. All the white and blue clumpings are regions of intense star formation where very massive and bright stars are born. These clumps are where regions of gas have condensed. The massive stars formed in the clumps light up the gas nearby. The main reason we see these clumps is because the high mass stars are 100,000 times as bright as our sun. The bar of yellower stars near the center of the galaxy indicates that those stars are at least 5 million years old. Other galaxies nearby in the constellation Canes Venatici are M51, M63, M94, and M106.

The image at X-ray wavelength indicates locations where stars in the galaxy have exploded in supernovae. Looking down and right of center you can see strong x-ray emission line up with a dense region of stars in the optical picture. The contour lines show the intensity and location of the x-ray emission.

The image (below) in the 21cm wavelength shows that NGC4449 is inside a huge halo of HI gas. HI gas is atomic hydrogen which are mainly in large clouds. HI clouds are relativly cold compared to the other gas in the galaxy. The top pictures show the optical images and the bottom pictures show radio emission from in the 21-cm wavelength. The size of this HI region is about 14 times the size of the optical image above.

The color coded image below of the HI region shows the Doppler shift. The Doppler shift shows the change in the apparent frequency of a wave as observer and source move toward or away from each other. The image shows that there is some counter rotation of some of the gas in the galaxy which means that the galaxy must have encountered another galaxy and NGC4449 took some of its gas.

This graph shows a profile of the major axis of the galaxy from 3 to 45 kpc. This shows that the surface brightness drops off exponentially which is typical for spiral galaxies surface brightnesses. The profile is the brightness of each pixel along a line on the major axis of the galaxy. The graph fits the exponential drop very well and the scale length of 38.5 +0.9. The scale length is when the surface brightness drops to 1/e of the central value. This gives a central surface brightness of 4174 + 156 counts/pixel in a 300 second clear exposure. From finding the scale length on the major and minor axis, the inclination is found to be 33 degrees.

References:
Elmegreen, D.M. 1998, Galaxies and Galactic Structure (New Jersey: Prentice Hall)

Fabbiano, G.; Kim, D.-W.; Trinchieri, G. An X-ray catalog and atlas of galaxies, 1992, Astrophysical Journal, 80, 531.

Hibbard, J.E.; van Gorkom, J.H.; Rupen, M. P.; Schiminovich, D. An HI Rogues Gallery

Hunter, D. A.. NGC4449

Jones, J. H. Boxes in the Sky

Kutner, M. L. 2003, Astronomy: A Physical Perspective, 2nd ed. (Cambridge:CambridgeUniversity Press)

Students for the Exploration and Development of Space, NGC4449

Students for the Exploration and Development of Space, Hartmut Frommert
Christine Kronberg. William Herschel's catalog of Deep Sky objects

Wang, W.-H. LMC

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.