Kwayera Davis's Research Project: University of Wisconsin-Madison REU
Kwayera Davis
College of Charleston
    Department of Physics & Astronomy
    101 Science Center
    58 Coming St.
    Charleston, SC 29424
    phone:(843) 953-5593
    Fax:(843) 953-4824
me on the far right standing in a VLA dish                                              Weather Prediction Chart for Madison,WI
                     Me on the far right standing in a VLA dish


Kwayera "Kiwi" Davis
    I will start my junior year at the College of Charleston (CofC) in the fall of 2003.  I am a Physics major with a concentration in Astronomy.  The path to my current level of study in Astronomy is a long one.  I can trace my interest in Astronomy back to my friend Chris Larson who introducted me to Star Trek: The Next Generation.  I had seen a handful of episodes by the time the episode "The Best of Both Worlds: Part 1" aired.  Needless to say I had a very grandiose mental image of what space looked like.  I would remain only passingly aware of Astronomy for the next seven years.  My interest in astronomy really began when I took a mountain climbing/camping trip to Mt. Mitchell NC.  After a long hike up the mountain our whole group was exausted.  The teens in the group couldn't believe it when, upon reaching the campsite, the counsellors wanted us to get out of the warm and soothing van and torture ourselves setting up tents.  Out of all the things I have been forced to do in my life,  it is being forced to get out of that van, for which I am most grateful.  The campsite was at an altitude of about 914m (3000ft) and in the middle of a utterly dark national park.  I set one foot on the ground, straining to see where I was stepping by the light of the van when I noticed that the ground was surprisingly not the brightest thing visible.  The light in the corner of my eye brought my gaze upward and I was never the same.  The Milky Way arced across the summer sky above me.  To this day, it is the most beautiful thing I have ever seen.  We only watched it for  twenty minutes before we all collapsed into bed.  Nevertheless, in that time we saw a handful of meteors that were washed out of ever other sky I had seen and more stars than I had ever imagined.  I  realized that the real universe was far more beautiful that the grandiose picture I had only moments ago. I also realized that I new almost nothing about what I was seeing and that I would be happy spending the rest of my life studiying those lights.  It is hard to put into  words a good description of the impression one gets looking at the Milky Way, however I have found one.  The following is an exerpt from William Faulkner's short story "Barn Burning." The description is intertwind with the story and is highlighted in red.

    "He could not hear either: the galloping mare was almost upon him before he heard her, and even then he held his course, as if the very urgency of is wild grief and need must in a moment more find him wings, waiting until the ultimate instant to hurl himself aside and into the weed-choked roadside ditch as the horse thundered past and on, for an instant in furious silhouette against the stars, the tranquil early summer night sky which, even before the shape of the horse and rider vanished, stained abruptly and violently upward: a long, swirling roar incredible and soundless, blotting the stars, and he springing up and into the road again, running again,..."        Full Text of William Faulkner's "Barn Burning"
My Research
   An Introduction to my project

Barred Magellanic Spiral Galaxies (SBms)
    SBms are morphologically inbetween normal spiral galaxies and irregular galaxies.  Spiral galaxies are named for the pinwheel pattern evident in their stars, gas and dust. Irregular galaxies, as their name implies, have no common structure that allows for easy classification.  They lack a complex spiral structure.  SBms have, in less definition, the properties of spirals and irregulars.  Although they have a visible spiral structure they are much more irregular in shape than normal spirals.  They are called barred because they have a bar shaped group of stars running through their cores.  This bar rotates as a ridged body while the stars further from the center no longer keep up with the others on the inside track and lag behind creating the spiral structure we observe.  They are called Magellanic because the most studied galaxy of this type is the Large Magellanic Cloud.

H I
    H I or atomic/neutral hydrogen is very common in SBms.  An H I atom is composed of one proton with one eletron in orbit.  It exists as a vast cloud of gas that ussualy extends twice as far as the radius of the stars from the center of the galaxy.  In H I the electron can have two spin states.  There is a small difference in energy between these two states which corresponds to slightly different orbitals for the electron.  It takes more energy to maintain the higher orbital.  If the electron is in the higher orbital and drops down to the lower one it must get rid of its extra energy and it does this by emmiting a photon.  The energy difference is so small that the photon must accordingly have a long wavelength.  This wavelength,  21 cm , puts it in the radio part of the spectrum.  This transition is very rare but there are so many H I atoms that we observe transitions happening in what is nearly a constant stream.

Observing H I with the Very Large Array (VLA)
    The VLA in Soccoro, NM is an interferometer. Twenty-seven radio telescopes are linked together to work as one instrument with increased sensitivity and resolution.  The dishes in the array can be moved along tracks changing the size of the array to allow different spacial resolutions. The data I am working with comes from the VLA in c array, its second most compact configuration. A array is the most spread out.  The 21cm line coresponds to a frequency of about 1.4 GHz . When H I emmision is coming from a distant galaxy that frequency will be decreased because the galaxy is redshifted.  The recessional velocity of the galaxy can be calculated because we know the rest wavelength of the emmision.  In addition to being able to determine the average velocity  that the H I is receeding with we can see the radial component of the gas in the galaxy.  If we can figure out how the galaxy is inclined with respect to us then we can say a great deal about how different sections of the galaxy are moving.  We can also create a rotation curve which allows us to further investigate the dynamics of the galaxy.
vla dish in work shed the KPNO REU 2002 group climbing into the dish looking our over the edge
us in the dish again VLA dish

Galaxy Rotation Curves
    To obtain a rotation curve we plot velocity vs radius.  The resulting curve tells us a lot about how the galaxy is rotating and the density throughout the galaxy.  In the inner regions of the galaxy the curve rises liniarly indicating the ridged body rotation of that region.  In the outer regions of the galaxy the curve levels out indicating that as the radius increases the stars are traveling at the same velocity and thus laging behind as they have a longer track to complete and would have to increase their velocity to keep up with the stars on the inside track.  The slope of the curve in the inner regions allows a determination of the density in that region.  The density is an important parameter because different dark matter models predict different density distributions throughout galaxies. 

Lambda- Cold Dark Matter Models
    The current popular dark matter models involves cold dark matter.  One of the predictions of this model is that the density will be high in the inner regions of galaxies.  This, however, is not what is observed.  The density of the inner regions, as infered from rotation curves, is not very high.  Somehow these observations must be reconsiled with the theory.  One idea is that supernovae are clearing out the regions. Perhaps the theory needs to be modified.  More work needs to be done to find out.  

My Project
    My project touches on some aspect of each section in the preceding introduction.  I am working with Eric Wilcots (His Webpage) who studies galaxies with the VLA and the WIYN telescope.   What I am doing is taking observations from the VLA, reducing them in AIPS and construction rotation curves from the images.  I hope to then describe the general properties of the galaxy and perhaps say something about the density typical to the inner regions of the galaxies I am working with.  With observations from the WIYN telescope in Tuscon, AZ I should be able to verify the properties of the galaxies.  

Links
    Astronomy Links
        APOD: Astronomy Picture of the Day
        Heavens Above: A satellite visibility prediction site
        Clear Dark Sky: A weather prediction site for astronomy
            Bad Astronomy: Philip Plait shows you what not to do
            Hubble Heritage Project: Beautiful Hubble images
     
    Funny Links
            The Onion: America's Finest News Source
            The Boondocks Cartoon Strip