Olivia Lanes
Dickinson College


REU program-Summer 2013
Univ. of Wisconsin - Madison
Madison, WI 53706

lanes at wisc.edu



Research projects of other REU students
Useful links
My conclusions
Picture of Washburn Observatory

Gas Kinematics of NGC3664 and CGCG048A & B

Introduction

Glaxies NGC3664, CGCG048A and CGCG048B (nicknamed the harp and ball galaxy for their distinctive shape) were observed with the WIYN 3.5-meter telescope at Kitt Peak. Sparsepak , a fiber field unit invented by Matt Bershady was used to study the kinematics of these objects. Sparsepak is a bundle of fibers, 75 image fibers arranged in a square and 7 sky fibers surrounding it. Sparsepak contains fibers that individually measure light intensity, providing a unique way to study close galaxies.

My Research


Fig. 1 . Overlay of Sparsepak on NGC3664

Fig.2. Overylay of Sparsepak on CGCG048A & B
Central Goal
  • Find an estimate of the velocity dispersion and redshift of these galaxies and use this to calculate the energy of the gas.
  • Data Reduction

    Sparsepak was overlayed on the galaxy to show which featues were measured with the fibers, as seen in Fig.1. The sky fiber main grid was positioned over the bar of the galaxies, with the 7 sky fibers located beyond the center grid so that they could be used to reduce the signal-to-noise ratio of the data.

    Data was reduced in IRAF using the packages ccdproc to perform zero-corrections and flat-field division, and dohydra to take the vertically oriented fiber images and convert them into compressed, horizontal images (sig Fig.3). It also calculated the dispersion correction. Cosmic rays were individually removed by hand, but to increase the signal-to-noise ratio, the fibers that obsereved the galaxy in similar areas were combined. To execute sky subtraction, we combined the 7 sky fibers with an average, then subtracted them from each individual image (as shown in Fig.4).

    Fig.3. The results of running the command Dohydra in IRAF
    Fig.4.Representation of how the combined sky fiber was removed from every fiber in our data

    The Full Width At Half Max, or the width of the emission line at half its' maximum height was also measured by hand on every emission line, using the 'splot' task in IRAF. These lines were estimated to be [O III] lines, due to the reported redshift and the measured location of our lines. The peak wavelength of these lines were used to calculate a redshift, which we compared to the alread reported one. The FWHM measurements were used to calculate the velocity dispersion.

    Fig.5. How I measured the Full Width at Half Max and peak wavelength on an [O III] emission line
    Extracting Data

    To determine the kinematical measurements, a spetral cross-correlation code developed by Westfall (et al. 2006) was ran on the data. The cross-correlation analysis measures the shifts in the emission lines in our data to a template. After a cross-correlation spectrum is produced, a Gaussian-fitting finds the peak in the spectrum. This peak is then used to calcualte the radial velocity of the galacies from every individual fiber. However, we had some problems in this stage of the research because often the signal-to-noise ratio in the fibers was too low to allow for detection of emission lines. They could not be used in this analysis. The Full Width at Half Max (FWHM) was used to calculate the dispersion in the galaxies.

    Results

    The cross-correlation software unfortunately could not extract stellar velocities from this data. The signal-to-noise ratio will need to be fixed before this can be attempted again. However, the redshift for NGC3664 was found to be 1389 km/s, which is consistent with previously reported studies. The average velocity dispersion ws found to be 55 km/s which corresponds to a kinetic energy of 3.2 *10^52 ergs. The redshift of CGCG048A was found to be 10,081 km/s; the velocity dispersion is 100 km/s, corresponding to an gaseous kinetic energy of 4.27*10^55 ergs. Lastly, CGCG048B was measured to have a redshift of 9,073 km/s, and a velocity dispersion of 62 km/s, and an energy of 1.65*10^55 ergs.

    The previous numbers reported for the energies of these galaxies are interesting if compared to the known energy of a supernova. Supernovae give off energy at about 10^51 ergs, so we can estimate that in NGC3664 there are about 30 supernova remnants. Solar winds might also account for some of the energy, but more research is needed to discovery how large a role this plays. CGCG048A & B have such high energies it is likely they contain starburts, or many supernova that exploded around the same time period.

    Future Work

    Hopefully these kinematical predictions can be used in the future to estimate the total mass and mass distribution of these galaxies. This will give insight into how the dark matter is distributed in the galaxies as well.

    Furthermore, more observation is being planned for CGCG048A and B in order to collect radio data. This radio data will be able to tell us more about when and how many supernovae occured.

    Thank you!

    Thank you for taking the time to read about my summer research. I am a rising senior at Dickinson College in Pennsylvania, majoring in physics and minoring in astronomy. My goal in the future is to keep exploring the "big questions" about the way our world works, and to do this through my passion of physics. I hope to have the chance to pursue this interest at the graduate level starting next year.

    A photo of me at the NASA Kennedy Space Center in Florida!

    Useful links

    The following links are very useful for looking up info on UNIX, web page making, and astrophysical dataand journals.

    SIMBAD (Stellar/Galactic database)

    NED (Extragalactic database)

    UNIX tutorial

    Web page basics

    NASA Astrophysics Data Service