Amanda A. Kepley

Publications (5)4.03 Total impact

• Source

  Available from: arxiv.org

  Article: Mapping the Extended H I Distribution of Three Dwarf Galaxies

  Deidre A. Hunter, Fakhri Zahedy, Emily C. Bowsher, Eric M. Wilcots, Amanda A. Kepley, and Veronika Gaal
  [show abstract] [hide abstract]
  ABSTRACT: We present large field H I-line emission maps obtained with the single-dish Green Bank Telescope centered on the dwarf irregular galaxies Sextans A, NGC 2366, and WLM. We do not detect the extended skirts of emission associated with the galaxies that were reported from Effelsberg observations. The ratio of H I at 1019 atoms cm–2 to optical extents of these galaxies is instead 2-3, which is normal for this type of galaxy. There is no evidence for a truncation in the H I distribution ≥1019 atoms cm–2.
  The Astronomical Journal 10/2011; 142(5):173. · 4.03 Impact Factor
• Source

  Available from: ArXiv

  Article: Mapping the Extended HI Distribution of Three Dwarf Galaxies

  Deidre A. Hunter, Fakhri Zahedy, Emily C. Bowsher, Eric M. Wilcots, Amanda A. Kepley, Veronika Gaal
  [show abstract] [hide abstract]
  ABSTRACT: We present large field HI-line emission maps obtained with the single-dish Green Bank Telescope centered on the dwarf irregular galaxies Sextans A, NGC 2366, and WLM. We do not detect the extended skirts of emission associated with the galaxies that were reported from Effelsberg observations (Huchtmeier et al. 1981). The ratio of HI at 10^19 atoms cm^-2 to optical extents of these galaxies are instead 2--3, which is normal for this type of galaxy. There is no evidence for a truncation in the HI distribution >/=10^19 atoms cm^-2.
  09/2011;
• Source

  Available from: ArXiv

  Article: Unveiling Extragalactic Star Formation Using Radio Recombination Lines: An EVLA Pilot Study with NGC 253

  Amanda A. Kepley, Laura Chomiuk, Kelsey E. Johnson, W. M. Goss, Dana S. Balser, D. J. Pisano
  [show abstract] [hide abstract]
  ABSTRACT: Radio recombination lines (RRLs) are powerful, extinction-free diagnostics of the ionized gas in young, star-forming regions. Unfortunately, these lines are difficult to detect in external galaxies. We present the results of EVLA observations of the RRL and radio continuum emission at 33 GHz from NGC 253, a nearby nuclear starburst galaxy. We detect the previously unobserved H58a and H59a RRLs and make simultaneous sensitive measurements of the continuum. We measure integrated line fluxes of $44.3 \pm 0.7$ W m$^{-2}$ and $39.9 \pm 0.8$ W m$^{-2}$ for the H58a and H59a lines, respectively. The thermal gas in NGC 253 is kinematically complex with multiple velocity components. We constrain the density of the thermal gas to $1.4 - 4 \times 10^4$ cm$^{-3}$ and estimate an ionizing photon flux of $1 \times 10^{53}$ s$^{-1}$. We use the RRL kinematics and the derived ionizing photon flux to show that the nuclear region of NGC 253 is not gravitationally bound, which is consistent with the outflow of gas inferred from the X-ray and Halpha measurements. The line profiles, fluxes, and kinematics of the H58a and H59a lines agree with those of RRLs at different frequencies confirming the accuracy of the previous, more difficult, high frequency observations. We find that the EVLA is an order of magnitude more efficient for extragalactic RRL observations than the VLA. These observations demonstrate both the power of the EVLA and the future potential of extragalactic RRL studies with the EVLA.
  06/2011;
• Source

  Available from: ArXiv

  Article: The Role of the Magnetic Field in the Interstellar Medium of the Post-Starburst Dwarf Irregular Galaxy NGC 1569

  Amanda A. Kepley, Stefanie Muehle, John Everett, Ellen G. Zweibel, Eric M. Wilcots, Uli Klein
  [show abstract] [hide abstract]
  ABSTRACT: (abridged) NGC 1569 is a nearby dwarf irregular galaxy which underwent an intense burst of star formation 10 to 40 Myr ago. We present observations that reach surface brightnesses two to eighty times fainter than previous radio continuum observations and the first radio continuum polarization observations. These observations allow us to probe the relationship of the magnetic field of NGC 1569 to the rest of its interstellar medium. We confirm the presence of an extended radio continuum halo at 20 cm and see for the first time the radio continuum feature associated with the western Halpha arm at wavelengths shorter than 20cm. The spectral index trends in this galaxy support the theory that there is a convective wind at work in this galaxy. We derive a total magnetic field strength of 38 microG in the central regions and 10-15 microG in the halo. The magnetic field is largely random in the center of the galaxy; the uniform field is ~3-9 microG and is strongest in the halo. We find that the magnetic pressure is the same order of magnitude but, in general, a factor of a few less than the other components of the interstellar medium in this galaxy. The uniform magnetic field in NGC 1569 is closely associated with the Halpha bubbles and filaments. We suggest that a supernova-driven dynamo may be operating in this galaxy. The outflow of hot gas from NGC 1569 is clearly shaping the magnetic field, but the magnetic field in turn may be aiding the outflow by channeling gas out of the disk of the galaxy. Dwarf galaxies with extended radio continuum halos like that of NGC 1569 may play an important role in magnetizing the intergalactic medium. Comment: ApJ accepted. 56 pages, 14 figures (low resolution), 8 tables. Version with high resolution figures at http://www.astro.virginia.edu/~aak8t/data/n1569/ms.pdf
  02/2010;
• Source

  Available from: ArXiv

  Article: Magnetic Fields in Irregular Galaxies

  Amanda A. Kepley, Stefanie Muehle, Eric M. Wilcots, John Everett, Ellen Zweibel, Timothy Robishaw, Carl Heiles
  [show abstract] [hide abstract]
  ABSTRACT: Magnetic fields are an important component of the interstellar medium, especially in low-mass galaxies like irregulars where the magnetic pressure may be significant. However, few irregular galaxies have observed magnetic field structures. Using the VLA, the GBT, and the ATCA, we have observed several irregular galaxies in the radio continuum to determine their magnetic field structures. Here we report on our results for the galaxies NGC 4214 and NGC 1569.
  09/2007;