A Photometric Study of the Dwarf Spheroidal Galaxies Leo IV and Boötes II Public Deposited

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  • March 19, 2019
Creator
  • Cheng, Haw
    • Affiliation: College of Arts and Sciences, Department of Physics and Astronomy
Abstract
  • A photometric study of the ultra-faint dwarf (UFD) galaxies Leo IV and Boötes II in the V and I[C] filters is here presented. The age of Leo IV relative to M92 was derived by fitting of Dartmouth isochrones, by a “standard” V[HB][TO] method, and by the V[HB][TO] method of VandenBerg et al. 2013. The age of Boötes II relative to M92 was derived by fitting of Dartmouth isochrones. Leo IV is found to be between 2 to 2.5 Gyr younger than M92 by these three methods. It is found to be predominantly old and metal poor and is well fit by isochrones of [Fe/H] = -2.46 and [α/Fe] = 0.2 and 0.4. An age spread with a plausible value of ~ 2 Gyr cannot be ruled out. A 10 Gyr old synthetic horizontal branch with [Fe/H] = -1.70 and [α/Fe] of 0.2 is fit to Leo IV’s red horizontal branch (RHB). The good fit of this model and its matching isochrone to Leo IV’s CMD suggests that the RHB is real and not an observational artifact as proposed by Okamoto et al. 2012. Two RR[ab] Lyraes previously observed by Moretti et al. 2009 were observed in Leo IV. One of the stars, V1, is observed to exhibit the Blazhko effect. No further RR Lyraes were uncovered in Leo IV. Comparison of the horizontal branch’s observed V magnitude to the absolute magnitudes of the RR Lyraes yields a distance modulus of (m-M)0 = 21.01 ± 0.07, in good agreement with previous studies. Leo IV’s possible population of blue stragglers is found to show no signs of central concentration, though this study’s sample and spatial coverage are too small for any detailed spatial distribution study. Boötes II’s CMD is found to be consistent with that of a single age, mono-metallicity system. It is well fit by isochrones of [Fe/H] = -1.79 and [α/Fe] = 0.2 and 0.4. Boötes II is found to be between 0.5 to 1.5 Gyr younger than M92. Distance was left as a free parameter in the fits. Boötes II is found to have distance modulus (m-M)0 lying between 18.02 to 18.15, in good agreement with previous studies. A single RRab Lyrae is discovered in Boötes II.
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  • In Copyright
Advisor
  • Karwowski, Hugon
  • Evans, Charles
  • Reichart, Daniel
  • Carney, Bruce
  • Cecil, Gerald
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2014
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  • Chapel Hill, NC
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