TRACING ABUNDANCES IN GALAXIES WITH THE SPITZER ...

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the extinctions, unfortunately we are unable to determine accurate abundances with respect to hydrogen, although we describe the process below. However, we can determine more accurate abundance ratios because in such ratios the amount of hydrogen cancels out. 4.3 Data Analysis 4.3.1 Extinction Correction We adopt extinctions for M51 H II regions from van der Hulst et al. (1988). They used 6 cm and 20 cm observations to determine the thermal radio emission and then determined the extinction from the Hα to radio ratio. Depending on the size of the H II region, they used apertures from 12 ′′ to 21 ′′ in diameter. Additionally, they did 9 ′′ -aperture optical spectrophotometry on several H II regions and thus also determined Balmer-decrement extinctions for a subset of H II regions with Hα/radio extinctions. Table 4.1 lists the Av values we adopt for determining abundances. 4.3.2 Electron Temperature and Density Table 4.1 also lists the temperatures for each region adopted for determining abundances. They are from Bresolin et al. (2004). The Te(Ne II, S III) is the temperature we adopt for determining abundances from Ne II and S III line fluxes; similarly, the Te(Ne III, S IV) is the temperature we adopt for determining abundances from Ne III and S IV line fluxes. The Te(Ne II, S III) we adopt is equal to Te(S +2 , Ar +2 ) from Bresolin et al. (2004) because the ionization potential of Ne II (21.56eV) is close to that of S III (23.34eV) and Ar III (27.63eV). Similarly, the Te(Ne III, 105
S IV) we employ is equal to Te(O +2 , Ne +2 ) of Bresolin et al. (2004) because the ionization potential of S IV (34.79eV) is close to that of O III (35.12eV) and Ne III (40.96eV). When Bresolin et al. (2004) do not give Te for a given H II region, we adopt the average temperature from their sample. However, if an H II region without a Te given by Bresolin et al. (2004) resides nearby another H II region with Te given, then we adopt the Te of the nearby region. Abundances derived from infrared lines depend only weakly on Te, and thus choosing an average Te or one from a nearby H II region will have little affect on the abundances. For the electron density we assume Ne = 100 cm −3 for all H II regions in M51. Bresolin et al. (2004) determined that Ne < 150 cm −3 for the H II regions in M51, and the adopted electron density does not have a large affect on the abundances. 4.3.3 Abundances We assume the above Hα flux, extinction, electron temperatures and density in order to derive the abundances for each ion, following the procedure outlined in §1.3.3. Our procedure employs the Hβ flux, so here we predict the observed Hβ flux from the Hα flux by using the theoretical ratio of (Hα flux)/(Hβ flux) = 3.0 for case B recombination for a gas at Te=5000 K and Ne= 100 cm −3 from Hummer & Storey (1987) and the extinction given in Table 4.1. Table 4.3 lists the ionic abundances (and upper limits for unobserved ions) for three ions of neon and two ions of sulfur. These abundances with respect to hydrogen should be viewed with caution because the Hα flux has a large uncertainty; however, ratios of abundances will not be affected. 106
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TRACING ABUNDANCES IN GALAXIES WITH
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TRACING ABUNDANCES IN GALAXIES WITH
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BIOGRAPHICAL SKETCH Shannon was bor
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ACKNOWLEDGEMENTS First and foremost
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thank my husband Ryan. The rest of
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3 Chemical Abundances and Dust in P
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LIST OF FIGURES 1.1 Diagram of the
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ditionally we find that these nebul
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seed nuclei relative to the β deca
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shape (Carollo et al., 2007). These
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Boltzmann velocity distribution cha
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etween recapture and photoionizatio
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a whole. Additionally, abundances f
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at the appropriate temperature and
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(a) 3.37 eV 1.40 eV 0.10 eV 0.04 eV
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(Iion), the radiative transition ra
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lines. For example, changing the ad
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Figure 1.4 Starburst99 synthetic sp
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Figure 1.5 Example of crystalline s
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H H H H H H H H H Anthanthrene C H
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year lifetime. Spitzer is in an Ear
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CHAPTER 2 THE SPITZER IRS INFRARED
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these elements than previous studie
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dust is seen in the spectrum. We se
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Figure 2.2 Close-ups of emission li
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2.4 Optical and UV Data We compleme
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2.5 Data Analysis Our goal is to ca
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2.5.2 Electron Density We assume an
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Table 2.6 Electron temperatures ass
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O, N, and C. The helium ionic abund
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Barlow (1994) use UV lines for impo
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is a spherical nebula with a low ma
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CHAPTER 3 CHEMICAL ABUNDANCES AND D
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Page 71 and 72: Table 3.2 Properties of observed GB
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Page 75 and 76: Table 3.3 Multiplicative scaling fa
Page 77 and 78: Table 3.4 Observed infrared line fl
Page 79 and 80: 3.5 Data Analysis 3.5.1 Abundances
Page 81 and 82: Table 3.6 Comparison of the derived
Page 83 and 84: from the most reliable line(s), and
Page 85 and 86: Table 3.7 Electron temperatures and
Page 87 and 88: Table 3.9 Ionic abundances Ion x a
Page 89 and 90: 3.5.2 Crystalline Silicates Crystal
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Page 93 and 94: Figure 3.2 Continuum subtracted spe
Page 95 and 96: Figure 3.3 Profiles of PAH features
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Page 101 and 102: towards the Galactic Center. On the
Page 103 and 104: Table 3.14 Parameters of linear fit
Page 105 and 106: models that show how a binary compa
Page 107 and 108: y an outer dense O-rich torus, indi
Page 109 and 110: CHAPTER 4 ABUNDANCES IN H II REGION
Page 111 and 112: expect their abundance ratio to rem
Page 113 and 114: We extract spectra processed throug
Page 115 and 116: Figure 4.2 IRS spectra of H II regi
Page 117: IRS slits from these WIRC observati
Page 121 and 122: Figure 4.3 M51 H II region Ne III/N
Page 123 and 124: Figure 4.4 shows a plot of the (Ne
Page 125 and 126: James Webb Space Telescope (JWST);
Page 127 and 128: Bernard-Salas, J. & Tielens, A. G.
Page 129 and 130: Edgar, R. G., Nordhaus, J., Blackma
Page 131 and 132: Hummer, D. G., Berrington, K. A., E
Page 133 and 134: Matsuura, M., Zijlstra, A. A., Mols
Page 135 and 136: Pradhan, A. K., Montenegro, M., Nah
Page 137: Vassiliadis, E. & Wood, P. R. 1993,
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