TRACING ABUNDANCES IN GALAXIES WITH THE SPITZER ...

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Oxygen Our values for the total oxygen abundance usually agree to within a factor of two of those in the literature, and often within 50%. For the one case where we can compare to the study in the literature with published ionic abundances (Wang & Liu, 2007), the ionic abundance of O + is higher by 50% in this work than in that study, but the ionic abundance of O +2 (the dominant ion) is lower by 10% than in that study, and the total elemental oxygen abundances agree within 10%. The IR data show that for one object (PNG000.7+03.2), the O +3 contributes significantly (∼30%) to the total oxygen abundance, and thus optical studies must either use an uncertain ICF or underestimate the total oxygen abundance in this object. Considering that we employ more observed stages of ionization than purely optical studies and also that we derive ionic abundances for the major contributors to the total elemental abundances for argon, neon, and sulfur from IR lines (which are less sensitive to CHβ and Te than abundances from optical lines), our GBPNe abundances for these elements are more accurate than previous studies. Our GBPNe abundance of oxygen, however, should be of similar accuracy to previous optical studies because we must rely on optical lines for the dominant ionization stages, but we make a slight improvement by measuring or placing an upper limit on the abundance from the O +3 infrared line. Comparison of Mean Abundances with the Literature We compare our mean Bulge abundance from the GBPNe to mean Bulge abundances derived from other GBPNe abundance studies, red giant stars, and H II regions in Table 3.12. The mean abundances of our GBPNe generally agree well with mean abundances of GBPNe determined from the optical studies. The mean neon abundances are the most discrepant, with ours being a factor of ∼2 higher than those in the literature (reasons for such a discrepancy are given in §3.6.1). Our 83
mean argon and sulfur abundances are within the range of the previous studies, while our mean oxygen abundance is only slightly lower. Cunha & Smith (2006) derive abundances for seven red giant stars in the Bulge, Lecureur et al. (2007) forty-seven, and Fulbright et al. (2007) twenty-five. Cunha & Smith (2006) derive oxygen abundances from lines of OH vibrational-rotational molecular transitions observed in infrared spectra, while Lecureur et al. (2007) and Fulbright et al. (2007) derive oxygen abundances from the [O I] line at 6300 ˚A in optical spectra. The oxygen abundances of our GBPNe fall well within the range of values for red giants from these studies, but the mean oxygen abundance of the GBPNe is a factor of ∼2 lower than that of the red giants. However, given the uncertainties, small sample size, and different methods used, there is a good agreement. Simpson et al. (1995) give abundances derived from IR lines for 18 H II regions between 0 and 10 kpc from the Galactic Center, while Martín-Hernández et al. (2002) use ISO spectra to derive abundances of 26 H II regions between 0 and 14 kpc (distances for both studies were redetermined so that R⊙=8.0 kpc). In order to determine a mean H II region Bulge abundance from these studies, we take the mean of all H II regions in each study within 4 kpc of the Galactic Center. The Bulge H II region abundances from these two studies generally agree well with our GBPNe abundances, but the Bulge oxygen abundance of Simpson et al. (1995) and Bulge argon abundance of Martín-Hernández et al. (2002) are a factor of ∼2 higher. There are only 5 objects in the central 4 kpc of Simpson et al. (1995) and only 3 in the central 4 kpc of Martín-Hernández et al. (2002) (and only 11 in our GBPNe sample), and thus the small size of the samples may suggest that the mean does not reflect a true average of the whole Bulge population. Our mean sulfur abundance is the same as that of Martín-Hernández et al. (2002), but over a factor 84
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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
Page 45 and 46: these elements than previous studie
Page 47 and 48: dust is seen in the spectrum. We se
Page 49 and 50: Figure 2.2 Close-ups of emission li
Page 51 and 52: 2.4 Optical and UV Data We compleme
Page 53 and 54: 2.5 Data Analysis Our goal is to ca
Page 55 and 56: 2.5.2 Electron Density We assume an
Page 57 and 58: Table 2.6 Electron temperatures ass
Page 59 and 60: O, N, and C. The helium ionic abund
Page 61 and 62: Barlow (1994) use UV lines for impo
Page 63 and 64: is a spherical nebula with a low ma
Page 65 and 66: CHAPTER 3 CHEMICAL ABUNDANCES AND D
Page 67 and 68: essential data on important ionizat
Page 69 and 70: are members of the Bulge, (Acker et
Page 71 and 72: Table 3.2 Properties of observed GB
Page 73 and 74: nod-averaged line fluxes. Uncertain
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
Page 91 and 92: argon, neon, and sulfur tend to be
Page 93 and 94: Figure 3.2 Continuum subtracted spe
Page 95: Figure 3.3 Profiles of PAH features
Page 99 and 100: of two smaller than that of Simpson
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 and 118: IRS slits from these WIRC observati
Page 119 and 120: S IV) we employ is equal to Te(O +2
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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