TRACING ABUNDANCES IN GALAXIES WITH THE SPITZER ...

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to the 3 P0 at 33.5 µm. Figure 1.3 (b) shows the predicted line flux ratio F([S III] 18.7 µm)/F([S III] 33.5 µm) as a function of the log of the electron density for sev- eral values of the electron temperature. The electron density is best determined by this ratio for values of the ratio between ∼1 and 11, corresponding to densities between ∼10 3 and 10 5 cm −3 , and it only has a small dependence on Te. However, other line ratios may also be used to determine Ne; for example, the ratio F([O II] 3729 ˚A)/F([O II] 3726 ˚A) which is more sensitive to slightly lower densities. The electron temperature (Te) can be determined by ratios of fluxes of pairs of emission lines emitted by a single ion from two upper levels which differ significantly in excitation energy. This ensures that the relative population of the levels depends on Te (Osterbrock, 1989). For example, the line flux ratio F([S III] at 6312 ˚A)/F([S III] at 18.7 µm) may be used to determine Te. The [S III] line at 6312 ˚A comes from the upper 1 S level while the 18.7 µm line arises from one of the lower 3 P levels (see Figure 1.3 (a)). The large difference in energy between the 1 S and 3 P levels leads to the relative rates of excitation of these levels depending strongly on Te (the higher the temperature, the more the 1 S level is populated relative to the 3 P levels), and thus it is possible to use the flux ratio of lines emitted from these levels to determine Te (see Figure 1.3 (c)). 1.3.3 Abundances Once the electron density and temperature are determined, it is possible to derive abundances of ions and elements by number with respect to hydrogen. In order to determine ionic abundances we take the ratio of an ionic line flux to the Hβ line flux. Then, we sum the ionic abundances for all of its expected stages of ionization to determine the total elemental abundance of an element. If an ionization stage is unobserved but expected to be present, we adopt an ionization correction factor 15
(a) 3.37 eV 1.40 eV 0.10 eV 0.04 eV 0.00 eV 33.5 o 9072 A S III o 6312 A µ m 18.7 µ m o 9535 A 1 S0 1D2 3 P2 3P1 3P0 (b) Figure 1.3 (a) The ground level configuration for S III. The splitting of the ground 3 P term is exaggerated in the figure, as can be seen from the energies marked on the left side. (b) The theoretical ratio of the [S III] 18.7 µm line flux over the [S III] 33.5 µm line flux as a function of the log of the electron density. The separate curves are for different adopted electron temperatures. (c) The theoretical ratio of the [S III] 6312 ˚A line flux over the [S III] 18.7 µm line flux as a function of the log of the electron temperature. The separate curves are for different adopted electron densities. 16 (c)
Page 1 and 2: TRACING ABUNDANCES IN GALAXIES WITH
Page 3 and 4: TRACING ABUNDANCES IN GALAXIES WITH
Page 5 and 6: BIOGRAPHICAL SKETCH Shannon was bor
Page 7 and 8: ACKNOWLEDGEMENTS First and foremost
Page 9 and 10: thank my husband Ryan. The rest of
Page 11 and 12: 3 Chemical Abundances and Dust in P
Page 13 and 14: LIST OF FIGURES 1.1 Diagram of the
Page 15 and 16: ditionally we find that these nebul
Page 17 and 18: seed nuclei relative to the β deca
Page 19 and 20: shape (Carollo et al., 2007). These
Page 21 and 22: Boltzmann velocity distribution cha
Page 23 and 24: etween recapture and photoionizatio
Page 25 and 26: a whole. Additionally, abundances f
Page 27: at the appropriate temperature and
Page 31 and 32: (Iion), the radiative transition ra
Page 33 and 34: lines. For example, changing the ad
Page 35 and 36: Figure 1.4 Starburst99 synthetic sp
Page 37 and 38: Figure 1.5 Example of crystalline s
Page 39 and 40: H H H H H H H H H Anthanthrene C H
Page 41 and 42: year lifetime. Spitzer is in an Ear
Page 43 and 44: 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
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Table 3.6 Comparison of the derived
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from the most reliable line(s), and
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Table 3.7 Electron temperatures and
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Table 3.9 Ionic abundances Ion x a
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3.5.2 Crystalline Silicates Crystal
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argon, neon, and sulfur tend to be
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Figure 3.2 Continuum subtracted spe
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Figure 3.3 Profiles of PAH features
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mean argon and sulfur abundances ar
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of two smaller than that of Simpson
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towards the Galactic Center. On the
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Table 3.14 Parameters of linear fit
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models that show how a binary compa
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y an outer dense O-rich torus, indi
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CHAPTER 4 ABUNDANCES IN H II REGION
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expect their abundance ratio to rem
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We extract spectra processed throug
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Figure 4.2 IRS spectra of H II regi
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IRS slits from these WIRC observati
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S IV) we employ is equal to Te(O +2
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Figure 4.3 M51 H II region Ne III/N
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Figure 4.4 shows a plot of the (Ne
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James Webb Space Telescope (JWST);
Page 127 and 128:
Bernard-Salas, J. & Tielens, A. G.
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Edgar, R. G., Nordhaus, J., Blackma
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Hummer, D. G., Berrington, K. A., E
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Matsuura, M., Zijlstra, A. A., Mols
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Pradhan, A. K., Montenegro, M., Nah
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Vassiliadis, E. & Wood, P. R. 1993,
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