TRACING ABUNDANCES IN GALAXIES WITH THE SPITZER ...

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CHAPTER 1 <strong>IN</strong>TRODUCTION On Earth, some snakes in the pit viper family have sacks on the sides of their heads that allow them to detect infrared light, or heat. This ability to “see” in the infrared allows the snakes to detect delectable rodents in dark underground tunnels where there is no optical light. Just as viewing objects on Earth in the infrared can uncover secrets hidden from optical light, viewing objects in space in the infrared allows astronomers to probe precious pieces of the cosmos unseen in the optical. For example, dust hinders optical studies because it absorbs optical light, but this same dust re-radiates the light in the infrared. Astronomers can identify the type of dust by looking at the features they produce in the infrared spectra (see §1.4). Infrared spectra also allow astronomers to determine the amounts of various elements (abundances) by measuring fluxes in infrared emission lines. Abundances from different locations in a galaxy give information about its formation and evolution. In the past, observations at optical wavelengths dominated abundance studies. However, studies at other wavelengths give new insights. This dissertation concentrates on what we can learn from infrared spectra of photoionization regions (specifically planetary nebulae and H II regions) in our Galaxy and M51 (NGC 5194). First we derive abundances of the planetary nebula IC 2448 in the Disk of the Milky Way, finding that it has abundances of argon, neon, sulfur, and oxygen slightly lower than solar which implies that the cloud from which the pro- genitor star formed had a subsolar abundance. Then we derive abundances for eleven planetary nebulae in the Galactic Bulge, finding that these nebulae do not follow the trend of abundance versus galactocentric distance displayed by nebulae in the Disk, thus indicating the separate evolution of the Bulge and the Disk. Ad- 1
ditionally we find that these nebulae in the Bulge have different dust properties than typical for nebulae in the Disk, and the dust signatures indicate that the progenitors of many of the Bulge nebulae probably evolved in binary systems. Fi- nally we derive abundances from H II regions across M51; while we cannot derive accurate abundances with respect to hydrogen, we can make an approximation of the neon to sulfur abundance ratio which appears to show that Ne/S decreases with increasing distance from the center, but this probably is not a real affect. The next section (§1.1) discusses the formation of elements and how determin- ing elemental abundances in different parts of a galaxy gives clues about how it formed and evolved. §1.2 summarizes the important properties of photoionization regions that are relevant to this work. Then §1.3 discusses what we can learn from spectra of these photoionization regions. §1.4 discusses the types of dust which produce features in infrared spectra of planetary nebulae and H II regions. §1.5 gives information about the Spitzer Space Telescope Infrared Spectrograph (IRS) which made the bulk of the observations for this dissertation. Finally §1.6 gives a brief description of the remaining chapters of the dissertation. 1.1 Elements and the Evolution of the Galaxy 1.1.1 Creation of the Elements Big Bang nucleosynthesis created the elements of hydrogen, helium, lithium, and trace amounts of beryllium. Stars create the rest. Understanding what types of stars make which elements and on what timescales these elements form is vital for understanding how galaxies form and evolve. A summary of when various elements are made in different types of stars follows; for more details see Matteucci (2001) on which this discussion is based. Massive stars with masses above ∼8 M⊙ end their lives in core collapse (Type 2
Page 1 and 2: TRACING ABUNDANCES IN GALAXIES WITH
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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: LIST OF FIGURES 1.1 Diagram of the
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 and 28: at the appropriate temperature and
Page 29 and 30: (a) 3.37 eV 1.40 eV 0.10 eV 0.04 eV
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
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Page 63 and 64: is a spherical nebula with a low ma
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CHAPTER 3 CHEMICAL ABUNDANCES AND D
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essential data on important ionizat
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are members of the Bulge, (Acker et
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Table 3.2 Properties of observed GB
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nod-averaged line fluxes. Uncertain
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Table 3.3 Multiplicative scaling fa
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Table 3.4 Observed infrared line fl
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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);
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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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