University of Groningen The opacity of spiral galaxy disks. Holwerda, Benne IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2005 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Holwerda, B. (2005). The opacity of spiral galaxy disks. s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 23-09-2021 RIJKSUNIVERSITEIT GRONINGEN The Opacity of Spiral Galaxy Disks PROEFSCHRIFT ter verkrijging van het doctoraat in de Wiskunde en Natuurwetenschappen aan de Rijksuniversiteit Groningen op gezag van de Rector Magnificus, dr. F. Zwarts, in het openbaar te verdedigen op maandag 17 Juni 2005 om 13.15 uur door Benne Willem Holwerda geboren op 24 December 1976 te Nijmegen Eerste promotor: Prof. dr. P.C. van der Kruit Tweede promotor: Prof. dr. R.J. Allen Beoordelingscommissie: Prof. dr. R.H. Sanders Prof. dr. R. Sancisi Prof. dr. J.M. van der Hulst ISBN 90-367-2282-9 ISBN 90-367-2283-7 (electronic version) for Robin aan Mars and Janke Cover – M51 by the Hubble Heritage Project and Nuit etoilee´ by Vincent van Gogh. Cover design by Robin J. Allen. IV Contents Acknowledgements IX Nederlandse Samenvatting XI English Summary XIX 1 Introduction: The dust content of spiral galaxies 1 1.1 Introduction ................................. 1 1.2 The importance of dust ........................... 3 1.3 Inclination effects on disks ......................... 3 1.3.1 The Holmberg test .......................... 4 1.3.2 Sample selection effects ....................... 4 1.4 Characterizing dust from stellar emission .................. 5 1.4.1 Dust and disk kinematics ...................... 5 1.4.2 Light models ............................ 5 1.5 Spectral energy distribution models ..................... 6 1.6 Dust emission ................................ 9 1.6.1 Dust composition from emission .................. 10 1.7 Direct extinction measurements ....................... 10 1.7.1 Occulting galaxies .......................... 10 1.7.2 Counts of distant galaxies ...................... 12 1.7.3 Calibrated Counts .......................... 16 1.8 Motivation of this thesis. .......................... 17 2 Automating the “Synthetic Field Method” 19 2.1 Introduction ................................. 20 2.2 The Synthetic Field Method ......................... 22 2.2.1 Limits of the Synthetic Field Method ................ 22 2.3 Automation of the method .......................... 22 2.3.1 Processing archival WFPC2 data .................. 23 2.3.2 Making object catalogs ....................... 24 2.3.3 Selection of field galaxy candidates using “fuzzy boundaries” .... 25 VI CONTENTS 2.3.4 Visual identification of contaminants ................ 29 2.4 Improvements in the “Synthetic Field Method” ............... 31 2.4.1 Foreground galaxy segmention ................... 31 2.4.2 Simulated fields ........................... 32 2.4.3 Field galaxy numbers: uncertainties and systematics ........ 33 2.4.4 Inclination correction ........................ 36 2.5 Examples: NGC 4536 and NGC 1365 .................... 36 2.5.1 NGC 4536, comparing observers .................. 37 2.5.2 NGC 1365: arm and inter-arm extinction .............. 39 2.5.3 NGC 4536 and NGC 1365: Radial profile of extinction ....... 40 2.5.4 Surface brightness .......................... 43 2.6 Conclusions ................................. 45 3 Radial Extinction Profiles 47 3.1 Introduction ................................. 48 3.2 The HST Archive Sample .......................... 49 3.3 SFM: Calibrating the field galaxy numbers. ................. 50 3.3.1 Galactic Extinction ......................... 53 3.4 Radial opacity measurements in individual WFPC2 fields .......... 54 3.5 Average Radial Opacity Plots ........................ 57 3.5.1 Inclination effects .......................... 57 3.5.2 The effect of spiral arms ....................... 62 3.5.3 Hubble Type ............................. 69 3.6 Average color of the field galaxies ...................... 69 3.7 Surface brightness and opacity ....................... 74 3.8 Discussion .................................. 74 3.9 Conclusions ................................. 76 4 Dust opacity, sub-mm emission and HI distributions 79 4.1 Introduction ................................. 80 4.2 The “Synthetic Field Method” ........................ 81 4.3 Individual galaxies: radial HI and opacity profiles .............. 83 4.4 Dust-to-HI ratio ............................... 85 4.5 Comparison to SCUBA profiles. ....................... 88 4.5.1 M51 ................................. 89 4.5.2 Comparing to sub-mm ........................ 89 4.6 Conclusions ................................. 89 4.7 Future Work ................................. 89 5 Extinction, stellar light and color 91 5.1 Introduction ................................. 92 5.2 The “Synthetic Field Method” ........................ 92 5.3 Discussion of systematic effects ....................... 93 5.3.1 Systematics of the Synthetic Field Method ............. 93 5.3.2 Sample selection effects ....................... 94 5.4 Surface brightness and disk opacity ..................... 95 CONTENTS VII 5.5 Surface brightness and opacity in arm and disk ............... 98 5.6 Disk opacity and NIR color ......................... 101 5.7 Dust and light scalelengths ......................... 102 5.8 Comparison to Cepheid Reddening ..................... 104 5.9 Discussion: Implication for our view of a spiral disk ............ 106 5.10 Conclusions ................................. 107 6 160 µm emission and opacity 109 6.1 Introduction ................................. 109 6.2 MIPS scan maps and reduction ....................... 110 6.3 Converting MIPS flux to optical depth .................... 111 6.4 Dust emission and extinction ........................ 111 6.4.1 Single WFPC2 fields ........................ 112 6.4.2 Two WFPC2 fields ......................... 115 6.5 Discussion .................................. 117 6.6 Concluding Remarks ............................ 119 7 The accuracy of galaxy counts as an extinction probe 121 7.1 Introduction ................................. 122 7.2 The “Synthetic Field Method” ........................ 122 7.3 Predicted limitations using Hubble ..................... 123 7.4 Comparison data and systematics ...................... 124 7.5 The effects of surface brightness ....................... 125 7.6 The effects on individual WFPC2 fields ................... 126 7.6.1 Distance ............................... 127 7.6.2 Granularity ............................. 129 7.6.3 Effects of structure and surface brightness .............. 131 7.7 Discussion: Optimum Distance for the SFM ................. 131 7.8 Conclusions ................................. 132 7.9 Future work ................................. 133 8 Future work with the Synthetic Field Method 135 8.1 Justification for more SFM analysis ..................... 135 8.2 ACS data .................................. 137 8.2.1 M101 ................................ 137 8.2.2 M51 ................................. 139 8.2.3 Object classification: the Self-Organizing Map ........... 140 8.3 Disk opacity mapping ............................ 140 8.4 Concluding remarks ............................. 142 9 Discussion and Outlook 143 9.1 Results from this thesis ........................... 143 9.2 Comparison of results with earlier work .................. 146 9.3 Implications of the results .......................... 147 9.3.1 Implications for our view of spiral galaxy disks ........... 148 9.3.2 Implication for observations of the high-redshift Universe ..... 149 9.4 Questions remaining... ............................ 149 VIII A Observations 163 A.1 Colour images ................................ 163 A.2 Masks .................................... 163 A.3 Checking basic data ............................. 164 A.3.1 Scale radius ............................. 164 A.3.2 Inclination .............................. 164 B Systematics & Uncertainties 199 B.1 Introduction ................................. 199 B.2 Uncertainties ................................ 199 B.2.1 Small number Poisson error ..................... 199 B.2.2 Clustering uncertainty ........................ 200 B.3 Total uncertainties .............................. 202 B.4 Systematics in the counts .......................... 203 B.4.1 Confusion in synthetic and science fields. .............. 203 B.4.2 Crowding .............................. 205 B.5 How average is the HDF? .......................... 205 B.6 Galactic extinction .............................. 207 C Synthetic Dust Models 209 Acknowledgements A book is said to be like a river, drawing on many sources. This is very true for a thesis, the subject of which started as a little stream of