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Gas Kinematics in the Haloes of Nearby Irregular Dwarf Galaxies

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Gas Kinematics in the Haloes of Nearby Irregular Dwarf Galaxies Gas Kinematics in the Haloes of Nearby Irregular Dwarf Galaxies Dissertation zur Erlangung des Grades „Doktor der Naturwissenschaften” in der Fakultät für Physik und Astronomie der Ruhr–Universität Bochum von Janine van Eymeren aus Essen Bochum 2008 1. Gutachter: Prof. Dr. Ralf–Jürgen Dettmar (AIRUB) 2. Gutachter: Priv. Doz. Dr. Dominik J. Bomans (AIRUB) 3. Gutachter: Dr. Bärbel Koribalski (ATNF) Tag der Disputation: 30.06.2008 This document has been created with LATEX 2ε To my godfather ( 11.01.2008) † and my grandmother ( 21.01.2008) † Contents 1 Introduction 1 1.1 Motivation...................................... 1 1.2 Thesample ....................................... 4 1.3 Organisation of the thesis . ....... 5 2 Fabry-Perot Interferometry 7 2.1 Multiple-beam interference . ........ 7 2.1.1 Interference at plane-parallel plates . .......... 7 2.1.2 Finesse, peak transmission and the contrast factor . ............. 10 2.1.3 Resolution and the free spectral range . ........ 10 2.1.4 The FP etalon as a wavelength filter . ..... 11 2.2 A scanning Fabry-Perot interferometer . ........... 11 2.3 Thedetector..................................... 12 2.3.1 Photon-counting systems vs. CCDs ...................... 12 2.3.2 An overview over the Image Photon Counting System . ........ 12 2.4 Observations and data reduction . ........ 13 2.5 Technical issues of the observations and the data reduction .............. 16 3 Spiral structure in NGC 2366 19 3.1 Introduction.................................... 19 3.2 Observations and data reduction . ........ 20 3.2.1 Opticalimaging................................ 20 3.2.2 Fabry-Perot interferometry . ...... 20 3.3 Results......................................... 22 3.3.1 Generalmorphology ...... ..... ...... ...... ..... 22 3.3.2 Hα velocities .................................. 22 3.4 Discussion of the peculiarities in NGC 2366 . ........... 22 3.4.1 TheGALEXview ............................... 22 3.4.2 H I ring ..................................... 23 3.4.3 Satellite galaxy to the west . ..... 24 3.4.4 Properties of (dwarf) spirals . ...... 24 3.5 Conclusions..................................... 24 4 A comparison of the gas kinematics in NGC 2366 27 4.1 Introduction.................................... 27 4.2 Observations and data reduction . ........ 29 4.2.1 Opticalimaging................................ 29 ii CONTENTS 4.2.2 TheFabry-Perotdata . 30 4.2.3 The H I data................................... 30 4.3 Generalmorphology ............................... 30 4.4 Kinematicanalysis ............................... 32 4.4.1 The Hα velocityfield.............................. 33 4.4.2 The H I velocityfield.............................. 35 4.4.3 A comparison of the neutral and ionised gas . ........ 37 4.5 Discussion...................................... 40 4.5.1 Theoutflows .................................. 41 4.5.2 Supperbubble blowout in NGC 2366? . 41 4.5.3 Spiral arm structure revisited . ....... 42 4.5.4 Outfloworgalacticwind? . 42 4.6 Summary ........................................ 43 4.A Appendix: Hα image and extension of the catalogue of ionised gas structures . 44 5 A comparison of the gas kinematics in NGC 4861 45 5.1 Introduction.................................... 45 5.2 Observations and data reduction . ........ 46 5.2.1 TheFabry-Perotdata . 46 5.2.2 Opticalimaging................................ 47 5.2.3 The H I data................................... 48 5.3 Generalmorphology ............................... 48 5.4 Kinematicanalysis ............................... 51 5.4.1 Hα velocityfield ................................ 51 5.4.2 H I velocityfield ................................ 52 5.5 Discussion...................................... 54 5.5.1 Comparison of the neutral and ionised gas . ........ 54 5.5.2 Outfloworgalacticwind? . 57 5.5.3 ComparisonwithNGC2366 . 58 5.5.4 H I cloudtotheeast............................... 58 5.6 Summary ........................................ 60 5.A Appendix: Hα image and extension of the catalogue of ionised gas structures . 61 6 The Local Volume HI Survey: Gas kinematics in IC 4662 and NGC 5408 63 6.1 Introduction.................................... 63 6.2 Observations and Data Reduction . ........ 64 6.2.1 ATCAradiodata ................................ 64 6.2.2 Opticaldata................................... 66 6.3 Generalmorphology ............................... 69 6.3.1 IC4661..................................... 70 6.3.2 NGC5408 ................................... 70 6.3.3 StarFormationrates ...... ..... ...... ...... ..... 71 6.4 Kinematicanalysis ............................... 74 6.4.1 The kinematics of the neutral gas – the H I velocity fields . 74 6.4.2 The kinematics of the neutral gas – the H I rotation curves . 74 6.4.3 The kinematics of the ionised gas – long-slit spectroscopy of the Hα line . 77 6.4.4 A comparison of the H I with the Hα kinematics . 80 CONTENTS iii 6.5 Outfloworgalacticwind?. ..... 82 6.6 Summary ........................................ 83 6.A Appendix: Hα ...................................... 84 7 Dark matter in dwarf galaxies 87 7.1 Introduction.................................... 87 7.2 Thedata......................................... 88 7.3 Rotationcurves .................................. 89 7.3.1 H I rotationcurves ............................... 89 7.3.2 Hα rotationcurves ............................... 89 7.4 Massmodels ...................................... 93 7.4.1 Dynamicalcomponents. 93 7.4.2 Darkmatterhalomodels . 93 7.4.3 Fittingprocess ................................ 94 7.5 Discussion...................................... 96 7.5.1 NGC2366 ................................... 96 7.5.2 NGC4861 ................................... 98 7.5.3 IC4662..................................... 99 7.5.4 NGC5408 ................................... 99 7.6 Summary ........................................ 99 8 Summary and Outlook 101 8.1 Summary ........................................ 101 8.1.1 Outflows of neutral and ionised gas in dwarf galaxies . ........... 102 8.1.2 The cusp-core discrepancy . 103 8.1.3 H I cloud in NGC 4861 – did we find a dark galaxy? . 103 8.2 Outlook ......................................... 104 A The Gaussian decomposition 105 B Adaptive filtering 109 C Deriving the rotation curves 111 C.1 H I rotationcurves.................................... 111 C.2 Hα rotationcurves ................................... 112 Bibliography 115 List of Figures 1.1 The chimney model by Norman & Ikeuchi (1989). ......... 3 1.2 Superbubble model by Mac Low & Ferrara (1999). ......... 3 2.1 The Fabry-Perot etalon. ...... 8 2.2 The transmission function It/Ii of a Fabry-Perot etalon. 9 2.3 Typical fringe patterns of monochromatic light sources................. 10 2.4 Schematic view of an IPCS (Gach et al. 2002). .......... 13 2.5 The FP interferometer attached to the 1.93 m telescope at theOHP........... 14 2.6 The most important steps of the Fabry-Perot data reduction............... 15 2.7 Schematic representation of the FP’s scanning process. ................ 16 2.8 Artefacts on the Hα velocity field of NGC 2366. 17 3.1 R-band image and continuum-subtracted Hα image of NGC 2366. 21 3.2 TheHα velocityfieldofNGC2366. 21 3.3 The GALEX FUV contours overlaid onto the continuum-subtracted Hα image. 23 3.4 Statistical properties of dwarf spirals. ............. 23 4.1 R-band image and continuum-subtracted Hα image of NGC 2366. 29 4.2 H I channel maps of NGC 2366 (contours) superposed on the R-band image. 31 4.3 TheH I momentmapsofNGC2366.. 33 4.4 A comparison of the Hα and H I morphology. ..................... 34 4.5 TheHα velocityfieldofNGC2366. 35 4.6 TheH I kinematicsofNGC2366. ... ..... ...... ...... ..... .. 37 4.7 A comparison of the neutral and ionised gas. ........... 38 4.8 Gaussian decomposition of the H I............................ 39 4.9 Some example H I lineprofiles.............................. 39 4.10 An enlargement of the central region of NGC 2366. ............ 40 4.11 A comparison of the escape and expansion velocities. ............... 43 4.12 Continuum-subtracted Hα imageofNGC2366. ...... ...... ..... .. 44 5.1 R-band and Hα imageofNGC4861........................... 47 5.2 H I channel maps of NGC 4861 (contours) superposed on the R-band image. 49 5.3 TheH I momentmapsofNGC4861.. 50 5.4 A comparison of the Hα and the H I morphology. 51 5.5 TheHα velocityfieldofNGC4861. 52 5.6 TheH I rotation curve of NGC 4861. 54 5.7 A comparison of the neutral and ionised gas. ........... 55 5.8 Gaussian decomposition of the H I............................ 56 5.9 Some example H I lineprofiles.............................. 56 vi LIST OF FIGURES 5.10 A comparison of the escape and expansion velocities. ............... 58 5.11 Deep R-band and V-band images of the surroundings of NGC 4861. 59 5.12 A kinematic study of the H I cloudNGC4861B.. ...... ...... ..... .. 60 5.13 Baryonic Tully-Fisher relation. ........... 61 5.14 Continuum-subtracted Hα imageofNGC4861. ...... ...... ..... .. 62 6.1 H I channel maps of IC 4662 (contours) superposed on our R-band image. 67 6.2 H I channel maps of NGC 5408 (contours) superposed on the R-band image. 68 6.3 R-band images of IC 4662 and NGC 5408. 69 6.4 H I momentmapsofIC4662............................... 71 6.5 Hα images of IC 4662 and NGC 5408 with H I contours overlaid. 72 6.6 Continuum-subtracted Hα images of IC 4662 and NGC 5408. 72 6.7 H I momentmapsofNGC5408. ............................ 73 6.8 ThekinematicsofIC4662. ..... 76 6.9 ThekinematicsofNGC5408. 77 6.10 Example spectra of IC 4662 and
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